Photonic Signal Processing for Phase-Agnostic Coherent Optical Reception

Coherent optical detection has eventually brushed off its flavor of being exclusively dedicated to longhaul and metro-scale data transmission. It is now introduced to the short-reach realm, where simplicity and cost/energy-effectiveness are paramount. Towards this direction, a photonic signal processing circuit for signal recovery is introduced and experimentally evaluated in two phase-agnostic coherent receiver architectures that build on either a 90° or 120° hybrid for mixing a free-running local oscillator with a real-valued data signal. The required envelope detection function after coherent detection is accomplished through re-translating the beat signal into the optical domain, which is accomplished by leveraging highly efficient current-to-frequency conversion that enables a direct-drive scheme for the photonic signal processing circuit without extra amplification of the detected photocurrent. Squaring and summing of the quadratures is then performed in the optical domain through either an interferometric filter or a compact micro-ring resonator. It is demonstrated that the photonic outline of the signal processing chain does not necessarily go with an overhead in energy and size - but can instead be more efficient than electronics-based analogue circuitry, both in terms of power consumption and device footprint.