Performance of an optical equalizer in a 10 G wavelength converting optical access network

Abstract

A centralized optical processing unit (COPU) that functions both as a wavelength converter (WC) and optical burst equaliser in a 10 Gb/s wavelength-converting optical access network is proposed and experimentally characterized. This COPU is designed to consolidate drifting wavelengths generated with an uncooled laser in the upstream direction into a stable wavelength channel for WDM backhaul transmission and to equalize the optical loud/soft burst power in order to relax the burst-mode receiver dynamic range requirement. The COPU consists of an optical power equaliser composed of two cascaded SOAs followed by a WC. Using an optical packet generator and a DC-coupled PIN-based digital burst-mode receiver, the COPU is characterized in terms of payload-BER for back-toback and backhaul transmission distances of 22, 40, and 62 km. We show that there is a compromise between the receiver sensitivity and overload points that can be optimized tuning the WC operating point for a particular backhaul fiber transmission distance. Using the optimized settings, sensitivities of 30.94, 30.17, and 27.26 dBm with overloads of 9.3, 5, and >-5 dBm were demonstrated for backhaul transmission distances of 22, 40 and 62 km, respectively.

Demonstration of a 10 Gbit/s Long Reach Wavelength Converting Optical Access Network

“…The optical burst power equaliser is based on a saturated semiconductor optical amplifier (SOA) to level bursts coming from ONUs at different distances from the exchange and reduce the receiver dynamic range requirement at the OLT [8]. Alternatively this could be achieved using an electronic automatic level control circuit between the cascaded SOAs [9].…”

“…The 10 Gbit/s digital burst-mode receiver (DBMRx) used a standard DC-coupled PIN photodiode and an integrated trans-impedance amplifier (TIA) connected to a Tektronix DPO72004B real-time oscilloscope, sampling at 25 GS/s to digitise the signal for subsequent offline Digital Signal Processing (DSP) in MATLAB. The DBMRx performs clock-and-data recovery in the digital domain and has a fixed threshold equal to λ=0, which saves some DSP resources and produces an acceptable sensitivity penalty of only 0.5 dB compared to more complex adaptive thresholding algorithms [8].…”

“…The driving current of all the SOAs was kept constant and the WC bias point was then tuned by controlling the polarization of the input bursts rather than adjusting the driving current of the SOAs, as described in Section III.C of this paper. Thus, to optimize the COPU performance, two optical bursts of −15 dBm and −25 dBm were generated, and the bias point of the wavelength converter was set such as that the superimposed eye diagrams were as similar as possible (maximum burst power equalization, named case A), as different as possible (minimum burst equalization, named case C), or at an intermediate state (case B) [8]. Cases A and B are illustrated in Fig.…”

“…7. For clarity, only BER for optimization case A is presented in this work because case A maximizes the receiver sensitivity [8]. Fig.…”

A Deeply Saturated Differentially-Biased SOA-MZI for 20 Gb/s Burst-Mode NRZ Traffic

“…However, when burst-mode traffic operation is targeted where data packets might have propagated through different fiber segments experiencing different losses and as such arriving with intense power fluctuations at the WC stage, wavelength conversion has to be preferably accompanied with power equalization capabilities on a per packet basis in order to ensure successful propagation of the wavelength converted signal into the next network segment. Although a large variety of burst-mode, regenerative, SOA-based WC schemes have already been proposed [23][24][25][26][27][28][29], most of them have been able to yield successful operation only with RZ data formats when linerates higher than 10 Gb/s are targeted [23][24][25]. When NRZ burst-mode operation is required, typically being the case in reach extender applications for Passive Optical Network (PON) uplink transmission or 5G digital fronthaul architectures [30], SOA-based WC schemes have been restricted to 10 Gb/s operational data-rates [26][27][28][29].…”