Growth and Production of As2S3 Waveguides

STTR topic DON27TZ02-NV003 (U.S. Department of Defense – Navy), Phase I and II. Open to U.S. small businesses; STTR projects partner with a U.S. research institution. Opens: December 2, 2026. Closes: January 6, 2027. Multiple academic papers have indicated that the reverse mode of the SBS interaction between acoustic phonons and coherent 1.55 µm photons can cause Stoke’s peak gain on RF sidebands. It is desirable to harvest that effect for application in the burgeoning field of RF photonics. However, for that to happen, it is desirable that methods be developed to optimize the growth and etching of quasi-epitaxial As2S3, the material with the largest known SBS coefficient. In order to achieve low optical loss, achieving extremely low surface roughness of as-deposited films (< 10 nm rms roughness) is required plus ways to preserve that in producing waveguides of around 100 nm thickness and with high confinement bottom and top cladding. While atomic layer deposition (ALD) growth has produced other chalcogenides with very flat, conformal surfaces, it has not been used for As2S3; moreover, that other material was amorphous as deposited and drastically changed optical properties when crystalized. It may be that highly directional growth onto pre-etched substrate mesas produce better performance waveguides in which to produce amplification. Lastly, it is essential to demonstrate a way to achieve extremely low loss signal transfer on and off the die if RF photonics is to outperform conventional electronics in the future. Phase I proposals for this STTR topic shall name the deposition and etching techniques that will be developed under the base award and estimate the surface smoothness of both the as-deposited material and the finished waveguides. The work plan must allow the validation of these estimates during the Base award so that the preliminary Phase II plan can define with good certainty the properties achievable in Phase II if awarded. Measurement of the…