Pulse-to-pulse relative intensity noise measurements for ultrafast lasers.

Relative intensity noise (RIN) can be used to characterize pulse-to-pulse energy variations of ultrafast lasers, and is a very important performance parameter when considering the suitability of a laser for an application. However, owing to a wide range of measurement and analysis techniques, comparison of RIN values is non-trivial. Here, we clearly layout a definition of RIN as a percentage value for ultrafast laser systems.

Supercontinuum noise reduction by fiber undertapering.

We demonstrate that the Relative Intensity Noise (RIN) of a supercontinuum source can be significantly reduced using the new concept of undertapering, where the fiber is tapered to a diameter that is smaller than the diameter that gives the shortest blue edge, which is typically regarded as the optimum. We show that undertapering allows to control the second zero dispersion wavelength and use it as a soliton barrier to stop the redshifting solitons at a pre-defined wavelength, and thereby strongly reduce the RIN. We demonstrate how undertapering can reduce the spectrally averaged RIN in the optical coherence tomography bands, 500-800nm and 1150-1450nm, by more than a factor two.

Polarization noise places severe constraints on coherence of all-normal dispersion femtosecond supercontinuum generation.

Supercontinuum (SC) generated with all-normal dispersion (ANDi) fibers has been of special interest in recent years due to its potentially superior coherence properties when compared to anomalous dispersion-pumped SC. However, care must be taken in the design of such sources since too long pump pulses and fiber length has been demonstrated to degrade the coherence. To assess the noise performance of ANDi fiber SC generation numerically, a scalar single-polarization model has so far been used, thereby excluding important sources of noise, such as polarization modulational instability (PMI).