100-Gbit/s PDM-QPSK Integrated Coherent Receiver Front-End for Optical Communications

This paper describes device and integration technologies for 100-Gbit/s polarization division multiplexed quadrature phase shift keying integrated coherent receiver front-end. The silica-based planar lightwave circuits for the optical passive circuits, InP-based photodiode for the opto-electrical conversion, and InP HBT for the transimpedance amplification are used to achieve high-performance. A module-level hybrid integration technology based on a chip-scale packaged O/E converter is applied as the integration technology. The fabricated receiver front-end has a wide dynamic range of around 20 dB with a constant local power of 13.5 dBm and an excellent common-mode rejection ratio of better than -25 dB up to 25 GHz.

I. Introduction

The internet protocol based data traffic is continuously increasing due to the spread of broadband application services. To meet the demand for increased optical transport network capacity, the combination of polarization division multiplexed (PDM) multi-level modulation formats and coherent detection with digital signal processing (DSP) has been attracting great interest [1]. The PDM quadrature phase shift keying (QPSK) is promising modulation format for 100Gbit/s/ch system with high spectral density of 50-GHz channel spacing [2]–[3]. The combination of the coherent detection and DSP provides high receiver sensitivity and high tolerance to transmission impairments such as chromatic dispersion and polarization mode dispersion. A coherent receiver front-end with high performance levels, including a wide dynamic range, a high polarization extinction ratio (PER), an excellent common-mode rejection ratio (CMRR), a high responsivity and a small phase error, is the key to coherent detection.