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Research On Fabrication And Characteristics Of Subwavelength Metallic Grating-based Polarimetric Sensor

Posted on:2017-01-13Degree:DoctorType:Dissertation
Country:ChinaCandidate:R WangFull Text:PDF
GTID:1108330503464323Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
Polarization, as an important element of electromagnetic field, is strongly dependent on surface and internal properties of the target, as well as the detection angle. Polarimetric imaging technique has a great potential to further improve target recognition. Compared with traditional polarimetric imaging, division of focal plane(Do FP) polarimetric imaging has distinct advantages of concise light path and instantaneous Stokes parameters, etc. In this paper, subwavelength metallic grating(SMG) as polarizer is monolithically integrated on In Ga As sensor, in order to detect polarization information in short-wave infrared(SWIR). Firstly, according to the work wavelength of In Ga As sensor, the structures of SMG were carefully designed. The influence of SMG parameters on polarization behavior was systematically simulated via finite-difference time-domain(FDTD) method, providing effective reference for following experimental fabrication. Secondly, two sets of polarimetric testing systems were built, which were capable of characterizing SMG polarizer and SMG-based In Ga As polarimetric sensor, respectively. Thirdly, the designed SMGs were fabricated on In P substrate by electron beam lithography(EBL). The optical performance of SMG polarizer was also measured and analyzed, finalizing the SMG parameters used in In Ga As polarimetric sensor. Finally, the In Ga As Do FP polarimetric sensor was successfully designed, fabricated and characterized based on previous work.The simulation of SMG integrated on In Ga As sensor was systematically studied using FDTD method. The polarization capability of SMG was investigated with different metal materials(Au, Al and Ag) and varying grating period in the range of 0.1-1.2 μm. It was found that when SMG was integrated directly on In P substrate, namely Metal grating/In P structure, SPP resonance was excited at 1.35 μm. The existence of SPP had a negative effect on TM transmission and extinction ratio obviously. SPP resonance could be effectively eliminated by inserting a layer of Si O2 into metal graing/In P interface to form Metal grating/Si O2/In P structure, leading to improved polarization capability. For further optimizing Metal grating/Si O2/In P structure, the influences of grating parameters(metal material, period, thickness and duty cycle) and Si O2 thickness on polarization performance were fully demonstrated. The results showed grating period was the most important parameter closely related to polarization capability. Moreover, Si O2 layer could play a role of anti-reflection layer at some specific wavelengths by adjusting its thickness. Given the current fabrication condition, the grating parameters are fixed to be: Al material, period = 400 nm, grating thickness = 100 nm, duty cycle = 0.5, Si O2 thickness = 100 nm.Two sets of polarimetric testing systems were built to characterize SMG polarizer and SMG-based In Ga As polarimetric sensor, respectively. Each testing system consists of two subsystems. The first subsystem was based on a FTIR spectrometer, which aimed to obtain the polarimetric transmission spectrum in short-wave infrared wavelength. The second subsystem was based on a 1342 nm laser, designed to calibrate the polarimetric transmission spectrum. On this basis, we introduced several important optical components, the design of light path, testing principle and data processing, etc. Then, the error sources of testing system were analyzed. It was found that FTIR-based subsystem would create a noticeable deviation to the results, because the incident light was not collimated. Utilizing these testing systems, it was possible to measure the polarization performance(TM, TE transmission, extinction ratio spectra) as a function of incident wavelength, incident angle and polarization angle.Under the guidance of simulation, three types of SMG polarizer were fabricated by EBL, which were Au grating/In P、Au grating/Si O2/In P and Al grating/Si O2/In P, respectively. Polarimetric testing systems were applied to characterize these fabricated polarizers, indicating a good agreement between simulated and measured data. The Au grating/In P structure proved that SPP resonance led to the decrease of TM transmission at 1.35 μm. The Au grating/Si O2/In P structure demonstrated that the SPP resonance could be totally removed with the help of a dielectric layer Si O2 of lower permittivity. The cavity mode started to play a leading role, improving the TM transmission and extinction ratio significantly. Then, by comparing Au grating/Si O2/In P and Al grating/Si O2/In P structures, it was found that Al grating presented a much better polarization behavior than Au grating. Finally, the optimum sample was chosen to be integrated on In Ga As sensor, with basic parameters of Al material, period = 400 nm, grating thickness = 100 nm, duty cycle = 0.5, Si O2 thickness = 100 nm. The measured polarization data at 1.35 μm were: TM transmission = 63.78%, TE transmission = 1.07%, extinction ratio = 60.In Ga As Do FP polarimetric sensor was fabricated, measured and analyzed. We explored the technical compatibility between In Ga As sensor and SMG in fabrication process. It was found that EBL process, such as high-temperature bake, e-beam radiation and long-time immergence in acetone, has little influence on front-illuminated In Ga As sensor. 10×1 linear array front-illuminated In Ga As polarimetric sensor was designed and fabricated, with pixel of four polarization orientations(0°,90°,45°、135°) and non-polarized, pixel area of 100 μm×84 μm and pixel pitch of 100 μm. Both Polarimetric characterization and non-polarimetric characterization were performed on the In Ga As polarimetric sensor. It shows the extinction ratios of 0°,90°,45°、135° polarized pixels were 16.59、26.28、33.30、24.37,respectively. Although the peak detectivity of polarized pixel is much smaller than non-polarized pixel, polarized peak detectivity could still reach above 8E11 cm Hz1/2/W.
Keywords/Search Tags:subwavelength metallic grating, In Ga As sensor, Surface plasmon polariton, finite-difference time-domain, infrared polarimetric imaging
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