Variable Optical Retarder Array TDM Reduction

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Solution Overview

Problem

Digitally driven Liquid Crystal on Silicon (LCoS) wavelength selective switches (WSS) experience significant time-domain modulation (TDM) issues due to non-linear saw tooth optical retardation profiles, leading to increased optical loss and sensitivity, which is detrimental in optical networking applications requiring stable and controllable optical throughput.

Innovation Solution

Neighboring pixels in a variable optical retarder array are driven with temporal bit sequences that are evenly distributed in time and uncorrelated with each other, reducing overall TDM amplitude, and a controller is used to apply these sequences to generate a spatial profile of optical retardation, thereby lessening time-domain modulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If digitally driven LCoS arrays are used to simplify driver circuitry and improve switching speed, then device complexity is reduced and productivity is improved, but time-domain modulation (TDM) increases leading to higher optical loss

Engineering Contradiction:

Improvedriver circuitry complexityVSAvoidoptical loss

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent changes the temporal distribution parameter of digital drive signals by spreading one-bits evenly across the frame period and using uncorrelated sequences for neighboring pixels. This parameter change in the driving waveform reduces TDM while maintaining the simplicity of digital driving architecture.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs periodic drive frames with specific bit distribution patterns within each frame. By structuring the periodic digital drive signals to have evenly distributed one-bits and using uncorrelated sequences across pixels, the system reduces constructive interference that causes TDM while maintaining regular frame-based operation.

Inventive Principle:

Principle #19Periodic action

2Speed

If non-linear saw tooth optical retardation profiles are used in digitally driven LCoS WSS, then switching speed is improved, but time-domain modulation (TDM) increases leading to increased optical loss and sensitivity

Engineering Contradiction:

Improveswitching speedVSAvoidoptical loss

Core Design Contradiction:

SpeedVSLoss of energy

Solution Approach 1:

The patent modifies the temporal parameter of the drive signal by evenly distributing one-bits throughout the frame period rather than concentrating them. This changes the time-domain characteristics of the optical retardation profile, reducing TDM while preserving the non-linear saw tooth spatial profile needed for fast switching.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent segments the digital drive signal into individual pixel control sequences that are uncorrelated with each other. By treating each pixel's bit sequence independently and ensuring they are uncorrelated, the system reduces constructive interference across the array while maintaining the overall saw tooth profile for fast switching.

Inventive Principle:

Principle #1Segmentation

3Ease of operation

If digital bit sequences are applied to LCoS arrays, then ease of operation is improved and device complexity is reduced, but time-domain modulation (TDM) amplitude increases

Engineering Contradiction:

Improvecontrol simplicityVSAvoidTDM amplitude

Core Design Contradiction:

Ease of operationVSObject-generated harmful factors

Solution Approach 1:

The patent changes the temporal distribution parameter of digital bit sequences by spreading one-bits evenly across the frame and using uncorrelated sequences for neighboring pixels. This maintains the simplicity of digital control while reducing the harmful TDM amplitude through improved bit sequencing.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses periodic frame-based digital drive signals with specific bit distribution patterns. By structuring the periodic operation to have evenly spaced one-bits and uncorrelated sequences across pixels, the system reduces TDM amplitude while maintaining the ease of digital control.

Inventive Principle:

Principle #19Periodic action

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 significantly reduces TDM, leading to lower optical loss and improved stability in optical networking devices, allowing for more efficient and controlled optical switching.

Implementation Method 1

The molecules align relative to the electric field due to induced electrical dipole interaction with an electric field of the applied voltage, changing effective refractive index of the liquid crystal layer

Methodology Applied

Scientific EffectElectrical dipole interaction: Dielectric

Data Source

PatentUS10031397B2Method and controller for operating a variable optical retarder and an array

Publication Date: 2018.07.24 WELLS FARGO BANK NA

AI summary

A method and a controller for operating an array of variable optical retarders are disclosed. Neighboring pixels of the array of variable optical retarders are driven with disordered temporal bit sequences. An optical beam illuminating the pixels tends to integrate time-domain modulation caused by individual pixels driven in a non-coordinated or disordered fashion, which reduces the overall time-domain modulation amplitude of the optical beam.