Fresnel diffraction effects in Fourier-transform arrayed waveguide grating spectrometer

Abstract

Abstract:We present an analysis of Fourier-transform arrayed waveguide gratings in the Fresnel diffraction regime. We report a distinct spatial modulation of the interference pattern referred to as the Moiré-Talbot effect. The effect and its influence in a FT AWG device is explained by deriving an original analytical expression for the modulated field, and is also confirmed by numerical simulations using the angular spectrum method to solve the Fresnel diffraction integral. We illustrate the retrieval of spectral information in a waveguide Fourier-transform spectrometer in the presence of the Moiré-Talbot effect. The simulated device comprises two interleaved waveguide arrays each with 180 waveguides and the interference order of 40. It is designed with a Rayleigh spectral resolution of 0.1 nm and 8 nm bandwidth at wavelength λ ∼ 1.5 μm. We also demonstrate by numerical simulations that the spectrometer crosstalk is reduced from −20 dB to −40 dB by Gaussian apodization.

Evaluation of Hyperspectral Snapshot Imagers onboard Nanosatellite Clusters for Multi-Angular Remote Sensing

“…For waveguide spectrometers, given the spectral ranges in Figure 11 and Equation 15, the total number of waveguides needed will be 2 * 85 = 170 -which has been demonstrated in the laboratory and published in literature 57,58 . For a 6 μm pitch of the waveguides 57 , the chip breadth will be ~12 mm (6 μm pitch times 200 waveguides).…”

“…For a 6 μm pitch of the waveguides 57 , the chip breadth will be ~12 mm (6 μm pitch times 200 waveguides). The length of the chip needed would be given by L max in Equation 16 57 where R is the resolution, is the wavenumber and is the mode effective index. For the wavelength resolutions and central wavelengths proposed in our spectrometer's 4 band ranges, the corresponding L max for the ranges are 18.75 mm, 15 mm, 47.95 mm and 33.3 mm.…”

Miniaturization of optical spectroscopes into Fresnel microspectrometers

“…2 Most of today's modern optical spectroscopes are founded upon Fraunhofer's diffraction principle except for a few noble instruments such as the Fourier transform infra-red spectroscope, fiber Bragg grating spectroscope and Raman spectroscope. [3][4][5][6][7][8][9][10] In Fraunhofer diffraction, the first order diffracted light has an angular dispersion with respect to the wavelength of light. Periodic linear lines, with constant gap spacing, reflect and diffract incoming photons into different angles with respect to the wavelengths.…”