JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 27, NO. 24, DECEMBER 15, 2009 5767 Polarization Insensitive Wavelength Conversion Based on Orthogonal Pump Four-Wave Mixing for Polarization Multiplexing Signal in High-Nonlinear Fiber Jia Lu, Lin Chen, Z. Dong, Z. Cao, and Shuangchun Wen Abstract—We have theoretically and experimentally investi- gated polarization insensitive all-optical wavelength conversion for polarization multiplexing signal based on orthogonal pump four-wave mixing in nonlinear optical fiber. After wavelength conversion based on 1 km high-nonlinear optical fiber with polar- ization insensitivity, the power penalties of 2.5 Gbit/s optical OOK intensity and 10 Gbit/s differential phase-shift keying orthogonal signals are less than 0.5 and 0.8 dB, respectively. Index Terms—Four-wave mixing (FWM), nonlinear optics, optical multiplexing, polarization insensitivity, wavelength conversion. I. INTRODUCTION W AVELENGTH conversion may play an important role in the future dynamic optical network. Different schemes by using nonlinear media such as nonlinear optical fiber and semiconductor optical amplifier (SOA) based on self-phase modulation (SPM), cross-gain modulation (XGM), and cross-phase modulation (XPM) can be used to realize all-optical wavelength conversion (AOWC) [1]–[29]. How- ever, four-wave mixing (FWM) is considered to be the most promising scheme, because it is fully transparent to the signal bit rate and modulation format [5]–[13]. FWM can be achieved by using single pump and dual pumps in high-nonlinear fiber (HNLF) [10], [12], [14]–[21]. The main drawback of wavelength conversion based on regular single-pump FWM scheme [10], [12] is polarization dependence, and the converted spectrum is inverted relative to that of the original signal. But one uses is the polarization-diversity scheme to overcome this problem [21]. Polarization insensitive AOWC based on FWM Manuscript received May 08, 2009; revised July 21, 2009. First published November 03, 2009; current version published November 30, 2009. This work was supported in part by the National “863” High-Tech Research and Develop- ment Program of China under Grant 2007AA01Z263, Grant 2009AA01Z222, Grant 2009AA01Z220, and in part by the Open Fund of Key Laboratory of Op- tical Communication and Lightwave Technologies (Beijing University of Posts and Telecommunications, Ministry of Education, China). The authors are with the Key Laboratory for Micro/Nano Opto-Electronic De- vices of Ministry of Education and the School of Computer and Communication, Hunan University, Changsha 410082, China (e-mail: liliuchen12@vip.163.com; scwen@vip.sina.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JLT.2009.2034611 can be achieved by using dual-pumps including copolarized or orthogonal pump schemes [6], [14]–[20], [22]–[26] in nonlinear fiber or SOA. In [22]–[26], the polarization issue can be solved by using dual-pumps scheme, but it needs additional compo- nents as well as a precise control of the polarization in the loop. The polarization sensitivity with different states of pumps is discussed in [6], [14]–[20]. However, in the copolarized pump architecture, the frequency spacing between the converted and original signals is small so that it is difficult to separate the converted signal from the original one. Based on orthogonal pump scheme, the frequency spacing between the converted signal and original one is quite large; therefore, the converted signal can be easily separated from the original signal. Al- though polarization insensitive AOWC based on orthogonal pump scheme has been demonstrated in [6], [14]–[17], the original signal only has single polarization direction. While in [18], a tunable AOWC and wavelength-multicasting scheme is proposed, in order to increase the transmission capacity, three different wavelengths are used as signal lightwaves. As we know that polarization multiplexing can be used to increase the capacity and spectral efficiency of the transmission signals [10], [31]–[33]. Recently, people have demonstrated polar- ization insensitive AOWC based on orthogonal pump scheme for high-speed polarization-multiplexing signals, but there lacks theoretical analysis in detail [35], [36]. In this paper, we have theoretically and experimentally investigated polarization insensitivity AOWC for polarization multiplexing signal based on orthogonal-pump FWM scheme. This paper is organized as follows: the theoretical analysis for polarization insensitive AOWC based on orthogonal-pump FWM for polarization multiplexing signal in HNLF are pre- sented in Section II. In Section III, we have experimentally demonstrated AOWC for polarization multiplexing 2.5 Gbit/s OOK intensity and 10 Gbit/s DPSK signals based on orthog- onal pump scheme. The conclusions are given in Section IV. II. THEORETICAL ANALYSIS Fig. 1 shows the principle of wavelength conversion based on the orthogonal-pump FWM scheme in nonlinear medium. The two pumps and signal lightwave are generated from external cavity laser (ECL1), ECL2, and ECL3. They can be written as , respec- tively. Here, , and are the wave vectors along the fiber, 0733-8724/$26.00 © 2009 IEEE