超宽带信号的产生及光纤传输的研究

提出了一种新的超宽带(UWB)脉冲产生的方法,并对其产生的数学原理进行了分析和实验验证。经过高斯信号调制的偏振控制器(PC)可以产生两个相位互补的相位调制信号,先通过PC调节两个正交的相位调制信号的静态相移,再经过偏振分束器(DBS)检偏后可以得到两路相位互补的高斯信号或二阶高斯信号,最后将这两路信号延时然后再经过偏振合路器(PBC)就可以分别得到一阶或三阶高斯信号。由于这3种脉冲的产生方式不同,频带宽度不同,在光纤中传输时对色散的容忍度也不一样,因此仿真分析了色散对这3种UWB信号传输特性的影响,得出了三阶高斯信号最适合UWB传输。     

Multitap Photonic Microwave Filters With Arbitrary Positive and Negative Coefficients Using a Polarization Modulator and an Optical Polarizer

A novel multitap photonic microwave filter with arbitrary positive and negative coefficients implemented using an electrooptic polarization modulator (PolM) and an optical polarizer is proposed and experimentally demonstrated. In the proposed filter, the optical polarizer is connected at the output of the PolM with its transmission axis aligned at an angle of 45 to one principal axis of the PolM. By adjusting the polarization direction of the input lightwave to be 45 or 135 to one principal axis of the PolM, an inverted or noninverted intensity-modulated optical microwave signal is obtained at the output of the optical polarizer, which leads to the generation of a negative or positive coefficient. A time delay difference between adjacent taps is generated by using a wavelength-dependent delay line. A five-tap photonic microwave filter with arbitrary positive and negative coefficients is demonstrated. The reconfigurability of the filter is also investigated.     

A Photonic UWB Generator Reconfigurable for Multiple Modulation Formats

In this letter, we propose and demonstrate a simple and flexible optical ultra-wideband (UWB) pulse generator that can be reconfigured for pulse-position modulation, biphase modulation, and pulse-shape modulation. The system is implemented using a dual-drive Mach-Zehnder modulator and an electrically reconfigurable asymmetric Mach-Zehnder interferometer (AMZI). The AMZI consists of a polarization modulator (PolM), a polarization controller (PC), a section of polarization-maintaining fiber, and an optical polarizer. By adjusting the PC and the drive voltage to the PolM, the system is reconfigured to generate UWB signals with different modulation formats. An experiment is performed, which verifies the proposed technique.     

一种基于偏振的PMD不敏感OSNR监测技术

在分析偏振模色散(PMD)引起传输信号去偏振导致偏振分光光信噪比(OSNR)监测方法测量误差问题的基础上,提出一种用扰偏振器和偏振分束器来克服PMD影响,实现OSNR精确监测的方案.波分复用传输信号经扰偏振器扰偏后解复用分离出待测信道信号,偏振分束器将待测信号分成偏振正交的两个支路信号,然后通过检测到的两支路信号功率之间的关系来得到信道的OSNR.仿真实验证实了新方法对PMD影响不敏感.     

光源谱型对保偏光纤应力传感信号的影响

保偏光纤对入射的线偏振光具有偏振保持能力,用白光干涉系统可实现准分布式应力、温度和位置传感。超辐射发光二极管(SLD)当驱动电流较小时,光谱服从高斯分布;随着驱动电流增加,中心波长向短波方向漂移,光谱畸变,可用两个高斯函数相加拟合。本文详细分析了SLD光源在不同驱动电流下的谱型分布及拟合曲线,并在保偏光纤应力传感系统中进行了实验,实验结果表明随着光源输出功率增加,在耦合点两侧对称分布着伪耦合点。当光源功率为15 mW时,伪耦合点的耦合强度比力致耦合点的耦合强度约小15 dB。     

Effects of magnetic field on pulse and CW operation of the large bore ionized gas laser

CW and pulse measurement distinguish between ion-drift gas pumping effects [1],[2] and other factors affecting laser output as a function of the confining magnetic field for large diameter (> 5 mm) ionized gas lasers. With pulse lengths too short for pumping to occur laser operation optimizes at 400 gauss, whereas in CW operation the optimum magnetic field may be > 2600 gauss (at low pressures).     

Photonic Microwave Bandpass Filter With Negative Coefficients Using a Polarization Modulator

A novel photonic microwave bandpass filter with negative coefficients implemented using a polarization modulator (PolM) is proposed and experimentally demonstrated. In the proposed filter, a lightwave from a tunable laser source (TLS) is sent to a PolM, with the incident lightwave adjusted to have its polarization direction aligned at an angle of plusmn45deg to the principal axes of the PolM. A microwave signal is applied to the PolM through its RF port. Thanks to the polarization modulation in the PolM, two complementary microwave signals with identical amplitudes carried by two optical carriers with orthogonal polarizations are generated. The two complementary optical microwave signals are then sent to an optical delay line consisting of one section or two sections of polarization-maintaining fiber (PMF), with the polarization directions aligned with the fast and slow axes of the PMF. A photonic microwave bandpass filter with two or four taps is obtained     

MD投影机中的光学元器件（二）——偏振光分光器与偏振光转换器

在LCD或LCoS投影机中要用到偏振光分光器（PBS）与偏振光转换器（PCS）,利用这种器件可以产生偏振光,提高光的利用率。根据物理光学原理,在不同介质界面处光线会发生反射和折射,从而得到振动方向相互垂直的S偏振光和P偏振光。在玻璃表面镀有多层不同介质的薄膜,可使光线在每层界面处均发生反射和折射,以得到消光比很高的偏振光,这种器件就是PBS。利用1/2波片改变偏振态的原理,可加工成PCS。     

Experimental Results on a 1.5 MW, 110 GHz Gyrotron with a Smooth Mirror Mode Converter

We present an internal mode converter (IMC) design for a 1.5 MW, 110 GHz gyrotron operating in the TE_22,6 mode. The launcher, designed using the codes Surf3d and LOT, converts the cavity waveguide mode into a nearly pure Gaussian beam. The Gaussian beam output from the launcher is shaped by a series of 4 smooth, curved mirrors to provide a circular output beam with a flat phase front at the gyrotron window. By employing smooth mirrors rather than mirrors with phase correcting surfaces, such an IMC is less sensitive to alignment issues and can more reliably operate with high efficiency. The IMC performance was verified by both cold test and hot test experiments. Beam pattern measurements in each case were in good agreement with theoretical predictions. The output beam was of high quality with calculations showing that the Gaussian Beam content was 95.8 ± 0.5% in both hot and cold test.     

基于级联外调制器的六倍频微波信号的光学生成技术研究

提出并实验验证了一种基于级联偏振调制器(Po lM)和双平行马赫-曾德尔调制器(DPMZM)的六 倍频微波信号的光学生成方法。PolM在射频(RF)信号调制下,会产生多个光边带,通过调 节偏振控制 器(PC)和检偏器仅获得奇数阶边带,然后通过DPMZM,其中一子MZM调制RF信号,工作在 最大 传输点(MATP),另一子MZM不调制RF信号,从而抑制掉一阶边带,保留三阶边带,经光 电探测器(PD)拍频获得六倍频微波信号。仿真结果表明,在不利用任何光、电滤波器的情况下,调 制器消光比为 理想状态(100dB)时,RF杂散抑制比(RFSSR) 为34dB。即使消光比为非理想状态(30dB)时,生成微波信号的RF SSR仍可以达到21dB。理论分析和实验结果均验证 了方案的可行性。