Full-Duplex 20/10 Gb/s WDM-PON with Remodulation of Chirped ASK and Multi-level Quaternary PAM and OFDM Jose A. Lazaro 1* , Bernhard Schrenk 2 , Alexandros Maziotis 2 , Ivan Cano 1 , Paraskevas Bakopoulos 2 , Josep Prat 1 , and Hercules Avramopoulos 2 1 Department of Signal Theory and Communications, Universitat Politecnica de Catalunya,Jordi Girona 1, 08034 Barcelona, Spain 2 School of Electrical & Computer Engineering, National Technical University of Athens, Iroon Polytechniou Street 9, 15773, Athens, Greece *Corresponding author: jose.lazaro@tsc.upc.edu Abstract: A full-duplex 20/10Gb/s WDM-PON is demonstrated by all-optical carrier recovery technique, showing that it is efficient and flexible for being applied to different downstream signals as non-/chirped ASK or multilevel signals as 4-PAM or OFDM. OCIS codes: (060.2330) Fiber optics communications; (060.4080) Modulation; (230.1150) All-optical devices 1. Introduction Fiber-to-the-Home has certainly received attention during the recent years. Multimedia services such as 3DTV are about to inundate nowadays communication networks, which face bottlenecks in the last mile when delivering such advanced applications. While traditional TDM-based telecommunication networks are subject to shared bandwidth, the WDM-based passive optical network (WDM-PON) is able to guarantee a high data throughput for each of the network users as it establishes virtual point-to-point links. Cost-effective devices for the customer premises equipment, such as the reflective semiconductor optical amplifier (RSOA), have been already operated at data rates up to 25 Gb/s in recent research work [1]. However, WDM-PONs are typically not able to cope with a high customer density as hybrid WDM/TDM-PONs do. An efficient utilization of the available wavelengths for supporting full-duplex transmission is therefore important. Methods to recycle optical carriers for this purpose have been demonstrated earlier [2], involving all-optical schemes with superior performance with respect to their electro- optical counterparts [3]. However, there has been no investigation of such a technique on chirped downstream signals and optical multi-level modulation formats. In this work, we present a performance evaluation for an all-optical wavelength reuse scheme for a full-duplex symmetric 10 Gb/s and asymmetric 20/10 Gb/s WDM-PON. Remodulation is applied to chirped amplitude shift keying (ASK) and quaternary pulse amplitude modulation (4-PAM) with extinction ratios (ER) up to 10.5 dB, and also proven in its principle with orthogonal frequency division multiplexing (OFDM). The compatible loss budget is limited by the optical seed of the reflective ONU to 20 dB, having margins of >9 dB for data transmission. 2. Remodulation Technique and Setup The wavelength reuse scheme is supported by a passive resonating circuit at the reflective optical network unit (ONU), which exploits its optical memory effect to recover the optical carrier of a data signal that was modulated with reduced ER. A fiber-based Fabry-Pérot filter (FPF) was used as resonator, having a free spectral range of 10 GHz, a finesse of 47 and an insertion loss of 2.7 dB. An integrated piezo- based circuit ensures that the comb-like transfer function of the FPF is automatically aligned with the incoming downstream signal, allowing plug&play operation. The multi-level driving signals for the downstream were generated with an arbitrary waveform generator (Tektronix AWG7122B) and had a RF swing of up to 1.4V pp . This is sufficient enough to reach a modulation ER of more than 13 dB in conjunction with an electro-absorption modulator (EAM), providing also an energy-efficient solution for the downstream transmitter. The downstream signal at 1560.2 nm was launched with 10 dBm from the optical line terminal (OLT) and transmitted over an optical distribution network consisting of a dual-feeder fiber with variable length (6 to 25 km), a 1x40 arrayed waveguide grating (AWG) and a 2.2 km long drop fiber span (Fig. 1). The loss budget of the WDM-PON, defined between the OLT and ONU, was kept constant at 20 dB by adjusting the attenuator A B , meaning an ONU input power of -10 dBm. The attenuator A B defines the seed loss budget as one of the limiting factors for the compatible optical loss budget of the PON. loss budget C O FPF ONU RX A B SMF F 6...25 km SMF D 2.2 km 6...25 km SMF F a AWG OLT LD BPF PIN TX RX REAM a A U APD EDFA EDFA EDFA TX MZM RSOA a A D loss budget C O FPF ONU RX RX A B SMF F 6...25 km SMF D 2.2 km SMF D 2.2 km 6...25 km SMF F a a AWG OLT LD BPF PIN TX RX RX REAM REAM a a A U APD EDFA EDFA EDFA TX TX MZM RSOA RSOA a a A D Fig.1. Experimental setup for the full-duplex 10/10 and 20/10 Gb/s WDM-PON. OTh1F.6.pdf 1 1/23/2012 11:48:47 AM OFC/NFOEC Technical Digest © 2012 OSA