Splice losses in holey optical fibers

Splice losses between standard step-index fiber and holey optical fibers were calculated for a range of fiber parameters and wavelengths using finite-difference time-domain simulations. The optimal holey fiber parameters for minimum splice loss were determined. It was found that the optimal parameters could also be predicted using analytical approximations incorporating the effective index model     

使光纤激光器产生变革的多孔光纤激光器

光子晶体光纤有一些独特的性能。光子晶体光纤激光器(多孔光纤激光器)可标定千瓦级的输出功率,给传统的大功率光纤激光器带来变革。在最近几年,多孔光纤激光器受到关注。文中介绍了多孔光纤及多孔光纤激光器的基本概念、特性及其典型器件。     

Designing Tapered Holey Fibers for Soliton Compression

We investigate numerically the compression of femtosecond solitons at 1.55-mum wavelength propagating in holey fibers which exhibit simultaneously decreasing dispersion and effective mode area. We determine optimal values of holey fiber parameters and fiber lengths for soliton compression in the adiabatic and nonadiabatic regimes. Compression factors in excess of ten are found for fibers as short as a few meters.     

Polarization-dependent confinement losses in actual holey fibers

Through the real-model simulations, the polarization-dependent confinement losses in actual holey fibers are, for the first time, numerically demonstrated. Furthermore, it is confirmed that the interstitial holes caused by the packing of the capillaries play a role to significantly reduce the confinement losses.     

A Design Method for Single-Polarization Holey Fibers With Improved Beam Quality Factor

Recently, there has been an increasing interest in developing single polarization fibers for applications such as polarization splitters, polarizers, high power lasers, etc. Usually, the polarization maintenance can be achieved by form birefringence, such as by creating elliptical cores, or material anisotropy, or by stress-applying parts inside the fiber. However, this results into the non-Gaussian field distributions due to the distortion of fiber core, therefore leading to the degradation of beam quality factor $M^{2}$. In this study, we propose a design method for single-polarization holey fibers with improved beam quality by introducing the resonant coupling phenomenon between the central depressed core and the elliptical cores arranged on either side of the central core. The proposed single-polarization holey fiber with 1-m length has the extinction ratio of 30 dB over 10-nm wavelength range and a good beam quality factor $M^{2}=1.31$.      

The role of confinement loss in highly nonlinear silica holey fibers

Small-core holey fibers (HFs) can offer tight mode confinement, and are, therefore, attractive for highly nonlinear fiber applications. However, we show here that confinement loss can significantly degrade the performance of devices based on such small core fibers. We also identify a range of fiber designs that result in high fiber nonlinearity and low confinement loss. In particular, we show that pure silica HFs can exhibit effective nonlinearities more than 50 times higher than conventional fibers, and that the confinement loss can be lowered below the loss of standard fiber types.     

High Power Highly Nonlinear Holey Fiber with Low Confinement Loss for Supercontinuum Light Sources

The high power holey fiber is an efficient supercontinuum light source by using picosecond pulse, which is a less expensive laser source compared with low power and expensive femtosecond laser sources. In this paper, a high power highly nonlinear holey fiber (HN-HF) with a low confinement loss is proposed for supercontinuum light sources. The finite difference method is used to calculate the different properties of the proposed HN-HF. High nonlinear coefficients are obtained at 1.06 μm, 1.31 μm, and 1.55 μm wavelengths with flattened chromatic dispersion and low confinement losses simultaneously. Moreover, numerical simulation results show that high power broad supercontinuum spectra with very short length of the proposed photonic crystal fiber are achieved.     

Dispersion controlled highly nonlinear fibers for all-optical processing at telecoms wavelengths

We review our recent progress in the development of lead silicate glass fibers with high nonlinearity and tailored near-zero dispersion at telecommunication wavelengths, encompassing holey, all-solid microstructured and W-type fiber designs. The fabrication techniques and relative merits of each fiber design are described in detail. The optical properties of the fabricated fibers are assessed both experimentally and through accurate numerical simulations. The significant potential of lead silicate highly nonlinear fibers for all-optical signal processing at telecommunication wavelengths is shown via a number of key experimental demonstrators.     

Broad-band second-harmonic generation in holey optical fibers

Holey fibers are shown to have an ideal geometry for efficient parametric processes due to their tailorable modal properties. These fibers can have the additional advantage of single-mode operation at all the interacting wavelengths. We demonstrate theoretically that by appropriate choice of holey fiber geometry, these fibers can be up to four orders of magnitude more efficient for second harmonic generation than conventional poled fibers     

Efficient low-threshold lasers based on an erbium-doped holey fiber

We report experimental results on the continuous-wave lasers based on a small core erbium-doped holey fiber. In a simple Fabry-Perot-type cavity with high output coupling, we demonstrate low-threshold (0.55 mw) high slope-efficiency (57.3%) operation confirming both the quality and exceptionally high gain efficiency of the fiber. In an all-fiber ring cavity where the cavity loss is reduced, we show that it is possible to achieve a low-threshold laser with extremely wide tunability (>100 nm around 1550 nm). Our results illustrate some of the unique opportunities provided by active small core holey fibers.     

Microcavities Using Holey Fibers

Microcavities consisting of microstructured holey fibers and separate end mirrors have been constructed and tested. These devices exhibit excellent transverse-mode confinement and the ability to control the percentage of power guided outside of the fiber core. As a result, these devices may be a useful tool for enhancing the interaction between light and an atomic medium.     

Nonsilica glasses for holey fibers

The authors of this paper investigated the thermal properties and optical properties of typical nonsilica glasses, including viscosity, surface tension, thermal conductivity, transmission, linear and nonlinear refractive index, and fiber attenuation in order to judge the feasibility of using nonsilica glasses as the background material of holey fibers (HFs). Novel techniques were presented to fabricate the nonsilica glass microstructured fiber preforms. Examples of fabricated nonsilica glass HFs with various promising optical applications were finally exhibited.     

Development of novel fibers for telecoms application

This paper reviews the current situations of optical fibers used for terrestrial and submarine transmission systems as well as up-to-date R&;D on these fibers. The current fibers include standard single mode fibers (SMFs), non-zero dispersion shifted fibers (NZ-DSFs), and dispersion managed lines (DMLs). Even though these fibers show quite high and matured properties, the internet traffic is continuously growing, and around 2015–2020, it is expected that the current transmission fibers would become inadequate. To prepare for the future ultra high-capacity transmission, there are three important R&;D directions for transmission fibers. (1) Reducing non-linearity by means of enlarging Aeff and/or reducing attenuation loss. It is very important in the case of transmission systems using new multi-level signal formats. (2) Expanding the transmission band more than the current C- and/or L-Band by utilizing new transmission fibers. For example, holey fibers (HFs), which have an endlessly single mode (ESM) property, are one of the interesting candidates of the new transmission fibers. (3) Using Space Division Multiplexing (SDM) by using multi-core fibers. The multi-core fiber literally multiples the core number within a fiber dimension, which enables multiple transmission capacity per one fiber. In addition to the developments of transmission fibers, component fibers have also been studied and developed. Examples of R&;D on these component fibers will be also discussed in the latter part of this paper.     

飞秒激光在多孔光纤中传输特性的研究

介绍了多孔光纤的特性以及对飞秒激光在多孔光纤中传输特性的研究。     

基于多孔光纤的参量波长变换

通过改变多孔光纤中的芯区面积、空气孔的直径和分布．可以灵活地设计其导波特性。利用耦合波方程分析了参量波长变换的基本原理．讨论了信号波长固定情况下相位失配和抽运波长之间的关系。对基于多孔光纤的参量波长变换的转换效率进行了数值模拟．并和实验测量的数据进行了比较．结果表明它们的结果相一致。采用15m长的多孔光纤可以获得约10nm的3dB调谐带宽．最大转换效率约为-16dB．并且采用较低色散斜率值的多孔光纤可以进一步增大调谐范围。因此．利用多孔光纤可以实现紧凑的波长变换器。     

High-nonlinearity dispersion-shifted lead-silicate holey fibers for efficient 1-/spl mu/m pumped supercontinuum generation

This paper reports on the recent progress in the design and fabrication of high-nonlinearity lead-silicate holey fibers (HFs). First, the fabrication of a fiber designed to offer close to the maximum possible nonlinearity per unit length in this glass type is described. A value of /spl gamma/=1860 W/sup -1//spl middot/km/sup -1/ at a wavelength of 1.55 /spl mu/m is achieved, which is believed to be a record for any fiber at this wavelength. Second, the design and fabrication of a fiber with a slightly reduced nonlinearity but with dispersion-shifted characteristics tailored to enhance broadband supercontinuum (SC) generation when pumped at a wavelength of 1.06 /spl mu/m-a wavelength readily generated using Yb-doped fiber lasers-are described. SC generation spanning more than 1000 nm is observed for modest pulse energies of /spl sim/ 100 pJ using a short length of this fiber. Finally, the results of numerical simulations of the SC process in the proposed fibers are presented, which are in good agreement with the experimental observations and highlight the importance of accurate control of the zero-dispersion wavelength (ZDW) when optimizing such fibers for SC performance.     

Characteristics of Q-switched cladding-pumped ytterbium-doped fiberlasers with different high-energy fiber designs

We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality     

Mode coupling contribution to radiation losses in curvatures for high and low numerical aperture plastic optical fibers

We have studied the optical power losses due to multiple curvatures in polymethylmetacrylate (PMMA) plastic optical fibers (POFs) of different numerical apertures (NAs) and attenuation. The fibers were tested for several configurations in order to assess the influence of different types of curved-to-straight fiber transitions in the amount of power radiation. We found that losses are below the standards for all tested fiber types, and thus, they are a suitable choice for local area network (LAN) applications. In addition, our results revealed the presence of modal interactions as confirmed using an experimental procedure to estimate the mode coupling strength for the same fibers.     

Method of assisting the fabrication process of holey fiber based on combination model of digital image processing and finite element method

In the fabrication process of holey fiber, the final geometry of the actual fiber usually deviates from the ideal. We propose a novel method based on the combination of digital image processing technique and finite element method to model the optical properties of the actual fiber rapidly. A polarization-maintaining holey fiber reported by crystal fiber A/S has been modeled and its numerical results accord with the parameters given by the data. Experimental result demonstrates that the optical properties of the fiber can be analyzed rapidly so that the draw parameters can be adjusted in time.     

Ultralow-loss fluoride-glass single-mode fiber design

The excess losses and dispersion in fluoride-glass single-mode fibers are theoretically evaluated. Microbending, splicing, coating material, and fiber stranding are considered as the causes of the excess losses. Based on these evaluations, the design for ultralow-loss fluoride-glass single-mode fibers is carried out. Relative refractive-index difference of 0.43