Integrated Optical Filter Design in InP for Coherent Optical Communications in Space

Abstract

Extraterrestrial photonic integrated circuits (EPIC) offer potential solutions to relieve the global communication bottleneck in the near future. This study focuses on the design of an important component for an EPIC project at German Aerospace Center (DLR), namely integrated optical filter design. The motivation behind this work is the promise of photonic integration that low loss, lightweight and flexibly tunable filters can be realized for extraterrestrial communication. Furthermore, integrated optical filters can significantly enhance the signal-to-noise ratio (SNR) of communication systems without the need for electro-optical conversions. Among different material platform options, the focus is mainly directed towards Indium Phosphide (InP). Regarding the investigated optical filter types, mainly ring resonator and Mach-Zehnder Interferometer (MZI) geometries are studied in this thesis. After a detailed examination, the design is finalized using a 2nd order MZI filter with 1.76 mm2 footprint and 31.25 GHz (0.25 nm) full-width at half-maximum (FWHM). Moreover, 137.5 GHz (1.10 nm) free spectral range (FSR), 25 dB on-off extinction ratio (ER), <1 dB insertion loss (IL) and 18-25 dB power suppression at the centers of the side channels are calculated with Beam Propagation Method (BPM) simulations, which are predicted with the preliminary scattering matrix (S-matrix) analyses. This thesis elaborates on the theoretical fundamentals of ring resonator and MZI filters, followed by the adopted methodology during the entire filter design process. In this regard, it provides a comparative investigation between the two filter types in the context of InP material platform. The performance of the finalized design with MZI is also discussed at the end, including the tuning considerations of the filter