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We report the development and testing of a photon-counting detector for space-borne quantum communication applications with an ultra-low dark count rate (10 counts per second) and low timing jitter (25 ps RMS, 140 ps 1%) at a non-cryogenic temperature of -60°C.
We present a field-programmable gate array (FPGA) implementation of a single photon-counting receive modem for a pulse position modulated signal. The modem is compliant with the Consultative Committee for Space Data Systems (CCSDS) High Photon Efficiency (HPE) Optical Communications Coding and Synchronization standard and is capable of a maximum data rate of 267 Mbps. The system is designed on a commercial off-the-shelf FPGA platform and utilizes superconducting nanowire single photon counting detectors, analog to digital converters (ADC s) to sample the detectors, and two FPGAs. Symbol timing recovery, photon counting, convolutional deinterleaving, and codeword synchronization areis performed in the first FPGA. The second FPGA performs iterative decoding on each codeword of the serially concatenated pulse position modulated (SCPPM) signal. A digital filter is included to compensate for timing jitter of the detector, and the decoder throughput can be modified adjusted through reconfigurable parallelization. The decoder also implements a resource-efficient, algorithmic polynomial interleaver and deinterleaver. Both FPGAs can be reconfigured to switch between pulse position modulation (PPM)-16 and PPM-32 with code rates 1/3, 1/2, and 2/3. In this paper, we describe the receiver architecture and FPGA implementation of the timing recovery loop and SCPPM decoder, FPGA utilization for the different modes, and receive modem characterization test results.
The National Aeronautics and Space Administration is developing a photon counting ground receiver for free-space optical communications. The receiver consists of a fiber interconnect, superconducting nanowire single photon counting detectors (SNSPDs), and a field programmable gate array (FPGA) based receive modem. This receiver is compliant with the Consultative Committee for Space Data Systems (CCSDS) Optical Communications High Photon Efficiency standard, which is used in the low photon flux communications regime, including on the upcoming Optical Artemis-2 Orion communications demonstration. The receiver architecture is modular, can be scaled for data rate, and is designed with primarily commercial-off-the-shelf technology. Two fiber interconnect and detector architectures are being prototyped. The first uses a few-mode-fiber coupled to a 16-channel SNSPD array and the second architecture uses a photonic lantern coupled to 7 single-pixel SNSPDs. Photon counting, symbol timing recovery, demodulation and decoding is done using several FPGA cards. This presentation describes the unique features of the ground receiver, performance test results, and challenges with using commercial SNSPDs in free-space optical communications.
Two methods of estimating received photon counts given a realistic noisy and bandlimited optical channel are presented. The function of estimating photon counts is critical in any optical communications receiver. The purpose of this work is to compare two methods, neither of which is generically optimal, with realistic channels-for the purpose of assessing which is more appropriate for application in a hardware receiver given the current state-of-the art.
A sensor, consisting of a thin dual-capacitor assembly with an outer film of thermal-control material, is used to detect micrometeoroid particles. A coincidence counting circuit is used to count the penetrations.
Liquid scintillation counting method with sonic oscillations, noting decreased preparation time and increased counting efficiency
Modified spectrometer system with a low-noise preamplifier reduces rate-dependent distortions at high counting rates, 25,000 counts per second. Pole-zero cancellation minimizes pulse undershoots due to multiple time constants, baseline restoration improves resolution and prevents spectral shifts.
Liquid scintillation counting technique is applied to the direct measurement of carbon-14 in carbon dioxide. This method has high counting efficiency and eliminates many of the basic problems encountered with previous techniques. The technique can be used to achieve a percent substitution reaction and is of interest as an analytical technique.
Counter includes one section which counts the first several pulses, and a second section which counts pulses from a clock between the beginning of a sampling interval and the receipt of the first pulse by the circuit. The number of clock pulses indicates receipt time of the first pulse.
Automatic correction for dead time losses in nuclear counting experiments is implemented by a simple live timer arrangement in which each counting interval is extended for compensation for the dead time during that interval. this method eliminates repetitious manual calculations, source of error, and dependence upon paralysis shifts.
Frequency counted measurements and phase locking to noisy oscillators, showing counted frequency method sample variance slow convergence to actual variance
The use of gamma-gamma coincidence spectrometry in the instrumental activation analysis of materials of geochemical interest can offer advantages of improved sensitivity and precision for certain elements over other counting techniques. An introduction to some of the theory and the practical considerations involved in the establishment of gamma-gamma coincidence counting systems is presented. Previous applications of this technique to the activation analysis of meteorites and rocks are reviewed, and some future applications are proposed.
Statistical description of a photoelectric detector is given. The photosensitive surface of the detector is divided into many small areas, and the moment generating function of the photo-counting statistic is derived for large time-bandwidth product. The detection of a specified optical image in the presence of the background light by using the hypothesis test is discussed. The ideal detector based on the likelihood ratio from a set of numbers of photoelectrons ejected from many small areas of the photosensitive surface is studied and compared with the threshold detector and a simple detector which is based on the likelihood ratio by counting the total number of photoelectrons from a finite area of the surface. The intensity of the image is assumed to be Gaussian distributed spatially against the uniformly distributed background light. The numerical approximation by the method of steepest descent is used, and the calculations of the reliabilities for the detectors are carried out by a digital computer.
Evolutionary sequences for the sun are presented which confirm that the Cl-37 neutrino counting rate will be greatly reduced if the high-energy tail of the Maxwellian distribution of relative energies is progressively depleted. Thermonuclear reaction rates and pressure are reevaluated for a distribution function modified by the correction factor suggested by Clayton (1974), and the effect of the results on solar models calculated with a simple Henyey code is discussed. It is shown that if the depletion is characterized by a certain exponential dependence on the distribution function, the counting rate will fall below 1 SNU for a distribution function of not less than 0.01. Suggestions are made for measuring the distribution function in the sun by means of neutrino spectroscopy and photography.
High-speed variation of counting digital filter implements count in a way which allows shortest permissible spacing between samples of input signal to be small fraction of time it takes to compute output sample.
The operation and performance of an array photometer with the ability to discriminate on single photoelectrons are discussed. The system consists of a 100 by 100 array of channels which count single photoelectrons. The photosensor is an Intensified Charge Coupled Device using a Fairchild CCD201 which was fabricated by the Electronic Vision Company. This system has demonstrated a noise level which permits single photoelectron discrimination, high scan rate (400 frames/sec), and low lag. The UMAP system has been successfully operated in the photon counting mode on a 36-inch telescope and on a 48-inch telescope. Data from these observations illustrate the system sensitivity and the spacial resolution which is better defined by the size of an individual pixel element on the CCD.
A multichannel detector system is described in which the positions of individual photon events in a high-gain image intensifier are decoded in the output of a video detector. The high-gain intensifier consists of a pair of three-stage electrostatic image-tube assemblies each containing three fiber-optically-coupled tubes potted in a rugged package with an internal high-voltage supply. Operation of the electrooptical system is discussed along with the pulse-detection process and the operation of the spectrograph in which the image-tube assembly is mounted. It is noted that the spectrometer detects 1.0 count/sec per A for an object of magnitude 13.0 at the peak of its response in the visual band when no light is lost on the slit, that a 10% coincidence correction is reached at an overall count rate of 860 per sec, and that the response follows an exponential law up to count rates of about 4000 per sec. The measured spectrum of the Seyfert galaxy NGC 5548 is provided as an example of the raw data produced by the instrument on a 1.5 meter telescope.
The accuracy and the applicability of the method of general star counts are discussed. The effects of statistical errors, pseudorandom errors, systematic errors, and sampling errors are considered. The conditions under which quantitatively useful results can be derived are identified. It is found that for plates reaching 17th to 20th mag, general star counts can be a useful technique for investigating the structure of dark cloud complexes located within 500 to 1000 pc of the sun.