Simultaneous multichannel wavelength conversion of polarization shift keying signal with different channel group-delay and state of polarization Md. Nur-Al-Safa Bhuiyan a, ⁎, Motoharu Matsuura b , Hung Nguyen Tan a , Naoto Kishi a a Department of Communication Engineering and Informatics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan b The Center for Frontier Science and Engineering, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu-shi, Tokyo 182-8585, Japan abstract article info Article history: Received 26 May 2010 Received in revised form 20 September 2010 Accepted 20 September 2010 Keywords: All-optical wavelength conversion Polarization-shift keying signal Four-wave-mixing Simultaneous wavelength conversion of multichannel polarization shift keying (PolSK) signal using four- wave-mixing in highly non-linear fiber is demonstrated. In the proposed wavelength converter, the wavelengths of four 10-Gb/s polarization shift keying channels are simultaneously converted without any performance degradation for the converted channels. We successfully achieved high conversion performances for all the converted channels even though the input PolSK channels have different delay time and state of polarization. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Multichannel wavelength conversion is one of the very important functions for future photonic networks. To realize the function, it is desirable to have a single wavelength converter with the ability to convert multiple channels simultaneously. This type of wavelength converter leads to a simpler scheme and lower power consumption of the network [1–4]. In simultaneous multichannel wavelength con- version, it is very important to maintain the quality of the converted channels so that all the converted channels will have similar performances. However, in realistic situation, multichannel signal to the converter have different channel-group delay and state of polarization (SOP), since these signals come from different nodes and are transmitted to different links in the photonic network. In such a case, the quality of the converted channels is severely degraded in simultaneous wavelength conversion of multichannel signals [5]. Hence, in multiwavelength converter, it is very useful to mitigate such degradation and convert simultaneously multichannel signals with equal performances. Polarization-shift keying (PolSK) is one of the attractive modulation formats for practical transmission systems and it is worth investigating this modulation format for multichannel wavelength conversion. PolSK signal utilizes the SOP of optical signalas the information bearing parameter. Information is sent by switching the polarization of the transmitted light wave between two linear orthogonal SOPs corresponding to binary signal “0” and “1”. On the Poincare sphere, these orthogonal SOP components are considered as two antipodal points and are used for signal constellation [6,7]. In a number of studies, PolSK modulation format has been theoretically and experimentally investigated [6–12]. Recently significant studies have been published related with polarization multiplexed signal [13–18]. The main advantage of PolSK is its constant envelope. In other words, optical power remains constant regardless of the data pattern. Consequently, when multiple PolSK signals are simultaneously wavelength converted, the signal does not suffer from data pattern dependent penalties, provided that the wavelength conversion mechanism is polarization insensitive. In the case of conventional on–off keying modulation format, interchannel crosstalk may severely degrade the quality of wavelength converted channels when multiple signals are passed simultaneously through the wavelength converter. In semiconductor optical amplifier (SOA), PolSK signal is free from patterning effect over a wide wavelength range. Thus PolSK is very effective for wide band wavelength-division-multiplexing (WDM) transmission systems using SOAs [11]. There are some advantages of PolSK over differential phase- shift keying (DPSK) modulation format. Binary and multilevel PolSK systems are insensitive to phase noise [19]. Moreover, multilevel PolSK has better sensitivity than DPSK for constellation containing eight or more signal points [20]. PolSK signal is more tolerant to nonlinear fiber effects and also shows reduced sensitivity to self-phase-modulation and cross-phase-modulation due to its constant envelop characteristics [21]. Furthermore, this type of modulation format also supports multilevel coding and enhances spectral efficiency, which is claimed to be one of the key issues in future high-capacity transoceanic links [20,22]. In future photonic networks, wavelength conversion is one of the key techniques for wavelength routing. However, very few studies have been published so far for wavelength conversion of PolSK signal Optics Communications 284 (2011) 665–669 ⁎ Corresponding author. Tel.: + 81 42 443 5206; fax: + 81 42 443 5797. E-mail address: safa@ice.uec.ac.jp (M.N.-A.-S. Bhuiyan). 0030-4018/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2010.09.056 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom