Ghost imaging with N-order speckle light

Equipment requirement, quality of reconstructed image, and reconstruction time are important factors in the realization of thermal-light ghost imaging system. In this paper, we propose a new ghost imaging scheme with multiple speckle patterns, named multiple speckle patterns differential compressive ghost imaging scheme. In this scheme, the high temporal resolution requirements for detectors is reduced by continuously detecting multiple independent speckle patterns. We eliminate the background and other noises in ghost imaging system by using differential ghost imaging method. And the reconstruction time is effectively reduced simultaneously to improve the reconstructed image quality by introducing the compressive sensing techniques. Numerical results show that for the two-level grayscale “N” image, the mean square error, in using the proposed scheme with 8000 measurements, is reduced by 96.9%, and the peak signal to noise ratio has improved by 15.1 dB, in comparison with those using the original multiple speckle patterns ghost imaging scheme with 35000 measurements. For the eight-level grayscale “Pepper” image, the peak signal to noise ratio is enhanced by 11.4 dB. The proposed scheme also can decrease the requirements of detection equipment to improve the image quality, and reduce the reconstruction time. Therefore, it may have a broad application prospect.

Remote-sensing applications within atmospheric scattering environments pose substantial challenges for traditional optical imaging systems owing to photon scattering, signal attenuation, and noise-induced degradation. This paper presents a ghost imaging technique operating in the Fourier domain, integrated with adaptive multistage post-processing enhancement algorithms to improve image reconstruction fidelity in the presence of scattering media. The experimental framework utilizes a digital micromirror device (DMD) to generate structured Fourier basis patterns in the reference arm, while the signal arm traverses controllable scattering media simulated using a precision-positioned ground glass (GG) diffuser. Image reconstruction is achieved through frequency-domain correlation processing employing a three-step phase-shifting algorithm, while reconstructed image degradation is mitigated through a multi-stage enhancement pipeline incorporating adaptive denoising, deblurring, and contrast optimization algorithms. Experimental validation demonstrates that the proposed methodology achieves recognizable image reconstruction using 25% of the Fourier coefficient set under high-scattering conditions, with enhancement algorithms providing up to 30% improvement in peak signal-to-noise ratio (PSNR) relative to unprocessed reconstructions. This investigation reveals fundamental limitations in dense scattering regimes and provides insights into the computational trade-offs inherent in ghost imaging systems under challenging environmental conditions.

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.

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.

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.

基于数字微镜器件的压缩感知关联成像研究

Optical design of high performance con-focal microscopy with digital micro-mirror and stray light filters

The mitigation of atmospheric effects is an essential component of any high-throughput optical satellite downlink. In this work, as part of the High-throughput and Secure Networks Challenge Program, we apply computational imaging approaches to turbulent wavefront estimation by capturing single pixel images of the speckle pattern from a simulated turbulence-corrupted wavefront. In particular, Hadamard patterns are sequentially displayed on a digital micromirror device (DMD) and used to reconstruct the turbulent speckle pattern. This speckle pattern can be used as an input to a phase-retrieval algorithm to estimate the wavefront phase that produced the speckle. We present the concepts of computational turbulent speckle imaging along with an experimental setup to demonstrate this approach. A spatial light modulator (SLM) is used to simulate turbulence-degraded wavefronts. These are then imaged onto a computational imaging system implemented with a DMD and balanced detection using two photodiodes. The experimental setup is described along with the image reconstruction algorithm. Preliminary computational speckle images are presented and compared with the predicted image obtained by numerically simulating the beam propagation through the optical system showing close agreement.

Foveated ghost imaging based on deep learning

Influence of detector response speed on the contrast-to-noise ratio of reflective ghost imaging

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.