Planar Lightwave Circuit Wavelength Selective Switch
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Solution Overview
Problem
Conventional wavelength selective switches (WSS) based on planar lightwave circuit (PLC) technology face challenges in integrating micro-electro-mechanical (MEMS) arrays within the PLC, requiring external bulk-optic lenses that are sensitive to misalignments and costly, due to the need for focusing wavelength channels outside the chip.
Innovation Solution
The solution involves a PLC chip with a curved interface between channel waveguides and slab waveguides to create a virtual pupil, focusing wavelength channels outside the chip, and using a field lens to straighten the focal plane and reduce spherical aberration, allowing for the placement of MEMS mirrors or other switching elements at the focal points for independent wavelength redirection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external bulk-optic lenses are used to focus wavelength channels outside the PLC chip, then the focusing function is achieved, but the device becomes sensitive to misalignments and cost increases
Solution Approach 1:
The patent merges the lensing function directly into the PLC chip by creating a curved interface between the waveguide layer and upper cladding layer. This integration eliminates the need for separate external bulk-optic lenses, thereby reducing alignment sensitivity and manufacturing cost while maintaining the focusing function.
Solution Approach 2:
The curved interface acts as an intermediary optical element that provides the necessary focusing power. Instead of using external lenses, the curved waveguide-cladding interface serves as the mediating structure that focuses wavelength channels to points on a circular focal plane, achieving the same function with improved integration.
2Adaptability or versatility
If wavelength channels are focused outside the PLC chip, then MEMS arrays can be placed at focal points for switching, but spherical aberration increases and requires corrective optics
Solution Approach 1:
The patent employs a curved interface between the waveguide layer and upper cladding layer, which naturally focuses light to a circular focal plane. This curvature is specifically designed to minimize spherical aberration while enabling the placement of MEMS arrays at the focal points for wavelength selective switching.
Solution Approach 2:
The patent optimizes the radius of curvature of the waveguide-cladding interface to balance focusing capability and aberration control. By carefully selecting this geometric parameter, the system achieves adequate focusing for MEMS placement while minimizing spherical aberration, reducing or eliminating the need for additional corrective optics.
3Power
If a curved interface is used to focus wavelength channels, then focusing power is provided, but the focal plane becomes curved requiring additional correction
Solution Approach 1:
The patent accepts the curved focal plane geometry as a feature rather than a defect by positioning MEMS mirror arrays on a corresponding circular arc. This transforms the problem of a curved focal plane into a solution where the switching elements naturally conform to the curved geometry, eliminating the need for planar correction optics.
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 configuration reduces aberrations significantly, minimizes the required mirror tilt range, and maintains robustness akin to a monolithic solution, while also reducing the cost by optimizing the channel/slab interface and using a cylindrical field lens, resulting in improved optical coupling and performance.
Implementation Method 1
an interface between the first array of channel waveguides and the input/output slab waveguide region is curved providing optical power, which focuses the wavelength channels along a curved focal plane outside of the PLC chip
Implementation Method 2
a field lens between the first edge of the PLC chip and the first array of switching elements for changing the focal plane of the wavelength channels from the curved line to along a straight line defining the first array of switching elements
Implementation Method 3
Each wavelength channels falls onto a different one of the tiltable mirrors 4, which redirect the individual wavelength channels back through the lensing 3 to whichever output AWG is desired
Data Source
AI summary
The present invention extends the concept of a standard array waveguide grating (AWG), which focuses each wavelength component launched via an input AWG to a Rowland circle inside a planar lightwave chip (PLC) where discrete waveguides are located, to one which focuses each wavelength component outside of the PLC chip along a straight line. An array of MEMS mirrors or other redirecting elements is positioned at the focus location for independently redirecting each of the wavelength channels back to any number of selected output AWGs formed on the same PLC chip as the input AWG.