Direct Optical Coupling of Photodetectors to AWG Outputs
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Solution Overview
Problem
In optical communications networks, particularly in multi-channel receiver optical subassemblies (ROSA) of wavelength division multiplexed (WDM) passive optical networks (PON), there is a challenge in achieving high receiver sensitivity due to limited space for optical and opto-electronic components, which complicates optical coupling between photodetectors and optical demultiplexer outputs, and requires expensive active alignment techniques.
Innovation Solution
A compact multi-channel ROSA design that uses a passive alignment technique to directly optically couple photodetectors to optical demultiplexer outputs without intermediate components like lenses or fiber arrays, utilizing an arrayed waveguide grating (AWG) and a photodetector mounting bar with spaced wire bond points to facilitate high coupling efficiency within a small form factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fiber arrays and lenses are used for optical coupling, then coupling efficiency is improved, but device complexity and space requirements increase
Solution Approach 1:
The patent removes intermediate optical coupling components (lenses, fiber arrays) from the system. The photodetector array is positioned to directly receive optical signals from the AWG outputs through air coupling, eliminating the need for complex optical coupling mechanisms while maintaining high coupling efficiency.
Solution Approach 2:
The patent integrates the photodetector array directly with the AWG outputs in a unified optical path. The photodetector array is mounted on a substrate that is optically coupled to the AWG, merging the signal separation and detection functions into a compact integrated structure.
2Manufacturing precision
If active alignment techniques are used, then alignment precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent employs passive alignment where the photodetector array and AWG are positioned and aligned during the manufacturing process through self-alignment features and precise substrate mounting. The optical path is designed to automatically align components without requiring expensive active alignment equipment or procedures.
3Volume of moving object
If ROSA size is reduced, then space utilization is improved, but optical coupling difficulty increases
Solution Approach 1:
The patent replaces complex mechanical optical coupling systems (lenses, fiber arrays) with a direct air-coupled optical interface. The photodetector array is positioned in direct optical contact with the AWG outputs, eliminating the need for mechanical alignment of intermediate optical components and enabling compact integration.
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 approach enables high coupling efficiency (>95%) and reduces the need for expensive active alignment, allowing for more efficient use of space in optical transceivers while maintaining high receiver sensitivity.
Implementation Method 1
an array of photodetectors aligned with and directly optically coupled to the multiple optical outputs
Data Source
AI summary
A multi-channel receiver optical subassembly (ROSA) such as an arrayed waveguide grating (AWG), with outputs directly optically coupled to respective photodetectors such as photodiodes. In one embodiment, an AWG may be configured such that optical components of the AWG do not interfere with direct optical coupling, and the wire bonding points on the photodiodes may also be configured such that wire bonding does not interfere with direct optical coupling. The photodetectors may also be mounted on a photodetector mounting bar with a pitch sufficiently spaced to allow connection to floating grounds. A passive alignment technique may be used to determine the mounting locations on the photodetector mounting bar such that the photodetectors are aligned with the optical outputs.