J. J. Carney

781 Mbit/s photon-counting optical communications using a superconducting nanowire detector

We demonstrate 1550 nm photon-counting optical communications with a NbN-nanowire superconducting single-photon detector. Source data are encoded with a rate-1/2 forward-error correcting code and transmitted by use of 32-ary pulse-position modulation at 5 and 10 GHz slot rates. Error-free performance is obtained with -0.5 detected photon per source bit at a source data rate of 781 Mbits/s. To the best of our knowledge, this is the highest reported data rate for a photon-counting receiver.

Ultra-wide-range multi-rate DPSK laser communications

We propose and demonstrate a scalable high-sensitivity approach for achieving multi-rate DPSK using a single transmitter and fixed-interferometer-receiver design. Near-theoretical real-time performance is demonstrated over static and fading channels at rates from 2.4Mbps to 2.5Gbps.

High-sensitivity multi-channel single-interferometer DPSK receiver

A high-sensitivity method of demodulating wavelength-division-multiplexed optical DPSK channels using a single interferometer is described and demonstrated. We show that this technique can operate within existing standards and achieve near-quantum-limited receiver performance. The resulting hardware simplification has potential to reduce the cost of deploying and scaling future wide-band optical-communication networks employing WDM-DPSK.

Demonstration of optical DPSK communication with 25 photons/bit receiver sensitivity

We demonstrate optically-matched preamplified-DPSK communications at 2.5 Gbit/sec and 1557 nm wavelength, with uncoded sensitivities of 25 photons/bit at 10-9 bit-error-rate, falling less than 1 dB from quantum-limited theory.

Design of a 40 Watt 1.55μm uplink transmitter for Lunar Laser Communications

A ground-based 40W 1.55μm uplink transmitter for lunar laser communications is described. The transmitter, which generates wavelength multiplexed communication and beacon signals, is implemented using four 10W spatial-diversity channels to reduce far-field atmospheric-turbulence-induced fading and facilitate high-power signal generation via parallel-spatial-combining of commercially-available EDFAs. Each transmitter channel can generate a 1 kHz modulated beacon for spatial acquisition, and a multi-rate 4-PPM communication signal at a 311 MHz slot rate with 16:1 and 32:1 duty cycles to support 38.9 Mbit/s and 19.4 Mbit/s channel rates, respectively. Details on the transmitter design, including the mitigation of optical nonlinear effects are discussed.

Superconducting nanowire single-photon detectors

We present our ongoing work on superconducting NbN-nanowire photodetectors, which deliver both high speed ( 50% at 1550 nm), promising access to new regimes in ultrafast photon counting applications.

A multi-rate DPSK modem for free-space laser communications

The multi-rate DPSK format, which enables efficient free-space laser communications over a wide range of data rates, is finding applications in NASA’s Laser Communications Relay Demonstration. We discuss the design and testing of an efficient and robust multi-rate DPSK modem, including aspects of the electrical, mechanical, thermal, and optical design. The modem includes an optically preamplified receiver, an 0.5-W average power transmitter, a LEON3 rad-hard microcontroller that provides the command and telemetry interface and supervisory control, and a Xilinx Virtex-5 radhard reprogrammable FPGA that both supports the high-speed data flow to and from the modem and controls the modem’s analog and digital subsystems. For additional flexibility, the transmitter and receiver can be configured to support operation with multi-rate PPM waveforms.

High-Sensitivity Demodulation of Multiple-Data-Rate WDM-DPSK Signals using a Single Interferometer

We demonstrate simultaneous reception of multiple-rate wavelength-division-multiplexed optical- DPSK signals using a single interferometer. The demodulation approach provides rate-flexibility and scalability, enabling penalty-free performance and compliance with existing channel-rate and channel-spacing standards.

Power-efficient Noise-insensitive Optical Modulation for High-sensitivity Laser Communications

We demonstrate power-efficient noise-insensitive optical waveform generation from directly modulated lasers combined with periodic time-frequency windowing. Real-time experiments with direct FPGA-driven lasers achieve near-theoretical communication performance at Gbit/s rates using flexible and scalable transceiver designs.

Multi-rate DPSK optical transceivers for free-space applications

We describe a flexible high-sensitivity laser communication transceiver design that can significantly benefit performance and cost of NASAs satellite-based Laser Communications Relay Demonstration. Optical communications using differential phase shift keying, widely deployed for use in long-haul fiber-optic networks, is well known for its superior sensitivity and link performance over on-off keying, while maintaining a relatively straightforward design. However, unlike fiber-optic links, free-space applications often require operation over a wide dynamic range of power due to variations in link distance and channel conditions, which can include rapid kHz-class fading when operating through the turbulent atmosphere. Here we discuss the implementation of a robust, near-quantum-limited multi-rate DPSK transceiver, co-located transmitter and receiver subsystems that can operate efficiently over the highly-variable free-space channel. Key performance features will be presented on the master oscillator power amplifier (MOPA) based TX, including a wavelength-stabilized master laser, high-extinction-ratio burst-mode modulator, and 0.5 W single polarization power amplifier, as well as low-noise optically preamplified DSPK receiver and built-in test capabilities.