Coherent Mixer Phase Deviation via Protective Layer Opening
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Actual coherent mixers exhibit larger phase deviations and imbalances compared to design values due to manufacturing variations, particularly in the film characteristics of the protective layer covering the multi-mode interference device, leading to reduced receiver sensitivity and crosstalk in phase-modulation optical transmission systems.
Innovation Solution
A coherent mixer design where at least a portion of the multi-mode interference device is partially exposed through an opening in the protective layer, allowing for improved balance and phase deviation alignment by reducing structural deviations and stress-induced refractive index changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the multi-mode interference device is entirely covered with a protective layer, then the protective layer provides protection to the multi-mode interference device, but the imbalance and phase deviation become large
Solution Approach 1:
The protective layer is segmented by forming an opening that exposes a specific region of the multi-mode interference device. This segmentation allows the protective layer to provide protection to certain areas while leaving other areas exposed, thereby reducing the harmful stress-induced refractive index changes that cause large imbalance and phase deviation, while still maintaining protective coverage for critical regions.
Solution Approach 2:
Different regions of the multi-mode interference device have different protective requirements. The opening in the protective layer is strategically positioned to expose specific regions where stress-induced refractive index changes are most problematic, while maintaining protective coverage in other regions. This local differentiation allows the system to achieve both protection and precision simultaneously.
2Reliability
If the protective layer covers the multi-mode interference device, then the multi-mode interference device is protected, but structural deviations and stress-induced refractive index changes occur
Solution Approach 1:
The protective layer is divided into covered and exposed regions through the opening. The exposed region allows the multi-mode interference device to maintain its original refractive index characteristics without stress-induced changes, while the covered regions provide protection. This segmentation resolves the contradiction between protection and refractive index stability.
Solution Approach 2:
The opening in the protective layer extracts or removes the protective layer material from a specific region, allowing the multi-mode interference device to be exposed in that area. This extraction eliminates the harmful stress-induced refractive index changes in the exposed region while maintaining protection in other regions, thereby stabilizing the overall refractive index composition.
3Manufacturing precision
If the multi-mode interference device is exposed through an opening in the protective layer, then phase deviation and imbalance are reduced, but the protective coverage is reduced
Solution Approach 1:
The protective layer is segmented into covered and exposed regions. The exposed region is strategically positioned to minimize its impact on protective coverage while maximizing its benefit in reducing phase deviation and imbalance. This segmentation allows the system to achieve both precision and adequate protection.
Solution Approach 2:
The opening is positioned to expose only the specific region of the multi-mode interference device where stress-induced refractive index changes are most problematic. The rest of the protective layer maintains its protective coverage, thereby achieving local optimization between precision and protection.
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
This design effectively reduces phase deviation and imbalance to desired ranges, enhancing receiver sensitivity and maintaining reliable performance in phase-modulation systems like QPSK, by minimizing the impact of manufacturing variations and stress on the multi-mode interference device.
Implementation Method 1
When the signal light and the reference light are input to the multi-mode interference device, the signal light and the reference light interfere with each other in the multi-mode interference device. Then, light propagating through the multi-mode interference device is coupled to output ports of the multi-mode interference device. The light from the output ports of the multi-mode interference device has an amplitude corresponding to the phase difference between the signal light and the reference light.
Implementation Method 2
In order to obtain photo-electric conversion characteristics in the waveguide-type photodiodes, the protective layer is formed on side surfaces and a top surface of each of the waveguide-type photodiodes to cover the waveguide-type photodiodes with the protective layer.
Data Source
AI summary
A coherent mixer includes a substrate including a principal surface, the principal surface having a first area and a second area; a multi-mode interference device provided on the first area of the substrate; a light-receiving device provided on the second area of the substrate, the light-receiving device including a plurality of waveguide-type photodiodes; a first input waveguide optically coupled to the multi-mode interference device; a second input waveguide optically coupled to the multi-mode interference device; a plurality of optical waveguides optically coupling the multi-mode interference device to the plurality of waveguide-type photodiodes; and a protective layer covering the first and second areas of the substrate, the protective layer covering the plurality of waveguide-type photodiodes. The protective layer has an opening in the first area of the substrate. In addition, the multi-mode interference device has a surface that is at least partially exposed at the opening of the protective layer.