DON27TZ02-NV003 — Growth and Production of As2S3 Waveguides

Determine and demonstrate how thin film deposits of As2S3 can be grown on an appropriate cladding material and etched to form a low loss waveguide for photonic applications of the Stimulated Brillouin Scattering (SBS) non-linearity in Radio Frequency (RF) applications.

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 optical properties of completed waveguides during the Base award is highly desirable. First demonstrations of a method of coupling to the waveguide with losses under 2 dB in the Phase I Option is also desirable. A work division where the non-profit develops the fabrication technology and the company develops the many GHz wide band amplifier and coupling technologies is one possible division of the work. A clear discussion of the dependencies and determinants of the ultimate performance as a photonic amplifier should be included in the initial proposal. It is highly desirable that, by the effort’s end, how feasible it is that by varying the optical carrier power in and the waveguide length, RF signal gains from 5 to 20 dB can be achieved with total noise figures including all coupling losses of <6 (threshold, 3 objective) dB. Paths to wafer scale fabrication yield above 90% should also be defined.

Determine the technical feasibility of using the proposed deposition and lithography techniques to produce an in-line photonic amplifier based on the SBS effect in As2S3. Demonstrate the potential compatibility of this material with use of SiN structures including surface grating couplers (desirable). Establish high reliability estimates of the ultimate performance feasible from this combination of materials, fabrication processes, and simple photonic circuit and technology roadblocks.

Develop prototype amplifier circuits via multiple design/fab/ test cycles in the Phase II Base period. Define paths to wafer scale fabrication yield above 90%. The Phase II Option period, if exercised, would then be spent improving the fabrication technology in order to deliver a specific many GHz wideband amplifier to the photonic circuit selected in collaboration with the governmental cost share source. Prepare a Phase III commercialization/transition plan.

This STTR topic is designed to create an enabling technology, that is a generic way of producing analog amplification of RF sidebands on photonic carriers so as to advance RF photonics. If the SiN out-couplers mentioned can also be perfected, these component devices could replace other inhomogeneous material technologies that are capable of producing localized, small amplification. In particular, the large size and difficult to control bursts of energy produced by EDFA amplifiers when used in not-CW applications can be avoided in full PIC circuits. Co-design of the SiN layer and a grating coupler to it will enable use in data center processor interconnects applications. In Phase III, the materials technology of this topic would be refined and combine with device maturation efforts. Commercial applications most likely in the telecommunications and SI world. Military applications will be within electromagnetic warfare systems.