2 × 56 GB/s From a Double Side Electroabsorption Modulated DFB Laser and Application in Novel Optical PAM4 Generation

In this paper, we present a novel device which comprises a DFB laser with electroabsorption modulators integrated on both sides. This integrated chip provides two independently modulated optical outputs from a single laser source and thus cuts the required number of chips for multilane applications in half. Both outputs can be simultaneously operated with 56 Gb/s NRZ leading to 112 Gb/s from a single chip. The performance of the chip is further tested in an optical PAM4 generation experiment. The two NRZ modulated outputs are combined with a polarization combiner to generate an optical PAM4 signal which on the receiver side is measured with a polarization insensitive photodetector.

I. Introduction

Electroabsorption modulators integrated with distributed feedback lasers (EML) are a well-developed technology and widely used due to their small size, high speed and large extinction ratio. They are especially attractive for short to medium reach applications where low cost components with intensity modulation and direct detection schemes are preferred in contrast to coherent systems. EMLs have proven to be well capable of keeping up with the demands on bandwidths, already record modulation speeds of up to 100 Gb/s have been demonstrated [1]. In order to further improve the performance of EML transmitters and reduce fabrication costs current research is investigating different approaches utilizing monolithic integration techniques. Ueda et al. demonstrated an enhancement of the dynamic extinction ratio by integrating an EML in a Mach-Zender like configuration [2]. The integration of a semiconductor optical amplifier together with an EML has proven to be an effective way of improving the EMLs performance regarding output power, efficiency and chirp behavior [3]– [5]. EML arrays monolithically integrated with multimode interference couplers allow for very compact transmitters in wavelength division multiplexing systems [6], [7].