visible silicon photonics

1. High Quality Factor Microdisk Resonators for Chip-scale Visible Sensing

2. overview 2 Introduction and motivation High Q SiN microcavities on substrate Critical Coupling to SiN waveguides Experimental demonstration Conclusions

3. SiN for Visible Sensing 3 Multi-modal sensing in visible Low water absorption [2] Fluorescence sensing Raman sensing :nanoparticles’ plasmon Silicon Nitride High index, low loss, low auto-fluorescence background Ease of fabrication (Planar/multilayer) (LPCVD) Source/detector integration (CMOS) [2] lsbu.ac.uk/water/

4. Fabrication of SiNMicrodisks 4 StoichiometricSiN on thermal oxide Electron beam lithography on ZEP reflow of ZEP ICP etching with CF4 gas (85deg, 5nm roughness) 200 nm 1 mm

5. Critical Coupling 5 Conventional straight WG Short coupling length-> narrow gaps Pedestal[1] Controlled etching time Increasing field overlap Pulley Coupling Waveguide looping around the disk Increasing coupling length R=20mm

6. Straight waveguide 6 Semi-phase-matching Short coupling length-> narrow gaps

7. Coupling vs. Waveguide Width 7

8. Pulley Scheme 8 Pulley Significant increase in coupling length Less coupling induced loss Phase matching -> mode selective Sensitive to waveguide width Large gap -> ZEP reflow for smooth sidewalls

9. Pulley Scheme’s Phase Matching 9 Long coupling length Strict phase matching requirements Sensitive to waveguide width for phase matching nwg=nd [R/(R+g+w/2)] r=10 mm

10. Disk-Waveguide Phase Matching 10 Phase matching optimized by choosing the waveguide width r=10 mm g= 100 nm g= 400 nm TE TE TM TE1 TM TE1 TE2 TE2 TM1

11. Pedestal and Pulley Coupling to R=100 mm disk 11 Phase matching larger gaps, single mode operation Gap=400 nm Normalized trasnmission (dB) Pulley Coupling Pedestal=40 nm Wavelength (nm) Wavelength (nm)

12. Effect of Phase Matching 12

13. m and W for phase matching 13

14. Splitting 14

15. Conclusions 15 SiN is an excellent material for visible and NIR photonics applications. By optimizing the fabrication process, microdisks with Qs as high as 8M can be achieved. Critical coupling to adjacent waveguides is achieved by using pedestal and pulley coupling schemes. Pulley coupling also enables critical coupling to selected mode(s) of the cavity without sacrificing Q.

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