This investigation will develop ultra-low size, weight and power (swap) laser transmitters for deep space optical communication by leveraging novel semiconductor external cavity laser designs and…

This federal contract award to the University of California, Santa Barbara (UCSB) is funded by the National Aeronautics and Space Administration (NASA) Space Technology Mission Directorate (STMD) Space Technology Research Grants (STRG) program. The $516,163 grant will support the development of ultra-low size, weight, and power (SWAP) laser transmitters for deep space optical communication. The project, titled "HELIOS: Heterogeneous Laser Transmitter Integration for Low SWAP", will leverage semiconductor external cavity laser designs and heterogeneous photonic integration technologies to create an integrated laser transmitter system-on-a-chip. This award does not have a set-aside designation, indicating UCSB competed for the opportunity in full and open competition. UCSB has extensive expertise in photonics, semiconductor devices, and federal research through both contracts and grants.

This investigation will develop ultra-low size, weight and power (swap) laser transmitters for deep space optical communication by leveraging novel semiconductor external cavity laser designs and heterogeneous photonic integration technologies. All required photonic components will be integrated on the same chip enabling the syste-on-chip concept. The lasers will be basedon quantum dots and quantum wells, and the optical modulators will be tailored for power efficient modulation formats such as pulse position modulation, phase shift keying, and frequency shift keying. Integration will not only enable low swap but will also generate a path for scaling optical power by employing coherent combining of light from arrays of integrated diode lasers. Although some integrated laser transmitters have been developed for telecommunications applications, their performance is not sufficient for space communications. Current laser transmitters for space applications are based on discrete components. The heterogeneous photonic integration technique proposed here will utilize the best material for each individual photonic component required. Therefore the performance will better than that achieved with discrete components while significantly reducing swap. These components could include a laser emitter, laser amplifier, optical modulator, photodiode element, phase tuning element, interconnect, combiner, filter, polarization control element, and coupling element. These components could all be integrated on one common material platform, such as indium phosphide (INP), however tradeoffs in performance would exist among the different integrated components. Heterogeneous integration is motivated so that the optimal material is utilized for each component. The materials will be integrated on a single chip using wafer bonding or flip-chip bonding to maximize performance, increase reliability, and minimize swap. The primary objective of the investigation is to develop innovative photonic integration solutions for realizing high-performance and low-swap laser transmitters. A number of performance specifications will be established for the laser transmitters. To generate these specifications, the PI will collaborate with leading researchers at MIT lincoln laboratory and jet propulsion laboratory to carefully translate system-level metrics defined in the proposal solicitation into device-level metrics, and to study the feasibility of photonic integration for deep space laser transmitters. Both monolithic and heterogeneous integration techniques will be evaluated and assessed for meeting the specified performance metrics. Monolithic solutions based on INP would yield simplicity and likely smaller footprint, however, may not yield the highest performance. Although INP is the strongest candidate for a monolithic solution and the most common material for 1550-NM lasers, INP-based modulators, while compact, do not perform as well as lithium niobate (LINBO3) modulators. Heterogeneous solutions, which would likely utilize INP for laser emission and amplification, LINBO3 for modulation, and silicon for passive functions, would offer the highest performance for each component. Although 5 w average optical power may be achievable with a single laser source, coherent combining of lasers will likely be required to achieve 20 w. The integration technologies developed here will allow for realizing arrays of lasers on a single chip and will provide additional important components such as on-chip dynamic phase tuning elements for the coherent combining as well as components for performance monitoring over time. And lastly, they will provide flexibility and RE-configurability by adding functionality on the chip. This proposal is associated with the NASA space technology mission directorate (stmd) space technology research grants (strg) program.