Boston Chapter of the IEEE Photonics Society

Abstract:  Flexible multi-rate capabilities are attractive for communications over the dynamic free-space optical (FSO) channel since it enables links to be efficiently established over a variety of distances, channel conditions, aperture sizes, and transmitter power levels.  Recently, multi-rate differential phase shift keying (DPSK) modulation has been shown to provide good performance with modest complexity over a wide range of data rates.  For these reasons, multi-rate DPSK has become the high-rate baseline format for NASA’s Laser Communication Relay Demonstration (LCRD) and other space-based FSO systems currently in development, operating at channel rates from 72 Mbit/s to 2.88 Gbit/s.  

Here, we report WDM-scalable optical-transceiver advances that can further extend single-channel rates by a factor of four to 11.52 Gbit/s using an LCRD-compatible implementation. Transmitter phase-modulation is implemented using power-efficient time-frequency-windowed directly modulated lasers (DMLs) that can generate burst-mode 2-DPSK and 4-DPSK waveforms at the standard LCRD 2.88 GHz symbol rate and twice the rate at 5.76 GHz.  At the receiver, a standard 2.88 GHz delay-line-interferometer (DLI) can implement non-adjacent (NA) 2-DPSK demodulation at 5.76 Gbit/s.  For 4-DPSK, a pair of 2.88 GHz DLIs biased at ±p/4 can demodulate the in-phase and quadrature components that convey 2-bits-per-symbol.  When combined, a common DPSK receiver platform may be used to demodulate standard multi-rate LCRD waveforms as well as 2- and 4-DSPK waveforms at 1x and 2x the standard symbol rate.

Biography:  David O. Caplan is a Senior Staff member in the Optical Communication Technology Group at MIT Lincoln Laboratory.  He graduated summa cum laude from Tufts University with a B.S. degree in Electrical Engineering, and received M.S. and Ph.D. degrees in Electrical Engineering from Northwestern University in the field of nonlinear and quantum optics.

Since joining the Laboratory in 1996, his research has focused on high-sensitivity laser communication systems and related technologies, with an emphasis on photon- and power-efficient transmitter and receiver designs – and extensions with agile multi-rate and multi-format capabilities to support future free-space optical network architectures.  He led the development of transmitter systems for the GeoLITE mission, the world’s first successful high-rate space-based laser communications system.  His work on high-sensitivity multi-rate optical transceivers has been incorporated into NASA’s deep-space interplanetary laser communication initiatives including the Mars and subsequent Lunar Laser Communication Demonstration (LLCD), and the ongoing Laser Communications Relay demonstration program.  He designed and oversaw the buildup of the uplink transmitter systems for the LLCD program – which increased the state-of-the-art data rates to the Moon by more than three orders of magnitude.

Dr. Caplan has been active in both OSA and IEEE professional societies and is currently serving as an Associate Editor for the IEEE Journal of Lightwave Technology.  He was a guest editor for the IEEE Journal of Selected Topics in Quantum Electronics (JSTQE), has served as a member of the OSA Conference on Lasers and Electro-Optics (CLEO) and IEEE Photonics Society technical program committees, chaired the CLEO Lightwave Communications and Optical Networks Technology committee, and is currently serving as a General Chair of the OSA Advanced Photonics Congress Photonics Networks Conference.  He has also been active in numerous educational initiatives, organizing and teaching courses both at MIT and MIT Lincoln Laboratory.  His work in the field has led to numerous patents and publications, including two book chapters, and was recognized with the MIT Lincoln Laboratory Technical Excellence Award.  In 2018, he received an R&D100 Award for the development of Multi-rate DPSK, which was highlighted as one of the 100 most technically significant products of the year.

Location:  MIT Lincoln Laboratory Forbes Road