Mark L. Stevens

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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(More)
The sensitivity of a high-rate photon-counting optical communications link depends on the performance of the photon counter used to detect the optical signal. In this paper, we focus on ways to reduce the effect of blocking, which is loss due to time periods in which the photon counter is inactive following a preceding detection event. This blocking loss(More)
We report the first demonstration of a near quantum-limited optical homodyne PSK receiver combined with powerful forward-error-correction coding, achieving 1.5 photons/bit sensitivity, within 4.5 dB of the Shannon limit. Phase-locking was achieved at 1.55 microm using an analog dither-based optical phase-locked loop with an external phase modulator.(More)
The Lunar Laser Communications Demonstration (LLCD) is an ongoing project to demonstrate a high-rate, bidirectional optical communications link between a lunar satellite and an Earth-based ground terminal. The optical downlink operates at data rates up to 622 Mbps and employs photon counting array receiver technology. While the use of a 16-PPM modulation(More)
We describe a simple 4-PPM demodulator that uses analog delay lines and simple 1-bit comparators to determine the least-significant bit and most-significant bit of the 4-PPM encoded data without additional digital signal processing. We show that with good optical filtering the comparator-based demodulator can theoretically operate with sensitivity only 0.23(More)
Space-to-ground optical communication systems can benefit from reducing the size, weight, and power profiles of space terminals. One way of reducing the required power-aperture product on a space platform is to implement effective, but costly, single-aperture ground terminals with large collection areas. In contrast, we present a ground terminal receiver(More)
Space terminals for free-space optical communication systems are under constant pressure to reduce their size, weight, and power profiles. Ground terminals with large collection areas are costly, but provide a means to reduce the aperture-power product on a space platform required to close a given link. We present a ground terminal receiver architecture in(More)
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(More)
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