Design of a bending-insensitive single-mode photonic crystal fiber

We present a design of a bending-insensitive single-mode photonic crystal fiber (PCF) based on the existence of a triangular core formed by three neighboring air holes missing in the center of the fiber, and two cladding layers of air holes with different diameters. By optimizing the design parameters, the designed PCF with bending-insensitive characteristics can match the requirements of fiber to the home applications very well. Simulation results show that the designed PCF has an effectively single-mode operation, a small bending loss below 0.15 dB/m for the bending radius of 5 mm, as well as a stable effective mode area of 80 μm² whatever the designed PCF is straight or bent, which can connect well with conventional single-mode fibers (SMFs).     

Design of a miniature lens for semiconductor laser to single-mode fiber coupling

A design method for a miniature optical lens tipped on a single-mode fiber end to improve power coupling from a semiconductor laser is described. The lens shapes studied are hemispherical, hemicylindrical, and hemiellipsoidal. The optimum coupling conditions and the obtained coupling efficiency are represented in terms of laser beam and fiber parameters. Preferable ranges of hemispherical and hemicylindrical lenses are classified according to the laser and fiber mode spot sizes. Fiber axis offset and tilt effects on coupling efficiency are also studied.     

单模光纤分布式喇曼温度传感系统设计

文章作者在对光纤背向喇曼散射温度效应进行理论分析的基础上,对基于反斯托克斯/斯托克斯散射光强比值型的光纤分布式喇曼温度传感系统作了详细的研究, 对系统主要器件的要求进行了计算,研制了基于单模光纤的5 km分布式温度传感器.实验表明,系统能精确地进行分布式测温,温度分辨率为1 ℃,空间分辨率为2 m.     

Design of a single-mode linear-cavity erbium fiber laser utilizingBragg reflectors

The design constraints required to achieve single-longitudinal-mode operation from a standing-wave, homogeneously broadened, three-level, fiber laser which utilizes intracore Bragg reflectors for cavity feedback are presented. In particular, a closed-form solution to the laser rate equations is found which bounds the region in which only single longitudinal mode operation is supported. The principal resonator geometry to be considered is a two-reflector cavity which utilizes only Bragg reflectors for feedback. Analytical and experimental results are discussed     

Polarimetric four-wave mixing in a single-mode fiber

We demonstrate a new polarimetric four-wave mixing process in a single-mode fiber with two wavelengths, where energy conversion takes place among the polarization components of the lightwaves. With a 6-km-long fiber, we obtain a conversion efficiency of ~1.2%. Although no new wavelengths can be generated from this process, it can result in polarization-induced crosstalk among wavelength-division-multiplexed channels. On the other hand, this process provides an effective means for transfer of baseband signals from one wavelength to another wavelength, which may find applications in wavelength conversion and system surveillance     

Polarization fluctuations in a single-mode optical fiber

Polarization fluctuation characteristics of single-mode optical fiber output are examined theoretically and experimentally. A fiber model for studying these characteristics from the perspective of probability on the Poinare sphere is proposed. The relationship of the degree of polarization fluctuation to time and fiber length is shown theoretically. Measurements of submarine and underground cables and long-haul fibers up to 270 km in length generally support the proposed model     

Design optimization for efficient erbium-doped fiber amplifiers

The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFAs) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λ _p=980 nm and λ_p=1.47 μm. Three designs of fiber-amplifier waveguides are considered: one with the same mode size as standard 1.5-μm communication fibers (type 1); one with the same mode size as standard 1.5-μm dispersion-shifted fibers (type 2); and one with mode size smaller than those of communication fibers (type 3). For the 1.47-μm pump, fundamental LP₀₁ mode excitation is assumed, while for the λ_p=980-nm pump, concurrent excitation of LP₁₁ modes is considered. It is shown that excitation of higher-order pump modes at 980 nm does not significantly affect the amplifier gain performance. The effect of concentrating the Er³⁺ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2     

Design considerations for minimizing macrobending loss inerbium-doped fiber amplifiers

Step-index fiber designs which minimize macrobending loss in erbium-doped fiber amplifiers pumped at 980 and 1490 nm are discussed. An important consideration for the compact packaging of these amplifiers for field use is the minimum tolerable bend radius of the doped fiber for small extrinsic macrobending loss. Only small shifts in the peak value of the mode field of the fiber due to bending, such that the gain of the amplifier is essentially unaffected, are considered     

Theoretical analysis of a coated single-mode fiber termination

The antireflection efficiency of a single layer coating in front of an abruptly terminated monomode optical fiber is treated analytically by means of an integral equation, that is appropriate to solve the corresponding boundary value problem. Both guided and radiation modes are taken into account, when describing the field inside the optical fiber region. Then the integral equation is solved approximately by a Neumann series procedure giving highly accurate results when the weakly guidance condition holds, which is a case of practical interest in the optical communications area. The reflection coefficient and the radiation pattern of this configuration are computed. Numerical results are given for several values of the parameters of the geometry under consideration.     

Appropriate method of core selection and crosstalk optimization in single-mode homogeneous multicore fiber

The approach for homogeneous core structure design and selection based on low crosstalk, low dispersion, and acceptable mode effective area have been explored. The forward and backward crosstalk behaviors with respect to wavelength, fiber bending radius, and twisting rate in 12-core, and 21-core single-mode trench-assisted homogenous multicore fiber have been analyzed. The new expression for forward crosstalk under bending and twisting conditions has been derived using the conventional method. For the analysis and optimization of crosstalk, three different core structures are considered, it helps to draw the attention to select the appropriate core structure model for multicore fiber, which follows the standards used in telecom services.     

Segmented-core single-mode fiber optimized for bending performance

The performance of a matched-clad single-mode fiber design presently under development is described. Fibers of this design, which is based on the segmented-core approach, have been fabricated with a higher delta than simple matched-clad step-index single-mode fibers without a sacrificial increase in either the fiber cutoff or zero dispersion wavelengths. The resulting improvements in both macrobending and microbending performance is detailed     

Exact splice loss prediction for single-mode fiber

This paper describes the direct measurement method of spot size for single-mode fibers and its application to the splice loss prediction. Using a core-centering-type automatic fusion splicing machine, predicted splice loss is examined for several MCVD and VAD fibers. The accuracy of splice loss predicted by this method is better than that calculated from core radius and refractive index. The experimental splice loss is equal to the sum of the loss predicted by this method and the loss caused by the splicing technique.     

用腐蚀熔融法制造单模激光二极管与单模光纤相耦合的半球微透镜

近年来由于单模光纤研究的极大成功，促进了单模光纤通信系统和单模光纤应用技术的迅速发展。单模光纤的实际损耗已降到接近理论值，因此为进一步改善单模光纤传输系统的信噪比，提高激     

Consistency of measurement methods for the mode field results in a single-mode fiber

The fields in the core, the far-field radiation pattern, and the transmission through an offset splice for single-mode fibers all are well approximated by Gaussian functions. However, the method used to fit the Gaussian function to measured data influences the resulting width of the Gaussian, which is called the mode field radius. Of the fitting methods studied, only maximization of the launch efficiency integral gives values of mode field radii which are consistent between near-field and far-field measurement methods. The transverse offset measurement method is consistent with these two if an unweighted truncated fit is used. Also. two published analytical formulas for the mode field radius are studied, and only one of the two gives accurate values. A third analytical formula, which is simpler and more accurate over a smaller range of wavelengths, is presented.     

Radiation losses in a periodically deformed single-mode fiber

Scattering of the fundamental mode on a step-index fiber subject to microbendings is considered. An analytical technique is developed which is applicable to fibers with arbitrary numerical apertures, large deformation periods, and radiation escaping at arbitrary angles to the fiber axis. Low and high radiation orders are compared as a function of the length of deformation period. In the case of a fiber deformed by corrugated plates, the maximum radiation loss associated with the fundamental spatial harmonic of a microbending structure with a given period is equal to the maximum radiation loss associated with thenthspatial harmonic of the microbending structure with a periodntimes longer. Unlike in multimode fibers, microbending losses in single-mode fibers depend strongly on the wavelength of the light source. It is found that these losses vary critically with core radius. The scattered radiation is almost equally composed of the TE and TM polarized waves.     

Efficient self-aligning multibeam coupling into a single-mode fiber

We present and demonstrate a method for efficient coupling of many beams into a single-mode fiber. Using the phase conjugating property for mutually incoherent beams of the double phase conjugate mirror (DPCM), we achieved coupling for a full 6×6 matrix of beams into a single-mode fiber. In principle, this number of input channels can be increased manyfold beyond the 36 used in our experiment. Of the phase conjugate generated by the DPCM in the direction of the fiber, over 97% (Fresnel corrected) entered the fiber, thus giving a highly accurate coupling. The DPCM transmission efficiency itself was measured at 40% (Fresnel corrected), thus giving an overall coupling efficiency of 39%. By optimizing the DPCM parameters, a significantly higher overall coupling could be achieved. An additional advantage of this method is that the DPCM will reconfigure if there are small changes in the system, thus making the system very robust. This multichannel coupling method can be of importance in the coupling of the output beams of a vertical cavity surface emitting laser (VCSEL) into a single-mode fiber where each channel may carry independently modulated information. This technique can be further generalized to a bidirectional multisingle-mode fiber interconnection system, of which a basic 3×2 system is demonstrated     

椭圆孔正方形点阵单偏振单模光子晶体光纤的设计

设计了一种椭圆空气孔正方形点阵单偏振单模光子晶体光纤,并以聚甲基丙烯酸甲酯为基材,利用基于棱边/节点混合元的全矢量有限元法对该光纤进行了数值模拟。结果发现,其偏振模场、快轴模和慢轴模截止波长完全依赖于光纤的结构参数;通过优化光纤的结构参数,发现该光纤传输基模的一个偏振态（慢轴模）在0.62μm至0.70μm可见光波长范围内;若调整该光纤结构具有9圈椭圆空气孔时,其偏振模约束损耗在波长0.65μm处可以降至0.13dB/m。该聚合物基低损耗单偏振单模光子晶体光纤可以有效消除传统保偏光纤固有的偏振串扰和偏振模色散。     

Interferometric measurements of dispersion-spectra variations in a single-mode fiber

Previous work has demonstrated that group-delay spectra in single-mode fibers can be measured with 0.1-ps resolution by a white-light cross-correlation technique. An application would be to pretest short fibers before drawing an entire preform. This could be particularly useful for achieving high draw yield for fibers whose dispersion spectra are sensitive to core diameter. This paper describes measurements of minimum-dispersion spectra that were obtained using 4-m lengths of fiber that were cut from each end of kilometer-long quadruple-clad, triangular-index, and step-index depressed-clad fibers. The axial uniformity of fiber dispersion was found to be very good. Results show that averaging dispersion spectra using short fiber segments from each end produces excellent agreement when compared with the dispersion spectrum determined from conventional pulse-delay measurements on a long length of fiber.     

Transmission of a Gaussian pulse in single-mode fiber systems

A formula for the calculation of the transmitted pulse shape through single-mode fiber systems has been derived by using the linear superposition method. It is then applied to the transmission of a Gaussian pulse in the systems with monochromatic, single-mode, and multilongitudinal-mode laser sources. Numerical results are obtained for the various envelopes of multilongitudinal laser spectra. Applicability of the theory to the power spectra of any shape, effects of side modes of a single-mode laser on pulse transmission, and the possibility of developing a technique for obtaining the chromatic dispersion of a fiber are pointed out.     

布里渊单模光纤环形腔激光器实验研究

实验研究了布里渊单模光纤环形腔激光器(BSFRL)的输出功率、输出光谱和输出时域特性。通过对激光输出功率和光谱特性与构建激光器的光纤长度和输出耦合器的反馈耦合比关系的研究与分析发现,当构建的BSFRL的输出耦合器反馈耦合比为0.4、光纤长度为1.5 km时,BSFRL具有低泵浦阈值、高转换效率和稳定的单模激光输出,此时激光器的泵浦阈值约为3 mW,光-光转化效率为65%。通过调节偏振控制器,得到稳定的锁模脉冲输出。讨论了BSFRL的时域不稳定性并给出了相应解释。