Near Infrared Fourier Transform Spectrophotometry based on a LiNbO3 Waveguide Mach-Zehnder Interferometer with Push-pull Electrodes

Abstract

A miniature stationary time-scanning Fourier Transform (FT) spectrometer was realized using a fiber-coupled LiNbO3 (LN) waveguide Mach-Zehnder interferometer (MZI) with push-pull electrodes. The spectrometer operates in the near infrared (NIR) region in which the MZI is a monomode device and allows to use a nonlinear voltage ramp to modulate the optical pathlength difference (OPD). The monotonous wavelength dependence of the half-wave voltage for the MZI used was measured using multiple DFB lasers of different wavelengths. The spectrometer utilizes the measured dispersion of half-wave voltage to convert the intermediate spectrum retrieved from the intensity-vs-voltage interferogram into the power spectrum of the input light source. In the previous work the spectrometer has been demonstrated to be able to accurately determine the laser wavelength. In this work, the spectrometer with a halogen-tungsten lamp source was used to implement the NIR absorption measurements of liquid and solid samples. Figure 1 shows the experimental results obtained with the miniature stationary FT spectrometer. Despite the lower spectral resolution of the present FT spectrometer, the peak position at 1451.5nm in the absorption spectrum exactly corresponds to the maximum absorption of water indicated in the literature.1