Mode-filtered large-core fiber for short-pulse delivery with reduced nonlinear effects

Abstract

We present a large-core fiber (LCF) with a reduced nonlinear property for a single-mode beam delivery of intense ultrashort pulses. A tapered-fiber mode filter was fabricated in an LCF with the core diameter decreased from 20 μm to 6 μm at the tapered waist region surrounded by index-matched liquid. By the tapered geometry, the high-order mode was rejected so that our mode-filtered LCF acted as a single-mode fiber despite the multimode property of the original LCF. It has been found that this fiber class is suitable for applications, such as an endoscopic multiphoton microscope, that demand a flexible short-distance (<4 m) delivery medium of ultrashort pulses.

Fig. 1

(Color online) Schematic of the tapered-fiber mode filter that illustrates the HOM rejection.

Fig. 2

(Color online) Mode-field images of the inputs and the outputs of the MF-LCF under the offset launch for the two different wavelengths, 850 nm and 1; 040 nm, respectively.

Fig. 3

(Color online) Normalized radial intensity distributions of the input [(a) and (c)] and those of the output [(b) and (d)] of the MF-LCF. ΔR(r) was multiplied by 10 for better visibility in (b) and (d).

Fig. 4

(Color online) Measured short-pulse spectra after being transmitted through the SMF (a) and our MF-LCF (b), respectively, displayed together with the mode-field images of the SMF, MF-LCF and the LMA-PCF acquired at λ = 850 nm (c).