共查询到20条相似文献,搜索用时 46 毫秒
1.
Tunable polarization diversity liquid-crystal wavelength filter 总被引:2,自引:0,他引:2
J.S. Patel M.W. Maeda 《Photonics Technology Letters, IEEE》1991,3(8):739-740
A compact polarization-insensitive liquid crystal filter is demonstrated using the polarization diversity technique. The incoming signal is split into two orthogonally polarized beams with a calcite crystal and the beams are filtered using two regions of the liquid crystal Fabry-Perot filter. The optic axes in these two regions are made orthogonal by controlling the surface structure. It is shown that a wide tuning range of 70 nm is possible with a band-pass of about 0.6 nm. Using arbitrarily polarized input light it is demonstrated that polarization-dependent power fluctuations are less than 1 dB.<> 相似文献
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M. Matsuura N. Kishi T. Miki 《Photonics Technology Letters, IEEE》2006,18(8):926-928
A novel broadband wavelength converter by multistage cascaded semiconductor optical amplifier (SOA)-based wavelength converters is proposed. We have demonstrated, for the first time, broadband wavelength conversion in the wavelength range of 1320-1610 nm by using three-stage cascaded SOA-based wavelength converters with each different gain band. 相似文献
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由于海水的吸收、散射衰减以及海洋湍流效应会引起水下无线光通信(Underwater wireless optical communication,UWOC)系统接收端光信号的闪烁,导致UWOC系统传输性能下降。基于Gamma-gamma分布的海洋湍流信道模型,根据海洋湍流参数和各向异性因子表示的等效结构参数,推导出波长分集UWOC系统中断概率(Outage probability,OP)与平均误码率(Bit error rate,BER)封闭表达式。研究分析随着各向异性因子的增加,具有不同波长分集阶的水下无线光通信系统中断概率与平均误码率的变化,比较接收端使用最佳组合(Optimal combining,OC)与等增益组合(Equal gain combining,EGC)技术的水下无线光通信系统平均误码率,并仿真不同海洋湍流参数、传输距离对波长分集UWOC系统性能的影响。数值结果表明,随着各向异性因子的增加,海洋湍流对水下无线光通信系统产生的影响逐渐减弱,使用波长分集技术的UWOC系统比无波长分集技术的UWOC系统中断概率与平均误码率明显改善。 相似文献
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A simple interferometric method for indirectly determining a value for the cutoff wavelength of single-mode optical fibres is described. The technique is accurate and no stringent requirements are placed on the experimental equipment. 相似文献
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Durhuus T. Mikkelsen B. Joergensen C. Lykke Danielsen S. Stubkjaer K.E. 《Lightwave Technology, Journal of》1996,14(6):942-954
Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber 相似文献
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Optical wavelength shifting of 1.054-nm laser pulses in excess of ± 10 wavenumbers (± 300 GHz) was demonstrated. The wavelength shifter consists of synchronous microwave and optical waveguides fabricated monolithically on LiNbO3. An optical pulse experiences a constant refractive index gradient that travels with the pulse and causes the wavelength shift 相似文献
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Light scattering and color change are two major sources of distortion for underwater photography. Light scattering is caused by light incident on objects reflected and deflected multiple times by particles present in the water before reaching the camera. This in turn lowers the visibility and contrast of the image captured. Color change corresponds to the varying degrees of attenuation encountered by light traveling in the water with different wavelengths, rendering ambient underwater environments dominated by a bluish tone. No existing underwater processing techniques can handle light scattering and color change distortions suffered by underwater images, and the possible presence of artificial lighting simultaneously. This paper proposes a novel systematic approach to enhance underwater images by a dehazing algorithm, to compensate the attenuation discrepancy along the propagation path, and to take the influence of the possible presence of an artifical light source into consideration. Once the depth map, i.e., distances between the objects and the camera, is estimated, the foreground and background within a scene are segmented. The light intensities of foreground and background are compared to determine whether an artificial light source is employed during the image capturing process. After compensating the effect of artifical light, the haze phenomenon and discrepancy in wavelength attenuation along the underwater propagation path to camera are corrected. Next, the water depth in the image scene is estimated according to the residual energy ratios of different color channels existing in the background light. Based on the amount of attenuation corresponding to each light wavelength, color change compensation is conducted to restore color balance. The performance of the proposed algorithm for wavelength compensation and image dehazing (WCID) is evaluated both objectively and subjectively by utilizing ground-truth color patches and video downloaded from the Youtube website. Both results demonstrate that images with significantly enhanced visibility and superior color fidelity are obtained by the WCID proposed. 相似文献
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Presents a heuristic algorithm for effectively assigning a limited number of wavelengths among the access stations of a multihop network wherein the physical medium consists of optical fiber segments which interconnect wavelength-selective optical switches. Such a physical medium permits the limited number of wavelengths to be re-used among the various fiber links, thereby offering very high aggregate capacity. Although the optical connectivity among the access station can be altered by changing the states of the various optical switches, the resulting optical connectivity pattern is constrained by the limitation imposed at the physical level. The authors also study two routing schemes, used to route requests for virtual connections. The heuristic is tested on a realistic traffic model, and the call blocking performance of new requests for virtual connections is studied through extensive simulations and compared against the blocking performance of an ideal infinite capacity centralized switch (lowest possible call blocking caused exclusively by congestion on the finite capacity user input/output links, never by the switch fabric itself). Surprisingly, the authors find that, for a wide range of parameters, the blocking performance of the lightwave network is almost the same as that of the ideal centralized switch. From these results, they conclude that the heuristic algorithm is effective and the routing scheme is efficient 相似文献
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Franzen D.L. Young M. Cherin A.H. Head E.D. Hackert M.J. Raine K.W. Baines J.G.N. 《Lightwave Technology, Journal of》1989,7(6):896-901
An industrywide study among members of the Electronic Industries Association was conducted to document differences among three numerical aperture measurement methods. Results on 12 multimode graded index fibers indicate systematic differences exist among commonly used far-field and index profile techniques. Differences can be explained by a wavelength-dependent factor and choice of definitions. Conversion factors can be used to relate the various methods 相似文献
12.
A novel control scheme for fast laser diode (LD) wavelength switching with rapid stabilisation is proposed, which is the key technology for wavelength-division multiplexing (WDM) data cell transfer networks. The obtained characteristics are suitable for 600 Mbit/s asynchronous transfer mode (ATM) cell transfer networks. The proposed control scheme can be applied to over 10 Gbit/s cell speed networks.<> 相似文献
13.
Hao Qin Shi Zhang Zengji Liu 《Communications Letters, IEEE》2003,7(3):136-138
We propose a dynamic routing and wavelength assignment algorithm in an all-optical network with limited-range wavelength conversions. For each randomly arrived request, the correlation of different wavelengths on different links in all possible routes is described by the wavelength weight in our algorithm. We try to assign wavelengths on each candidate route using a shortest-path algorithm based on the wavelength weight and choose the best as its route and wavelength assignment scheme. Numerical results obtained for NSFNET and a 12-node ring show that our algorithm can greatly reduce the blocking probability and the number of required conversions under uniform traffic or traffic dominated by larger hop routes. 相似文献
14.
《Solid-State Circuits, IEEE Journal of》1982,17(4):731-738
Integrated circuit flip-flop resolving time parameters, required for calculation of synchronizer performance and reliability, are measured by wafer probing, without the need for dicing or bonding, by incorporation of test structures on an IC along with the flip-flop to be measured. The circuit has five digital inputs, five digital outputs, including one for frequency measurements, and two analog inputs plus power and ground connections. Several delays that are fabricated as part of the test circuit, including a voltage controlled delay with a few picosecond resolution, are calibrated as part of the test procedure by grating them into and out of the delay path of a ring oscillator. Each of the delay values is calculated by subtracting the period of the ring oscillator with the delay omitted, from the period of the ring oscillator with the delay included. A frequency divider is fabricated as part of the test structure to reduce the output of the ring oscillator to less than 200 kHz so no high-frequency inputs of outputs from the IC are required. 相似文献
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Qin Zhang Brown D.A. Reinhart L. Morse T.F. Wang J.Q. Gang Xiao 《Photonics Technology Letters, IEEE》1994,6(7):839-841
Bragg gratings at a specific wavelength are made using an excimer KrF laser and a phase mask. The wavelength can be varied for fine tuning and multiplexing applications by straining the optical fiber during UV illumination. When the strain is removed, the grating formed is at a smaller wavelength than that dictated by the phase mask for the unstrained fiber. This technique was demonstrated by writing two gratings located at the same point in the optical fiber. The transmission from the first grating was used as a means for in situ absolute wavelength tuning. The second grating made with approximately 0.2% axial strain was at 1534.54 nm. Once the grating was made, the strain was removed from the fiber leaving the second grating tuned to 1532.04 nm, a wavelength shift of 2.5 nm 相似文献
19.
Durhuus T. Joergensen C. Mikkelsen B. Pedersen R.J.S. Stubkjaer K.E. 《Photonics Technology Letters, IEEE》1994,6(1):53-55
Penalty free wavelength conversion is demonstrated at 2.5 Gbit/s over a wavelength span of 12 nm by the use of semiconductor optical amplifier (SOA)'s in a Mach-Zehnder configuration. An increase in the extinction ratio is measured for the converted signal compared to the input signal implying signal regeneration as well as wavelength conversion 相似文献
20.
Optical wavelength converters 总被引:1,自引:0,他引:1
Offside M.J. Carroll J.E. Bray M.E. Hadjifotiou A. 《Electronics & Communication Engineering Journal》1995,7(2):59-71
Devices and techniques for shifting the frequency/wavelength of an optical carrier wave are reviewed, with particular reference to applications in wavelength/frequency division multiplexed optical communication systems. Considered first are devices which make use of semiconductor laser amplifiers or oscillators. Some of these techniques come close to satisfying the requirements for a suitable wavelength shifter, though none appear to offer the potential for a transparent network independent of data modulation format. A second main category, using nonlinear optical materials, promises to satisfy the requirements for frequency translation in a network which is fully transparent to the modulation format. However, the conversion efficiencies currently available appear too low for cost-effective communication systems engineering so that further advances in nonlinear optical materials/techniques are still required. It seems likely that guided wave techniques will provide the best means of improving the efficiency by increasing the interaction length and the optical intensity for a given power. Schematic examples of such a converter are discussed. All of the existing techniques have some deficiencies compared to an ideal system so that wavelength conversion for optical communication systems is still a problem in search of a good solution 相似文献