Study Of Broadband Silicon Waveguides And Devices In The Mid-infrared

The mid-infrared(mid-IR)regime generally refers to the spectrum with a wavelength range of 2 to 20 μm.This band includes the “fingerprint regime” for many chemical and biological molecules,as well as two atmospheric transparency windows of 3 to 5 μm and 8 to 14 μm.Thus,it has great potential on monitoring,free space communications,laser ranging,remote sensing and infrared countermeasures.Silicon-based optoelectronics devices are based on complementary metal oxide semiconductor(COMS)compatible technology to realize integrated,broadband and low-loss optical devices,which has been a research hotspot in recent years.The advantages are as follows: First,the silicon waveguide has a low-loss transmission window in the mid-IR regime.Secondly,the two-photon absorption for the wavelength over 2.2 μm is negligible.Finally,the 2 μm wave band is proposed as the potential candidate for next generation telecommunications,owing to the gain spectrum of the thulium-doped fiber amplifier.Therefore,realizing low-loss and high-efficiency midinfrared devices on a silicon-based platform with large-bandwidth in both telecommunication band and the mid-IR is worthy of further exploration.In this paper,silicon-based mid-IR broadband optoelectronic devices were investigated.This study introduced the operation principles,numerical calculation methods and design methods.A multi-mode interferometer(MMI)that works in the 1.55 μm band and the 2 μm band,a cascaded Mach-Zehnder wavelength filters,a power splitter which works at 2 μm were designed and fabricated.Then a power splitter works at 3.8 μm as well as a largescanning-angle optical phased array(OPA)were designed.The main contents are as follows:(1)The working principle of silicon-based waveguides and its mode field distribution of the mid-IR regime are discussed.Taking straight waveguides and directional couplers as examples,the basic processes of simulating are shown.(2)A broadband MMI and a 2 μm cascaded Mach-Zehnder wavelength filter are designed and fabricated.First,the meaning and conventional methods of these two devices are proposed.The simulation results are then discussed.A coupling platform is built to test the device performance of these two devices and the experimental results were discussed.(3)The basic principle of power splitter is introduced and two types of power splitter,one type based on silicon-on-insulator platform and the other is based on germanium-on-silicon platform are investigated.They work at 2 μm and 3.8 μm respectively.The 2 μm power splitter is fabricated and performances are then discussed.(4)Based on the research of multiple broadband devices on the silicon-on-insulator platform,an OPA that works in both the communication band and the 2 μm band is proposed and designed.It can realize One-dimensional large-angle scanning.The basic parameters of OPA are analyzed,and simulation results are discussed.