Achromatized Diffractive Spatial Light Modulator for Multi-Wavelength Operation
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Solution Overview
Problem
Current spatial light modulators (SLMs) face limitations in their ability to handle multiple wavelengths effectively, particularly in applications requiring high precision, high power handling, and high throughput, such as optical data processing, image projection, lithography, and holography, where they often struggle with wavelength-dependent performance and lack of coherent light modulation.
Innovation Solution
The development of achromatized diffractive SLMs with surface profiles and phase steps that allow for independent wavelength operation by dividing mirror areas into specific phase regions, enabling the creation of arbitrary complex amplitudes and polarization states, and the use of tilting and piston mirrors with phase biases to achieve fully complex modulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If diffractive SLMs are used to modulate light, then light modulation capability is improved, but wavelength dependence increases causing performance degradation at different wavelengths
Solution Approach 1:
The mirror surface is divided into multiple discrete height levels (typically two or more steps) rather than a continuous surface. Each segment corresponds to a specific phase delay, allowing the SLM to maintain controlled diffraction efficiency across multiple wavelengths by distributing the phase modulation across discrete levels that work effectively for different wavelength ranges.
Solution Approach 2:
The patent modifies the physical parameters of the mirror surface by introducing controlled height steps with specific phase delays (e.g., 0, π, or other quantized values). These parameter changes in surface topology transform the continuous phase modulation problem into a discrete level problem that is less sensitive to wavelength variations, thereby improving multi-wavelength performance.
2Ease of manufacture
If mirror surfaces are made flat and simple, then manufacturing ease is improved, but light manipulation precision deteriorates
Solution Approach 1:
Instead of requiring a continuously variable complex surface profile that would be difficult to manufacture, the patent segments the surface into a small number of discrete height levels. This segmentation simplifies the manufacturing process while still achieving precise light manipulation through controlled diffraction from the stepped structure.
Solution Approach 2:
The patent applies different local surface properties (different height levels) to different regions of the mirror surface to achieve the desired phase modulation. Each local region has a specific height that provides the appropriate phase delay for its function, allowing precise light manipulation while keeping each local region simple to manufacture.
3Device complexity
If single wavelength operation is used, then device complexity is reduced, but adaptability to multiple wavelengths deteriorates
Solution Approach 1:
The patent designs the mirror surface with a universal stepped structure that can effectively modulate light across multiple wavelengths simultaneously. The discrete height levels are chosen to provide appropriate phase delays for a range of wavelengths, making the device multi-functional without requiring separate optimized surfaces for each wavelength.
Solution Approach 2:
By changing the parameter of surface height to discrete quantized levels, the patent creates a device whose performance characteristics change favorably across different wavelengths. The specific height values are selected to provide robust phase control that maintains effectiveness over a wavelength range, reducing the need for wavelength-specific design optimizations.
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 enhances the SLMs' ability to maintain high extinction ratios across a wide range of wavelengths, supports coherent light modulation, and allows for flexible light manipulation, improving their suitability for applications like holography and lithography by reducing wavelength dependence and enabling the use of multiple wavelengths simultaneously.
Implementation Method 1
others by diffraction, like most other types. In diffraction, the phase differences within pixels or between pixels are used to modulate the light
Implementation Method 2
Some work by specular reflection, like TI's DMDs (US Patent No. 5,583,688)
Implementation Method 3
They create darkness through destructive interference and the destructive phase relation is perfect at only one wavelength
Implementation Method 4
In specular reflection the direction of the pixel surface sends the reflected beam into the accepting aperture of the optics, or outside of it
Data Source
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Figure 2a~2d
Figure 3a~3c
AI summary
The invention relates to methods to improve SLMs, in particular to reflecting micromechanical SLMs, for applications with simple system architecture, high precision, high power handling capability, high throughput, and/or high optical processing capability. Applications include optical data processing, image projection, lithography, image enhancement, holography, optical metrology, coherence and wavefront control, and adaptive optics. A particular aspect of the invention is the achromatization of diffractive SLMs so they can be used with multiple wavelengths sequentially, simultaneously or as a result of spectral broadening in very short pulses.