Performance evaluation of optical beamforming-based wideband antenna array

A wideband-generalized pattern multiplication approach to evaluate the performance of an optical beamforming-based wideband antenna array is proposed and experimentally demonstrated, which enables the far-field measurement of a large wideband array with a small anechoic chamber. Because the optimum reception of a wideband microwave signal is highly related to the time-domain distortions of the beamforming system, a correlation-receiver-based radiation pattern is applied to take the fidelity of the wideband signals into account.A four-element optical beamforming system is built to verify the feasibility of the proposed method. The results achieved by the proposed method agree well with the conventional direct measurements.     

Investigations of Linearly Chirped Fiber Bragg Gratings for Time-Steered Array Antennas

The use of linearly chirped fiber Bragg gratings as dispersive delay line elements in optical true time-delay beamformers is investigated. Two different dispersive prism beamforming architectures are considered as is their impact on the grating specifications. Microwave double-sideband and single-sideband characterization is carried out on gratings suitable for both architectures with an emphasis on the group delay ripple of single and cascaded gratings. Results indicate that commercially available gratings are suitable for beamforming applications.     

Investigations of Linearly Chirped Fiber Bragg Gratings for Time-Steered Array Antennas

The use of linearly chirped fiber Bragg gratings as dispersive delay line elements in optical true time-delay beamformers is investigated. Two different dispersive prism beamforming architectures are considered as is their impact on the grating specifications. Microwave double-sideband and single-sideband characterization is carried out on gratings suitable for both architectures with an emphasis on the group delay ripple of single and cascaded gratings. Results indicate that commercially available gratings are suitable for beamforming applications.     

The further investigation of the true time delay unit based on discrete fiber Bragg gratings

A true time delay (TTD) unit based on discrete fiber Bragg gratings (FBGs) for the phased array antenna (PAA) beamforming system is further investigated using the wave interference theory. The theoretical analysis shows that a PAA system using the TTD unit based on discrete FBGs can work at high frequency as long as the FBGs can be manufactured in high precision.     

Compact photonic delay line constructed by holographic optical elements

To fully support phased-array antenna and other applications, a 3-range (long time, moderate time, and short time) delay line structures with holographic optical elements is proposed. Flexibility, light-weight, on-axis coupling, easy alignment, easy fabrication, and compactness are their advantages. When use holographic optical elements to build the photonic delay line system, all of the delay and non-delay paths in these three photonic delay lines are setting in a compact structure. They do not need any extra components, such as mirrors and optical paths in free space, and can bear stronger vibration. Therefore, the holographic optical elements are more suitable to design the photonic delay lines. In these three structures, their losses and crosstalk s are balanced. All of delay and non-delay cases in these three delay line structures, their crosstalk, signal-to-noise ratio, and loss are 1/81,000, 59.1 dB, and 3.2 dB, respectively. Finally, to support complete applications, a polarization independent photonic delay line system with holographic optical elements is proposed, too.     

Tunable Chirped Fiber Grating Based Variable Time-Delay Network for Phased-Array Antenna Beamforming

In this paper, we present a photonics continuous beamforming system for optically controlled phased-array antenna based on a tunable fiber ring laser source and a novel variable true-time delay network consisting of one single-mode fiber delay line and four tunable chirped grating delay lines. The chirp rate of each chirped grating is tuned by bending a uniform fiber Bragg grating (FBG) bonded at a slant onto the lateral surface of a simply supported beam. This kind of variable true-time delay network can provide five-channel time-delayed signals that can be fed to an antenna array to achieve continuously beam scanning. The proposed true-time-delay unit with 5-element phased array steerer is suitable for phased-array antenna beamforming at frequencies up to 12 GHz.     

Control Strategy of True Time Delay Lines

This article presents the control of adjustable true time delays applied to an optical beamforming system. First is introduced the response of ring resonators of two and four ports and the cascade and lattice structures. The coupling factor and the phase modulation are employed as the control parameters for the adjustable group delay. The strategy of control is proposed and applied to a cascade of five ring resonators for producing wideband true time delays in the picosecond–nanosecond range with 2-GHz bandwidth and extremely low ripple. Ripples lower than 0.1% were obtained for the adjusted group delays. The proposed strategy can be simply extended if more resonators are added to increase the bandwidth of the system.     

时间延迟对偶极子光导天线空间功率合成影响分析

对偶极子光导天线空间功率合成中时间延迟的影响进行了分析。利用太赫兹时域光谱技术分别获取了34, 500, 1000 m偶极子光导天线的太赫兹时域光谱。采用数值模拟方法分析时间延迟对空间功率合成的影响。结果发现:在满足空间功率合成时域相干度60%的条件下,两个34, 500, 1000 m偶极子光导天线阵列的相对最大时间延迟分别为350.7, 467.6, 450.9 fs;三个34, 500, 1000 m偶极子光导天线阵列的相对最大时间延迟分别为191.1, 250.5, 267.2 fs;四个34, 500, 1000 m偶极子光导天线阵列的相对最大时间延迟分别为167, 200.4, 217.1 fs。试验结果表明,空间功率合成数值模拟仿真能为偶极子光导天线阵列的物理实验提供重要依据。     

频域反射法光纤延时精密测量

本文提出了一种应用于光纤延时系统中实现光纤延时精密测量的新方法,用以提高光纤延时测量的精度和准确性.该方法以1064 nm激光调制信号作为光源,通过测量回波信号的幅值和相位信息得到被测通道的频率响应,采用快速傅里叶逆变换得到被测目标的延时信息,实现光纤延时测量.本文通过理论分析和延时测量实验对频域反射法与传统的时域测量方法进行对比,使用频域反射法在调制频率范围10—200 MHz,采样频率间隔0.5 MHz的实验条件下,实现了3.3 ps延时测量分辨率,并证明了该方法具有比时域方法更高的测量精度,测量结果的准确性更好.     

Photonic true-time delay unit for broadband adaptive nulling in antenna arrays

An Opto-VLSI-based (VLSI: very-large-scale-integration) tunable true-time delay (TTD) generation unit used for adaptive null steering in phased array antennas is presented. The system is based on continuous tunable optical TTD technique. Arbitrary multiple true-time delays to generate multiple broadband nulls can simultaneously be synthesised for each antenna element. The proposed structured are characterised both theoretically and experimentally. Experimental results demonstrating the principle of the true-time delay for null generations are presented. The maximum time delay measured for a wavelength tuning from 1530 to 1560 nm is 9.5 ns.     

基于磁光开关的高精度光实时延时线

 给出了基于高速磁光开关的光实时延时技术的方案。研究了拓扑结构和磁光开关对光延时性能的影响。研制了5 bit,32位的光实时延时系统,并建立了光延时的测试平台,经测试,延时线延时精度优于3 ps。对光延时单元插损进行测试,结果显示:32态单元插损为0.12~0.88 dB,各态变化呈随机性。     

A 7-bit photonic true-time-delay system based on an 8 × 8 MOEMS optical switch

We demonstrate a 7-bit photonic true-time-delay （TTD） system which uses an 8 × 8 micro-optical-electro- mechanical system （MOEMS） optical switch for phased array antennas （PAAs） beamforming applications. The switch controls the optical signal to pass by the fiber delay lines （FDLs） of different lengths. Different time delays between adjacent channels are obtained due to the chromatic dispersion of FDLs. Therefore, the system cannot be disturbed by the environment. The measured time delay responses are nearly linear with the wavelength spacing between optical carriers as well as the lengths of FDLs, which agrees well with the theoretical analysis.     

A novel wavelength switchable fiber laser source and its application in photonics beamforming for optically controlled phased array antenna

A novel wavelength-switchable fiber laser source that can individually scan 14 required wavelengths within 40 ms, and its application in photonics true time delay beamforming is presented in this paper. The laser source is constructed using a unidirectional fiber ring cavity, a tunable fiber Fabry–Perot filter and two cascaded sampled fiber Bragg gratings with the wavelength spacing of 1.6 nm. A five-channel true-time-delay system using the proposed fiber laser source cooperating with a single-mode fiber and four chirped-grating-based is constructed and demonstrated for the application of phased array antenna beam steering. Continuous beam steering at the microwave frequency up to 20 GHz has been achieved. PACS 42.55.Wd; 42.81.Wg; 84.40.Ba     

Demonstration of optical coherent transient true-time delay at 4 Gbits/s

Multigigabit-per-second true time delay (TTD) was experimentally demonstrated by use of optical coherent transient techniques in a Tm(3+):YAG crystal. A delay accuracy of 1 ps and a delay resolution of 7 ps (both measurement limited) were achieved. The retrieved data retained good fidelity.     

On the relation between retarded and advanced arrival of a pulse at the output of an optical system

It is shown that the possibility of negative delay time of a pulse at the output of an optical system (compared to the pulse at its input) is a necessary consequence of the possibility of positive delay time of the pulse and the superposition principle. In particular, two optical systems with different positive delay times are sufficient for creating an optical system with a negative delay time. The negative delay time of a pulse can be considered as a spline extrapolation of its time dependence resulting from the interference of several copies of the pulse with different delays. It is shown that a negative delay time of a pulse arises necessarily in any interferometer in an area of destructive interference of two copies of the initial pulse that are similar in amplitude and undergo different delay times.     

Investigation on performance of all optical buffer with large dynamical delay time based on cascaded double loop optical buffers

Optical buffers are critical for optical signal processing in future optical packet-switched networks. In this paper, a theoretical study as well as an experimental demonstration on a new optical buffer with large dynamical delay time is carried out based on cascaded double loop optical buffers (DLOBs). It is found that pulse distortion can be restrained by a negative optical control mode when the optical packet is in the loop. Noise analysis indicates that it is feasible to realise a large variable delay range by cascaded DLOBs. These conclusions are validated by the experiment system with 4-stage cascaded DLOBs. Both the theoretical simulations and the experimental results indicate that a large delay range of 1-9999 times the basic delay unit and a fine granularity of 25 ns can be achieved by the cascaded DLOBs. The performance of the cascaded DLOBs is suitable for the all optical networks.     

卡塞格伦光学天线偏轴及性能分析

设计了具有抛物面结构的卡塞格伦光学天线.通过对偏轴下的卡塞格伦光学天线系统的分析,得到了不同偏转角所对应的接收光斑面积表达式和功率衰减曲线.讨论了偏轴下的接收天线增益与波长及偏转角的关系,仿真出在偏轴与轴对准两种情形下的增益曲线.仿真结果表明,〖JP2〗最大偏轴比轴对准情形增益降低了6.564dB.最后分别针对轴对准与某种偏轴情形下的系统做了光斑测试实验与天线耦合效率测试实验.结果为：偏轴下天线耦合效率降低了26.966%.这些研究为星间光通信中控制系统实现光轴的精确对准提供了理论依据,具有重要的实用价值 关键词： 偏轴 卡塞格伦光学天线 偏转角 增益     

非视线散射大气光通信的光学天线

由于大气衰减的影响,非视线散射大气光通信需要使用光学天线以提高对光信号的采集能力,进而增加通信距离。针对非视线大气光通信的需求,利用ZEMAX软件对半球透镜、复合抛物面聚光器（CPC）和卡塞格伦望远镜等光学天线进行了性能分析。分析表明：半球透镜和CPC视场较大,增益值高。利用蒙特卡罗法模拟计算了一定条件下,非视线散射光通信在有无半球透镜或CPC作光学天线时到达探测元件的能量随通信距离的变化。结果表明：CPC聚光能力更强,适合作为非视线散射光通信的光学天线。     

Non-feedback precoder for optical DQPSK modulation

A novel non-feedback precoder circuit for high-speed parallel optical differential quadrature phase shift keying （DQPSK） modulation is proposed. The alternative control signal is introduced in replacement of the conventional feedback one, which eliminates the speed limitation due to the electronic propagation delay. The proposed precoder consists of four differential encoders, an exclusive OR gate, a cross switch, and delay lines. It is demonstrated by a true pseudo random bit sequence （PRBS） transmission at 20 Gb/s.