RESUMEN
We proposed and demonstrated mode cleaning in a high-power fiber laser by integrating an anti-resonant hollow-core fiber (AR-HCF) into a multimode laser cavity of an ytterbium (Yb)-doped fiber (YDF). An in-house mode-matched AR-HCF was fusion-spliced to a commercial multimode LMA-YDF, ensuring efficient fundamental mode coupling. The AR-HCF inflicts a high propagation loss selectively on higher-order modes, facilitating fundamental mode operation. Thus, the AR-HCF works as an efficient spatial mode filter embedded in the multimode fiber laser cavity and reinforces preferential amplification of the fundamental mode. Beam quality factor enhancement was achieved from M2 = 2.09 to 1.39 at an output power of 57.7 W (pump-power limited). The beam quality can be further improved by refining the AR-HCF fabrication. The proposed technique has a great potential to be exploited in other multimode fiber laser cavities involving erbium- or thulium-doped fibers and obviates the need for complicated specialty active fiber designs. Compared with the commonly used fiber bending technique, our method can achieve an efficient higher-order mode suppression without inducing mode-field deterioration.
RESUMEN
We present the selective excitation of the fundamental mode in an anti-resonant hollow-core fiber (ARHCF) fusion-spliced with a commercial large mode area (LMA) fiber. By designing and fabricating a single-ring ARHCF that is mode-matched to a LMA fiber and by splicing the two using a CO2 laser-based splicer, we achieve a coupling efficiency of 91.2% into the fundamental mode. We also demonstrate an all-fiber integration of an ARHCF with a commercial ytterbium-doped fiber in a laser cavity for beam delivery application. Coupling of the single-mode laser output beam into the fundamental mode of the ARHCF is demonstrated with 90.4% efficiency (<0.45dB loss) for up to 50 W continuous wave beam in a stable and alignment-free all-fiber laser setup.
RESUMEN
We present an antiresonant hollow-core fiber-based bandpass optical filter. The device is realized by tapering down a section of tubular hollow-core fiber to a ratio of less than 0.5. Sweeping of the tube wall thickness-induced resonant bands in the down- and up-transition sections of the taper suppresses the blue side of the spectrum, while the red side filtering exploits the increased confinement loss at the taper waist that depends sharply on the wavelength-to-core-diameter ratio. These working principles of the filter make it possible to customize the location and width of the passband by tailoring the fiber design and taper profile. We achieve a 350-nm-wide bandpass filter with the minimum insertion loss of 1.3 dB in the passband and up to 40 dB suppression in the lossbands. We anticipate the filter to become one of the essential components in all-hollow-core fiberized optical systems.
RESUMEN
We demonstrate frequency down-conversions of femtosecond pulses through dispersive wave generation and degenerate four-wave mixing in a gas-filled anti-resonant hollow-core fiber. These are achieved by exploiting the rapid variation of the dispersion in the fiber's transmission band edge. In this approach, the wavelength of the down-shifted radiation is governed solely by the thickness of the dielectric wall at the core-cladding interface, while other system parameters are accountable only for inducing sufficient nonlinear phase shifts. With the right choice of cladding wall thickness, the concept can be applied directly for generating high-power mid-infrared femtosecond pulses.
RESUMEN
In this paper, we present the development and testing of an optical-based sensor for monitoring the corrosion of reinforcement rebar. The testing was carried out using an 80% etched-cladding Fibre Bragg grating sensor to monitor the production of corrosion waste in a localized region of the rebar. Progression of corrosion can be sensed by observing the reflected wavelength shift of the FBG sensor. With the presence of corrosion, the etched-FBG reflected spectrum was shifted by 1.0 nm. In addition, with an increase in fringe pattern and continuously, step-like drop in power of the Bragg reflected spectrum was also displayed.