Optical diffraction simulation of a digital micromirror device

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).

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.

As 3D printer technology has rapidly developed and penetrated into a wide range of applications, several methods for creating 3D objects have been explored and developed. One such method utilizes UV curing of special resins, where the patterning of each layer of the 3D object is determined by a digital micromirror device (DMD) controlled by a digital light processing (DLP) system. This method possesses important advantages over other methods in terms of variable object composition, high spatial resolution, and reduced build times, but usually requires specialized knowledge to program and control the DMD and other printer systems. Not all potential users of 3D printers will be able or willing to acquire this knowledge in order to take full advantage of all th at 3D printing has to offer in their ideas or applications. new software package called Design23DPrint has been developed that provides a user-friendly and intuitive interface for importing, manipulating, and editing 3D objects and has the ability to be readily interfaced with many different DLP and printer control systems. Both layer creation and the positioning of supports can be automated or be manually controlled. Integration of Design23DPrint with existing software packages for DMD control allows the user to edit layers on a pixel-by-pixel basis. The software was integrated with a new 3D printer design developed by Texas Instruments to demonstrate the capabilities of the software to control the printing process and to interface with resident control systems. Keywords: 3D Printer, DLP, DMD, software, interface

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.

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.

A digital micromirror device (DMD) is a kind of widely used spatial light modulator. We apply DMD as wavelength selector in tunable fiber lasers. Based on the two-dimensional diffraction theory, the diffraction of DMD and its effect on properties of fiber laser parameters are analyzed in detail. The theoretical results show that the diffraction efficiency is strongly dependent upon the angle of incident light and the pixel spacing of DMD. Compared with the other models of DMDs, the 0.55 in. DMD grating is an approximate blazed state in our configuration, which makes most of the diffracted radiation concentrated into one order. It is therefore a better choice to improve the stability and reliability of tunable fiber laser systems.

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.

In recent years, the popular adaptive front-lighting automobile headlight system has become a main emphasis of research that manufacturers will continue to focus great efforts on in the future. In this research we propose a new integral optical design for an automotive headlight system with an advanced light-emitting diode and digital micromirror device (DMD). Traditionally, automobile headlights have all been designed as a low beam light module, whereas the high beam light module still requires using accessory lamps. In anticipation of this new concept of integral optical design, we have researched and designed a single optical system with high and low beam capabilities. To switch on and off the beams, a DMD is typically used. Because DMDs have the capability of redirecting incident light into a specific angle, they also determine the shape of the high or low light beam in order to match the standard of headlight illumination. With collocation of the multicurvature reflection lens design, a DMD can control the light energy distribution and thereby reinforce the resolution of the light beam.

Passive hyperspectral imaging (HSI) sensors are essential in many space-borne surveillance missions because rich spectral information can improve the ability to analyze and classify oceanic and terrestrial parameters and objects/areas of interest. A significant technical challenge is that the amount of raw data acquired by these sensors will begin to exceed the data transmission bandwidths between the spacecraft and the ground station using classical approaches such as imaging onto a detector array. In this paper, the Compressive Line Sensing (CLS) imaging concept, originally developed for energy-efficient active laser imaging, is extended to the implementation of a hyperspectral imaging sensor. CLS HSI imaging is achieved using a digital micromirror device (DMD) spatial light modulator. A DMD generates a series of 2D binary sensing patterns from a codebook that can be used to encode cross-track spatial-spectral slices in a push-broom type imaging device. A high sensitivity single-element detector can then be used to acquire the target reflections from the DMD as the encoder output. The target image can be reconstructed using the encoder output and the encoding codebook. The proposed system architecture is presented. The initial simulation and experimental results comparing the proposed design with the state-of-the-art are discussed.

A major limiting factor of optical imaging in biological applications is the diffusion of light by tissue, preventing focusing at depths greater than ~1 mm in the body. To overcome this issue, phase-based wavefront shaping alters the phase of sections of the incident wavefront to counteract aberrations in phase caused by scattering. This enables focusing through scattering media beyond the optical diffusion limit and increases signal compared to amplitude-based compensation. However, in previous studies, speed of optimization has typically been limited by the use of a liquid crystal spatial light modulator (SLM) for measurement and display. SLMs usually have refresh rates of less than 100 Hz and require much longer than the speckle correlation time of tissue in vivo, usually on the order of milliseconds, to determine the optimal wavefront. Here, we present a phase-based iterative wavefront shaping method based on an onaxis digital micromirror device (DMD) in conjunction with an electro-optic modulator (EOM) for measurement and a fast SLM for display. By combining phase modulation from an EOM with the modal selection of the DMD, we take advantage of DMDs higher refresh rate, approximately 23 kHz, for iterative phase measurement. The slower SLM requires one update for display following the rapid determination of the optimal wavefront via the DMD, allowing for high-speed wavefront shaping. Using this system, we are able to focus through scattering media using 64 modes in under 8 milliseconds, on the order of the speckle correlation time for tissue in vivo.

When light propagates through complex medium, such as biological tissue and multimode fiber, refractive index inhomogeneity causes multiple scattering and distortion. This phenomenon is usually seen as obstacles for biomedical imaging, telecommunications, photodynamic therapy and so on. Thus, manipulation of the incident wavefront to compensate for the wavefront distortion due to multiple scattering has been an interdisciplinary subject of interest. Fortunately, wavefront shaping technologies have emerged to provide versatile solutions to minimize the influence of light scattering. By modulating the incident light into a special wavefront with a spatial light modulator, focusing through scattering medium is obtained. To date, several wavefront shaping techniques have been proposed, mainly including transmission matrix inversion, feedback based iterative optimization, and digital optical phase conjugation. Unlike a planar wavefront, the modulated light with special wavefront is transformed into a bright optical focus spot or a desired focus pattern after the scattering medium. Among the proposed approaches, the transmission matrix is considered as a significant tool to characterize a multiple scattering medium with the purpose of manipulating light propagation through it, which contains all the information related to the input field and the scattered output field. In this work, we experimentally measure the transmission matrix of scattering media based on self-reference interference method with a digital micromirror device. Unlike the conventional setup, which divides the incident wavefront into a signal part and reference part, in the self-reference interference method, the reference light is superimposed directly on the signal light to form a new set of input light fields. This self-reference interference method effectively improves the degree of freedom of optical field modulation. Moreover, the intensity ratio between the signal light and the reference light can be adjusted conveniently. In our experiment, this superimposed field is generated by a digital micromirror device with superpixel method. We measure the Hadamard basis and the OAM-basis transmission matrices of scattering medium, respectively. With the measured transmission matrices, single-spot, multi-spot and vortex focusing are achieved after scattering medium, verifying the accuracy of the measured transmission matrices. The strong diagonal presented in the norm of focusing operator also proves the accuracy of the measured transmission matrices. The proposed method may have potential applications in optical imaging and optical communication under scattering environment.

Programable spatial light modulators (SLMs) have significantly advanced the configurable optical trapping of particles. Typically, these devices are utilized in the Fourier plane of an optical system, but direct imaging of an amplitude pattern can potentially result in increased simplicity and computational speed. Here we demonstrate high-resolution direct imaging of a digital micromirror device (DMD) at high numerical apertures (NA), which we apply to the optical trapping of a Bose-Einstein condensate (BEC). We utilise a (1200 x 1920) pixel DMD and commercially available 0.45 NA microscope objectives, finding that atoms confined in a hybrid optical/magnetic or all-optical potential can be patterned using repulsive blue-detuned (532 nm) light with 630(10) nm full-width at half-maximum (FWHM) resolution, within 5% of the diffraction limit. The result is near arbitrary control of the density the BEC without the need for expensive custom optics. We also introduce the technique of time-averaged DMD potentials, demonstrating the ability to produce multiple grayscale levels with minimal heating of the atomic cloud, by utilising the high switching speed (20 kHz maximum) of the DMD. These techniques will enable the realization and control of diverse optical potentials for superfluid dynamics and atomtronics applications with quantum gases. The performance of this system in a direct imaging configuration has wider application for optical trapping at non-trivial NAs.

The binary computer-generated hologram (BCGH) has attracted much attention recently because it can address the high-speed binary spatial light modulator (SLM), such as a digital micromirror device (DMD) SLM. In this paper, our concern is the development of an algorithm to produce high-quality BCGHs. In particular, simulated annealing (SA) is an efficient algorithm used to produce a phase-only computer-generated hologram. In the study of SA for the production of a BCGH, we found some inherent shortcomings of SA, and the quality of the produced BCGHs is limited. Accordingly, we have modified SA and propose the simulated-annealing binary search (SABS) algorithm. We have also proposed a method to quickly determine the parameters for SABS. In the comparison with SA, the mean square error of the SABS BCGHs decreases by 32% on average. Therefore, the SABS is a promising technique for a high-quality holographic display by DMD.

Exquisite manipulations of light can be performed with devices such as spatial light modulators (SLMs) and digital micromirror devices (DMDs). These devices can be used to simulate transverse paraxial beam wavefunction eigenstates such as the Hermite–Laguerre–Gaussian mode families. We investigate several beam shaping methods in terms of the wavefunctions of scattered light. Our analysis of the efficiency, behaviour and limitations of beam shaping methods is applied to both theory and experiment. The deviation from the ideal output from a valid beam shaping method is shown to be due to experimental factors which are not necessarily being accounted for. Incident beam mode shape, aberration, and the amplitude/phase transfer functions of the DMD and SLM impact the distribution of scattered light and hence the effectiveness and efficiency of a beam shaping method. Correcting for these particular details of the optical system accounts for all differences in efficiency and mode fidelity between experiment and theory. We explicitly show the impact of experimental parameter variations so that these problems may be diagnosed and corrected in an experimental beam shaping apparatus. We show that several beam shaping methods can be used for the production of beam modes in a single pass and the choice is based on the particular experimental conditions.