We demonstrate a 1480 nm cascaded Raman fiber laser with a new high efficiency architecture providing a record output power of 204 W. We achieve this through multiple Raman shifts of a high power 1117nm Yb-doped fiber laser in a single pass configuration mediated at all intermediate wavelengths using a seed source comprising a low power conventional 1480nm Raman laser. The conversion efficiency from 1117nm to 1480nm is ~65% (for a quantum limited efficiency of 75%). Enhancement in efficiency is achieved by elimination of excess optical loss present in the conventional cascaded Raman resonator based architecture.
We demonstrate a cascaded Raman fiber laser with a record output power of 104 W at 1480 nm. We achieve
this with an 1117 nm Yb-doped fiber laser pumping a cascaded Raman conversion to 1480nm. Enhanced efficiency is
achieved in the Raman cavity using a fiber with a long wavelength cut-off which prevents further Raman conversion of
1480 nm light and thus allowing for longer cavity lengths. The output is single mode making it a bright source for core
or cladding pumping of erbium-doped fiber lasers.
Chirped pulse amplification is a durable and widely used scheme for producing short pulses with duration less than 1ps
and pulse energies from μJ to even mJ levels. The compressor unit needs to be able to handle high peak powers and is
therefore traditionally made out of free space diffraction gratings. The stretcher unit, on the other hand, only has to
handle low peak power and can therefore be realized with a dispersion managed fiber. We review our work on stretcher
fiber design and dispersion managed modules in the Ytterbium gain band and Erbium gain band and present a modified
stretcher fiber for managing numerically higher third and fourth order dispersion. The modified design allows for a lower
incident angle on the compressor gratings and thereby reducing the grating separation and compressor size.
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/(nm•km) (β2 = -0.0355ps2/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 pre-chirping.