Tunable all-fiber intracavity wavelength converter without external pumps

A new architecture for tunable broadband wavelength conversion in a dispersion-shifted fiber is presented. Conversion is achieved by using four-wave-mixing in a dispersion-shifted fiber in a single fiber-ring cavity. Wide tunability is achieved by the self-generation of two tunable orthogonal pumps in the cavity. This effect is due to the introduction of two tunable fiber Bragg gratings written in high birefringence fibers which act as selective polarization and wavelength filters. The results show conversion efficiencies up to −2 dB with the signal-to-noise ratio of the converted signal up to 26 dB.     

基于十字变形结构的高效超宽带线性极化转换超表面

提出了一种基于十字变形结构超表面的极化转换器,在反射模式下获得了高效超宽带的交叉极化反射.在8.4到20.7GHz频段内交叉极化反射率大于-0.2dB,而共极化反射率小于-12dB,在谐振频率点处交叉极化反射率大于-0.03dB,而共极化反射率达到-60dB,即在谐振点处几乎可实现完全的交叉极化转换;相对带宽达84.5%,交叉极化的平均转换效率为96.7%;此外,利用电路板刻蚀制备了此极化转换器样品,实验测试其交叉极化反射率在工作频段内大于-1dB,而共极化反射率小于-10dB,实验结果与模拟结果吻合,验证了此超表面可以在超宽的频带内实现线极化电磁波的交叉极化转换.本文设计的超宽带极化转换超表面具有转换效率高和几何结构简单的优点,可被扩展到太赫兹甚至是可见光频段.     

Polarization-insensitive all-optical wavelength conversion of 320 Gb/s RZ-DQPSK signals using a Ti:PPLN waveguide

Polarization-insensitive wavelength conversion of a single channel 320 Gb/s RZ-DQPSK data signal using a Ti:PPLN waveguide in a bi-directional loop configuration with less than 0.5 dB polarization sensitivity is reported. The conversion efficiency with polarization scrambling of the signal was ?21 dB, which includes 9.2 dB of passive losses in the whole Ti:PPLN subsystem. In BER measurements error-free operation with 2 dB OSNR penalty for the converted signal was achieved. Theoretical and experimental investigations of the temporal shape and chirp of the converted data pulses show only very little broadening and chirping, indicating the potential for wavelength conversion of even much higher data rates.     

一种高功率折线栅极化转换天线罩的设计

设计了一种用于高功率径向线螺旋阵列天线的极化转换天线罩。利用三层介质层包夹双层金属折线,形成密封的埋入式折线栅结构。在实现圆极化与线极化相互转换的同时,又避免金属与空气接触,可以提高功率容量。分析了埋入式折线栅单元各参数的影响,并优化单元参数,以此构建埋入式折线栅极化转换天线罩并加载至X波段高功率径向线螺旋阵列天线,分析了天线的基本性能以及功率容量。仿真结果显示:天线匹配良好,增益和波束宽度变化很小,中心频率轴比由1.16 dB变为40 dB,圆极化波转换为线极化波效果良好;经初步分析,极化转换天线罩的功率容量为121 MW,实现了极化转换天线罩的高功率应用。     

Linearized analog photonic links based on a dual-parallel polarization modulator

A linearized analog photonic link (APL) is proposed based on an integratable electro-optic dual-parallel polarization modulator (DPPolM), which consists of two polarization beam splitters and two polarization modulators (PolMs). Theoretical analysis shows that the APL is potentially free from the third-order nonlinear distortion if a polarization controller placed before the DPPolM is carefully adjusted. A proof-of-concept experiment is carried out. A reduction of the third-order intermodulation components as high as 40 dB and an improvement of the spurious-free dynamic range as large as 15.5 dB is achieved as compared with a single PolM-based link. The DPPolM-based APL is simple, compact, and power efficient since it requires only one laser, one modulator, and one photodetector.     

基于极化旋转超表面的圆极化天线设计

本文通过设计出一种反射型极化旋转超表面,在8—12 GHz频域内实现高效的极化旋转,并将其加载于微带缝隙天线下方构成新型的极化旋转超表面天线,利用超表面的90°极化旋转效应,成功实现了天线的圆极化辐射调制.仿真与实验结果表明:圆极化天线的中心工作频率为GHz,阻抗带宽为8.3—10 GHz.当微带缝隙天线与极化旋转超表面的间距H=4.5mm时,天线在8.3—8.8 GHz频带内实现了圆极化辐射;当mm时,天线在8.8—9.3 GHz频带内实现了圆极化辐射;当=8mm时,天线在9.3—10 GHz频带内实现了圆极化辐射.实验结果与仿真结果相符,证明了此种设计方法的有效性,也为微带缝隙天线的圆极化设计提供了一种新的途径.     

Performance improvement of 10-Gb/s XGM wavelength conversion by using polarization control structure

By utilizing the cross polarization modulation effect in semiconductor optical amplifier(SOA), the extinc tion ratio of cross gain modulation(XGM)wavelength conversion was enhanced, the pattern effect was significantly reduced,and the power penalty of wavelength conversion was reduced by 5 dB simultane-ously. Furthermore, by adjusting the settings of polarization controllers, both inverted and non-inverted wavelength conversion can be achieved right in the same wavelength converter.     

Efficient and compact TE-TM polarization converter built on silicon-on-insulator platform with a simple fabrication process

An efficient TE-TM polarization converter built on a silicon-on-insulator nanophotonic platform is demonstrated. The strong cross-polarization coupling effect in air-cladded photonic-wire waveguides is employed to realize the conversion. A peak TE-TM coupling efficiency of 87% (-0.6 dB insertion loss) is measured experimentally. A polarization conversion efficiency of >92% with an overall insertion loss of <-1.6 dB is obtained in a wavelength range of 40 nm. The proposed device is compact, with a total length of 44 μm and can be fabricated with one lithography and etching step.     

基于半导体光放大器交叉偏振调制效应实现正、反相波长变换

利用琼斯矩阵,对基于半导体光放大器中的交叉偏振调制效应实现全光波长变换进行了理论分析.结果表明,利用这种机制可以实现同相与反相波长变换.在实验上同时实现了10Gb/s归零信号的正相与反相波长变换,输出消光比分别达到了6.9 dB和8.1 dB.     

A novel polarization converter based on the band-stop frequency selective surface

A dual-passband single-polarized converter based on the band-stop frequency selective surface(FSS)with a low radar cross-section(RCS)is designed in this article.The unit cell of the proposed converter is formed by a polarization layer attached to the band-stop frequency selective surface.The simulation results reveal that the co-polarization reflection coefficients below-10 d B are achieved in 3.82–13.64 GHz with a 112.4%fractional bandwidth(the ratio of the signal bandwidth to the central frequency).Meanwhile,a polarization conversion band is realized from 8.14 GHz to 9.27 GHz with a polarization conversion ratio which is over 80%.Moreover,the 1 d B transmission window is obtained in two nonadjacent bands of 3.42–7.02 GHz and 10.04–13.91 GHz corresponding to the relative bandwidths of 68.9%and 32.3%,respectively.Furthermore,the radar cross-section of the designed structure can be reduced in the wideband from 2.28 GHz to 14 GHz,and the 10 d B RCS reduction in the range of 4.10–13.35 GHz is achieved.In addition,the equivalent circuit model of this converter is established,and the simulation results of the Advanced Design System(ADS)match well with those of CST Microwave Studio(CST).The archetype of the designed converter is manufactured and measured.The experiment results match the simulation results well,which proves the reliability of the simulation results.     

基于SPGD算法的非保偏-保偏光自适应偏振转换

报道了一种基于随机并行梯度下降(SPGD)算法的高消光比非保偏-保偏光自适应偏振转换系统。该系统利用偏振控制器对非保偏光的偏振分量进行直接控制,通过SPGD算法对输出的偏振消光比进行优化,最终实现了自适应的非保偏-保偏光的偏振转换。理论上,结合SPGD算法和偏振控制器的原理,对系统进行分析,建立了非保偏-保偏光自适应偏振转换的数学模型。实验上,利用该系统实现了非保偏到保偏光的转换,获得了14.1dB的线偏振光输出;并利用该系统将任意方向(0~360°)偏振态的线偏振光转换为期望偏振态的高消光比线偏光,其输出线偏光的平均消光比约为12dB。     

I/Q intensity-demodulation analog photonic link based on polarization modulator

We experimentally investigate a high-linearity analog photonic link based on polarization-modulation in-phase/quadrature (I/Q) intensity-demodulation. In the proposed system, a light wave with its polarization direction oriented at an angle of 45° with respect to the principal axis of the polarization modulator (PolM) is polarization modulated by a drive signal. In the receiver, the polarization-modulated signal is split into two paths using a 50:50 optical coupler (OC). In each path, a polarization beam splitter (PBS) is connected to the PolM via a polarization controller (PC) to realize the in-phase and quadrature signal, respectively. Thanks to the polarization-modulation to intensity-modulation conversion, the fluctuation of the optical phase noise has no impact on the coherent signals. In addition, the use of a single PolM allows the link avoids the matching requirements of dual modulator schemes. The linearization leads to suppression of the third-order intermodulation (IMD3) by more than 40 dB, compared to the quadrature signal. Experimental results show that the link gain is -11.5 dB, noise figure is 26.5 dB, and the third-order limited spurious free dynamic range (SFDR) is 124 dB in a 1 Hz bandwidth.     

A polarization splitter based on self-imaging phenomena in an anisotropic photonic crystal with an absolute photonic band gap

In a multi-mode waveguide of an anisotropic photonic crystal with an absolute photonic band gap, self-imaging phenomena are achieved for both TE and TM polarizations. Through careful choice of structure parameters, or the working frequency, the field of TE and TM polarization components can be separated in space after a certain propagating distance, based on which a polarization splitter is designed and numerically simulated. The numerical simulation shows that the polarization extinction ratio of the polarization splitter can reach a value of 22.9 dB and 19.2 dB at its two output ports, respectively.     

Microwave photonics reconfigurable mixer based on polarization modulator

A reconfigurable and stable mixer is proposed and demonstrated in this paper. It mainly consists of a dual-driven Mach–Zehnder modulator and a polarization modulator with several polarization controllers (PC) and polarizers (Pol). According to the theoretical analysis, different functions (such as single ended mixer, balanced mixer, I/Q mixer and image rejection mixer) can be realized by adjusting the PCs and Pols. The simulation results verify the possibility of multi-functions that realized by the reconfigurable mixer. In addition, another research on how the non-ideal parameters affect the image rejection ratio (ISR) and conversion efficiency of the mixer is also carried. The results show that both of them perform better as the extinction ratio gets higher. However, they are incurring a sharp decrease if the DC bias points deviate from the settled values. In the meantime, the results also indicate that the higher modulation indices lead to a better ISR. A 57.12 dB ISR can be achieved with conversion efficiency of ? 9.53 dB.     

All-fiber single polarized Yb-doped fiber laser with a high extinction ratio

We present an all-fiber design for a single polarization Yb-doped fiber laser with all-fiber connections spliced. Single polarization with a high extinction ratio was achieved by the design of a laser cavity consisting of a fiber Bragg grating inscribed on a single-polarization fiber as a high reflective mirror and a piece of end-cleaved single-polarization fiber as an output coupler. The fiber laser operates at 1063.25 nm with an output power of 1.7 W, an optical signal- to-noise ratio of 70 dB and a narrow bandwidth of 54 pm. The laser output has a polarization extinction ratio of 700:1 or 28 dB, and a very stable power output.     

Compact polarization rotator on silicon for polarization-diversified circuits

We demonstrate a polarization rotator based on adiabatic mode evolution on silicon for polarization-diversified circuits. The rotator has a device length of 420?μm, a polarization-conversion efficiency of more than 90%, and an insertion loss less than 1?dB for a wavelength range of 80?nm. Combining the rotator with a compact, broadband polarization beam splitter based on cascaded directional couplers enhances the polarization conversion extinction ratio to over 30?dB with less than 1.5?dB total insertion loss over a 60?nm spectral range.     

Design of diamond-shape photonic crystal fiber polarization filter based on surface plasma resonance effect

A novel plasmonic polarization filter based on the diamond-shape photonic crystal fiber(PCF) is proposed. The resonant coupling characteristics of the PCF polarization filter are investigated by the full-vector finite-element method. By optimizing the geometric parameters of the PCF, when the fiber length is 5 mm, the polarization filter has a bandwidth of 990 nm and an extinction ratio(ER) of lower than -20 dB. Moreover, a single wavelength polarization filter can also be achieved, along with an ER of -279.78 dB at wavelength 1.55 μm. It is believed that the proposed PCF polarization filter will be very useful in laser and optical communication systems.     

Compact polarization rotators for integrated polarization diversity in InP-based waveguides

We present the design, fabrication, and operation of a polarization converter based on angled waveguides in the InP/InGaAsP material system. By combining design elements from mode evolution and birefringent devices, the total device length is kept short (less than 50 microm) and the insertion efficiency high at 81%+/-19%, which corresponds to an insertion loss of 1 dB. Devices operate broadband, i.e., the polarization conversion exceeds 15 dB over a 100 nm wavelength range. A polarization rotator with these specifications is a prime candidate for use in an integrated polarization diversity scheme.     

Broadband Terahertz Polarization Converter and Asymmetric Transmission Based on Coupled Dielectric‐Metal Grating

Coupled dielectric‐metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high‐efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission.     

液晶填充碲酸盐光子晶体光纤偏振旋转器

提出一种液晶填充碲酸盐玻璃的柚子型光子晶体光纤偏振旋转器,利用全矢量有限元法,对液晶填充碲酸盐玻璃的柚子型光子晶体光纤的偏振旋转特性进行数值模拟,并分析了光纤结构参数、环境温度、工作波长等对光纤偏振旋转特性的影响.研究结果表明:此种偏振旋转器具有较高的旋转效率、较低的工作串扰和较短的旋转长度,在工作波长为1.55μm、偏振角度为45°时,其值分别达到99.947%、-32.84dB和197μm;另外,随着光纤薄壁厚度的增加,旋转长度随之升高,随着工作波长的变大,旋转长度随之降低,随着温度的增加,旋转长度随之升高.这种新型的光子晶体光纤为偏振旋转器的研发提供了参考.