Planar Lightwave Circuit Spatial Filter Array for Large Coherent Optical Systems
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Solution Overview
Problem
Existing spatial filter arrays based on fiber arrays face significant challenges in alignment and assembly, particularly for large arrays, making it difficult to produce coherent arrays larger than 30x30 channels due to the complexity of aligning individual fibers with microlens arrays.
Innovation Solution
A two-dimensional planar lightwave circuit (PLC) spatial filter array is developed, comprising a 2D PLC array coupled with lenslet arrays at the input and output, where the PLC waveguides are precisely positioned using photolithography, and mode filters are integrated to maintain spatial and temporal coherence, allowing for the assembly of large coherent arrays like 30x30 without the need for individual fiber alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If fiber arrays are used to create spatial filter arrays, then the array can be fabricated, but alignment difficulties with microlens arrays make it difficult to produce large coherent arrays (30x30 or larger)
Solution Approach 1:
The patent replaces the mechanical alignment system of fiber arrays with a planar lightwave circuit system. Instead of mechanically aligning individual fibers to microlens arrays, the PLC uses a planar waveguide structure where light is guided through integrated optical paths, eliminating the need for complex mechanical alignment while enabling large array sizes.
Solution Approach 2:
The patent extracts the alignment problem from the system by removing individual fiber elements and replacing them with an integrated planar waveguide structure. This extraction eliminates the need for fiber-to-microlens alignment, allowing the system to achieve large coherent arrays without the alignment limitations that plague fiber-based approaches.
2Ease of manufacture
If individual fibers are aligned with microlens arrays, then the spatial filter array can be assembled, but the assembly and alignment process becomes extremely complex and difficult
Solution Approach 1:
The patent merges multiple individual fiber alignment operations into a single integrated planar waveguide structure. Instead of assembling and aligning many separate fibers to microlens arrays, the PLC combines all waveguides into a unified planar circuit that is fabricated as a single integrated component, dramatically simplifying the manufacturing process.
Solution Approach 2:
The patent substitutes mechanical alignment procedures with an integrated planar fabrication process. The PLC waveguides are formed through standard semiconductor fabrication techniques (photolithography, etching) rather than mechanical assembly, eliminating the complex alignment steps required for fiber arrays while maintaining optical performance.
3Productivity
If fiber arrays are used, then the spatial filter array can be created, but the fill factor and optical throughput are reduced due to alignment limitations
Solution Approach 1:
The patent replaces mechanical fiber alignment with an integrated planar waveguide structure where optical paths are precisely defined by the waveguide geometry itself. This substitution eliminates alignment losses and enables tighter packing of waveguides, improving both fill factor and optical throughput simultaneously.
Solution Approach 2:
The patent optimizes the local optical properties of each waveguide region in the PLC. By designing waveguides with specific geometries and materials that are locally optimized for their function, the system achieves high optical throughput and fill factor without requiring precise mechanical alignment, as the optical paths are inherently defined by the planar structure.
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 PLC array enables the production of large coherent spatial filter arrays with improved alignment precision and optical throughput, maintaining spatial and temporal coherence, and optimizing fill factor, thus overcoming the limitations of fiber-based arrays.
Implementation Method 1
The PLC waveguides are produced by deposition of a plural number of silica layers on the silicon wafer, followed by photolithography and reactive ion etching (RIE) processes
Implementation Method 2
A plural number of mode filters are included in the silica-on-silicon waveguide such that the PLC waveguide is transparent to the fundamental mode but higher order modes are attenuated by 40 dB or more
Implementation Method 3
A large coherent two-dimensional (2D) spatial filter array (SFA), 30 by 30 or larger, is produced by coupling a 2D planar lightwave circuit (PLC) array with a pair of lenslet arrays at the input and output side
Implementation Method 4
All waveguides are precisely positioned by photolithography to precision align to the two microlens arrays
Data Source
AI summary
A large coherent two-dimensional (2D) spatial filter array (SFA), 30 by 30 or larger, is produced by coupling a 2D planar lightwave circuit (PLC) array with a pair of lenslet arrays at the input and output side. The 2D PLC array is produced by stacking a plurality of chips, each chip with a plural number of straight PLC waveguides. A pupil array is coated onto the focal plane of the lenslet array. The PLC waveguides are produced by deposition of a plural number of silica layers on the silicon wafer, followed by photolithography and reactive ion etching (RIE) processes. A plural number of mode filters are included in the silica-on-silicon waveguide such that the PLC waveguide is transparent to the fundamental mode but higher order modes are attenuated by 40 dB or more.