All-fiber higher-order-mode module with anomalous dispersion below 800nm

摘要

We present an all-silica fiber-based module with anomalous dispersion below 800nm. The fiber module is based on propagation in a higher-order-mode (HOM), and mode conversion is achieved using UV inscribed broadband longperiod gratings. The large normal material dispersion in silica in the near infrared is compensated by anomalous waveguide dispersion of the HOM resulting in a total HOM dispersion of +112.7ps/(nmkm) (β_2=-0.0355ps~2/m)at 770nm. The dispersion has been calculated from the preform index profile and measured with a white light interferometer. The operation bandwidth is ～20nm with an insertion loss of ～1.5dB. The multipath interference noise is less than -27dB in the operation bandwidth. Nearly linear pulse propagation can be obtained for pulse energies up to 65pJ at 75fs pulse duration. This power regime is interesting for e.g. medical two-photon fluorescence imaging. The proposed anomalous dispersion module is demonstrated in a 3.6m long femtosecond fiber delivery application to deliver 110fs pulses directly from the output of a Ti:Sapphire femtosecond laser without the need for prechirping.