Massachusetts Institute of Technology

Don M Boroson

Bryan Shawn Robinson

Scott A Hamilton

David O Caplan

Bryan M Reid

Hemonth G Rao

Shelby J Savage

Marc Norvig

Steven Constantine

Farzana I Khatri

Jamie W Burnside

Neal W Spellmeyer

Mark L Stevens

Kathleen Michelle Riesing

Jason Stewart

David Jason Geisler

Timothy M Yarnall

John Rush

Kenneth Perko

Marius A Albota

Daniel V Murphy

Jade Wang

Curt Schieler

Bryan C Bilyeu

Jessica Chang

Zachary Darling

Robert J Menrad

Communication systems and methods for high-data-rate, high-efficiency, free-space communications are described. High-speed optical modems and automatic repeat request can be employed to transmit large data files without data errors between remote devices, such as an earth-orbiting satellite and ground station. Data rates over 100 Gb/s can be achieved.

Free-space optical communication system and methods for efficient data delivery

Traditional satellite-to-earth data transmission systems are constrained by inefficient relay schemes and/or short-duration data transfers at low data rates. Communication systems described herein achieve extremely high burst rate (e.g., 10 Gbps or greater) direct-to-Earth (DTE) data transmission over a free-space optical link between a spacecraft and a remote terminal, which may be a ground terminal or another space terminal. The optical link is established, for example, when the remote terminal is at an elevation of 20&#xb0; with respect to a horizon of the remote terminal. In some embodiments, a data transmission burst contains at least 1 Terabyte of information and has a duration of 6 minutes or less. The communication system can include forward error correction by detecting a degradation of a received free-space optical signal and re-transmitting at least a portion of the free-space optical signal.

Network of extremely high burst rate optical downlinks

Traditional satellite-to-earth data transmission systems are constrained by inefficient relay schemes and/or short-duration data transfers at low data rates. Communication systems described herein achieve extremely high burst rate (e.g., 10 Gbps or greater) direct-to-Earth (DTE) data transmission over a free-space optical link between a spacecraft and a remote terminal, which may be a ground terminal or another space terminal. The optical link is established, for example, when the remote terminal is at an elevation of 20&#xb0; with respect to a horizon of the remote terminal. In some embodiments, a data transmission burst contains at least 1 Terabyte of information, and has a duration of 6 minutes or less. The communication system can include forward error correction by detecting a degradation of a received free-space optical signal and re-transmitting at least a portion of the free-space optical signal.

A wide-field telescope and focal plane array (FPA) that look at Earth and satellites in low- and medium-Earth orbit (LEO and MEO) from a satellite in higher orbit, such as geostationary Earth orbit (GEO), can serve as a node in an on-demand, optical multiple access (OMA) communications network. The FPA receives asynchronous low-rate signals from LEO and MEO satellites and ground stations at a signal rate determined in part by the FPA frame rate (e.g., kHz to MHz). A controller tracks the low-rate signals across the FPA as the signal sources orbit Earth. The node also includes one or more transmitters that relay the received information to other nodes via wavelength-division multiplexed (WDM) free-space optical signals. These other signals may include low-rate telemetry communications, burst transmissions, and continuous data relay links.

Methods, systems, and apparatus for global multiple-access optical communications

Challenges of direct-to-Earth (DTE) laser communications (lasercom) between spacecraft in low-Earth orbit (LEO) or medium-Earth orbit (MEO) and ground terminals can include short duration transmission windows, long time gaps between the transmission windows, deleterious effects of atmospheric turbulence, and the inability to operate in cloudy weather. Direct-link optical communications systems described herein can have data rates that are high enough to empty high-capacity on-board buffer(s) (e.g., having a capacity of at least about 1 Tb to hundreds of Tb) of a spacecraft in a single pass lasting only tens of seconds to a few minutes (e.g., 1-15 minutes), and overprovisioning the buffer capacity accounts for variations in the latency between links. One or more distributed networks of compact optical ground terminals, connected via terrestrial data networks, receive and demodulate WDM optical data transmissions from a plurality of orbiting spacecraft (e.g., satellites).

Ground terminal design for high rate direct to earth optical communications

A satellite in low-Earth orbit (LEO) or medium-Earth orbit (MEO) with a modern image sensor and/or other remote sensing device can collect data at rates of 10 Mbps or higher. At these collection rates, the satellite can accumulate more data between its passes over a given ground station than it can transmit to the ground station in a single pass using radio-frequency (RF) communications. Put differently, the sensors fill the spacecraft's memory faster than the spacecraft can empty it. Fortunately, free-space optical communications signals can carry far more data than RF communications signals. In particular, a spacecraft can transmit over 1 Tb of data in a single pass using burst wavelength-division multiplexed (WDM) optical signals. Each burst may last seconds to minutes, and can include tens to hundreds of WDM channels, each of which is modulated at 10 Gbps or more.

Link architecture and spacecraft terminal for high rate direct to earth optical 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

Described are an FSK modulator and a method for large-alphabet FSK modulation. The FSK modulator and the method are based on filtering of a multi-tone optical source such as a mode-locked laser which provides a comb distribution of tones. A frequency-selective component selects for transmission a subset of the tones. In various embodiments the frequency-selective component is a Mach-Zehnder interferometer filter or a microring resonator filter. A second frequency-selective component selects a subset of the tones from the comb distribution provided by the first frequency-selective component. Still more frequency-selective components can be used according to the number of tones supplied by the multi-tone optical source to the FSK modulator. The optical signal exiting the last frequency-selective component includes only a single tone which corresponds to the symbol to be transmitted.

Modulator for frequency-shift keying of optical signals

Disclosed herein are a system and method for three-dimensional imaging using a single transducer. A laser in a transmitter emits a sequence of short pulses, each of which is at a different center wavelength (frequency). A dispersive element in the transmitter spatially separates the pulses according to wavelength, with different pulses mapped to different spatial locations in a target volume via a lens. The pulses travel to the target, which scatters or back-reflects the pulses towards the dispersive element via the lens. The lens collects the returned pulses and transmits them to a single transducer via the dispersive element. The transducer measures the time of arrival for each returned pulse. Because the arrival time depends on the range to the object in the portion of the target illuminated by the corresponding emitted pulse, the measured arrival time can be used to reconstruct a 3D (angle-angle-range) image of the object.

Single-transducer, three-dimensional laser imaging system and method

A variable-bit-rate communication system is described. The communication system includes a variable-bit-rate transmitter that generates digital data at a first or a second bit rate and a variable-bit-rate receiver that receives the digital data. The digital data comprises a sequence of signaling waveforms having a first or a second duty cycle, respectively, wherein each signaling waveform has the same shape.

Variable-rate communication system with optimal filtering

An optical modulator includes an optical pulse train generator that forms an optical pulse train of a predetermined frequency at a generator output. The optical modulator also includes an optical pulse train modifier having a first input optically coupled to the output of the pulse train generator, a second input, and an optical output. The modifier produces a modulated optical pulse train related to a signal appearing at the second input and having an optical sub-carrier frequency related to the predetermined frequency of the optical pulse train at the first input.

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Needham, MA, United States of America

Don M Boroson