Novel Integrated Optical Waveguides And Their Applications In Optical Communications For The Mid-infrared

The mid-IR regime(2 to 20 ?m)covers both atmospheric transmission windows and the material “fingerprint region” for various chemical and biological molecules.Thus it is proving to be very important for a wide range of applications including sensing,medical diagnostics,free space communications,thermal imaging,and infrared countermeasures.Mid-infrared semiconductor photonics is an emerging field with wide-ranging applications.One stream of research is focused on extending the well-developed silicon-based waveguide platforms into longer wavelength regimes because of the inherent transparency window of silicon in the mid-infrared regime.The 2 ?m wave is the most interesting spectral for the next generation telecommunications,thanks to the gain spectrum of the thulium-doped fiber amplifier and the lowest loss window of the hollow-core band-gap crystal fiber.The integrated CMOS compatible photonic platform like silicon-on-insulator(SOI)could be the preferred solution as its advantages such as high volume,small footprint,and low-cost fabrication still exist for this new wavelength band and many techniques and equipment available for telecom applications can be seamlessly mitigated into this region.In this study,integrated silicon devices for 2 ?m communication were investigated,including thermo-optic switches and mode(de)multiplexers.The operation principle,characteristic parameters,and numerical calculation methods were developed.A 2 ?m thermo-optic switch based on SOI waveguide was proposed and characterized.An on-chip mode(de)multiplexer based on asymmetric directional coupler was also designed and fabricated.A 2 ?m mode-division multiplexing communication system was built,where the 2-channel and 4-channel mode(de)multiplexer were tested.The thesis is organized as follows:(1)In Chapter 2,light guiding mechanism of the silicon-based optical waveguide,loss measurement,and mode distribution are introduced;simulation of passive devices such as a straight waveguide,multimode interferometer,asymmetric directional coupler,and grating coupler are presented.(2)In Chapter 3,a 2 ?m thermal-optical switch based on silicon-on-insulator waveguides is designed.The testing results of the vertical grating coupler and its performance optimization scheme are investigated.The simulation and experimental results of the vertical grating coupler are introduced.The working principle of the optical switch and the heat distribution are exhibited.In addition,the power consumption and response time of the 2 ?m thermo-optical switch are characterized.(3)In Chapter 4,a 2 ?m multi-channel mode(de)multiplexer based on cascaded asymmetric directional coupler is designed.The working principle and design process of the device is introduced.The 2 ?m on-chip communication system is built,and the two channels and four channels devices are respectively tested with detailed discussions about the experimental results.(4)Finally,Chapter 5 summarises the work over the master period and outlines future experimental possibilities to follow the work presented in this report.