IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 23, NO. 2, JANUARY 15, 2011 109 Wavelength Translation Across 210 nm in the Visible Using Vector Bragg Scattering in a Birefringent Photonic Crystal Fiber H. J. McGuinness, M. G. Raymer, C. J. McKinstrie, and S. Radic, Member, IEEE Abstract—Wideband optical wavelength translation across a record range from the near-infrared to the visible based on the Bragg scattering four-wave-mixing process has been demonstrated in birefringent photonic crystal fiber. The process was vectorial in nature, where the pumps and the signal and idler fields were polarized on orthogonal axes. Bragg scattering is a theoretically noiseless process (and thus is termed translation), although the signal and idler channels are often contaminated by Raman generated by the pumps. Vector Bragg scattering has the potential to be less contaminated by Raman noise than scalar (copolarized) Bragg scattering. Index Terms—Band translation, four-photon mixing, para- metric process. I. INTRODUCTION I N recent years there has been much interest in optical wave- length conversion through the various parametric processes of four-wave mixing (FWM) [1]–[3]. The modulation insta- bility (MI) process, which uses one pump laser to generate side- bands symmetrically located on either side of the pump in fre- quency space, has been used to convert signals across 1000 nm, from telecommunication to visible wavelengths [4]. For MI, and its two-pump generalization, phase conjugation (PC), the input signal simultaneously seeds sideband generation while both sidebands are being amplified. Hence conversion efficien- cies can be arbitrarily engineered to be over 100 percent. The price to be paid for such amplification is increased noise in both signal and idler channels [5], a factor that becomes important for low-intensity signal inputs such as single-photon states. The other two-pump FWM process, Bragg scattering (BS), does not rely on amplification to convert a field from one wavelength to another, and therefore is theoretically noiseless and limited to 100 percent conversion efficiency [6]. Wave- length conversion processes with these properties are called Manuscript received July 13, 2010; revised October 11, 2010; accepted November 06, 2010. Date of publication November 11, 2010; date of cur- rent version January 04, 2011. This work was supported by NSF Grant ECCS-0802109. H. J. McGuinness and M. G. Raymer are with the Department of Physics, University of Oregon, Eugene, OR 97403 USA (e-mail: hmcguinn@uoregon. edu; raymer@uoregon.edu). C. J. McKinstrie is with Bell Laboratories, Holmdel, NJ 07733 USA (e-mail: mckinstrie@alcatel-lucent.com). S. Radic is with the University of California San Diego, La Jolla, CA 92093- 0407 USA (e-mail: sradic@ucsd.edu). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2010.2091950 Fig. 1. Four possible pump-sideband configurations. The parallel and perpen- dicular axes represent either the slow or fast fiber polarization axis. Large arrows represent the polarization direction of the pumps, while small ones represent po- larizations of the signal and idler. (a) All fields are copolarized along one axis. (b) Pumps and sidebands are orthogonal. Wavelengths shown correspond to the wavelengths used in the experiment. (c) Pumps are orthogonal and sidebands are orthogonal. (d) Similar to (c), but beams that are annihilated/created together are orthogonal. translation. Here efficiency is defined by power in the converted channel at the output divided by power in the initial channel at the input. In BS, pairs of photons (one from the signal and one from one of the pumps) are annihilated, while pairs of photons (in the idler and one in the other pump) are created, constrained by energy conservation and phase matching considerations. The overall efficiency of the process is governed not only by pump powers, fiber diameter and length, but also by the magnitude of the wavelength separation of signal and idler and whether all fields are copolarized or some are polarized orthogonal to one another (Fig. 1 shows the possible pump-sideband config- urations for BS). Such a dependence is greatly increased due to imperfections of phase matching resulting from nonuniformity of a fiber’s properties along its length [7]. Even for a uniform fiber, if there are orthogonally polarized fields, the nonlinearity of the process drops to 1/3 of its copolarized value [8]. Photonic crystal fiber (PCF) offers a distinct advantage over step-index fiber for BS. To get high efficiency conversion, the average of the wavelengths of the fields in a BS process is usually chosen to be close to the zero-dispersion wavelengths (ZDW) of the fiber [6]. Even custom-made dispersion-shifted 1041-1135/$26.00 © 2011 IEEE