Disorder enhanced on-chip spectrometers.

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The ability to accurately measure the power and frequency (or wavelength) distribution of an optical signal is crucial to a vast range of applications, for spectroscopy in medicine, ensuring the safety of food or pharmaceuticals to remote sensing of gasses and fundamental science, e.g. characterising short laser pulses or finding the atmospheres of extrasolar planets. Currently, this is achieved using Optical Spectrum analyzers or optical monochromators, which have a key limitation. To achieve high-resolution they need a large optical path length and therefore large footprint (optical path length on the order of 0.5-1 m is common). Thus these devices are bulky and expensive. While not an issue for lab-based low-volume applications, this excludes their use - and thus the use of high-resolution spectroscopy - in large volume, or footprint and weight-sensitive applications, e.g. integration into lab-on-a-chip devices, mobile phones and low mass satellites (e.g. cube-sat). These applications can only be served by integrated on-chip spectrometers. Here the use of speckle spectrometers, using the random scattering of light to achieve a high wavelength resolution in an ultra-small footprint would be highly promising if it were not for the case that typical the multiple scattering needed to create the speckle results in most of the light being scattered out of the device before it can be detected. However, over the last decade, several groups (including myself) have shown that the statistical distribution of scattering sites can be used to control the amount and direction (e.g. within the plane of the device vs out-of-plane) of light scattering. In this project we merge these advances with speckle spectrometers, i.e. using controlled disorder to efficiently generate a speckle pattern, while virtually eliminating out-of-plane scattering and optical losses. Building on this advance we will demonstrate a high resolution, low footprint on-chip spectrometer that outperforms the state of the art by orders of magnitude (in device footprint) without sacrificing the device resolution. We will also demonstrate that these devices are suitable for future large scale manufacturing, using pre-existing CMOS facilities, are suitable for gas spectroscopy and laser pulse spectrum analysis and compatible with future integration with optical detectors for a direct electronic readout. This would present a game-changing advance in the field of integrated spectrometers and lay the foundation for future commercialization of integrated speckle spectrometers.