Enhanced thermo-optic effects in silicon nitride photonic integrated circuits via polymer claddings
Journal of Nanophotonics(2023)
摘要
Silicon nitride (SiN) has been receiving increased attention for photonic integrated circuits (PICs) due to its ultra-low optical losses, phase stability, and broadband transparency. However, SiN waveguides have a low thermo-optic coefficient and exhibit weak electro-optic effects. For this reason, most foundry-processed SiN PICs remain passive or exhibit inefficient tuning. In this work, we investigate polymer claddings to enhance the thermo-optic phase shifting in foundry-processed low-loss, thin core SiN PICs. We first develop a thermal testing setup and measure the response of standard foundry SiN / SiO2 waveguides. By taking advantage of the differing TE and TM modal overlap with the SiN core and SiO2 cladding, we extract the LPCVD-SiN thermo-optic coefficient as dnSiN / dT = 2.57 × 10 − 5 / ° C at λ = 1550 nm and dnSiN / dT = 2.82 × 10 − 5 / ° C at λ = 780 nm. We next consider SiN waveguides in which the top SiO2 cladding is replaced with a spin-coated thermo-optic polymer. The thin waveguide core (tSiN = 150 to 220 nm) enables a weakly confined mode with a large overlap with the top polymer cladding. Measurements at λ = 780 nm wavelength show up to a 12-fold improvement in the thermo-optic phase shift of these polymer-cladded SiN waveguides compared with SiO2 cladded devices while inducing negligible excess loss. Finally, we show broadband Mach–Zehnder interferometer measurements demonstrating thermo-optic tuning at visible wavelengths. The simple spin-coat post-processing of foundry SiN PICs in this work offers a potential path toward efficient optical phase shifting in low-loss SiN waveguides over a broad wavelength range
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关键词
polymer claddings,silicon nitride,thermo-optic
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