Miniature Fourier transform spectrometer based on wavelength dependence of half-wave voltage of a LiNbO_3 waveguide interferometer

Abstract

A simple and reliable spectrum-retrieval method was proposed for the development of miniature stationary Fourier transform (FT) spectrometers based on a LiNbO₃ (LN) waveguide Mach-Zehnder interferometer (MZI) modulator. The method takes into account the wavelength dependence of the optical pathlength difference (OPD) and allows us to use a nonlinear voltage ramp to modulate the OPD. The method is based on the dispersion of the half-wave voltage, which was measured to be a monotonous polynomial function of the wavelength for the LN waveguide MZI used. With the measured dispersion of the half-wave voltage, the OPD, as a linear function of the modulating voltage, can be accurately determined at each wavelength in the near-infrared region in which the MZI used is a single-mode device. A prototype FT spectrometer was prepared using a LN waveguide MZI modulator based on the above method. The experimental results demonstrated that the spectrometer can be used for accurate determination of the laser wavelength and for liquid absorptiometry.

Fourier transform spectrometer on silicon with thermo-optic non-linearity and dispersion correction

“…In the latter, a spatial—rather than temporal—interferogram is formed by the standing wave pattern generated by the interference of two counter-propagating beams inside a waveguide. Designs based on the traditional Fourier transform spectrometer (FTS) 29 , in which a temporal interferogram is measured varying the optical path between the arms of an interferometer, have also been investigated using micro-electro-mechanical systems 15 , 16 and lithium-niobate planar photonic circuits 17 .…”

A Prototype Stationary Fourier Transform Spectrometer for Near-Infrared Absorption Spectroscopy

“…The values of V π (Λ) at various wavelengths were experimentally measured using a series of lasers having different wavelengths. 26 The measured interferogram is processed with the discrete Fourier transform method, leading to a plot of the input power against the half-wave voltage. By using the monotonic relationship between wavelength and the half-wave voltage obtained in the NIR region in which the MZI used is a single-mode device (Fig.…”

“…The findings indicate that the prototype FTS has a low spectral resolution, but even so it can be used to measure laser wavelength. 26 The spectral resolution of the prototype FTS can be enhanced by simply increasing the length of the modulating electrode, 26,27 which, however, will lead to an increased size of the device. An alternative approach to enhancing the spectral resolution while keeping the device size unchanged is to use the end-face reflection structure.…”

“…19 To overcome this challenge, a mirrorless miniature FTS was proposed based on integrated optical technology. 20–26 The two waveguides were applied to creation of a miniature FTS: a liquid-crystal-clad waveguide 24 and a LiNbO 3 (LN) waveguide Mach-Zehnder interferometer (MZI) with push-pull electrodes. 25–27 These waveguides make use of the electro-optical (EO) effect to modulate the optical path length difference (OPD), rendering the miniature FTS free of movable components and high modulation speed.…”

“…In previous work, a prototype mirrorless FTS was constructed using an LN waveguide MZI device combined with a novel spectrum retrieval method. 26 This method is based on the wavelength dependence of half-wave voltage of the MZI, enabling us to precisely recover the spectrum of input light source from the interferogram generated with linear or nonlinear scanning of the modulating voltage. This work demonstrates the absorption spectroscopy capability of the prototype mirrorless FTS.…”