共查询到20条相似文献,搜索用时 31 毫秒
1.
Kwang Yong Song In Kag Hwang Seok Hyun Yun Byoung Yoon Kim 《Photonics Technology Letters, IEEE》2002,14(4):501-503
In this letter, we demonstrate a high performance fused-type mode selective coupler that couples the LP11 mode in one fiber and the LP01 mode in another using highly elliptical core two-mode fibers. The phase-matching condition was achieved by etching and prepulling portions of two-mode fibers. The coupling efficiency and the mode extinction ratio of 56% to 80% and 22-32 dB, respectively, were achieved with high temperature stability over 1515- to 1595-nm wavelength range 相似文献
2.
We propose and demonstrate a mode coupler which converts either of the LP01 polarization states in a two-mode high-birefringence (Hi-Bi) fiber to the LP11 mode with the same polarization. We use coupled-mode theory to develop design rules based on the polarization splitting of the beat length between the two lower-order modes. The device can be operated either as a narrow-band device in a region with large intermodal group delay difference or as a broadband device in a region with zero group delay difference. We use this novel device as a key component in a two-mode Hi-Bi fiber polarizer. In this configuration either of the polarization eigenstates can be selected and transmitted with an adjustable extinction ratio which can be as large as 30 dB. The coupling loss in the transmitted state of polarization can be less than 0.2 dB. In the broadband polarizer we demonstrate -20 dB extinction over 42 nm with a potential for considerable improvement. We also propose and experimentally investigate an increased differential group delay obtained by propagating one polarization state in the LP11 mode instead of in the LP01 mode. The largest differential group delay measured in this configuration is 14.5 ps/m which is seven times larger than the differential group delay between the polarization modes. We discuss several possible uses in fiber sensors and measure the transmission of a proposed two-coupler configuration 相似文献
3.
We have utilized a traveling acoustic pulse in a two-mode optical fiber to create a moving beam splitter coupling light from LP01 to LP11 mode. As these optical modes have different group velocities, a variable intermodal delay is generated as a function of acoustic pulse position in the fiber. The device can be used as a receiving interferometer in low-coherence interferometry to scan time delay for carrying out fast extended range absolute measurement using simple analog electronic circuits. With this scanning technique we demonstrate measurement of absolute strain over 1600 με in the temperature range from 20 to 60°C with resolutions of the order of 40 με and 0.7°C, respectively, employing highly birefringent fibers as sensing elements 相似文献
4.
The practical implementation of erbium-doped fiber amplifiers with gain at 1.55 μm allows long unrepeatered transmission distances. However, in order to realize high data rates over these distances with already installed standard single mode fiber, techniques must be found to overcome the pulse spreading due to the positive chromatic dispersion of the transmission fiber in this window, we review a compensation technique based on propagating the signals through a specially designed fiber with large negative dispersion for the LP01 mode, thereby ending up with zero net pulse spreading. The basis of the concept are discussed and a key figure of merit for dispersion compensating devices is defined. The design and optimization of dispersion compensating (DC) fiber is described with special attention to practical concerns including packaging and manufacturability. We describe experimental fabrication results of DC fiber, results of using the fiber to make compact dispersion compensating modules, and the outcome of recent systems experiments incorporating the fiber 相似文献
5.
The design of heavy metal fluoride fibers having segmented-core refractive index profiles and operating a bimodal regime, with small modal dispersion or good equalization, between the LP01 and LP11 modes in the 1.3-μm wavelength region is discussed. The concept of effective cutoff of the LP02 mode has been used in order to maximize the operating V value. A practical bimodal equalized design example which has negligible extrinsic losses is provided in which equalization between the modes is within ±25 ps/km over a wavelength interval of 160 nm (~1.2-1.36 μm). Hence, the predicted bandwidth of the bimodal fiber is high over a broad wavelength interval 相似文献
6.
Pagnoux D. Blondy J.-M. Di Bin P. Faugeras P. Facq P. 《Lightwave Technology, Journal of》1994,12(3):385-391
The spectral analysis of the optical power transmitted through a bow tie slit rotating in the far-field pattern of a single-mode fiber provides an easy and accurate mean of determining the effective cutoff wavelength of the fiber. The principle of this technique is described. Theoretical considerations show that the ratio between the optical powers carried by the LP11 mode and the fundamental mode, respectively, is directly related to the amplitude of two particular lines in the spectrum. The degree of coherence of the analyzed field is shown to be related to the amplitude of a third line. Owing to the sensitivity of the method, the detectable amount of the total power which is contained in the LP11 mode is as small as 0.5%. The effects of length and curvature on the effective cutoff wavelength are measured over wide ranges for different kinds of single-mode fibers. The behavior of a quadruple-clad flattened dispersion fiber is shown to be somewhat different from that of a typical depressed cladding fiber 相似文献
7.
Efficient conversion between the LP01 and LP11 modes in a two-mode fibre is achieved by periodically ablating the fibre surface with a CO2 laser and then annealing the fibre with an electric arc. The resulting periodic core deformation produces 99% mode conversion over a 37 nm bandwidth around 1540 nm and 0.38 dB insertion loss 相似文献
8.
The measured attenuation coefficient of the LP11 modes in curved optical fibers for various radii of curvature in the wavelength region below the cutoff wavelength for LP11 modes is discussed. The experimental results indicate that the attenuation coefficient may be strongly enhanced at certain wavelengths due to phase-matched coupling between the LP11 modes of the fiber core and whispering gallery modes of cladding. Implications for measurements of the effective cutoff wavelength in optical fibers are discussed 相似文献
9.
Design optimization for efficient erbium-doped fiber amplifiers 总被引:3,自引:0,他引:3
The gain and pumping efficiency of aluminosilicate erbium-doped fiber amplifiers (EDFAs) are analyzed as a function of guiding parameters and Er-doping profile for two pump wavelengths of λ p=980 nm and λp=1.47 μm. Three designs of fiber-amplifier waveguides are considered: one with the same mode size as standard 1.5-μm communication fibers (type 1); one with the same mode size as standard 1.5-μm dispersion-shifted fibers (type 2); and one with mode size smaller than those of communication fibers (type 3). For the 1.47-μm pump, fundamental LP01 mode excitation is assumed, while for the λp=980-nm pump, concurrent excitation of LP11 modes is considered. It is shown that excitation of higher-order pump modes at 980 nm does not significantly affect the amplifier gain performance. The effect of concentrating the Er3+ doping near the center of the fiber core is shown to increase the amplifier gain coefficients by a factor of 1.5 to 2 相似文献
10.
横模不稳定效应已经逐渐成为引起高功率光纤激光光束质量急剧恶化并限制其输出功率进一步提升的首要瓶颈问题。基于全光纤化正向泵浦的窄线宽高功率放大平台,对大模场光纤激光器中的横模不稳定效应进行了一系列的探索研究。根据耦合模方程的计算结果,所用大模场光纤25/400 μm中LP01、LP11模之间的非线性耦合强度最大,这也直接诱导了横模不稳定效应的发生。为了抑制LP11模在主放大级的产生和放大,通过弯曲限模这种可操作性强的模式滤波技术,将主放增益光纤的弯曲半径从6 cm缩小至5 cm的过程中,高功率光纤激光系统的横模不稳定阈值从1000 W量级提高到了1600 W量级,而且激光器的其他输出性能几乎没有受到影响。这为构建实际的窄线宽高功率全光纤化的激光系统提供了强有力的实验参照。 相似文献
11.
A comprehensive numerical fiber amplifier model has been used to optimize Er3+-Yb3+ codoped active fiber for maximum gain and quantum conversion efficiency (QCE) at large signal operation. The optimum cutoff wavelength of the LP11 mode has been found to increase from 800 mm at low pump powers (≈50 mW) to 1400 mn at pump powers higher than 500 mW. While at low pump powers fibers with higher numerical aperture give higher QCE, at high pump levels better large signal performance is achieved with fibers having lower numerical aperture 相似文献
12.
Optical bistability in reflective fiber gratings 总被引:3,自引:0,他引:3
Chao-Xiang Shi 《Quantum Electronics, IEEE Journal of》1995,31(11):2037-2043
Optical bistability in a nonlinearly reflective fiber grating through the mode coupling between the LP01 and counter propagation LP02 modes (i,e., the reflective LP01&rlhar2;LP02 mode converter) is investigated by using the coupled-mode theory. Both the transmissive and the reflective properties of this nonlinear device are analyzed, which show that the output-versus-input relation exhibits the optical bistability. The switching power and the bistable hysteresis performances are also discussed. In addition, the comparison between the nonlinearly reflective mode converter (LP01&rlhar2;LP02) and the nonlinear fiber Bragg grating reflector (i,e., the LP01 and counter-propagation LP01 modes) is also presented. It is shown that the former has much lower switching power than the latter 相似文献
13.
Mahmoud S.W.Z. Wiedenmann D. Kicherer M. Unold H. Jager R. Michalzik R. Ebeling K.J. 《Photonics Technology Letters, IEEE》2001,13(11):1152-1154
Data transmission experiments with single-mode as well as multimode 850-nm vertical-cavity surface-emitting lasers (VCSELs) are carried out from a near-field point of view. Special attention is paid to important quantities like on/off-ratio and bit error rate (BER). A single-mode VCSEL oscillating on the fundamental LP01 mode shows no change in eye opening, on/off-ratio, and BER at different lateral fiber coupling positions. In the case of a multimode VCSEL oscillating both on the LP01 mode and LP11 donut mode, we observe a significant lateral change in the on/off-ratio, which plays an important role in BER measurements 相似文献
14.
Polarization analysis of LP01 and LP11intermodal interference in highly birefringent bow-tie optical fibers 总被引:1,自引:0,他引:1
A polarization analysis of bimodal highly birefringent fibers in which LP01, LP11, interference takes place is performed. The polarization state of the interference pattern is theoretically described in terms of recently proposed spatial Stokes parameters on the basis of coupled-mode equations and Jones matrix formalism. The general quasimonochromatic case is considered and depolarization as well as interference fading are accounted for. Special attention is paid to application of the results to fiber-optic sensors, and the basic schemes for the detection of the interference beat signal are discussed. The theoretical conclusions are supported by experiments in which the modal polarization and intermodal interferometric response to elongation of a bow-tie bimodal fiber is investigated. Measurements are carried out on both a separate fiber and on a multifiber assembly at various input conditions 相似文献
15.
The authors discuss an optical fiber characterized by a core of divergent parabolic graded-index profile. A general formulation is developed to study this fiber as well as other types, including standard step-index and convergent parabolic profiles. An analytical approach to solve the basic differential propagation equation is developed. The solution takes the form of a summation of Bessel functions. An algorithm is programmed and simulations are carried out. Main characteristics of divergent profile fibers, such as propagation constant, dispersion, and power distribution, are presented and compared to those of standard fibers. It is found that the principal mode LP01 exhibits a flat top distribution that better fills core's fiber, suggesting possible applications for laser fibers and amplifiers 相似文献
16.
Bend loss in buffered over-moded optical fibre: LP11mode and `whispering gallery' mode interaction 总被引:2,自引:0,他引:2
Bend loss in over-moded fibre has been measured as a function of temperature. For the LP11 mode, an oscillatory loss dependence on temperature was observed, caused by coupling between the LP11 mode and a `whispering gallery' mode. These interactions could have a significant effect on singlemode cutoff wavelength measurements 相似文献
17.
The fiber-optic LP01&lrarr2;LP11 mode transducers are analyzed by a scalar coupled-mode theory with vector correction. The authors deal with fiber-optic mode transducers made of a single fiber with periodic perturbations due to microbends, acoustic waves, or a photoinduced index grating. Both the couplings caused by the index perturbations and by the vector property of the fields (polarization effect) are taken into account in the analysis. Approximate analytical solutions to the coupled-mode equations are obtained. The power exchange among the modes along the fiber and spectral properties of the mode transducers are examined. The functions of the mode transducers used as wavelength filters and polarizers are studied 相似文献
18.
Chao-Xiang Shi 《Quantum Electronics, IEEE Journal of》1996,32(8):1360-1368
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 相似文献
19.
Huang R. Alhassen F. Tseng D. Boyraz O. Lee H. P. 《Photonics Technology Letters, IEEE》2007,19(9):665-667
In this letter, we investigate coherent acoustooptic coherent mode coupling from the LP01 core mode to LP1m cladding mode of a polarization-maintaining fiber (PMF) induced by two acoustic gratings. We show narrowband variable attenuation along either birefringent axis of the PMF by varying the relative phase between the two acoustic gratings. By launching two acoustic gratings at different frequencies, variable attenuation and low crosstalk along either birefringent axis within the acoustooptic coupling bandwidth are demonstrated 相似文献
20.
Strictly speaking, an ordinary axially symmetrical single-mode fiber is a "two-mode" fiber because two orthogonally polarized HE11 modes can be propagated in it. This fact results in the instability of the polarization state of the propagated mode when geometrical perturbation exists in the fiber, and also the so-called polarization mode dispersion. These are harmful in some applications of single-mode fibers to communication and measurement. To prevent these adverse effects, single-polarization single-mode (SPSM) optical fibers have been developed. Three basic types of the SPSM fiber are elliptical-core fiber, stress-induced birefringent fiber, and side-pit fiber. This paper describes the principles of these three types, performance obtained experimentally, theoretical approaches, and measurement techniques related to the SPSM fibers. Finally, relevant technical tasks in the future are mentioned. 相似文献