Voltage dependent avalanche photodetector
Keywords
optical, electrical, unidirectional
Ports
Name  Type 

input  Optical Signal 
output  Electrical Signal 
bias  Electrical Signal 
Properties
General Properties
Name  Default value  Default unit  Range 

name Defines the name of the element. 
VD Avalanche Photodetector     
annotate Defines whether or not to display annotations on the schematic editor. 
true    [true, false] 
enabled Defines whether or not the element is enabled. 
true    [true, false] 
type Defines the element unique type (read only). 
VD Avalanche Photodetector     
description A brief description of the elements functionality. 
Voltage dependent avalanche photodetector     
prefix Defines the element name prefix. 
VD_APD     
model Defines the element model name. 
     
library Defines the element location or source in the library (custom or design kit). 
     
local path Defines the local path or working folder $LOCAL for the element. 
     
url An optional URL address pointing to the element online help. 
     
Standard Properties
Name  Default value  Default unit  Range 

frequency at max power Defines whether or not to automatically set the frequency of operation of the element at the location of the peak with maximum value. 
true    [true, false] 
frequency Central frequency of operation. 
193.1  THz* *std. unit is Hz 
(0, +∞) 
input parameter Defines whether to provide the responsivity or a table with frequency dependent values. 
constant    [constant, table 
responsivity The responsivity of the photodetector. 
1  A/W  (0, +∞) 
load from file Defines whether or not to load measurements from an input file or to use the currently stored values. 
false    [true, false] 
measurement filename The file containing the frequency dependent responsivity values. 
     
measurement The table containing the frequency dependent responsivity values. 
<2> [193.1e+012, 1]     
dark current The dark current for the photodetector. 
0  A  [0, +∞) 
thermal noise The thermal noise for the photodetector. 
100e024  A/Hz^.5* *std. unit is W/Hz 
[0, +∞) 
saturation power The saturation power of the photodetector. 
20  mW* *std. unit is W 
(0, +∞) 
Numerical Properties
Name  Default value  Default unit  Range 

enable power saturation Defines whether or not to enable power saturation. 
false    [true, false] 
enable thermal noise Defines whether or not to enable thermal noise. If 'true', the user will have to specify the 'thermal noise' value. 
true    [true, false] 
enable shot noise Defines whether or not to enable shot noise. If 'true', the shot noise will be calculated and added to the signal. 
true    [true, false] 
convert noise bins Defines if noise bins are incorporated into the signal waveform. 
true    [true, false] 
automatic seed Defines whether or not to automatically create an unique seed value for each instance of this element. The seed will be the same for each simulation run. 
true    [true, false] 
seed The value of the seed for the random number generator. A value zero recreates an unique seed for each simulation run. 
1    [0, +∞) 
Numerical/Digital Filter Properties
Name  Default value  Default unit  Range 

single tap filter Defines whether or not to use a single tap digital filter to represent the element transfer function in time domain. 
false    [true, false] 
number of taps estimation Defines the method used to estimate the number of taps of the digital filter. 
fit tolerance    [disabled, fit tolerance, group delay 
filter fit tolerance Defines the mean square error for the fitting function. 
0.001    (0, 1) 
window function Defines the window type for the digital filter. 
rectangular    [rectangular, hamming, hanning 
number of fir taps Defines the number of coefficients for digital filter. 
256    [1, +∞) 
maximum number of fir taps Defines the number of coefficients for digital filter. 
4096    [1, +∞) 
filter delay Defines the time delay equivalent to a number of coefficients for digital filter. 
0  s  [0, +∞) 
initialize filter taps Defines whether to use the initial input signal to initialize filter state values or to set them to zero values. 
false    [true, false] 
Diagnostic Properties
Name  Default value  Default unit  Range 

run diagnostic Enables the frequency response of the designed filter implementation and the ideal frequency response to be generated as results. 
false    [true, false] 
diagnostic size The number of frequency points used when calculating the filter frequency response. 
1024    [2, +∞) 
Multiplication Factor Properties
Name  Default value  Default unit  Range 

multiplication factor type The multiplication factor type for the Avalanche Photodetector. 
bias dependent table    [constant, bias dependent table, power and bias dependent table 
multiplication factor constant The multiplication factor constant for the Voltage Dependent Avalanche Photodetector. 
1    [0, +∞) 
load multiplication factor from file Defines whether to load multiplication factor from an input file or to use the stored values. 
false    [true, false] 
multiplication factor filename The file containing the bias/power dependent multiplication factor values. 
     
multiplication factor table The table containing the bias/power dependent multiplication factor values. 
<2> [1, 1]     
Ionization Ratio Properties
Name  Default value  Default unit  Range 

ionization ratio type The ionization ratio type for the Avalanche Photodetector. 
table    [constant, table 
ionization ratio constant The ionization ratio constant for the Voltage Dependent Avalanche Photodetector 
1    (0, 1] 
load ionization ratio from file Defines whether to load multiplication factor from an input file or to ignore it. 
false    [true, false] 
ionization ratio filename Defines whether to load multiplication factor parameters from an input file or to use the currently stored values. 
     
ionization ratio table The table containing the multiplication factor, loaded from file. 
<2> [1, 1]     
Results
Name  Description 

diagnostic/response #/transmission  The complex transmission vs. frequency corresponding to the ideal and designed filter. 
diagnostic/response #/gain  The gain vs. frequency corresponding to the ideal and designed filter. 
diagnostic/response #/error  Mean square error comparing the frequency response of the designed filter implementation with the ideal frequency response. 
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Implementation Details
This avalanche photodetector model implements a biasdependent multiplication factor to model biasdependent dark current and responsivity of the photodetector. The dark current and responsivity values that are input to the model must be given at unity gain bias (i.e., the bias where the multiplication factor is equal to one). Here, we define the unity gain bias to be where the second derivative of the photocurrent with respect to the voltage is zero [1]. For more information on extracting the multiplication factor as a function of bias, please see Avalanche photodetector, and 10V GeonSi APD with Si multiplication.
This model interpolates multiplication factor values at bias points that are not provided in the multiplication factor table. The multiplication factor table should provide sufficient bias points to accurately model the photodetector behavior, especially near the breakdown bias where multiplication factor values may vary significantly.
There are three options for the multiplication factor types available in the model:
 constant: user can provide a constant number of multiplication fator to the model
 bias dependent table: user can provide an N*2 multiplication factor table to the model. N is the number of bias voltage points, and the two columns are bias voltage values and corresponding multiplication factor values, respectively. User can also use the load from file option to load in the same table defined in a file.
 power and bias dependent table: user can provide an N*3 multiplication table to the model. N is the number of bias voltage points * number of power points, and the 3 columns are bias voltage values, optical power values and corresponding multiplication factor values, respectively. This option requires the entry for every (voltage, power) pair; for example, if we have 3 bias voltege valuies and 2 optical power values, we will need to define 6 entries (rows) in the multiplication factore table for all the (voltage, power) pairs. User can also use the load from file option to load in the same table defined in a file.
When the power and bias dependent multiplication factor table is provided and the factor type switches to bias depenedent table, the bias values and corresponding multiplication factors for the first power value in the table will be kept as the new bias dependent table:
When the bias dependent multiplication factor table is provided and the factor type switches to power and bias depenedent table, solver will pad 0s to the optical power values for the new table:
The APD is a highly sensitive semiconductor photodetector. For the demonstration of the VD APD photodetector, please see the example file VD_APD.icp, following is a figure of the demonstration system.
The settings of the APD element are shown below. The major parameters that should be taken into consideration when doing simulation are: the multiplication factor, dark current, and responsivity of the photodiode and the noises.


The following two figures are the eye diagrams of the system, at two different bias points with the values set according to the above table.
Please see also the APD photodetector.
[1]. H. T. J. Meier, "Design, characterization and simulation of avalanche photodiodes," Ph.D. dissertation, ETH Zurich, no. 19519, 2011.