Massachusetts Institute of Technology

Hemonth G Rao

Scott A Hamilton

David O Caplan

Don M Boroson

Bryan Shawn Robinson

Marc Norvig

Neal W Spellmeyer

Marvin Scheinbart

Andrew Fletcher

Nicholas Hardy

A multi-rate, burst-mode, photon-counting receiver can communicate at data rates up to 10.416 Mb/s over a 30-foot water channel. With added attenuation, the maximum link loss is 97.1 dB at &#x3bb;=517 nm. In clear ocean water, this equates to link distances up to 148 meters. For &#x3bb;=470 nm, the achievable link distance in clear ocean water is 450 meters. The receiver incorporates soft-decision forward error correction (FEC) that supports multiple code rates to achieve error-free performance. A burst-mode receiver architecture provides robust performance with respect to unpredictable channel obstructions. The receiver can detect the data rate on-the-fly and adapts to changing levels of signal and background light. The receiver updates its phase alignment and channel estimates every frame, allowing for rapid changes in water quality as well as motion between transmitter and receiver.

Methods and apparatus for free-space undersea communications

A burst-mode phase shift keying (PSK) communications apparatus according to an embodiment of the present invention enables practical, power-efficient, multi-rate communications between an optical transmitter and receiver. Embodiments may operate on differential PSK (DPSK) signals. An embodiment of the apparatus includes an average power limited optical transmitter that transmits at a selectable data rate with data transmitted in bursts, the data rate being a function of a burst-on duty cycle. DPSK symbols are transmitted in bursts, and the data rate may be varied by changing the ratio of the burst-on time to the burst-off time. This approach offers a number of advantages over conventional DPSK implementations, including near-optimum photon efficiency over a wide range of data rates, simplified multi-rate transceiver implementation, and relaxed transmit laser line-width requirements at low data rates.

Method and apparatus for transmitting phase shift keyed optical signals

A burst-mode phase shift keying (PSK) communications system according to an embodiment of the present invention enables practical, power-efficient, multi-rate communications between an optical transmitter and receiver. Embodiments may operate on differential PSK (DPSK) signals. An embodiment of the system utilizes a single interferometer in the receiver with a relative path delay that is matched to the DPSK symbol rate of the link. DPSK symbols are transmitted in bursts, and the data rate may be varied by changing the ratio of the burst-on time to the burst-off time. This approach offers a number of advantages over conventional DPSK implementations, including near-optimum photon efficiency over a wide range of data rates, simplified multi-rate transceiver implementation, and relaxed transmit laser line-width requirements at low data rates.

Method and apparatus for phase shift keyed optical communications

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Bedford, MA, United States of America

Hemonth G Rao