A reconfigurable Single-Photon Avalanche Diode integrating receiver in standard 130 nm CMOS is presented for optical links with an array readout bandwidth of 100 MHz. A maximum count rate of 58 G photon/s is observed, with a dynamic range of ≈ 79 dB, a sensitivity of ≈ - 31.7 dBm at 100 MHz and a BER of ≈ 1 ×10-9. The sensor core draws 89 mW at the maximum count rate and obtains a peak SNR of ≈157 dB. We investigate the properties of the receiver for optical communications in the visible spectrum, using its added functionality and reconfigurability to experimentally explore non-ideal influences. The all-digital 32 × 32 SPAD array, achieves a minimum dead time of 5.9 ns, and a median dark count rate of 2.5 kHz/SPAD. The internal gain of SPADs and spatio-temporal summation removes the need for analogue amplification. High noise devices can be weighted or removed to optimize the SNR. The power requirements, transient response and received data are explored and limiting factors similar to those of photodiode receivers are observed.

A Reconfigurable Single-Photon-Counting Integrating Receiver for Optical Communications

To meet the increasing demand from quantum communications and other photon starved applications, we have developed various InP-based single-photon detectors, including discrete single-photon avalanche diodes (SPADs), negative feedback avalanche diodes (NFADs), and Geiger-mode avalanche photodiode (GmAPD) arrays. A large quantity of InP SPADs have been fabricated. Out of 1000 devices with a 25-μm active area diameter, operated under gated mode at temperature of 233 K, with a pulse repetition rate of 1 MHz and pulse width of 1 ns, the average dark count rate and afterpulsing probability are 30 kHz and 8 × 10
 -5
, respectively. Smaller (16-μm active area diameter) and larger (40-μm active area diameter) discrete devices have been fabricated as well, and their performances are presented along with the 25-μm diameter devices. NFAD devices can operate in free running mode and photon detection efficiency of 10-15% can be achieved without applying any hold-off time externally. When the temperature decreases from 240 to 160 K, the noise equivalent power (NEP) decreasesfrom1.9 × 10
 -16
 to 1.8 × 10
 -18
WHz
 -1/2
, with the activation energy being 0.2 eV. The very low NEP at 160 K makes NFAD devices an ideal choice for long distance, entanglement-based quantum key distributions. GmAPD arrays provide an enabling technology for many active optical applications, such as 3-D laser detection and ranging (LADAR) and photon starved optical communications. Both 32 × 32 and 128 × 32 GmAPD arrays have been fabricated with high performance and good uniformity. GmAPD focal plane arrays (FPAs) with framed readout mode have enabled very high-performance flash LADAR systems. GmAPD FPAs with asynchronous readout mode will enable high rate quantum key distributions and other quantum communications applications.

InP-Based Single-Photon Detectors and Geiger-Mode APD Arrays for Quantum Communications Applications

We demonstrate a $256 \times 256$ passive photon counting imager based on hybridization of back-illuminated silicon Geiger-mode avalanche photodiodes to an all-digital CMOS counting chip. Photon detection efficiencies in the 10%–20% are observed at visible wavelengths. The detection efficiency is currently limited by optical crosstalk that leads to elevation of dark count rates as the bias voltage on the photodiodes is increased. Both the time dependence of dark count activity during a gate time and the spatial structure of dark images were successfully explained using crosstalk-based models.

A Study of Crosstalk in a $256 \times 256$ Photon Counting Imager Based on Silicon Geiger-Mode Avalanche Photodiodes

A reconfigurable Single-Photon Avalanche Diode integration mode receiver in 130nm CMOS is presented for optical links with an array readout bandwidth of 100MHz. The all-digital 32×32 SPAD array achieves a minimum dead time of 5.9ns, and a median dark count rate of 2.5kHz per SPAD. Pulse shortening increases the dynamic range by preventing pulse overlap. An in-pixel feedback loop allows synchronous or self-clocked asynchronous time division multiplexing. The internal gain of SPADs and spatio-temporal summation removes the need for analogue amplification. A maximum count rate of 58GHz is observed, with SNR of 79dB, a sensitivity of −31.7dBm at 100MHz and a BER of 10−9. The sensor core draws 89mW at maximum count rate.

A reconfigurable 14-bit 60GPhoton/s Single-Photon receiver for visible light communications

We describe work on the development of an optical link budget tool for an intensity-modulated direct-detected photon-counting channel utilizing pulse-position-modulation (PPM). We provide new material in several areas. First, we provide an approximation to the channel capacity, which is not known in closed form, to enable efficient search algorithms over the trade space. The expression also illustrates clearly the trade-offs between signal and noise power, and modulation parameters. We provide an approximation to the losses due to log-normal fading, which may be used to model scintillation. We provide approximations for the loss due to photo-detector blocking and jitter. Lastly, we describe a methodology to choose an optimum detector sub-array in the presence of dark noise, blocking, and an arbitrary point spread function.

An optical communications link design tool for long-term mission planning for deep-space missions

The Flight Laser Transceiver (FLT) is the space-based subsystem of the Deep- space Optical Terminals (DOT) project. The FLT supports retirement of all major risks for deployment of operational deep-space optical communications at ranges out to about 5 AU. Architecture, key requirements, major trades results, selected concept design, required tech- nology maturation, and future scalability are discussed.

https://ipnpr.jpl.nasa.gov/progress_report/42-185/185D.pdf

Overview and Design of the DOT Flight Laser Transceiver

Early applications driving the development of single photon sensitive detectors, such as fluorescence and
photoluminescence spectroscopy, simply required low noise performance with kiloHertz and lower count rate
requirements and minimal or no timing resolution. Newer applications, such as high data rate photon starved free space
optical communications require photon counting at flux rates into megaphoton or gigaphoton per second regimes
coupled with sub-nanosecond timing accuracy. With deep space optical communications as our application driver, we
have developed and implemented systems to both characterize gigaHertz bandwidth single photon detectors as well as
process photon count signals at rates beyond 100 megaphotons per second to implement communications links at data
rates exceeding 100 megabits per second with efficiencies greater than two bits per detected photon. With these
systems, we have implemented high bandwidth real-time systems using intensified photodiodes, visible light photon
counter detectors, superconducting nanowire detectors, Geiger-mode semiconductor avalanche photodiodes, and
negative avalanche feedback photon counters.

Dan Nguyen

Papers

Overview and Design of the DOT Flight Laser Transceiver

Gigahertz bandwidth photon counting