The Phase-Only Spatial Light Modulator (PLM) is a piston-mode design of the Digital Micromirror Device (DMD) that Texas Instruments DLP® Products has been developing in recent years. While the manufacturing of the PLM shares many of the same process steps of the traditional DMD, the optical system integration of the two devices are fundamentally different. As a result, new optimization is needed to maximize the performance of the PLM based on the device characteristics. This paper covers the optimization of key pixel parameters – array fill factor, mirror flatness, mirror tilt – and generally how the parameters affect a device performance metric we call Zeroth-Order Efficiency. The various improvements are modeled to ascertain expected performance gains and at what point the performance benefits achieve asymptotic behavior. Theoretical and empirical results are shown for the improved key pixel parameters and their corresponding gains made to Zeroth-Order Efficiency.
Phase light modulator has been used in many underwater applications, such as turbulence mitigation, or laser beam shaping, to improve imaging and communication in the underwater environment. Liquid crystal on silicon (LCOS) or Liquid Crystal Display (LCD)-based phase light modulators are used in these applications. In recent years, Texas Instruments Digital Light Processing division developed a piston-mode Phase Light Modulator MEMS device (TI-PLM). One of the benefits of the device is its capability of supporting a high frame rate (i.e., 5.7kframes/sec). In this paper, we evaluated this TI-PLM device on an optical benchtop. While the main focus was the image quality of the Computer-Generated Hologram (CGH), the results also shed some light on this device’s capability for other PLM applications.
The Digital Micromirror Device (DMD), developed by Texas Instruments (TI), has been in production for over 25 years. It is a Micro-optical-electro-mechanical system (MOEMS) that functions as a spatial light modulator (SLM) by directing millions of points of light into or out of the projection optics path. TI is now developing a new MOEMS device based on the same processes, equipment sets, and design knowledge as the DMD. This new device operates in a piston mode with each mirror moving up and down instead of rotating left and right as the DMD does. By operating in a piston mode, the mirrors can modulate the phase of light and function as a phase light modulator (PLM). This paper focuses on the reliability of the PLM device. TI has a strong foundation for MOEMS reliability resulting in the mature and reliable DMD. Early results from various life tests and environmental tests confirm that PLM reliability is comparable to DMD reliability. The paper will discuss reliability test results and related performance metrics.
Over the last few years, DLP® Products at Texas Instruments, Inc. has been developing a MEMS-based phase-only spatial light modulator that we call the Phase Light Modulator or PLM. The device which shares many of the process steps with the DLP micromirror device consists of a vertically actuated mirror on top of a CMOS array. The current reflective device provides enough vertical range to be suitable for visible wavelengths. This paper discusses a number of metrics important to the performance of a phase-only spatial light modulator and the corresponding characteristics of the PLM. The metrics include diffraction efficiency, number of phase levels, resolution, speed, and die flatness. The paper also discusses in depth recent design improvements such as increasing the number of phase levels to improve efficiency and reduce image noise. Recent lifetime test results collected over more than 1000 hours are also presented. Finally, there is a discussion of our possible approaches to testing the device in a high-volume production environment.
Computer-generated holography, a disruptive technology for projection displays, enables variable projection distance by combining a variable lens hologram with an image hologram and encoding it onto a phase-modulating spatial light modulator. The basic structure of a holographic projector includes a spatial light modulator (SLM) to modulate the phase of an incident reconstruction light beam, i.e., a coherent light source (i.e., LASER). Speckle appears in the projected content due to the quasi-random interference of a coherent light source on an optically rough surface that serves as a projection screen. A partially coherent light source, such as a light emitting diode can be used in holographic projection, but image sharpness is sacrificed. Furthermore, due to the limitation of the phase retrieval algorithm, which calculates the hologram to be encoded on the spatial light modulator from a given graphic, the resulting projected content can look speckly due to phase retrieval algorithm imperfections. In this work, we demonstrate reduction in speckle arising from phase retrieval algorithm imperfections through the use of a piston-mode spatial light modulator. The SLM is a two-dimensional micromirror array with extraordinarily fast switching characteristics that enables the implementation of a temporal averaging method for speckle reduction without additional optical components and keeps the benefits of holographic projection.
Piston‐mode Fourier based optical imaging created using an adaptation of the base DLP® Products torsional, spatial light modulator technology is presented. Technology, advancements and performance metrics such as, actuation speed, efficiency, and pixel coupling are shown for this 10.8 μm pitched pixel array. Device potential includes upwards of 5.7kframes/sec actuation.
A prototype of a Phase Spatial Light Modulator (PLM) device has been developed and demonstrated using DLP Micro-ElectroMechanical System (MEMS) based technology. Designed for a visible (405nm to 632nm) laser, this device uses an array of individually-addressable, digitally-controlled PLM micromirrors that can be addressed to multiple discrete vertical positions. The MEMS superstructure process flow used for DMD micromirrors was adapted to enable manufacturing this device on top of an existing DLP technology CMOS device. The prototype has demonstrated good uniformity across the array and the ability to steer light using phase light modulation. A discussion of some initial performance metrics as well as potential applications will be presented.
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