Launch Optics Optical Path Compensation Wavelength Selective Switch
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Solution Overview
Problem
In optical networks using Wavelength Selective Switches (WSS), there is a discrepancy in the optical path lengths traversed by orthogonally polarized optical beam portions, leading to propagation differences that can be significant compared to the Rayleigh range, especially when dealing with astigmatic beams, which affects the routing accuracy.
Innovation Solution
The implementation of a method using two walk-off crystals oriented in opposite directions, combined with a half-wave plate, to adjust the optical path lengths of orthogonally polarized optical beam portions, ensuring they propagate over the same path length by rotating their polarization states and compensating for the differential path lengths introduced by the crystals and the half-wave plate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a single walk-off crystal is used to separate orthogonally polarized optical beams, then spatial separation is achieved, but optical path length difference between the two polarized portions increases
Solution Approach 1:
The patent divides the optical path compensation into two separate walk-off crystals oriented in opposite directions. The first walk-off crystal separates the input beam into two orthogonally polarized portions, while the second walk-off crystal, oriented oppositely, recombines them. This segmentation allows independent control of the optical paths for each polarization state, enabling compensation of path length differences while maintaining spatial separation.
Solution Approach 2:
The second walk-off crystal is oriented in the opposite direction to the first walk-off crystal. This inversion of orientation causes the second crystal to undo the path length difference introduced by the first crystal. Specifically, if the first crystal introduces a path length difference of ΔL for one polarization state, the oppositely oriented second crystal introduces a path length difference of -ΔL, thereby compensating the total path length difference to zero.
2Measurement precision
If walk-off crystals and half-wave plates are added to compensate path lengths, then routing accuracy improves, but device complexity increases
Solution Approach 1:
The walk-off crystals serve multiple functions: they spatially separate orthogonally polarized beams, introduce controlled optical path length differences, and when oriented oppositely, compensate for path length variations. The half-wave plate similarly serves multiple purposes by rotating polarization states to control which beam portion is walked-off by each crystal. This multi-functionality reduces the need for additional separate components for each function.
Solution Approach 2:
The patent uses parameter changes in the form of varying crystal thicknesses and orientations to achieve path length compensation. By selecting specific thicknesses for the first and second walk-off crystals and orienting them in opposite directions, the system compensates for optical path length differences without requiring complex active adjustment mechanisms. The half-wave plate's orientation is adjusted to rotate polarization states as needed.
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 effectively compensates for the path length differences, ensuring that both orthogonally polarized beam portions propagate over the same distance, thereby improving the routing accuracy and stability in optical networks, particularly for astigmatic beams.
Implementation Method 1
a first walk-off crystal for spatially separating the optical beam into first and second optical portions that are in first and second polarization states, respectively
Implementation Method 2
The first half-wave plate rotates the polarization state of the first and second optical portions of the optical beams
Data Source
Figure 1~2
Figure 3A~3B
AI summary
An optical device includes an optical port array, a first walk-off crystal, a first half-wave plate, a second walk-off crystal and a segmented half-wave plate. The optical port array has a first and second plurality of ports for receiving optical beams. The first walk-off crystal spatially separates the beams into first and second portions that are in first and second orthogonal polarization states, respectively. The first portions are walked-off by the first walk-off crystal and the second portions pass therethrough without being walked-off. The first half-wave plate rotates the polarization state of the first and second portions of the optical beams. The second walk-off crystal is oriented in an opposite direction from the first walk-off crystal such that the second portions are walked-off by the second walk-off crystal and the first portions pass therethrough without being walked-off. The segmented half-wave plate receives the first or second portions of the beams.