Infrared supercontinuum generation in soft-glass photonic crystal fiber pumped with a femtosecond Er-doped fiber laser mode-locked by grapheme saturable absorber

Abstract

Summary form only given. Most of the research work related to supercontinuum generation in photonic crystal fibres (PCFs) has, to date, been focused on the more conventional mainly silica based fibres operating in the visible and near infrared (NIR) ranges [1]. PCFs based on soft glasses have also been used successfully for broadband supercontinuum generation [2]. The use of broadband mid infrared (mid-IR) sources in the fields of sensing and spectroscopy has seen a tremendous increase in recent years.We have developed highly nonlinear PCF using lead-bismuth-galatte soft glass (Fig. 1a). The photonic cladding consists of 8 rings of air holes with a fibre core diameter of 3.1 gm and a lattice constant of 2.4 gm. The dispersion characteristic is determined mainly by the material dispersion and the diameter of the first ring of holes in the cladding with a filling factor of 0.73. The filling factor of the remaining 7 rings is 0.54 which allows single mode performance of the fibre in the infrared range. The fibre has a zero dispersion wavelength of 1460 nm which allows the use of 1560 nm wavelength as an efficient pump in the anomalous dispersion regime (Fig. 1a). As a pump for supercontinuum generation we have used a Chirped Pulse Amplification (CPA) system seeded by a graphene mode-locked laser [3]. The system consists of a mode-locked Er-fiber oscillator operating at 1560 nm wavelength [4], a grating-based pulse stretcher, two-stage amplifier and a grating compressor. The laser setup allows to amplify the seed up to 1 W of average power (1000 times amplification) with linearly polarized 810 fs pulses and 20 nJ pulse energy at 55 MHz repetition rate. With a 4 cm PCF sample, we have obtained a broad supercontinuum spanning from 0.88 gm to 1.7 gm. A flatness of 7 dB was observed in the spectral range 970 -1620 nm despite the pump peak.