Chromatic dispersion measurements over a 50-km single-mode fiber

Chromatic dispersion has been measured over a 50-km-long single-mode fiber, using five sinusoidally modulated laser diodes. Results indicate that chromatic dispersion characteristics for single-mode fibers with 33-dB optical loss can be evaluated in the1.2-1.6-mum spectral region.     

Unrepeated transmission of 20-Gb/s optical quadrature phase-shift-keying signal over 200-km standard single-mode fiber based on digital processing of homodyne-detected signal for Group-velocity dispersion compensation

We demonstrate unrepeated optical transmission of 20-Gb/s quadrature phase-shift-keying (QPSK) signals over a 200-km-long standard single-mode fiber (SMF) without using any optical dispersion compensator. By employing optical homodyne detection, which can restore the entire information of the complex amplitude of the transmitted signal, group-velocity dispersion (GVD) of the SMF can be compensated electrically by a linear equalizer at the receiver. From off-line bit-error-rate measurements, we find that a simple transversal filter implemented in digital signal processing circuits after homodyne detection can effectively cancel the fiber GVD of up to 4000 ps/nm, enabling successful 20-Gb/s QPSK transmission.     

多信道数字与模拟RoF系统性能比较

综合比较多信道数字RoF和模拟RoF的传输系统方案和性能,并分析数字RoF如何利用带通采样的特点实现只需要用ADC和DAC就可以完成频率迁移.推导和分析多信道模拟RoF与数字RoF受到的非线性影响,并通过Optisystem进行仿真.理论和仿真都证明DRoF链路比模拟RoF链路有着更好的SNR性能和动态范围,更适合远距离传输.     

单模光纤模场直径标准研究

单模光纤的模场直径测量是二十多年前大家就非常关注的技术课题.国内外技术人员对此做了大量的研究,发表了很多相关的文章.各大标准化组织都有相关的标准.现行有效的国际国内标准规定的模场直径的测量方法大多是直接或者间接的基于Petermann Ⅱ定义.IEC在2001年发布了IEC 60793-1-45:2001标准,随后2002年发布了一个勘误.自1993年起,ITU-T共发布了3个版本的模场直径测量标准,目前最新有效版本是第3版ITU-T G.650.1(2010)(2010.7.29批准).国标最新有效版本是GB/T15972.45-2008.作者在对这些标准进行深入的研究后发现IEC、ITU-T和国标对同一个测试方法的计算公式有多处不一致.文章就这些问题从模场直径的定义出发进行了理论推导,从量纲角度进行验证,并对广泛使用的测试仪表的内部计算方法进行了调研.最终认为ITU-T和IEC关于模场直径的现行标准中均有多处计算公式错误,并建议相关国际组织的相关标准尽快进行讨论修改.     

双向EDFA对长距离光纤时间传递影响研究

设计实现了用于光纤时间传递系统的BEDFA,理论分析了该BEDFA对长距离光纤时间传递性能的影响并进行了相应仿真,得出每增加一个BEDFA时间系统精度降低50ps、稳定度降低5×10-11/s(-25dBm接收光功率和典型参数)的结论。利用环回法时间传递样机设计相应实验对理论进行了验证。     

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.     

Performance improvement for a WCDMA radio over fiber system using digital pre-distorter

In this paper, a Radio Over Fiber (ROF) system with a Digital Pre-Distorter (DPD) for WCDMA signal transmission is investigated. A Look-Up Table (LUT) based DPD and a Memory Polynomial (MP) DPD are applied in the ROF link so as to suppress the out-of-band spurious spectrum and improve the transmission performance. The experimental results show that the out-of-band emission due to existence of the third-order Inter-Modulation Distortion (IMD3) is obviously suppressed by these two DPD. An Adjacent Channel Power Ratio (ACPR) improvement of 8 dB is obtained for a single-carrier WCDMA signal transmission. These two DPD have equal ability in linearization of the ROF system for a three-carrier WCDMA signal transmission. There is no apparent memory effects exist in the ROF link.     

高功率激光单模光纤远距离传输实验研究

受激拉曼散射（SRS）效应是制约高功率激光单模光纤远距离传输应用的瓶颈因素。采用1550nm非偏振连续波单模光纤激光器作为光源, 通过实验研究了不同注入光功率条件下经过103km单模光纤传输所产生的受激拉曼散射现象,运用级联长周期光纤光栅带阻滤波器进行了受激拉曼散射抑制实验,并进行了相应的理论分析。提出了光纤受激拉曼散射抑制有效性判据,实验演示了受激拉曼散射现象,验证了级联长周期光纤光栅带阻滤波器对受激拉曼散射抑制的有效性。     

Coupling sensitivity of an edge-emitting LED to single-mode fiber

An edge-emitting LED coupled to a single-mode fiber shows increased coupling sensitivity to fiber displacement compared with multimode fiber. Sensitivity to lateral misalignment in the direction perpendicular to the junction plane of the LED increases by at least a factor of three, regardless of the coupling scheme used. A reciprocal relationship between peak coupling efficiency and sensitivity to misalignment is observed. We show that a previous theory for laser coupling can be extended to include edge-emitting LED's, and that it predicts this relationship. The results for different coupling schemes are discussed with respect to LED packaging.     

Determining the mode-field diameter of single-mode optical fiber: An interlaboratory comparison

The National Bureau of Standards, in cooperation with the Electronic Industries Association, conducted an interlaboratory measurement comparison among fiber manufacturers. Evaluated were transverse splice offset, near-field, far-field, and variable aperture far-field methods for determining mode-field diameter. Measurements were performed on five single-mode fibers at both 1300- and 1550-nm wavelengths. At 1300 nm, agreement was fairly good with the average one standard deviation being 0.15 μm for mode-field diameters in the8-11 mum range. Distinct systematic differences among various techniques were observed at 1550 nm where mode distributions are not as Gaussian.     

CF-RZ-DPSK for suppression of XPM on dispersion-managed long-hauloptical WDM transmission on standard single-mode fiber

We present a new optical modulation format chirp-free return-to-zero differential phase shift keying (CF-RZ-DPSK), which enables wavelength-division-multiplexing (WDM) transmission at 10 Gb/s/ch at a channel spacing of 100 GHz over 3000 km without significant impairments due to cross-phase modulation (XPM). A transmitter setup is presented, which allows a simple implementation of CF-RZ-DPSK with two Mach-Zehnder modulators in push-pull operation. The robustness toward XPM is shown theoretically with the help of a simple analytical model for the XPM-induced phase modulation. The superior performance of CF-RZ-DPSK over other modulation formats [RZ-ampfitude shift keying (ASK), nonreturn-to-zero (NRZ)-DPSK, and NRZ-ASK, respectively] is clarified. Finally, simulation results for CF-RZ-DPSK in comparison to RZ-ASK show the superior performance of the newly proposed modulation format in a dense WDM setup     

Performance comparison of various configurations of single-pump dispersion-compensating Raman/EDFA hybrid amplifiers

We show experimental performance comparison of three types of single-pump highly efficient dispersion-compensating Raman/erbium-doped fiber amplifier (EDFA) hybrid amplifiers with respect to gain, noise figure (NF), and stimulated Brillouin scattering (SBS)-induced penalty: Raman/EDFA hybrid amplifiers recycling residual Raman pump in a cascaded erbium-doped fiber located either after (Type I) or prior to (Type II) a dispersion-compensating fiber, and a Raman assisted EDFA (Type III). Type I shows high small-signal gains, moderate large-signal gains, moderate NFs, and high SBS tolerances. Type II shows high small-signal gains, low NFs, and low SBS tolerances. Type III shows moderate small-signal gains, high large-signal gains, moderate NFs, and high SBS tolerances.     

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).     

Real-time location of multiple time-varying strain disturbances,acting over a 40-km fiber section, using a novel dual-Sagnacinterferometer

Updated results using a novel sensing architecture based on a Sagnac interferometer are presented and, for the first time, real-time separation and positioning of multiple disturbances has been realized. A 40-km long dual-Sagnac sensor was formed by spectral slicing of light from a single, broad-band erbium-doped-fiber super-luminescent source and wavelength division multiplexed (WDM) routing around the loop to form an inherently low loss system. Independent active phase biasing of each Sagnac was employed, allowing the use of a single optical detector. The effects of residual optical cross talk between the two Sagnacs has been accurately modeled, allowing resulting errors to be corrected. The new system has capability for narrow-band fast Fourier transform (FFT) analysis of detected disturbance signals, and hence their separation in the frequency domain. For audio-frequency excitation, an average positional resolution of 100 m over a 40-km length was achieved with a postdetection signal processing bandwidth of 8 Hz     

Performance comparison of MRC and EGC on a MC-CDMA system with synchronization errors over fading channels

This work derives the average bit error rate (BER) of the uplink and downlink multicarrier code division multiple access (MC-CDMA) systems using maximum ratio combining (MRC) and equal gain combining (EGC) with synchronization errors over fading channels. The derived equation can simultaneously incorporate the parameters of the fading channel and all of the synchronization errors, including frequency offset, carrier phase jitter, and timing jitter. Numerical results indicate that those two combining schemes on the uplink and downlink MC-CDMA systems are degraded by all of the normalized synchronization errors over 10⁻². The comparison outcomes between MRC and EGC reveal that the MRC generally outperforms EGC in the uplink MC-CDMA system. However, EGC achieves better performance when the number of users is small, the normalized synchronization errors are low and the signal to noise ratio (SNR) is high. In the downlink system, EGC mainly outperforms MRC when the SNR and the number of users are gradually increased and the normalized synchronization errors are low. Therefore, the selection of MRC or EGC depends on the SNR, the synchronization errors and the number of users in uplink and downlink MC-CDMA systems.     

长周期光纤光栅用于EDFA的增益平坦展宽

基于EDFA的能级结构和粒子转换理论,分析了EDFA的各种参数和性能,并通过实验得到EDFA达到最佳效果时,抽运能量不易过大的结论。从理论和实验上研究了长周期光纤光栅用于掺铒光纤放大器自发发射谱增益平坦展宽的特性、自增益谱的荧光峰和可用带宽。实验上利用抽运能量的改变,可以控制吸收波长的峰值位置,得到长周期光纤光栅用于EDFA自发发射谱增益平坦展宽的结果。     

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。     

Design of distributed Raman temperature sensing system based on single-mode optical fiber

The distributed optical fiber temperature sensor system based on Raman scattering has developed rapidly since it was invented in 1970s. The optical wavelengths used in most of the distributed temperature optical fiber sensor system based on the Raman scattering are around from 840 to 1330 nm, and the system operates with multimode optical fibers. However, this wavelength range is not suitable for long-distance transmission due to the high attenuation and dispersion of the transmission optical fiber. A novel distributed optical fiber Raman temperature sensor system based on standard single-mode optical fiber is proposed. The system employs the wavelength of 1550 nm as the probe light and the standard communication optical fiber as the sensing medium to increase the sensing distance. This system mainly includes three modules: the probe light transmitting module, the light magnifying and transmission module, and the signal acquisition module.     

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