Single-pixel Photodetector Research Articles

A Single-Pixel Event Photoactive Device for Real-Time, In-Sensor Spatiotemporal Optical Information Processing.

The increasing demand for energy-efficient, sophisticated optical sensing technologies in various applications, from machine vision to optical communication, highlights the necessity for innovations in spatiotemporal information sensing and processing at a nearly single-pixel scale. Traditional methods, including multi-pixel photodetector arrays and event-based camera systems, often fail to provide rapid, real-time detection and processing of dynamic events within the sensor. This shortcoming is particularly notable in handling high-dimensional spatiotemporal data, where the dependency on sequential data input and external processing tools leads to latency, reduced throughput, and heightened energy consumption, thereby impeding real-time parallel data processing capabilities. Here, a carrier-selective, single-pixel, position-sensitive planar photoactive device that integrates spatiotemporal event sensing with inherent short-term memory capabilities is introduced. The proof-of-concept single-pixel event photoactive device enables in-sensor spatiotemporal parallel optical information processing, efficiently managing multibit (>4 bit) data simultaneously and facilitating ultrafast (≈0.4µs) recognition of input patterns with low energy consumption (25 femtojoules). Additionally, by adjusting the operating speed from continuous to pulsed light illumination, the sensor array can detect trajectories and absolute position of events, offering in-sensor optical flow detection. This single-pixel event photodetector marks significant advancement toward developing compact, energy-efficient, ultrafast sensors suitable for a wide range of in sensor-based photonic applications.

Quantitative determination of fractional topological charge based on the rotational Doppler effect

The utilization of fractional-order vortex beams extends the diversity of optical field manipulation, permits for more flexible control over beam propagation, and provides novel applications in optical communications, edge enhancement imaging, and particle manipulation. However, compared with the integer-order vortex beams, the topological charge measurement techniques for fractional-order vortex beams are not well developed, impeding the further exploration of its applications. In this paper, the frequency signal of rotational Doppler effect and corresponding broadening behavior under the fractional-order vortex beam illumination were analyzed. When the fractional topological charge approaches a half integer, the broadening is minimized. Leveraging this relationship, we designed a phase-compensated scheme coupled with signal-to-noise ratio detection to realize the real-time fractional topological charge measurement. The single pixel photodetector was used and eliminated the need for two-dimensional image acquisition and analysis, ensuring efficient acquisition and quantitative analysis. Both theoretical and experimental results confirm the feasibility of this method, thereby advancing the comprehension of the optical Doppler effect and potentially paving the way for future investigations into fractional vortex beams.

A compressive hyperspectral video imaging system using a single-pixel detector

Capturing fine spatial, spectral, and temporal information of the scene is highly desirable in many applications. However, recording data of such high dimensionality requires significant transmission bandwidth. Current computational imaging methods can partially address this challenge but are still limited in reducing input data throughput. In this paper, we report a video-rate hyperspectral imager based on a single-pixel photodetector which can achieve high-throughput hyperspectral video recording at a low bandwidth. We leverage the insight that 4-dimensional (4D) hyperspectral videos are considerably more compressible than 2D grayscale images. We propose a joint spatial-spectral capturing scheme encoding the scene into highly compressed measurements and obtaining temporal correlation at the same time. Furthermore, we propose a reconstruction method relying on a signal sparsity model in 4D space and a deep learning reconstruction approach greatly accelerating reconstruction. We demonstrate reconstruction of 128 × 128 hyperspectral images with 64 spectral bands at more than 4 frames per second offering a 900× data throughput compared to conventional imaging, which we believe is a first-of-its kind of a single-pixel-based hyperspectral imager.

Predictive analysis of the power spectral irradiance from blackbody radiation source using single pixel detector

Accurate spectral irradiance measurement in the near-infrared range is significant for the design and characterization of photodetector and photovoltaic cells. Approximation method is commonly used to solve for the input power using estimated spectral irradiance, where the dependency on wavelength and temperature remains uncertain. This study aims to determine the power spectrum at different radiation temperatures using a single pixel photodetector, taking into consideration factors such as transmission spectra of alumina radiator, CaF2 collimating lens, responsivity, and measured photocurrent information of photodetectors. Utilizing predictive mathematical model, five commercial photodetectors, including Silicon, Germanium, In0.53Ga0.47As, In0.73Ga0.27As, and In0.83Ga0.17As were used to solve for the power densities as a function of wavelengths at radiation temperatures of 1000 °C and 1500 °C. The spectral irradiance of photodetectors was determined with a percentage difference of <4.9 %, presenting an accurate power density estimation for the spectrum at a wide range of radiation temperatures. Power irradiance data obtained were validated in the narrow wavelength range with 1000 nm, 1400 nm, 1500 nm, and 2000 nm bandpass filters. The reported work demonstrates a simple and efficient way which could contribute to develop a cost-effective method of measuring and determining the spectrum irradiances of objects at different radiation temperatures. This predictive analysis method hopefully intensifies the progress of efforts to reduce the reliance on complex optoelectronic instruments in accurately solving power irradiance information.

BM3D-based color computational ghost imaging

In this study, we develop a BM3D-based algorithm to improve the performance of color computational ghost imaging. Specifically, we respectively project the speckle patterns of red, green and blue onto the object. Then, we adopt the single-pixel photodetector to record the total light intensity reflected by the target object. Finally, we calculate the correlation between the light intensity sequence and the corresponding speckle patterns based on BM3D algorithm. Our simulation results show that the developed scheme can achieve high-quality reconstruction image even at low sampling ratio.

Spectroscopic measurement of the two-dimensional flame temperature based on a perovskite single photodetector.

Existing non-contact flame temperature measuring methods depend on complex, bulky and expensive optical instruments, which make it difficult for portable applications and high-density distributed networking monitoring. Here, we demonstrate a flame temperature imaging method based on a perovskite single photodetector. High-quality perovskite film epitaxy grows on the SiO2/Si substrate to fabricate the photodetector. Duo to the Si/MAPbBr3 heterojunction, the light detection wavelength is extended from 400 nm to 900 nm. Then, a perovskite single photodetector spectrometer has been developed using the deep-learning method for spectroscopic measurement of flame temperature. In the temperature test experiment, the spectral line of doping element K+ has been selected to measure the flame temperature. The photoresponsivity function of the wavelength was learned based on a commercial standard blackbody source. The spectral line of element K+ has been reconstructed using the photocurrents matrix by the regression solving photoresponsivity function. As a validation experiment, the "NUC" pattern is realized by scanning the perovskite single-pixel photodetector. Finally, the flame temperature of adulterated element K+ has been imaged with the error of 5%. It provides a way to develop high precision, portable, low-cost flame temperature imaging technology.

Complex-amplitude Fourier single-pixel imaging via coherent structured illumination

We propose a method of complex-amplitude Fourier single-pixel imaging (CFSI) with coherent structured illumination to acquire both the amplitude and phase of an object. In the proposed method, an object is illustrated by a series of coherent structured light fields, which are generated by a phase-only spatial light modulator, the complex Fourier spectrum of the object can be acquired sequentially by a single-pixel photodetector. Then the desired complex-amplitude image can be retrieved directly by applying an inverse Fourier transform. We experimentally implemented this CFSI with several different types of objects. The experimental results show that the proposed method provides a promising complex-amplitude imaging approach with high quality and a stable configuration. Thus, it might find broad applications in optical metrology and biomedical science.

Computationally convolutional ghost imaging

The idea of using a single-pixel photodetector to sense the world may sound a little bit ambitious. However, a new type of computational imaging technology termed computational ghost imaging (CGI), is indeed making it a reality. No longer satisfied with using a non-spatially resolved photodetector to “see” the target, the computationally convolutional ghost imaging (CCGI) proposed in this paper can directly “see” the target’s features of interest without imaging first anymore. Rather than a conventional 4-f optical system, the CCGI scheme completes the convolution operations by optical methods with a single-pixel photodetector and an engineered structured illumination. Meanwhile, our CCGI scheme can adaptively work under sub-Nyquist sampling conditions, and it can facilitate real-time non-imaging edge detection of the real scene. With some multiplexing schemes, the prototype of CCGI has the potential as a new type of single-pixel computer vision that might be used as an optical frontend of a lightweight convolutional neural network to recognize objects intelligently. Our scheme brings new insights into both the convolution operation and the CGI technology, greatly broadening the application scenarios of CGI.

Imaging through scattering media via spatial–temporal encoded pattern illumination

Optical imaging through scattering media has long been a challenge. Many approaches have been developed for focusing light or imaging objects through scattering media, but usually, they are either invasive, limited to stationary or slow-moving media, or require high-resolution cameras and complex algorithms to retrieve the images. By utilizing spatial–temporal encoded patterns (STEPs), we introduce a technique for the computation of imaging that overcomes these restrictions. With a single-pixel photodetector, we demonstrate non-invasive imaging through scattering media. This technique is insensitive to the motion of the media. Furthermore, we demonstrate that our image reconstruction algorithm is much more efficient than correlation-based algorithms for single-pixel imaging, which may allow fast imaging for applications with limited computing resources.

Complex-amplitude single-pixel imaging using coherent structured illumination

This research presents a coherent structured illumination single-pixel imaging scheme to image objects with complex amplitudes. By utilizing a phase-only spatial light modulator for phase modulation, we can efficiently generate the Hadamard basis structured light and the reference light that interfere with each other to form the coherent structured illumination. Using the 4-step phase-shifting, the spectrum of the object is acquired by detecting the zero-frequency component of the object light with a single-pixel photodetector. The desired complex-amplitude image can be further retrieved by applying an inverse Hadamard transform. The proposed scheme is experimentally demonstrated by imaging two etched glass objects, a dragonfly wing, and a resolution test chart. Benefiting from the phase modulation, this scheme has a high efficiency, a high imaging quality, a high spatial resolution, and a simple and stable configuration to obtain both the phase and amplitude information of the target object. The proposed scheme provides a promising complex-amplitude imaging modality with single-pixel detection. Thus it might find broad applications in optical metrology and biomedical science.

Ghost panorama using a convex mirror.

Computational ghost imaging or single-pixel imaging enables the image formation of an unknown scene using a lens-free photodetector. In this Letter, we present a computational panoramic ghost imaging system that can achieve a full-color panorama using a single-pixel photodetector, where a convex mirror performs the optical transformation of the engineered Hadamard-based circular illumination pattern from unidirectionally to omnidirectionally. To our best knowledge, it is the first time to propose the concept of ghost panoramas and realize preliminary experimentations. It is foreseeable that ghost panoramas will have more advantages in imaging and detection in many extreme conditions (e.g., scattering/turbulence and unconventional spectra), as well as broad application prospects.

Compressive Sensing Absorption Spectroscopy Based on Photoelastic Modulation and Single-Pixel Detection

Conventional absorption spectroscopy falls short in complexity and measurement speed. Here, a new type of compressive sensing absorption spectroscopy technique employing a photoelastic modulator (PEM) is presented to address these challenges. The PEM is used to modulate the input spectrum and create multiple harmonic orders as the measurement channels. A sensing matrix is formed by randomly selecting elements from the modulation matrix. The measurement results of different frequency channels are simultaneously captured via a single-pixel photodetector without changing the physical parameters (such as PEM configurations or modulation frequencies). In a measurement example, the first five orders of harmonics are selected, and the input optical spectrum is successfully measured with a compression ratio of 1/16. To further verify the utility of our approach, the infrared spectrum with CO2 absorption is successfully reconstructed with low error.

Image reconstruction using different speckles and methods

Ghost imaging (GI) is an imaging method that uses photon correlation for image restoration. In this study, we design two different color speckle fields and use a digital light projector to display them onto a color object that is measured by a single-pixel photodetector. The first is uniformly distributed with red, green, and blue colors, while patterns are generated through linear mapping of a Hadamard matrix in the second. We evaluated three original image reconstruction schemes based on multi-color speckle (MS) pattern: traditional ghost imaging and pseudo-inverse ghost imaging based on uniform speckle field and single- pixel imaging (MS-HSI) based on Hadamard matrix linear mapping speckle field. Simulation and experimental results show that these methods can effectively restore color objects. We also compare the advantages and disadvantages of the three methods, and optimize the GI strategy of color objects. Among the three methods, the background noise of MS-HSI based on Hadamard matrix linear mapping is lower, more details are retained, and the signal-to-noise ratio is the highest.

High-speed single-pixel imaging by frequency-time-division multiplexing.

We propose and experimentally demonstrate high-speed single-pixel imaging by integrating frequency-division multiplexing and time-division multiplexing (techniques used widely in telecommunications) and applying the combined technique, namely, frequency-time-division multiplexing (FTDM), to optical imaging. Specifically, FTDM single-pixel imaging uses an array of broadband, spatially distributed, dual-frequency combs (i.e., spatial dual combs) for multidimensional illumination and detects an image-encoded time-domain signal with a single-pixel photodetector in a FTDM manner. As a proof-of-principle demonstration, we use the method to show ultrafast two-color (bright-field and fluorescence) single-pixel microscopy of breast cancer cells at a high frame rate of 32,000 fps and ultrafast image velocimetry of fluorescent particles flowing at a high speed of ${ \gt }{2}\;{\rm m/s}$>2m/s.

In-Situ Tailoring of Vertically Coupled InAs p-i-p Quantum-Dot Infrared Photodetectors: Toward Homogeneous Dot Size Distribution and Minimization of In–Ga Intermixing

The authors report a detailed analysis of an epitaxial growth technique for indium arsenide (InAs) Quantum-dot infrared photodetectors circumvent the detrimental effects arising from the progressively increasing dot-size in vertically coupled heterostructures. Constant overgrowth percentage of the vertically coupled dot-layers has been achieved with the implementation of the growth strategy, which has been validated by cross-sectional transmission electron microscopy (X-TEM) images of the samples. The optical characteristics of these samples have been analyzed through photoluminescence spectroscopy and photoluminescence excitation spectroscopy (PL and PLE) measurements which show longer wavelength response and reduced full width at half-maxima (fwhm) upon implementation of the growth strategy. X-TEM and in-plane and out-of-plane high resolution X-ray diffraction (HR-XRD) measurements suggest morphological improvement upon implementation of the growth strategy, with a reduction in the indium desorption and lowering of defects and dislocation densities. Excellent correlation has been found between the different experimental results and also their theoretical simulations. The fabricated single-pixel photodetectors at low temperature (T = 14 K) show a broad response extending up to the MWIR region (∼4.5 μm) for one of the samples. Also, a strong spectral response in the SWIR region is obtained even at room temperature (T = 300 K). The highest responsivity (Rp) and specific detectivity (D*) values obtained are 166.17 A/W and 8.39 × 1010 cm Hz1/2 W–1 at a bias of 5 V and 300 K temperature.

Single-Pixel MEMS Spectrometer Based on Compressive Sensing

This letter demonstrates a miniature spectrometer suitable for transmission spectroscopy. A MEMS oscillating mask is designed to encode the light distribution dispersed along a slit. A single-pixel photodetector is employed to collect the encoded light, and thus the proposed principle is workable for any wavelength range. Compressive sensing theory is used to design the encoding patterns implemented on the MEMS encoder to release the requirement for long travel range of MEMS actuators and to improve the spectral resolution. The experimental results prove that the proposed spectrometer works efficiently to recover typical transmission spectra with a real spectral resolution of 2 nm from 446 nm to 652 nm. This resolution can be furtherly enhanced, and this technology can be used to establish portable spectrometers for chemical sensing applications.

Ultrafast Photodetector by Integrating Perovskite Directly on Silicon Wafer.

Single-crystal (SC) perovskite is currently a promising material due to its high quantum efficiency and long diffusion length. However, the reported perovskite photodetection range (<800 nm) and response time (>10 μs) are still limited. Here, to promote the development of perovskite-integrated optoelectronic devices, this work demonstrates wider photodetection range and shorter response time perovskite photodetector by integrating the SC CH3NH3PbBr3 (MAPbBr3) perovskite on silicon (Si). The Si/MAPbBr3 heterojunction photodetector with an improved interface exhibits high-speed, broad-spectrum, and long-term stability performances. To the best of our knowledge, the measured detectable spectrum (405-1064 nm) largely expands the widest response range reported in previous perovskite-based photodetectors. In addition, the rise time is as fast as 520 ns, which is comparable to that of commercial germanium photodetectors. Moreover, the Si/MAPbBr3 device can maintain excellent photocurrent performance for up to 3 months. Furthermore, typical gray scale face imaging is realized by scanning the Si/MAPbBr3 single-pixel photodetector. This work using an ultrafast photodetector by directly integrating perovskite on Si can promote advances in next-generation integrated optoelectronic technology.

Color single-pixel digital holography with a phase-encoded reference wave.

We propose and demonstrate a multicolor single-pixel digital holography technique. The intensity and phase images of an object are simultaneously obtained from the time-sequence intensity data captured using a single-pixel photodetector. Moreover, phase-structured light and phase-shifting interferometry are implemented using only a spatial light modulator without any mechanical movements. The adopted configuration dramatically simplifies the optical setup by removing both imaging optics and the resultant chromatic aberration. The effectiveness of the proposed technique is demonstrated numerically and experimentally.

Cameraless high-throughput three-dimensional imaging flow cytometry

Today’s imaging flow cytometer (IFC) systems are limited by the projection problem: collapsing three-dimensional (3D) information onto a two-dimensional (2D) image causes a lack of tomographic 3D resolution and reduced information content, limiting the reliability of spot counting or co-localization crucial to cell phenotyping. We present 3D imaging flow cytometry as a solution to the problem. Our high-throughput 3D cell imager based on optical sectioning microscopy combines orthogonal light-sheet scanning illumination with our previous spatiotemporal transformation detection to produce 3D cell image reconstruction from a cameraless single-pixel photodetector readout. We demonstrate this capability by cocapturing 3D fluorescence and label-free side-scattering images of single cells in flow with a throughput of approximately 500 cells per second.

Mid-wavelength infrared InAsSb/InAs nBn detectors and FPAs with very low dark current density

There was a significant improvement in the performance of infrared nBn detectors utilizing InAs/InAsSb absorbers culminating in the development of infrared focal plane arrays (FPAs) with excellent operability (99.7%) and operating at temperature significantly higher than InSb FPAs. In this work, we demonstrated that these detectors can operate with very low dark current densities enabling their use in applications with a low-to-medium level of background illumination. We showed that single pixel photodetectors with a cut-off wavelength of 4.8 μm and a quantum efficiency of QEmax = 35% under backside-illumination have a dark current density of 1 × 10−10 A/cm2 at an operating bias of −0.1 V and temperature T = 100 K. Additionally, we compared the single pixel dark current results with measurements of the dark current in FPAs. The FPA showed excellent performance with an operability of 99.7% and was able to reach a mode dark current density of 5 × 10−11 A/cm2 at 80 K.