Digital Micromirror Device Pixel Research Articles

Microsphere photolithography with dynamic angular spectra control for metasurface fabrication.

Microsphere photolithography (MPL) is a promising technique for cost-effective fabrication of large-scale metasurfaces. This approach generates an array of photonic jets by the collimated illumination of self-assembled microspheres. The photonic jets can be precisely steered within the unit cell defined by each microsphere by changing the angle of incidence. This allows for the creation of complex metasurface element geometries. Computer controlled articulation of the substrate relative to a static UV source allows the direct-write of different metasurface elements. However, this is time-consuming and requires registration between each exposure for complex features. This paper investigates a single exposure method with the dynamic continuous angle of incidence control provided by a Digital Micromirror Device (DMD) in the front Fourier plane of the projection system. The grayscale values of the DMD pixels can be adjusted to provide optical proximity correction. Larger patterns can be achieved by scanning the substrate relative to the exposure beam. This approach is demonstrated with the creation of hierarchical patterns. This work greatly simplifies the MPL exposure process for complex resonators and provides potential for full light field control.

Compressive space-dimensional dual-coded hyperspectral polarimeter (CSDHP) and interactive design method.

A compressive space-dimensional dual-coded hyperspectral polarimeter (CSDHP) and interactive design method are introduced. A digital micromirror device (DMD), a micro polarizer array detector (MPA), and a prism grating prism (PGP) are combined to achieve single-shot hyperspectral polarization imaging. The longitudinal chromatic aberration (LCA) and spectral smile of the system are both eliminated to guarantee the matching accuracy of DMD and MPA pixels. A 4D data cube with 100 channels and 3 Stocks parameters is reconstructed in the experiment. The feasibility and fidelity are verified from the image and spectral reconstruction evaluations. It is demonstrated that the target material can be distinguished by CSDHP.

DMD-based pure-phase superpixel method for digital holography

In this work, we implement a pure-phase superpixel (PPSP) method with a digital micromirror device (DMD). Here the DMD acts in an unconventional mode, i.e. as a phase-only modulator with hundreds of phase levels. An iterative Fourier transform algorithm is adapted to the DMD with high quality in a 2f-configuration without filters. When using 1600 × 1600 DMD pixels, the simulations show that the PPSP method in combination with the mixed-region amplitude freedom algorithm reduces the root-mean-square error by at least 33.5% compared with the conventional amplitude and phase modulation methods, and provides higher efficiency by 7.3%.

Long-distance mid-wave infrared super-resolution compressive imaging

Super-resolution imaging (SRI) for mid-wave infrared (MWIR) has attracted increasing attention in recent years due to the expensive price for a large number of pixels MWIR cameras. Investigation of the compressed sensing method can partially improves the resolution. However, the quality of SRI is highly related to the transfer function matrix of the optical system, which is difficult to be accurately measured because of the noise existed in MWIR detection, especially in long-distance systems. In this work, we propose a transfer function matrix calculation method which overcomes the issues of low imaging contrast and signal-to-noise ratio compared with previous studies. And we further establish a long-distance focal plane array-based compressive imaging system with a resolution of two digital micro-mirror device pixels which just satisfies the system diffraction limit. In addition, we achieve the 4 × 4 times super-resolution high-quality reconstruction of long-distance digital and physical objects with only six measurements.

Compressive spectral image fusion via a single aperture high throughput imaging system

Spectral image fusion techniques combine the detailed spatial information of a multispectral (MS) image and the rich spectral information of a hyperspectral (HS) image into a high-spatial and high-spectral resolution image. Due to the data deluge entailed by such images, new imaging modalities have exploited their intrinsic correlations in such a way that, a computational algorithm can fuse them from few multiplexed linear projections. The latter has been coined compressive spectral image fusion. State-of-the-art research work have focused mainly on the algorithmic part, simulating instrumentation characteristics and assuming independently registered sensors to conduct compressed MS and HS imaging. In this manuscript, we report on the construction of a unified computational imaging framework that includes a proof-of-concept optical testbed to simultaneously acquire MS and HS compressed projections, and an alternating direction method of multipliers algorithm to reconstruct high-spatial and high-spectral resolution images from the fused compressed measurements. The testbed employs a digital micro-mirror device (DMD) to encode and split the input light towards two compressive imaging arms, which collect MS and HS measurements, respectively. This strategy entails full light throughput sensing since no light is thrown away by the coding process. Further, different resolutions can be dynamically tested by binning the DMD and sensors pixels. Real spectral responses and optical characteristics of the employed equipment are obtained through a per-pixel point spread function calibration approach to enable accurate compressed image fusion performance. The proposed framework is demonstrated through real experiments within the visible spectral range using as few as 5% of the data.

A Resolution-Enhanced Digital Micromirror Device (DMD) Projection System

In this paper we present a resolution-enhanced system for digital micromirror device (DMD) projected images by utilizing time multiplexing and birefringence in order to achieve this with static components only. This provides a less expensive solution than reducing the size of the hardware pixels and can also be applied to higher resolution displays, as and when, these become available. Birefringent materials have different refractive indices for linearly polarized light with orthogonal polarization directions. A high-resolution projected image can be observed by overlapping two or three native resolution images at shifts of one half or one third of a DMD pixel diagonal respectively on successive frames. The optical components comprise a custom-made quartz plate as the birefringent component and an off-the-shelf twisted nematic liquid crystal display (TN-LCD) screen as a polarization rotator that is synchronized with the DMD frame rate. This paper covers the principle of operation and the system design. The functioning of the display is verified using enlarged images of the letter `R' and a checkerboard pattern that are formed from a small number of DMD pixels.

Complex-Amplitude Holographic Projection With a Digital Micromirror Device (DMD) and Error Diffusion Algorithm

Conventionally, a digital micromirror device (DMD) can only perform binary amplitude modulation of a light field. Simultaneous amplitude and phase modulation with a DMD is achieved by our proposed error diffusion scheme with a 4f double-lens setup for the first time. The DMD pixels are encoded by adaptive global optimization of binarization errors. In holographic projection, the object image can be optically reconstructed from a complex-amplitude hologram with this scheme. Experimental results show that our proposed error diffusion scheme outperforms the previous superpixel scheme in terms of the image quality and light efficiency of holographic reconstruction results under the same conditions.

Hadamard transform-based calibration method for programmable optical filters based on digital micro-mirror device.

Digital micromirror device (DMD) based optical filters provide a new avenue for spectral modulation in many research applications. Traditional sequential channel scanning method for the calibration of such filters may suffer from compromised spectral tuning accuracy due to the signal to noise ratio restriction on the minimum pixel number of each channel. In this work, we propose a Hadamard transform based calibration method to address this issue. A DMD-based programmable optical filter is constructed and calibrated using both the sequential scanning method and the proposed method for the subsequent synthesis of three representative filters (i.e., the bandpass filter, Gaussian filter, and principal component based filter). The spectral tuning accuracy is evaluated by calculating the relative root mean square error (RMSE) between the synthesized transmittance spectrum and the target spectrum. The results show that when calibrated with the proposed method, the programmable filter exhibits a consistent decrease in the relative RMSE with an increasing channel number for all filters. The smallest relative RMSE values are therefore achieved when each channel contains only one DMD pixel. In contrast, for the sequential scanning method, the relative RMSE increases dramatically when each channel contains three or fewer DMD pixels. This suggests that our method is superior to the sequential scanning method in spectral tuning accuracy when the signal level is low.

Edge smoothness enhancement in DMD scanning lithography system based on a wobulation technique.

The resolution of digital micro-mirror device (DMD) scanning lithography is limited in the transverse direction (the scanning direction is vertical) as a result of the compacted size of the DMD micro-mirror and the low magnification of the projection lens. Above-stated restrictions lead to an unsatisfactory saw-tooth edge (size ~one DMD pixel) after the lithography process within all directions except for the scanning orientation. In order to smooth the edge, an optimized sub-pattern construction method, described as the combination of wobulation techniques and the continuous scanning lithography process, is proposed. Afterward, lithography experiments were implemented by introducing the wobulation techniques within the DMD scanning lithography system. The experimental results show that the saw-tooth edge is reduced to nearly 0.5 pixel size after 1/2 pixel dislocation superposition exposure, and is even scaled down to less than 0.1 pixel after 1/4 pixel dislocation superposition exposure. At this point, the edge of the lithography pattern is appropriately smoothed. The effectiveness of the above-mentioned method that improves the edge smoothness of the lithography pattern is demonstrated.

Superpixel-based spatial amplitude and phase modulation using a digital micromirror device.

We present a superpixel method for full spatial phase and amplitude control of a light beam using a digital micromirror device (DMD) combined with a spatial filter. We combine square regions of nearby micromirrors into superpixels by low pass filtering in a Fourier plane of the DMD. At each superpixel we are able to independently modulate the phase and the amplitude of light, while retaining a high resolution and the very high speed of a DMD. The method achieves a measured fidelity F = 0.98 for a target field with fully independent phase and amplitude at a resolution of 8 × 8 pixels per diffraction limited spot. For the LG10 orbital angular momentum mode the calculated fidelity is F = 0.99993, using 768 × 768 DMD pixels. The superpixel method reduces the errors when compared to the state of the art Lee holography method for these test fields by 50% and 18%, with a comparable light efficiency of around 5%. Our control software is publicly available.

(Invited) The Journey of the DMD Pixel Design Evolution

The Digital Micromirror Device (DMD) has enabled the world’s top display products ranging from large cinema projectors to small pico projectors that can fit in smartphones. This paper will walk through the journey of the DMD pixel design evolution from the original digital micromirror concept to the most popular FTP pixel design. The motivations, challenges and impacts of major design changes of four generations of DMD pixels will be discussed including pixel size shrink from 17μm pixel to 10.8μm pixel and tilt angle increase from 10 to 12 degrees.

Pixel-based partially coherent image method for maskless lithography system

Maskless lithography (ML) provides a fast and low-cost method for projecting the images of IC or micro features onto photoresist. However, it needs an efficient simulation method to evaluate the performance of lithography process. In this paper, a pixel-based partially coherent image method for digital micro-mirror device (DMD) based ML is proposed based on the linear invariant theory. In our method, the mask is sampled by DMD pixel (each pixel corresponding to each micro-mirror) and expressed by rect function. Using the shift theory of Fourier transform and the stacked pupil operator approach, we build a matrix Φ for system response function of rect function. If the DMD pixel state matrix is S, then the aerial image can be calculated with two matrix multiplication I(x,y)=SΦ.

Grayscale laser image formation using a programmable binary mask

We present grayscale laser image formation from a programmable binary mask using a digital micromirror device (DMD) followed by a telescope with an adjustable pinhole low-pass filter. System performance was measured by comparing the intensity conformity with respect to the target image and by the energy conversion efficiency. A theoretical analysis of image precision proved high-precision image formation and inspired the iterative pattern refinement process based on the point spread function of a single DMD pixel to seek optimized image quality. We derived the diffraction efficiency formula of the DMD and discussed the overall system energy efficiency with operation wavelengths. Actual image precision performance was evaluated by measuring the root-mean-square (RMS) error of a series of sinusoidal-flattop profiles with different system bandwidths. We produced grayscale laser images with different spatial spectral content using intensity profiles of Laguerre-Gaussian, Hermite-Gaussian, and Lena-flattop beams. Measured RMS errors of all examples of various bandwidths were consistent with the image precision of the sinusoidal reference patterns. The ripple effect caused by the sharp-edged pinhole was the major contributor to the residual error in the output images. Error histograms had a zero-mean Gaussian distribution with standard deviation equal to the value of the RMS error.

High-precision laser beam shaping using a binary-amplitude spatial light modulator

We have achieved high-precision laser beam shaping by using a binary-amplitude spatial light modulator, a digital micromirror device (DMD), followed by an imaging telescope that contains a pinhole low-pass filter (LPF). An error diffusion algorithm was used to design the initial DMD pixel pattern based on the measured input beam profile. This pattern was iteratively refined by simulating the optically low-pass filtered DMD image and changing DMD pixels to lift valleys and suppress peaks. We noted the gap between the experimental result of 1.4% root-mean-square (RMS) error and the simulated result for the same DMD pattern of 0.3% RMS error. Therefore, we deemed it necessary to introduce iterative refinement based on actual measurements of the output image to further improve the uniformity of the beam. Using this method, we have demonstrated the ability to shape raw, non-spatially filtered laser beams (quasi-Gaussian beams) into beams with precisely controlled profiles that have an unprecedented level of RMS error with respect to the target profile. We have shown that our iterative refinement process is able to improve the light intensity uniformity to around 1% RMS error in a raw camera image for both 633 and 1064 nm laser beams. The use of a digital LPF on the camera image is justified in that it matches the performance of the pinhole filter in the experimental setup. The digital low-pass filtered results reveal that the actual optical beam profiles have RMS error down to 0.23%. Our approach has also demonstrated the ability to produce a range of target profiles as long as they have similar spatial-frequency content (i.e., a slowly varying beam profile). Circular and square cross-section flat-top beams and beams with a linear intensity variation within a circular and square cross section were produced with similarly low RMS errors. The measured errors were about twice the ultimate limit of 0.1% RMS error based on the number of binary DMD pixels that participate in the beam-formation process.