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Three fold symmetric microstructured fibers for customized sub-nanosecond supercontinuum generation
Abstract
We present three fold symmetric microstructured fibers and their application potential for customized single mode supercontinuum generation. In our microstructured fibers we simultaneously achieve high nonlinearity and single mode operation by increasing three cladding air holes, which are next to the core. Selectively modified microstructures allow a large degree of freedom in the dispersion profile design. With the use of sub nanosecond pump source at the wavelength of 1064 nm we show, that the designed microstructure provides various ways of generating a unique flat and broadband spectrum.
... However, this sacrifices mechanical strength. Existing research has shown that larger air-filling ratios are achievable [41][42][43][44], and various two-sized circular designs have been proven feasible [45][46][47]. Several structures that are structurally similar to the proposed PCF have been successfully fabricated [48][49][50]. ...
An exceptionally high-performance, high-birefringent photonic crystal fiber (PCF) is meticulously designed. The core design features a unique arrangement in which the central row of circular air holes is substituted by three rows of smaller circular holes. Subsequently, the middle row is adjusted to achieve various rectangular mode field configurations. With the optimized structure parameters, the birefringence of the PCF can reach 3.57 × 10−2 at a wavelength of 1.55 μm. The confinement loss is as low as 8.4 × 10−6 dB/m. The nonlinear coefficient is up to 41 W−1·km−1. The dispersion is relatively flat within the range from 1.3 μm to 1.9 μm. These remarkable characteristics render the proposed PCF a strong candidate for applications in polarization preservation, dispersion compensation, wideband supercontinuum generation, and other related fields.
... The means of fiber development of natural, regenerated, manmade, high-modulus/high-tenacity, inorganic, high-quality, and smart fibers have become the special attention of the world so that reflect a great impact on the way of life [5]. Historically, advancements have been customized in terms of the development of ideas of fiber structure, polymer assembly, Means of investigating fiber structure, especially crystal structures in high-performance fibers [6,7] macromolecular hypothesis, fundamentals of polymer crystallization, relations between fiber structure and performance [8]. ...
The current situation of the textile fibers has been on a great deal for scientific applications and environmental concerns. Transformations have been taken place due to the need of improved properties in the new age group end requests. Textile fiber polymers will bring about a revolution as they have started replacing the metals and will make the bright future due to the various research and development activities of the world. The main thrust has been in nano-technologies applied to textiles and clothing to improve the properties and performance of existing materials. Overall, this review has covered the most prominent new polymeric fibers in the next generation especially biodegradable fibers, high-performance application fibers, and the nano technology and its impact on the next generation fibers.
All-fiber ultraviolet (UV) light sources are of great practical interest for a multitude of applications spanned across different sectors, from industrial processes such as nonthermal, high-resolution materials processing, to biomedical applications such as eye surgery, to name a few. However, production of UV light sources with high beam quality has been a problem to this day as the fiber designs required to reach UV wavelengths by four-wave mixing with widely available pumps (i.e., 532 nm) are challenging because of their small size and increased risk of material damage. In this Letter, a specific pumping scheme is presented that allows the conversion of two pump photons in different modes to UV light in the fundamental mode and the corresponding idler in a higher order mode. The process has also been shown to work experimentally, and UV light at 390.5 nm in the fundamental mode was successfully generated.
A compact light source module for ultrabroadband coherent anti-Stoke Raman scattering (CARS) microscopy was developed. It mainly consists of a nanosecond microchip laser, a photonic crystal fiber for Stokes light generation, and a single mode polarization maintaining fiber for pump light propagation. It is alignment-free and relatively low-cost compared with previous light sources of CARS microscopy. By using an assembled module, we successfully observed an ultrabroadband CARS spectrum and a CARS image of a murine adipocyte. The module is expected to greatly spread the CARS microscopy to various fields by its extreme easiness to handle.
A low-loss suspended core As38Se62 fiber with core diameter of 4.5 μm and a zero-dispersion wavelength of 3.5 μm was used for mid-infrared supercontinuum generation. The dispersion of the fiber was measured from 2.9 to 4.2 μm and was in good correspondence with the calculated dispersion. An optical parametric amplifier delivering 320 fs pulses with a peak power of 14.8 kW at a repetition rate of 21 MHz was used to pump 18 cm of suspended core fiber at different wavelengths from 3.3 to 4.7 μm. By pumping at 4.4 μm with a peak power of 5.2 kW coupled to the fiber a supercontinuum spanning from 1.7 to 7.5 μm with an average output power of 15.6 mW and an average power >5.0 μm of 4.7 mW was obtained.
Dispersion control with axially nonuniform photonic crystal fibers (PCFs) permits supercontinuum (SC) generation into the deep-blue from an ytterbium pump laser. In this Letter, we exploit the full degrees of freedom afforded by PCFs to fabricate a fiber with longitudinally increasing air-fill fraction and decreasing diameter directly on the draw-tower. We demonstrate SC generation extending down to 375 nm in one such monolithic fiber device that is single-mode at 1064 nm at the input end.
We have studied the excitation of higher-order modes and their role in supercontinuum generation in a three-hole silica suspended-core fiber, both experimentally and numerically. We find that pump coupling optimized to highest transmission can yield substantial excitation of higher order modes. With up to about 40% of the pump power coupled to higher order modes, we have studied supercontinuum generation in this fiber. In agreement with experiments, simulation results based on the multimode generalized nonlinear Schrödinger equation confirm that the spectral width is determined by spectral broadening in the fundamental mode, whereas the numerical analysis reveals that intermodal nonlinear interactions are strongly suppressed.
We report on supercontinuum generation (SG) in a hexagonal lattice tellurite photonic crystal fiber (PCF). The fiber has a regular lattice with a lattice constant , linear filling factor , and a solid core 2.7 μm in diameter. Dispersion, calculated from scanning electron microscope (SEM) image of drawn fiber, has zero dispersion wavelength (ZDW) at 1410 and 4236 nm with a maximum of at 2800 nm. Under pumping with pulses, supercontinuum spectrum in a bandwidth from 800 nm to over 2500 nm was observed in a 2 cm long PCF sample, which is comparable to results reported for suspended core tellurite PCFs pumped at wavelengths over 1800 nm. Measured spectrum is analyzed numerically with good agreement, and observed spectral broadening is interpreted. To our best knowledge, tellurite glass, regular lattice PCFs for successful SG in this bandwidth have not been reported before.
Ge O 2 -doped-core photonic crystal fibers show greatly enhanced Kerr and Raman responses with respect to pure silica without any significant modification of the group-velocity dispersion curve. We show that such fibers allow a significant improvement of cw-pumped supercontinuum generation. We report for the first time to our knowledge the generation of a white-light cw-pumped supercontinuum spanning from 470 nm to more than 1750 nm .
We demonstrate an experimental study of the chromatic dispersion properties for a series of microstructured fibers (MSFs) dedicated for a supercontinuum generation. With white-light interferometry application we analyze experimentally how the small variations of structural parameters, i.e. an air-hole diameter and a lattice constant, influence dispersion characteristics in different groups of MSFs. Our study provides useful information on how to design the fiber which is less sensitive to the fabrication imperfections. Moreover those investigations are the initial step to the development of the customized or tunable supercontinuum light sources based on MSFs with slightly changed structural parameters which can generate light with a different spectrum range, adapted to a proper application.
A GeO2 doped triangular-core photonic-crystal fiber (PCF) is designed and fabricated to allow the generation of a hollow beam through a nonlinear-optical transformation by femtosecond pulses at 1040 nm from a high power Yb-doped PCF laser oscillator. The hollow beam supercontinuum is obtained at far field by adjusting incident light polarization to excite the high order supermode, behaving as a mode convertor. The supercontinuum ranging from 540 to 1540 nm is achieved with an average power of 1.04 W.
Brillouin scattering property in a highly nonlinear photonic crystal fiber (HNL-PCF) with hybrid-core structure is experimentally investigated. The HNL-PCF comprises a highly Ge-doped core surrounded by a triangularly-arranged F-doped buffer. It is experimentally shown that there exist five Brillouin resonance peaks with ~300 MHz frequency spacing in the Brillouin gain spectrum, which can be classified into two groups physcially attributed to two spatially separated layers of Ge-doped and F-doped regions. These peaks have similar linear dispersion characteristics and their effective acoustic velocities increase monotonically by the order of the peaks. The acousto-optic overlapping efficiency in the fiber is measured to be ~50%, which indicates that the stimulated Brillouin scattering threshold in the HNL-PCF is twofold enhanced. The temperature and strain dependences of the first resonance peak are also investigated, showing the similar behaviors as those in all-silica optical fibers.
We have developed a new multimodal molecular imaging system that combines CARS (coherent anti-Stokes Raman scattering), SHG (second harmonic generation), THG (third harmonic generation) and multiplex TSFG (third-order sum frequency generation) using a subnanosecond white-light laser source. Molecular composition and their distribution in living cells are clearly visualized with different contrast enhancements through different mechanisms of CARS, SHG, THG and TSFG. A correlation image of CARS and TSF reveals that the TSF signal is generated predominantly from lipid droplets inside a cell as well as the peripheral cell wall.
Recently, the generation of coherent, octave-spanning, and recompressible supercontinuum (SC) light has been demonstrated in optical fibers with all-normal group velocity dispersion (GVD) behavior by femtosecond pumping. In the normal dispersion regime, soliton dynamics are suppressed and the SC generation process is mainly due to self-phase modulation and optical wave breaking. This makes such white light sources suitable for time-resolved applications. The broadest spectra can be obtained when the pump wavelength equals the wavelength of maximum all-normal GVD. Therefore each available pump wavelength requires a specifically designed optical fiber with suitable GVD to unfold its full power. We investigate the possibilities to shift the all-normal maximum dispersion wavelength in microstructured optical fibers from the near infra red (NIR) to the ultra violet (UV). In general, a submicron guiding fiber core surrounded by a holey region is required to overcome the material dispersion of silica. Photonic crystal fibers (PCFs) with a hexagonal array of holes as well as suspended core fibers are simulated for this purpose over a wide field of parameters. The PCFs are varied concerning their air hole diameter and pitch and the suspended core fibers are varied concerning the number of supporting walls and the wall width. We show that these two fiber types complement each other well in their possible wavelength regions for all-normal GVD. While the PCFs are suitable for obtaining a maximum all-normal GVD in the NIR, suspended core fibers are well applicable in the visible wavelength range.
Using a low-cost microchip laser and a long photonic crystal fiber taper, we report a supercontinuum source with a very efficient visible conversion, especially in the blue region (around 420 nm). About 30 % of the total average output power is located in the 350–600 nm band, which is of primary importance in a number of biophotonics applications such as flow cytometry or fluorescence imaging microscopy for instance. We successfully demonstrate the use of this visible-enhanced source for a three-color imaging of HeLa cells in wide-field microscopy.
Photonic crystal fibres exhibiting endlessly single-mode operation and dispersion zero in the range 1040 to 1100 nm are demonstrated. A sub-ns pump source at 1064 nm generates a parametric output at 732 nm with an efficiency of 35%, or parametric gain of 55 dB at 1315 nm. A broad, flat supercontinuum extending from 500 nm to beyond 1750 nm is also demonstrated using the same pump source.
Photonic crystal fibers are highly attractive as nonlinear media as they combine a large nonlinear coefficient and a highly customizable zero dispersion wavelength - flexibility not found in any other medium. However, the high dispersion slope at the zero-dispersion wavelength demonstrated so far is very limiting to the useful bandwidth. We propose a new fiber design comprising a hybrid core-region with three-fold symmetry that enables unprecedented dispersion control while maintaining low loss and a high nonlinear coefficient. The lowest dispersion slope obtained is 1·10⁻³ps/(km·nm²) or one order of magnitude lower than for conventional slope reduced nonlinear fibers. The nonlinear coefficient is more than 11 (W·km)⁻¹ and loss below 7.9 dB/km at 1.55 µm has been achieved.
We report a new approach for the fabrication of nanowires: the direct drawing of optical fibers with air suspended nanoscale cores. The fibers were made from lead silicate glass using the extrusion technique for preform and jacket tube fabrication. Fibers with core diameters in the range of 420–720 nm and practical outer diameters of 110–200 μm were produced, the smallest core sizes produced to date within optical fibers without tapering. We explored the impact of the core size on the effective mode area and propagation loss of these suspended nanowires relative to circular nanowires reported to date. As for circular nanowires, the propagation loss of these suspended nanowires is dominated by surface roughness induced scattering.
Modulation instability of a continuous infrared wave leading to red-shifting solitons and blue-shifting dispersive waves and then subsequent soliton trapping is shown to enable the generation of blue solitary waves in optical fibers. The physical mechanism is described in the context of continuous wave supercontinuum generation leading to a spectrum which spans the visible and near infrared within practical experimental conditions.
We study the effect of stimulated Raman scattering on four-wave mixing sidebands generated by pumping in the normal dispersion regime of a photonic crystal fiber. Q-switch nanosecond pulses at 1064 nm are used to generate signal and idler wavelengths by degenerate four-wave mixing. These three waves generate their own Raman Stokes orders, leading to a broadband supercontinuum.
We present an experimental and numerical study of supercontinuum generation extended in the visible part of the spectrum by using a selective optical coupling of the pump wave in the largely anomalous dispersion regime. The broadband frequency generation is induced by an initial four-wave mixing process that converts the pump wave at 1064 nm into 831 nm anti-Stokes and 1478 nm Stokes wavelengths. Phase matching is ensured on such a large frequency shift thanks to a microstructured multimodal fiber with a specific design. Continuum generation is therefore enhanced around the two generated sidebands.
We present a series of three fold symmetric silica microstructured fibers for nonlinear application. The fibers are designed to have zero dispersion wavelength far from the pump wavelength. In our fibers a domination of nonlinear effects is precisely controlled by selectively increased three air holes in the vicinity of the core. Our fibers allow for the broadband single mode spectrum generation and the achievement of flat spectra even after changes of fiber dispersion caused by fabrication inaccuracies.
Tapering of photonic crystal fibers has proven to be an effective way of blueshifting the dispersive wavelength edge of a supercontinuum spectrum down in the deep-blue. In this article we will review the state-of-the-art in fiber tapers, and discuss the underlying mechanisms of supercontinuum generation in tapers. We show, by introducing the concept of a group-acceleration mismatch, that for a given taper length, the downtapering section should be as long as possible to enhance the amount of blueshifted light. We also discuss the noise properties of supercontinuum generation in uniform and tapered fibers, and we demonstrate that the intensity noise at the spectral edges of the generated supercontinuum is at a constant level independent on the pump power in both tapered and uniform fibers.
A new nonlinear dispersion flattened photonic crystal fiber with low confinement loss is proposed. This fiber has threefold symmetry core. The doped region in the core and the big air-holes in the 1st ring can make high nonlinearity in the PCF. And the small air-holes in the 1st ring and the radial increasing diameters air-holes rings in cladding can be used to achieve the dispersion properties of the PCF. We can achieve the optimized optical properties by carefully selecting the PCFs structure parameters. A PCF with flattened dispersion is obtained. The dispersion is less than 0.8 ps/(nm km) and is larger than −0.7 ps/(nm km) from 1.515 μm to 1.622 μm. The nonlinear coefficient is about 12.6456 W−1 km−1, the fundamental mode area is about 10.2579 μm2. The confinement loss is 0.30641 dB/km. This work may be useful for effective design and fabrication of dispersion flattened photonic crystal fibers with high nonlinearities.
We present experimental results on the suppression of a complete Raman cascade in a holey fiber by using gain competition with parametric processes. The modulation instabilities which strongly affect the stimulated Raman scattering (SRS) gain are induced by two pump wavelengths (532 nm, 1064 nm) placed far and quasi symmetrically on each side of the zero dispersion wavelength (ZDW) of the fiber (790 nm). The competition between these two nonlinear effects takes place in large normal dispersion regime. We experimentally determinate the quantity of energy needed at each pump wavelength to obtain total suppression of the SRS and we evaluate the sensitivity of this effect with respect to the ZDW position.