High energy femtosecond supercontinuum light generation in large mode area photonic crystal ﬁber Rim Cherif a, ⁎, Mourad Zghal a , Ivaylo Nikolov b , Miltcho Danailov b a Cirta'Com laboratory, Engineering School of Communication of Tunis (Sup'Com), Technopark El Ghazala, 2088, Ariana, Tunisia b Laser laboratory, Sincrotrone Elettra-Trieste, SS14, km 163.5, 34012 Trieste, Italy abstract article info Article history: Received 29 January 2010 Received in revised form 11 May 2010 Accepted 22 June 2010 Keywords: Nonlinear optics Large mode area photonic crystal ﬁber Supercontinuum generation Pulse propagation and solitons A large mode area photonic crystal ﬁber (LMA PCF) with an effective area of 180 μm 2 is used to generate a high energy, micro-joule range, ﬂat, octave spanning supercontinuum (SC) extending from ~ 600 nm to ~ 1720 nm. A train of femtosecond pulses from a widely-tunable parametric ampliﬁer pumped by a Ti: Sapphire regenerative ampliﬁer system are coupled into a 20 cm length of LMA PCF generating a SC of 1.4 μJ energy. We present an experimental study of the high energy SC as a function of the input power and the pumping wavelength. The spectrum obtained at a pump wavelength of 1260 nm presents spectral ﬂatness variation less than 12 dB over more than 1.1 octave bandwidth. The physical processes behind the SC formation are described in the normal and the anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation. © 2010 Elsevier B.V. All rights reserved. 1. Introduction A lot of effort has been dedicated to supercontinuum generation (SCG) in photonic crystal ﬁbers (PCF) since 1999 [1,2]. This process occurs when intense light is coupled into such ﬁber and is characterized by the appearance of several new spectral compo- nents on both sides of the pump wavelength which gradually evolve to a wide continuum covering in some cases more than an octave span [3]. Most studies in this ﬁeld have reported the SCG in a highly nonlinear photonic crystal ﬁber pumped in femto [4–9], pico [10,11], and nanosecond [5] regimes, with pulses of relatively low energy (pJ–nJ range). In most cases, small core PCF in which the dimensions of the core is about few μm 2 have been used, and the maximum coupled (and therefore output) power has been limited because of the high local intensity which can damage the ﬁber face. Large mode area photonic crystal ﬁbers (LMA PCF) exhibit large core size with typically two orders of magnitude higher area and thus can support higher energy pulses delivered from the pumping laser. Besides, the larger dimensions of the LMA PCF facilitate the coupling into the ﬁber and in addition allow a better control during the fabrication process, eliminating the birefringence that can be introduced. The special properties of these ﬁbers open the way to compact, single-mode, high energy supercontinuum sources with a low divergence of the output beam [12]. Few works only reported on the SCG in PCF LMA. Genty et al. studied the SCG by pumping 90–100 m long LMA PCF with 3 ns pulses [12]. Mitrofanov et al. obtained SC radiation in a 380 μm 2 LMA PCF spanning from 700 to 1800 nm with a total energy of 1.15 μJ [13]. In this paper we demonstrate that, a high energy supercontinuum of energy as high as 1.4 μJ and a ﬂat spectrum extending from ~600 nm to ~1720 nm can be generated in 20 cm length LMA PCF. We present an experimental characterization of the properties of the supercontinuum generation in the LMA PCF at different input powers and pumping wavelengths. A train of 100 fs pulses of 28 nm spectral width resulting in a time-bandwidth product of ~0.54 at 1260 nm is used to generate the continuum. The pump source consists of a parametric ampliﬁer pumped by a Ti:Sapphire regenerative ampliﬁer system tunable from 1080 nm to 2600 nm at a repetition rate of 1 kHz. The ﬁber exhibits a zero dispersion wavelength (ZDW) at λ ZDW = 1250 nm and an effective area of 180 μm 2 at λ =1260 nm. A SC of a maximum energy of 1.4 μJ is generated into the fundamental mode of the ﬁber at λ = 1260 nm, corresponding to a peak power at the ﬁber output of 14 MW. The physical processes leading to the construction of the continuum spectrum are studied by monitoring the growth of the SC while increasing the input optical power. The SC formation is investigated in both normal and anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation. 2. Fiber properties and SCG modelling The ﬁber used in our experiment is a commercial Crystal-Fiber LMA PCF with a triangular lattice cladding having an effective area of ~180 μm 2 . The effective area A eff of the ﬁber was calculated by means Optics Communications 283 (2010) 4378–4382 ⁎ Corresponding author. Tel.: +216 71 857 000; fax: +216 71 856 829. E-mail addresses: rim.cherif@supcom.rnu.tn (R. Cherif), mourad.zghal@supcom.rnu.tn (M. Zghal), ivaylo.nikolov@elettra.trieste.it (I. Nikolov), danailovm@elettra.trieste.it (M. Danailov). 0030-4018/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2010.06.070 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom