We present a photonic tensor accelerator (PTA) employing nearly all dimensions (complex amplitude, polarization, wavelength and spatial mode) of light for scalable tensor multiplication. In this architecture, multiplications are performed through coherent mixing and accumulations are performed via simultaneous photodetection of multiple degrees of freedom within one dimension of light. We have implemented the PTA on micro-optics and integrated-photonics platforms. Experimental results of the PTA as well as its applications in artificial neural networks and computing will be presented.
Extending the multi-plane light conversion (MPLC) technique, we propose and demonstrate a 3D micro-optic system capable of performing matrix/tensor multiplications. Our proposed approach, called multi-plane light processing (MPLP), is passive and utilizes all degrees of freedom of light which makes it well-suited to surpass electronic accelerators in both scalability and energy efficiency. MPLP is an all-in-one system capable of spatial mode conversion and multiplexing, wavelength demultiplexing, hybrid coupling, and optical routing. As a result, the proposed device can perform matrix/tensor multiplications in a single clock cycle with tens of GHz speed limited by the optical modulators and photodetectors’ bandwidth. We have experimentally demonstrated proof-of-concept MPLP utilizing a spatial mode modulator performing 2×2 matrix-matrix multiplication and discuss the scaling methods to enhance its computation power. We envision the proposed PTA competing with electronic accelerators for large-scale and power-efficient artificial intelligence (AI) applications.
In the post-Moore’s law era, dedicated digital accelerators have played an indispensable role in the success of artificial neural networks (ANNs) and their applications in artificial intelligence (AI). As the complexity of ANNS grows, analog electrical and optical computing are being considered as alternatives for achieving sustainable scalability and energy efficiency. In this talk we will present photonic accelerators that can potentially provide orders of magnitude increases in scalability and energy efficiency towards brain-like AI with hundred billion-neuron neural processing power.
We demonstrate a deep-learning-based fiber imaging system that can transfer real-time artifact-free cell images through a meter-long Anderson localizing optical fiber. The cell samples are illuminated by an incoherent LED light source. A deep convolutional neural network is applied to the image reconstruction process. The network training uses data generated by a setup with straight fiber at room temperature (∼20 ° C) but can be utilized directly for high-fidelity reconstruction of cell images that are transported through fiber with a few degrees bend or fiber with segments heated up to 50°C. In addition, cell images located several millimeters away from the bare fiber end can be transported and recovered successfully without the assistance of distal optics. We provide evidence that the trained neural network is able to transfer its learning to recover images of cells featuring very different morphologies and classes that are never “seen” during the training process.
X-ray diffraction tomography (XDT) resolves the spatially-variant XRD profiles within the object, and provides improved material contrast compared to the conventional transmission-based computed tomography (CT). Due to the small diffraction cross-section, a typical full field-of-view XDT scan takes tens of hours using a table-top X-ray tube. In medical and industrial imaging applications, oftentimes only the XRD measurement within a region-of-interest (ROI) is required, which, together with the demand to reduce imaging time and radiation dose to the sample, motivates the development of interior XDT systems that scan and reconstruct only an internal region within the sample. However, existing interior reconstruction frameworks rely on a known region or piecewise constant constraint within the ROI, which do not apply to all the samples in XDT. In this presentation, we propose a quasi-interior XDT scheme that incorporates a small fraction of projection information from the exterior region to assist interior reconstruction. The low-resolution exterior projection data obviates the requirement for prior knowledge on the object, and allows the ROI reconstruction to be performed with the fast, widely-used filtered back-projection algorithm for easy integration into real-time XDT imaging modules. We also demonstrate the material classification based on the XDT profile reconstructed from pure interior and our combined ROI and exterior measurements.
Task-specific adaptive sensing in computed tomography (CT) scan is critical to dose reduction and scanning acceleration. Due to the sequential nature of the CT acquisition process, the information of the objects aggregates as the measurement process progresses. Conventional adaptive sensing methods, aiming to maximize the task-specific information acquisition, formulate the measurement strategy as an optimization problem with assumptions in object distributions (for example, Gaussian mixture model), which requires considerable computational time and resource during the acquisition. In our work, we propose a machine learning approach to learn task-specific data-acquisition policy, with the only assumption on the locality and composition of the objects, which shifts the computation load to the pre-acquisition stage. We analyze our learned method on public dataset comparing to a stochastic policy which plans the acquisition randomly and a uniform policy which plans the acquisition with a fixed interval. Based on our experiments the learned method requires at least 25% fewer acquisition steps than the stochastic and uniform policies.
Computational imaging systems apply encoding on the physical layer of the imaging device, demonstrating superior performance in resolution, dynamic range, and acquisition speed, compared to conventional point-to-point mapping imaging system. However, accurate mathematical models is required for such systems, and the calibration is a major concern for practical implementation. In this invited talk, we will discuss the efforts in applying the learning approach in computational imaging system from the Optical Imaging System Lab at the University of Central Florida. Specifically, the talk will be focus on a demonstration of such approach in fully flexible lensless fiber imaging.
Conventional X-ray computed tomography (CT) only reconstructs the attenuation map. X-ray coherent scattering computed tomography (CSCT) probes the angular-dependent scattering profiles of the three-dimensional (3D) object, achieving a high structural specificity among materials with similar electron density. However, due to the low level of interaction of coherent scattering and the 3D scattering profiles of crystalline materials, the real-life anomaly detection using coherent scattering signature posed challenges in acquisition speed, algorithm efficiency, reconstruction quality, and detection accuracy. In this invited talk, we will discuss the efforts in accelerating the image acquisition speed while maintaining object-specific information from the Optical Imaging System Lab at the University of Central Florida. Specifically, the talk will be focus on maximize the system detection efficiency and improve the classification/reconstruction performance for low photon detection level to meet the need of practical detection.
The radiation dosage delivered to the sample is a constant challenge facing X-ray imaging systems. In conventional transmission-based computed tomography (CT), a beam penetrating through thick, high-attenuation region in the sample results in low signal on the detector, and therefore a higher power (e.g., tube current modulation) or longer integration time is often required to maintain signal quality. The issue of radiation dose becomes more sever in coherent scattering X-ray tomography, in which the scattering signal is typically orders of magnitude weaker than the transmitted beam. With X-ray photon-counting detectors, transmitted (or scattered) X-ray photons can be acquired at extremely low photon flux, which enables us to greatly reduce the imaging time and dose administrated to the sample. Instead of counting the average the number of photons within a fixed time interval, the arrival times of only a few photons detected in sequence contain sufficient information to estimate the attenuation (or scattering) property, which allows object reconstruction based on our measurement geometry and noise model. We will also discuss compressive or adaptive data acquisition schemes to implement material identification utilizing the energy sensitivity of X-ray photon-counting detector. Our method can be further parallelized with a photon-counting detector array to achieve fast, low-dose X-ray tomographic imaging based on either attenuation or scattering signals, which could find broad applications in medical diagnosis and security screening.
Conventional computed tomography (CT) only reconstructs the attenuation map within a sample. X-ray coherent scattering computed tomography (CSCT), which probes the angular-dependent scattering profiles of a 3D object, achieves high-contrast and specificity among materials or tissues with similar attenuation cross-section. Due to the weak coherent scattering cross-section, CSCT using a pencil-beam either requires a brilliant source, such as synchrotron, or tens of hours in image acquisition using a traditional X-ray tube. Fan-beam CSCT using table-top source has been proposed to parallelize the acquisition of each projection, but the use of collimators on the detector plane limits the collection efficiency. Moreover, conventional CSCT systems cannot further parallelize the image acquisition among layers by switching to cone-beam illumination, because the scattering signal from different layers will overlap on the detector. Here we propose a fast, high-efficiency multiplexing scheme using structured cone-beam illumination to image a 3D sample. Our system improves the source utilization compared to pencil-beam CSCT, yet does not require detector collimator to localize and resolve the scattering profile of each point. We have reconstructed the coherent scattering profile within a volumetric object, and demonstrated the material classification of the 3D sample. Compared to previous systems, our method reduces the imaging time by one order of magnitude. We believe our multiplexed CSCT scheme could become the next generation X-ray coherent scattering tomography system.
Video compressive imaging system reconstructs high-speed image sequence from a single, coded snapshot. In this paper, we report a compressive video sensing system that captures the side information in addition to the main measurement to aid the reconstruction of high-speed scenes. The integration of the side information not only improves the quality of reconstruction, but also reduces the dependence of the reconstruction on regularization. We have implemented a system prototype, which splits the field of view of a single camera into two channels: one channel captures the coded, low-frame-rate measurement for high speed video reconstruction; the other channel captures a direct measurement without coding as the side information. A joint reconstruction model is developed to recover the high-speed videos from the two channels.
Conventional computed tomography reconstructs the attenuation only high-dimensional images. Coherent scatter computed tomography, which reconstructs the angular dependent scattering profiles of 3D objects, can provide molecular signatures that improves the accuracy of material identification and classification. Coherent scatter tomography are traditionally acquired by setups similar to x-ray powder diffraction machine; a collimated source in combination with 2D or 1D detector collimation in order to localize the scattering point. In addition, the coherent scatter cross-section is often 3 orders of magnitude lower than that of the absorption cross-section for the same material. Coded aperture and structured illumination approaches has been shown to greatly improve the collection efficiency. In many applications, especially in security imaging and medical diagnosis, fast and accurate identification of the material composition of a small volume within the whole object would lead to an accelerated imaging procedure and reduced radiation dose. Here, we report an imaging method to reconstruct the material coherent scatter profile within a small volume. The reconstruction along one radial direction can reconstruct a scalar coherent scattering tomographic image. Our methods takes advantage of the finite support of the scattering profile in small angle regime. Our system uses a pencil beam setup without using any detector side collimation. Coherent scatter profile of a 10 mm scattering sample embedded in a 30 mm diameter phantom was reconstructed. The setup has small form factor and is suitable for various portable non-destructive detection applications.
Small-angle X-ray scattering (SAXS) measures the signature of angular-dependent coherently scattered X-rays, which contains richer information in material composition and structure compared to conventional absorption-based computed tomography. SAXS image reconstruction method of a 2 or 3 dimensional object based on computed tomography, termed as coherent scattering computed tomography (CSCT), enables the detection of spatially-resolved, material-specific isotropic scattering signature inside an extended object, and provides improved contrast for medical diagnosis, security screening, and material characterization applications. However, traditional CSCT methods assumes materials are fine powders or amorphous, and possess isotropic scattering profiles, which is not generally true for all materials. Anisotropic scatters cannot be captured using conventional CSCT method and result in reconstruction errors. To obtain correct information from the sample, we designed new imaging strategy which incorporates extra degree of detector motion into X-ray scattering tomography for the detection of anisotropic scattered photons from a series of two-dimensional intensity measurements. Using a table-top, narrow-band X-ray source and a panel detector, we demonstrate the anisotropic scattering profile captured from an extended object and the reconstruction of a three-dimensional object. For materials possessing a well-organized crystalline structure with certain symmetry, the scatter texture is more predictable. We will also discuss the compressive schemes and implementation of data acquisition to improve the collection efficiency and accelerate the imaging process.
Small-angle X-ray scattering (SAXS) detects the angular-dependent, coherently scattered X-ray photons, which provide improved contrast among different types of tissues or materials in medical diagnosis and material characterizations. By combining SAXS with computed tomography (CT), coherent scattering computed tomography (CSCT) enables the detection of spatially-resolved, material-specific scattering profile inside an extended object. However, conventional CSCT lacks the ability to distinguish direction-dependent coherent scattering signal, because of its assumptions that the materials are amorphous with isotropic scattering profiles. To overcome this issue, we propose a new CSCT imaging strategy, which can resolve the three-dimensional scattering profile for each object pixel, by incorporating detector movement into each CSCT projection measurement. The full reconstruction of the three-dimensional momentum transfer profile of a two-dimensional object has been successfully demonstrated. Our setup only requires a table-top Xray source and a panel detector. The presented method demonstrates the potential to achieve low-cost, high-specificity X-ray tissue imaging and material characterization.
Fluorescence Talbot microscope is a scalable field-of-view (FOV) imaging platform, which takes advantage of the phase sensitivity of the self-image of a periodic structure. Such a system can maintain the microscopic resolution and extend the FOV for the whole slide (15 mm×15 mm) scanning. Previously reported Talbot fluorescence systems, tabletop and on-chip device alike, rely on the coherence of the illumination source, limiting their potential applications in low-resource setting environment. A more cost-effective setup using a light-emitting diode, which has an area of 4 mm2 and a full width at half maximum of 16 nm in wavelength, is demonstrated. Compared to the illumination that is spatially filtered by a single pinhole, our system has achieved an illumination intensity that is 357 times higher. The reconstructed image quality is comparable to that of a 10× microscope objective. Various samples, such as fluorescent beads, green fluorescence protein-labeled HeLa cells, and a mouse kidney slide, were reconstructed by the system.
Two-photon-excited fluorescence and second-harmonic generation are characterized as a function of laser pulse duration as short as sub-10-fs. A comparative study is performed where pulse duration is varied by introducing dispersion, as reported previously, and by tailoring pulse spectral width and minimizing its time-bandwidth product (transform-limited pulses). Experimental data and calculations show that characterizing a two-photon signal with the two schemes to vary pulse duration measures different phenomena. Two-photon signal characterization using dispersion-broadened pulses measures only the effect of chirp on the pulse two-photon-excitation spectrum and is independent of molecular response. Transform-limited pulses are used to measure the dependence of two-photon signal generation on pulse duration. Calculations show that deviation from the 1/Tp relationship would be expected as the transform-limited pulse spectral width approaches the molecular two-photon absorption linewidth and exhibits asymptotic behavior for pulse spectral widths 10 times greater than the absorption linewidth. Experimental measurements are consistent with the predicted behavior. The impact of using ultrashort laser pulses on the performance characteristics of nonlinear optical microscopy is discussed.
Optical resonances in microspheres have recently been applied to biosensing applications. The resonances, known as
Whispering Gallery Modes (WGMs) result from the total internal reflection of the light propagating inside the high index
spherical surface within a lower index medium. The evanescent field of the WGM, which extends beyond the
microsphere surface, is sensitive to the changes in the local refractive index in the surrounding medium. The high Q
factor associated with WGMs enables a highly sensitive sensor element. Here we present a refractometric sensor with
high sensitivity based on quantum dot (QD) embedded polystyrene microspheres. Ultrashort laser pulses are used to
induce two photon excited luminescence from the QDs inside the microspheres. By optimizing the detection area of the
microsphere, an enhanced resonance signal to background ratio can be achieved. Theoretical calculations of the
resonance peak shifts are compared with the experimental data. Refractometric sensing based on WGMs is a technique
that does not require analyte labeling. In this work, QDs are used as a local, broadband light source within the
microspheres to enable remote excitation of the resonant modes. The sensor has great potential in many biosensing
applications.
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