High-data-rate deep space optical communication (DSOC) links are desired by NASA and other space agencies to support future advanced science instruments, live high-definition (HD) video feeds, telepresence, and human exploration of Mars and beyond. Optical communications can provide a 10 to 100× increase in data rates from deep space for equivalent spacecraft mass and power as compared to state-of-the-art deep space Ka-band RF communication systems. One of the key technologies for DSOC is a large-area photon-counting detector array for the ground-based receiver.
A new type of SNSPD array based on tungsten silicide (WSi) instead of NbN was developed. WSi is amorphous, so it does not have the strict dependence on the crystal phase affecting NbN, which greatly simplifies the material deposition. Furthermore, WSi has a lower superconducting energy gap than NbN, easing the need for ultra-narrow wires and allowing wires to be reliably fabricated on a large scale using photolithography. The pixel yield is far higher than in NbN, with 93% of the pixels functioning on a recently measured device, and overall device yield of ≈70% across a wafer. This technology is readily scalable to the telescope aperture sizes required for future deep space ground stations.
A gold mirror layer was deposited on an oxidized silicon wafer, and amorphous-state WSi was sputtered from a compound target at a thickness of 5 nm. The WSi nanowire was embedded at the center of a three-layer vertical optical cavity consisting of two silica layers and a titanium oxide antireflective coating. The layer thicknesses were chosen to optimize efficiency at the target communication wavelength of 1,550 nm, and to minimize the polarization dependence of the detector response.
The detector modules differ from the previous state of the art in several key respects. First, the superconducting material used for the nanowires was amorphous WSi, rather than a refractory metal such as NbN or NbTiN. This allowed a much greater active area than has been possible due to the lower incidence of nanowire constrictions. In the future, this will allow coupling to a much larger telescope aperture than has previously been demonstrated in an optical communication experiment.
This work was done by Matthew D. Shaw, Francesco Marsili, Andrew D. Beyer, and Jeffrey A. Stern of Caltech for NASA’s Jet Propulsion Laboratory. NPO-49463
This Brief includes a Technical Support Package (TSP).
Free-Space, Coupled, Multi-Element Detector for Deep Space Optical Communication
(reference NPO-49463) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA, specifically focusing on the Free-Space, Coupled, Multi-Element Detector for Deep Space Optical Communication, referenced in NPO-49463 of NASA Tech Briefs. It outlines significant advancements in optical communication technologies developed by the Jet Propulsion Laboratory (JPL) at the California Institute of Technology.
Key highlights include the development of a 64-pixel WSi superconducting nanowire single-photon detector (SNSPD) array, which is crucial for high-speed data transmission in deep space communication. The document details a successful real-time video communication link established using this 64-pixel array, achieving a data rate of 47 Mb/s with a high-definition TV signal. The system operates at cryogenic temperatures (around 40K) and utilizes advanced components such as SiGe cryogenic channel combiners and a 6.4 GHz receiver clock, demonstrating a low error rate and high efficiency.
The document also discusses the architecture of the readout system, which includes a 64-pixel array capable of being read out in quadrants, allowing for efficient data processing. The system is designed to handle a total count rate of 38 MHz with a dark count rate of less than 1 kHz, indicating its effectiveness in detecting weak signals in deep space environments.
Additionally, the document emphasizes the importance of this technology as a technical milestone, paving the way for scaling up to more complex systems with multiple combiners. The advancements in pulse-position modulation (PPM) and the integration of optical and electrical components are highlighted as critical for enhancing the bandwidth and reliability of deep space communication links.
The Technical Support Package serves not only as a documentation of these technological advancements but also as a resource for potential applications in various fields beyond aerospace, showcasing the broader implications of NASA's research and development efforts. For further inquiries or assistance, the document provides contact information for the Innovative Technology Assets Management at JPL.
In summary, this document encapsulates the cutting-edge developments in optical communication technology at JPL, emphasizing their potential to revolutionize deep space communication and their applicability in other technological domains.
