Polymer Based Hybrid Integrated Coherent Receiver for Next Generation Optical Access Networks Abongwa Theurer 1 , Richard Seidel 1 , Reinhold Ziegler 1 , Crispin Zawadzki 2 , Ziyang Zhang 2 , Norbert Keil², Andreas Matiss 1 and Andreas G. Steffan 1 1 u2t Photonics AG, Reuchlinstrasse 10/11, 10553 Berlin, Germany, Phone: +49 30 726 113-552, Fax: +49 30 726 113-800, e-mail theurer@u2t.de 2 Fraunhofer Institute for Telecommunications, Heinrich Hertz Institute, Einsteinufer 37, D-10587 Berlin, Germany, e-mail: norbert.keil@hhi.fraunhofer.de Abstract: A hybrid integrated coherent dual polarization receiver based on polymer planar lightwave circuit is presented. The chip comprises polarization beam splitter, multimode interference couplers and photodiodes. Responsivity of 0.03A/W and bandwidth of 23GHz were achieved. OCIS codes: (060.1155), (130.1750 ), (130.3120), (130.5440) 1. Introduction The increasing demand for high data rates by the end user is growing as fast as the number of new broadband internet services both for mobile and stationary devices. As well, efficiency and power consumption of the service providing networks is of high interest in order to reduce the costs of such networks. To reach that optical communication technology is getting closer to the end user because of several advantages. With coherent receiver architectures long fiber optical communication links of up to 100 km can be achieved without signal restoration and also very high splitting factors of 1:1000 can be realized [1] and [2]. Fiber to the premises networks (FTTx) can meet the demands by bringing optical technology closer to the end user offering a symmetrical data rate of up to 1 Gb/s per user [3]. To enable filterless ultra-dense wavelength division multiplexing networks (WDM) heterodyne receivers can be used. With the coherent receiver approach high sensitivities and wavelength selectivity is achieved and new PON based network architectures can be realized [4] and [3]. It is desirable to integrate the single subcomponents of coherent receivers in a planar lightwave circuit (PLC) and into one single package leading to decreased packaging costs and smaller footprint size. As a hybrid integration concept the polymer technology is gaining interest because of using low cost polymer material as wave guiding motherboard including coherent heterodyning of Signal and Local Oscillator (LO) inputs. It also functions as a carrier for the polarization beam splitter in thin film technology as well as for the photo detectors in III/V InP material. The polymer technology benefits from the optimized functionalities of the subcomponents what makes it a suitable hybrid integration platform for coherent receiver chips [5]. Due to the wavelength sensitive coherent reception, the WDM signal is optically pre-amplified and converted into the electrical domain. The receiver is flexible regarding the deployed modulation format and because of the low data rate per channel of 1 Gb/s demodulation is done electrically with common electronic circuits. 2. Integration Concept For the coherent heterodyne receiver a hybrid integration concept was chosen. Using the hybrid concept each subcomponent can be optimized independently: 1) The polymer PLC routes the optical signal and gives basic functionality of coherent optical heterodyning in multimode interference couplers (MMI). At the same time mechanical functionalities are complied by carrying other subcomponents such as PBS and photo detector array. 2) The mixing and opto-electronic transformation is done by a PIN photo diode in III/V InP material. The photo detector array is assembled on top of the polymer PLC and the light is reflected upwards into the diode with a 45° micro-milled and metalized mirror. 3) Polarization beam splitting is achieved using an ultra thin film element which is plunged into a trench on the polymer motherboard. Fig. 1 (a) visualizes the hybrid integration concept showing the polymer PLC, a 45° mirror, an InP photo diode and the fiber coupling. The four channel photo diode array is assembled using a Flip-Chip Bonder with only visual alignment during assembly. In this way the benefits of each single subcomponent is used. Wave guiding tasks are done by the low cost polymer PLC which is easy in production. Opto-electronic conversion is done by a high performance InP pin diode.