Specs
Mach Zehnder Variable Coupler
Optical Switch
WDM Splitter/Combiner
Model for performance inviestigation
The graph shows output X, for a number of wavelengths with corresponding intensities. input at A, The output Y is (1-X). Path length difference (L1 – L2) is fine tuned by the piezo wafers in the linking arms L1 and L2. The initial path difference can be determined at assembly as zero or any other preset value.Variation of the input parameters is shown in the input screen.
The number of points is chosen for screen resolution and the graph shows the output over the stretch length stating at the Optical path difference selected. Selection of input spectrum gives a bar chart of the input wavelength and intensity. Selection of the coupling ratio shows the predicted ratio for the set of wavelengths
The Center Wavelength is that for which couplers are set 0.5 (50/50 or 3dB) ratio The ratios of the couplers can be changed to simulate manufacturing tolerances Wavelengths can be input along with the corresponding intensities to model a source with a given bandwidth, or a number of narrow band sources, or a combination of many source parameters.
The wavelengths can be summed to give an integrated output for all inputs and the lower part of the graph can be magnified to enable cross talk to be investigated accurately.
In practice the operation is by a small piezo stretch of little more than one wavelength, which allows switching or action as a variable ratio coupler. The model allows large stretches for investigation. The path difference can then be set to a chosen value and the stretch reduced to allow detailed observation at that path difference.
Refractive index is set at 1.460 but acts only as a scaling parameter. ( dispersion and birefringent axes are not considered in this model) although it is expected that the device will operate with PM couplers used on the slow axis.
The defaults are graphed by simply pressing "Load/Run". Pressing Example buttons loads data and pressing "Load/Run" generates the output. The parameters can be changed to any values and "Load/Run" will generate an output. Check the boxes for input spectrum and coupling ratio graphs.
The default is for a narrow band source, with 50/50 couplers set at the center wavelength. Fringe visibility is essentially 100%.
Example 1 shows the degeneration of fringe visibility compared to the defaults, by setting coupling ratios off the optimum 50/50 (0.5) setting, and setting at a lower wavelength.
Example 2 shows a WDM application for two wavelengths.
Example 3 shows a 1550 switch application at zero OPD which is the most thermally and acoustically stable state.
External inputs for wavelength and intensity are loaded from dataW.txt and dataI.txt files stored in a C:\CIRLsw directory. These files can be made with a word processor and saved with the .txt option.
Bandwidth
The couplers within the assembly are wavelength dependent. The Bandwidth figure shows three curves that illustrate spectral response for different core to core separation. Coupling ratio is defined as Y/(X+Y). The slope of the curves becomes zero at 100% coupling and then becomes negative. This model is general for most fiber types. The program MZV V1.0 limits wavelengths to 0.8 and 1.5 times the center wavelength to maintain singlemode operation and adequate guidance.
Driver PCB/Control Unit
The driver PCB card has inputs for both an analog variable path length (0 to 8V input) and a logic (0 to 5V ) input that drives factory preset voltage levels to switch from X to Y output at a specified wavelength. The device in this case acts as an optical switch. The voltage levels can be adjusted for a new wavelength.
The logic input is filtered and switching time is over a few msec as the piezo tends to ring if driven by a square wave.. There is a settling time of several tens of msec after switching to allow for hysteresis and plastic creep of the fiber jacket. Analog signals of up to 200Hz are followed well.
The unit is encapsulated in a silicone elastomer and is thermally stable. The zero path difference case is self compensating. The package, like all piezo devices, is micro-phonic and should be mounted free of vibration.
The driver PCB requires +/- 15V DC and +180V DC regulated power supplies and appropriate input signals. A Control unit is supplied that has the power supplies included.
The logic input is filtered and switching time is over a few msec as the piezo tends to ring if driven by a square wave. There is a settling time of several tens of msec after switching to allow for hysteresis and plastic creep of the fiber jacket. Analog signals of up to 200Hz are followed well.
The unit is encapsulated in a silicone elastomer and is thermally stable. The zero path difference case is self compensating. The package, like all piezo devices, is micro-phonic and should be mounted free of vibration.
The driver PCB requires +/- 15V DC and +180V DC regulated power supplies and appropriate input signals. A Control unit is supplied that has the power supplies included.