A Vernier S-shaped fiber double-loop resonator with double couplersand degenerate two-wave mixing

The use of degenerate two-mixing in a S-shaped fiber double-loop resonator with double couplers to achieve the Vernier operation is proposed. The degenerate two-wave mixing is implemented by inserting a short strand of a photorefractive fiber into the common segment of two fiber loops. With a suitable two-wave mixing gain and a suitable ratio between the free spectral ranges of the two fiber loop resonators, the effective free spectral range can be increased significantly     

Performance parameters of a wavelength-division demultiplexer madewith a single 3×3 coupler optical fiber ring or loopresonator

The performance parameters of a two-channel demultiplexer made with a single 3×3 coupler fiber ring or loop resonator are evaluated theoretically. These parameters include crosstalk, output intensity of the selected channel, and channel separation. Their dependence on the parameters of the coupler and the fiber such as the coupling length of the coupler, kd, the phase change of the fiber delay line, &thetas;, and the round-trip amplitude transmission coefficient of the fiber ring or loop G, which is the product of the amplitude transmission coefficients of the coupler and the fiber delay line and the amplitude gain of the degenerate two-wave mixing, is investigated. It is found that the best performance can be obtained at G=1     

Optical fiber filter comprising a single-coupler fiber ring (orloop) and a double-coupler fiber mirror

A theoretical study of an optical fiber filter comprising a double-coupler fiber loop mirror and a single-coupler fiber ring (or loop) is presented. An active scheme using degenerate two-wave mixing is also proposed. The circulating, transmitted and reflected output fields and intensities, as well as some performance parameters such as the peak transmission, contrast and contrasted transmission, are computed and presented in graphical form. The characteristics and potential applications of this filter are discussed. It is found that the use of degenerate two-wave mixing results in a significant increase in the finesse and a dramatic change in the output characteristics of the filter     

A Vernier fiber double-ring resonator with a 3×3 fibercoupler and degenerate two-wave mixing

A theoretical study of a new and simple Vernier fiber ring resonator is presented. The ring resonator consists of two fiber rings constructed from a single-mode 3×3 fiber directional coupler and two single-mode fiber delay lines. Degenerate two-wave mixing is used to achieve the Vernier operation, which significantly increases the free spectral range of the device. In addition, the input beam is also amplified. This device can be used as a wavelength division demultiplexer     

A single-mode optical fiber ring resonator using a planar 3×3fiber coupler and a Sagnac loop

We present the first theoretical analysis of an optical fiber ring resonator using a planar 3×3 fiber directional coupler and a fiber Sagnac loop. In the planar 3×3 fiber directional coupler, the three fibers inside the coupler lie in the same plane. Expressions for the circulating (resonant) and the output fields of the fiber ring resonator are obtained. It is found that this fiber ring resonator has a special property where there are two or more main resonance peaks or dips inside a period 2π of the phase change of the fiber ring resonator. This ring resonator may have applications as a sensor with high-phase sensitivity and a densely spaced two-channel wavelength division multi/demultiplexer     

可实现连续激光-脉冲转换的全光纤声光耦合环形谐振腔

研究了光纤声光耦合环形腔独特的谐振特性。结果表明利用光纤声光耦合器的移频与滤波特性 ,可研制成一种全新结构的光纤声光耦合环形谐振腔。从理论和实验上证明了 :基于腔内累积声光移频分量的多光束干涉 ,光纤声光耦合环形谐振腔可将注入的连续激光将转换为脉冲列输出。     

Laser Stabilization on a Fiber Ring Resonator and Application to RF Filtering

The potential of optical fiber ring resonators for radio frequency (RF) or microwave signals filtering on optical carriers is demonstrated on a short length high Q resonator. The problem of the frequency shift due to the resonator self heating with the optical power is solved thanks to a Pound-Drever feedback loop. A multifrequency RF filter is obtained, with a frequency step of 205 MHz between resonances, and a 3-dB bandwidth of 2.4 MHz. This corresponds to the computed optical resonator 3-dB bandwidth, and thus represents an efficient technique for the measurement of ultrahigh Q optical resonators. In the field of microwave applications, the equivalent Q -factor obtained is particularly interesting in the upper microwave range.     

Response characteristic analysis of polarization maintaining fiber ring resonator with dual-coupler for sensing application

A polarization maintaining fiber ring resonator with dual-coupler (PMDC-FRR) for sensing application is presented in this paper. Polarization maintaining directional fiber couplers and fiber loop are employed to eliminate the polarization fading in the fiber ring resonator. Three important characteristic parameters associated with the sensing application, which are the visibility of the output intensities, the free spectral range and the finesse, are discussed as functions of the coupler coefficients and the fiber loop length in detail. In addition, the critical drive voltage of the tunable laser to keep the output intensities stable is also analyzed, when the fiber ring resonator with dual-coupler is utilized as fiber sensor with phase modulation. A PMDC-FRR is designed practically in experiment with the power coupling coefficients of 0.5 and the loop length of 22 m. The experimental results provide sufficient arguments for the theoretical predicts. The theoretical and experimental analysis results will be useful to the sensing application of the PMDC-FRR.     

Theoretical analysis of Sagnac loop mirror with an inline high birefringence fiber ring resonator: Application in single-frequency fiber lasers

We newly propose and theoretically analyze a Sagnac loop mirror with an inline ring resonator containing a piece of high birefringence fiber (HBF) and erbium-doped fiber (EDF). With the EDF properly pumped to offset the passive loss in the inline ring resonator, narrowband transmission peaks with large effective free spectral range can be realized by the intrinsic vernier effect between orthogonally polarized lights traveling along the two primary axes in the HBF. In addition, this property is independent of polarization states of the input signal, which makes the proposed Sagnac loop mirror suitable for a narrowband filter applied to single-frequency fiber lasers.     

Anisotropic polarization maintaining optical fiber ring resonators

Suppression of the polarization drift of optical fiber ring resonators is investigated both theoretically and experimentally by employing anisotropy in a polarization maintaining fiber ring. A general analytic expression for the transmission of the device is derived allowing the fiber modes to exhibit any combination of polarization crosstalk, differential loss or differential coupling. The analysis shows that a moderate level of ring anisotropy, such as that of 10 dB in line polarizer or polarization selective coupler, is sufficient to greatly suppress the drift of the eigenstates of polarization (ESOPs), finesse and resonant point, restoring the device's suitability for most practical applications. An inevitable consequence of introducing ring anisotropy is the loss of orthogonality of the ESOPs. This effect limits the anticipated benefit in high sensitivity applications. A practical anisotropic PMRR is demonstrated by inserting a thin film of nematic liquid crystal between the two halves of the polished coupler of the ring. This resonator demonstrates a polarization response immune to environmental perturbations     

Performance of single- and double-ring resonators using 3×3optical-fiber coupler

This paper investigates theoretically the transmission characteristics of single- and double-ring resonators using 3×3 optical-fiber couplers. Two configurations of a 3×3 coupler are considered: configuration A, with the three fibers centered at the vertices of an equilateral triangle, and configuration B, with their centers aligned in a straight line. It is found that a ring resonator using configuration A does not show any performance improvement over ring resonators using 2×2 couplers. On the other hand, a single-ring resonator using configuration B has a performance close to resonators using 2×2 couplers. It is also shown that a double-ring resonator using a 3×3 coupler exhibits resonance with a double peak, which may find application in the filtering of coherent frequency-shift keying (FSK) signals after optical amplification in an optical-fiber line repeater     

有源光纤环形腔的频率滤波特性

本文首先从理论上通过简单的分析得以了有源光纤环形腔的输出谱密度函数公式，该式清楚地表明光纤环形腔的频率滤波特性。从该公式出发，详细分析了环形腔输入光纤宽和环形腔参数对输出光谱谱型和线宽的影响。最后，通过设计不同的环形腔的自由谱宽和不同线宽的激光器作为输出光源，对上述理论分析做了实验验证。理论和实验表明，由于环形腔的强度传递函数是多峰的响应函数，环形腔自由谱宽和输入激光线宽的大小直接影响到环形腔输出光频谱形状，即是单峰输出还是多峰输出，对于不同形状的光谱输出，输出激光的线宽受环形腔的参数影响也各不相同。     

可调谐单纵模多波长光纤激光器的研究

为了实现对台阶高度和绝对距离等物理量的高精度干涉测量,采用在一个光纤激光器中构建多个激光谐振腔的方法,构建了能同时发出多波长激光的光纤激光器。每个激光谐振腔都利用掺铒光纤作为增益介质,利用光纤光栅作为波长选择元件,改变光纤光栅的布喇格波长,即可改变对应谐振腔的激光波长。各个激光谐振腔独立但部分重叠,在重叠区域利用光纤耦合器构成复合子腔,使每个激光谐振腔都是复合激光谐振腔,从而使每个激光谐振腔都发出单纵模激光。结果表明,该光纤激光器能同时发出功率和频率都稳定的多波长激光,且每个波长都是单纵模激光;在4h内,每个波长的波长稳定性优于0.01nm。该设计对可调谐单纵模多波长光纤激光器的研究是有帮助的。     

Realization of a dual-mode bandpass filter exhibiting either a Chebyshev or an elliptic characteristic by changing perturbation's size

A dual-mode resonator with square patches attached to inner corners of a conventional microstrip loop resonator is proposed. The two types of coupling between the degenerate modes are described by changing the perturbation's size for realization of either a Chebyshev or an elliptic function filter. A novel type of dual-mode microstrip bandpass filter using degenerate modes of this type of dual-mode resonators is developed. It is shown that the perturbation's size determines the filter characteristic, whether it is Chebyshev characteristic or elliptic characteristic.     

Microwave resonators with dual-mode oscillations

Analysis of microwave resonators with dual-mode oscillations is conducted. A new type of resonators is discovered in which dual-node oscillations are observed. It represents a half-wave resonator with a short-circuit in the middle part. The length of such a resonator is twice less than the length of a widely used ring resonator. It is shown that in resonators of the loop type combined frequency tuning of dual-mode oscillations is accomplished using capacity and inductance. In the loop-type resonators with a stub frequency tuning of dual-mode oscillations is accomplishing with two capacities synchronously changing their values according to a specific law. Resonance equations are obtained.     

Sagnac fiber interferometer with the population grating for fiber Bragg grating dynamic strain sensing

A Sagnac fiber interferometer with the population grating formed in saturable erbium-doped fiber (EDF) for fiber Bragg grating (FBG) dynamic strain sensing is proposed. In this configuration, a semiconductor optical amplifier (SOA)-based fiber ring laser with an FBG reflector is employed in the sensing part and a Sagnac interferometer based on transient two-wave mixing (TWM) via dynamic population gratings in single-mode polarization maintaining erbium-doped fiber (PM-EDF) is used in this detecting part. Experimental results show that the Sagnac fiber interferometer detection system can stably respond to dynamic strains at high frequencies. As an example of application, the response of the sensor system to continuous sinusoidal ultrasonic signals is presented. The proposed simple and robust configuration has an all-fiber design based on commercially available elements, which makes it promising for applications in fiber optic ultrasonic sensors.     

保偏光纤环形谐振腔研究

报道了一种用于角速度测量的光纤谐振式传感器保偏光纤环形谐振腔的研究,给出了测量的原理、实验装置和实验结果.根据计算和实验结果,对影响系统性能的几个重要光学参数进行了设计和优化.该谐振腔已在传感器系统中得到应用.     

Analysis of steady-state cascaded stimulated Brillouin scatteringin a fiber Fabry-Perot resonator

We investigate the steady-state properties of cascaded stimulated Brillouin scattering (CSBS) in a fiber Fabry-Perot resonator with reflection mirrors by numerically solving the coupled-power equations under the boundary conditions at the two mirrors. The dependence of CSBS on the input power is calculated for the symmetric and asymmetric fiber resonators. The threshold powers for the first- and second-order Stokes waves are calculated as a function of the mirror reflectance for the symmetric resonator     

Novel Dual-Mode Bandpass Filters Using Hexagonal Loop Resonators

Novel dual-mode hexagonal loop resonators with the patch and notch perturbation are proposed in this paper. The field patterns of the degenerate modes and their mode splitting characteristics are investigated. The applications of the dual-mode hexagonal loop resonator as bandpass filters are presented. It is shown that different responses can be realized using only a single dual-mode resonator by changing the position of the perturbation. A coupling and routing scheme is presented to model the operations of these filters. Two- and four-pole filters of this type are demonstrated for the first time. All the theoretical analysis and design procedures have been verified by experimental results.     

Spectral properties of a semiconductor laser coupled to a single mode fiber resonator

The effect of optical feedback from a single mode fiber resonator on the instantaneous frequency fluctuation spectrum and on the field fluctuation spectrum of an AlGaAs semiconductor laser is studied theoretically and experimentally. Single mode fiber resonators of different lengths and finesses are used for the experiments. The minimum linewidth conditions are given and it is shown that the linewidth reduction ratio increases with the fiber resonator selectivity. The limit for multistability operation depends on the resonator finesse. Theory and experiments are found to be in good agreement. Finally, the effect of resonator loaded semiconductor laser phase noise on BER performance in optical DPSK heterodyne systems is theoretically analyzed.