WDM-PON Upstream Budget Extension for 4×10 Gbit/s DPSK Directly Modulated Lasers A. Emsia, T. Q. Le, T. von Lerber, D. Briggmann, F. Küppers Institute for Microwave Engineering and Photonics, TU Darmstadt, Merckstr. 25, 64283 Darmstadt, Germany emsia@imp.tu-darmstadt.de Abstract—We present a novel WDM-PON optical power budget extender which provides 61 dB power budget improvement. We demonstrate it experimentally for a 4×10 Gbit/s DPSK WDM-PON upstream scenario. Keywords-Semiconductor optical amplifier (SOA), Saturated collision amplifier (SCA), Differential phase-shift keying (DPSK), Passive optical networks (PON). I. INTRODUCTION Every day demand for higher data rate in optical access networks is rising. Various standards are provided to meet the bandwidth requirements of customers [1]. Among those Passive Optical Networks (PONs) are highly desired, as it delivers higher bandwidth in the access network. To increase the bandwidth more than today's deployed copper-based access networks, WDM-PONs has been introduced in which the upstream and downstream transmissions are feasible at higher bit rates, although it is not commercially available yet. In WDM-PON, different wavelengths can be launched into the terminal line in up and down directions leading to a higher capacity. Operator always seek for lower deployment and operation costs of the access network. In other words, they try to increase the transmission distance, number of users, and data rates through power budget enhancement [2]. This optical power budget upgrade is termed as "the reach extension." Semiconductor optical amplifiers have been already proposed by various authors [3,4,5]. These amplifiers have shown to be a favorable option to overcome the losses in WDM-PON. In this paper, we will report a novel budget extension method for WDM-PONs. We will consider upstream case 4 channels WDM-PON with Chirped Managed directly modulated Lasers (CML). Due to various power budgets from different ONUs, the OLT receiver needs to have a high dynamic range. To alleviate this problem, power budget extension is utilized to reduce the dynamic range for upstream transmission. The direct modulation of laser is a cost-effective option and it needs lower driving voltage in comparison to external modulation. DPSK modulation format is employed as it is more robust against nonlinearities as well as chromatic dispersion. Our method is based on Saturated Collision Amplifier (SCA) [8]. We will represent a 61 dB optical power budget enhancement using our setup. In [5] double stages SOA has been used, but in case of loud packages the penalty is high. We will mitigate this problem by our scheme. Additionally, we will demonstrate the advantage of our scheme over single SOA represented in [8]. II. WDM PON REACH EXTENSION ARCHITECTURE The WDM-PON extension scheme utilizes the SCA. The SCA is comprised of an SOA as preamplification, Delay Line Interferometer (DLI), two circulators , and SOA as depicted in Figure 1. The DLI converts the DPSK signal into ASK. Two outputs enter from opposite sides into the SOA and interfere inside the device. This lets the SOA operate in saturation and give a constant output power. The eye remains open as the gain is dependent upon sum of the optical powers. The patterning effect does not occur since every bit has nearly the same power. The comparison between single SOA (first SOA+DLI in the setup) and SCA (as in the figure 1) will be presented in the following section. Figure 1. WDM-PON Extender upstream scenario III. RESULTS AND DISCUSSIONS As Figure 1 illustrates, the transmitter consists of a pulse pattern generator which produces 2 31 -1 bit sequence, and an NRZ to IRZ (inverse RZ) encoder. The 10 Gbit/s data is modulated using direct lasers at 1535 nm, 1536 nm, 1537 nm, and 1538 nm. The CML lasers generate DPSK signals. The Rx DLI SOA MUX CML BERT SOA CML CML DeMUX Feeder line Access line PON Extender CML 34 ME3 (Contributed Oral) 9:00 AM – 9:15 AM 978-1-61284-0733-9/12/$26.00 ©2012 IEEE