Optical Amplification in Hollow-Core Negative-Curvature Fibers Doped with Perovskite CsPbBr3 Nanocrystals

Abstract

We report a hollow-core negative-curvature fiber (HC-NCF) optical signal amplifier fabricated by the filling of the air microchannels of the fiber with all-inorganic CsPbBr₃ perovskite nanocrystals (PNCs). The optimum fabrication conditions were found to enhance the optical gain, up to +3 dB in the best device. Experimental results were approximately reproduced by a gain assisted mechanism based on the nonlinear optical properties of the PNCs, indicating that signal regeneration can be achieved under low pump powers, much below the threshold of stimulated emission. The results can pave the road of new functionalities of the HC-NCF with PNCs, such as optical amplification, nonlinear frequency conversion and gas sensors.

Keywords: hollow core fibers; nonlinear optical properties; perovskite nanocrystals; signal regeneration/amplification.

Figure 1

(a) Absorbance (blue continuous line) and PL (green continuous line) spectra of CsPbBr₃ PNCs dispersed in hexane; and (b) TEM image of cubic CsPbBr₃ PNCs. The average cube side is around 10 nm.

Figure 2

Experimental setup for optical gain measurements, consisting of two tip-shaped fibers coupled at both ends of the HC-NCF facets. CW-pump (405 nm) and probe signal (515 nm) beams are combined inside the first fiber by a fused fiber coupler (FC), whereas the second fiber collects light at the output of the HC-NCF into a spectrometer after a 450 nm long-pass filter.

Figure 3

(a) Cross section of an undoped fiber taken with optical microscopy; (b) picture of the whole doped HC-NCF being pumped with the 405 nm CW laser and zoomed axial fragment (this image was registered with an optical microscope that assists the experimental setup described in Figure 2). (c,d) PL cross-section images at input and intermediate (after cleaving) faces of the HC-NCF, respectively; (e) simulation of the modal field distribution of the seven-tube HC-NCF fiber operating at a wavelength of 515 nm in the absence of PNCs. Z-axis corresponds to the propagation direction; and (f) modal field distribution of the HC-NCF doped with PNCs concentrated on the tube walls after considering a PNC layer with 55 nm thickness.

Figure 4

(a) Spectra recorded at the extreme of a 140 mm long HC-NCF filled with PNCs (concentration of 1 mg/mL) for different laser pumping powers. Symbols correspond to the experimental data and solid lines to the fitting by the sum of two Gaussian lineshapes (the PL of the PNCs and the regenerated 515 nm laser line, or probe). (b) Integrated intensity of the PL (brown circles) and probe (green circles) signals deconvoluted from the spectrum in (a) for the 140 mm long HC-NCF. (c) Optical amplification ratio P_out/P_in for different HC-NCF lengths, as a function of the laser pumping power. (d) Gain in dB as a function of the absorbed laser power in the 140 mm long HC-NCF doped with colloidal PNCs. Continuous curves stand for calculated ASE gain (green line) and parametric amplification (orange line). The inset shows the FWHM of the probe signal with error bars as extracted from fitting experimental curves in (a) (the x-axis range is the same as in the main figure).