Polarization- and mode-dependent anti-Stokes emission in a birefringent microstructure fiber

We have studied the polarization dependence of frequency-upconversion of 35-fs pulses of 820-nm Ti : sapphire laser radiation in a birefringent microstructure fiber with a high air-filling-fraction cladding. The central wavelength of frequency-upconverted radiation and its transverse intensity profile are controlled in our experiments through a selective coupling of the pump field into higher order modes of the fiber and polarization-sensitive phase matching in parametric four-wave mixing, allowing the central wavelength of the anti-Stokes fiber output to be tuned and its transverse intensity profile to be modified by varying the polarization state of the input pump field.