Optical Detector Arrays Research Articles

Measurement and analysis of instantaneous microwave frequency based on an optical frequency comb.

A microwave photonics instantaneous frequency measurement scheme with 14 channels based on an optical frequency comb (OFC) is proposed. In this scheme, a 14-line flat OFC is generated by cascading a dual-parallel Mach-Zehnder modulator (DPMZM) with a Mach-Zehnder modulator (MZM). The intercepted microwave signal with multiple-frequency components can be measured by using DPMZM, Fabry-Perot filter (FPF), wavelength division multiplexer (WDM), and optical power detector array. This scheme can measure and analyze the frequency of microwave signals in the ranges of 0.5-13.5 GHz, 13.5-26.5 GHz, and 26.5-39.5 GHz with the measurement accuracy of ±0.5GHz. The reconfigurability of the system can be realized by adjusting the comb-line spacing of the OFC and the free spectral range (FSR) of the FPF.

Highly sensitive organic phototransistor for flexible optical detector arrays

Innovative applications in light signal sensing require flexibility, lightweight, low-cost and low temperature processability, as well as high sensitivity and quantitative photoresponse. We report on flexible organic phototransistors (OPTs) with excellent reproducibility in the detection of outstandingly low light intensities of few nW cm−2. The optical response of the phototransistor was thoroughly characterized as a function of the wavelength, the incident optical intensity and the electrical polarizations. The photodetectors work reliably under bending and pulse cycling in different environmental conditions, at low polarizations down to the range 0.1–5 V. Based on these outcomes, arrays for broadband or multiple wavelength detection were implemented and successfully tested. The proposed device structure, derived from a layered p-p heterojunction, was developed to be easily implementable in each wavelength of interest. These results show a prospect of highly sensitive flexible OPT arrays for both experimental research and innovative optoelectronic systems.

High-resolution and compact serpentine integrated grating spectrometer

Integrated astrophotonic spectrometers are integrated variants of conventional free-space spectrometers that offer significantly reduced size, weight, and cost and immunity to alignment errors, and can be readily integrated with other astrophotonic instruments such as nulling interferometers. Current integrated dispersive astrophotonic spectrometers are one-dimensional devices such as arrayed waveguide gratings or planar echelle gratings. These devices have been limited to 10 4 resolving powers and < 1000 spectral bins due to having limited total optical delay paths and 1D detector array pixel densities. In this paper, we propose and demonstrate a high-resolution and compact astrophotonic serpentine integrated grating (SIG) spectrometer design based on a 2D dispersive serpentine optical phased array. The SIG device combines a 5.2 cm long folded delay line with grating couplers to create a large optical delay path along two dimensions in a compact integrated device footprint. Analogous to free-space crossed-dispersion high-resolution spectrometers, the SIG spectrometer maps spectral content to a 2D wavelength-beam-steered folded-raster emission pattern focused onto a 2D detector array. We demonstrate a SIG spectrometer with ∼ 100 k resolving power and ∼ 6750 spectral bins, which are approximately an order of magnitude higher than previous integrated photonic designs that operate over a wide bandwidth, in a 0.4 m m 2 footprint. We measure a Rayleigh resolution of 1.93 ± 0.07 G H z and an operational bandwidth from 1540 nm to 1650 nm. Finally, we discuss refinements of the SIG spectrometer that improve its resolution, bandwidth, and throughput. These results show that SIG spectrometer technology provides a path towards miniaturized, high-resolution spectrometers for applications in astronomy and beyond.

A universal 3D imaging sensor on a silicon photonics platform.

Accurate three-dimensional (3D) imaging is essential for machines to map and interact with the physical world1,2. Although numerous 3D imaging technologies exist, each addressing niche applications with varying degrees of success, none has achieved the breadth of applicability and impact that digital image sensors have in the two-dimensional imaging world3-10. A large-scale two-dimensional array of coherent detector pixels operating as a light detection and ranging system could serve as a universal 3D imaging platform. Such a system would offer high depth accuracy and immunity to interference from sunlight, as well as the ability to measure the velocity of moving objects directly11. Owing to difficulties in providing electrical and photonic connections to every pixel, previous systems have been restricted to fewer than 20 pixels12-15. Here we demonstrate the operation of a large-scale coherent detector array, consisting of 512 pixels, in a 3D imaging system. Leveraging recent advances in the monolithic integration of photonic and electronic circuits, a dense array of optical heterodyne detectors is combined with an integrated electronic readout architecture, enabling straightforward scaling to arbitrarily large arrays. Two-axis solid-state beam steering eliminates any trade-off between field of view and range. Operating at the quantum noise limit16,17, our system achieves an accuracy of 3.1millimetres at a distance of 75metres when using only 4milliwatts of light, an order of magnitude more accurate than existing solid-state systems at such ranges. Future reductions of pixel size using state-of-the-art components could yield resolutions in excess of 20megapixels for arrays the size of a consumer camera sensor. This result paves the way for the development and proliferation of low-cost, compact and high-performance 3D imaging cameras that could be used in applications from robotics and autonomous navigation to augmented reality and healthcare.

Parallel single-cell optical transit dielectrophoresis cytometer.

In this work, we present an optical transit DEP flow cytometer for parallel single-cell analysis. Each cell's dielectric property is inferred from velocity perturbations due to DEP actuation in a microfluidic channel. Dual LED sources facilitate velocity measurement by producing two transit shadows for each cell passing through the channel. These shadows are detected using a 256-pixel linear optical array detector. Massively parallel analysis is possible as each pixel of the detector can independently analyze the passing cells. A wide channel (∼18mm) was employed to carry many particles simultaneously, and the system was capable of detecting the velocity of over 200 cells simultaneously. We have achieved analysis rates for 10µm diameter polystyrene spheres response exceeding 250 per second. With appropriate calibration, this DEP cytometer can quantitatively measure the dielectric response. The dielectric response (Clausius-Mossotti factor) of viable CHO cells was measured over the frequency range of 100kHz to 6MHz, and the obtained response matches the previously measured values by our group. The DEP cytometer uses simple modular components to achieve high throughput label-free single-cell dielectric analysis and can begin analyzing particles within 10s after starting to pump the sample into the channel.

The Effect of Surface Waves on Airborne Lidar Bathymetry (ALB) Measurement Uncertainties

Airborne Lidar Bathymetry (ALB) provides a rapid means of data collection that provides seamless digital elevation maps across land and water. However, environmental factors such as water surface induce significant uncertainty in the ALB measurements. In this study, the effect of water surface on the ALB measurements is characterized both theoretically and empirically. Theoretical analysis includes Monte Carlo ray-tracing simulations that evaluate different environmental and hardware conditions such as wind speed, laser beam footprint diameter and off-nadir angle that are typically observed in ALB survey conditions. The empirical study includes development of an optical detector array to measure and analyze the refraction angle of the laser beam under a variety of environmental and hardware conditions. The results suggest that the refraction angle deviations ( 2 σ ) in the along-wind direction vary between 3–5° when variations in wind speed, laser beam footprint size and the laser beam incidence angle are taken into account.

Position, Orientation and Velocity Detection of Unmanned Underwater Vehicles (UUVs) Using an Optical Detector Array.

This paper presents a proof-of-concept optical detector array sensor system to be used in Unmanned Underwater Vehicle (UUV) navigation. The performance of the developed optical detector array was evaluated for its capability to estimate the position, orientation and forward velocity of UUVs with respect to a light source fixed in underwater. The evaluations were conducted through Monte Carlo simulations and empirical tests under a variety of motion configurations. Monte Carlo simulations also evaluated the system total propagated uncertainty (TPU) by taking into account variations in the water column turbidity, temperature and hardware noise that may degrade the system performance. Empirical tests were conducted to estimate UUV position and velocity during its navigation to a light beacon. Monte Carlo simulation and empirical results support the use of the detector array system for optics based position feedback for UUV positioning applications.

Optical beam position estimation in free-space optical communication

The position of the optical beam on an optical detector array is an important parameter for optimal decoding in free-space optical communication systems; thus, its accurate estimation is essential. In this paper, the performance of three estimators (maximum likelihood, center of gravity, and template matching) for the estimation of center of the beam on a detector array is compared in terms of mean square error and complexity. Simulation results show that the maximum likelihood estimate achieves the lowest mean square error and especially performs significantly better than center of gravity under poor signal-to-noise ratio conditions, for both the continuous and discrete/quantized arrays.

Wide-area and omnidirectional optical detector arrays using modular optical elements.

This paper presents novel, modular optical detector arrays of various shapes and configurations. Recently developed Modular Optical Wireless Elements (MOWE) architecture serves as the basis for large and complex optical detector arrays that can be constructed as geometric shells and provide wide-area even omnidirectional field-of-view (FoV). Programmable optical modules synchronously sample the environment, and then route measurements to the user through a dedicated electrical backbone. The arrays are inexpensive, easy to construct, and can be made with homogeneous/inhomogeneous optical properties. Applications include remote sensing, motion detection, optical navigation, and medical imaging, among others. We present the MOWE detector array concept with a detailed optical analysis and a suggested design methodology, as well as a number of various demonstrations. We also utilize wavelength-diversity of MOWE arrays to demodulate two overlapping signals, showing that many diversity-based algorithms can be conveniently prototyped and implemented.

Optical Detector Array Design for Navigational Feedback Between Unmanned Underwater Vehicles (UUVs)

Designs for an optical sensor detector array for use in autonomous control of unmanned underwater vehicles (UUVs), or between UUVs and docking station, are studied in this paper. Here, various optical detector arrays are designed for the purpose of determining and distinguishing relative 5 degrees-of-freedom (DOF) motion between UUVs: 3-DOF translation and 2-DOF rotation (pitch and yaw). In this paper, a numerically based simulator is developed to evaluate varying detector array designs. The simulator includes a single light source as a guiding beacon for a variety of UUV motion types. The output images of the light field intersecting the detector array are calculated based on detector hardware characteristics, the optical properties of water, and expected noise sources. Using the simulator, the performance of planar and curved detector array designs (of varying size arrays) are analytically compared and evaluated. Output images are validated using empirical in situ measurements conducted in underwater facilities at the University of New Hampshire, Durham, NH, USA. Results of this study show that the optical detector array is able to distinguish relative 5-DOF motion with respect to the simulator light source. Furthermore, tests confirm that the proposed detector array design is able to distinguish positional changes of 0.2 m and rotational changes of 10 $^{\circ}$ within 4–8 m range in x-axis based on given output images.

Resolution analysis in computational imaging with patterned illumination and bucket detection.

In computational imaging by pattern projection, a sequence of microstructured light patterns codified onto a programmable spatial light modulator is used to sample an object. The patterns are used as generalized measurement modes where the object information is expressed. In this Letter, we show that the resolution of the recovered image is only limited by the numerical aperture of the projecting optics regardless of the quality of the collection optics. We provide proof-of-principle experiments where the single-pixel detection strategy outperforms the resolution achieved using a conventional optical array detector for optical imaging. It is advantageous in the presence of real-world conditions, such as optical aberrations and optical imperfections in between the sample and the sensor. We provide experimental verification of image retrieval even when an optical diffuser prevents imaging with a megapixel array camera.

Measurements of the cosmic ray spectrum and average mass with IceCube

Located at the South Pole, IceCube is a particle-astrophysics observatory composed of a square-kilometer surface air shower array (IceTop) and a 1.4km deep cubic-kilometer optical Cherenkov detector array. We review results of measurements of the cosmic ray spectrum and average mass in the energy range 1PeV to 1EeV.

A Spartan 6 FPGA-based data acquisition system for dedicated imagers in nuclear medicine**This paper was originally submitted for inclusion in the special feature on Imaging Systems and Techniques 2011.

We present the development of a four-channel low-cost hardware system for data acquisition, with application in dedicated nuclear medicine imagers. A 12 bit octal channel high-speed analogue to digital converter, with up to 65 Msps sampling rate, was used for the digitization of analogue signals. The digitized data are fed into a field programmable gate array (FPGA), which contains an interface to a bank of double data rate 2 (DDR2)-type memory. The FPGA processes the digitized data and stores the results into the DDR2. An ethernet link was used for data transmission to a personal computer. The embedded system was designed using Xilinx's embedded development kit (EDK) and was based on Xilinx's Microblaze soft-core processor. The system has been evaluated using two different discrete optical detector arrays (a position-sensitive photomultiplier tube and a silicon photomultiplier) with two different pixelated scintillator arrays (BGO, LSO:Ce). The energy resolution for both detectors was approximately 25%. A clear identification of all crystal elements was achieved in all cases. The data rate of the system with this implementation can reach 60 Mbits s−1. The results have shown that this FPGA data acquisition system is a compact and flexible solution for single-photon-detection applications.

Automatic and robust calibration of optical detector arrays for biomedical diffuse optical spectroscopy

The design and testing of a new, fully automated, calibration approach is described. The process was used to calibrate an image-guided diffuse optical spectroscopy system with 16 photomultiplier tubes (PMTs), but can be extended to any large array of optical detectors and associated imaging geometry. The design goals were accomplished by developing a routine for robust automated calibration of the multi-detector array within 45 minutes. Our process was able to characterize individual detectors to a median norm of the residuals of 0.03 V for amplitude and 4.4 degrees in phase and achieved less than 5% variation between all the detectors at the 95% confidence interval for equivalent measurements. Repeatability of the calibrated data from the imaging system was found to be within 0.05 V for amplitude and 0.2 degrees for phase, and was used to evaluate tissue-simulating phantoms in two separate imaging geometries. Spectroscopic imaging of total hemoglobin concentration was recovered to within 5% of the true value in both cases. Future work will focus on streamlining the technology for use in a clinical setting with expectations of achieving accurate quantification of suspicious lesions in the breast.

A high-resolution spectrometer based on a compact planar two dimensional photonic crystal cavity array

We demonstrate a compact spectrometer based on an array of high-quality-factor photonic crystal nanocavities, coupled via a planar two-dimensional waveguide. This architecture enables spectral analysis of incident light with resolution as high as the bandwidth of the cavity mode–0.3 nm at 840 nm for our device. The design is easily extended to the visible and deep-infrared spectral ranges. The two-dimensional cavity array can be mated to commercial two-dimensional optical detector arrays, creating a compact and high-resolution spectrometer suitable for a range of applications including materials and chemical analysis.

Integrated receiver architectures for board-to-board free-space optical interconnects

In many computer and server communications copper cables and wires are currently being used for data transmission and interconnects. However, due to significant shortcomings, such as long transmission time, high noise level, unstable electrical properties, and high power consumption for cooling, researchers are increasingly turning their research interests toward alternatives, such as fiber optic interconnects and free-space optical communication technologies. In this paper, we present design considerations for an integrated receiver for high-speed free-space line-of-sight optical interconnects for distortion-free data transmission in an environment with mechanical vibrations and air turbulences. The receiver consists of an array of high-speed photodiodes for data communication and an array of quadrant photodiodes for real-time beam tracking in order to compensate for the beam misalignment caused by vibrations in servers. Different configurations for spatially positioning the quadrant and data photodiodes are discussed for 4×4 and 9×9 multielement optical detector arrays. We also introduce a new beam tracking device, termed the strip quadrant photodiodes, in order to accurately track highly focused optical beams with very small beam diameter.

Bayesian estimation for selective trace gas detection

We present a Bayesian estimation analysis for a particular trace gas detection technique with species separation provided by differential diffusion. The proposed method collects a sample containing multiple gas species into a common volume, and then allows it to diffuse across a linear array of optical absorption detectors, using, for example, high-finesse Fabry-Perot cavities. The estimation procedure assumes that all gas parameters (e.g. diffusion constants, optical cross sections) are known except for the number population of each species, which are determined from the time-of-flight absorption profiles in each detector.

Smart-Optical Detector CMOS Array for Biochemical Parameters Analysis in Physiological Fluids

This paper describes the implementation of a smart-optical detector array for detection and concentration measurement of biochemical parameters in physiological fluids. Its application is in the low-cost microchip size analytical laboratories that use colorimetric detection, by optical absorption, as the analytical technique. The microlaboratory structure is composed of a microplate cuvette array containing the physiological fluids into analysis and an optical detector array underneath, which quantifies the light absorbed by those fluids. The detectors, together with their analog-to-digital (A/D) conversion, are designed and fabricated using a standard CMOS process. The on-chip A/D conversion is performed, simultaneously, using a 1-b first-order sigma-delta converter for each optical detector. The output signal of the device is a bit stream containing information about the absorbed light, which allows simple microcontroller interfacing. The proposed architecture has the main advantage of performing the simultaneous measurement of the light absorbed by the fluids, which avoids the errors that can be introduced due to light fluctuations in uncontrolled environments. In addition, the architecture allows on-chip calibration during each measurement. This means that the device can be reliably used in environments with noncalibrated light sources, e.g., in a doctor's office. The A/D conversion design described here represents significant improvements when compared with the existing designs. Moreover, the microlaboratory application holds great promise, by both improving benefits (quality of health services provided) and reducing costs (of physiological fluid analysis services).

A pixelated MIMO wireless optical communication system

This paper introduces the pixelated wireless optical channel, which transmits data at high rates using a series of coded time-varying images. This multiple-input/multiple-output point-to-point wireless optical channel uses arrays of optical intensity transmitters and detectors to exploit the inherent spatial degrees of freedom and to realize significant gains in spectral efficiency over single-element systems. Spatial discrete multitone modulation is introduced as a means to combat low-pass spatial distortion and to alleviate spatial alignment problems of previous systems. The capacity of pixelated wireless optical channels is estimated by way of a water-pouring spectrum. A proof-of-concept experimental prototype is constructed using a 512times512 pixel liquid crystal display panel and 154times154 pixels of a charge-coupled device camera. A channel model is developed and the capacity estimated to be 22.4 kb/frame. An unoptimized multilevel code and multistage decoder is applied over the spatial frequency bins and shown to yield spectral efficiencies of approximately 1.7 kb/s/Hz over a range of 2 m

Analysis of the performance of a wireless optical multi-input to multi-output communication system

We investigate robust optical wireless communication in a highly scattering propagation medium using multielement optical detector arrays. The communication setup consists of synchronized multiple transmitters that send information to a receiver array and an atmospheric propagation channel. The mathematical model that best describes this scenario is multi-input to multi-output communication through stochastic slow changing channels. In this model, signals from m transmitters are received by n receiver-detectors. The channel transfer function matrix is G, and its size is n x m. G(i,j) is the transfer function from transmitter i to detector j, and m > or = n. We adopt a quasi-stationary approach in which the channel time variation has a negligible effect on communication performance over a burst. The G matrix is calculated on the basis of the optical transfer function of the atmospheric channel (composed of aerosol and turbulence elements) and the receiver's optics. In this work we derive a performance model using environmental data, such as documented turbulence and aerosol models and noise statistics. We also present the results of simulations conducted for the proposed detection algorithm.