Fully programmable holographic diffraction grating for NIR synthetic spectra generation in correlation spectroscopy

Abstract

Correlation spectroscopy is a powerful analytical tool for gaseous species detection, with improved sensitivity and enhanced selectivity. The application in the field of this spectroscopic technique, for remote sensing purposes, has long been prevented due to the necessity to equip the instrument with a reference ‘cell’ containing an actual sample of the target molecules to perform correlation measurements. A new photonic chip, based on LNOI (lithium niobate on insulator) substrates, has been developed and tested by applying MEOS (micro electro optical system) micromachining techniques. The novel photonic chip allows to dynamically generate synthetic spectra of in principle any chemical species detectable in the transparency range of LNOI (350 nm – 5500 nm wavelength). The synthetic spectrum is generated by producing a well-defined holographic phase map in the active layer of the LNOI substrate, by applying through an array of driving electrodes a calculated voltage distribution, thus rendering the photonic chip fully programmable even in real-time. The developed photonic chip is therefore able to replace the classical sample cell and can be also used to act as a reference signal modulator, as requested in a correlation spectrometer. In this work, a description of the developed technology is reported together with some preliminary results obtained in different experimental conditions.