On-Chip Fourier Transform Spectrometer on Thin Film Lithium Niobate

We demonstrated experimentally an on-chip Fourier transform spectrometer based on an ultra-low half-wave voltage electro-optic modulator fabricated on thin film lithium niobate platform. The spectrometer has a pair of identical folded modulation arms with a waveguide length of 15.34 cm and an electrode length of 11.2 cm, showing a half-wave voltage as low as 0.266 V at 1550 nm wavelength. The wavelength-dependent losses of the fabricated spectrometer were measured and hence the transfer function of the spectrometer was obtained. Further, by applying a ramp voltage ranging from −100 V to 100 V to the electrodes, the intensity-voltage interferogram was obtained with a photodetector. The spectrum of the input light was retrieved by performing a Fourier transform on the interferogram combined with the wavelength-dependent equation of the half-wave voltage of the spectrometer. The results indicate that our fabricated spectrometer can achieve a resolution of 5.32 nm, an operation bandwidth beyond 100 nm, and a sub-microsecond measurement time.