Long period fibre gratings for tunable spectral enhancement of a supercontinuum

In this paper, we report that a fibre grating written into a PCF can be used to create a narrow enhancement feature in a supercontinuum spectrum. The self-phase modulation (SPM) acts on an ultrafast pulse spectrally shaped by a narrow-band phase or amplitude filter, creating spectral enhancement by a process of interference between the sharp spectral feature and the broad-band ultrafast pulse. Thus the idea can be extended to other types of filter, and here we demonstrate the creation of tunable spectral enhancement with a long-period fibre grating.