Universal programmable and self-configuring optical filter

Spectral filters are widely used in sensing and communicating with light, such as for separating wavelength channels in communications or sensing the specific spectra of some object or material of interest. The filter function is, however, often fixed, and precise filtering can require precise manufacturing. 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 a 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 an automatic measurement of the temporal coherency matrix and physical separation into the Karhunen–Loève expansion of temporally partially coherent light fields. With this approach, a wide range of spectral operations can be controllably, automatically, and precisely performed by an integrated photonic device with simple programmability.