Soliton molecules, referred to as closely bounded solitons, have recently attracted considerable interest in both fundamental nonlinear physics research and refreshed application promises. To date, extensive efforts have been made on the generation of quadratic soliton molecules. These are soliton molecules whose formation exclusively involves second-order dispersion and Kerr nonlinearity. Here, for the first time, we demonstrate the realization of various third-order dispersion-supported soliton molecules, including vector dark–anti-dark solitons, vector anti-dark solitons, and vector anti-dark soliton molecules formed in a fiber laser with net cavity dispersion near the zero-group-velocity-dispersion point. High-order dispersion could greatly alter the internal soliton interaction within a soliton molecule. This finding could open exciting new avenues in soliton research.
We experimentally and numerically demonstrate a simple and general technique to reduce the noise of modulational instability and soliton-based broadband supercontinuum lasers at the pulse-to-pulse level. Because of the requirement of low cost and high average power, such supercontinuum lasers constitute 99% of today’s commercially available supercontinuum lasers. The technique relies on adding a short normal dispersion fiber to force the spectrally and temporally distributed solitons to spectrally broaden through self-phase modulation (SPM) and thereby overlap to average out the noise. We experimentally demonstrate that this SPM technique provides significant noise reduction over a broad bandwidth.
Mid-infrared supercontinuum lasers are spatially coherent and can cover a wide spectral range of 2-10 μm. This makes them useful in many important applications, such as spectroscopy and optical coherence tomography. 2.8 μm ultrafast lasers are an important emerging pump wavelength for mid-infrared supercontinuum sources. We present our work on MHz repetition rate 2.8 μm erbium-doped ZBLAN fiber lasers using a MOPA architecture to boost the output power. Performing pulse break-up in a highly Germania-doped silica fiber and pumping this spectrum into a highly nonlinear sulfide fiber, we demonstrate both the noise and bandwidth achievable with the novel fiber cascade. We acknowledge funding from Villum Fonden (2021 Villum Investigator project no. 00037822: Table-Top Synchrotrons).
Large mode area (LMA) fibers form an important part of high-power fiber lasers. There is significant research interest in achieving larger mode field area (MFA) for output power scaling and it is equally desirable to have single-mode operation in these fibers to maintain a good beam quality and suppress transverse mode instabilities. An increase in MFA is typically associated with high sensitivity to bend-induced losses and mode-shrinkage, necessitating several ultra-LMA fiber designs to be supported by thick outer jackets to form a rod-shape fiber. We present a hybrid light guidance mechanism in an all-solid antiresonant fiber, which combines antiresonance guidance with total internal reflection guidance to reduce the confinement loss and bending-induced losses by orders of magnitude. Low-index rods are strategically placed in the cladding to cover the gaps between the antiresonant elements to reduce confinement loss in straight fiber and suppress bending-induced leakage loss by orders of magnitude. We present detailed numerical analysis of a typical hybrid-guidance antiresonant fiber (HGARF) with core diameter 80 μm, optimized for operation in 1 μm wavelength range. The wavelength range of operation in the HGARF is decided solely by the wall thickness of the antiresonant elements and therefore the design principles can be extended to the 2 μm wavelength range.
We report a novel method to enhance the modal interference pattern in an anti-resonant negative curvature hollow-core fiber (NCHCF), enabling in-fiber multimodal interferometer in a short (few mm) length. The enhanced interference provides well defined fringes suitable for sensing; and their application for mechanical sensing is demonstrated. An 8 mm length of NCHCF was exposed to periodic arcs from a conventional splicer, leading to periodic modulation of fiber parameters along the length of the fiber. This periodic modulation alters the interaction between interfering modal fields, causing enhanced modal overlap and a four-fold increase in the intensity variation of the interference pattern. The enhanced interference dips are observed to be sensitive, with a linear response, to external mechanical forces like curvature, while being insensitive to thermal crosstalk by virtue of the hollow core design.
In fiber lasers, operating in normal dispersion regime benefits high peak power operation thanks to no pulse breakup as in anomalous dispersion. However, the spectral range of Thulium (Tm) emission lies in anomalous dispersion regime for conventional optical fibers. Hence, a customized W-type step-index Normal Dispersion Thulium Fiber (NDTF) is designed to have strong waveguide dispersion at the Tm emission band. The dispersion of NDTF is -28.97 ps/nm.km at 1.9 μm wavelength. An all-fiber seed source based on a ring oscillator was built with the NDTF as the active fiber and produce mode-locked soliton pulses near 2 μm. Subsequently, the pulses are amplified through the NDTF in an all-fiber amplifier stage. The NDTF amplifier produced pulses of ~593 nJ pulse energy in a ~4.4 ps FWHM pulse width. The amplified pulse is then compressed to ~1.91 ps giving a peak power of ~310 kW in an all-fiber compressor consisting of SMF28 fiber. This represents a potential to generate high peak powers in ultrashort pulses at 2 μm wavelength in all-fiber configuration.
We demonstrate a 70 mol % GeO2 doped fiber for mid-infrared supercontinuum generation. Experiments ensure a highest output power for a broadest spectrum from 1000nm to 3000nm from this fiber, while being pumped by a broadband 4 stage Erbium fiber based MOPA. Our investigations reveal the unexploited potential of Germania doped fiber for mid-infrared supercontinuum generation. To the best of our knowledge, this is the record power, for an ultrabroadband, all-fiberized, and compact device size supercontinuum light source based on Silica and Germania fiber, ever demonstrated to the date.
Hollow-core anti-resonant fiber (HAF) shows promising applications. Nevertheless, there has been a persistent problem when it comes to all-fiber integration due to lack of HAF based fiber components. Interconnecting a solid core based fiber component with HAFs remains limited solutions. As a result, most of the HAF based optical systems rely on free space optical components that make the system cumbersome and increases the complexity of the system.
In response to this remained challenge, we investigate a reliable, versatile, and efficient method to convert a HAF into a fiber filter. By locally heating a HAF with a CO2 laser, the fiber structure gets deformed and cladding capillaries shrink to produce a thicker wall. This process is analogous to "writing" a new fiber with a thicker wall on the original fiber, resulting in creating new high loss regions (resonant wavelengths) in the original transmission bands. Thus, construction of a fiber filter is realized by “writing” a new fiber on the original fiber. Feasibility of this method is confirmed through experiments, adopting both one and two-layer HAF. The HAF based fiber filters are found to have transmission spectra consistent with simulation prediction. Both band pass and band reject fiber filters with more than 20 dB extinction ratio are obtainable without extra loss. Thus, an in-fiber HAF filter is demonstrated by CO2 writing process. Its versatile approach promises controlled band selection, and would find interesting applications to be discussed.
We demonstrate a 74 mol % GeO2 doped fiber for mid-infrared supercontinuum generation. Experiments ensure a highest output power for a broadest spectrum from 700nm to 3200nm from this fiber, while being pumped by a broadband 4 stage Erbium fiber based MOPA. The effect of repetition rate of pump source and length of Germania-doped fiber has also been investigated.
Further, Germania doped fiber has been pumped by conventional Silica based photonic crystal fiber supercontinuum source. At low power, a considerable broadening of 200-300nm was observed. Further broadening of spectrum was limited due to limited power of pump source. Our investigations reveal the unexploited potential of Germania doped fiber for mid-infrared supercontinuum generation. This measurement ensures a possibility of Germania based photonic crystal fiber or a step-index fiber supercontinuum source for high power ultra-broad band emission being pumped a 1060nm or a 1550nm laser source. To the best of our knowledge, this is the record power, ultra-broadband, and all-fiberized SC light source based on Silica and Germania fiber ever demonstrated to the date.
In this work we present the theoretical study of transverse mode instability (TMI) in ytterbium (Yb)-doped rectangular core fibers with different core aspect ratios using the fast Fourier transform (FFT) beam propagation method (BPM). As expected, the rectangular core fiber with larger aspect ratio (AR.) offers more efficient heat dissipation than a circular core fiber. However, it is found that the rectangular core fiber does not benefit from the better heat dissipation to suppress the TMI when compared to the circular core counterpart. The temperature building in the rectangular core fiber decreases by up to 24.6% with a 10:1 aspect ratio core, while threshold pump power drops by up to 38.3% when compared with a circular core fiber with the same core area. Our study reveals that a smaller effective refractive index difference between modes and a weaker gain saturation effect compensate the thermal advantage from more efficient heat dissipation.
A split cladding fibers (SCF) is proposed as an additional design to the anti-resonant type fiber. The introduced split cladding helps to reduce the fabrication distortion. We use numerical simulations to compare the Kagome fibers (KFs) and the proposed split cladding fibers (SCFs) over two normalized transmission bands. It reveals that SCFs are able to maintain the desired round shape of silica cladding walls, hence improving the confinement loss (CL) compared to the KF. Fabrication of the SCF is demonstrated by the stack-and-draw technique. The near filed mode patterns are measured to prove the feasibility of this fiber design.
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