Theory & modelling

Understanding the linear and nonlinear properties of all the types of photonic crystal fibre we make, provides an essential complement to our experimental work, and requires the use of a wide variety of numerical and theoretical techniques. To study the linear properties, we primarily use finite element modelling, plane-wave expansion methods, and generalized Mie theory, along with analytical methods, e.g., for describing the resonances and polarization properties of helically twisted fibres [1]. We carry out design optimizations of existing fibres and develop new design approaches and theories for understanding the observed optical phenomena. The propagation of ultrashort laser pulses through gas-filled photonic-crystal fibres can lead to some extreme, and highly novel, nonlinear effects. For example, we recently discovered a new interaction between optical-solitons and photoionization of the filling gas [2–4]. Our numerical and theoretical work is strongly coupled to experiments, in which we are aiming at more extreme UV and infra-red light generation, and the creation of sub-femtosecond light pulses.  We solve both the generalized Schrodinger equation and full carrier-resolved electric field equations, using an existing code base which includes the linear and nonlinear material and geometrical effects along with high-field effects such as photoionization and the resulting phase-modulation resulting from the dynamics of the free-electrons. We are also developing new codes to study the nonlinear spatial effects in more detail, along with the co-propagation of high-harmonics in the extreme UV and X-ray spectral region.


  1. G. K. L. Wong, M. S. Kang, H. W. Lee, F. Biancalana, C. Conti, T. Weiss and P. St.J. Russell, Orbital angular momentum resonances in helically twisted photonic crystal fiber, Science 27, 446-449 (2012).
  2. P. Hölzer, W. Chang, J. C. Travers, A. Nazarkin, J. Nold, N. Y. Joly, M. F. Saleh, F. Biancalana and P. St.J. Russell, Femtosecond Nonlinear Fiber Optics in the Ionization Regime, Phys. Rev. Lett. 107, 203901 (2011).
  3. W. Chang, A. Nazarkin, J. C. Travers, J. Nold, P. Hölzer, N. Y. Joly and P. St.J. Russell, Influence of ionization on ultrafast gas-based nonlinear fiber optics, Opt. Express 19, 21018–21027 (2011).
  4. M. F. Saleh, W. Chang, P. Hölzer, A. Nazarkin, J. C. Travers, N. Y. Joly, P. St.J. Russell and F. Biancalana, Theory of Photoionization-Induced Blueshift of Ultrashort Solitons in Gas-Filled Hollow-Core Photonic Crystal Fibers, Phys. Rev. Lett. 107, 203902 (2011).

Figure: Pulses propagating in gas-filled kagomé PCF can experience dramatic self-compression down to few-cycles (here at ~ 7 cm) which can serve as a strong driver for the generation of a UV pulse.


Dr. Thomas Weiss (