A novel joint technique for PAPR reduction in CO-OFDM systems

For the high peak-to-average power ratio （PAPR） of coherent optical orthogonal frequency division multiplexing （CO-OFDM） system, a novel joint technique which is the combination of iterative partial transmit sequence （IPTS） and clipping technique is proposed. Simulation results demonstrate that the PAPR and bit error rate （BER） performance of the proposed technique both outperform those of the single techniques. Under the same conditions, the threshold value and peak power of IPTS clipping joint technique are optimized by 3.44 dB and 0.86 dBm compared with those of IPTS techinque, respectively. At the BER of 103, the optical signal to noise ratios （OSNRs） of the novel joint technique after 320 km and 400 km single-mode fiber （SMF） transmission are 0.68 dB and 1.18 dB smaller than those of clipping technique, respectively.     

A variable coefficient microwave photonic filter based on multi-wavelength fiber laser and Mach-Zehnder interferometer

A microwave photonic filter（MPF） with variable coefficient is proposed and demonstrated, which is constructed by a multi-wavelength fiber laser and Mach-Zehnder interferometer（MZI）. Through changing the slope characteristics of Mach-Zehnder interference spectrum adjusted by optical variable delay line（OVDL）, the conversion from phase modulation（PM） to intensity modulation（IM） is realized. The multi-wavelength fiber laser with Lyot-Sagnac optical filter has variable wavelength spacing. So the designed filter has a variable number of taps and tap weights. As a result, the tunable range of passband center frequency is 2.6 GHz. The reconfigurability of MPF can be also realized by adjusting the output of fiber laser.     

Simultaneous measurement of temperature and refractive index based on a core-offset Mach-Zehnder interferometer cascaded with a long-period fiber grating

An all-fiber sensor based on a cascaded optical fiber device is proposed and demonstrated, and its sensor head is composed of a core-offset Mach-Zehnder interferometer(MZI) and a long-period fiber grating(LPFG). In the experiment, two dips shaped by the intermodulation between the interference fringe of MZI and the resonant wavelength of LPFG are monitored. Experimental results show that temperature sensitivities of two dips are 0.060 7 nm/°C and 0.056 3 pm/°C, and the refractive index(RI) sensitivities are –18.025 nm/RIU and –55.06 nm/RIU, respectively. The simultaneous measurement of the temperature and external RI is demonstrated based on the sensitive matrix. Its low fabrication cost, simple configuration and high sensitivity make this sensor have potential applications in chemical and biological sensing.     

基于单边带调制的前馈技术压缩半导体激光器线宽

提出了一种基于电光单边带调制的前馈线宽压缩系统,该系统主要包括相位噪声检测和单边带调制两大部分。相位噪声检测部分输出一个与相位误差成比例的误差电压信号,电压信号通过线性调频作用于单边带强度调制器,实现对激光信号的调制。单边带调制器采用马赫增德尔强度调制器的结构,相当于内嵌四个相位调制器,通过相位调制达到强度调制的目的,最终得到线宽压缩的激光信号。实验针对波长为1552.52nm、功率10mW 的分布反馈（DFB）半导体激光器,通过对闭环系统的搭建与仿真,激光器的线宽从原来的0.5nm减小到0.016 nm,实现了对半导体激光器线宽的压窄。     

基因脉冲导入仪的原理及应用

在过去的20年,电穿孔技术的机理和应用受到了很大的关注,而且细胞电穿孔是一种生物工程新技术.本文简要介绍了天津理工大学研制的基因脉冲导入仪的原理及其应用.     

半导体激光器稳频技术的研究进展

半导体激光器广泛应用于光纤传感和光纤通信等领域,它的频率受周围环境的影响很大,作为通信光源频率波动会给信道带宽造成很大的浪费,同时限制了长距离传感的应用,因此,半导体激光器的稳频至关重要.对各种稳频的方法进行了比较,讨论了各自的特点和发展趋势.     

Coupling characteristics of the high-polarization dual-core photonic crystal fiber with mixing air holes

A high-polarization dual-core photonic crystal fiber (PCF) with mixing air holes is designed. The full-vector finite element method and coupled-mode theory are used to investigate the birefringence, coupling length, dispersion characteristics, normalized power and extinction ratio of this fiber. Numerical investigations demonstrate that by changing the structural parameters of the fiber, the birefringence is up to 1.48×10-2 at 1.55 μm, the coupling lengths are 79 μm and 94 μm for x-polarized and y-polarized modes, the fiber has two zero dispersion points, and the dispersion is very flat at the ultra-wide waveband scope from 0.7 μm to 1.7 μm.     

Simultaneous measurement of refractive index, temperature and strain based on core diameter mismatch and polarization-maintaining FBG

A kind of fiber-optic sensor for simultaneous measurement of refractive index of surrounding medium, temperature and strain is described. Based on core diameter mismatch, a multimode-single mode-multimode (MSM) structure is presented. It is demonstrated that the three parameters can be measured respectively by the interference of the core mode and cladding modes excited in the single mode fiber (SMF). Then combined with a polarization-maintaining fiber Bragg grating (PMFBG) which has different sensing properties from MSM structure, three parameters are measured simultaneously. The experimental results show that PMFBG is insensitive to the refractive index and the refractive index sensitivity of the MSM structure is 96.04 nm·RIU^?1; the temperature sensitivities of the characteristic wavelength for MSM structure and the center wavelengths of fast and slow axes for PMFBG are 0.0911 nm · °C^?1, 0.00976 nm · °C^?1 and 0.0105 nm · °C^?1, respectively; the strain sensitivities of those are ?0.013 nm · μ?^?1, 0.012 nm · μ?^?1 and 0.012 nm · μ?^?1, respectively.     

HFC网络可靠性的分析

在分析CATV可靠性低的原因的基础上,介绍了采用HFC网络提高可靠性的方案及改进的措施。     

CO-OFDM系统不同调制方式的性能分析(本期优秀论文)

在没有色散补偿的情况下,对不同调制方式的相干光正交频分复用(CO-OFDM)系统的性能进行研究.结果表明:2PSK抗误码性能较好,频带利用率较低;4QAM频带利用率是2PSK的两倍,当系统误码率在10<'-3>以内时,所需OSNR约为9dB;8QAM频带利用率比前两者高,但抗误码性能较前两者差.因此,设计通信系统时,要...