Chaotic on off keying for secure communications

We experimentally demonstrate a chaotic on-off keying method for secure communications by using chaos synchronization in two microchip lasers. The output of the microchip laser in the transmitter is externally modulated with an acousto-optic modulator at ~4 MHz . One encodes a digital message in the chaotic carrier by turning the modulation on and off at 100 kHz. Because the accuracy of synchronization for the slave laser in the receiver tends to be degraded in the presence of external modulation in the injection laser signal, one can distinguish two binary states. The digital message can be recovered as an envelope of the chaotic oscillation when the difference between the two laser outputs of the transmitter and the receiver is calculated.     

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.     

Microwave Photonic Phase Shifter Based on an Integrated Dual-polarization Dual-parallel Mach-Zehnder Modulator without Optical Filter

ABSTRACT

A frequency-doubled microwave photonic phase shifter (MPPS) without optical filter is proposed. The MPPS is based on an integrated dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM) and a polarization modulator (PolM). The DP-DPMZM with a 90° polarization rotator in one arm is used to generate an optical carrier suppressed double sideband (OCS-DSB) signal with orthogonal polarization, and the PolM with two modes opposite phase modulation is used to introduce the optical phase shift between the two orthogonally polarized tones. Simulations show that the MPPS can realize a continuously tunable phase shift of 360° with only one DC bias voltage, and is not sensitive to the optical carrier wavelength and microwave signal frequency since no optical filter is used.     

Polarization insensitive linear intensity modulation in a Sagnac fiber-optic loop with an electro-optic cell and optoelectronic feedback

We present a modulation scheme consisting of a fiber-optic Sagnac interferometer, which has an electro-optic modulator (Pockels cell) in the loop of the interferometer. In order to diminish the nonlinearity of the Sagnac interferometer transmittance function, we monitor a very small part of the output light intensity by means of a photodiode and then amplify this signal by a constant factor ξ. This amplified signal is added to the electrical modulating signal that is being applied to the electro-optical modulator. The consequence of introducing this feedback loop is that by properly choosing the amplifying factor ξ, we can increase the linearity of the modulation. The device is insensitive to the polarization state of the input light, so it should be used for intensity modulation of nonpolarized light with up to 100% modulation depth. The theoretical and experimental examination of the device is presented.     

Photonic instantaneous microwave frequency measurement based on two different phase modulation to intensity modulation conversions

A novel photonic technique for instantaneous frequency measurement of microwave signal based on phase modulation to intensity modulation conversion is proposed and demonstrated. In the proposed system, an optical carrier is modulated by a microwave signal with its frequency to be measured through a phase modulator. The phase-modulated optical signal is then converted to intensity-modulated signals in two independent paths using a dispersive media and a frequency discriminator respectively. Since the dependence of the received microwave power on the input microwave frequency in the two paths differs, the microwave power ratio between the two paths can be used to uniquely determine the microwave frequency. The major advantages of the approach lie in that only one laser source and the bias-free phase modulator is employed in the system, which improves the stability of the system. Experimental demonstrations of the frequency measurement based on the proposed approach are presented.     

Integration of spectral and temporal cues in discrimination of nonspeech sounds: a psychoacoustic analysis

This study presents a psychoacoustic analysis of the integration of spectral and temporal cues in the discrimination of simple nonspeech sounds. The experimental task was a same-different discrimination between a standard and a comparison pair of tones. Each pair consists of two 80-ms, 1500-Hz tone bursts separated by a 60-ms interval. The just-discriminable (d' = 2.0) increment in duration delta t, of one of the bursts was measured as a function of increments in the frequency delta f, of the other burst. A trade off between the values of delta t and delta f required to perform at d' = 2.0 was observed, which suggests that listeners integrate the evidence from the two dimensions. Integration occurred with both sub- and supra-threshold values of delta t or delta f, regardless of the order in which the cues were presented. The performance associated to the integration of cues was found to be determined by the discriminability of delta t plus that of delta f, and thus, it is within the psychophysical limits of auditory processing. To a first approximation the results agreed with the prediction of orthogonal vector summation of evidence stemming from signal detection theory. It is proposed that the ability to integrate spectral and temporal cues is in the repertoire of auditory processing capabilities. This integration does not appear to depend on perceiving sounds as members of phonetic classes.     

电光调制在被动综合孔径成像探测中的应用

介绍了一种新型被动综合孔径成像探测方法:视场辐射信号被接收和放大后,通过电光幅度调制将其幅度和相位信息加载到光波上,经光纤传输在末端形成阵列,通过光学系统直接成像,将视场实时恢复出来.该方法可实现工作在微波、毫米波和太赫兹波段的高分辨力实时成像探测的目的.深入分析了电光调制器在综合孔径成像探测中的应用,建立电光调制模型,讨论了在小信号调制下的电光幅度调制近似理论.通过数值计算与仿真分析,得到综合孔径成像探测中电光调制器的调制信号强度限制的有关结论.结果表明,利用上变频电光调制技术和光信息处理,所得到的成像仿真图的半峰全宽和信噪比性能都优于传统的基于下变频技术的成像仿真结果.     

基于石墨烯的宽带全光空间调制器

提出了单层石墨烯包裹微纳光纤的全光空间调制.石墨烯作为可饱和吸收体包裹在通过二氧化碳激光器加热制备的微纳光纤上,当信号光沿着微纳光纤传输时部分光将以倏逝场的形式沿着微纳光纤表面传递,并与石墨烯产生作用被吸收.同时将波长为808 nm的抽运光从空间垂直入射到石墨烯包裹的微纳光纤处,依据石墨烯的优先吸收特性,通过抽运光控制石墨烯对信号光的吸收,实现了宽带全光空间调制.在1095 nm波长处获得最大调制深度约为6 dB,调制带宽约为50 nm,调制速率约为1.5 kHz.空间全光调制器具有输出信号光“干净”的特点.与传统石墨烯微纳光纤全光调制器相比,输出端不需要对抽运光进行光学滤波而直接获得已调信号.该复合波导全光空间调制器以更为灵活、高效的方式打开了微纳超快信号处理的大门.     

Cross-phase-modulation-based wavelength conversion using intersubband transition in InGaAs/AlAs/AlAsSb coupled quantum wells

We report an ultrafast cross phase modulation (XPM) effect in intersubband transition (ISBT) of InGaAs/AlAs/AlAsSb coupled quantum wells, where the ISBT absorption of a transverse-magnetic mode pump signal induces phase modulation of a transverse-electric mode probe signal. Using waveguide-type ISBT devices, we have achieved XPM-based 10 Gbit/s wavelength conversion with a power penalty of 2.53 dB. Also, we propose XPM-based signal processing circuits for gate switching and modulation format conversion.     

基于受激布里渊散射的宽带宽和高精度的微波频率瞬时测量

提出了一种基于受激布里渊散射效应的瞬时频率测量方法.未知信号经过强度调制作为泵浦光,矢量网络分析仪产生的信号经过相位调制作为扫描信号光,当泵浦光和扫描信号光之间满足相位匹配条件时,受激布里渊散射效应发生并实现相位调制到强度调制的转换,未知信号的频率被测量.实验验证可以测量0.5 GHz-27 GHz的微波信号的频率,最大误差小于20 MHz.     

基于插入损耗的光纤信号调制器

基于光纤连接的横向偏移造成的插入损耗研制了一种的新型的光纤信号光调制器。调节对接光纤的横向偏移,可以调节对接光纤间的光耦合效率,利用调制信号调制横向偏移可实现对光纤传输光信号的调制。实验中,将调制电信号放大并加载于压电陶瓷使其振荡,由此控制对接光纤的横向偏移与调制信号同步变化,实现了对下一级光纤输出端光强的调制。这种光纤信号调制器主要针对光的振幅调制,实验中获得调制度优于95%,信噪比约为20dB,带宽约为200kHz。具有价格低廉、调制度高的特点,可应用于光纤传输信号的调制及信号斩波等。     

Auditory nerve fiber responses to electric stimulation: modulated and unmodulated pulse trains

Many modern cochlear implants use sound processing strategies that stimulate the cochlea with modulated pulse trains. Rubinstein et al. [Hear. Res. 127, 108 (1999)] suggested that representation of the modulator in auditory nerve responses might be improved by the addition of a sustained, high-rate, desynchronizing pulse train (DPT). In addition, activity in response to the DPT may mimic the spontaneous activity (SA) in a healthy ear. The goals of this study were to compare responses of auditory nerve fibers in acutely deafened, anesthetized cats elicited by high-rate electric pulse trains delivered through an intracochlear electrode with SA, and to measure responses of these fibers to amplitude-modulated pulse trains superimposed upon a DPT. Responses to pulse trains showed variability from presentation to presentation, but differed from SA in the shape of the envelope of the interval histogram (IH) for pulse rates above 4.8 kpps (kilo pulses per second). These IHs had a prominent mode near 5 ms that was followed by a long tail. Responses to modulated biphasic pulse trains resembled responses to tones in intact ears for small (<10%) modulation depths, suggesting that acousticlike responses to sinusoidal stimuli might be obtained with a DPT. However, realistic responses were only observed over a narrow range of levels and modulation depths. Improved coding of complex stimulus waveforms may be achieved by signal processing strategies for cochlear implants that properly incorporate a DPT.     

Photonic microwave multi-band frequency conversion based on a DP-QPSK modulator for satellite communication

We propose and demonstrate a simple, flexible and stably operated multi-band frequency conversion approach based on a dual-polarization quadrature phase shift keying modulator (DP-QPSK). The modulator incorporating two dual parallel Mach–Zehnder modulators (DPMZMs) which perform as OFC generator and +1st carrier suppressed single sideband generator, respectively, to achieve the purpose of frequency conversion. The theoretical analysis indicates that by properly adjusting six DC bias points in the integrated modulator and two modulation indices, a frequency of received RF signal can be directly converted into different frequencies that cover different bands simultaneously. The simulation results verified the possibility. For example, the received C band frequency of 3.8 GHz can be converted into X, Ku, K and Ka bands. An X band frequency of 9.6 GHz can be down-converted to C band and up-converted to Ku, K, Ka band. In addition, the simulation also focuses on how the adjustable parameters (such as DC bias points and modulation index) influence the conversion results. It demonstrates stable conversion efficiency against the DC drafting.     

OOK-to-QPSK modulation-format conversion based on two gain-transparent SOAs

In this paper, the system scheme of on–off keying (OOK) to quadrature phase-shift keying (QPSK) format conversion is proposed, which is based on two gain-transparent semiconductor optical amplifiers (GT-SOA). GT-SOA is used as a simple all-optical phase modulator, which is no effects of cross gain modulation and four-wave mixing existing in conventional SOA. The assistant light is used to speed up the SOA carrier recovery time. The principles of OOK to QPSK format conversion are expounded. The influences of the assistant light power and signal light power on the conversions are numerically analyzed. The OOK signal can still be exactly converted to the QPSK signal with the power of OOK signal being changed within a certain range.     

Experimental study of NRZ format wavelength conversion using electroabsorption modulator

In this paper, NRZ format wavelength conversion using cross absorption modulation (XAM) in InGaAsP MQW electroabsorption modulator (EAM) is investigated experimentally in detail for the first time, to the best of our knowledge. The influence of two key operating parameters, input signal power and bias voltage of EAM, on wavelength conversion performance is studied. Experimental results indicate that there exists optimal bias voltage for fixed input signal power and that there exists also optimal input signal power for fixed bias voltage and the lowest power penalty of 0.9 dB is obtained by optimizing these two parameters. The physical explanations are given for these results based on operating characteristic of EAM device. Finally, the probe light wavelength dependence of wavelength conversion is studied for span of 1530–1560 nm.     

Light modulation by an electrooptic device with feedback

Light modulation by an electrooptic nonlinear device is examined theoretically and experimentally. Very low voltage light modulation may be achieved in a conventional electrooptic polarization modulator when a signal proportional to the optical output power is fed back to the modulator crystal. Very linear light modulation may also be implemented in the other mode of such a device.     

Nonlinear-optical modulator for high-power fiber lasers

We propose a novel nonlinear-optical fiber modulator for high-power (>1-W) single-mode fiber lasers. The device is based on transferring the amplitude modulation from a low-power signal at the Stokes frequency onto a high-power beam through stimulated Raman scattering. The efficiency and limitations of the Raman modulator when highly Ge-doped fiber is used is considered. An insertion loss of less than 0.4 dB and an extinction ratio of 20 dB are predicted for modulation of a 10-W single-mode Nd-doped fiber laser.     

基于一阶时滞混沌系统参数辨识的保密通信方案

基于参数调制原理,针对一阶时滞Logistic混沌系统设计了相应的参数观测器,仅传递单路信号就可以成功辨识出系统中的未知参数,从而恢复出调制在参数中的模拟信号,并在此基础上采用不同频率信号代替“0”或“1”,设计出具体的数字保密通信方案.数值仿真验证了本方法的有效性. 关键词： 观测器 混沌保密通信 参数调制 滤波     

光电雷达红外调制检测技术

因红外调制检测技术用于检测扫描积分型光电雷达调制器的工作性能,为此设计一套与调制器固有属性匹配的光学传递和激光准直系统。运用标准伺服控制理论为调制脉码信号建立Ⅲ型条件稳定的轴系扫描模型,通过截获、跟踪视场切换及驱动电压调幅,使模拟红外汇聚的激光扫描光束与3°×3°、40′×40′十字靶标重合,计量扫描视场及零位精度偏差,采集标定反射镜振动位置和扫描频率的过零脉冲,用以实现红外信号调制性能的检测。测试结果表明,该红外调制检测技术对调制器扫描视场的精度测量优于0.5′(1σ),零位误差的精度测量不大于5′(1σ),系统检测的相对误差不大于±1%,满足光电雷达红外光轴瞄准线工艺装配的精度要求,可应用于线列扫积型调制器的性能检测。