Wavelength Division Multiplexer Crosstalk Reduction
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Solution Overview
Problem
Optical wavelength division multiplexers and demultiplexers based on cascaded Mach-Zehnder interferometers (MZIs) are sensitive to fabrication variations, leading to wavelength drift and inconsistent channel crosstalk due to process imperfections and wavelength-dependent responses of power splitting directional couplers.
Innovation Solution
A wavelength division multiplexer and demultiplexer design incorporating a first-stage MZI structure and multiple second-stage MZI structures, with phase delayed waveguides having relative optical path phase shifts of 0 and π, and alternately coupled optical couplers, to align output spectra with defined center wavelengths and reduce crosstalk by configuring MZI structures in cross-state conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If cascaded MZI structures are used for wavelength division multiplexing, then low insertion loss and flat-top passband are achieved, but spectral response becomes sensitive to fabrication variations causing wavelength drift
Solution Approach 1:
The patent changes the physical parameters of the waveguides by introducing deliberate length differences between parallel waveguides in each MZI arm. This creates fixed optical path differences that establish predetermined phase shifts, making the spectral response robust against fabrication variations. The length difference parameter is specifically designed to compensate for process imperfections and align the passband centers with ITU-T wavelength grids without requiring additional phase shifters.
2Measurement precision
If phase shifters are added to compensate phase error in MZI arms, then spectral response can be aligned to wavelength grids, but device complexity and fabrication sensitivity increase
Solution Approach 1:
The patent performs preliminary action by pre-establishing the required phase shifts through fixed length differences in the waveguide structures during fabrication. This eliminates the need for additional active phase shifters that would be required in conventional designs. The phase compensation is built into the structure itself, simplifying the device while achieving precise wavelength alignment to ITU-T grids.
3Ease of operation
If power splitting directional couplers are used in MZI structures, then optical beam splitting is achieved, but channel crosstalk becomes inconsistent across wavelengths due to wavelength-dependent response
Solution Approach 1:
The patent addresses the wavelength-dependent crosstalk issue by carefully designing the coupling parameters and length differences of the directional couplers. By optimizing these parameters, the couplers achieve more consistent splitting ratios across the operating wavelength range, reducing the variation in channel crosstalk. The length differences in the waveguides also help equalize the optical paths, further improving crosstalk consistency across different wavelengths.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design effectively reduces wavelength drift and channel crosstalk, enhancing fabrication tolerance and improving device production yield by aligning output spectra with target wavelengths and minimizing optical crosstalk among channels.
Implementation Method 1
phase delayed waveguides having relative optical path phase shifts of 0 and π, such that the output spectra are respectively aligned with the first and second center wavelengths
Implementation Method 2
phase delayed waveguides that are alternately coupled, and lengths and widths of two waveguide arms in the same set of phase delayed waveguides are different to each other
Implementation Method 3
at least two optical couplers and at least one set of phase delayed waveguides that are alternately coupled
Implementation Method 4
a waveguide structure with a first-stage MZI structure and two second-stage MZI structures
Data Source
AI summary
A waveguide division multiplexer and demultiplexer includes a first-stage Mach-Zehnder interferometer (MZI) and two second-stage MZIs. The first-stage MZI includes two input ends and two output ends, in which one of the inputs is configured to receive an input optical beam with a first center wavelength and a second center wavelength, and the output ends are configured to respectively transmit first-stage output optical beams respectively with the first center wavelength and the second center wavelength. One input terminals of the second-stage MZI are configured to respectively receive the first-stage output optical beams, and one output terminals of the second-stage MZI are configured to transmit second-stage output optical beams with the first and second center wavelengths, respectively. Each second-stage MZI is configured in cross-state condition.