modulates an optical signal depending on electrical signal
Keywords
electrical, optical, bidirectional
Ports
| Name | Type |
|---|---|
| port 1 | Optical Signal |
| modulation | Electrical Signal |
| port 2 | Optical Signal |
Properties
General Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
name Defines the name of the element. |
Optical Modulator Measured | - | - |
|
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). |
Optical Modulator Measured | - | - |
|
description A brief description of the elements functionality. |
modulates an optical signal depending on electrical signal | - | - |
|
prefix Defines the element name prefix. |
OM | - | - |
|
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 |
|---|---|---|---|
|
configuration Defines the bidirectional or unidirectional element configuration. |
bidirectional | - | [bidirectional, unidirectional |
|
frequency Central frequency of operation. |
193.1 |
THz* *std. unit is Hz |
(0, +∞) |
|
length The interaction length of the modulator. |
1 | m | [0, +∞) |
|
input parameter Defines whether the input parameter is a table with voltage dependent values or coefficients of a polynomial function. |
table | - | [table, coefficients |
Standard/Table Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
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 measurement data. Refer to the Implementation Details section for the format expected. |
- | - | - |
|
measurement type Defines the type of measurement data. |
effective index | - | [absorption & phase, effective index |
|
measurement A matrix editor for users to read the element current modulation data values. |
<11,3> [-5, -4.5, -4,...] | - | - |
Standard/Coefficients Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
absorption coefficient a The polynomial coefficient for the absorption function. |
-0.0617 | dB/V^3/m | (-∞, +∞) |
|
absorption coefficient b The polynomial coefficient for the absorption function. |
-0.2804 | dB/V^2/m | (-∞, +∞) |
|
absorption coefficient c The polynomial coefficient for the absorption function. |
-0.6635 | dB/V/m | (-∞, +∞) |
|
absorption coefficient d The polynomial coefficient for the absorption function. |
-0.0719 | dB/m | (-∞, +∞) |
|
phase coefficient a The polynomial coefficient for the phase function. |
-0.0038 | rad/V^3/m | (-∞, +∞) |
|
phase coefficient b The polynomial coefficient for the phase function. |
0.1132 | rad/V^2/m | (-∞, +∞) |
|
phase coefficient c The polynomial coefficient for the phase function. |
-0.4825 | rad/V/m | (-∞, +∞) |
|
phase coefficient d The polynomial coefficient for the phase function. |
-0.0107 | rad/m | (-∞, +∞) |
Waveguide Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
modes List of optical mode labels supported by the element. |
TE,TM | - | - |
Enhanced Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
electrode type Defines the electrode type. Types include 'lumped' or 'traveling wave'. |
lumped | - | [lumped, traveling wave |
|
microwave loss Defines the microwave loss. |
0 | dB/m | [0, +∞) |
|
microwave index Defines the the microwave group index. |
3 | - | [0, +∞) |
|
optical index Defines the waveguide effective index. |
3 | - | [0, +∞) |
|
impedance mismatch Defines whether or not to include impedance mismatch effect. |
false | - | [true, false] |
|
source impedance Defines the source impedance. |
50 | Ohms | [0, +∞) |
|
characteristic impedance Defines the characteristic impedance. |
50 | Ohms | [0, +∞) |
|
terminating impedance Defines the terminating impedance. |
50 | Ohms | [0, +∞) |
Numerical Properties
| Name | Default value | Default unit | Range |
|---|---|---|---|
|
number of steps The number of discretization steps for the waveguide. |
30 | - | [2, +∞) |
====================================
Implementation Details
The Optical Modulator Measured (OMM) element shifts the phase of an optical signal based on an electrical signal input. The relationship between the electrical input and the phase shift can be defined using either polynomial coefficients or a table of values.
If a table of values is used, the phase shift can be directly specified using values for the phase shift and absorption, or the real and imaginary parts of the effective index. If the electrical signal amplitude is not one of the voltages specified in the table linear interpolation will be used. If coefficients are used, only the absorption and phase shift can be specified.
Note that this element is not meant to replace a straight waveguide element. Typically, to represent a modulated waveguide, these two elements are used together, as shown below:
When used in this way, these two elements can be thought of as overlapping each other. The waveguide element should have the properties of the unmodulated waveguide. The perturbation in effective index or phase/absorption due to the modulation can then specified by the OMM element. The straight waveguide element should have the length of the entire (modulated and unmodulated) waveguide, and the OMM element should have the length of the modulated section of the waveguide.
The "electrode type" can be "lumped" or "traveling wave". If the traveling wave option is selected, the "microwave loss", "microwave index", and "optical index" must be specified. An impedance mismatch can be included by specifying the "source impedance", "characteristic impedance", and "terminating impedance". For examples of the OMM element with traveling-wave electrode type, see the Traveling wave modulators with distributed electrodes example.
| NOTE: It is important to note that while the modulator and source give the appearance of an electro-optic modulator, the modulator input can represent any scalar value that affects the material index of the waveguide and therefore the effective index of its guiding mode. Hence, the modulating signal could just as well represent temperature as in a silicon waveguide with a heater. |
File Format
The working principle of the optical modulator (OM) measured is the same as the normal phase modulator, while it requires some user input information to define the modulator's characteristics. Please see the example file [[OM_Measured.icp]].
When the "input parameter" under the "Standard" category is set to "coefficient", the absorption coefficients and phase coefficients can be entered under the "Coefficients" category.
When the "input parameter" is set to be "table", input measurement file is required. The measurement type of the table can be set to be "absorption & phase" or "effective index".
If "absorption & phase" is selected under measurement type, the file format is:
(voltage(a.u.) absorption(dB/m) phase(rad/m))
-5.0 4.03632 5.67270
-4.5 2.77182 4.84456
-4.0 1.96181 3.99819
-3.5 1.44273 3.21548
-3.0 1.13272 2.51455
-2.5 0.88636 1.93182
-2.0 0.67634 1.45819
-1.5 0.46636 1.02092
-1.0 0.29273 0.60180
-0.5 0.13727 0.21909
0.0 0.0 0.0
Please see the example file abs_phase.txt. Please note that the unit for the "absorption" coefficient in dB/m and the unit for the "phase" coefficient is rad/m.
If "effective index" is selected under measurement type, the file format is:
(voltage(a.u.) real(neff) imag(neff))
-5 1.40392e-6 1.14823e-7
-4.5 1.19705e-6 7.88514e-8
-4 9.8792e-7 5.58086e-8
-3.5 7.94519e-7 4.10421e-8
-3 6.21325e-7 3.22231e-8
-2.5 4.77337e-7 2.52147e-8
-2 3.60305e-7 1.92402e-8
-1.5 2.52256e-7 1.32679e-8
-1 1.48701e-7 8.3277e-9
-0.5 5.41354e-8 3.90499e-9
0 0 0
Please see the example file [[effective_index.txt]].
In this example, the characteristics of the OM can be visualized by analyzers, following are the analyzers' output to measure the system.
|
|
|
| Fig. 1 Optical oscilloscope output for "coefficients" input parameter | Fig. 2 Optical spectrum analyzer output for "coefficients" input parameter |
|
|
|
|
Fig. 3 Optical oscilloscope output for "table" input parameter |
Fig. 4 Optical spectrum analyzer output for "table" input parameter |
Similar Elements
- Traveling Wave Optical Modulator (TWM): The TWM element is similar to the OMM element with the traveling wave electrode type, but it has two bidirectional electrical ports and relies on external elements to determine the impedance.
- Optical Amplitude Modulator (AM): The Optical Amplitude Modulator element directly modulates the optical signal, multiplying the power of the signal by a value proportional to the electrical signal.
- Optical Modulator Scripted: The relationship between the effective index or angle/loss properties and the input electrical signal in the Optical Modulator Scripted element is specified by a script rather than a table of values or coefficients.
Examples
The Optical Modulator Measured element is used in the following examples: