Digital Mirror Device Research Articles

Ghost Imaging with Deep Learning for Position Mapping of Weakly Scattered Light Source

We propose ghost imaging (GI) with deep learning to improve detection speed. GI, which uses an illumination light with random patterns and a single-pixel detector, is correlation-based and thus suitable for detecting weak light. However, its detection time is too long for practical inspection. To overcome this problem, we applied a convolutional neural network that was constructed based on a classification of the causes of ghost image degradation. A feasibility experiment showed that when using a digital mirror device projector and a photodiode, the proposed method improved the quality of ghost images.

低空高分辨率激光雷达光学系统设计

Aiming at the problems of optical imaging for low altitude, low speed and small target recognition ability and low signal-to-noise ratio, a low altitude and high resolution lidar optical system was designed. The MEMS mirror was used by the scanning device of the transmitting optical system, and the beam expanding system was designed to ensure the beam quality of the laser emitted at different scanning angles. The digital mirror device combine with objective lens, polarizing device were used for receiving optical system, the background noise was greatly lower than laser receiving system using single-point detector and could realize laser echo receiving and visible light imaging at the same time. The structure parameters of the optical system were given, an optical system was designed using optical design software. The optical system has a spatial resolution of 0.5 mrad/pixel and an array scale of 200×200. The simulation results show that design method is feasible. The detection distance can reach 1000 m, and the background noise can be reduced by about 22162 times compared to the single-point detector receiving system.ystem.

Digital mirror device combined with microscopy technique illuminates biological mechanisms

By optimizing the blazed grating of a digital mirror device, researchers developed a low-cost, multi-color, super-resolution microscope with doubled spatial resolution.

DMD-based three-dimensional chromatic confocal microscopy.

In this paper, a digital mirror device (DMD)-based chromatic confocal microscopy is proposed and demonstrated for three-dimensional (3D) surface profiling without any mechanical scanning. In this method, the DMD works as the multipoint source and multi-pinhole at the same time to achieve the lateral scanning. Moreover, axial scanning is realized through the chromatic aberration of the confocal optics. Since the micromirror array of the DMD is not perpendicular to the confocal imaging axis, a corresponding calibration is needed to eliminate the tilt effects and perform accurate 3D imaging. The measurement range with the current optical system is 45 µm over 505-650 nm working spectrum and can be increased by using a custom objective with large chromatic aberration. The system performance has been demonstrated with a multistep sample.

Effects of the Layer Height and Exposure Energy on the Lateral Resolution of Zirconia Parts Printed by Lithography-Based Additive Manufacturing.

Lithography-based ceramics manufacturing (LCM) processes enable the sophisticated 3 dimensional (3D) shaping of ceramics by additive manufacturing (AM). The build-up occurs, like many other AM processes, layer by layer, and is initiated by light. The built-in digital mirror device (DMD) enables the specific exposure of desired pixels for every layer, giving as a consequence a first estimation of the printing resolution in the x and y axes. In this work, a commercial zirconia slurry and the CeraFab 7500, both from Lithoz GmbH (Vienna, Austria), were used to investigate the potential of reaching this resolution. The results showed that the precision of a part is strongly dependent on the applied exposure energy. Higher exposure energies resulted in oversized dimensions of a part, whereas too low energy was not able to guarantee the formation of a stable part. Furthermore, the investigation of the layer thickness showed that the applied exposure energy (mJ/cm2) was acting in a volume, and the impact is visible in x, y, and z dimensions. The lowest applied exposure energy was 83 mJ/cm2 and showed the most accurate results for a layer thickness of 25 μm. With this energy, holes and gaps smaller than 500 μm could be printed; however, the measurements differed significantly from the dimensions defined in the design. Holes and gaps larger than 500 μm showed deviations smaller than 50 μm from the design and could be printed reliably. The thinnest printable gaps were between 100 and 200 μm. Concerning the wall thickness, the experiments were conducted to a height of 1 cm. Taking into account the stability and deformation of the walls as well, the best results after sintering were achieved with thicknesses of 200–300 μm.

Rapid Prototyping of a Dammann Grating in DMD-Based Maskless Lithography

Microstructures are fabricated with a fast fabrication speed, submicron-scale precision and a minimum feature size of 1.5 μm. The proposed rapid prototyping fabrication method takes advantage of the maskless lithography technique based on a digital mirror device (DMD) and photocurable resin, which has a broad range of uses in three-dimensional (3D) printing. To illustrate the feasibility of this method, a Dammann grating is fabricated. Using a series of experiments and optimized designs, we analyze the characteristics of the photocurable resin, quantify the dose modulation for lithography and redesign the mask pattern. Consequently, a Dammann grating with a 50% diffraction efficiency is successfully fabricated, which can not only guarantee the precision but also maintain the fabrication speed. This work demonstrates the potential of this method to rapidly and directly manufacture binary optical elements or structures at the nanoscale based on photocurable resin and DMD-based maskless lithography.

High-resolution VSDI retinotopic mapping via a DLP-based projection system.

High-resolution recording of visual cortex activity is an important tool for vision research. Using a customized digital mirror device (DMD) - based system equipped with retinal imaging, we projected visual stimuli directly on the rat retina and recorded cortical responses by voltage-sensitive dye imaging. We obtained robust cortical responses and generated high-resolution retinotopic maps at an unprecedented retinal resolution of 4.6 degrees in the field of view, while further distinguishing between normal and pathological retinal areas. This system is a useful tool for studying the cortical response to localized retinal stimulation and may shed light on various cortical plasticity processes.

High-resolution VSDI retinotopic mapping via a DLP-based projection system.

High-resolution recording of visual cortex activity is an important tool for vision research. Using a customized digital mirror device (DMD) - based system equipped with retinal imaging, we projected visual stimuli directly on the rat retina and recorded cortical responses by voltage-sensitive dye imaging. We obtained robust cortical responses and generated high-resolution retinotopic maps at an unprecedented retinal resolution of 4.6 degrees in the field of view, while further distinguishing between normal and pathological retinal areas. This system is a useful tool for studying the cortical response to localized retinal stimulation and may shed light on various cortical plasticity processes.

High-resolution femtosecond laser beam shaping via digital holography.

We propose a method to achieve high-resolution femtosecond laser beam shaping (HR-FLBS) via digital holography based on a digital mirror device (DMD) and optimized optical design. By programming the hologram on the DMD, we captured several patterns such as light spots, decorated letters of "HUST" (Huazhong University of Science and Technology), and a series of concentric annuli whose fine structure approaches the optical diffraction limit. The experimental results confirm that the proposed method can shape the amplitude and phase of a femtosecond laser arbitrarily with high resolution.

Improving the Signal-to-Noise Ratio of Superresolution Imaging Based on Single-Pixel Camera

Based on the theories of single-pixel camera and compressed sensing image reconstruction, the sparse basis, the projection method of measurement matrix, and the signal reconstruction algorithm are optimized. First, for the sparse representation of image, the restraint matrix is designed combining the characteristics of wavelet sparse coefficients to enhance the sparse representation ability of the discrete wavelet base, which improves the quality of image reconstruction and imaging by single-pixel camera. Then, in the single-pixel camera system, the projection method is improved according to the characteristics of the digital mirror device micromirror, and a new bilateral projection method based on the block diagonal measurement matrix is proposed to realize the superresolution imaging of the outdoor scene, reducing the number of measurement and improving the imaging quality. Finally, for the algorithm of image reconstruction, combining the characteristics of convex optimization and nonconvex optimization algorithms, a new algorithm from convex optimization approximately to nonconvex optimization algorithm is proposed, and compared with the traditional image reconstruction algorithm, such as greedy pursuit algorithm, minimum norm algorithm, and image interpolation, the peak signal-to-noise ratio and imaging quality of reconstructed images are effectively improved. The feasibility of the proposed methods is demonstrated by simulation experiments and imaging experiments of single-pixel camera.

Maskless lithography based on digital micromirror device (DMD) and double sided microlens and spatial filter array

A new type of maskless lithography system based on digital mirror device (DMD) is proposed, constructed, and experimentally demonstrated. It includes a pin-hole array sandwiched by two microlens arrays on each side, known as double-sided microlens/spatial-filter array (D-MSFA), and aligned with a DMD. Ultraviolet (UV) light reflected by DMD is first collected by the first microlens array, filtered through the pin-hole array, and then re-focused by the second microlens array into a UV spot array. Along with an obliquely scanning method, this D-MSFA/DMD-based maskless lithography system can perform not only 2D but also 3D UV patterning. Experimental testing successfully generates complicated patterns with a minimum line-width of 3.36 μm. Direct 3D patterning and 3D microfabrication are also experimentally demonstrated on a photoresist layer. Excellent profile accuracy and surface structure qualities are observed with great potentials for future 2D and 3D microfabrication in a maskless manner.

Calibration of an array projector used for high-speed three-dimensional shape measurements using a single camera.

Geometric calibration of digital light processing projectors in single-camera, fringe-projecting 3D measurement systems have been studied assuming the projector is inverse pinhole modeled. Conversely, a high-speed multi-aperture array projector (MAAP) projecting aperiodic fringes is not dependent on a digital mirror device and cannot be pinhole modeled. With MAAP projection, a stereo camera setup is required. This paper presents a model-less method to calibrate a MAAP by direct measurement of its illumination field and re-enables 3D measurements with a single camera even with surface discontinuities present. Experimental proof of principle and preliminary measurement performance are shown.

Rapid measurement of transmission matrix with the sequential semi-definite programming method**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFB1104500), the Natural Science Foundation of Beijing (Grant No. 7182091), and the National Natural Science Foundation of China (Grant No. 21627813).

This paper puts forward for the first time a combined transmission matrix (TM) method to measure the monochromatic TM of scattering media without a reference beam. This method can be named a sequential semi-definite programming method which combines the sequential algorithm and the semi-definite programming method. Firstly, each part of the TM is calculated respectively in proper sequence. Then every part of TM is combined to form a complete TM in accordance with a certain rule. The phase modulation of the incident light is achieved by using a high speed digital mirror device with the superpixel method. We have experimentally demonstrated that the incident light field is focused at the target through scattering media using the measured TM to optimize the wavefront of the incident light. Compared with the semi-definite programming method, our method takes less computational time and occupies less memory space. The sequential semi-definite programming method shows potential applications in imaging through biological tissues.

Benchmarking modern algorithms to holographically create optical tweezers for laser-cooled atoms

ABSTRACTWe discuss and compare three methods to generate holograms for optical tweezers: simple rounding, Floyd–Steinberg error diffusion dithering and mixed-region amplitude freedom (MRAF). These schemes are optimized for producing large arrays of tightly focused luminous spots. The algorithms are compared in terms of their speed, efficiency and accuracy, for periodic arrangements of traps; an arrangement of particular interest for the trapping and manipulation of single laser-cooled atoms in the field of quantum computing. We simulate the image formation using each of a binary amplitude modulating digital mirror device (DMD) and a phase modulating spatial light modulator (PSLM) as the display element. While a DMD allows for fast frame rates, the slower PSLM is more efficient and provides higher accuracy with a quasi-continuous variation of phase. We discuss the relative merits of each algorithm for use with both a DMD and a PSLM, allowing one to choose the ideal approach depending on the circumstances.

Functional characterization of the retinal output upon optogenetic stimulation

Functional characterization of the retinal output upon optogenetic stimulation

In vivo real-time imaging of cutaneous hemoglobin concentration, oxygen saturation, scattering properties, melanin content, and epidermal thickness with visible spatially modulated light.

We present the real-time single snapshot multiple frequency demodulation - spatial frequency domain imaging (SSMD-SFDI) platform implemented with a visible digital mirror device that is capable of imaging and monitoring dynamic turbid medium and processes over a large field of view. One challenge in quantitative imaging of biological tissue such as the skin is the complex structure rendering techniques based on homogeneous medium models to fail. To address this difficulty we have also developed a novel method that maps the layered structure to a homogeneous medium for spatial frequency domain imaging. The varying penetration depth of spatially modulated light on its wavelength and modulation frequency is used to resolve the layered structure. The efficacy of the real-time SSMD-SFDI platform and this two-layer model is demonstrated by imaging forearms of 6 healthy subjects under the reactive hyperemia protocol. The results show that our approach not only successfully decouples light absorption by melanin from that by hemoglobin and yields accurate determination of cutaneous hemoglobin concentration and oxygen saturation, but also provides reliable estimation of the scattering properties, the melanin content and the epidermal thickness in real time. Potential applications of our system in imaging skin physiological and functional states, cancer screening, and microcirculation monitoring are discussed at the end.

Visuomotor Response to Object Expansion in Free-Flying Bumble Bees

The flight control systems of flying insects enable many kinds of sophisticated maneuvers, including avoidance of midair collisions. Visuomotor response to an approaching object, received as image expansion on insects’ retina, is a complex event in a dynamic environment where both animals and objects are moving. There are intensive free flight studies on the landing response in which insects receive image expansion by their own movement. However, few studies have been conducted regarding how freely flying insects respond to approaching objects. Here, using common laboratory insects for behavioral research, the bumblebee Bombus ignitus, we examined their visual response to an approaching object in the free-flying condition. While the insect was slowly flying in a free-flight arena, an expanding stripe was projected laterally from one side of the arena with a high-speed digital mirror device projector. Rather than turning away reported before, the bumble bees performed complex flight maneuvers. We synchronized flight trajectories, orientations and wing stroke frequencies with projection parameters of temporal resolution in 0.5 ms, and analyzed the instantaneous relationship between visual input and behavioral output. In their complex behavioral responses, we identified the following two visuomotor behaviors: increasing stroke frequency when the bumble bees confront the stripe expansion, and turning towards (not away) the stripe expansion when it is located laterally to the bee. Our results suggested that the response to object expansion is not a simple and reflexive escape but includes object fixation, presumably for subsequent behavioral choice.

Super-Resolution Imaging Through Scattering Medium Based on Parallel Compressed Sensing

Recent studies show that compressed sensing (CS) can recover sparse signal with much fewer measurements than traditional Nyquist theorem. From another point of view, it provides a new idea for super-resolution imaging, like the emergence of single pixel camera. However, traditional methods implemented measurement matrix by digital mirror device (DMD) or spatial light modulator, which is a serial imaging process and makes the method inefficient. In this paper, we propose a super resolution imaging system based on parallel compressed sensing. The proposed method first measures the transmission matrix of the scattering sheet and then recover high resolution objects by “two-step phase shift” technology and CS reconstruction algorithm. Unlike traditional methods, the proposed method realizes parallel measurement matrix by a simple scattering sheet. Parallel means that charge-coupled device camera can obtain enough measurements at once instead of changing the patterns on the DMD repeatedly. Simulations and experimental results show the effectiveness of the proposed method.

Development of targeted STORM for super resolution imaging of biological samples using digital micro-mirror device

We demonstrate a simple illumination system based on a digital mirror device which allows for fine control over the power and pattern of illumination. We apply this to localization microscopy (LM), specifically stochastic optical reconstruction microscopy (STORM). Using this targeted STORM, we were able to image a selected area of a labelled cell without causing photo-damage to the surrounding areas of the cell.

Programmable light source based on an echellogram of a supercontinuum laser.

Illumination systems with tunable spectrums have been receiving an increasing amount of attention due to their wide application and unique capability. This paper proposes a programmable light source in the visible range based on the combination of a prism and an echelle grating. A supercontinuum laser is utilized as the primary source, whose echellogram is projected to a digital mirror device for wavelength selection. A complete calibration procedure is developed to generate any target spectrum of choice. Experiments have shown that spectral peaks with a full width at half-maximum of 1 nm can be easily generated and the wavelength tuning resolution can reach as small as 0.01 nm.