Performance Optimization Of Infrared Spectroscopy And Miniaturization Of Fourier Transform Infrared Spectrometers

Infrared(IR)spectroscopy can achieve the real-time and in-situ quantitative detection of substances,providing an efficient analytical technique for the development of biomedical engineering.This thesis is dedicated to improving and developing the technology and instrumentation for IR spectroscopic detection.Performance optimization of IR detection was realized through physical and digital optimization methods.Moreover,on-chip miniaturization of IR spectroscopic devices was promoted for greatly improving the flexibility and reducing the cost in the IR detection.In this way,IR spectroscopy can have a wider application in various complex scenarios.The main research contents in this thesis include:1.In the physical optimization of IR detection systems,three schemes were proposed and validated for the light source,absorption sampling and spectral detection,respectively.(?)In the optimization of IR source modulation,light modulation and multi-channel scanning detection were combined effectively with a galvanometer,realizing better modulation efficiency as well as a common optical path for nondispersive infrared detection.(?)In the optimization of transmission probes for liquid detection,the probe body was manufactured by integral molding of glass,realizing better versatility and reliability of IR liquid detection.(?)In the optimization of interferogram sampling,equal-time hardware-triggering oversampling was applied,increasing the sampling frequency and ensuring the sampling accuracy.2.In the digital optimization of IR detection performance,the digital Jacquinot stop(J-Stop)method was proposed and validated to address the conflict between the optical throughput and spectral resolution in the Fourier transform spectrometers(FTSs).In the digital J-Stop method,the high-throughput Fourier transform spectra with width-broadening and peak-shifting are recovered through the numerical iterative calculation,realizing high signal-to-noise ratio(SNR)and high spectral resolution as well as better wavenumber accuracy in the IR detection.The digital optimization is based on the physical mechanism of large-aperture J-Stop affecting spectral performance.In addition,the digital J-Stop method can be introduced into the grating spectrometers,addressing the strong conflict between the optical throughput and spectral resolution caused by the physical input slit.3.In the on-chip miniaturization of IR spectroscopic devices,two new techniques were proposed and validated to break through the performance and application limitations on the silicon photonic spatial heterodyne FTS(SH-FTS).(?)Dual-polarized detection was applied to alleviate the conflict between the spectral performance and device footprint.The propagation constant difference between two orthogonal polarizations,which results from the birefringence effect of rectangular waveguides,doubles the sampling optical path difference points provided by a single Mach-Zehnder interferometer(MZI).(?)Polarization-insensitive two-dimensional grating couplers were applied as the input port of an IR system,splitting the two orthogonal polarizations of incident light and then coupling each polarization to the transverse electric(TE)mode of waveguides.Spectra of both polarizations are measured by the regular polarization-sensitive MZI array in the TE-polarized operation,achieving the polarization-insensitive spectral detection.The main innovations in this thesis include:1.The digital J-Stop method was proposed to break through the conflict between the optical throughput and spectral resolution in the FTSs for the first time.The widthbroadening in the Fourier transform spectra caused by the large-aperture J-Stop can be removed,and the SNR can be improved by 3 times.2.The on-chip silicon photonic SH-FTSs by dual-polarized detection were proposed based on the propagation constant difference resulting from the birefringence effect of rectangular waveguides,halving the MZI number and reducing the device footprint by 25%.3.The on-chip polarization-insensitive SH-FTSs were proposed using a twodimensional grating coupler.The two orthogonal polarizations can be simultaneously measured by a single MZI array in the bidirectional operation,ensuring the uniformity of spectral measurement.In this way,the polarization limitation on the silicon photonic SH-FTSs can be removed,which comes from the birefringence effect of rectangular waveguides.