Universal programmable and self-configuring optical filter

TL;DR

This paper introduces a versatile, self-configuring optical filter that can be programmed to perform various spectral filtering functions, automatically compensating for fabrication imperfections and enabling advanced analysis of light coherence.

Contribution

It presents a novel integrated optical filtering approach that is fully programmable, self-configuring, and capable of multiple simultaneous functions, surpassing traditional fixed filters.

Findings

Supports arbitrary spectral filtering functions

Automatically compensates for fabrication imperfections

Enables measurement of temporal coherence and Karhunen-Loève expansion

Abstract

We propose an approach to integrated optical spectral filtering that allows arbitrary programmability, can compensate automatically for imperfections in filter fabrication, allows multiple simultaneous and separately programmable filter functions on the same input, and can configure itself automatically to the problem of interest, for example to filter or reject multiple arbitrarily chosen frequencies. The approach exploits splitting the input light into an array of multiple waveguides of different lengths that then feed a programmable interferometer array that can also self-configure. It can give spectral response similar to arrayed waveguide gratings but offers many other filtering functions, as well as supporting other structures based on non-redundant arrays for precise spectral filtering. Simultaneous filtering also allows, for the first time to our knowledge, an automatic measurement of the temporal coherency matrix and physical separation into the Karhunen-Lo\`eve expansion of temporally partially coherent light fields.