1448 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 16, NO. 5, SEPTEMBER/OCTOBER 2010 All-Optical Wavelength Conversion of 10 Gb/s RZ-OOK Data in a Silicon Nanowire via Cross-Phase Modulation: Experiment and Theoretical Investigation Jeffrey B. Driscoll, W. Astar, Xiaoping Liu, Student Member, IEEE, Jerry I. Dadap, William M. J. Green, Member, IEEE, Yurii A. Vlasov, Senior Member, IEEE, Gary M. Carter, Fellow, IEEE, and Richard M. Osgood, Jr., Fellow, IEEE Abstract—Wavelength conversion of a 10 Gb/s 2.7%-duty-cycle return-to-zero (RZ) OOK (RZ-OOK) signal using XPM in a com- pact silicon nanowire waveguide (Si nanowire) and a detuned filter is successfully demonstrated for the first time. A 10 -9 -BER re- ceiver sensitivity penalty of <1 dB was measured for the converted signal relative to the baseline signal, with a filter-probe detuning of 0.6 nm. The system is numerically modeled and the results are shown to match well with the experimental results. The numeri- cal model is further used to design an optimal filter that would eliminate filter-probe detuning. Index Terms—Integrated optics, nonlinear optics, optical fre- quency conversion, optical signal processing, optical waveguides, silicon-on-insulator technology. I. INTRODUCTION W ITH the growing need for transparent processing methods to alleviate latency, power, footprint, cost, and component-count disadvantages of conventional optical– electrical–optical (OEO) conversion, all-optical wavelength conversion (WC) techniques represent a possible building block for future all-optical network architectures, especially with continued upgrades of dense wavelength-division-multiplexed (DWDM) networks [1]. In optical cross-connects (OXCs), WC can be used in conjunction with wavelength-channel routing schemes to efficiently route high-speed data streams, and to min- imize channel contention entirely in the optical domain [2], [3]. Manuscript received September 3, 2009; revised November 3, 2009; accepted November 23, 2009. Date of publication April 1, 2010; date of current version October 6, 2010. This work was supported by the Defense Advanced Research Projects Agency under Contract FA9550-05-1-0428. J. B. Driscoll, X. Liu, J. I. Dadap, and R. M. Osgood, Jr. are with the Microelectronics Sciences Laboratories, Columbia University, NY 10027 USA (e-mail: jbd2112@columbia.edu). W. Astar is with the Laboratory for Physical Sciences, Digital Fiber Trans- mission, College Park, MD 20740 USA, and also with the Center for Ad- vanced Studies in Photonic Research, Baltimore, MD 21250 USA (e-mail: notilos@lps.umd.edu). W. M. J. Green and Y. A. Vlasov are with the IBM T. J. Watson Research Center, Yorktown Heights, NY 10598 USA. G. M. Carter is with the Laboratory for Physical Sciences, College Park, MD 20740 USA, with the Center for Advanced Studies in Photonic Research, Balti- more, MD 21250 USA, and also with the Department of Computer Science and Electrical Engineering, University of Maryland, Baltimore County, Baltimore, MD 21250 USA. 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/JSTQE.2009.2038352 WC may also find use over long-haul networks, where the fiber span can change from one favorable to DWDM C-band (1530– 1565 nm) transmission, to one detrimental to DWDM transmis- sion, such as dispersion-shifted fiber (DSF), where four-wave mixing (FWM) becomes a serious impairment. In such cases, re- assignment of C-band channels to L-band (1565–1610 nm) can minimize FWM impairments. Additionally, it has been shown that the reassignment of some wavelength channels to an un- equally spaced channel plan can help mitigate C-band transmis- sion difficulties over DSF [4]. All-optical solutions to WC have been heavily researched, however, recent advances in which WC is performed in deeply scaled silicon (Si) nanowire waveguides (Si nanowires) on the silicon-on-insulator (SOI) platform have been of particular inter- est [5]–[13]. Leveraging mature CMOS processing techniques with the inherently high index-of-refraction (n) contrast between the Si core (n Si ∼ 3.5) and the surrounding claddings (n air ∼ 1, n oxide ∼ 1.44) allow the realization of tight modal confinement in waveguides of subwavelength dimensions. This high modal confinement leads to high optical intensities and an effective en- hancement of Si’s intrinsically large third-order nonlinear Kerr susceptibility (χ (3) ) [11]–[13]. In fact, the standard nonlinear coefficient (γ ) realized in Si nanowires can be more than 10 5 times larger than in transmission fiber [14], which can lead to ul- trasmall footprint devices and the possibility of packaging many integrated optical devices on a single chip. Nonlinear processing in Si also allows the potential for bit-rate transparency owing to the ultrafast electronic response of χ (3) , and a number of nonlinear all-optical applications have been demonstrated on- chip, including modulation [15], switching [16], [17], optical regeneration [18], multicasting [19], super-continuum genera- tion [20], [21], amplification [22], [23], format conversion [24], and WC [5]–[13]. One common method for achieving WC in nanowires is through partially degenerate FWM, a nonlinear parametric pro- cess, where two pump photons and one probe photon interact in a nonlinear medium to create a new photon at a unique frequency (termed the idler) in accordance with conservation of energy and momentum. Efficient FWM relies on net-zero-phase mismatch between the interacting optical waves, which includes the influ- ence of the power-dependent nonlinear phase shifts due to self- phase modulation (SPM) and XPM. Optimizing phase matching 1077-260X/$26.00 © 2010 IEEE