Abstract:We demonstrate parametric amplification around 2 μm in a dispersion engineered tapered microstructured chalcogenide fiber. Almost 5 dB of signal amplification was achieved by 125 mW coupled power from a thulium-doped fiber pump laser.OCIS codes: (060.4005) Microstructured fibers; (190.4410) Nonlinear optics, parametric processes; (230.4480) Optical amplifiers 1. Introduction Continuous-wave (CW) pumped parametric wavelength conversion and amplification was demonstrated to possess ultrahigh response together with reduced nonlinear noise, enabling high performances in all-optical processing using highly nonlinear fibers in the telecom band [1]. Due to the excessive loss of silica fibers beyond 2 μm, several new platforms were developed to translate parametric processes in the mid-infrared (MIR). Parametric amplification was achieved in planar silicon waveguide [2] and tapered As2Se3 fiber [3] in the 2µm wavelength range using a pulsed pump. However, both platforms have high propagation loss in orders of dB/cm, inhibiting CW operation.Here, we demonstrate in an all-fibered platform, MIR CW pumped parametric amplification in a tapered Ge10As22Se68 photonic crystal fiber (PCF). The PCF is engineered to blue shift the zero dispersion wavelength (ZDW) in the thulium emission band and features single mode operation over a large wavelength span, low propagation losses, and high nonlinearity [4]. We obtained signal amplification of 4.5 dB and idler conversion efficiency (CE) of 2 dB in a one meter-long fiber with only 125mW from a telecom pumped Tm-doped fiber laser [5]. This result nominates Chalcogenide glass (ChG) PCF as one of the most promising waveguide platform for advanced nonlinear applications in MIR.
Experimental result and discussionThe cross-section of the PCF is composed by three hexagonal concentric rings of air holes and was initially designed to feature a diameter to pitch ratio (ρ) of 0.6 with a core diameter of 4 μm. These parameters allow the maximum blue shift of the ZDW, near 3 micron, within a single drawing process. To further shift the ZDW in the 2 micron range, we tapered the fiber to have a core diameter in the waist region of about 1.5 μm. An optical image of the cross-section of the two different regions of the fiber is shown in Fig. 1a, while a sketch of the fiber with its parameters is reported in Fig. 1b. The set-up consists in two custom made Tm-doped fiber lasers pumped with Lband erbium-doped fiber amplifiers (EDFAs). The pump wavelength is selected by using different fiber Bragg gratings (FBGs), featuring a constant linewidth of about 0.08 nm, while the signal wavelength is tunable from 1950 nm to 2050 nm.