Massachusetts Institute of Technology

Jason Stewart

Juejun Hu

Don M Boroson

Bryan Shawn Robinson

Jeffrey Chou

William D Herzog

Vladimir Liberman

Yifei Zhang

Farzana I Khatri

Steven Constantine

Christopher Roberts

David Jason Geisler

Timothy M Yarnall

Daniel V Murphy

Zachary Darling

Alloys of GeSbSeTe (GSST) can be used to make actively tunable infrared transmission filters that are small, fast, and solid-state. These filters can be used for hyperspectral imaging, 3D LIDAR, portable bio/chem sensing systems, thermal emission control, and tunable filters. GSST is a low-loss phase-change material that can switch from a low-index (n=3), amorphous state to a high-index (n=4.5), hexagonal state with low loss (k&#x3c;0.3) over a wavelength range of 2-10 microns or more. The GSST thickness can be selected to provide pure phase modulation, pure amplitude modulation, or coupled phase and amplitude modulation. GSST can be switched thermally in an oven, optically with visible light, or electrically via Joule heating at speeds from kilohertz to Gigahertz. It operates with reversible and polarization independent transmission switching over a wide incident angle (e.g., 0-60 degrees).

Methods and apparatus for modulating light with phase change materials

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

Growing community of inventors

Stow, MA, United States of America

Jason Stewart