Photodetector Passive Alignment in Compact ROSA Demultiplexer Coupling
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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 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, allowing for efficient alignment and coupling within a small form factor, utilizing a photodetector mounting bar with spaced wire bond points to prevent interference and achieve high coupling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fiber arrays and lenses are used for optical coupling between photodiodes and demultiplexer outputs, then coupling efficiency is improved, but device size increases beyond available space in ROSA housing
Solution Approach 1:
The patent removes intermediate optical components (lenses and fiber arrays) from the coupling path between photodiodes and demultiplexer outputs. By directly coupling the photodiode arrays to the waveguide outputs of the demultiplexer, the solution eliminates the space-consuming intermediate components while maintaining effective optical coupling, thus resolving the contradiction between coupling efficiency and device size.
Solution Approach 2:
The patent merges the photodiode array and demultiplexer output interfaces into a direct coupling configuration. Instead of separate components (demultiplexer → fiber array → lenses → photodiodes), the design integrates them into a direct path (demultiplexer waveguide outputs → photodiode active areas), combining multiple functions into a compact arrangement that fits within ROSA housing constraints.
2Manufacturing precision
If active alignment techniques are used to align photodiodes with demultiplexer outputs, then alignment precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent incorporates alignment markings on the demultiplexer component that indicate the precise locations of waveguide outputs before assembly. These pre-marked positions allow photodiodes to be placed and bonded directly at the correct locations without requiring expensive active alignment equipment during manufacturing, thus achieving high alignment precision through preliminary preparation rather than costly real-time adjustment.
Solution Approach 2:
The patent uses simple, inexpensive alignment markings (such as printed or etched indicators) instead of expensive active alignment systems. These markings serve as disposable, single-use guides during assembly that eliminate the need for costly alignment equipment, achieving the same alignment precision at a fraction of the manufacturing cost.
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 solution enables high coupling efficiency and compact design in ROSA, facilitating efficient information transmission over multiple channel wavelengths while reducing the need for expensive active alignment methods and accommodating the limited space within the ROSA housing.
Implementation Method 1
an array of photodetectors aligned with and directly optically coupled to the multiple optical outputs
Data Source
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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.