We investigate correlations between the configuration statistics of random metasurfaces and their spectral response. Our metasurfaces consist of a two-dimensional array of silicon nanopillars with widths sampled from a normal distribution placed on a silica substrate. We explore the effect of tuning the parameters characterizing the distribution of nanopillar widths on the wavelength-dependent transmissivity of the random metasurface in the 400 – 800 nm wavelength range. This analysis helps us create a direct mapping between the parameters of the nanopillar width distribution and the spectral responses of the random metasurfaces. We exploit this mapping to design a photonic device encoding spectrally encrypted image data in the visible wavelength range. Our findings offer new insight into the optical properties of random media and provide avenues for developing such systems for a broad range of applications.
Sensor limitations often result in devices with particularly high spatial-imaging resolution or high sampling rates but not both concurrently. Adaptive optics control mechanisms, for example, rely on high-fidelity sensing technology to predictively correct wavefront phase aberrations. We propose fusing these two categories of sensors: those with high spatial resolution and those with high temporal resolution. As a prototype, we first sub-sample simulations of the Kuramoto-Sivashinsky equation, known for its chaotic flow from diffusive instability, and build a map between such simulated sensors using a Shallow Decoder Neural Network. We then examine how to fuse the merits of a common sensor in aero-optical sensing, the Shack-Hartmann wavefront sensor, with the increased spatial information of a Digital Holography wavefront sensor, training on supersonic wind-tunnel wavefront data provided by the Aero-Effects Laboratory at the Air Force Research Laboratory Directed Energy Directorate. These maps merge the high-temporal and high-spatial resolutions from each respective sensor, demonstrating a proof-of-concept for wavefront sensor fusion for adaptive optical applications.
Aero-optical beam control relies on the development of low-latency forecasting techniques to quickly predict wavefronts aberrated by the turbulent boundary layer around an airborne optical system, and its study applies to a multidomain need from astronomy to microscopy for high-fidelity laser propagation. We leverage the forecasting capabilities of the dynamic mode decomposition (DMD) — an equation-free, data-driven method for identifying coherent flow structures and their associated spatiotemporal dynamics — to estimate future state wavefront phase aberrations to feed into an adaptive optic control loop. We specifically leverage the optimized DMD (opt-DMD) algorithm on a subset of the Airborne Aero-Optics Laboratory-Transonic experimental dataset, characterizing aberrated wavefront dynamics for 23 beam propagation directions via the spatiotemporal decomposition underlying DMD. Critically, we show that opt-DMD produces an optimally debiased eigenvalue spectrum with imaginary eigenvalues, allowing for arbitrarily long forecasting to produce a robust future state prediction, while exact DMD loses structural information due to modal decay rates.
Purpose: Handling low-quality and few-feature medical images is a challenging task in automatic panorama mosaicking. Current mosaicking methods for disordered input images are based on feature point matching, whereas in this case intensity-based registration achieves better performance than feature-point registration methods. We propose a mosaicking method that enables the use of mutual information (MI) registration for mosaicking randomly ordered input images with insufficient features.
Approach: Dimensionality reduction is used to map disordered input images into a low dimensional space. Based on the low dimensional representation, the image global correspondence can be recognized efficiently. For adjacent image pairs, we optimize the MI metric for registration. The panorama is then created after image blending. We demonstrate our method on relatively lower-cost handheld devices that acquire images from the retina in vivo, kidney ex vivo, and bladder phantom, all of which contain sparse features.
Results: Our method is compared with three baselines: AutoStitch, “dimension reduction + SIFT,” and “MI-Only.” Our method compared to the first two feature-point based methods exhibits 1.25 (ex vivo microscope dataset) to two times (in vivo retina dataset) rate of mosaic completion, and MI-Only has the lowest complete rate among three datasets. When comparing the subsequent complete mosaics, our target registration errors can be 2.2 and 3.8 times reduced when using the microscopy and bladder phantom datasets.
Conclusions: Using dimensional reduction increases the success rate of detecting adjacent images, which makes MI-based registration feasible and narrows the search range of MI optimization. To the best of our knowledge, this is the first mosaicking method that allows automatic stitching of disordered images with intensity-based alignment, which provides more robust and accurate results when there are insufficient features for classic mosaicking methods.
KEYWORDS: Digital micromirror devices, Control systems, Data modeling, Wavefronts, Systems modeling, Machine learning, Transient nonlinear optics, Near field optics, Mathematical modeling, Algorithm development
We demonstrate the use of physics-informed machine learning algorithms for the adaptive, real-time characterization of aero-optical systems. From deep learning algorithms to nonlinear control methods, the optical sciences are an ideal platform for integrating data-driven control and machine learning for robust characterization and system identification. For the specific case of aero-optics, the ability to extract dominant coherent structures, transients and turbulent behaviors is critical for a diverse number of applications, including the complex and dynamic aero-optic effects on airborne-based laser platforms. Specifically, aero-optical beam control relies on the development of low-latency predictors that can quickly predict aberrated wavefronts to feed into an adaptive optic control loop. We propose develop a number of data-driven methods, including the dynamic mode decomposition (DMD), for real-time forecasting and control.
Advanced methods in data science are driving the characterization and control of nonlinear dynamical systems in optics. In this work, we investigate the use of machine learning, sparsity methods and adaptive control to develop a self-tuning fiber laser, which automatically learns and adapts to maintain high-energy ultrashort pulses. In particular, a two-stage procedure is introduced consisting of a machine learning algorithm to recognize different dynamical regimes with distinct behavior, followed by an adaptive control algorithm to reject disturbances and track optimal solutions despite stochastically varying system parameters. The machine learning algorithm, called sparse representation for classification, comes from machine vision and is typically used for image recognition. The adaptive control algorithm is extremum-seeking control, which has been applied to a wide range of systems in engineering; extremum-seeking is beneficial because of rigorous stability guarantees and ease of implementation.
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