High-throughput doubly-encoded single-pixel spectrometer with an extended aperture.

Infrared devices are increasingly used in industrial, medical, and environmental monitoring applications. Cost-effectiveness, robustness, and portability are characteristics that are highly sought after and they can be enabled by a dispersive spectrometer carrying a single-pixel detector. In this paper, we demonstrate a novel, high-throughput dispersive spectrometer that has its spectral resolution decoupled from its throughput. The proposed spectrometer implements a two-stage Hadamard transform encoding process that allows significantly more light into the system to enhance its signal-to-noise ratio. As a single-pixel detector is used to collect the spectral information, the proposed system can be easily implemented in other desired wavelengths. Furthermore, we develop a method to remove the need for uniform illumination at the entrance aperture by taking into consideration its spatial information during the reconstruction process, thereby increasing the ease of the design of devices required for in situ measurement.

TDI-like multi-slit hyperspectral imaging for enhanced throughput via the Kalman filter.

The time-delay integration (TDI) technique is increasingly used to improve the signal-to-noise ratio (SNR) of remote sensing and imaging by exposing the scene multiple times. Inspired by the principle of TDI, we propose a TDI-like pushbroom multi-slit hyperspectral imaging (MSHSI) approach. In our system, multiple slits are used to significantly improve the throughput of the system, thereby enhancing the sensitivity and SNR through multiple exposures of the same scene during pushbroom scan. Meanwhile, a linear dynamic model for the pushbroom MSHSI is established, where the Kalman filter (KF) is employed to reconstruct the time-varying overlapped spectral images on a single conventional image sensor. Further, we designed and fabricated a customized optical system that can operate in both multi-slit and single slit modes to experimentally verify the feasibility of the proposed method. Experimental results indicate that the developed system improved SNR by a factor of about 7 compared to that of the single slit mode, while demonstrating excellent resolution in both spatial and spectral dimensions.

Review of Miniaturized Computational Spectrometers.

Spectrometers are key instruments in diverse fields, notably in medical and biosensing applications. Recent advancements in nanophotonics and computational techniques have contributed to new spectrometer designs characterized by miniaturization and enhanced performance. This paper presents a comprehensive review of miniaturized computational spectrometers (MCS). We examine major MCS designs based on waveguides, random structures, nanowires, photonic crystals, and more. Additionally, we delve into computational methodologies that facilitate their operation, including compressive sensing and deep learning. We also compare various structural models and highlight their unique features. This review also emphasizes the growing applications of MCS in biosensing and consumer electronics and provides a thoughtful perspective on their future potential. Lastly, we discuss potential avenues for future research and applications.

Design and fabrication of composite polygonal Fresnel lenses.

High fill factor for Fresnel lens arrays has been achieved with the aid of polygonal lenses. This has been done for both circular trimmed lenses and full polygonal lenses, both of which present some optical drawbacks. The composite polygonal Fresnel lens (CPFL) avoids these issues with its unique design - a radial symmetric Fresnel center filling into a polygon, avoiding any intersecting facets within the lens by introducing fillets. To manufacture the CPFL, diamond shaping is applied to not only meet the strict standards required for optical fabrication but also maneuver around the curvilinear features that cannot be fabricated using conventional turning techniques. As such, direct diamond shaping (DDS) was employed to generate an array of CPFLs on a PMMA substrate. Optical simulation was used to validate the performance of the CPFL before production of the lens array, followed by testing of the fabricated lenses, showing less overall noise with better focus compared to conventional polygonal lenses.

Cascaded, self-calibrated, single-pixel mid-infrared Hadamard transform spectrometer.

In this paper, a single-pixel mid-infrared (mid-IR) Hadamard transform spectrometer is developed. The spectrometer's design, fabrication and experimental results are discussed. The single-pixel mid-IR Hadamard transform spectrometer has dual cascaded encoding regions, 2875 nm to 3500 nm and 3500 nm to 4077 nm, to reduce the travel range required by the moving mask. The encoded wavelength band is determined by the bandpass filter used. A collection optics consisting of a reverse spectrometer is used to collect the encoded signal onto a single-pixel detector with a small sensing area. A 635 nm laser is used as a reference within the spectrometer to calibrate the recovered spectrum with accurate positioning. Our experiments demonstrate that mid-IR spectrums can be accurately recovered in the designed wavelength range. The proposed spectrometer, with dimensions of 200 mm × 200 mm × 84 mm and a weight of 1.8 kg, can be made portable and at low cost, suitable for IR spectroscopy in the field.

MEMS-based self-referencing cascaded line-scan camera using single-pixel detectors.

A microelectromechanical systems (MEMS) based self-referencing cascaded line-scan camera using single-pixel detectors is proposed and verified. Single-pixel detectors make it an attractive low-cost alternative of a traditional line-scan camera that can operate at any wavelength. The proposed system is composed of several identical cascaded line imager units driven by a common actuator. Each unit is an integration of an imaging slit, a MEMS encoding mask, a light concentrator and a single-pixel detector. The spatial resolution of the proposed line-scan camera can thus be N-fold immediately by cascading N units to achieve high spatial resolution. For prototype demonstration, a cascaded line-scan camera composed of two imager units are prepared, with each unit having a single-pixel detector and being capable of resolving 71 spatial pixels along the slit. Hadamard transform multiplexing detection is applied to enhance the camera's signal-to-noise ratio (SNR). The MEMS encoding mask is resonantly driven at 250 Hz indicating an ideal frame-rate of 500 fps of the line-scan camera prototype. Further increase of frame-rate can be achieved through optimization of the MEMS actuator. Additionally, the MEMS encoding mask incorporates a self-referencing design which simplifies data acquisition process, thus enabling the camera system to work in a simple but efficient open-loop condition.

A Collapsible Soft Actuator Facilitates Performance in Constrained Environments.

Complex environments, such as those found in surgical and search-and-rescue applications, require soft devices to adapt to minimal space conditions without sacrificing the ability to complete dexterous tasks. Stacked Balloon Actuators (SBAs) are capable of large deformations despite folding nearly flat when deflated, making them ideal candidates for such applications. This paper presents the design, fabrication, modeling, and characterization of monolithic, inflatable, soft SBAs. Modeling is presented using analytical principles based on geometry, and then using conventional and real-time finite element methods. Both one and three degree-of-freedom (DoF) SBAs are fully characterized with regards to stroke, force, and workspace. Finally, three representative demonstrations show the SBA's small-aperture navigation, bracing, and workspace-enhancing capabilities.

Single-Pixel MEMS Imaging Systems.

Single-pixel imaging technology is an attractive technology considering the increasing demand of imagers that can operate in wavelengths where traditional cameras have limited efficiency. Meanwhile, the miniaturization of imaging systems is also desired to build affordable and portable devices for field applications. Therefore, single-pixel imaging systems based on microelectromechanical systems (MEMS) is an effective solution to develop truly miniaturized imagers, owing to their ability to integrate multiple functionalities within a small device. MEMS-based single-pixel imaging systems have mainly been explored in two research directions, namely the encoding-based approach and the scanning-based approach. The scanning method utilizes a variety of MEMS scanners to scan the target scenery and has potential applications in the biological imaging field. The encoding-based system typically employs MEMS modulators and a single-pixel detector to encode the light intensities of the scenery, and the images are constructed by harvesting the power of computational technology. This has the capability to capture non-visible images and 3D images. Thus, this review discusses the two approaches in detail, and their applications are also reviewed to evaluate the efficiency and advantages in various fields.