LCOS Wavelength Selective Switch Crosstalk Suppression
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Solution Overview
Problem
Existing wavelength selective switches (WSS) based on liquid crystal on silicon (LCOS) suffer from crosstalk issues due to the generation of diffraction orders other than the primary +1 order, which affects system performance and requires effective suppression to meet the Flexgrid requirement.
Innovation Solution
The LCOS panel is deflected by a small angle using either the wavelength direction or port direction as an axis, and a blazed-grating-like structure is configured to adjust diffraction angles, ensuring that only +1-order diffractive light is output from the correct port, while other orders are directed to peripheral areas, preventing crosstalk without adding additional components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LCOS is used to implement Flexgrid filter function, then spectrum utilization is improved and no spectrum gap exists, but crosstalk signals are generated due to high-order diffraction light
Solution Approach 1:
The patent extracts and removes the harmful high-order diffraction light from the optical path by positioning it outside the fiber array coverage area, while retaining the useful +1-order diffractive light. This is achieved by deflecting the LCOS panel to create a blazed grating structure that spatially separates different diffraction orders, effectively taking out the harmful components without affecting the desired signal transmission.
Solution Approach 2:
The patent converts the harmful effect of high-order diffraction light into a beneficial spatial separation mechanism. By utilizing the natural diffraction phenomenon and deflecting the LCOS panel, the high-order light that would normally cause crosstalk is redirected to peripheral areas outside the fiber array, transforming a harmful effect into a useful tool for wavelength selective switching with automatic crosstalk rejection.
2Reliability
If LCOS panel is deflected to suppress crosstalk, then system performance is improved, but device complexity increases
Solution Approach 1:
The patent implements dynamics by making the LCOS panel deflectable rather than fixed. The panel can be tilted by a small angle around a wavelength direction axis or port direction axis, allowing dynamic adjustment of the blazed grating structure. This dynamic capability enables the system to adaptively suppress crosstalk for different wavelength configurations while maintaining a relatively simple overall device structure without requiring additional optical components.
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 effectively suppresses crosstalk, meeting the requirement of less than -30 dB crosstalk suppression with low costs by ensuring that only +1-order diffractive light enters the intended output port, thereby enhancing system performance.
Implementation Method 1
Because of a birefrigent effect of liquid crystal, the different voltages are corresponding to different phase delays, thereby forming a structure similar to a blazed grating (Blazed grating)
Implementation Method 2
A diffraction angle of the blazed grating depends on a grating period of the blazed grating. Therefore, a diffraction angle of incident light may be controlled merely by changing grating periods corresponding to different positions on the LCOS
Implementation Method 3
The LCOS panel is deflected by a small angle using either the wavelength direction or port direction as an axis, and a blazed-grating-like structure is configured to adjust diffraction angles
Data Source
Figure 1~2
Figure 3
Figure 4~5
AI summary
According to a WSS provided by embodiments of the present invention, without adding any additional component, other diffractive light different from +1-order diffractive light can be prevented from entering any input port or output port, provided that an LCOS panel is correspondingly rotated. This suppresses crosstalk with low costs.