High-energy picosecond fiber optical parametric oscillator emitting in the biological window around 1.7 pm

摘要

Ultrafast laser sources emitting in the spectral range 1600-1800 nm are very attractive for many biomedical applications such as multi-photon microscopy and laser surgery. Taking into account tissue scattering and absorption, it has indeed been shown that the optimum wavelength window in terms of penetration lies around 1700 nm. The development of fiber-based ultrafast lasers to address these applications is highly desired to offer reliable and cost effective laser solutions. The first approach to achieve this goal consists in developing mode-locked lasers based of Tm-Ho- or Bi-doped fibers and emitting directly around 1700 nm. Unfortunately, the performances of these sources are far from target in terms of pulse energy and laser dynamics. The second approach relies on nonlinear conversion of a pump pulse centred at 1550 nm through intrapulse stimulated Raman scattering or by exploiting fiber-based optical parametric oscillators (FOPO). Here, we demonstrate a DSF-based FOPO pumped by a dissipative soliton Er-doped fiber laser. We report, to the best of our knowledge, the highest energy at 1665 nm for a degenerate FWM FOPO pumped by ps pulses. The tuning of the FOPO was performed via the adjustment of the pump wavelength along with the time-dispersion-tuning technique. Optimizing the pump wavelength along with the FOPO cavity length allowed a broad tunability from 1617 to 1876 nm for the idler and from 1319 to 1518 nm for the signal. For a pump wavelength of 1566 nm, 4 ps idler pulses with 3 nJ energy have been obtained at 1665 nm, with a record-high internal conversion efficiency of 55 %. Pulse evolution within the cavity was also numerically investigated using a generalized nonlinear Schro?dinger equation (GNLSE) model and an excellent agreement with the experimental results was found. Amplitude noise measurements have been performed on both the pump and idler pulses and a good relative intensity noise (RIN) level lower than -140dBc/Hz have been measured. This work thus paves the way for the use of such a fiberized source in nonlinear imaging experiments such as coherent Raman microscopy and optical coherence tomography.