Spin Hall Optical Modulator for High-Frequency Polarization Control

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Solution Overview

Problem

Existing optical modulators for linear polarization of a light source either operate at low frequencies and narrow wavelength ranges or are limited to slow modulation, failing to meet the need for high-frequency modulation across a broad range of wavelengths.

Innovation Solution

The method involves using a spin Hall material, such as W film, with a modulated electric current applied perpendicular to the propagation direction of linearly polarized light, leveraging the magneto-optical Kerr effect to rotate the polarization of the light, allowing for high-frequency modulation across a wide range of wavelengths through multiple reflections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If liquid crystal modulators are used, then linear polarization modulation is achieved, but the modulation frequency is limited to low range (0-10 kHz)

Engineering Contradiction:

Improvemodulation frequencyVSAvoidmodulation bandwidth

Core Design Contradiction:

SpeedVSProductivity

Solution Approach 1:

The patent replaces the mechanical/liquid crystal system with a magneto-optical system using spin Hall materials. Instead of using liquid crystal molecules oriented by electric fields (mechanical/electrical system), the invention uses the magneto-optical Kerr effect where spin-polarized currents generate magnetic fields that rotate light polarization. This substitution enables modulation frequencies up to 100 GHz, overcoming the 0-10 kHz limitation of liquid crystal modulators.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the fundamental operating parameter from electric field control (liquid crystals) to spin current control (magneto-optical effect). By using spin-polarized currents that generate transient magnetic fields via the spin Hall effect, the system achieves ultrafast modulation speeds. The parameter change from static/dynamic electric field control to ultrafast spin current control enables the bandwidth expansion from kHz to GHz range.

Inventive Principle:

Principle #35Parameter changes

2Speed

If photoelastic modulators are used, then high frequency modulation (100 kHz) is achieved, but the wavelength range remains narrow

Engineering Contradiction:

Improvemodulation frequencyVSAvoidwavelength range

Core Design Contradiction:

SpeedVSAdaptability or versatility

Solution Approach 1:

The patent achieves universality by using the magneto-optical Kerr effect, which is a fundamental interaction between light and magnetic moments that is largely wavelength-independent. The spin Hall materials (e.g., CoFeB, CoFe) generate magnetic fields that interact with the magnetic moments of reflected light across a broad spectrum. This allows the same modulator structure to operate effectively across multiple wavelengths, unlike photoelastic modulators that are optimized for specific wavelength ranges.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Adaptability or versatility

If mechanical rotation of fixed retarder is used, then large wavelength range is achieved, but modulation speed becomes slow

Engineering Contradiction:

Improvewavelength rangeVSAvoidmodulation frequency

Core Design Contradiction:

Adaptability or versatilityVSSpeed

Solution Approach 1:

The patent replaces the mechanical rotation system with a magneto-optical system. Instead of physically rotating a fixed retarder (mechanical motion limited by inertia and friction), the invention uses spin-polarized currents to generate transient magnetic fields that instantly rotate the polarization plane of reflected light. This substitution eliminates mechanical limitations and enables modulation frequencies up to 100 GHz while maintaining broad wavelength coverage through the wavelength-insensitive magneto-optical Kerr effect.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 enables fast and broad-range modulation of linear polarization, capable of frequencies up to 100 GHz and multiple wavelengths, with the degree of rotation controllable by the current and enhanced by additional reflections and layers, making it suitable for advanced optical studies and applications.

Implementation Method 1

leveraging the magneto-optical Kerr effect to rotate the polarization of the light

Methodology Applied

Scientific EffectMagneto-optical Kerr effect: Magneto-Optic Kerr Effect

Implementation Method 2

Optical modulator using the spin hall effect in metals

Methodology Applied

Scientific EffectSpin Hall effect: Hall Effect

Data Source

PatentUS10663773B2Optical modulator using the spin hall effect in metals

Publication Date: 2020.05.26 THE GOVERNMENT OF THE UNITED STATES OF AMERICA AS REPRESENTED BY THE SECRETARY DEPARTMENT OF HEALTH & HUMAN SERVICES

AI summary

The spin-Hall effect can be used to modulate the linear polarization of light via the magneto-optical Kerr effect. A central area of an outer surface of an added layer atop a spin Hall material is illuminated while simultaneously passing a modulated electric current through the material, so that reflected light has a new linear polarization that differs from the initial linear polarization to a degree depending on the amplitude of the modulated electric current.