Abstract

We investigate and compare the performance of wavelength conversion for two different non-return-to-zero (NRZ) modulation formats at 40 Gb/s: on off keying (OOK) and differential phase-shift keying (DPSK). To achieve wide wavelength coverage and integrability, we use a dual pump scheme exploiting four-wave mixing in semiconductor optical amplifiers. For phase stability, we use a quantum-dash mode-locked laser (QD-MLL) as a multi-wavelength source for the dual pumps, with tunability provided by the output filter. The significant sidelobes of the DPSK spectrum (relative to OOK) require the balancing of the pump proximity to the original signal (facilitating high conversion efficiency) with the signal degradation from the pump spectrum overlapping the converted DPSK signal. We achieve a conversion efficiency near –3.6 dB for OOK and –5.4 dB for DPSK across a 12 nm tuning range with low input powers (1 dBm). We measure bit error rate (BER) and obtain error free transmission (BER < 10−9) with a power penalty less than 2 dB for OOK and 3 dB for DPSK.

Highlights

  • Future optical networks will adopt advanced modulation formats to increase bit rate and improve spectral efficiency [1]

  • We recently proposed a wavelength conversion scheme exploiting a quantum-dash mode-locked laser (QD-MLL) combined with a frequency selective filter to provide two tunable wavelength pumps for Four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs)

  • We demonstrate wavelength conversion at 40 Gb/s based on FWM in an extremely nonlinear SOA

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Summary

Introduction

Future optical networks will adopt advanced modulation formats to increase bit rate and improve spectral efficiency [1]. Adding wavelength conversion to the mix achieves the most flexible, dynamically-reconfigurable network [2,3,4]. Wavelength converters must be able to support both legacy intensity modulation systems and more challenging formats incorporating phase modulation. Several wavelength conversion technologies have been proposed; semiconductor optical amplifiers (SOAs) offer many advantages over other solutions, such as ultra-fast response time, cost-effectiveness, compactness and the possibility of photonic integration [5]. Four-wave mixing (FWM) in SOAs for wavelength conversion preserves both the signal phase and amplitude, offering compatibility across modulation formats, as well as supporting high bit rates [6,7,8]. A 100 nm tuning range was achieved in [11]

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