All integrated Lithium Niobate Standing Wave Fourier Transform Spectrometer to improve sampling resolution

High resolution spectrometers are nowadays developed in compact devices using passive integrated optics. The stationary wave integrated Fourier transform spectrometer [1,2] has in particular proved its efficiency for the high-rate high-resolution analysis of laser sources [3], without any moving parts, in the visible and near–IR domain. The key point of this approach is to obtain in a channel waveguide a standing wave by interference of a forward and backward beam, the last obtained by Fresnel reflexion at the waveguide output. Then, the standing wave is sampled using diffusing centers set on the waveguide's surface. The regular and discrete measurement of the wave's amplitude by the sampling centers allows obtaining the spectrum of the source, thanks to an adapted Fourier-like transform. But, since each of them must be coupled with one pixel of a linear detector array, the size of the current sensors (typically 20 µm) is a limit for a complete sampling of the wave, according to the Nyquist-Shannon criteria (typically (λ/2n)/2 = 150 nm for λ = 1 µm and n = 1.5).