Dynamic infrared scene simulation using grayscale modulation of digital micro-mirror device

The digital micromirror device DMD is widely used in visible light projection, special-purpose spatial light modulation, and infrared scene simulation, due to its high resolution, uniformity and energy concentration. In some applications that require high frame rate scene image display, it is necessary to ensure that the DMD displays high gray level images at a high frame rate. However, the display frame rate of the pulse width modulation (PWM) method is limited by the minimum time required for DMD loading data, unable to achieve high frame rate display. Although the DMD binary display mode can meet the requirements of high frame rate display, it cannot meet the requirements of high gray level. The paper proposes an image display method that uses light source and DMD to synchronize modulation. Decompose the high-order gray image into bit planes according to the gray threshold, and the DMD displays each bit plane in binary mode under the trigger of an sync pulse. The intensity of the illumination laser source is modulated by an acousto-optic modulator to match the bit plane and the radiated laser power. This method makes use of the function of high frame rate display in DMD binary mode cooperate with light intensity modulation of illumination laser source, and realizes high frame rate and high dynamic range image display. With this method, the maximum frame rate of 8-bit gray level image with 1920 ×1080 resolution can reach 2KHz. The experimental system has realized 200Hz frame rate display of 8-bit gray level image with 1920 ×1080 resolution.

OPTRA is developing a two-band midwave infrared scene simulator based on digital micromirror devices (DMD). The simulator is intended for testing a number of different infrared tracking technologies. Our approach allows for the relative intensities of the two spectral bands to be varied for realistic simulations of an approaching target. The system employs a broadband IR (thermal) source whose energy is spectrally filtered via a series of bandpass filters acting as dichroic beamsplitters prior to being imaged onto two DMDs - one for each spectral band. The "on" reflected images from the two DMDs are then fused, expanded by a telescope, and transmitted towards the unit under test. The relative intensities of each spatial element of the two bands are controlled through the duty cycle of "on" versus "off" of the related micromirror. In this paper we present a breadboard design, build, and test which establishes the feasibility of our approach. A description of the opto-mechanical system is given along with radiometric performance projections. Results from breadboard testing, including maximum radiant intensity and radiant intensity resolution, and a series of simulated images are shown.

OPTRA is developing a next generation digital micromirror device (DMD) based two-band infrared scene projector (IRSP) with infinite bit depth independent of frame rate and an order of magnitude improvement in contrast over the state of the art. Traditionally, DMD-based IRSPs have offered larger format, superior uniformity, and pixel operability relative to resistive and diode arrays. However, they have been limited in contrast and also by the inherent bit depth/frame rate tradeoff imposed by pulse width modulation (PWM). OPTRA’s high dynamic range IRSP (HIDRA SP) has broken this dependency with a dynamic structured illumination solution. The HIDRA SP uses a source-conditioning DMD to impose the structured illumination on two projector DMDs—one for each spectral band. The source-conditioning DMD is operated in binary mode, and the relay optics that form the structured illumination act as a low-pass spatial filter. The structured illumination is, therefore, spatially grayscaled and more importantly is analog with no PWM. In addition, the structured illumination concentrates energy where bright objects will be projected and extinguishes energy in dark regions; the result is a significant improvement in contrast. The projector DMDs are operated with 8-bit PWM; however, the total projected image is analog with no bit depth/frame rate dependency. We describe our progress toward the development, building, and testing of a prototype HIDRA SP.

Digital micromirror devices (DMDs) are micro-electro- mechanical systems, originally developed to display images in projector systems. A DMD in the focal plane of an imaging system can be used as a reprogrammable slit mask of a multi-object spectrometer (MOS) by tilting some of the mirrors towards the spectrometer and tilting the rest of the mirrors away, thereby rejecting the unwanted light (due to the background and foreground objects). A DMD-based MOS can generate new, arbitrary slit patterns in seconds, which significantly reduces the overhead time during astronomical observations. Critically, DMD-based slit masks are extremely lightweight, compact and mechanically robust, which makes them attractive for use in space-based telescopes. As part of a larger effort to investigate the use of DMDs in space telescopes (sponsored by a NASA Strategic Astrophysics Technologies grant), we characterized the optical performance of Texas Instruments DMDs to determine their suitability for use in multi-object spectrometers. The performance of a DMD-based MOS is significantly affected by its optical throughput (reflectance), contrast ratio (the ability of the DMD to reject unwanted light) and scattering properties (which could lead to crosstalk and reduced signal-to-noise ratio in the spectrometer). We measured and quantified the throughput and contrast ratio of a Texas Instruments DMD in several configurations (which emulate the operation of a typical DMD-based MOS) and investigated the scattering properties of the individual DMD mirrors. In this work we present the results of our analysis, describe the performance of a typical DMD- based MOS and discuss the practical limitations of these instruments (such as maximum density of sources and expected signal-to- noise ratio).

Digital micromirror devices (DMDs) are commercial micro-electromechanical systems, consisting of millions of mirrors which can be individually addressed and tilted into one of two states (+/-12deg). These devices were developed to create binary patterns in video projectors, in the visible range. Commercially available DMDs are hermetically sealed and extremely reliable. Recently, DMDs have been identified as an alternative to microshutter arrays for space-based multi-object spectrometers (MOS). Specifically, the MOS at the heart of the proposed Galactic Evolution Spectroscopic Explorer (GESE) uses the DMD as a reprogrammable slit mask. Unfortunately, the protective borosilicate windows limit the use of DMDs in the UV and IR regimes, where the glass has insufficient throughput. In this work, we present our efforts to replace standard DMD windows with custom windows made from UV-grade fused silica, low-absorption optical sapphire (LAOS) and magnesium fluoride (MgF2). We present transmission measurements of the antireflection coated windows and the reflectance of bare (window removed) DMDs. Furthermore, we investigated the long-term stability of the DMD reflectance and experiments for coating DMD active area with a layer of pure aluminum (Al) to boost reflectance performance in the UV spectral range (200400 nm).

Phase-shifting method effectively attains high resolution and high accuracy in analyzing phase information on a projected grating. It is difficult to apply dynamically, however, because it usually requires several images. We developed a camera based on digital micromirror device (DMD) technology for high-speed phase analysis and shape measurement, called a DMD reflection-type CCD camera or DMD camera. Implementing DMD technology enables accurate control of intensity reaching the imaging detector of a camera. Moiré is used to adjust pixel-to-pixel correspondence highly accuracy. We introduce a controllable high-speed DMD operation board to control DMD mirrors at high-speed, so each DMD mirror operates as a controllable high-speed shutter for the corresponding CCD pixel. In experiments with an application, we conducted DMD integrated phase-shifting method using correlation to analyze phase distributions of projected gratings from images recorded by the DMD camera. We then discuss principles and experimental results under dynamic conditions. This paper is a revised version of one presented at the SPIE International Symposium on Optomechatronic Technologies (ISOT 2005), December 4-7, 2005 at the Sapporo Convention Center, Japan. That paper appears in SPIE Proceedings Vol.6049, 60490I.

The scene projector (SP) can provide simulated scene images with same optical characteristics as the real scenes to evaluate imaging systems in hard-ware-in-the-loop (HWIL) simulation testing. The single scene generation device (SGD) based SP typically projects 8-bit images at 220 fps, which is insufficient to fulfill the requirements of ultra-high frame rate imaging systems, such as star trackers and space debris detectors. In this paper, an innovative quaternary pulse width modulation (PWM) based SP is developed and implemented to realize the ultra-high frame rate projection. By optically overlapping modulation layers of two digital micro-mirror devices (DMDs) in parallel, and illuminating them with light intensities, a quaternary SGD is built up to modulate quaternary digit-planes (QDs) with four grayscale levels. And the quaternary digit-plane de-composition (QDD) is adopted to decompose an 8-bit image into 4 QDs. In addition, the exposure time of each QD is controlled by quaternary PWM, and the base time is optimized to 8 µs. The experimental results prove that the total exposure time of all QDs sequentially modulated by quaternary PWM is approximately 760 µs, namely projecting 8-bit images at 1300 fps. The quaternary PWM using two DMDs in parallel dramatically improves the grayscale modulation efficiency compared to the existing projection technologies, which provides a new approach for the SP design with ultra-high frame rate.

We present a 3D electromagnetic simulation of a digital micromirror device (DMD) from 0.4 µm to 5 µm, which accurately models DMD reflectance and contrast ratio, including the effects of diffraction. A DMD is a spatial light modulator with a wide range of applications, including projection displays, 3D printing, and imaging spectroscopy. The physical structure of the DMD induces strong wavelength-dependent diffraction effects that impact the stray light, optical throughput, and pupil illumination distribution of a system. To quantify this, we perform a 3-dimensional electromagnetic finite-difference time-domain simulation, illuminating the DMD with a focused, incoherent beam, explicitly calculating the near-field electric fields, and calculating the far-field distribution of light. The far-field data determines diffraction efficiency and the distribution of light across the pupil. With these models, we are able to study the DMD’s optical efficiency in three key regimes: the specular regime, where the DMD behaves like a segmented mirror with a diffractive component (λ < 1 µm); the diffraction-dominated regime, which is also described by analytic diffraction grating theory (3 µm < λ < 5 µm); and, uniquely, the transition region, where the specular reflection and diffraction contributions are comparable (1 µm < λ < 3 µm). Our results inform system performance parameters, provide optical design constraints, and create a framework of use cases for DMDs.

The digital micromirror device (DMD) which is one kind of Micro-Electro-Mechanical System has been widely adapted for use in lighting projection systems, and some new imaging systems such as high-dynamic range imaging, aperture-coded spectral imaging, or medical imaging. The micromirrors on the DMD surface are non-continuous distribution and capable of tilt relative to individual rotation axis, which is different from the plane mirror. Therefore, when the DMD is applied in a convergence imaging path, there is an optical path difference (OPD) between the off-axis chief ray and the on-axis chief ray, and moreover severe non-symmetric imaging on the focal plane. Based on the geometrical optics and aberration theory, this paper proposes a calculation formula that gives the OPD as a function of the image height, the incident angle, the DMD pixel size and the DMD tilt angle in the convergent imaging path. This formula can give the OPD of the system when the optical axis is vertical to the surface of the DMD in an ideal state, which has great significance to the design and adjustment of optical path using DMD devices.

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This paper presents our implementation of a multi-view autostereoscopic 3D display system by using time-multiplexing approach, digital micro-mirror devices (DMD), and the optical Wedgereg. The whole system consists of three major parts: high frame rate DMD projector, an active shutter, and an optical Wedgereg. This research investigates and develops the approaches to interface and control DMDs at very high bit rates and ultra-high frame rates to drive a novel flicker-free 3D flat panel device, with a wide viewing area and without need of special viewing glasses or head-tracking system. It needs to design a digital interface circuit capable of receiving video image data in a conventional format and translating it into a form appropriate for display on a DMD light modulator. This approach differs from existing ones in that it facilitates the modulation of the DMD to achieve much high frame rates, though with a trade-off in greyscale resolution. The outcomes of this research will have the great potential for commercialising the autostereoscopic display systems

Digital Micro-mirror Device (DMD) is an important tool in holographic display owning high-speed refresh rate and good diffraction efficiency. However, the reconstruction light source has great impact to image quality. A new holographic display system based on DMD for using light-emitting diodes (LEDs), is proposed in this paper. LEDs are chosen as light source to replace the laser, since it can reduce the speckle noise effectively, which is caused by both temporal and spatial coherence of laser. In order to solve the problem using LED as DMD holographic display light source, the characteristics of DMD as the display device for holographic displays are studied. An aspheric collimator for LED is used to improve the optical efficiency. A spatial filter is used to improve the coherence. The experimental results show that this lighting system has a good display quality.

Diagnostics are crucial to the operation of all particle accelerator facilities. They provide a means of optimising beam parameters and monitoring beam quality for users. However, for the next generation of accelerators, operating in extreme parameter spaces, most current beam diagnostics will fail; either through material failure or lack of resolution. This thesis presents three new diagnostic concepts to address this imminent diagnostic need. These novel diagnostics are supported by a simulation-based algorithm, successfully benchmarked throughout this work. All work has been conducted by the Author unless otherwise stated and referenced. The first technique measures sub-micron transverse beam profiles using optical transition radiation (OTR). Simulations were used to design a new imaging system, which was then installed at KEK (Japan). OTR images were then collected for a range of beam sizes. Comparisons were then made with simulations to successfully achieve sub-micron beam size measurements. Validation of these results was found in the agreement across different imaging systems for fixed beam parameters, providing a self-consistency check for the algorithm in lieu of alternate corroboration. The next diagnostic is a bunch length monitor for ∼<100 fs particle bunches; based on imaging the spatial distribution of coherent transition radiation (CTR) in the THz regime. Simulations demonstrated a relationship between image width and intensity, with bunch length. A THz imaging system was then installed at MAX IV (Sweden). CTR images were taken for a range of compressions. Maximum compression was successfully identified by monitoring relative changes in the properties of the images. Bunch lengths were then acquired from these images through comparison with simulations. Finally, the optical performance of a Digital Micro-mirror Device (DMD) was assessed. Image resolution produced by a DMD was quantified by measuring the Point Spread Function (PSF) of an imaging system, which was capable of remotely replacing a DMD with a planar mirror. The PSFs were measured using the sub-micron focus of a laser. Results show no measurable alteration to a PSF with the introduction of a DMD. This provides a foundation for the development of future diagnostics centred around this device. This thesis provides several validated proof-of-principle experimental results and supporting simulations. Future work has been identified for each topic, only possible following the results presented here, which will provide an array of novel next generation diagnostics.

Noncontacting shape measurement for 3-D objects is important in automated manufacturing, component quality control, reverse engineering, etc. Phase-shifting method effectively attains high resolution and high accuracy in analyzing phase information on a projected grating. This technique, however, is difficult to be applied to dynamic condition since usually it requires several images. We developed a digital micromirror device (DMD) camera for phase analysis. In this paper, an one-shot shape and deformation measurement method using a DMD camera is proposed. The DMD camera consists of a DMD, a CCD, and two imaging lenses. In optics of the DMD camera, individual DMD mirrors correspond to individual CCD pixels. The DMD on-off binary pattern can be changed more than 6900 times in one second using an accessory light modulator package (ALP) controller board. Individual DMD mirrors operate as controllable high-speed shutters for corresponding CCD pixels. The four phase-shifted images can be recorded within one frame of the CCD camera. Therefore, shape measurement in dynamic condition can be realized without using a high-speed camera. In order to obtain the 3-D information of shape, multiple reference planes are used to calibrate the relationship between phase value and 3D coordinates. The principle and hardware are presented. In an experiment under dynamic condition, 3D shape information can be analyzed from only one captured image.

We focus our attention on complex lithographic pattern generation on a huge substrate with no manipulation of the light source shape for Digital Micromirror Device (DMD) based maskless lithography. To overcome the limitations of existing pattern generation methods developed upon the assessment of lithographic paths of the reflected beam spots rather than the recognition of patterns, we place our primary concern on the pattern. We consider pattern generation for maskless lithography using the DMD as a graphic recognition field problem. The pattern generation process is conceptualized as dual pattern recognition in two contrary views, which are the substrate’s view and the DMD’s view. For pattern recognition in the DMD’s view, a unique criterion, the area ratio, is devised for approval of the on/off reflection of the DMD mirror. The Region-based Pattern Generation (RPG) scheme based upon the area ratio is proposed. For verification, a prototype RPG system is implemented, and lithography using the system is performed to fabricate an actual Flat Panel Display (FPD) glass. The results verify that the RPG scheme is robust enough to generate lithographic patterns in any possible lithographic configuration and the RPG system is precise enough to attain the lithographic quality required by the FPD manufacturer.