Design study of random spectrometers for applications at optical frequencies

TL;DR

This paper presents a design study of compact, high-resolution random spectrometers based on disordered waveguides, emphasizing the role of scattering properties and practical implementation in integrated optics.

Contribution

It combines theoretical and simulation approaches to optimize random spectrometer design, showing effective performance without requiring a fully diffusive regime.

Findings

Performance depends on scattering efficiency and asymmetry parameter.

Efficient devices are achievable with weakly scattering low-index inclusions.

Design enables compact spectrometers for visible and near-infrared applications.

Abstract

Compact spectrometers based on disordered planar waveguides exhibit a rather high resolution with a relatively small footprint as compared to conventional spectrometers. This is achieved by multiple scattering of light which - if properly engineered - significantly enhances the effective optical path length. Here a design study of random spectrometers for TE- and TM-polarized light is presented that combines the results of Mie theory, multiple-scattering theory and full electromagnetic simulations. It is shown that the performance of such random spectrometers depends on single scattering quantities, notably on the overall scattering efficiency and the asymmetry parameter. Further, the study shows that a well-developed diffusive regime is not required in practice and that a standard integrated-optical layout is sufficient to obtain efficient devices even for rather weakly scattering systems consisting of low index inclusions in high-index matrices such as pores in planar silicon-nitride based waveguides. This allows for both significant reductions in footprint with acceptable losses in resolution and for device operation in the visible and near-infrared frequency range.