Dynamic response of a fiber-optic ring resonator: Analysis with influences of light-source parameters

In practice, dynamic behavior of fiber-optic ring resonator (FORR) appears as a detrimental factor to influence the transmission response of the FORR. This paper presents dynamic response analysis of the FORR by considering phase modulation of the FORR loop and sinewave modulation of input signal applied to the FORR from a laser diode. The analysis investigates the influences of modulation frequency and amplitude modulation index of laser diode, loop delay time of the FORR, phase angle between FM and AM response of laser diode, and laser diode line-width on dynamic response of the FORR. The analysis shows that the transient response of the FORR strongly depends on the product of modulation frequency and loop delay time, coupling and transmission coefficients of the FORR. The analyses presented here may have applications in optical systems employing an FORR with a laser diode source.     

Observation of coherence effects in a quasi-monochromatic fiber-optic gyroscope

The sensitivity reduction resulting from a loss of fringe visibility due to the limited coherence of the broad-band source in a fiber-optic gyroscope is observed. The experimental data is well described by coherence theory assuming a Gaussian spectral shape for the superluminescent diode source.     

多线程的光陀螺信号采集系统设计

为满足导弹对光陀螺信号实时性的要求,设计并实现了光纤陀螺的信号实时采集,并进行实时数据的动态显示与处理。采用C Builder5.0平台来设计光纤陀螺信号采集部分。陀螺信号的采集通过计算机的串口传输。该光纤陀螺的输出为RS232格式,通过调用Windows API函数实现RS232串口通信程序,并采用了多线程的技术来增强实时性和自动接收信号的能力。通讯速率38.4 kB,通讯期间可以完成数据处理,并且基本没有丢数现象;完成了数据包的解算;实现了线程间的数据共享与数据的实时处理。基于C Builder5.0和Windows系统的多线程串行通信可以实现实时数据的采集,同时可以在另一个线程中进行数据的实时处理。数据接收稳定可靠,取得了良好的效果。     

Observation of low noise in a passive fibre gyroscope

We report short-term noise levels of < 1 deg/h and 10 min drift of < 2 deg/h in a passive fibre gyroscope utilising a fused 3 × 3 fibre coupler and a broadband and partially polarised superluminescent diode. Partially polarised operation of the source is shown to result in less noise than polarised operation.     

Demodulation of interferometric sensors using a fiber-optic passive quadrature demodulator

The passive quadrature demodulator (PQD) eliminates the phase stretcher and feedback electronics frequently used in fiber interferometric sensors by passively extracting the desired signal using two distinct interferometers which differ in phase bypi/2. A fusion technique is described to fabricate a fiber PQD which is sufficiently stable with respect to temperature, polarization, and wavelength to maintain the sensitivity of interferometric sensors constant to 0.25 dB.     

A novel fiber-optic Fabry-Perot resonator with two mode-conversionmirrors: proposal and application

A novel fiber-optic Fabry-Perot resonator composed of a piece of fiber with two LP₀₁&rlarr2;LP₀₂ mode-conversion reflectors is proposed and theoretically investigated. The reflective fiber-optic LP₀₁&rlarr2;LP₀₂ mode converter is analyzed based on the coupled-mode theory. The resonance characteristics including the transmission, reflection, and circulation of this novel fiber resonator are examined. In addition, we also describe the application of this device as an optical filter which can be used for FDM/WDM communications, etc. In contrast to a conventional Fabry-Perot optical filter with a periodic output spectrum, our proposed optical filter has only one peak in output spectrum, while the bandwidth of the filter spectrum is very narrow, with several Megahertz determined mainly by the cavity length of the fiber resonator. Finally, it is demonstrated that the characteristic of this optical frequency filter can be greatly improved by introducing a gain mechanism using a rare-earth-doped fiber. The tunable performances of this optical filter are also presented     

Analysis of optical phase noise in fiber-optic systems employing a laser source with arbitrary coherence time

Performance of many optical circuits and systems, such as signal processing and sensing devices, is influenced by random fluctuations of the optical source emission field. This paper outlines a formalism for the analysis of laser phase noise effects on a general linear time-invariant optical system. Theoretical expressions are presented for the autocovariance function of the instantaneous output intensity which are valid for any source coherence time as long as the source intensity fluctuations are assumed to be negligible. Applications of the results to some fiber-optic systems such as Mach-Zehnder and recirculating delay line devices also are demonstrated, both in the coherent and incoherent regimes. Although the analysis is not limited just to fiber-optical systems, our attention is focused on fiber optics.     

光纤陀螺系统中信号光反馈下的激光光源强度噪声特性研究

从建立光纤陀螺激光光源受信号光反馈作用时的等效腔模型出发,对影响光源强度噪声的诸因素进行了理论分析,结果与实验很好符合,并提出了消除信号光反馈对系统性能影响的方法.     

高精度光纤陀螺用掺铒光纤光源辐照性能试验

针对高精度光纤陀螺的空间应用,理论分析了用于高精度光纤陀螺的不同结构掺铒光纤光源的抗辐照性能,指出了单通后向结构的掺铒光纤光源具有更好的抗辐照性能。对单通后向结构采用不同掺杂浓度的掺铒光纤设计并研制了掺铒光纤光源,在实验室用Co60辐照源进行了大小两个剂量率的辐照试验,监测了掺铒光纤光源平均波长和输出光功率随辐照总剂量的变化,试验结果表明:掺铒光纤掺杂浓度较高时,掺铒光纤光源的抗辐照能力较强;辐照剂量率较小时,掺铒光纤光源功率随辐照总剂量的降低速度更慢。掺杂浓度较高的掺铒光纤光源可以满足高精度光纤陀螺空间应用的要求。     

Dependence of modal noise on source coherence and fibre length

A transmission model for optical communication systems with partially coherent sources has been developed and the dependence of modal noise and distortion on (a) the fibre length between source and connector, and (b) the lateral offset at the connector was investigated.     

The vibration error of the fiber-optic gyroscope rotation rate and methods of its suppression

The error of the fiber-optic gyroscope (FOG) rotation rate measurement is considered. This error is induced by FOG vibrations (for open- and closed-loop FOGs). For a closed-loop FOG, a differential equation describing the loop dynamics is derived. The coefficients of this equation contain terms varying in time with the vibration frequency. For the first time, it is shown that, in addition to the traditional rotation rate measurement error due to the superimposition of vibration-induced optical power oscillations and the phase difference in the FOG coil, there is one more error, which is due to vibration modulation of the loop bandwidth. Alternative methods of information processing are investigated, and, on the basis of them, a new circuit is proposed for the suppression of vibration errors.     

Coupling parameters for a side-coupled ring resonator and amicrostrip line

A ring resonator side coupled to a microstrip line shows two close but distinct resonance peaks. These are identified as due to even-mode (magnetic field) and odd-mode (electric field) coupling. Equivalent circuit models for both cases have been proposed and coupling parameters are calculated using piecewise, coupled-line approximations. The calculated coupling coefficients for the two cases are compared with the experimentally-measured coupling coefficients and show very good agreement with the models used     

Influence of a low-Q shunting medium on the equivalent parameters of a cavity resonator

The influence of the dielectric loss of a low-Q shunting medium on the parameters of the equivalent circuit of a cavity resonator is analyzed. The effect is studied for a radial cavity resonator partially filled with a lossy medium. The influence of field absorption by the shunting medium on the frequency and Q factor of the oscillation excited in the cavity and, consequently, on the parameters of the equivalent oscillatory circuit is studied by means of electrodynamic modeling. It has been found that the loss level changes not only the Q factor but the characteristic impedance of the equivalent circuit.     

Exploiting the attenuation of fiber-optic passive taps to createlarge high-capacity LANs and MANs

A local- or metropolitan-area network (LAN or MAN) that exploits the power losses of fiber-optic passive taps so that wavelengths can be reused in different portions of the network is proposed. This wavelength reuse makes it possible to design a large, high-capacity, multichannel network with many concurrent transmissions. An arbitrary number of nodes is supported by allowing packets to take multiple hops, when necessary, to reach their destinations. In one example configuration, there are two closed circular loops of fiber, one for transmissions in the clockwise direction and one for counterclockwise transmissions. Each node has one passive tap (per fiber), which is used for both a fixed-wavelength transmitter and a fixed-wavelength receiver     

Optical design and performance of wavelength-division-multiplexed optical repeater for fiber-optic passive star networks connection

New optical repeaters that use a wavelength-division-multiplexing (WDM) technique to connect CSMA/CD-based fiber-optic passive star networks are discussed. Two types of optical filters that are essential for obviation of closed-loop formation in construction of such repeaters, have been designed and fabricated. Results of a field trial of the filters and optical modules using the filters show good agreement with design values. The repeaters were also found to operate reliably.     

Dependence of thermal sensitivity of LPFG on waveguide and material parameters

This article demonstrates the effect of waveguide and material parameters on thermal sensitivity trends adopted by different cladding modes based on long-period fiber grating. Three-layer fiber geometry-based mathematical model has been implemented to estimate cladding modes. It is observed that for a cladding mode, the sign and magnitude of thermal sensitivity slope depend upon the designed grating period closer to period at dispersion turn around point. The \(\hbox {LP}_{10}\) and \(\hbox {LP}_{11}\) cladding modes have shown blueshift and maximum thermal sensitivity above all other modes at designed grating periods of 225 and \(195\,\upmu \hbox {m}\), respectively. The material parameter of fiber (thermo-optic coefficient) has also resulted in increment in sensitivity with the increase in difference amid its values for core and cladding region.     

Influence of the second harmonic of a resonator on the parameters of a Gunn generator for transit and hybrid modes

The results of computer calculations of Gunn-oscillator performance are given for a bias voltage containing the fundamental and the second harmonic. The dependence of the efficiency on the bias voltage, harmonic amplitudes, phase difference, doping level and frequency is presented.     

光电雷达对目标参数被动测量的方法研究

根据光电雷达测量到的目标方位信息,运用自适应修正增益扩展卡尔曼滤波理论。可以估计出空中目标相对载机的位置和速度参数。文章首先推导了坐标系的转换矩阵,建立数学模型后推导对应的自适应修正增益扩展卡尔曼滤波方程,通过对所得的算法进行仿真验证,表明该算法具有较好的实用性,能够满足载机对目标参数被动探测的要求。     

Analysis of optical bistability in a nonlinear distributivelycoupled resonator

A nonlinear distributively coupled resonator (NDCR) used as a bistable element is studied. The resonator is an integrated optics implementation of a nonlinear Fabry-Perot resonator with a variable reflectivity mirror. Under certain conditions, the intensity-dependent reflectivity and tuning of the resonator contribute constructively and enhance nonlinear properties of the device. Numerical methods are used to optimize NDCR design parameters and show that the critical intensity required for onset of bistability is reduced by 30% relative to a comparable regular Fabry-Perot. Similarly, the minimum required index change is reduced by 10%     

Dependence of GaAs power MESFET microwave performance on device and material parameters

The results of recent X-band measurements on GaAs Power FET's are described. These devices are fabricated with a simple planar process and at least 1-W output power at 9 GHz with 4-dB gain has been obtained from more than 25 slices having carrier concentrations in the range 5 to 15 × 10¹⁶cm^-3. The highest output powers observed to date are 1.0 W at 11 GHz and 3.6 W at 8 GHz with 4-dB gain. Devices have had up to 46-percent power-added efficiency at 8 GHz. The fabrication process is briefly described and the factors contributing to the high output powers reported here are discussed. Some of these factors are epitaxial carrier concentration near 8 × 10¹⁶cm^-3, good device heatsinking, and low parasitic resistance. The observed dependence of microwave performance on total gate width, gate length, pinchoff voltage, epitaxial doping level, etc., is described.