Colorless devices and reception techniques for polarization multiplexed communications

Abstract

Future optical networks call for flexible, high performance and low cost coherent optical receivers. We present here several advances towards such receivers, including integrated optical couplers with ultra-broad bandwidth, as well as novel reception techniques and architectures that will enable high performance coherent reception without filtering and polarization splitting elements.Keywords: coherent receivers, colorless operation, multimode interference couplers, polarization splitters, OSNR penalty, receiver architectures INTRODUCTIONOptical transmission networks are evolving from classical long-haul scenarios towards flexible, high speed optical access networks [1]. These networks call for optical components that offer high performance and low cost while being suitable for diverse network scenarios. This has spurred interest in coherent receivers that can provide colorless operation in a broad spectral range and can work with a wide range of input powers, i.e. offer high dynamic range [2]. In order to achieve rugged devices and reduced costs, such receivers would ideally be fabricated as monolithically integrated chips. As shown in Fig. 1, this requires, among other factors, the integration of polarization beam splitters (for polarization multiplexing) and high performance 90º hybrids combined with high speed photodiodes (for optical down-conversion); trans-impedance amplifiers are typically wire-bonded to the optical chip. While important advances have been achieved in both aspects [3], [4], it is still challenging to achieve high-yield (and thus economically viable) solutions for 90º hybrids simultaneously covering the C+L bands (1530nm -1625nm) or fully passive on-chip polarization splitters.