Invited Papers Supercontinuum generation in non-silica fibers Jonathan H.V. Price ⇑ , Xian Feng, Alexander M. Heidt, Gilberto Brambilla, Peter Horak, Francesco Poletti, Giorgio Ponzo, Periklis Petropoulos, Marco Petrovich, Jindan Shi, Morten Ibsen, Wei H. Loh, Harvey N. Rutt, David J. Richardson Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK article info Article history: Available online 29 August 2012 Keywords: Soft glass Non-silica glass Microstructured fiber (MOF) Tellurite Supercontinuum Mid-infrared (mid-IR) abstract The development of super continuum sources is driven by the requirements of a wide range of emerging applications. This paper points out how non-silica fibers are of benefit not only because their broad mid- IR transparency enables continuum generation in the 2–5 lm region but also since the high intrinsic non- linearity of the glasses reduces the power-threshold for devices at wavelengths below 2 lm. For these glasses, the material zero-dispersion wavelength is typically shifted to long wavelengths compared to sil- ica so dispersion tailoring is key to creating sources based on practical, near-IR, solid state pump lasers. We show how modeling work has produced fiber designs that provide flattened dispersion profiles with high nonlinearity coefficients and zero-dispersion wavelengths in the near-IR. Building on this flexibility, modeling of the pulse dynamics then demonstrates how coherent mid-IR supercontinuum sources could be developed. We also show the importance of the second zero-dispersion wavelength using bismuth fibers as an example. Nonlinear mode-coupling is shown to be a factor in larger core fibers for high-power applications. Demonstrations of supercontinuum in microstructured tellurite fibers, all-solid lead–silicate (SF57) fibers and in bismuth fibers and tapers are then reported to show what has been achieved exper- imentally using a range of materials and fiber geometries. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Supercontinuum (SC) is now widely used in analytical spectros- copy and tomographic imaging applications across the visible and near IR range [1–4]. Moving to longer wavelengths, continuum generation in the mid-IR is an emerging research area driven by the large number of potential applications that require moderate to high brightness sources with wide bandwidths that are not adequately served by thermal emitters or quantum-cascade lasers. While optical parametric oscillators and amplifiers (OPO/OPAs) [5,6] have been used successfully, they are often complex and costly components that require high initial investment and main- tenance. Fiber based sources using well established high power fiber and solid state near-IR laser sources are therefore attractive [7–9]. Beyond a wavelength of 2 lm, due to the onset of losses in silica, it is often necessary to use non-silica glasses. Research on non-silica fibers has been ongoing for many years for sensing and imaging applications and for CO 2 laser beam delivery, where their low mid-IR loss is critical. However it is not only for long wavelength applications that these glasses provide potential advantages. The nonlinear properties of these glasses can enhance supercontinuum generation as they can have intrinsic nonlineari- ties 10 to 100 that of silica [9]. The use of microstructured optical fiber (MOF) technology, and tapering, provides a further enhancement to the nonlinearity and enables control over the dis- persion profile for both telecommunications switching [10–14], and for supercontinuum generation [15]. Dispersion control is critical in that it allows greater flexibility in terms of choice of SC pump wavelength since the zero-disper- sion wavelengths (ZDWs) of these materials are generally longer than for silica, as illustrated in previous work [7,9] and the material dispersion curves for bismuth and tellurite glasses are shown in la- ter sections of this paper. The waveguide dispersion of the fibers is therefore used to improve their compatibility with near-IR pump lasers, and in particular the Yb band at 1.05 lm, the Er band at 1.55 lm and the Tm/Ho band at 1.7–2.2 lm. In practice, dispersion tailoring is achieved by using high index contrast between the core and cladding either using fiber tapers, air holes in microstructured fibers or high-index-contrast glasses in the core and cladding of the fiber. The ability to tailor the fiber dispersion profile is a theme underlying all of our work and one which cuts across all the glasses and fiber designs. One of the primary advantages of MOF technol- ogy is that it provides for an enormous amount of design flexibility. The development of advanced numerical modeling tools has been 1068-5200/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.yofte.2012.07.013 ⇑ Corresponding author. E-mail address: jhvp@orc.soton.ac.uk (J.H.V. Price). Optical Fiber Technology 18 (2012) 327–344 Contents lists available at SciVerse ScienceDirect Optical Fiber Technology www.elsevier.com/locate/yofte