Ultra-broadband InP-based Photoreceiver With Integrated Travelling Wave Amplifier For 40 Gbit/s Detection

A monolithic InP-based photoreceiver for h = 1.55 pm is presented. Its opto-electronic conversion capabilities for 40 Gbit/s RZand NRZ-modulated PRBS data streams are demonstrated. Introduction and Overview Advanced TDM transmission systems operate at bit rates up to 40 Gbit/s to manage increasing . traffic on fibre-based communication networks. Although non-return to zero (NRZ) coding is widely applied [I], return to zero (RZ) modulation promises advantages with respect to achievable transmission length along standard fibers compared to the NRZ format [2]. In either case ultra-broadband frontends are needed €or opto-electronic ((YE) signal conversion. A monolithic InP-based opto-electronic receiver (Rx) is presented, which substitutes a commercially available photodiode in a 40 Gbit/s detection experiment on the way to a 40 Gbit/s OEIC technology. The receiver OEIC comprises a waveguide-integrated photodiode and a travelling wave amplifier (TWA) providing additional signal amplification. Its O E power transfer h c t i o n is demonstrated to cover properly the spectral range of a 40 Gbit/s NFZ data stream. In an 40 Gbit/s detection experiment, applying an optical TDM (OTDM) PRBS RZ modulated source, the direct detection of the received 40 Gbit/s pulse sequence by the InP-based photoreceiver is demonstrated. The design of the complete receiver module is described as well as its signal conversion properties for 40 Gbit/s TDM applications. Opto-Electronic Receiver Design for fast TDM Systems For TDM transmission systems, which support the SDH standard, an opto-electronic receiver has to fulfill several requirements in order to guarantee a well opened eye pattern at its output. Photoreceivers are needed which exhibit a flat gain characteristics down to some 10 kHz to ensure the transmission of the frame synchronisation of the synchronous transport modules (STM-1,4, 16, 64 ...). The components of a photoreceiver (photodiode and amplifier stage) should provide both a good power linearity as well as flat conversion properties within the frequency span of the bit rate. Furthermore a group delay time scatter less than 1+151 % of the bit period and an output reflexion factor less than -10 dB over the full bandwidth is desirable [3]. The polarisation sensitivity should not exceed I_+ 1/ dB, e.g., to compensate for the loss of pofarisation orientation in standard fibers and to allow for some pol.arization scrambling of stringed bits in optical multiplexing experiments. Monolithic Photoreceiver The photoreceiver OEIC comprises a photodiode with integrated optical waveguide [4] and a HEMT based travelling wave amplifier, both monolithically integrated on semi-insulating InP substrate [SI. The layer stack of the evanescent field coupled GaInAs pin-photodiode is optimized to achieve an internal quantum efficiency of about 85 % for photodiodes with a size of 5 20 pm'. The transit-time limited electrical 3 -dB bandwidth amounts to 35 GHz. Optical measurements show an overall external quantum efficiency of 30 % with an almost polarisation-insensitive behaviour (I I + 11 dB). The AlInAs/GaInAs-HEMT layers are regrown by MBE after locally removing the photodiode layers [SI. Further technological details of the fabricated photoreceiver OEIC with dimensions of approx. 1 * 3 mm2 are provided in [3]. The amplifier stage is the photodiode reverse bias. Fig.2 depicts the power transfer Fig. 1 : View into the 40 Gbit/s photoreceiver module; receiver OEIC interconnected to a TMM-CPW-transmission line leading to a Ktype connector; the optical fiber irradiates the chip waveguide from the left hand side.