Mikko Lehtonen

Spectral broadening of femtosecond pulses into continuum radiation in microstructured fibers

We report on the influence of the choice of the pump wavelength relative to the zero-dispersion wavelength for continuum generation in microstructured fibers. Different nonlinear mechanisms are observed depending on whether the pump is located in the normal or anomalous dispersion region. Raman scattering and the wavelength dependence of the group delay of the fiber are found to play an important role in the process. We give an experimental and numerical analysis of the observed phenomena and find a good agreement between the two.

Supercontinuum generation in a highly birefringent microstructured fiber

We present experimental results on supercontinuum generation in a highly birefringent microstructured fiber. We show that such a fiber offers clear advantages for continuum generation over weakly birefringent fibers. In particular, the polarization is preserved along the fiber for all the spectral components. Furthermore, the two eigenpolarizations exhibit different dispersion characteristics, which provide a convenient way of tuning the properties of the generated continuum. We investigate the impact of the pump wavelength and pulse duration on the continuum and use the results to generate an ultrabroadband continuum extending from 400 to 1750 nm.

Enhanced bandwidth of supercontinuum generated in microstructured fibers.

Enhancement of the bandwidth of supercontinuum generated in microstructured fibers with a tailored dispersion profile is demonstrated experimentally. The fibers are designed to have two zero-dispersion wavelengths separated by more than 700 nm, which results in an amplification of two dispersive waves at visible and infrared wavelengths. The underlying physics behind the broad continuum formation is discussed and analyzed in detail. The experimental observations are confirmed through numerical simulations.

Route to broadband blue-light generation in microstructured fibers

We explore theoretically the possibility of generating broadband blue light by copropagating a short soliton pump pulse and a broader signal pulse in a microstructured fiber with a zero-dispersion wavelength located between the center wavelength of the pump and the signal pulses. We show that the unique properties of microstructured fibers should allow for broadening of the signal pulses spectrum by as much as a factor of 50 through the conjugate action of cross-phase modulation and a soliton self-frequency shift. The physical mechanism that leads to this large spectral broadening is analyzed by use of an extended nonlinear Schrödinger equation.

Supercontinuum generation in highly birefringent photonic crystal fiber

We report on the influence of pump laser polarization and wavelength on the supercontinuum generated in a highly birefringent photonic crystal fiber. We were able to produce a continuum that extends from 400 to 1700 nm. It can be used, e.g., for optical frequency synthesis.

Route to supercontinuum in photonic crystal fibers

Summary from only given. We have observed that when the pump wavelength is located in the anomalous dispersion regime, an ultrabroad continuum can be generated even if the pump wavelength is detuned more than 130 nm away from the zero-dispersion wavelength. In contrast, when the pump wavelength is located in the normal dispersion regime, the width of the continuum generated is smaller. We attribute the difference to be due to the mechanisms involved being different and to the behavior of the third-order dispersion parameter whose positive value decreases with wavelength for the particular fibers used.

Spectral modulation due to pulse reshaping in photonic crystal fibers

Summary form only given. We report here on experimental observations on strong modulation in the spectrum of short optical pulses propagating in a photonic crystal fibre (PCF). The modulation is explained to result from interference between the soliton and the radiation field, which is created when the Gaussian input pulse evolves into an asymptotic soliton.

Birefringent microstructured fibers: Properties and applications

Development of sophisticated techniques for manufacturing microstructured fibers has enabled the production of fibers with precisely controlled structures. For instance, fibers with very low or high birefringence have been demonstrated. We present the status of our work on characterization of the dispersion properties of birefringent microstructured fibers and discuss their use for generation of supercontinuum radiation.