Design And Fabrication Of Suspended-waveguide-based Silicon Thermo-optic Devices

Silicon photonics has become a promising technology for next-generation on-chip optical network due to the advantages of low power consumption,low cost,high-density integration and complementary metal-oxide-semiconductor(CMOS)compatibility.Tunable photonic integrated devices are one of key components and have attracted much attention for its ability to achieve flexible and reconfigurable optical network.Furthermore,since silicon has a high thermo-optic coefficient and a high heat conductivity,thermal method is often used to achieve efficient tuning.Nevertheless,the high power consumption limits their applications in photonic integrated circuits.In this thesis,the high power consumption of thermally tuned silicon-based photonic integrated devices with long waveguide structures are investigated.The specific works are as follows:(1)An air gap beneath the waveguide is designed and demonstrated to form a suspended waveguide,the ultra-low thermal conductivity of air hinders the heat from vertically flowing,thus leading to a significant reduction of power consumption;Nevertheless,the undercut structure may degrade the mechanical robustness and the temporal response.To solve the problem,the periodic lateral silicon pillars are designed to substantially improve the mechanical stability and reasonably decrease the temporal response.Therefore,the overall structure has a high performance.(2)Based on the previously designed suspended waveguide with lateral silicon pillars,keeping with a sidewall Bragg grating as the filtering element,we design and fabricate a high performance broadband and a narrow-band band-stop filter using uniform gratings and misaligned gratings,respectively.The experimental results show that the fabricated device has a high power efficiency,a reasonable temporal response and a relatively high mechanical strength,satisfying well with the theoretical predictions.(3)Firstly,we design a ridge-waveguide-based 3 dB wavelength-independent directional coupler(WIDC)using transfer matrix method(TMM),then we design and fabricate a broadband high-performance thermo-optic Mach-Zehnder switch(MZS)by combining the designed WIDC and the laterally-supported suspended phase arms that was optimized before.The tested results demonstrate that the fabricated MZS has a low switching power,fast response,low insertion loss and compact size.The proposed device has a more superior performance for potential applications in photonic integrated circuits(PICs).