On-chip interrogator based on Fourier Transform spectroscopy.

2018 
We designed and characterized a new interrogator based on integrated Fourier Transform spectroscopy. To the best of our knowledge, this is the first integrated Fourier Transform spectrometer used for such application. It consists of a planar spatial heterodyne spectrometer based on Fourier transform (SHS-FT), which is implemented using an array of Mach-Zehnder interferometers (MZIs) with different optical path differences. Each MZI employs a 3$\times$3 multi-mode interferometer, allowing the retrieval of the complex Fourier coefficients. We derive a system of non-linear equations whose solution gives the modulation of the peak wavelength of the sensors spectra. Two cases are studied here: (a) for two photonic sensors, where we solve the non-linear system analytically, we discuss the origin of the non physical solutions and how to identify them; (b) for multiple sensors we numerically solved the non-linear system using Newton's method. The minimum modulation amplitude experimentally obtained is 400 fm.
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