High Optical Quality Factor Arsenic Tri-Sulfide Free-standing Microdisks On A Silicon Chip

In recent years, optical micro-resonators have attracted much attention. Whispering gallery mode(WGM) optical micro-resonator, which has ultra-high quality factor and relatively low mode volume, indicates great potential on optical research. With great compatibility with CMOS process, chip-based silica micro-WGM resonator has been studied on a world wide scale and great progress have been achieved. However, silica is untransparent in mid-infrared region and has low nonlinear coefficient, which makes it necessary to fabricate ultra-high Q micro-resonators in the mid-infrared wavelength region using other material. Owning to its wide mid-IR transmission window and high nonlinearity, chalcogenide glass is a promising material for mid-IR photonics. So far, many chalcogenide optical devices have been reported.Here, for the first time we fabricate a free-standing AS2S3 microdisk resonator on a silicon chip with an intrinsic optical quality factor higher than 2×106. The fabrication process of As2S3 microdisk resonators is CMOS compatible, which makes it can be massively produced. The main content of the thesis is listed as follows:1. Physical vapor deposition of As2S3 film process is studied. High quality As2S3 film has been achieved by reducing deposition rate and cleaning the vacuum chamber. SEM image of the deposited film indicates very smooth film surface, which ensures low surface scattering. Annealing effect on the As2S3 film has also been studied.2. By using a sandwich structure of an AS2S3 microdisk covered by photoresist and silica microdisk, we successfully undercut the silicon pillar using SF6 without etching the As2S3 microdisk. Smooth sidewall of the As2S3 disk results in low scattering loss.3. A tapered silica fiber is used to measure the optical quality factor of the As2S3 microdisk resonator. Intrinsic optical quality factor as high as 2.1×106 is obtained from a 60 μm As2S3 microdisk resonator with a thickness of 900 nm. Also, coupling depth of 98.6% is obtained from another sample with an optical quality factor of 8.4×105. The diameter and the thickness of this microdisk is 50 μm and 900 nm, respectively.