A INM ASTER A STER G AIN
TM
Amplifier Design Software Manual Revision 1.1
This manual is intended for use with GainMaster™ v. 1.1. ©
GainMaster™ is copyrighted in 2004 by Fibercore Limited. Fibercore Limited Fibercore House, University Parkway, Chilworth Science Park, Southampton, Hampshire, SO16 7QQ, United Kingdom Tel: +44 (0)23 8076 9893 Fax: +44 (0)23 8076 9895 Email:
[email protected] USA and Canada Tel: 1 630 778 0519 Fax: 1 630 420 7393
June 11, 2004
INTRODUCTION This manual describes the use of Fibercore Limited’s GainMaster TM amplifier design software package. GainMaster™ is a self-contained program for use on personal computers using the Microsoft Windows TM operating systems, including Windows 95/98/2000/ME/NT. The program contains an intuitive Graphical User Interface (GUI) for entering and modifying optical amplifiers in a schematic fashion. Fibercore Limited erbium fiber is supplied with component data files that can be loaded into the program and used, along with many other component types, to design and model optical amplifiers and ASE sources. In this version the user can run a simulation with set parameters • iteratively run simulations for the purpose of optimizing any component’s parameters or for • modeling the effects of component variations run predefined optimization algorithms for common tasks, such as designing gain flattening • filters model the effects of erbium fiber temperature by specifying and varying the operating • temperature of each individual section of erbium fiber. Other optimizations will be added in future versions.
INTRODUCTION This manual describes the use of Fibercore Limited’s GainMaster TM amplifier design software package. GainMaster™ is a self-contained program for use on personal computers using the Microsoft Windows TM operating systems, including Windows 95/98/2000/ME/NT. The program contains an intuitive Graphical User Interface (GUI) for entering and modifying optical amplifiers in a schematic fashion. Fibercore Limited erbium fiber is supplied with component data files that can be loaded into the program and used, along with many other component types, to design and model optical amplifiers and ASE sources. In this version the user can run a simulation with set parameters • iteratively run simulations for the purpose of optimizing any component’s parameters or for • modeling the effects of component variations run predefined optimization algorithms for common tasks, such as designing gain flattening • filters model the effects of erbium fiber temperature by specifying and varying the operating • temperature of each individual section of erbium fiber. Other optimizations will be added in future versions.
CONTENTS Introduction............................ ...................................................... ............................................................................................ ...................................... 2 Design Philosophy............................................. ...................................................... ................................................................. ........... 4 Running GainMaster™ ........................................... ................................................... ....... 6 Getting Started.............................................................................................................. 7 Computer Requirements ................................................ ............................................. 7 Loading the Program..................................................... .............................................. 7 Suggested Folder Organization......................................................... Organization....... .................................................. .......................... 7 Starting GainMaster™ .............................................. .................................................. 9 Entering a Design........................................................................................................ 11 Using Probes ..................................................... ........................................................................................................... ........................................................ .. 13 Component Types ........................................... ................................................... ....... 15 Inserting a New Component ............................................. ........................................ 20 Loading a Previously Saved Component .............................................. .................... 21 Connecting Components with Fiber ............................................ ............................. 22 Moving and Deleting Components and Fiber................................................ Fiber ................................................ ........... 22 Using Probes and Probe Leads .............................................. ................................... 23 Editing Component Parameters ........................................... ..................................... 23 Saving Components to Disk.................................................. Disk...................................................................................... .................................... 42 Saving Components to Disk.................................................. Disk...................................................................................... .................................... 43 Saving the Simulation to Disk .............................................. .................................... 43 Running the Basic Simulation ................................................................................... 44 Setting up Global Parameters............................................. Parameters.................................................................................... ....................................... 44 Running the Simulation .......................................... ............................................... ... 46 Simulation Progress Dialog .......................................... ............................................ 47 Prematurely Terminating the Simulation................ ............................................... ... 48 Simulation Data Status....................... ............................................... ........................ 48 Saving the Simulation ......................................... ............................................... ....... 48 Viewing Basic Simulation Data ................................................................................. 49 Viewing Probe Data............................................ Data ............................................ .................................................. .... 49 Viewing Optical Power in a Fiber .................................................. .......................... 51 Viewing Erbium Fiber Component Data ............................................ ...................... 53 Optimizations ............................................... ................................................... ............ 55 GFF (Gain Flattening Filter) Optimization.................... Optimization............................................................... ........................................... 55 Running Iterative Simulations................................................................................... 56 Setting Up and Running Iterations......................................... ................................... 56 Viewing Iterated Simulation Results ............................................... ......................... 59 Examples ............................................... .................................................. ......................... 61 Index ....................................................... ............................................................................................................. .......................................................................... .................... 62
DESIGN PHILOSOPHY GainMaster ™ is a software package intended to assist optical engineers in the design of erbium-doped optical amplifiers (EDFA’s), reducing the amount of time involved in bringing a successful amplifier design to production. The software allows for schematic representations of an optical amplifier to be input via a graphical user interface which mimics the symbolic language often used by engineers to outline a design on paper. Designs are component-driven, meaning that the important aspects of the amplifier are the selected components and the connections between their ports, made with optical fibers. The general approach is similar to many common electrical circuit design programs. An optical engineer can lay out an amplifier design by introducing components and connecting their ports with fibers. The general convention used is that the signal path travels from left to right, and direction-sensitive components are designed to make this direction convenient. Each component’s optical parameters can be specified to match those to be actually used, based either on vendor data or the user’s own measurements. Once a design has been entered, with all the components’ parameters set to their appropriate values, the user can run a simple simulation. The program tracks the optical power through the design, integrating the differential equations to solve the propagation of signal, pump, and amplified spontaneous emission (ASE) bands through all erbium fiber sections. Once a simulation is complete, the user may look inside the design by graphing the power propagating through any fiber in the design, as well as through the length of all erbium fiber sections. Also, by use of the probe component, the user may make common two-point measurements of interest, such as gain, noise figure, conversion efficiencies, etc. Optical parameters of any component may be changed and the simulation re-run to observe the effects on amplifier performance. The entire amplifier design may be saved to disk at any time, which includes the current state of all components and fibers, including all the optical power data. Different states of an amplifier can be saved to different files. Individual components can be saved to separate files, which is especially convenient in the making of a user library of common components used in many different designs. All pertinent optical parameters are saved with the individual component file, including any wavelength-dependent data uploaded by the user. Different important design parameters may be op timized by running iterated simulations, which allow the individual or combined variation of component parameters in several automatically run simulations. Output graphs can be easily created to view the effects of the variations on the optical power propagating into our out of all components, and also on any parameter measured by probes in the design. A built-in gain-flattening filter (GFF) optimization routine can also be used to automatically design a filter shape which flattens the gain of an amplifier design within user-defined specifications.
The rest of the manual describes how to start using the program, enter a design, run the basic simulation, view important simulation data, running optimization routines, and how to generate, run, and view the results of iterative simulations.
RUNNING G AINM ASTER™
GETTING STARTED COMPUTER REQUIREMENTS GainMaster™ requires a personal computer running Windows 95/98/2000/ME/NT or equivalent. Because of the computationally-intensive nature of modeling optical amplifiers, it is recommended that a computer with at least 64MB of RAM and a 500MHz Pentium III processor (or equivalent) is used for adequate performance. The software is typically distributed on a CD-ROM, requiring the computer to have some method of loading data from a CD drive.
L OADING THE PROGRAM Load the CD-ROM into the CD drive. Run the Setup.exe program located on the CDROM. An install wizard will then run. After the license agreement is accepted, the program will automatically be loaded under \Program Files\ GainMaster on the C: drive of your computer. When the installation procedure is completed, you can run the program from this folder, or you can create a shortcut to the program on your desktop by rightclicking on the program and then selecting “Send To” and “Desktop.” Finally, doubleclick the program icon on the desktop to start the program.
SUGGESTED FOLDER ORGANIZATION The program automatically creates a sub-folder named GainMaster under the Program Files folder on your hard disk. The main program, GainMaster.exe, is contained in this folder. Four other sub-folders are created under the GainMaster folder: Components, Designs, Demos, and Manual.
\COMPONENTS The Components folder is intended to be a convenient place to locate all saved component files. The sample erbium fiber component, entitled ErbiumFiber.edf, is located in this folder. Because all components have type-specific extensions which make searching and browsing for a given component type easy, it is not necessary to have a different sub-folder for each component type, although the user is free to create folders and store component files anywhere desired.
\DESIGNS The Designs folder is intended to be a convenient place to store the user’s amplifier designs, stored as “.amp” files. Other sub-folders can be created at the user’s discretion.
\DEMOS The Demos folder contains example amplifier designs for quick and easy practice in using the software. The amplifiers in these designs are in no way “good” amplifier
designs, but are only dummy designs intended for software training and demonstrating the basic capabilities of the program.
\M ANUAL The Manual folder contains a PDF version of the GainMaster™ manual. The file can be TM read or printed with Adobe Acrobat. A free copy of the Acrobat Reader is available from the Adobe website at http://www.adobe.com/products/acrobat/readstep.html.
STARTING G AINM ASTER™ TM
TM
GainMaster is a Windows -based program and is launched like other Windows programs. If a shortcut is created on the computer desktop, double-clicking its icon launches the program.
Once the program is launched, the main window will appear. Within the main window is a sub-window that contains a design space for entering the amplifier design schematic. GainMaster™ is a multiple-document application, meaning that several designs can be open at one time, with each one having its own design space window within the main window. GainMaster™ automatically generates one blank design space when started.
Clicking on “View” and “Component Toolbar” from the main menu can close the component toolbar on the left of the window.
To create a new blank design, save an existing design, or open a design from a disk file, the standard file tool buttons at the top of the window can be used. Also, the File dropdown menu can be used to perform the same functions.
ENTERING A DESIGN The software allows for intuitive, schematic-based entry of amplifier designs. There are two methods to add a component to the design: adding a new component, or loading a previously saved component from disk. Located on the main menu are two drop-down menus: New Component and Load Component. Use New Component to add a component with default properties, and use Load Component to retrieve a previously saved component from disk. (Erbium Fiber components must be loaded from the disk – there are no default Erbium Fiber components.) Select the type of component desired (from the sub-menus for Optical Sources or WDM’s) and the new component will be added to the upper left corner of the design space.
New components can also be added by clicking o n that component’s icon in the component toolbar (if the component toolbar is currently visible.) Previously saved components can also be loaded by clicking on the load component icon (which looks like a file folder with an emerging component) in the main toolbar. Select the desired type of component in the “Files of type:” drop-down list at the bottom of the dialog box to view components of that type.
Once a component is added to the design space, it can be moved by placing the cursor over its icon, holding down the left mouse button, and moving the cursor. The component’s icon is shown in reverse color when selected in this way. To add a connecting fiber, place the cursor anywhere in the design space outside of a component icon and hold down the left mouse button. As the mouse is moved, the fiber is extended until the left mouse button is released. (If the fiber is extremely short, it is deleted to avoid inadvertent additions from accidental mouse clicks, etc.) If either end of the fiber is within a component port, the fiber is connected to that port. A component’s port color is changed from black to red to indicate that it is connected to a fiber. Once a fiber is connected to a component port, the only way to break the connection is to eliminate either the fiber or the component.
To delete a component or a fiber, it must be selected. To select, place the cursor over the desired component’s icon or somewhere on the desired fiber. Click the left mouse button once. The component (fiber) is indicated as being selected by its predominant color being changed to black (blue). Once selected, the component or fiber can be deleted by pressing the delete key or clicking on the scissors icon in the toolbar.
USING PROBES The only exception to the above method of entering a design occurs when using Probe components. Probes are used to make measurements such as gain and noise figure
between two points in an amplifier. A probe is entered into the design normally. However, once a connection fiber is attached to a probe port, that fiber becomes a “probe lead.” Once it is a probe lead, it can only be attached to connection fibers, not other component ports. This is because probe leads make measurements of the optical power in particular fibers. The connection fiber must be attached to the probe port first in order to define it as a probe lead. Once connected to a probe port, the other end of the probe lead can be attached to a fiber by moving the opposite end and dropping it (releasing the left mouse button) above the fiber to which it should be attached. A large black circle drawn at the point of connection of the probe lead and the fiber indicates the probe lead attachment. Deleting the probe lead or the fiber breaks this connection. For purposes of performing two-point calculations, the probe’s left port is the “input” side, and the right port is the “output” side. This is convenient for amplifiers with forward propagation direction from left to right.
COMPONENT TYPES Several different component types are available, each with different optical characteristics. The different types of components, along with their associated icons, are described below
ERBIUM FIBER
Erbium fibers are the most important components in an amplifier design. Modeling of 1 erbium fibers is based upon the standard Giles model, with temperature effects based on 2 the model by Bolshtyansky, et. al. All Giles parameters are contained within the Fibercore Limited-supplied erbium component files (*.edf) and can be viewed, but not altered, from the erbium component dialog box, Erbium fiber parameters that can be changed by the user include length, input and output splice loss, and temperature. The power spectrum for the Signal, Pump and ASE bands propagating in either direction can be graphed at all points in the fiber.
ITU SOURCE
ITU source components are designed to make creation of any signal spectrum associated with the ITU grid fast and easy. Grid spacings of 50, 100, 150, and 200GHz are automatically generated, with arbitrary power levels for each individual channel easily set. The final output spectrum of the source can be graphed and saved as an ASCII file.
MULTIPLE CHANNEL SOURCE
1
Giles, C.R., C.A. Burrus, D.J. DiGiovanni, N.K. Dutta, and G. Raybon, “Characterization of ErbiumDoped Fibers and Application to Modeling 980-nm and 1480-nm Pumped Amplifiers,” IEEE Phot. Tech. Letters, Vol. 3, No. 4, April 1991. 2 Bolshtyansky, M., P. Wysocki, and N. Conti, “Model of Temperature Dependence for Gain Shape of Erbium-Doped Fiber Amplifier,” Journ. of Light. Tech., Vol. 18, No. 11, November 2000.
Multiple channel components are designed to easily create sources with equally-spaced channels not tied to the ITU grid. The beginning and ending wavelengths can be specified, as well as the number of channels, which are evenly spread throughout the th band. The power per channel can be set, and optionally every n channel can be automatically eliminated to simulate band edges.
SINGLE CHANNEL SOURCE
Single channel components are simple representations of a single wavelength source, whose wavelength and power can be defined.
980NM PUMP
980nm pumps are similar to single channel sources in that they have one wavelength and power level to set. They have a separate icon and naming sche me for convenience and aesthetics.
1480NM PUMP
1480nm pumps are similar to single channel sources in that they have one wavelength and power level to set. They have a separate icon and naming scheme for convenience and aesthetics.
PUMP COUPLING WDM
Pump coupler components are used to couple pump power into the signal path, or remove pump power from the signal path. Both 1x2 and 2x1 coupler icons are available for convenience in representing forward or backward pumping schemes, etc., but otherwise
both types behave identically. The operating wavelengths for both the signal and pump band can be defined. Optical parameters including insertion loss, return loss, isolation, and directivity can be specified for both the pump and signal bands as single values, or with user-defined wavelength dependence which is assigned by uploading spectral data from an ASCII file. The wavelength dependence of these parameters can be graphed for verification of the data.
ISOLATOR
Isolator components allow optical propagation in only one direction. The isolator component in this software is designed for left-to-right propagation, as indicated by the direction of the arrow in the component icon (meant to mimic an electrical diode symbol.) The operating wavelength range for the isolator can be defined by choosing a minimum and maximum wavelength. Optical parameters including range, isolation, insertion loss, and input & output return loss can be defined as single values or have userdefined wavelength dependence assigned by uploading spectral data from an ASCII file. The wavelength dependence of these parameters can be graphed for verification of the data.
FILTER
Filters are used to selectively remove power at certain wavelengths. Common uses include removing certain channels, adding spectral tilt, and flattening amplifier gain. All such filters are represented by the generic filter component. The insertion loss and input & output return losses can be specified as single values. The loss spectrum can be uploaded from an ASCII file, or alternatively optimization algorithms, such as the Gain Flattening Filter (GFF) optimization, can calculate it. The loss spectrum can be graphed, either across the full band or just at the signal wavelengths. Also, the loss spectrum can be saved to an ASCII file.
ATTENUATOR
Attenuators are typically used to reduce the optical power equally across the entire signal spectrum. However, special attenuators are sometimes constructed with predefined slopes or shapes to their wavelength dependence. The operating wavelength range can be defined by choosing a minimum and maximum wavelength. Optical parameters such as the attenuation and input & output return loss can be defined as single values, or with a wavelength dependent function uploaded from an ASCII file. These parameters can be graphed to verify the data.
CIRCULATOR
Circulators are used to separate counter-propagating light into separate paths. This is indicated in the component icon by the circular arrow pointing in the clockwise direction. Light entering from the upper left port is transmitted out of the right port, whereas light entering the right port is transmitted out of the lower left port.
SPLICE
Splice components are included to allow modeling of splice losses resulting from splicing fibers together in the assembly of an amplifier. While these losses can be lumped together with component insertion losses, it is more convenient for schematic display as well as for running iterative simulations (see Running Iterative Simulations, p. 56) to have a separate component. The operating wavelength ranges for both the signal and pump band can be defined, and separate splice loss values for the two bands can be specified.
CONNECTOR
Connector components are included to represent the use of optical connectors to mate two fibers instead of splices. The operating wavelength ranges for both the signal and pump band can be defined, and separate connector loss values for the two bands can be specified. Also, the return loss in both directions can be specified.
T AP
Taps are used to extract a small amount of optical power from the signal path, typically for monitoring purposes. The main signal path is between both upper ports, with the extracted tap power exiting the lower right port.
FIBER BRAGG GRATING
Fiber Bragg Gratings are similar to filters except that optical power rejected by the filter is reflected back into the fiber in the opposite direction. Otherwise, they behave identically to filters.
SPLITTER
Splitters take optical power input to any port and output the user-prescribed percentage of that power from diametrically opposed port on the other side of the component (minus any insertion losses, etc.) They can be used to generically combine multiple sources and pumps, or mix signals from multiple input paths.
PROBE
Probes are used to make two-point measurements, such as Gain, α and Noise Figure. The left port is the “input” port, and should be connected to the fiber containing the forward propagating amplifier input signal. The right port is the “output” port and should be connected to the fiber containing the forward-propagating amplifier output signal. (The ports can be attached to any two fibers. The measurements reported by the probe will be between those two fibers, and not the amplifier as a whole.)
INSERTING A NEW COMPONENT A new component of any type (except erbium fiber) may be created by selecting “New Component” from the main menu and then selecting the appropriate component type. (Erbium fiber components may only be loaded from disk, as discussed in the next section.) The new component is generated with default parameter values that can be changed as discussed below in “Editing Component Parameters.” A new component can also be entered by clicking on its icon in the component toolbar.
L OADING A PREVIOUSLY S AVED COMPONENT Load a previously saved component by selecting “Load Component” from the main menu, selecting the component type, and then selecting the component file to be loaded. The “load a component” button located in the main toolbar (the button containing an open file folder with an emerging component symbol) can be clicked instead to open the file selection dialog box. The type of component can be selected in the “Files of type” field at the bottom to show only files of that type (i.e., with that component type’s extension.)
CONNECTING COMPONENTS WITH FIBER Connect components in a design by attaching fibers between their ports. To connect a fiber to a component port, a free fiber end can be moved onto a free component port, or a component can be moved such that its free port overlaps the free end of a fiber. A successful fiber/port connection is indicated by the component’s port turning red. To break a connection, the fiber on the component must be selected and deleted.
MOVING AND DELETING COMPONENTS AND FIBER Move a component by placing the cursor on its icon, holding down the left mouse button, and moving the mouse. Any fibers currently connected to that component’s ports are adjusted to remain connected to that component. The colors of a component’s icon are reversed (highlighted) whenever it is “selected.” A component is selected whenever the left mouse button is clicked or held down while the cursor is on its icon. Only one component or fiber may be selected at a given time. To delete a component, select it and hit the [Delete] key, or click on the scissors (cut) icon in the main menu. When a component is deleted, any fiber ends that were connected to its ports are free to be connected to other components. The colors of a fiber are reversed when it is selected. A fiber is selected in exactly the same manner as a component, except that the cursor must be placed over the fiber instead of the component icon. Only one component or fiber may be selected at a given time. The fiber is deleted in exactly the same manner as a component once it is selected. Once a fiber is deleted, any component ports it was attached to are free to connect to other fibers (as indicated by those ports returning to their black “open” color.)
USING PROBES AND PROBE L EADS Probes are created, moved, and deleted exactly as other components. However, “fibers” connected to probes are not really fibers, but are “probe leads,” and have properties different than fibers. This is indicated by their color changing to green after being connected to a probe port, indicating their change to probe lead status. It may only be connected to a probe port if neither of its ends is connected to any component port. Once it has become a probe lead, its other end may not be connected to a component port (not even another probe port). A probe lead’s free end may only be “attached” to another fiber (not another probe lead). This is done by moving the probe lead and “dropping” it on the selected fiber, or by moving a fiber such that it overlaps the free end of the probe lead. A large black circle at the intersection of the probe lead and the fiber indicate that it is a probe lead attachment. When a probe is deleted, its leads are automatically deleted with it.
EDITING COMPONENT P ARAMETERS Every component has parameter values required to model it. To edit the parameters, double-click on the component icon and a dialog box will appear. The type of dialog box created depends upon the type of component selected, as each component type has different parameters. At the top of each component dialog box (except for erbium fibers) is the component name. At the bottom of each component dialog box are three buttons: Save, Apply (or Okay), and Cancel. These are explained below.
COMPONENT N AME Each component (except for erbium fibers) has a component name that is displayed just below the component’s icon in the
design space. When first created, new components are given generic names that are based upon that component’s type. Each name in a given design must be unique, an underscore and numerical subscript are added to the generic name if required to make the name unique. The user may change the name of all components (except for erbium fiber components) by typing a new name in the “Component Name” edit control located at the top of the component dialog box. However, if the name typed in by the user is not unique, an underscore and numerical subscript are added to make it unique.
S AVE COMPONENT A component can be saved as a separate file to disk. This is useful for storing components with particular parameter values or transfer functions for use in later designs without having to redefine those values. Clicking on the Save button will bring up a standard Windows file dialog box which allows the user to select the location and name for the file to be saved. The program automatically appends an extension to the name. The extension is particular to the type of component being saved so that when subsequently loading a component, only components of the desired type are searched.
APPLY (OKAY) Clicking on the Apply (or Okay) button will update the component with all the user’s changes made in the dialog box. It is only after clicking this button that the component’s values in the design are actually updated.
C ANCEL Clicking on the Cancel button will reject all of the changes the user made in the dialog box. The component’s parameter values will be the same as they were before the component dialog box was opened
OPERATING W AVELENGTHS When appropriate, the operating wavelength range for components can be defined. They will typically be given by a minimum and maximum wavelength for both the signal and pump bands. Any wavelength outside of these two ranges will be cons idered completely blocked by the simulation. Therefore, the operating wavelength for the signal band should be made large enough to accommodate the desired ASE band, as selected in Setting up Global Parameters on page 44. Editing the remaining parameters are described for each component type, with its individual dialog box, in the sections below:
ERBIUM FIBER After double-clicking on the erbium fiber component icon, the erbium fiber dialog box is displayed. The values of the first four parameters in the dialog box can be changed by the u ser. The Fiber Length parameter is the length of the erbium fiber in meters. The Input and Output Splice Losses are for the left and right, respectively, ends (ports) of the erbium fiber component, and are in units of dB (positive for loss.) The temperature is in degrees Celsius. The Giles parameters are also viewable, but not editable, by the user: The Saturation Parameter value is displayed in a read-only control beneath the temperature. By clicking on any of the three buttons just below, a graph of either the αsignal, α pump, and g* spectra can be displayed. Once a simulation has been run, the optical data inside the fiber can be viewed by clicking either of the two buttons in the “Simulation Data” section of the dialog box. (See Viewing Erbium Fiber Component Data on p. 53 for more information about viewing the erbium fiber’s simulation data.)
ITU SOURCE The ITU Signal Source component is designed to make creation of an ITUlocked source fast and simple. Channel spacings of 25, 50, 100, and 200GHz can be generated automatically, with any channels easily dropped and the power of each channel individually controllable. After double-clicking on the ITU Signal component icon, its dialog box is displayed.
The available channels are shown in the list box on the left of the dialog box. Which channels are available depends upon the current channel spacing. The default value is 200GHz. The channels can be displayed either in wavelength (nm) or frequency (THz) format by selecting the desired unit’s button. Removed channels are displayed with square brackets around their wavelength/frequency value, for example [1520.25], to indicate that channel is on the ITU grid, but removed from the source spectrum.
CHANGING THE CHANNEL SPACING To change the channel spacing, choose the desired value from the “Channel Spacing” drop-down list and then click on the “Set Source To ITU Grid” button. This will reset the entire source spectrum to the new channel spacing and reset all power levels to their default value.
SELECTING CHANNELS To change the status of any channel or group of channels, they first must be selected. Channels are selected by highlighting their wavelength/frequency in the list box. This is accomplished by clicking with the mouse. Multiple selections may be made pressing the [Ctrl] key while making a selection with the mouse, or by using the [Ctrl] key and the up/down arrow keys. In addition, channel selection can be accomplished using the selection buttons in the “Select/Deselect Channels” section of the dialog box. The function of each of the buttons in this section is described below: -
Select All: highlights all available channels in the list box. Select Existing: highlights only existing (non-removed) channels Remove: removes all highlighted channels Deselect All: removes highlighting from all channels Select Removed: highlights only removed channels Restore: returns any highlighted removed channels to “on” status
CHANGING CHANNEL POWER The power level of all currently highlighted channels can be changed by entering the desired power in the “Power” box, located in the “Set Power Levels” section at the bottom of the dialog box. The numerical value entered is assumed to be in the current units, which can be changed by selecting the desired units in the adjacent drop-down selection box. No channels are changed until the “Set Power Level for all Selected Channels” button is clicked. Only those channels currently selected (highlighted) will have their power modified to the current power level displayed. GRAPHING THE SOURCE SPECTRUM Clicking on the “Graph” button will display a graph of the current source spectrum.
MULTIPLE CHANNEL SOURCE This source is intended for use when a multiple channel signal is desired that is not locked to the ITU grid. It creates an evenly-spaced multiple wavelength source of constant channel power. After double-clicking on the Multiple Channel Signal Source component, its dialog box is displayed. The “First wavelength” and “Last wavelength” parameters will be the first and last channel of the source. The “Number of wavelengths” parameter indicates how many channels this source will have, including the first and last channel. The “Skip every [n] wavelength” th indicates that every n channel will have zero power, with n being the number selected (0 if all channels are to be used.) For example, entering 3 will mean every third channel will have zero power. The first channel is never skipped. The optical power of each channel is equal and the value is determined by the value entered in the “Power” box. Note that the units may be selected in the adjacent units box, and that the numerical power entered by the user is assumed to be in the currently selected units. Changing the units will automatically convert the displayed numerical power to the new units.
SINGLE CHANNEL SOURCE This source is intended for use when only a single source channel is desired.
After double-clicking on the Single Channel Signal Source component, its dialog box is displayed. The single wavelength is entered in the “Wavelength” box. The power entered in the “Power” box is assumed to be in the currently selected units. The adjacent drop-down box is used to set the current units. Changing the units will automatically convert the displayed numerical power to the new units.
980NM PUMP The 980nm Pump component is a single-wavelength source intended for pumping near 980nm.
After double-clicking on the 980nm Pump component, its dialog box is displayed. The single wavelength is entered in the “Wavelength” box. The power entered in the “Power” box is assumed to be in the currently selected units. The adjacent drop-down box is used to set the current units. Changing the units will automatically convert the displayed numerical power to the new units.
1480NM PUMP The 1480nm Pump component is a single-wavelength source intended for pumping near 1480nm.
After double-clicking on the 1480nm Pump component, its dialog box is displayed. The single wavelength is entered in the “Wavelength” box. The power entered in the “Power” box is assumed to be in the currently selected units. The adjacent drop-down box is used to set the current units. Changing the units will automatically convert the displayed numerical power to the new units.
PUMP COUPLING WDM WDM Pump Coupler components are used to couple pump laser output into the signal path. Two types of pump coupling WDM components are provided: 1x2 (for backward pumping) and 2x1 (for forward pumping.) After double-clicking on the WDM component, its dialog box is displayed.
The optical performance specifications, in the bottom half of the dialog box, are divided into four groups based upon the input and output ports for the given parameter. For example, signal insertion loss and pump isolation are both concerned with signal-tocommon port optical transfer function, while pump insertion and signal isolation are both
concerned with the pump-to-common port optical transfer function. Ports connected to red lines inside the component’s icon are the signal path, while those attached to blue lines are on the pump path. Ports with both red and blue internally connected lines are common to both the signal and pump paths. For all parameters, a single number can be used by typing that value into the appropriate edit box. This numerical value will then be used at all appropriate wavelengths. A wavelength-dependent function can also be uploaded from an ASCII file by clicking on the “From File” button located next to the desired parameter and then browsing to find the desired file. The program expects the file to be in the format of ASCII data, tab delimited, in two columns: the first column is the wavelength in nanometers, and the second column is the transmission in dB. For example, a flat 50% transmission, corresponding to a 3dB loss, would be represented in an ASCII file as: 1530 1531 1532 λ N
-3 -3 -3 dB N
The current optical transfer function for each parameter can be viewed by clicking the “Graph” button next to the desired parameter. The current optical transfer function is displayed. If a wavelength-dependent transfer function has been uploaded for a given parameter and you would like to revert back to using the single numerical value for that parameter, click on the “Reset” button next to the desired parameter. The previously uploaded wavelength-dependent function will be deleted and the current values in the corresponding edit boxes will be used instead. To use the wavelength-dependent function again, it must be reloaded from a file as before.
ISOLATOR Isolators are used to allow optical propagation in only one direction, much like diodes are used in electrical circuits. The icon for an isolator is the same as that commonly used in electronics. The direction of allowed propagation is indicated by the direction of the arrow, or left-to-right in this case. After double-clicking on the component icon, the isolator’s parameter dialog box is displayed. The four parameters (isolation, insertion loss, input return loss, and output return loss) can be given a single numerical value, or use a wavelength-dependent transfer function uploaded from an ASCII file. A wavelengthdependent function is uploaded from an ASCII file by clicking on the “From File” button located next to the desired parameter and then browsing to find the desired file. The program expects the file to be in the format of ASCII data, tab delimited, in two columns: the first column is the wavelength in nanometers, and the second column is the transmission in dB. For example, a flat 50% transmission, corresponding to a 3dB loss, would be represented in an ASCII file as: 1533 1534 1535 λ N
-3 -3 -3 dB N
The current transfer functions can also be graphed by clicking on the “Graph” button and reverted to single values by clicking on the “Reset” button, again just as described for WDM components.
FILTER Filters are used to selectively eliminate different wavelengths of light from the optical path. In this simulation, filters work identically for light propagating in either direction, and the amount of light reflected from either port is controlled by the input and output return losses only. When first created, filters have a unity transmission (minus any insertion and return losses). To create a filter of a desired shape, a spectrum can be uploaded from an ASCII file by clicking on the “Load Spectrum From File” button and selecting the desired file. The program expects the ASCII file to be in a two-column, tabdelimited format as follows: Wavelength (nm)
Transmission (dB)
For example, a spectrally flat 50% filter file would look like: 1530 1531 1532 λ N
-3 -3 -3 dB N
This is identical to the format expected for loading transfer functions for other components. The current insertion loss is subtracted from the loaded spectrum. In order to make the filter’s spectrum identical to that loaded from a file, set the insertion loss to 0 first. Filter shapes can also be automatically created by optimization routines. For example, the GFF optimization routine (see GFF (Gain Flattening Filter) Optimization, p. 55) will automatically generate a desired spectrum for the selected filter. This spectrum can then be saved from the spectral graph for use in specifying a GFF filter shape. To view the current filter spectrum, click on either the “Loss Spectrum – Signal Band” or “Loss Spectrum – Full Band” to see the spectrum for the respective band.
ATTENUATOR Attenuators are used to reduce the optical power across the spectrum by a constant amount, somewhat similar in application to neutral density filters in visible and infrared optical systems. Some attenuators also have a wavelength-dependent loss. Both types of attenuators can be modelled. The minimum and maximum wavelengths determine the operating range of the attenuator. Any wavelengths outside of this range are rejected (unless using a wavelength-dependent transfer function uploaded by the user from an ASCII file). The attenuation, input return loss, and output return loss can be specified with a single value, or a wavelengthdependent function can be uploaded from an ASCII file by clicking on the “From File” button. The program expects the file to be in the format of ASCII data, tab delimited, in two columns: the first column is the wavelength in nanometers, and the second column is the transmission in dB. For example, a flat 50% transmission, corresponding to a 3dB loss, would be represented in an ASCII file as: 1536 1537 1538 λ N
-3 -3 -3 dB N
The current attenuator transfer functions can be viewed by clicking on the respective “Graph” button, and a parameter can revert to the single value by clicking on the “Reset” button. Attenuators that use single values for parameters (as opposed to wavelength-dependent parameters) are particularly convenient because they can be used in iterative simulations (see Running Iterative Simulations on p. 56) for varying values. If a wavelengthdependent attenuation is uploaded, the attenuation can not be changed in iterated simulations.
CIRCULATOR Circulators are used to split counter-propagating light into different paths. Light propagates either from the upper left port to the right port, or from the right port to the lower left port. As indicated by the bar in the icon, light is not meant to propagate between the upper and lower left ports. The minimum and maximum operating wavelengths determine the operating range of the circulator. Any wavelength outside of this operating range is rejected. The insertion loss, return loss, isolation, and directivity can be specified. For the purposes of this simulation, the isolation refers to rejection of light propagating from the right port to the upper left port, and from the lower left port to the right port. The directivity refers to light propagating between the upper left and lower left port.
SPLICE Splices are simple representations of splice losses found anywhere fibers are spliced together. They are separate components for purposes of aesthetics, and for explicit use in iterative simulations, where the effects of splice loss variations can be examined. Splice losses to components can either be modelled implicitly, through a component’s insertion loss, or explicitly, but placement of a splice component, depending upon the user’s needs and preferences. Splices have operating wavelength ranges, and any wavelength outside of these ranges is eliminated. Two different splice losses can be specified: signal and pump band. The signal band also covers the ASE band, so the signal minimum and maximum wavelength should define a range large enough to accommodate the entire ASE band as well.
CONNECTOR Connectors represent two connectorized fibers mated through a bulkhead. For purposes of the simulation, connectors behave identically to splices, described above. A separate connector component is included for aesthetic purposes and clarity in the schematic representation of the design. The parameters for a connector are identical to that for a splice, described above, except for the inclusion of back-reflection from both ports, which is incorporated through the return loss parameter.
T AP Taps are used to remove a small portion of the signal band, typically for power monitoring applications. The two top ports are the signal ports, and the one bottom port on the right is the tap output port. The operating range is defined by the minimum and maximum wavelength parameters. Any wavelength outside of this range is rejected. The tap percentage is the amount of light input to the left port that is output of the lower right (tap) port, after accounting for the insertion loss.
FIBER BRAGG GRATING Fiber Bragg Gratings (FBG’s) are used to either selectively filter or reflect light at different wavelengths. In this simulation, they work identically to filters except that all light rejected (from either direction) by the filter shape is actually reflected and propagated in the opposite direction. Otherwise, the parameters and dialog box for FBG’s are identical to that of filters described above (see Filter on p. 17 above.) The current insertion loss is subtracted from the loaded spectrum. In order to make the grating’s spectrum identical to that loaded from a file, set the insertion loss to 0 first. As is the case for filters, FBG shapes can be generated via the GFF optimization routine [see GFF (Gain Flattening Filter) Optimization on p. 55] by selecting the desired FBG component as the GFF filter. However, when using FBG’s as gain flattening filters, the spectrum reflected by the FBG is taken into account, so the optimized, gain-flattening FBG spectrum will be slightly different than that which would be obtained from using a (thin-film) filter component as the gain flattening filter.
SPLITTER Splitters are used for dividing a signal equally into two separate output fibers. The component represented by a splitter in this simulation takes any optical power input to a port and divides it equally into two output spectra emerging from the ports on the opposite side (after accounting for the insertion loss.) The minimum and maximum wavelength parameters define the operating range. Any wavelength outside this operating range is rejected. The split percentage is defined as the percentage of light input into any port (minus insertion loss) which is output of the diametrically opposed port.
PROBE Probes do not model real components, but rather are a convenient method of making two-point measurements of interest in an amplifier design. Probes do not actually “participate” in the simulation, and therefore can be added or deleted after a simulation has been running without affecting the simulation data. (Because of this, the status light in the status bar will not change solely due to addition or deletion of a probe.) In order to use a probe to make measurements, both of its ports must be connected to the desired test points. To do this, fibers must be connected to the ports. This is accomplished in the same way as for normal components, with the exception that once a fiber has been attached to a probe port, it is no longer a “fiber” but is rather a “probe lead.” Once it is a probe lead, it can no longer be attached to any other component’s port. (Also, any fiber that is currently attached to a component port cannot be attached to a probe port.) Probe leads can only be attached to other fibers (not other probe leads). This is done by “dropping” the free end of the probe lead onto a fiber. A successful connection of a probe lead to a fiber is indicated by a large black circle appearing at the point of intersection of the probe lead and the fiber. Once a probe’s ports are connected to desired fibers, measurements can be made between those two points by double-clicking on the probe icon. The measurements and graphs that can be viewed are described in Viewing Probe Data on page 49.
S AVING COMPONENTS TO DISK A component can be saved to disk by clicking on the “Save” button at the lower left corner of its dialog box. When a component is saved to disk, all of its user-specified parameters are saved, including the optical transfer function information. Each component type has a unique file extension added to it for ease of future identification. By saving components to disk in this way, a library of user-specific components can be built up to be conveniently used in other designs.
S AVING THE SIMULATION TO DISK Clicking on the disk icon in the main menu, or selecting “File” and “Save” or “Save As,” allows the user to save the amplifier design, in its current state, to the disk. Every amplifier design is saved with a “.amp” file extension. The design is saved in its current state, meaning that the latest simulation run (or incomplete run, if prematurely terminated), and the latest iterative simulation run are saved. To save different simulation runs of the same design, a separate file with a different name should be used.
RUNNING THE B ASIC SIMULATION SETTING UP GLOBAL P ARAMETERS There are several global parameters which affect the accuracy and speed of the simulation. The default values have been chosen to give a good compromise between speed and accuracy. However, in certain circumstances, such as verifying a final design or doing a quick initial estimation, the user may wish to change these parameters. To do so, select “Global” and “Simulation Parameters” from the main menu. The Global Simulation Parameters dialog box will then be displayed. The purpose and effects of each available parameter are outlined below:
ERROR TOLERANCE This is the maximum estimated error allowed during each step of the RungeKutta differential equation solving algorithm, given as a ratio of the estimated error in optical power to the current optical power at a given point in the fiber. If the algorithm estimates that the error will be larger than this minimum value, the algorithm’s step size is reduced. Therefore, a smaller error tolerance will lead to longer simulation times. The default value is 0.01, which is acceptable for initial design simulations, but it is recommended that for final design verification a value of 0.001 be used.
MINIMUM STEP SIZE This is the minimum step size that the differential equation solver allows in solving the erbium fiber equations. As mentioned above, the algorithm will reduce the step size if it estimates too large an error. However, the algorithm will never be a llowed to reduce the step size below this minimum step size, even if the estimated error is larger than the error tolerance. The default value is 0.1m, but for final design verification it is recommended that a value of 0.01m be used.
M AXIMUM STEP SIZE This is the maximum step size that the differential equation solver will ever allow. In addition to decreasing the step size if the estimated error is too large, the algorithm also increases the step size if it estimates that the error is extremely small, in order to speed calculations. However, the algorithm will never be allowed to increase the step size above this maximum value. The default value is 0.5m and it should be acceptable to leave it at this value for all cases.
M AXIMUM FIBER P ASSES This is the maximum number of times the differential equation solver will make a forward and backward pass through the fiber in an attempt to reach convergence. The default value is 15. It is recommended that this number be at least 5.
M AXIMUM INVERSION CHANGE If the maximum change in inversion at any point in the fiber from one pass to the subsequent pass is less than this number the differential equation solver will assume convergence has occurred. Decreasing this number will increase simulation time by requiring more fiber passes. The default value is 0.01, but it is recommended that a value of 0.001 be used for final design validation.
INVERSION STEP SIZE This is the distance between points within each erbium fiber for which the inversion level will be calculated. The default value is 0.1m. Decreasing this number will slightly increase the accuracy of the inversion interpolation between points, but will increase memory usage and the size of the resulting amplifier design file.
M AXIMUM NUMBER OF INVERSION STEPS This is the maximum number of points within each erbium fiber for which the inversion level will be calculated. If a given erbium fiber is so long that the inversion step size value would generate more than this number of data points, the inversion step size will be adjusted so that this maximum number of points is not exceeded. The default value is 500 points. Increasing this number will increase the inversion interpolation accuracy for very long fibers, but could increase memory usage and the size of the resulting amplifier design file.
MINIMUM NUMBER OF INVERSION STEPS This is the minimum number of points within each erbium fiber for which the inversion level will be calculated. If a given erbium fiber is so short that the inversion step size value would generate less than this number of data points, the inversion step size will be adjusted so that this minimum number of points is always used.
ASE STARTING W AVELENGTH This is the lower bound for the amplified spontaneous emission wavelength band calculated by the simulation.
ASE ENDING W AVELENGTH This is the upper bound for the amplified spontaneous emission wavelength band calculated by the simulation.
NUMBER OF ASE W AVELENGTH BINS This is the number of discrete ASE wavelengths that are calculated in the ASE band. The bins are uniformly distributed between the starting and ending ASE wavelength values selected above.
M AXIMUM NUMBER OF NETWORK P ASSES This is the maximum number of times the program will attempt to run the simulation through the network to check if convergence is reached. If convergence is not reached in the allotted number of passes through the network, the program will terminate, indicate an error, and leave the design with the data from its last pass. The data from a simulation that gave a convergence error should is not accurate. To solve this problem, either increase this maximum number of network passes, or look for places in the design where there are large back-reflectances and reduce them.
RUNNING THE SIMULATION The simulation can be initiated either by choosing “Simulation” and “Run” from the main menu, or clicking the start button (green arrow) on the toolbar.
SIMULATION PROGRESS DIALOG While the simulation is running, a dialog box is displayed indicating the progress of the simulation and several running values of interest.
CURRENT SIMULATION T ASK This control displays a description of the current simulation task. Most commonly it displays the name of the erbium fiber currently being solved, as this is the most timeconsuming calculation.
FIBER C ALC. # This counts the number of fiber calculations performed by the simulation. The displayed value is the number of the current calculation.
FIBER P ASS # This counts the number of passes through the current erbium fiber being calculated. A pass is defined here as a single forward and backward propagation of the algorithm through the fiber. The value displayed is the number of the pass currently being performed.
DIRECTION This displays the direction currently being propagated through the fiber, either “forward” or “backward.”
STEP SIZE This is the current step size (in meters) being used by the differential equation solver. This value is adjusted during calculation based on estimated errors but should never be outside the maximum and minimum values specified by the user in the Global Parameters menu.
LOCAL INVERSION This is the value of the erbium fiber inversion between 0 (completely non-inverted) and 1 (completely inverted) at the current fiber position.
FIBER POSITION This is the current position (in meters, starting from the fiber’s “left” end) being calculated by the algorithm.
INVERSION CHANGE This is the maximum inversion difference at any point in the fiber for the last two complete passes through the fiber. For convergence, this number must be less than that specified by the user in the Global Parameters menu.
PROGRESS B AR This progress bar indicates the status of the current forward or backward propagation pass. Both a forward and backward propagation must be completed for one complete fiber pass.
CURRENT GLOBAL T ASK This control displays a description of the current global task. This can be a normal simulation, an optimization, or an iterative simulation, depending upon what the user has selected.
GLOBAL PROGRESS B AR This progress bar indicates the status of the current global task, such as a normal simulation, optimizations, or iterative simulations.
PREMATURELY TERMINATING THE SIMULATION Pressing the Escape key (or clicking on the red “stop sign” icon in the toolbar) while the GainMaster™ window is the active window will terminate the simulation. Note that if the simulation is prematurely terminated the data contained in the design is not correct, as indicated by the red “Simulation data not current” light at the bottom left of the window.
A TA STATUS SIMULATION D ATA The light at the bottom left of the window is green if the design des ign data is current (i.e., the simulator has been run since the last change). The light is red if the design data is not current (i.e. the data does not represent the completed simulation of the latest changes).
A VING THE SIMULATION S AVING The simulation can be saved to disk (as an *.amp file) by clicking on the disk button in the toolbar or selecting “File” and “Save” or “Save As” from the main menu.
A SIC SIMULATION D ATA A TA VIEWING B ASIC A TA VIEWING PROBE D ATA Double-clicking on a probe component will display that probe’s dialog box. The user may view or select several measured parameters:
G AIN SPECTRUM Clicking on the Gain Spectrum button will display a graph of the gain as measured between the two fibers attached to this probe’s leads. Gain is defined as the ratio of the forward-propagating signal powers, with the lead attached to the probe’s left port considered the “input” for purposes of this measurement, and the lead attached to the probe’s right port considered the “output”. By clicking on the “Save” button in the gain graph window, an ASCII file of the plotted data can be saved to disk. The user-supplied filename is appended with a “.dat” extension to indicate it is an ASCII data file. The data file is in the form of two columns, tabdelimited, with a single header row indicating the type of data and units.
NOISE FIGURE SPECTRUM Clicking on the Noise Figure Spectrum button will display a graph of the noise figure with the same conventions as used in the above Gain Spectrum measurement. The noise figure is calculated assuming a shot-noise limited optical signal-to-noise ratio for the “input” signal. By clicking on the “Save” button in the noise figure graph window, and ASCII file of the plotted data can be saved to disk. The user-supplied filename is appended with a “.dat” extension to indicate it is an ASCII data file. The data file is in the form of two columns, tab-delimited, with a single header row indicating the type of data and units.
AVERAGE G AIN The displayed value is the average gain (in dB) over the entire signal band.
M AXIMUM G AIN The displayed value is the maximum gain (in dB) over the entire signal band.
MINIMUM G AIN The displayed value is the minimum gain (in dB) over the entire signal band.
G AIN FLATNESS (P-P) The displayed value is the peak-to-peak gain flatness (in dB) over the entire signal band.
G AIN FLATNESS (RMS) The displayed value is the root-mean-square gain flatness (in dB) over the entire signal band.
G AIN TILT The displayed value is the difference (in dB) of the gain at the shortest and longest wavelengths in the signal band.
POWER CONVERSION EFFICIENCY The displayed value is the power conversion efficiency calculated using all pump powers and the total signal power as measured by the probe’s output lead.
QUANTUM CONVERSION EFFICIENCY The displayed value is the quantum conversion efficiency calculated using all pump powers and their associated wavelengths and the total signal power as measured b y the probe’s output lead.
VIEWING OPTICAL POWER IN A FIBER Optical power in any fiber (other than probe leads) can be viewed by double-clicking on that fiber. A graph is displayed showing the forward signal power in the currently selected fiber. At the top of the graph are several options which the user may select as described below:
POWER B AND The user may select between the signal, pump, or ASE bands by selecting the appropriate button. The currently selected band is indicated by the solid black dot appearing next to the selected band name.
SIGNAL PROPAGATION DIRECTION The user may select between forward and backward-propagating optical power choosing the button next to the desired direction.
POWER UNITS The user can set the power units in which to see the data plotted by selecting the appropriate button next to the desired unit. Both the plot and the displayed power will be in these units.
IN-B AND POWER The total (integrated) in-band power is displayed in the currently selected units from above.
CHANGING GRAPH SCALE Right-clicking anywhere on the graph will display a pop-up menu. Selecting the “change y-axis scale” displays a dialog box that sets the minimum and maximum values of the graph. Changing these values will cause the graph to be redrawn with the new limits. Note that the units used for the limits are the currently selected units in the graph.
S AVING D ATA Clicking on the “Save Data” button will display a file dialog box. The user may type in a name or select a filename using this dialog box’s features. When the user clicks on “Save” an ASCII file will be created with a “.dat” extension. The ASCII file will contain the plotted data, in the currently selected units, in the form of two tab-delimited columns. The first column will contain the wavelength in nanometers, and the second column will contain the power value in the currently selected units. Each column will have a header indicating the type of data and units.
VIEWING ERBIUM FIBER COMPONENT D ATA Double-clicking on an erbium fiber component will display the erbium fiber component dialog box.
FIBER INVERSION VS. POSITION Clicking on the “Inversion vs. Position” button displays the plot of fiber inversion versus position. The inversion is the ratio of erbium ions in the upper state to the total number of ions, a number between 0 (non-inverted) and 1 (completely inverted). The position in the fiber is measured from the “left” end of the fiber. The number of data points in the graph is determined by the settings defined under the “Global Parameters” section, which can be accessed by selecting “Global” and then “Simulation Parameters” from the main menu. The scale of the y-axis can be changed by right-clicking anywhere on the graph and selecting “change y-axis scale,” then typing in the desired graph limits. This procedure is described in Changing Graph Scale shown in Viewing Optical Power in a Fiber above.
FIBER POWER VS. POSITION Clicking on the “Power vs. Position” button displays the plot of optical power within the erbium fiber. This plot is similar to that for normal fibers except for three important differences: 1) The slider located in the upper-right corner of the graph shows the current position in the erbium fiber. By moving this slider the user can display all optical power information, forward and backward, anywhere along the length of the fiber. 2) The “Lock Scale” button will adjust the yaxis scale of the graph to display the currently selected optical band and power units along the length of the fiber without change. This allows the user view the optical power through the fiber without the graph scale changing. 3) There are four numerical displays just above the graph that give the total optical power in all bands, for the pump, for the signal band, and for the ASE. The numerical values are in the currently selected units.
OPTIMIZATIONS One of the more powerful features of the software is its ability to optimize a given design. Optimization routines are automated algorithms that run a design’s simulation many times, changing various component parameters to achieve a desired performance goal.
GFF (G AIN FLATTENING FILTER) OPTIMIZATION In order to perform a GFF optimization, the current amplifier design must have at least one Probe and one Filter or Fiber Bragg component. The gain of the probe will be used as the feedback for the optimization algorithm, which will attempt to make the gain flatness for this probe below that specified by the user. Because of this, the probe leads should be attached between “input” and “output” points in the amplifier for which flat gain is desired. To initiate a GFF optimization, select “Optimize” and then “GFF” from the main menu. The “GFF Optimization Parameters” dialog box will be displayed. Choose the desired filter and probes by selecting their component names from their respective dropdown lists at the top of the dialog box. In the “Gain Flatness Specification” section, choose the maximum gain flatness allowed in dB, selecting either Peak-To-Peak or RMS. The optimization procedure will stop as soon as this specification is met. The final two parameters, located in the “Optimization Routine Parameters” section, are the Damping Factor and Maximum Iterations. The Damping Factor is a number used to multiply the gain error from flatness before using it to modify the filter shape. It should be < 1. A number very close to one will slightly speed up the convergence of the algorithm, but also increases the chances of creating “oscillations” around the desired solution. The Maximum Iterations parameter sets the number of loo ps the algorithm will make before failing to find an optimal filter shape.
RUNNING ITERATIVE SIMULATIONS A powerful method of optimizing and analyzing an amplifier design is the use of iterative simulations. Simply put, iterative simulations allow the us er to automatically run many simulations for designs with different component parameter values. This allows the user to examine the effects of design changes, production deviations, etc., on the performance of the amplifier design. Iterations are divided into two broad categories: Non-nested and nested. The choice between the two is made in the iterative setup dialog box. The iterative setup dialog box is accessed by selecting “Iterations” and “Setup & Run” from the main menu.
SETTING UP AND RUNNING ITERATIONS Once the iteration setup dialog box is displayed, the user must select the parameters to be varied. The parameters are selected by first choosing the component, and then the particular parameter to be varied. Current selections are displayed in the upper half of the dialog box labeled “Currently Selected Iterations.” There are 5 edit boxes in this section giving the component name, parameter name, start, end, and # steps values for each iteration currently in the list. To choose a new parameter, the following steps are performed: 1) In the “Add/Remove Component Iteration” section in the lower left part of the dialog box, choose the desired component from the “COMPONENT NAME” drop-down box. 2) Once a component is selected, its available parameters will be added to the “PARAMETER” drop-down box, located just to the right. Select the desired parameter in this box. 3) In the sub-section called “Parameter Iteration Values” located just below these two boxes are controls for the actual parameter values to use. In the “START” box, type the beginning numerical value for the parameter. 4) In the “END” box, type the last numerical value for the parameter. 5) In the “# STEPS” box, type the total number of iterations desired, including the first and last (minimum of 2 required.) 6) Under “STEP SPACING,” choose either Linear or Log for the type of spacing. For linear spacing, the program will run simulations with different parameter values spaced evenly between the first and last value. For log spacing, the program will run simulations with different parameter values spaced evenly on a logarithmic scale between the first and last value. 7) Select the “Apply to all components of the same type” box if this iteration is to apply to all components of the same type. For example, to iteratively vary the temperature of all erbium fibers, create an iteration for only one erbium fiber and then check this box; the temperature of all erbium fibers in the design will be varied according to the specified iteration parameters. (For purposes of iterative
simulations, each separate “component type” is indicated as having a separate icon on the component toolbar, so, for example, 1x2 and 2x1 WDM’s are considered separate component types.) 8) Once all the appropriate selections have been made, click on the “Add” button located at the very bottom left of the dialog box to add this particular iteration to the list. This iteration, with its numerical values, should now be displayed in the “Currently Selected Iterations” section at the top of the dialog box. 9) In the “Iteration Options” section located at the lower right of the dialog box, check the “Nest Iterative Loops” for nested iterations, or uncheck it for normal iterations.
Only one iteration of a particular component/parameter combination can be selected. This is to ensure easy display of the results later. To edit a particular iteration, click on that iteration’s data in any of the edit boxes in the “Currently Selected Iterations” section; the values for the chosen iteration will now appear in the edit boxes of the “Add/Remove Component Iteration” section. Any of the values for that iteration can be modified, although the data isn’t actually changed in the list until the “Add” button is clicked.
Alternatively, clicking the “Remove” button deletes the currently selected iteration from the list. Clicking the “Remove All” button deletes all the iterations from the list Once all the changes have been made, clicking on the “Save Setup” will save this iteration setup and return to the design space. The current iteration setup will be displayed the next time the “Iterations – Setup & Run” menu item is selected. Clicking on “Run Iterations” will run the current iterations automatically through to completion.
VIEWING ITERATED SIMULATION RESULTS Once the iterated simulations have been run, the results may be viewed by selecting “Iteration” and “Graph Results” from the main menu. Regardless of whether non-nested or nested iterations were selected, the same dialog box is displayed, although the bottom half of the dialog box is used only for nested iterations.
Graphs for viewing iterative simulations are built by selecting an x-axis (independent) variable from the list of parameters that were iterated, then selecting a y-axis (dependent) variable, which can be any available parameter from any component in the design. To choose the independent variable, select one of the iterated parameters from the dropdown box labeled “x-axis variable” in the “Select an iteration parameters as the independent (x) variable for a graph” section of the dialog box. To choose the dependent variable, select a component and parameter in the two “y-axis variable” boxes located in the “Select a parameter as the dependent (y) parameter for the graph” section of the dialog box. If the selected parameter is wavelength-dependent, select the wavelength to graph from the list of available wavelengths in the “Wavelength (nm)” drop-down box. If the iterated simulations were not nested, then clicking the “Graph” button at the bottom of the dialog box will generate the desired graph.
If the iterated simulations were nested, there will be component/parameter items displayed in the list boxes entitled “Remaining Iterated Parameters” and “Graph Value” located in the “VALUES FOR OTHER ITERATED PARAMETERS (ONLY FOR NESTED ITERATIONS)” section of the dialog box. Because every parameter value is varied for all other parameter values in nested iterations, it is necessary for the user to choose the parameter values desired for those parameters not used as the independent or dependent variables. To choose these parameter values, click on a component/parameter combination in the “Remaining Iterated Parameters” list box. The possible values for the particular parameter are then displayed in the “Graph Value” box. Select the value to be used in the graph by clicking on the desired value in the “Graph Value” list box. The desired value should now be highlighted. Once all the desired values have been selected for the remaining iterated parameters, clicking on the “Graph” button will display the graph using data only from simulations where the parameters in the Remaining Iterated Parameter list are equal to those selected by the user.
EXAMPLES In the \Demos subdirectory are three example .amp files. These are in no way intended to be suggested amplifier designs, but are merely examples to show how to use the s oftware to design amplifiers. Any resemblance to actual amplifier designs are purely coincidental. The simulations in all three examples have been run and the data is saved and ready for viewing. The two files, 3StageDemo.amp and 3StageFlattenedDemo.amp contain a sample 3-stage amplifier design, with and without a gain-flattening filter, respectively. The flattened design has a filter whose shape was created using the GFF optimization routine, with less than 0.1dB gain flatness specified. The flattened design also has a pre-run iterative simulation varying the length of the third-stage fiber. The effects of this variation can be viewed as described in Viewing Iterated Simulation Results on page 59. The file Bidirectional.amp is an example of a bidirectional amplifier using two circulators to split the two propagation directions into different paths. The two probes, named Forward Probe and Backward Probe, are setup to show the amplifier performance for the forward and backward propagating signal paths.
Index Amplifier............................. ........................ 2, 5, 7, 9, 10, 12, 14, 15, 16, 41, 42, 44, 54, 55 Apply...................................................... ........................................................................... 56 ASCII ............................................... ................................. 12, 14, 15, 30, 31, 32, 34, 48, 51 Attenuator ................................................ ................................................................... 15, 34 Band .............................................. ...... 12, 13, 14, 15, 22, 32, 36, 38, 45, 48, 49, 50, 51, 53 Full ................................................................................................................................ 32 Signal .................................................. .......................................................................... 32 Channel ........................................... .............................................. 12, 13, 14, 24, 25, 26, 27 Component. 3, 5, 7, 9, 10, 12, 13, 14, 15, 18, 19, 20, 21, 22, 23, 29, 31, 32, 36, 41, 42, 52, 55, 56, 57 Connector............................................. ................................................... .................... 15, 37 Coupler.................................. ............................................................................................ 14 Delete ........................................... .................................................. ............................. 19, 57 Design ................. 2, 5, 7, 8, 9, 10, 12, 19, 21, 22, 37, 41, 42, 43, 44, 47, 54, 55, 56, 57, 58 Efficiency Conversion .................................................. .................................................. ................ 49 Erbium........................................................ ... 2, 5, 12, 18, 20, 21, 23, 43, 44, 46, 52, 53, 56 Error ............................................ .................................................. .................. 43, 44, 46, 54 Fiber. 2, 5, 10, 12, 15, 16, 18, 19, 20, 21, 23, 36, 37, 40, 41, 43, 44, 46, 47, 48, 50, 52, 53, 56 Filter.................................................. .............................................. 2, 14, 16, 32, 34, 39, 54 Fiber Bragg Grating ............................................. ............................................... .... 16, 39 Gain Flattening Filter............................................. ................................. 3, 15, 32, 39, 54 Flatness .............................................. ............................................... .......................... 49, 54 Frequency........................................................................ ............................................ 24, 25 G Star ................................................................................................................................ 23 Gain............................................................ ..................................... 2, 10, 14, 39, 48, 49, 54 Global................................... ....................................................................................... 43, 47 Global Parameter ................................................. .................................................. ....... 43 Graph................................................... 23, 25, 30, 31, 32, 34, 41, 48, 50, 51, 52, 53, 58, 59 Inversion .............................................. ................................................... ........ 44, 46, 47, 52 Isolator ........................................................................................................................ 14, 31 Iteration ............................................... ........................ 15, 34, 36, 42, 47, 55, 56, 57, 58, 59 ITU................................................ .................................................................. 12, 13, 24, 26 Grid ............................................................................................................................... 24 Source ................................................. .................................................................... 12, 24 Load .............................................................................................................. 5, 9, 18, 22, 32 Loss .............................................. ..................................................................................... 32 Loss Spectrum............................. .................................................................................. 32 Move .................................................. ................................................... .... 10, 11, 19, 20, 53 Nest .............................................. ................................................................... 55, 56, 58, 59 Noise ........................................................................................................................... 10, 48 Noise Figure..................................................... ................................................... .... 10, 48 Optimization ................................................... ................................ 2, 14, 32, 39, 47, 54, 55
