A Proposal and Demonstration for Photonic Generation of a Microwave Signal by Incorporating a Microring Resonator

A proposal for photonic generation of a microwave signal is presented by employing a dual wavelength erbiumdoped fibre ring laser. In the laser, a microring resonator is cascaded with a tunable bandpass filter to serve as a dual-wavelength selector, an unpumped polarization maintaining erbium-doped fibre is used as a saturable absorber. By replacing the microring resonator with a delay interferometer to verify the proposal, a wavelengthtunable dual wavelength single longitudinal mode laser is demonstrated, and a microwave signal at 10.01 GHz with a linewidth of less than 25 kHz is obtained by beating the two wavelengths at a photodetector.     

Multi-functional fibre-optic microwave links

The multi-functionality of microwave links based on remote heterodyne detection of signals from a dual-frequency laser transmitter is discussed and experimentally demonstrated in this paper. Typically, direct detection in conjunction with optical intensity modulation is used to implement fibre-optic microwave links. The resulting links are inherently transparent and mainly used for signal transmission. As opposed to direct detection links, remote heterodyne detection links can directly perform functionalities such as modulation, frequency conversion, and transparent signal recovery in addition to signal transmission. All three functionalities are presented and experimentally demonstrated with a remote heterodyne detection link based on a dual-frequency laser transmitter with two offset phase locked semiconductor lasers. In the modulating link a 1Gbit/s baseband signal is QPSK modulated onto a 9GHz RF carrier. The frequency converting link demonstrates up-conversion of a 100Mbit/s PSK signal from a 2GHz carrier to a 9GHz carrier with penalty-free transmission over 25km of optical fibre. Finally, the transparent signal recovering link transmits a standard FM video 7.6GHz radio-link signal over 25km of optical fibre without measurable distortion.     

Observation of the optoacoustic effect in an optical fibre

The rediationless absorption of light propagating in optical fibres induces both stress waves and thermal waves in the fibre medium. Detection of such waves is termed the optoacoustic effect. Successful detection in optical fibres is easily obscured by scattered light impinging on the detector. We have obtained a signal of 2 mV on a piezoceramic transducer attached to a commercial step-index optical fibre after passage of a 1 J ruby laser light pulse along the fibre axis. No signal was, however, produced when the transducer was not in contact with the fibre. Similar results were obtained using chopped cw laser radiation but then more care had to be taken since the transducers used had a measureable sensitivity to the low frequency chopped radiation emitted perpendicular to the optical fibre axis.     

Power penalty in multitone radio-over-fibre system employing direct and external modulation with optical amplifiers

This paper presents a multitone RoF system employing a central station and a remote antenna station to transmit modulated microwave or mm-wave signals. Two configurations of the system employing direct and external modulation are presented. First, at the central station, the modulating signal is directly and externally modulated at 1549.5 and 1550.5 nm, respectively, and the combined signal is then transmitted using wireless mode. In the second configuration, the combined signal is transmitted over 20 km to the remote antenna station using optical fibre connectivity. At the remote antenna station, both channel wavelengths are separated and amplified with an EDFA and SOA and are detected. The demonstration results show that there exists a small power penalty between the direct and the external modulation. But a large power penalty is reported depending upon the choice of optical amplifier viz. EDFA or SOA. Better performance is recorded in later case. The results also show that power is being distributed among the operating frequency and sidebands adjacent to it after transmission over a fibre link.     

Tunable microwave generation based on a Brillouin fiber ring laser and reflected pump

A simple approach for photonic generation of a tunable microwave signal is proposed and successfully demonstrated. By mixing the output from a single-longitudinal-mode Brillouin fiber ring laser with the reflected laser pump at photodetector, a microwave signal at the Brillouin shift can be obtained. Since the Brillouin shift can be changed by tuning the pump wavelength, tunable microwave can be generated. As a result a microwave signal tunable from 10.39 to 10.67 GHz has been achieved, with linewidth less than 600 KHz.     

Photonic generation of a millimeter-wave signal based on sextuple-frequency multiplication

A millimeter-wave signal with sextuple-frequency multiplication of a microwave source is obtained with two cascaded optical modulators, which are driven by the same microwave source with phase deviation of pi/2 introduced by an electrical phase shifter. Without any optical filter, a wideband continuously tunable millimeter-wave signal is easily generated.     

Resonance modes in optical fibres

The weakly nonlinear boundary value problem of wave propagation in an optical fibere(for the transverse electric mode,for example)is formulated and a modified linear solution is obained.It is shown that a self-consistent theory of fibre optics should be weakly nonlinear,The mode of critical refraction that does not exist in the linear theory is obtained,showing that it is a mode consisting of resonance modes,It is shown that the signal carriers in a long fibre are of resonance modes,not normal modes,Some experimental data are given for comparison with the theoretical predictions and the agreement seems satisfactory.     

A curve fitting signal processing scheme for a white-light interferometric system with a synthetic source

A white-light interferometric system, which comprises two Michelson interferometers linked by a 100 μm diameter core multimode step index fibre has been investigated, where a signal processing scheme, using curve fitting, has been introduced to suppress the noise induced in the system. The theoretical resolution of such a sensor with the use of an appropriate curve fitting signal processing scheme has been discussed. The experimental results obtained show the short term repeatability (to three standard deviations) to be better than 5 nm after signal processing, under conditions where the fibre is constantly vibrated in a known and reproducible way.     

Efficient Fibre Amplifiers Based on a Highly Er3＋/Yb3＋ Codoped Phosphate Glass-Fibre

Highly Er3＋ /yb3＋-codoped single-mode phosphate glass fibre is fabricated by the rod-in-tube technique. The performances of high-concentration Er3＋ /yb3＋-codoped phosphate glass fibre amplifiers are investigated and discussed. An efficient optical fibre amplifier with a gain of 12.6 dB based on a 3.0 cm long Era＋ /ybe＋-codoped phosphate glass fibre is demonstrated under a dual-pump configuration with two 976 nm fibre-pigtail laser diodes, which make it attractive for compact Er3＋-doped fibre amplifiers. The obtedned noise figures of signal wavelength from 1525 to 1565nm are less than 6.0dB. Gain saturation behaviour at 1535nm is also investigated, and the obtained saturation output power is larger than 10 dBm.     

基于平行偏振光注入的1550nm波段垂直腔表面发射激光器获取窄线宽光子微波的理论和实验研究

提出一种基于1550 nm垂直腔表面发射激光器(1550 nm-VCSEL)获取高质量微波信号的全光方案.在该方案中,采用波长位于VCSEL中被抑制模式的中心波长附近、振动方向与VCSEL中主导模式相同的偏振光注入(即平行注入)1550 nm-VCSEL获取高频微波,并借助双光反馈对该高频微波的线宽进行窄化.一方面,基于VCSEL的自旋反转模型,从理论上分析了采用该方案产生微波信号的可行性;另一方面,通过构建相应的实验系统,对该方案产生的微波的特性进行初步实验研究.实验结果表明:在合适的注入条件下,1550 nm-VCSEL能够产生30 GHz左右的微波信号,但该信号的线宽较宽(百兆水平);引入双光反馈后,微波线宽可被压窄两个数量级以上,得到了线宽低于1 MHz、信噪比大于40 d B的微波信号.     

基于次谐波调制光注入半导体激光器获取窄线宽微波信号的实验研究

实验研究了处于单周期振荡的光注入半导体激光器在频率等于单周期振荡频率一半的1/2次谐波调制下所产生的微波信号的特性.实验结果显示:在合适的注入条件下,处于单周期(P1)振荡的光注入半导体激光器可输出频率可达26.5 GHz、光谱具有单边带结构的光生微波信号,但微波信号的线宽比较宽(MHz量级);通过采用频率为单周期振荡频率一半的次谐波信号调制光注入半导体激光器,可将微波线宽从十几MHz压缩到几十k Hz.进一步分析了次谐波调制信号的功率以及频率对微波信号的相位噪声的影响,并在由次谐波调制信号的功率和频率构成的参数空间绘制出了能实现次谐波频率锁定的分布区域.     

Microwave irradiation effects on random telegraph signal in a MOSFET

We report on the change of the characteristic times of the random telegraph signal (RTS) in a MOSFET operated under microwave irradiation up to 40 GHz as the microwave field power is raised. The effect is explained by considering the time dependency of the transition probabilities due to a harmonic voltage generated by the microwave field that couples with the wires connecting the MOSFET. The RTS experimental data are in agreement with the prediction obtained with our model.     

无光滤波六倍频微波信号产生的系统设计

基于两个级联偏振调制器,提出了一种高频谱纯度、稳定的六倍频微波信号产生方法。该方法通过适当调整偏振片的偏振方向、射频驱动信号电压和相位,实现无光滤波器条件下、任何波段六倍频微波信号的产生。利用Optisystem平台搭建的仿真系统,以S波段4 GHz信号为例,验证了该设计系统产生的六倍频信号质量,并分析了非理想射频驱动电压和相位对六倍频信号质量的影响,结果表明:该设计系统能产生最大光边带抑制比、射频无杂散抑制比分别为21.3,15.2 dB的六倍频微波信号;且非理想驱动电压和相位差的偏离应控制在理想值5%的范围之内。     

Photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer

We realize a novel photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer. A near-linear phase shifter exceeding 180 degrees and a phase modulation with 2.5 Gbit/s baseband signal are obtained for a 10 GHz microwave signal by this proposed device.     

光子型远程分布式微波信号接收码元速率估计

基于光子学技术,设计了一种针对远程分布式微波信号接收的码元速率估计方案。首先,远程终端将接收的微波信号经电光调制器对连续激光源进行载波抑制双边带调制,生成携带微波信号的两个光边带信号;此光信号经光纤链路传输至中心站在光域滤除其中一个边带;其次,进行光电探测,通过分析电频谱的谐波实现微波信号码元速率估计。针对此方案,搭建仿真及实验系统装置:仿真成功地从60 GHz微波信号中提取出0.8 GBaud和6 GBaud的二进制伪随机码(PRBS)信号码元速率、从25 GHz微波信号中提取出3GBaud的PRBS码元速率;实验成功地从25 GHz的微波信号中提取出3 GBaud和5 GBaud的PRBS码元速率。     

分析光纤特性的新颖方法

本文从波动理论出发,引入用于分析微波传输线的方法-二维CC-FD-TD方法对光纤的色散特性进行研究。并利用电磁场的叠加原理对分析光纤时在圆心处出现的奇点进行了处理,最后利用计算例证明这一方法的可行性。     

Microwave Photonic Up- and Down-Converter with Tunable Phase Shift Based on an Integrated Dual-Polarization Dual-Parallel Mach–Zehnder Modulator without Optically Filtering

ABSTRACT

In this paper, we propose and numerically simulate a microwave photonic phase-tunable frequency converter (MPPTFC) without optically filtering to realize both frequency up- and down-conversion and a full 360° phase-shift for the microwave signal based on an integrated dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM). In the proposed scheme, both microwave RF signal and frequency-tunable local oscillator (LO) are modulated on the lightwave by single-sideband carrier suppression (SSB-CS) modulation to generate optical orthogonally polarized optical tones carrying RF signal with up- or down-converted frequency. A PolM that can support lightwave modulation with opposite modulation indices in transverse electric (TE) and transverse magnetic (TM) modes is used to introduce a phase difference between the two modes. Then the orthogonally polarized optical tones are aligned into a single polarized state by a polarizer (Pol) and detected by a photodiode (PD), a frequency-converted and phase-shifted microwave signal can be obtained. Simulation results demonstrate that the proposed MPPTFC can up-/down-convert the microwave signal with a tunable frequency shift of LO frequency and realize a 360° continuously tunable phase shift via the DC bias voltage of the PolM simultaneously.     

Optical fibre modulator based on electrostatic attraction

A fibre-based electrostatic deflector is described that enables modulating the optical signal in fibre systems. A 2.5-cm long fibre length was gold coated and deflected through the application of voltage between the fibre and an external electrode. Static measurements showed that the device is suitable for e-field sensing, and 100% power modulation was obtained for resonant frequencies 1 kHz. A peak voltage as low as 2 V gave a 15% modulation depth with 65 μm diameter fibre, and the maximum frequency measured for a 65 μm fibre was 40 kHz. In a proof-of-principle experiment, a 1.61-μm wavelength Er³⁺/Yb³⁺ fibre laser was Q-switched by placing the electrostatic fibre modulator inside the cavity, generating pulses of 4-μs duration.     

Microwave photonic filter’s application on the microwave signal generation based on an active mode-locked fiber laser

A novel scheme which utilizes the microwave photonic filter technique for the optical generation of a microwave signal based on an active mode-locked fiber laser is proposed. A microwave signal generator using a microwave photonic filter based on a 2: 1 optical coupler with a fiber loop which can effectively suppress a low-order frequency component of the microwave signal is demonstrated and a ～10-GHz microwave signal is achieved based on an active mode-locked fiber laser with the original pulse repetition rate of ～5 GHz.     

测试生物样品的ESR成像系统

本文介绍建造一个利用电子自旋共振信息获得生物体断层图像的系统。系统的微波频率安排在L波段,并用单匝平面线圈代替谐振腔,从而有效地减小了微波对生物体的热效应和方便地获得样品的断层信息。系统中用计算机控制磁场扫描,并同步地完成ESR信号的数据采集。通过多次扫描、采集数据、叠加和平均,提高了系统从噪声中检测微弱信号的能力。最后采用卷积滤波反投影重建法获得样品的断层图像,本系统具有价廉和容易构建的特点。