MEMS Phase Light Modulator Optical Enhancement for LIDAR Beam Steering
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Solution Overview
Problem
Existing phase light modulators, particularly those based on Liquid Crystal on Silicon (LCoS) and Liquid Crystal (LC), have slow switching speeds, making them unsuitable for high-speed applications like LIDAR, which requires fast laser beam modulation for beam steering.
Innovation Solution
A MEMS phase light modulator with pixelated micromirrors that can vary in height to modulate the phase of light, achieving a 2π phase modulation by maximizing the displacement of micromirrors to λ/2, and an optical enhancement system that includes a polarized beam splitter, quarter wave plate, and mirror to enhance phase modulation depth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Liquid Crystal (LC) based phase light modulators are used, then phase modulation capability is achieved, but switching speed becomes slow
Solution Approach 1:
The patent replaces the liquid crystal material-based phase modulation mechanism with a mechanical micromirror array system. Each micromirror element can be independently actuated to change its height position, providing phase modulation through mechanical displacement rather than optical property changes. This substitution enables switching speeds in the microsecond range, significantly faster than liquid crystal devices while maintaining phase modulation functionality.
2Manufacturing precision
If micromirror displacement is increased to achieve 2π phase modulation, then phase modulation depth is improved, but device complexity increases
Solution Approach 1:
The phase modulation device is segmented into an array of independent micromirror elements, where each element can be controlled individually. This segmentation allows the system to achieve complex phase modulation patterns by coordinating simple movements of individual mirrors, rather than requiring each mirror to perform complex functions alone. The segmentation enables 2π phase modulation through coordinated displacement of multiple mirror elements.
Solution Approach 2:
The patent introduces a height dimension (z-axis displacement) for the micromirrors in addition to the conventional x-y plane positioning. By allowing micromirrors to move vertically along the direction of light incidence, the system achieves phase modulation through height variation d(i,j), creating a three-dimensional control space that enables 2π phase modulation while maintaining relatively simple mirror structures.
3Productivity
If phase modulation depth is increased for longer wavelengths, then LIDAR application performance is improved, but diffraction efficiency decreases
Solution Approach 1:
The patent optimizes the micromirror displacement parameters specifically for longer wavelengths (905 nm and 1550 nm). By adjusting the height displacement range d(i,j) to achieve 2π phase modulation at these wavelengths, the system maximizes beam steering efficiency while compensating for the natural decrease in diffraction efficiency at longer wavelengths. The phase modulation depth is tuned to match the wavelength-specific requirements for optimal LIDAR performance.
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 enables faster and more efficient beam steering, particularly for longer wavelengths like 905 nm and 1550 nm, by increasing the phase modulation depth and diffraction efficiency, making it suitable for LIDAR applications.
Implementation Method 1
a quarter wave plate positioned such that the light deflected by the polarized beam splitter passes therethrough and converts linear polarization light to right circular polarization light
Implementation Method 2
a polarized beam splitter positioned in the light path to receive and deflect the vertically polarized and collimated light
Implementation Method 3
phase of light is modulated 2kd(i,j) where k is a light propagation constant in free space, 2π/λ
Implementation Method 4
a mirror positioned in spaced relation to the other side of the quarter wave plate and a half Talbot distance from the phase light modulator
Data Source
AI summary
An optical architecture for enhancing phase modulation depth for a phase light modulator includes a laser light source, a 4f, 1:1 relay where a tilted mirror with a center hole is placed at the backfocal point of the first lens. A vertically polarized (VP) and collimated light is deflected by a polarized beam splitter (PBS), followed by passing through a Quarter Wave Plate (QWP) that converts linear polarization (LP) to right circular polarization (RCP). Upon interaction of the RCP light with PLM, spatial phase is modulated by 2kd(i,j). PLM reflects and modulates phase of light while changing the handness of polarization from RHP to left hand circular polarization (LCP). The 2nd interaction with QWP changes polarization of light from LCP to horizontally polarized (HP) light. The mirror M1 is placed at a half of the Talbot distance from the PLM as described later. The reflected light by M1 is a HP light, therefore it goes through the PBS and is converted to RCP by the 3rd interaction with QWP. Finally the light is modulated by the PLM with the same phase modulation profile and reflected to the direction along the incident laser beam via QWP and PBS. After the laser beam is doubly modulated, the laser beam diffracted towards direction defined by the CGH pattern displayed on PLM. The diffracted beam is reflected by the mirror placed in the 4f 1:1 collimating optics followed by a collimating optics for beam steering.