An equivalent step-index model for single-mode fibers based onmatching of bend loss and spot size at one wavelength: a simulationstudy

A method for the determination of equivalent step index (ESI) parameters for a given single-mode fiber is presented. The method is based on the matching of bend loss characteristics and (Petermann II) spot size at one wavelength. Numerical simulation studies have been carried out for fibers with parabolic and triangular index profiles having zero total dispersion at 1300 or 1550 nm. The results show that the method gives a model that is both stable with respect to the matched wavelength in the 1500-1600-nm range and accurate for predicting fiber characteristics such as spot size, waveguide dispersion, bend loss, and the cutoff wavelength (of the next higher mode) over this range of wavelength     

Analysis on splice, microbending, macrobending, and Rayleigh losses in GeO2-doped dispersion-shifted single-mode fibers

Independent of the actual index profile of a single-cladded dispersion-shifted single-mode fiber, it is shown that the loss components given in the headline at the zero dispersion wavelength λ0accurately can be obtained by simple expressions that only depend on the Laplace spot size value at λ0. Withlambda_{0} = 1.55 mum, these relations are used to estimate and minimize the total loss in single-cladded dispersion-shifted fibers with arbitrary core-index profiles.     

Dispersion-shifted dual-shape core fibers. Optimization based onspot size definitions

Design features, for very low bend and splice losses, in dispersion-shifted dual-shape core (DSC) single-mode fibers are obtained in terms of characteristic mode spot sizes W¯ responsible for splice loss, and W_∞ responsible for bend loss. Dual-shape core fiber designs are given with W¯_∞/W lying between 1.16 and 1.33 while maintaining the mode spot size between 4 and 5 μm at the operating wavelength of 1550 nm. With this design goal it is shown that bending loss would be lower in a step-index than in a graded-index DSC fiber. Further, conventional single clad step-index or triangular-index dispersion-shifted fibers are seen to have higher bending loss than well-designed DSC fibers     

800 nm处为零色散的光子晶体光纤的计算与设计

基于Galerkin方法计算并设计了在 80 0nm处具有零色散的光子晶体光纤。在数值计算中采用了足够大的求解区域和足够多的基函数 ,从而提高了计算和设计精度。波长 80 0nm是广泛使用的钛宝石飞秒激光器的工作波长 ,因此 ,该光纤对于飞秒激光的应用具有重要意义。     

48 fs,108 MHz色散管理孤子掺Er3+光纤激光器

提出了一种基于商售光纤构建的适用于精密光谱光频梳应用的100 MHz重复频率色散管理孤子光纤激光器的设计方案.通过采用低负色散光纤调控重复频率、高正色散光纤增大腔内脉冲呼吸比,构建了重复频率为108 MHz、中心波长为1550 nm的基于正色散掺铒光纤的色散管理孤子光纤激光器,该激光器腔内净色散为-0.0023 ps2,直接输出脉冲宽度为70 fs,经光纤压缩后脉冲宽度为48 fs,且脉冲中心波长处在1550 nm.     

A comparison of far-field methods for determining mode fielddiameter of single-mode fibers using both Gaussian and Petermanndefinitions

An interlaboratory comparison is presented of far-field measurement methods for determining mode field diameter of single-mode fibers. The comparison was conducted by member of the Electronic Industries Association. Measurements were made on dispersion-unshifted and dispersion-shifted fibers at 1300 and 1550 nm. Results were calculated using both Petermann and Gaussian definitions. The Petermann definition gave better agreement than the Gaussian in all cases. A systematic offset of 0.52 μm was observed between methods when applied to dispersion-shifted fibers. Such an offset may be caused by limited angular collection     

Transmission limitations due to fiber nonlinearities in optical FDMsystems

Transmission limitations due to stimulated Brillouin scattering and four-wave mixing processes are investigated for optical frequency division multiplexing (FDM) systems. The applicability of the dispersion-shifted (DS) and nondispersion-shifted (NDS) fibers is discussed, taking account of channel frequency separation, total channel numbers, input signal power, transmission length, and receiver sensitivity degradation. Experimental results on Brillouin gain spectra and the wave generation efficiency in four-wave mixing processes are also presented to discuss the applicability of the two types of single-node fiber. It was found that NDS fibers operated at a wavelength of 1550 nm can be widely deployed in multichannel systems both for the long-haul and information distribution transmissions, if the signal waveform distortion due to fiber chromatic dispersion is precluded. The delay equalizer will be useful for a high-speed system employing bit rates over 10 Gb/s and repeaterless spans over 300 km. For such an application, DS fiber is preferable. Concerning information distribution network applications, the NDS fiber should be more attractive as a transmission medium for FDM system applications     

Waveguide dispersion measurement technique for single-mode fibersusing wavelength dependence of mode field radius

A waveguide dispersion measurement technique using a simple fitting function for wavelength dependence of the root-mean-square width in the far field and its theoretical measurement error are discussed. Results indicate that waveguide dispersion can be evaluated with theoretical accuracy of 0.5 ps/km/nm using this technique. The waveguide dispersions for conventional and dispersion-shifted fibers have been measured using the far-field pattern method. Good agreement between measured and theoretical values of waveguide dispersion was obtained. Material dispersion and dispersion sensitivity evaluation methods that are applications of this technique are also described     

Grating compensation of third-order fiber dispersion

Subpicosecond optical pulses propagating in single-mode fibers are severely distorted by third-order dispersion even at the fiber's zero-dispersion wavelength (λ₀). Using cross-correlation techniques, the authors measured the broadening of a 100-fs pulse to more than 5 ps after passing through 400 m of fiber near λ₀. The measured asymmetric and oscillatory pulse shape is in agreement with calculations. A grating and telescope apparatus was configured to simultaneously equalize both third- and second-order dispersion for wavelengths slightly longer than λ ₀. Nearly complete compensation has been demonstrated for fiber lengths of 400 m and 3 km of dispersion-shifted fiber at wavelengths of 1560-1580 nm. For the longer fibers, fourth-order dispersion due to the grating becomes important     

一种新型高双折射光子晶体光纤的特性研究

设计了一种新型结构的光子晶体光纤,建立了对应的数学模型并采用全矢量有限元法对该结构的模场强度、有效折射率、双折射、色散特性和限制损耗进行了分析。研究表明,该光纤在1 550nm处可以获得高达7.66×10-3的双折射和低至12ps/(nm·km)的色散值,同时在800～1 600nm波长范围内,始终保持1.498×10-6 dB/m以下的极低限制损耗,可用于制造极低色散值的保偏光纤。     

Bend-optimized dispersion-shifted single-mode designs

A bend-optimized design for a dispersion-shifted single-mode fiber with segmented-core profile is described. With this design, dispersion-shifted fibers having the highest cutoff wavelengths reported to date have been achieved. Results on dispersion, attenuation, mode radius, bending, and microbending loss for such fibers are presented and compared to alternate designs.     

Highly birefringent photonic crystal fibers with flattened dispersion and low confinement loss

A highly birefringent index-guiding photonic crystal fiber (PCF) with flattened dispersion and low confinement loss is proposed by introducing two small air holes with the same diameter in the core area. The fundamental mode field, birefringence, confinement loss, effective mode area and dispersion characteristic of the fibers are studied by the full-vector finite element method (FEM). Simulation results show that a high birefringence with the order of 10 -3 and a low confinement loss of 0.001 dB/km are obtained at 1550 nm. Furthermore, flattened chromatic dispersion from 1450 nm to 1590 nm is obtained.     

Screening dispersion-shifted fibers for polarization-modedispersion due to core ellipticity

An attempt to relate polarization dispersion directly to some physical property and then use this as a means by which to characterize polarization-mode dispersion (PMD) is reported. A new diagnostic procedure has been developed and tested for screening dispersion-shifted (DS) fibers with PMD due to core ellipticity. Measurements of far-field radiation profiles across major and minor core axes are used to characterize polarization-mode dispersion. This technique is a relatively simple and quick method of screening dispersion-shifted fibers for polarization-mode dispersion greater than 5 ps/km. Differences in these far-field pattern widths were then correlated with direct core ovality measurements performed using the near-field refraction technique. The authors outline the test procedure in detail, analyze sources of error, and discuss detection limitations     

Extended 10 Gb/s fiber transmission distance at 1538 nm using aduobinary receiver

Chromatic dispersion penalties at 10 Gb/s and 1550 nm wavelength depend on the transmission bandwidth, not just the baseband information bandwidth. Duobinary transmission is known to reduce the transmission bandwidth relative to that of binary transmission. Using binary transmission, with both negative and zero chirp modulators, we present the first comparison of binary and duobinary reception and achieve an improvement in the chromatic dispersion limited transmission distance using duobinary reception. A 3.8 dB dispersion penalty is observed at 160 km using negative chirped binary transmission coupled to a receiver with a duobinary filter and decision circuit     

Low-loss dispersion-shifted single-mode fiber manufactured by the OVD process

The development of a low-loss dispersion-shifted single-mode fiber with a segmented-core profile is reported. The combination of low dispersion in the 1550-nm window, 0.21-dB/km median attenuation at 1550 nm, excellent bend resistance (lambda_{c} = 1200nm), and good splicing behavior make this fiber an economically viable alternative for long-haul high-data-rate operation utilizing multilongitudinal mode lasers. System experiments have demonstrated bit rates as high as 1.3 Gbit/s over 107 km and repeaterless spans of up to 233 km.     

Optimal transmission condition of nonlinear optical pulses insingle-mode fibers

Optimal conditions for transmission of nonlinear optical pulses in single-mode fibers are presented. When an optical pulse propagates in a fiber, it suffers fiber loss, group velocity dispersion, and self-phase modulation. An optimal output pulse can be obtained by choosing a suitable optical carrier wavelength and an initial input pulse. The system under optimal conditions not only has a more stable performance than the dispersion-free system, but also achieves maximum transmission bit rate for a fixed transmission distance. A bit-length product up to 8550 Gb/s-km or more can be achieved by using dispersion-shifted fibers without amplification     

Dispersion-flattened Bragg photonic crystal fiber for large capacity optical communication system

A novelty dispersion ultra-flattened Bragg photonic crystal fiber (PCF) has been fabricated in this paper.The fiber is composed of compound cores and periodical claddings with 11 coaxial rings.It has flattened dispersion of 8.54±1.3 ps-(nm· km)-1 in the communication wavelength range of 1460-1625 nm.Its dispersion slope alters from -0.0428 to 0.0392ps·nm-2·km-1.The low attenuation of 0.52 dB/km and low bending loss of 0.09 dB at 1550 nm of the fiber are also achieved.The Bragg PCF has enormously potential application in the fields of dense wavelength division multiplexing systems because of its superior dispersion properties and easy splicing performances.     

Investigation on bismuth-oxide photonic crystal fiber for optical parametric amplification

A hexagonal solid-core bismuth-oxide micro-structure fiber is developed to balance its dispersion and nonlinearity.This simulation and calculation results show that the bismuth-oxide photonic crystal fiber(Bi-PCF) has near zero dispersion around 1550 nm.Its dispersion slop in the communication wavelength range is also relatively flat.Moreover,both nonlinear coefficient and model field distribution are obtained.Compared with the experimental results by SiO2-PCF,it can be seen that the Bi-PCF shows excellent characteristics for the optical parametric amplification(OPA).     

A 1580-nm band WDM transmission technology employing opticalduobinary coding

This paper reports 1580-nm band wavelength division multiplexed (WDM) transmission employing optical duobinary coding over dispersion-shifted fibers. By using the 1580 nm band, the generation of four-wave mixing (FWM) over dispersion-shifted fibers (DSFs) can he suppressed. Optical duobinary coding is dispersion-tolerant because of its narrow bandwidth, and enables the use of the conventional binary intensity modulated direct detection (IM-DD) receiver. First, comparisons are made for WDM transmission performance in the 1580-nm band between conventional binary nonreturn-to-zero (NRZ) coding with and without postdispersion compensation, and optical duobinary coding by computer simulation is described. From the numerical simulations, it is found that the optical duobinary coding has superior transmission performance to the conventional binary coding without any dispersion compensation, and that the difference in the transmission performance between two coding methods is very small even if postdispersion compensation at the optical receiver is applied to the NRZ coding method. Second, transmission performance between the conventional binary NRZ and the optical duobinary signals without any dispersion compensation is compared with the straight-line experiment over 500-km dispersion-shifted fiber. The experimental results reveal that the transmission distance with optical duobinary coding is doubled in comparison with that of the conventional binary NRZ signals. Finally, 16-channel, 10-Gb/s optical duobinary WDM signals in the 1580-nm band are successfully transmitted over 640 km (80 km×8) of DSF without any dispersion compensation or management     

Highly accurate long-span chromatic dispersion measurement system by a new phase-shift technique

A highly accurate long span chromatic dispersion measurement system, which is based on a wavelength-division-multiplexing phase-shift technique and utilizes six laser diodes in1.2 sim 1.6 mum spectral region, has been developed. It is intrinsically free from error due to the fiber length variation caused by temperature changes under the measurement. The measurement accuracies of dispersion and Zero-dispersion wavelength are extremely good and within ±0.02 ps/km . nm and ±0.1 nm in 1250 ∼ 1450 nm spectral region in the case of a 10.5-km single-mode fiber measurement. The dynamic range is over 50 dB excluding system theS/Nmargin of 5 dB. Using this system, chromatic dispersion measurements of a 101.9-km pure-silica-core single-mode fiber and a 100.7 km concatenated dispersion-shifted single-mode fiber have been successfully carried out. The measured result has coincided with the arithmetical mean of those of constituent fibers.