Phase-Change Infrared Mirrors Using GeTe Alloys

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Solution Overview

Problem

Existing spatial light modulators (SLMs) face limitations in switching speed, angle of deflection, and operational range, particularly in the infrared spectrum, with MEMS-based SLMs having limited deflection angles and low switching speeds, and LCoS devices only functioning below 1.6 μm wavelength.

Innovation Solution

The development of spatial light modulators using phase-change materials (PCMs) with a PCM heater to thermally modulate the phase of the PCM, allowing for high-speed modulation of infrared light by controlling the material's phase change between crystalline and amorphous states, enabling a wider range of applications, including a programmable infrared mirror with improved switching speed and angle of deflection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If MEMS-based SLMs are used, then a broader wavelength range is achieved, but the angle of deflection is limited to ±12 degrees and switching speed is below 100 kHz

Engineering Contradiction:

Improvewavelength rangeVSAvoidswitching speed

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent replaces the mechanical moving mirror system of MEMS with a stationary phase-change material layer that modulates light through phase transitions (amorphous to crystalline and vice versa). This eliminates mechanical inertia and actuator limitations, enabling switching speeds exceeding 100 kHz while maintaining broad infrared wavelength coverage from 2-15 μm.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention utilizes phase transitions of chalcogenide materials (specifically Ge2Sb2Te5 and similar alloys) between amorphous and crystalline states to modulate optical properties. The phase change alters the refractive index and absorption coefficient, enabling high-speed optical modulation without mechanical movement, thus resolving the contradiction between versatility and switching speed.

Inventive Principle:

Principle #36Phase transitions

2Reliability

If LCoS-based SLMs are used, then good performance is achieved, but operation is limited to wavelengths below 1.6 μm

Engineering Contradiction:

Improveperformance qualityVSAvoidoperational wavelength range

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent changes the fundamental operating parameter from liquid crystal optical modulation (LCoS) to phase-change material optical modulation. This parameter change enables operation in the mid-to-long wavelength infrared range (2-15 μm) where LCoS is ineffective, while maintaining high modulation contrast and switching reliability through the distinct optical properties of amorphous and crystalline phase-change materials in the infrared spectrum.

Inventive Principle:

Principle #35Parameter changes

3Speed

If higher switching speeds are achieved with phase-change materials, then modulation frequency increases, but thermal management becomes more challenging

Engineering Contradiction:

Improveswitching speedVSAvoidthermal control

Core Design Contradiction:

SpeedVSTemperature

Solution Approach 1:

The patent divides the phase-change material into an array of independently addressable micropixels or micropatches, each with its own heating electrode. This segmentation allows localized thermal control, where only the required pixels are heated for phase transition, minimizing overall thermal load and enabling high-speed switching across the entire array through parallel operation of individual elements.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention employs periodic pulsed heating to achieve phase transitions, where short duration heat pulses (microseconds to milliseconds) are applied to melt and rapidly cool the phase-change material into the amorphous state, or where controlled heating cycles transition material between phases. This periodic action enables high switching speeds while allowing thermal dissipation between pulses, managing thermal accumulation.

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

The PCM-based SLMs achieve high-speed modulation and improved angle of deflection, enabling efficient operation across a broader infrared spectrum, overcoming the limitations of traditional SLMs by utilizing the reversible phase change properties of materials like Germanium Tellurium (GeTe) alloys for enhanced light modulation.

Implementation Method 1

phase-change materials (PCMs) with a PCM heater to thermally modulate the phase of the PCM, allowing for high-speed modulation of infrared light by controlling the material's phase change between crystalline and amorphous states

Methodology Applied

Scientific EffectPhase change: Phase Change

Implementation Method 2

a PCM heater thermal conductively coupled to the PCM

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS11314109B1Electrically switchable infrared mirrors using phase-change chalcogenides materials

Publication Date: 2022.04.26 HRL LAB

AI summary

A spatial light modulator cell and arrays of spatial light modulator cells are disclosed. The spatial light modulator cells can comprise a phase change material (PCM) having a first side and a second side; an optical reflector configured to reflect an optical beam passing from the first side to the second side; and a PCM heater thermal conductively coupled to the PCM, wherein thermal modulation of the PCM modulates a phase of the PCM which varies light transmission through the PCM. Methods of making spatial light modulator cells and arrays are also disclosed.