LCoS Phase Profile Optimization for Wavelength Selective Switches
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Solution Overview
Problem
Liquid crystal-based optical wavelength selective switches (WSS) face limitations in insertion loss and crosstalk due to phase reset and pixelization effects, which are not adequately minimized for optical communication network applications.
Innovation Solution
A two-step optimization process is employed to determine an optimized phase profile for the liquid crystal spatial light modulator (SLM), using nonlinear constrained optimization and phase scaling to create a programmable hologram that maximizes diffraction efficiency while minimizing crosstalk, with crosstalk threshold adjustments to achieve acceptable levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a liquid crystal spatial light modulator is used for wavelength switching, then beam steering between input port and multiple output ports is achieved, but insertion loss and crosstalk levels are increased due to phase reset and pixelization effects
Solution Approach 1:
The patent applies parameter changes by optimizing the phase profile parameters of the liquid crystal spatial light modulator. Specifically, it uses nonlinear constrained optimization to determine optimal phase values for each pixel, adjusting the phase distribution to maximize diffraction efficiency and minimize insertion loss. The optimization changes the phase parameters from conventional uniform distributions to non-uniform optimized profiles that account for the specific requirements of wavelength switching.
Solution Approach 2:
The patent implements feedback through an iterative optimization process. The system calculates the diffraction pattern resulting from a given phase profile, compares it against desired performance criteria (insertion loss, crosstalk levels), and uses this feedback to adjust the phase profile parameters. This iterative feedback loop continues until the phase profile achieves acceptable performance metrics, allowing the system to adapt and refine its operation.
2Ease of operation
If a liquid crystal spatial light modulator is used for wavelength switching, then beam steering between input port and multiple output ports is achieved, but crosstalk levels are increased due to phase reset and pixelization effects
Solution Approach 1:
The patent applies parameter changes by optimizing the phase profile parameters to minimize crosstalk. The nonlinear constrained optimization adjusts phase values to create a phase distribution that concentrates energy at the desired output port while suppressing energy at other ports. The optimization changes phase parameters to eliminate harmful crosstalk effects while preserving the beam steering function.
Solution Approach 2:
The patent uses feedback through iterative optimization to reduce crosstalk. The system evaluates the diffraction pattern and crosstalk levels resulting from a phase profile, uses this feedback to adjust the phase parameters, and repeats the process until crosstalk is minimized to acceptable levels. This feedback mechanism allows continuous refinement of the phase profile to eliminate harmful crosstalk.
3Productivity
If an ideal phase blazed grating is used, then diffraction efficiency is maximized, but phase reset and pixelization effects prevent achieving minimum insertion loss and crosstalk values
Solution Approach 1:
The patent applies parameter changes by transitioning from an ideal continuous phase blazed grating to a discrete pixelated phase profile with optimized parameters. The nonlinear constrained optimization adjusts the phase values at each pixel to approximate the ideal blazed grating as closely as possible while accounting for the pixelization constraints. This parameter optimization maximizes diffraction efficiency within the limitations of the pixelated structure.
Solution Approach 2:
The patent applies segmentation by dividing the continuous phase profile into discrete pixel elements. Each pixel can be independently controlled to provide a specific phase shift, allowing the system to approximate the ideal blazed grating using discrete segments. This segmentation approach enables the liquid crystal spatial light modulator to achieve performance close to the theoretical ideal while managing the practical constraints of pixelated operation.
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 optimized phase profile significantly reduces crosstalk and insertion loss, ensuring high diffraction efficiency and meeting industry standards for optical communication networks, particularly in high-port-count switches.
Implementation Method 1
As a result of the birefringent effect of the LC material, the different voltages correspond to different phase delays
Implementation Method 2
a diffraction angle of incident light may be controlled merely by changing the grating period of this pseudo-blazed grating
Data Source
AI summary
A two-step optimization process is utilized to define an optimal phase profile for a LCoS spatial light modulator. The two-step optimization process first utilizes a nonlinear constrained optimization (NCO) program to determine the specific parameters required to obtain an optimal phase profile (hologram), where the “optimal phase profile” is typically defined as that profile which achieves maximum diffraction efficiency for optical switching. Following this first step, phase scaling (and perhaps an adjustment in the number of pixels per period) is employed to slightly modify the values of the optimal phase profile to effectively suppress crosstalk peaks. If any orders still exhibit an unacceptable level of crosstalk, these orders are then subtracted from the phase profile to create the final design.