Side pumping of double-clad photonic crystal fibers

Side pumping of double-clad photonic crystal fibers is experimentally demonstrated. Optical access to the multimode cladding is obtained by collapsing the airholes over a short length of fiber while leaving the inner single-mode core undisturbed. Coupling efficiencies greater than 90% are obtained. A side-pumped Yb fiber laser with a slope efficiency of 81% is demonstrated with this method.     

Enhanced nonlinear effects in photonic crystal fibers

Photonic crystal fibers are a new class of single-material optical fibers with wavelength-scale air holes running down the entire fiber length. Photonic crystal fibers were first developed in 1996 and have subsequently been the focus of increasing scientific and technological interest in the field of fiber optics. The manufacturing, principles, basic properties, and some applications of photonic crystal fibers are briefly described in this paper. A review of our recent work on the nonlinear effects in photonic crystal fibers is presented, and special emphasis is placed on such effects as supercontinuum generation, frequency conversion, and solitons observed when femtosecond light pulses propagate in these fibers.     

Achieving both high birefringence and low leakage loss in double-clad photonic crystal fibers

In this paper, a novel double-clad photonic crystal fiber (DC-PCF) is proposed for achieving both high birefringence and low leakage loss. According to numerical simulation of the proposed PCF, the extraordinarily high birefringence (over 2×10⁻²) and low leakage loss of the order of 0.0001 dB/km over a large wavelength range are achieved simultaneously. Single-polarization single-mode (SPSM) operation with low leakage loss is also discussed and can be realized and optimized in the PCF by adopting suitable structure parameters.     

High-power double-clad large-mode-area photonic crystal fiber laser

A high power double-clad ytterbium-doped large-mode-area photonic crystal fiber (LMA PCF) laser was demonstrated using a unique Fabry-Perot (F-P) configuration. The pump source is a fiber coupled diode array operating at 976 nm. A continuous wave (CW) output power of 50 W at ～ 1.04 μm with a slope efficiency of 76.3% is obtained. Single transverse mode operation is achieved without any thermal-optical problems. This laser has the potential for scaling to much higher output power.     

Optical sensing with photonic crystal fibers

A review of optical fiber sensing demonstrations based on photonic crystal fibers is presented. The text is organized in five main sections: the first three deal with sensing approaches relying on fiber Bragg gratings, long‐period gratings and interferometric structures; the fourth one reports applications of these fibers for gas and liquid sensing; finally, the last section focuses on the exploitation of nonlinear effects in photonic crystal fibers for sensing.     

Polarization squeezing with photonic crystal fibers

We report on the generation of polarization squeezing by employing intense, ultrashort light pulses in a single pass method in photonic crystal fibers. We investigated the squeezing behavior near the zero-dispersion wavelength and in the anomalous dispersion regime by using two distinct fibers. We observed a maximal squeezing at 810 nm of −3.3 ± 0.3 dB with an excess noise of +16.8 ± 0.3 dB in the anomalous regime. Correcting for linear and interference losses between the polarization modes, this corresponds to −6 ± 1 dB. The ratio of squeezing to excess noise indicates the creation of a much purer state; this ratio indeed lies an order of magnitude below those squeezing experiments that exploit traditional fibers [1]. We attribute this increased state of purity to increased effective nonlinearity and to the reduction of scattering on acoustic modes in the fiber. Original Text ? Astro, Ltd., 2007.     

Elliptical-hole photonic crystal fibers

We study the dispersive properties of photonic crystal fibers (PCF's) with elliptical air holes. The unusual guidance of PCF leads to novel behavior of the birefringence, group-velocity walk-off, and dispersion parameters, including the possibility of zero walk-off with high birefringence in the single-mode regime. A number of these effects are closely tied to the underlying radiation states of the air-hole lattice.     

Hydrophobic photonic crystal fibers

We propose and demonstrate hydrophobic photonic crystal fibers (PCFs). A chemical surface treatment for making PCFs hydrophobic is introduced. This repels water from the holes of PCFs, so that their optical properties remain unchanged even when they are immersed in water. The combination of a hollow core and a water-repellent inner surface of the hydrophobic PCF provides an ultracompact dissolved-gas sensor element, which is demonstrated for the sensing of dissolved ammonia gas.     

Modelling photonic crystal fibers with localized functions

In this paper we present an overview of of the standard methods used when modelling photonic crystal fibers with Hermite-Gaussian functions, as well as a new variant of this modelling scheme, based solely on Hermite-Gaussian expansion series, which introduces the possibility of directly modelling fibers with finite claddings. We investigate the challenges and advantages of such a model and compare it to a proven modelling tool, namely the plane wave method.     

Enhanced red-shifted radiation by pulse trapping in photonic crystal fibers with two zero-dispersion wavelengths

A theoretical investigation on the two pulses copropagation and the red-shifted radiation generation in a photonic crystal fiber with two zero-dispersion wavelengths are presented. It is found the intensity of the red-shifted radiation components can be enhanced when the fiber is pumped with two pulses and the pulse trapping occurs. As the input peak power of the pump pulse is increased under the phenomenon of pulse trapping, the intensity of the red-shift radiation can be further enhanced. The above effects can be explained by the energy transfer from the Raman soliton to the red-shifted radiation components due to the effect of pulse trapping and the effect of higher-order dispersion.     

All-solid silica-based photonic crystal fibers

An index-guiding all-solid photonic crystal fiber (PCF) composed entirely of silica material is proposed in this paper. The core of this optical fiber is composed of pure silica, and the cladding consists of doped silica rod in the background of pure silica. The dependence of confinement loss on the diameter of the doped rods, the number of doped-rod rings, and the doping level is investigated numerically. In addition, the proposed fiber possesses a shorter cutoff wavelength as compared with the air/silica PCF, which is directly confirmed by the V parameter, and explained based on a scalar approximation method. Furthermore, the bending loss for the fiber is predicted. A low-loss single-mode all-solid silica-based PCF with a large-mode-area is possible by the appropriate selection of configuration parameters.     

Highly birefringent photonic crystal fibers

We report a strongly anisotropic photonic crystal fiber. Twofold rotational symmetry was introduced into a single-mode fiber structure by creation of a regular array of airholes of two sizes disposed about a pure-silica core. Based on spectral measurements of the polarization mode beating, we estimate that the fiber has a beat length of approximately 0.4 mm at a wavelength of 1540 nm, in good agreement with the results of modeling.     

Analysis of photonic crystal fibers infiltrated with nematic liquid crystal

The spectral characteristic of a nematic liquid crystal photonic crystal fiber is analyzed. The locations of the transmission minima in the transmission spectrum can be evaluated by examining the modal cutoffs of specific modes in the liquid crystal inclusion. The selection criteria for these specific modes are based on the fraction of power residing in the core. Explicit expressions for these modal cutoffs are also derived.     

Estimation of Rayleigh scattering loss in a double-clad photonic crystal fiber

In this paper the effect of photonic crystal fiber’s structure parameters on Rayleigh scattering was investigated. Rayleigh scattering loss (RSL) has been numerically estimated by average Rayleigh scattering coefficient based on the empirical relations for \(V\) and \(W\) parameters of double-clad photonic crystal fibers (DC PCFs). The dependence of RSL on the two structural parameters—the air hole diameter and the hole pitch was demonstrated. We have shown that RSL depends on the index profiles because of the different optical power confinement factors in every layer of DC PCF. Using these results, the RSL can be optimized by adjusting the fiber parameters—air-hole diameter as well as the air-hole pitch.     

Group-velocity dispersion in photonic crystal fibers

The dispersion properties of photonic crystal fibers are calculated by expression of the modal field as a sum of localized orthogonal functions. Even simple designs of these fibers can yield zero dispersion at wavelengths shorter than 1.27 mum when the fibers are single mode, or a large normal dispersion that is suitable for dispersion compensation at 1.55 mum.     

Elongation sensitivity of photonic crystal fibers

We determined theoretically a phase elongation sensitivity of the Photonic Crystal Fibers by means of the Multipole Method. The sensitivity was confirmed experimentally with good agreement for LMA-8 PCF.     

光子晶体光纤非线性特性的研究

光子晶体光纤是近年来出现的一种通常由单一介质构成，并由波长量级的空气孔构成微结构包层的新型光纤．文章介绍了光子晶体光纤的制作工艺、工作原理、基本特性、目前的研究重点和进展情况，重点评述了光子晶体光纤非线性特性方面的研究，特别是在超连续光谱的产生、光孤子效应以及频率变换等方面的实验和理论成果以及潜在的应用．     

Tomographic imaging of photonic crystal fibers

The tomographic reconstruction of the refractive index distribution in a large-mode-area photonic fiber is presented. The results of the diffraction tomographic algorithm and classical filtered backprojection method are compared. Additionally, the application of the synthetic aperture technique to tomographic interferometry, as a tool for resolution enhancement, is presented and discussed.