2 results
7 - Increasing the blue-shift of a picosecond pumped supercontinuum
- Edited by J. M. Dudley, Université de Franche-Comté, J. R. Taylor, Imperial College of Science, Technology and Medicine, London
-
- Book:
- Supercontinuum Generation in Optical Fibers
- Published online:
- 06 July 2010
- Print publication:
- 01 April 2010, pp 119-141
-
- Chapter
- Export citation
-
Summary
Introduction
The first experiments with supercontinuum generation in a photonic crystal fibre (PCF) demonstrated impressive spectra spanning from 400 nm to 1500 nm using 100 fs pulses (Ranka et al., 2000). Often, one does not require the use of the entire supercontinuum bandwidth, or the spectrum needs to be concentrated in a specific spectral region where other lasers are not readily available. One method is to use the soliton self-frequency shift to simply red-shift a laser pulse over a desired wavelength range, which can be done over 900 nm (Chan et al., 2008). This provides a basis for tunable lasers with applications including broadband spectroscopy (Walewski et al., 2004), and coherent anti-Stokes Raman scattering (CARS) microspectroscopy (Andresen et al., 2007). ZBLAN fluoride (a mixture of zirconium, barium, lanthanum, aluminium, and sodium fluorides) fibres have been used to extend a supercontinuum spectrum beyond 4.5 μm with potential applications in spectroscopy (Xia et al., 2006). Besides these examples of generating light in the near- or mid-infrared, one also finds examples of generating light in the ultraviolet–blue region of the spectrum. This wavelength region is highly interesting for several reasons. Primarily, many fluorescent molecules are excited in a wavelength range from ∼600 nm down to ∼350 nm (Prasad, 2003). Supercontinuum light sources covering this wavelength range are highly useful for fluorescence microscopy. In particular, a high spectral density over a broad wavelength range removes the need for using several lasers, each corresponding to the excitation wavelength of a specific fluorescent molecule.
3 - Nonlinear fibre optics overview
- Edited by J. M. Dudley, Université de Franche-Comté, J. R. Taylor, Imperial College of Science, Technology and Medicine, London
-
- Book:
- Supercontinuum Generation in Optical Fibers
- Published online:
- 06 July 2010
- Print publication:
- 01 April 2010, pp 32-51
-
- Chapter
- Export citation
-
Summary
Introduction
This chapter provides a succinct overview of the various nonlinear effects that can occur when a light field propagates in an optical fibre. Given that nonlinear fibre optics is a very mature research field, it has been covered in much detail by many previous reviews and monographs. The reader is particularly referred to Agrawal (2007) for a treatment that combines a review of both theory and experiments in a way that is simultaneously accessible and technically comprehensive. Other monographs that contain valuable material and references to the original literature include Taylor (2005) and Alfano (2006). In this treatment we provide only a brief introduction to the major concepts, placing particular emphasis on effects that play an important role in supercontinuum generation. Where appropriate, these effects will be discussed in more detail in other chapters. We do, however, treat the numerical modelling of nonlinear pulse propagation in more depth than is usually found in the literature.
Modelling nonlinear pulse propagation
The propagation of an electromagnetic wave or pulse depends on the medium in which it propagates. In vacuum a pulse can propagate unchanged. When propagating in a medium, however, an electromagnetic field interacts with the atoms, which generally means that the pulse experiences loss and dispersion. The latter effect occurs because the different wavelength components of the pulse travel at different velocities due to the wavelength dependence of the refractive index. In an optical waveguide, the total dispersion has an additional component due to the light confinement called waveguide dispersion, which cannot be neglected.