Design of a lithium niobate Fabry-Perot étalon-based spectrometer

The design of a tunable Fabry-Perot étalon-based filter that has a passband of 0.01 nm and a free spectral band larger than 50 nm when operated in the center of the visible spectrum is described. The filter consists of two Y-cut lithium niobate étalons having thicknesses in a vernier ratio. The polarization state of light passing through the tandem étalons is rotated 90 degrees before again being transmitted through the étalon pair. If the components are arranged in a symmetrical manner, the filter will operate with unpolarized incident light. Each étalon in double pass will have a greater transmittance than two individual étalons of the same average optical thicknesses, since variations in the physical thickness due to fabrication errors are correlated.