High resolution optical spectral filtering technology: Reaching the sub-GHz resolution range

Abstract

Fine optical filtering is instrumental in fully utilizing the optical gain bandwidth with communication signals. We present the design of a hybrid guided-wave / free-space filtering apparatus based on high resolution Arrayed Waveguide Gratings (AWG). These hybrid systems, called photonic spectral processors (PSP), can access and manipulate the fine spectral components of a lightwave signal with a spatial light modulator. In order to achieve sub-GHz resolution of the PSP, an AWG with large number of waveguides and long incremental waveguide lengths is needed. Such an AWG require careful design in order to enable relatively compact realization with a dense waveguide count, and an additional step of phase error correction which are inevitable in such design. In this paper we review the design consideration of a high resolution AWG with 200 GHz FSR and sub-GHZ spectral resolution and describe the phase errors interferometric measurement system and the UV trimming system which is needed as an essential post production process.