AWG-DBR-based WDM Transmitter fabricated in an InP Generic Foundry Platform

Abstract

Abstract:We report a novel narrow-linewidth WDM transmitter operating at 10 Gbps per transmission channel with 275 kHz optical linewidth. The device, which integrates an AWGbased laser using selective DBR-mirrors with a Mach-Zehnder modulator array, has been fabricated in a multi-project wafer run in a generic InP-based foundry process. IntroductionIn this paper we present a novel 8-channel multiwavelength transmitter (MWT) with very narrow linewidth, realized in a generic indium phosphide (InP)-based foundry process [1,2]. The generic foundry approach allows for rapid prototyping at low cost, by participating in so called Multi-Project Wafer runs. These are fabrication runs in a standardized foundry process in which a number of different designs are combined on a single wafer, thus sharing the cost of a run. This approach has been practiced for a few years in silicon photonics, but recently it has become also available for advanced InP-based integration processes [3,4].The MWT reported here is based on the operational principle of a linear arrayed waveguide grating-based laser (AWGL) [5,6] and is an alternative design to the MWTs presented in [7,8]. The wavelength-selective mirrors, implemented as DBR-based gratings, will prevent lasing of the source in unwanted AWG orders, thus guaranteeing operation in the central free spectral range [6]. The schematic and a photograph of the fabricated circuit are presented in Fig. 1. The cavity of the AWGL is formed between the highly reflective (HR) coated cleaved facet of the chip and the DBR grating. Because the DBR mirrors can be positioned freely on the chip, the length of the laser cavity can be reduced and the longitudinal mode spacing can be controlled. Recently reported on-chip mirrors, multi-mode interference reflectors [9] also provide such flexibility, but are broadband and therefore cannot be used as wavelength selective filters. In our configuration employing DBR gratings, we obtain single mode operation without mode hops and a narrow linewidth thanks to the relatively long extended cavity of the AWGL. The sources are easier to drive, as compared to traditional AWGLs. In addition, the tuning precision can be enhanced by introducing phase elements (PH) within the resonant cavity.