LCoS Spatial Light Modulator Phase Calibration via Lookup Tables
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Solution Overview
Problem
Existing spatial light modulators using liquid crystal on silicon (LCoS) face challenges in achieving accurate phase modulation due to nonlinear voltage-dependent phase modulation characteristics and voltage-independent distortion, leading to irregularities in phase modulation amounts across pixels.
Innovation Solution
A phase-modulating apparatus and method that includes a spatial light modulator with a control unit to set input values, convert them to control values, and drive pixels with corresponding voltage values, using look-up tables (LUTs) to calibrate voltage-dependent phase modulation characteristics and correct voltage-independent distortion, ensuring linear phase modulation across pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage is applied to pixel electrode to modulate phase, then phase modulation is achieved, but phase modulation amount changes nonlinearly relative to voltage
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the nonlinear voltage-phase relationships in lookup tables before actual operation. The system measures the actual phase modulation characteristics of each pixel during manufacturing or initialization, then stores correction data in lookup tables that are used during normal operation to compensate for nonlinearities, ensuring accurate phase modulation without requiring real-time complex calculations.
Solution Approach 2:
The patent changes the parameter representation by transforming the direct voltage control approach into a lookup table-based index control approach. Instead of applying voltage directly proportional to desired phase modulation, the system uses lookup tables that map digital input values to pre-calculated voltage values, effectively changing the control parameter from linear voltage to nonlinear voltage lookup indices that account for pixel-specific characteristics.
2Ease of manufacture
If LCoS silicon substrate is made thin for manufacturing, then manufacturing is easier, but mechanical strength decreases and stress distortion occurs
Solution Approach 1:
The patent applies local quality by addressing the distortion problem at the pixel level rather than requiring a uniformly thick substrate. Each pixel's phase modulation characteristics are measured individually and stored in separate lookup tables, allowing the system to compensate for local variations in substrate thickness and stress distribution. This enables the use of thin substrates for ease of manufacturing while maintaining overall system performance through localized correction.
3Ease of manufacture
If liquid crystal layer thickness varies across pixels, then manufacturing is simplified, but phase modulation uniformity deteriorates
Solution Approach 1:
The patent applies preliminary action by measuring and characterizing the actual liquid crystal layer thickness effects on each pixel during initialization or manufacturing, then storing compensation data in lookup tables before the device enters normal operation. This preliminary characterization allows the system to compensate for thickness variations without requiring precise control during the manufacturing process itself.
Solution Approach 2:
The patent applies local quality by treating each pixel's liquid crystal layer thickness as a unique characteristic that requires individual correction. The lookup tables store pixel-specific voltage compensation values that account for local thickness variations, allowing the system to maintain uniform phase modulation performance across all pixels despite manufacturing variations in liquid crystal layer thickness.
4Ease of operation
If conventional phase modulation control is used, then device operation is simple, but measurement precision of phase modulation amount deteriorates
Solution Approach 1:
The patent introduces an intermediary layer between the simple digital input and the actual phase modulation. The lookup tables serve as this intermediary, translating simple digital input values into precisely calculated voltage values that account for nonlinearities and pixel-specific characteristics. This maintains ease of operation with simple digital controls while achieving high measurement precision through the intermediary lookup table conversion process.
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 solution achieves accurate and linear phase modulation by calibrating voltage-dependent and voltage-independent distortions, improving the precision of phase modulation in spatial light modulators and enhancing their performance.
Implementation Method 1
A spatial light modulator (SLM) using liquid crystal on silicon (LCoS) is well known in the art. When a voltage is applied to a pixel electrode, liquid crystal molecules in the LCoS rotate within a vertical plane of the substrate, modifying the phase modulation amount of incident light.
Implementation Method 2
φ(V,x,y)=2Δn(V)d(x,y) where Δn(V) is the birefringence index for the polarization component whose electric field that oscillates in a direction parallel to the liquid crystal orientation
Data Source
AI summary
In an apparatus for modulating light, a spatial light modulator includes a plurality of pixels and configured to modulate input light in response to a drive voltage for each of the pixels. An input value setting unit is configured to set an input value for the each of pixels. The input value is a digital value, an entire gray level of the digital value is “N”, and “N” is a natural number. A converting unit is configured to convert the input value to a control value. A control value is a digital value, an entire gray level of the control value is “M”, and “M” is a natural number greater than “N”. A driving unit is configured to convert the control value to a voltage value and drive the each of the pixels in response to the drive voltage corresponding to the voltage value.