Image credit: Bhupesh Kumar
We demonstrate Compact on-chip spectrometers on a silicon on insulator based on correlated periodic disordered planar waveguides with high spectral resolution and small footprint compared to conventional spectrometers. Propagation of light through the scattering medium generates a granular distribution of intensity called speckle pattern which is frequency-dependent. The working principle of the disorder spectrometer is based on the analysis of the speckle pattern. Spectral to spatial mapping is stored in a calibration transmission matrix. Later unknown spectrum is reconstructed by matrix inversion. However, current disorder-based speckle spectrometers have prohibitively high optical losses – most of the light is scattered out-of-plane, and never reaches the detection region, resulting in poor efficiency and signal to noise ratio. we propose a game-changing, disorder-enhanced wavelength separation region that creates an in-plane speckle and simultaneously suppresses out-of-plane scattering, leading to compact and sensitive high-resolution spectrometers. Controlled disorder, with known scattering statistics, is superposed onto a period PhC lattice. The device combines the ideal parts of random and perfectly ordered photonic devices and provides the missing component for high-resolution, USB-key-sized spectrometers. Advantage of the random spectrometer is that it can operate over an extremely broad frequency range without any structural modification. This is not the case in grating-based spectrometer, which requires a rotation of the grating to diffract light of varying frequency to the detector.
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