Study on the effect of ellipticity and misalignment on OAM modes in a ring fiber

Based on the optical fiber mode theory and employing the expertized software COMSOL, we study the effect of ellipticity and misalignment on the effective refractive indices, walk-off and intensity distribution of the even and odd eigenmodes that form the basis of the orbital angular momentum (OAM) modes in a ring fiber. Our results show that the effective refractive index difference and the walk-off increase with the ellipticity and misalignment, thus reducing the stability of the OAM modes. We find that the misalignment has a greater impact on the OAM modes than the ellipticity, and both the misalignment and ellipticity affect the lower-order OAM modes more significantly, suggesting that the higher-order OAM modes are more stable during propagation.     

Design of novel circular lattice photonic crystal fiber suitable for transporting 48 OAM modes

In this paper, we propose and numerically investigate a novel circular lattice photonic crystal fiber (CL-PCF) using controllable GeO2 doped silica, suitable for modes carrying quantized orbital angular momentum (OAM). Large effective index separations between 25 supported vector modes (≥10-4) are confirmed over large bandwidth (C+L bands) leading to 48 OAM modes bearing information. The simulations show that the modes in the proposed CL-PCF have good features including low and flat dispersion (within 51.82 ps/km/nm), low confinement loss (lower than 0.002 dB/m), high effective mode area (88.5 μm2) and low nonlinearity (1.22 W-1.km-1). These promising results show that the proposed CL-PCF could be an arguably candidate in fiber-based OAM multiplexing or other applications using OAM states.     

Study on the chaotic dynamics of the mode-locked fiber ring laser

In this paper, we study the chaotic dynamics of the mode-locked fiber laser by numerical simulation. The structures of the passively mode-locked fiber laser and the actively mode-locked fiber laser are studied by modeling and analysis. By appropriately adjusting the small signal gain of the optical fiber amplifier, we observe the period-doubling bifurcations and route to chaos in the passively mode-locked fiber laser based on nonlinear polarization rotation effect. Chaos in the actively mode-locked erbium-doped fiber laser is obtained by adjusting the elliptic modulus parameter of the active modulator and the intra-cavity length. Simulation results have theoretical significance for the practical application of chaotic soliton communication.     

EPON的OAM子层研究

由于以太网技术的成熟和广泛应用,以太网无源光网络（EPON）接入方式已经成为宽带接入网技术的最新发展趋势.文章总结了EPON中的运行管理维护（OAM）功能、OAM协议数据单元（OAMPDU）和OAM子层组成模块,举例说明了其功能的应用过程,另外还简要讨论了OAM子层在网络管理中的作用。     

Frequency locking of modes in a ring laser

The locking of two countertraveling ring laser modes due to light scattering is investigated. It is found that the mutual locking of two free-running oscillating modes is different from locking due to an externally injected signal. The text defines two kinds of mode-to-mode scattering: conservative and nonconservative. The former leads to no locking, to a high degree of approximation. Examples of conservative scatterers are nonabsorbing particles, small compared to a wavelength, and loss-free objects of larger size that represent only a weak perturbation of the dielectric constant in the cavity. The presence of two types of scatterers makes it impossible, in general, to calculate lockbands from measured scattering intensities from optical components such as mirrors. The relationship between the present theory, the conventional Adler theory, and measurable laser component properties such as scattering coefficients is discussed. The findings are of importance for the development of mirrors and optical coating processes in ring lasers.     

基于偏振混沌环形激光器的光纤分布传感系统

以混沌对初值的敏感性作传感机理,提出一种基于偏振混沌环形激光器(PCRL)的分布光纤传感系统,并从理论和实验上研究其检测特性。数值计算和初步实验结果表明,利用PCRL输出时域波形的变化可检测引起光纤延迟角改变的应力和振动。为提高观测灵敏度,进而提出一种比直接观察波形更有效的方法,即通过监测相邻环形周期时间内混沌波形的互相关函数峰值来检测偏振混沌分布传感系统是否受到扰动,而且这种检测方法还能对扰动进行定位。初步实验结果表明,PCRL可用于检测引起光纤横向受冲击的分布传感。     

Study of vectorial properties of optical-fiber modes using a fiber resonator

Each eigenmode in optical fibers is experimentally analyzed individually by changing the resonance condition of the eigenmode in optical-fiber resonators. When a stress is applied to fibers, it is found that eigenmodes in a single-mode fiber and a two-mode fiber are LP modes, and eigenmodes in a fiber Faraday rotator are elliptically polarized modes. A significant result for the two-mode fiber is that the directions of polarization and orientation of the LP11modes are those of a transverse pressure and principal axes of the elliptical core, respectively. A coupled-mode theory is also presented to explain these experimental results.     

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.     

Tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier

The tunable microwave photonic filter based on a fiber ring and erbium-doped fiber amplifier （EDFA） was proposed. By introducing a section of erbium-doped fiber （EDF） into the fiber ring, the loss of the signal can be compensated by the EDFA gain through adjusting the pump power. This can largely increase the number of the effective sampling taps, and then improve the performance of the microwave photonic filter notably. When the pump power was set to be 42.7 roW, a microwave bandpass filter with the 3-dB bandwidth of 0.15 MHz, the Q factor up to 100 and extinction ratio up to 20 dB was achieved. By employing a tunable optical delay line in the above fiber ring, a tunable microwave photonic filter has been realized through tuning the length of the optical delay line. The proposed tunable microwave photonic filter can fred great applications in microwave signal processing and ROF system.     

Distributed feedback modes in a partially filled ring cavity

We have studied the threshold longitudinal modes of a structure composed of a ring cavity partially filled with a distributed feedback (DFB) medium. An eigenvalue equation and dispersion relation for the propagation constant, threshold gain, and mode location are derived and numerically solved for a number of cases. We show that the incommensurate nature of the unfilled ring cavity eigenfrequencies and DFB eigenfrequencies can lead to an enhancement of the frequency selectivity of the distributed feedback laser. The analysis is extended to consider finite linewidth and dispersion.     

Comparative study on the effect of misalignment on bordered and borderless contacts

Continued shrinking of feature sizes in integrated circuits has raised increasing reliability concern. In order to achieve higher packing density, interconnects are migrating toward borderless contacts and vias. The penalty with the absence of metal extension, however, is the decrease in electromigration lifetimes. The issue is particularly critical when there is a misalignment between the contact and metal line, which may occur due to process variability. In this paper, we studied the effect of misalignment on the electromigration lifetimes for bordered and borderless contacts. We found that the misalignment effect becomes more pronounced in borderless contacts. We also studied the case of multiple contact configuration. The results indicate that electromigration lifetimes increase with increasing number of contacts in series. The experimental data is consistent with finite element modeling results.     

高功率光纤激光器光纤器件封装应力影响研究

高功率激光器无源器件制作过程中封装不当引入的应力,会导致信号光光束质量劣化和光纤温升,为了解决此问题,理论分析了光纤形变对信号光模式分布的影响,利用有限元方法建立包层光导致光纤发热模型,实验研究了不同封装方式对光纤发热情况和信号光光束质量的影响。实验表明,应力导致的光纤形变会造成信号光M2值在受力方向上略微变小而其垂直方向上变大,在输出100 W信号光时,施加应力导致的M2值的变化最高为0.39,与仿真结果相符。在光纤温升方面,相比于使用硬质胶水带来的12 ℃温升,使用硅橡胶封装的剥离器将温升控制在5 ℃以内,且其封装应力引入的M2值的变化在0.05以内。     

Study on the similarity of photonic crystal ring resonator cavity modes and whispering-gallery-like modes in order to design more efficient optical power dividers

In this study, we discuss the wave pattern characteristics of confined cavity modes inside photonic crystal ring resonators (PCRRs). Despite different physical origins, these cavity modes are analogous to the whispering-gallery (WG-like) modes. Because of the absence of perfectly circular symmetry in our PC cavity, the WG-like modes are not degenerate, but they form a close doublet in which the field pattern of each of these doublets repeats itself by \(180^{\circ }/m\) where “m” is the azimuthal index number of WG-like modes. The cavity modes are named according to their symmetric field pattern, and WG-like ones are named by their azimuthal mode numbers “m.” Based on the study of these similarities, we propose a \(1\times 2\) and a \(1\times 4\) T-junction- like power dividers. Through study of the similar properties of these cavity modes with WG-like modes, we have enhanced the output power of both dividers to 49.6 and 24.5 %, respectively. The permittivity of the hexagonal photonic crystal rod is \(\varepsilon _{h}= 12.04\) surrounded by air as the background medium. For our PCRR, the dominant resonating mode is the cavity mode with hexapole field pattern or equivalently WG-like mode with azimuthal mode number of \(m\,=\,6\). The normalized frequencies for this mode and its doublet are \(a/\lambda = 0.348066\) and 0.348301, respectively. The photonic band structure, PC waveguide guided mode and electric field patterns of the confined cavity modes inside the PCRR are calculated using the PWE method, and the transmission spectra are calculated by means of 2D-FDTD simulation method.     

腔失调对模耦合的影响

综合分析了腔失配和腔失调对模耦合的影响，分别讨论了模的功率耦合系数与失配参量、失调位移及失调角的相互关系。     

Sensitivity analysis of a fiber ring resonator based on an air-core photonic-bandgap fiber

The fiber ring resonator (FRR) is the core sensing element in a resonator fiber optic gyroscope (R-FOG), and its sensitivity determines the performance of the R-FOG. This paper presents an in-depth analysis of the sensitivity of the FRR which is made of an air-core photonic-bandgap fiber (PBF), in which the characteristics of the FRR using PBF are compared with that of an FRR using a conventional single mode fiber. When using PBF instead of conventional fiber, it is found that the resonance curve is changed, and the sensitivity of the FRR is decreased a little when a narrow spectral linewidth laser is used. However, the degree of the decrease in sensitivity is not big enough to deny the advantages of PBF in improving the performance of the R-FOG considering that PBF is much better than conventional fiber in reducing the drift. Also, the optimal parameters of the directional coupler for sensitivity are discussed. It is found that the optimal intensity coupling coefficient when using PBF is nearly two times larger than that when using conventional fiber, and the optimal coupler intensity loss when using PBF is smaller than that when using conventional fiber.     

Influence of the fiber index profile on vectorial fiber modes and application to tapered fiber devices

The correspondence between the scalar modes LP and the nearly degenerate true vectorial modes in circular two-layer fibers is well established. For example, LP/sub 21/ corresponds to a combination of EH/sub 11/ and HE/sub 31/, while LP/sub 02/ is composed only of HE/sub 12/. For the multilayer fibers, inversion of the correspondences for certain modes can occur. We illustrate this inversion for a three-layer fiber. We propose a method permitting to distinguish the hybrid modes HE/sub /spl nu//spl mu// and EH/sub /spl nu//spl mu// in such fibers and we show the possibility of major taper-induced power coupling between these modes in SMF-28 fiber.     

Frequency pulling in a Brillouin fiber ring laser

The lasing frequencies of a Brillouin fiber ring laser are shifted slightly from the resonant frequencies of the cold fiber ring resonator due to the optical Kerr effect and the nonlinear phase shift associated with stimulated Brillouin scattering (SBS) used as the gain mechanism in this type of laser. These frequency pulling effects are investigated in detail both theoretically and experimentally. The results of this study are useful in many Brillouin fiber ring laser applications such as Brillouin fiber optic gyroscopes, microwave generators, and frequency shifters. To the authors' knowledge this is the first time the frequency pulling effect caused by the nonlinear phase shift associated with SBS is reported     

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     

环形激光器中的光场偏振度

对采用四频差动法偏频的环形激光器中光场偏振度进行了计算和讨论.光场的偏振用圆基坐标下的琼斯矩阵表示.光场的偏振度由反射膜片和水晶片的光学性质决定,在环形腔中的不同位置处,光场的偏振度不同.     

环形激光器中的光场偏振度

对采用四频差动法偏频的环形激光器中光场偏振度进行了计算和讨论.光场的偏振用圆基坐标下的琼斯矩阵表示.光场的偏振度由反射膜片和水晶片的光学性质决定,在环形腔中的不同位置处,光场的偏振度不同.