Enhanced degree of temporal coherence through temporal and spatial phase coupling within a focused supercontinuum

In the diffraction of a supercontinuum source, a redistribution of amplitude and phase at the focal region is incurred by the coupling between the supercontinuum and the spatial phase caused by the lens diffraction, making it extremely difficult to predict the focal behaviour. We show that the coupling between the temporal phase of a SC source and the spatial phase from the diffraction by a low numerical aperture (NA) lens causes dramatic alterations in the spectra and the temporal coherence near the focal region, and that this effect is maximized in points of singularity. Furthermore, we show that such an enhancement in temporal coherence can be controlled by the pulse evolution through the photonic crystal fiber, in which nonlinear and disperive effects such as the soliton fission process provides the key phase evolution necessary for dramatically changing the coherence time of the focused electromagnetic wave

Polarization effects in a highly birefringent nonlinear photonic crystal fiber with two-zero dispersion wavelengths

A theoretical and experimental study is presented on polarized pulsed propagation from a highly birefringent nonlinear photonic crystal fiber with two-zero dispersion wavelengths. Experimental observations show that the input polarization state can maintain its linearity and that the fiber birefringence creates different spectral properties dependent on the input polarization orientation. The most extensive spectra are obtained for a coupling polarization angles aligned with the fast and slow axis, which is created by the high-order dispersion and Kerr nonlinearity

Effect of depolarization on temporal coherence within a focused supercontinuum

Under the conditions of vectorial diffraction, an increase in refraction at the extremities of the lens rotates the incident polarization state which transfers energy from the initial state to the orthogonal transverse field and the longitudinal field, which is known as depolarization. Since the field is a vectorial field containing three polarization components, the theory for the degree of coherence is first extended to incorporate cross-correlation effects within these vectorial components which are calculated through a coherency matrix. The use of this matrix provides an insight into interesting correlation effects between copropagating vectorial fields such as the coupled modes (linear polarized modes) of the supercontinuum generated by a photonic crystal fiber. An investigation is presented on the coherence times for the supercontinuum field generated by cross coupling into the photonic crystal fiber. The coherence times under cross-coupling conditions show that the degree of coherence of the two coupled modes from the fiber are different, which is due to the differences in phase. For a supercontinuum with a linear polarization state, the coherence times along the x, y, and z axes are different, with the most significant change occurring along the optical axis (z) where the coherence time changes by an order of magnitude when the numerical aperture is increased from 0.1 to 1

Media 1: Enhanced degree of temporal coherence through temporal and spatial phase coupling within a focused supercontinuum

Originally published in Optics Express on 26 October 2009 (oe-17-22-20140