ABSTRACT
Nonlinear optical effects are remarkable physical phenomena that can occur when a high-intensity light beam propagates through an optical medium [1]. If the pump beam is intense enough and the medium exhibits suitable nonlinear behavior, the typical properties of the medium (absorption, refractive index) can alter because of the input beam. Unlike the linear propagation of light where the spectral and spatial components of light do not affect each other in a medium, the nonlinear interaction of light with matter gives rise to complex coupling between the light components through the medium [2]. These effects have been very often regarded as detrimental to fiberbased optical communication systems [3]. However, they also offer new and exciting potential applications, such as devices in which light can be controlled by light [4]. Due to their strong light confinement capabilities, optical fibers have been long recognized as an ideal medium to exploit the nonlinear effects for all-optical processing applications in telecommunication and fiber laser industries [5]. This research field has recently been dramatically stimulated by the development of a new generation of highly nonlinear optical fibers which has an array of tiny holes running through the whole length of the fiber (see Chap. 7 for a complete description). These so-called photonic crystal or microstructured fibers allow conversion of a single-color laser beam into a white light supercontinuum spanning two octaves in frequency [6] (i.e., a laser rainbow extending from the ultraviolet well into the infrared, as shown in Fig. 5.1). This new light source has revolutionized optical metrology, making absolute measurements of optical frequencies with unprecedented accuracy, and optical coherence tomography (OCT) with enhanced resolution. This topic will be described in more detail in Chapter 8.
