Abstract

Ultrafast laser sources emitting in the spectral range 1600-1800 nm are very attractive for many biomedical applications such as multi-photon microscopy [1] and laser surgery [2]. 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 [3]. 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 [3-4]. Unfortunately, the performances of these sources are far from target in terms of pulse energy and laser dynamics [3-4]. The second approach relies on nonlinear conversion of a pump pulse centred at 1550 nm through intrapulse stimulated Raman scattering [1] or by exploiting fiber-based optical parametric oscillators (FOPO) [5]. Here, we demonstrate a DSF-based FOPO pumped by a dissipative soliton Er-doped fiber laser [6]. 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 (Fig. 1(a)). 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 (Fig. 1 (b)). 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 Schrödinger 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.

© 2017 IEEE