Compact in-fiber mode adapter based on double-cladding fiber for multimode fiber access networks

A simple method for coupling light from a laser diode (LD) to multimode fiber (MMF) by using a compact in-fiber mode adapter, which is constructed with double-cladding fiber is presented, for the first time. Strong cladding-mode resonance across the thin-thickness inner cladding is used to excite the cladding modes. Principle of proposed mode adapter is theoretically investigated and its performances are experimentally verified by measurement results. By comparing the direct connection between LD and MMF, the coupling efficient of transmission power is improved by using our proposed adapter.     

Application of Turbo codes in optical OFDM multimode fiber communication system

In this paper, Turbo Code is proposed in optical OFDM multimode fiber communication system in order to decrease the bit error rate (BER) of the system, which is mainly affected by the deep nulls of the magnitude response of multimode fiber in the high frequency region (above 3 dB). A simulation system in SIMULINK is established. Based on the system, the BER of the system with Turbo Code is compare to the systems with another two typical coding schemes including convolutional code (CC) and serially concatenated code (SCC) which uses a concatenation of convolutional and RS codes when transmitting 10 Gbps data over various length multimode fibers. Different transmitting rate is also considered. The results show that Turbo coded system has a lower BER than the other two systems and the Turbo coded system can transmit 10 Gbps data to the distance of 300 m with BER below 1e−6.     

A novel bits loading algorithm for adaptive modulation OFDM multimode fiber communication system

A novel bits loading algorithm is proposed for adaptively modulated optical OFDM (AMOOFDM) multimode fiber communication system to decrease the system bit error rate (BER) caused by some OFDM subcarriers located at the deep nulls in the high frequency region of multimode fiber. The simulation results show that the performance of the new algorithm is approximate to the optimal algorithm-Greedy algorithm, but its computational complexity is considerably lower, thus the new algorithm is easy to implement. Comparing to fixed bits loading, adaptive bits loading can reduce the system BER effectively.     

Theoretical analysis of multimode fiber amplifiers and lasers containing spatial filters

By the use of the coupling theory of the modes and the multimode rate equations, the performances of the multimode fiber amplifiers or lasers containing a spatial filter have been discussed. After the rate equations applicable to amplifiers are solved, the beam quality factors of the output from a multimode fiber amplifier with and without a single mode filter have been evaluated and compared. By the use of the analytical expression of the threshold pump power applicable to the multimode fiber lasers with the spatial filter and doped with quasi two-energy-level ions, and two example fibers had been selected which may guide 4 and 9 transversal modes, respectively, the threshold pump power for each transversal fiber mode has been evaluated. The results indicate that the single mode filter, does introduce a very strong discrimination for the modes between the high order modes and the fundamental mode. This should considerably favor the operation of the fundamental mode in the lasers with a homogeneously broadened active medium.     

Calculation of the frequency response in step-index plastic optical fibers using the time-dependent power flow equation

The time-dependent power flow equation, which is reduced to its time-independent counterpart is employed to calculate frequency response and bandwidth in addition to mode coupling and mode-dependent attenuation in a step-index plastic optical fiber. The frequency response is specified as a function of distance from the input fiber end. This is compared to reported measurements. Mode-dependent attenuation and mode dispersion and coupling are known to be strong in plastic optical fibers, leading to major implications for their frequency response in data transmission systems.     

Coupling efficiency of laser beam to multimode fiber

The coupling efficiency of laser beam to multimode fiber is given by geometrical optics, and the relation between the maximum coupling efficiency and the beam propagation factor M² is analyzed. An equivalent factor for the multimode fiber is introduced to characterize the fiber coupling capability. The coupling efficiency of laser beam to multimode fiber is calculated in respect of the ratio by the overlapping integral theory. The optimal coupling efficiency can be roughly estimated by the ratio of M² to but with a large error range. The deviation comes from the lacks of information on the detail of phase and intensity profile in the beam factor M².     

选择模激励下塑料光纤频率响应特性的研究

由于塑料光纤有诸多优点,可以替代同轴电缆作为短距离通信网的传输介质。给出梯度塑料光纤的带宽计算模型,利用该模型计算了一系列选择模激励条件下塑料光纤频率响应特性,从而研究其带宽特性,并研究了不同光源线宽对光纤系统带宽的影响,得出的结论对塑料光纤的实际应用有一定指导意义。     

Adaptive Bit allocation algorithm based on unsaturated bandwidth of multimode fiber for optical OFDM system

An adaptive bit allocation algorithm for Orthogonal Frequency Division Multiplexing (OFDM) multimode fiber communication system is proposed in this paper, aimed at utilizing the infinite bandwidth of multimode fiber in high frequency region. The algorithm breaks through the limitation that bits are formerly allocated only in fixed bandwidth, and is proved to be effective by simulation. Compared with greedy algorithm, new algorithm is easy to implement, and lowers bit error rate (BER) of each subcarrier effectively.     

Performance of directly modulated OFDM data over multimode fiber link

The performance of orthogonal-frequency-division-multiplexing (OFDM) technology in the multimode fiber (MMF) optical communication system is investigated numerically. The mode dispersion in MMF is analyzed by utilizing the optical angular spectrum analysis method. Simulation results in terms of bit-error-rate (BER) and signal-to-noise ratio (SNR) show that the transmission distance can reach up to 2.5-km at 10^− 3 BER for 40-Gb/s data. Results of different modulation formats further indicate that better performance can be achieved by adopting multi-level modulation format.     

Mesoscopic effect of spectral modulation for the light transmitted by a SNOM tip

The effect of a tapered metal-coated optical fiber terminated by a sub-wavelength aperture (SWA) on the spectrum of the transmitted light is investigated experimentally. Under certain conditions a remarkable spectral modulation of the transmitted light can be observed. This effect is of a mesoscopic origin, occurring only for a certain interval of SWA diameters. One can conclude that a noticeable modulation appears when the number of the transmitted fiber modes is small but exceeds unity, thus indicating the presence of a phase shift between different modes. To discern between two possible sources of such phase shift, the fiber length dependence of the output spectrum has been studied. According to the results obtained for the used sample of 200 nm SNOM tip, the observed phase shift is mostly caused rather by the inherent modal dispersion of the multimode fiber than by the mode-dependent light slowdown in the tapered region close to SWA due to the coupling to surface plasmons of the metal coating. The SWA acts here mainly as an effective mode filter.     

基于光纤的光学频率传递研究

随着光钟研究的发展, 光钟的稳定度和不确定度均达到10^-18量级. 通过光纤可以实现光钟频率信号的高精度传输, 有望用于未来“秒”定义的复现. 演示了百公里级实验室光纤上的光学频率传递. 对于在实验室70 km光纤盘上实现的光频传递, 光纤相位噪声抑制在1-250 Hz傅里叶频率范围内均接近于光纤延时极限, 对应传输稳定度(Allan偏差)为秒级稳定度1.2×10^-15, 10000 s稳定度为1.4×10^-18. 实验室100 km光纤的光频传递秒级稳定度也达到了5×10^-15. 提出了光纤噪声用户端补偿的方案, 可以简化星形传递网络中心站的复杂度. 在25 km光纤上演示了该传递方案, 实现的传输稳定度接近传统前置补偿传递方案.     

光纤耦合器制造中的动态监测系统

本文报道在研制熔接光纤耦合器中所建立的动态监测系统。这个系统由于利用了时间延迟技术,不仅能较高精度地数字显示成品光纤耦合器的静态分束比;而且能在器件的制造过程中监测分束比的变化,进而控制工艺,大大提高器件的成品率。     

一种新型的专用于光学相干层析系统的宽带光纤光源

报道了一种新型的专用于光学相干层析系统的输出光谱为准高斯型的宽带超荧光光纤光源.该光源采用掺饵光纤作为增益介质.其关键技术是在抽运源的输出端增加了光耦合器，并在光源输出端插入多级长周期光纤光栅对铒离子的自发光谱进行调制和整形；同时采用光控器和温控器来控制抽运源的输出以提高光源输出功率的稳定性.该光源的中心波长为1.57μm，输出光谱的3dB带宽大于75nm，输出功率为27mW.实验结果表明，该光源输出光谱的自相关函数的旁瓣峰被大大削弱，可以满足光学相干层析系统的应用. 关键词： 光学相干层析术 超荧光光纤光源 长周期光纤光栅 光耦合器     

Mid-infrared supercontinuum and optical frequency comb generations in a multimode tellurite photonic crystal fiber

We numerically investigate the mid-infrared(MIR) supercontinuum(SC) and SC-based optical frequency comb(OFC) generations when the three optical modes(LP01, LP02, and LP12) are considered in a multimode tellurite photonic crystal fiber(MM-TPCF). The geometrical parameters of the MM-TPCF are optimized to support the multimode propagation and obtain the desired dispersion characteristics of the considered three optical modes. When the pump pulse with center wavelength λ = 2.5 μm, width T = 80 fs, and peak power P = 18 k W is coupled into the anomalous dispersion region of the LP01, LP02, and LP12 modes of the MM-TPCF, the-40-d B bandwidth of the generated MIR SCs can be up to2.56, 1.39, and 1.12 octaves, respectively, along with good coherence. Moreover, the nonlinear dynamics of the generated SCs are analyzed. Finally, the MIR SCs-based OFCs are demonstrated when a train of 50 pulses at 1-GHz repetition rate is used as the pump source and launched into the MM-TPCF.     

光纤面板刀口响应测试仪误差分析

为满足光学纤维面板生产厂、研究所和计量站的检测需要，我们分别研制了ＤＸ－１、ＤＸ－９２１和ＤＸＺ－９０１三种型号的光纤板刀口响应测试仪。本文针对测试精度最高的ＤＸＺ－９０１型仪器进行误差分析，首先给出光纤板刀口响应的曲线拟合，然后分析和计算该测试仪的扫描误差、光度测量误差和狭缝影响等误差因素及其误差贡献，并将测试仪的有关参数代入，最后得出该测试仪的刀口响应的总不确定度，以便对仪器的测值可信度有个理论上的估计。     

Experimental demonstration of single-mode fiber coupling using adaptive fiber coupler

Coupling plane wave into a single-mode fiber(SMF) with high and steady coupling efficiency is crucial for fiberbased free-space laser systems, where random angular jitters are the main influencing factors of fiber coupling. In this paper, we verified a new adaptive-optic device named adaptive fiber coupler(AFC) which could compensate angular jitters and improve the SMF coupling efficiency in some degree. Experiments of SMF coupling under the angular jitter situation using AFC have been achieved. Stochastic parallel gradient descent(SPGD) algorithm is employed as the control strategy, of which the iteration rate is 625 Hz. In closed loop, the coupling efficiency keeps above 65% when angular errors are below 80 μrad. The compensation bandwidth is 35 Hz at sine-jitter of 15 μrad amplitude with average coupling efficiency of above 60%. Also, experiments with simulated turbulence have been studied. The average coupling efficiency increases from 31.97% in open loop to 61.33% in closed loop, and mean square error(MSE) of coupling efficiency drops from 7.43% to 1.75%.     

匹配液的折射率对光纤定向耦合器分光比的影响

本文从理论和实验二个方面研究了光纤定向耦合器中使用不同折射率的匹配液对其分光比的影响。做出了分光比在1/1～1/30之间变化的光纤定向耦合器。     

长时间精密锁定的掺Er光纤飞秒光学频率梳

自行研制了基于掺Er光纤飞秒激光器的光学频率梳并实现了重复频率 f_r信号和载波包络偏移频率(Carrier-envelope offset, f_o) 信号的精密锁定, 锁定后的 f_r信号和 f_o 信号的频率抖动量的标准偏差分别为0.515 mHz和93.13 mHz.     

一种新型结构的单模光纤1×4分束器

以线性耦合波方程为基础，分析了具有平面型结构的五光纤耦合系统的功率耦合特性，提出了研制新型结构的单模光纤１×４分束器的方法，并经实验验证。所研制的１×４分束器的性能和外形尺寸与常规的２×２单模光纤耦合器相比，都较为接近。     

利用偏振控制器连续调节光纤环镜的反射率

研究了一种新型光纤环镜(FLM)的原理与特性，这种FLM由在普通光纤环镜中插入光纤型偏振控制器(PC)构成.通过等效光路分析建立了该FLM的理论模型，并对其反射特性进行了数值模拟.研究表明，通过改变PC的状态，即改变其双折射效应的快轴取向或强度，可连续调节FLM的反射率，反射率谱具有宽带特性，主要受光纤耦合器工作带宽的影响.此外，对FLM的反射特性还进行了实验研究.实验结果也证实，通过调节PC状态，FLM反射率可在其最大和最小值之间连续调节，实验测得FLM最大和最小反射率分别可达93%和2%.根据PC双折 关键词： 光纤环镜 偏振控制器 光纤耦合器 反射率