共查询到20条相似文献,搜索用时 15 毫秒
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Because of the power imbalance between the two arms of an interferometer in an electro-optic modulator (EOM), the output of the EOM is combined amplitude modulation (AM) and phase modulation (PM) for the probe signal consisting of the pulse and the dc component. Because of this PM, the Brillouin gain-loss spectrum becomes asymmetric. The central Brillouin frequency is shifted from that of an AM pulse. The maximum extinction ratio of the EOM is limited to approximately 29 dB for a power-splitting ratio of 51% to 49%. The asymmetric property induced by PM is not pulse shape dependent; for both Gaussian- and super-Gaussian-shaped pulses the Brillouin loss spectrum is symmetric for AM and asymmetric for combined AM and PM (power imbalance). 相似文献
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Jiu-sheng Li 《Optik》2008,119(1):19-22
A novel optical modulator using SiO2 waveguides on a silicon substrate is proposed. The modulator is analyzed and designed with the finite element method. The numerical results have shown that an optimally designed modulator can give a broad bandwidth, good impedance match, and low cost. The proposed modulator can be fabricated easily using Si-based very large-scale integrated technology, and it is very suitable for opto-electronic integrated circuits. 相似文献
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This paper reviews the use of surface Brillouin scattering (SBS) and acoustic microscopy (AM) in studying the surface dynamics of solids in order to obtain information about the near-surface elastic properties of solids and thin supported films. The vibrational modes that are probed by these means include Rayleigh surface and pseudo-surface acoustic waves, longitudinal lateral waves (surface skimming bulk longitudinal waves) and various thin film guided modes, such as Sezawa and Love waves. SBS is the inelastic scattering of light, mediated by thermodynamic fluctuations in the surface elevation and near surface elastic strains. The scattering cross-section is conveniently expressed in terms of Fourier domain elastodynamic Green's functions. AM depends on the insonification of a surface through a coupling fluid, and the resulting excitation and subsequent decay of the various surface modes. The complex reflectivity of the fluid-loaded surface, and the line and point force surface Green's functions are invoked in the interpretation of different modalities of AM, yielding much the same information about the surface dynamics. The focus in this paper is on the Green's function approach. A number of illustrative examples, drawn from the authors' research, are provided. 相似文献
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This article is concerned with the detection of mixed modulation (MM), i.e., simultaneously occurring amplitude modulation (AM) and frequency modulation (FM). In experiment 1, an adaptive two-alternative forced-choice task was used to determine thresholds for detecting AM alone. Then, thresholds for detecting FM were determined for stimuli which had a fixed amount of AM in the signal interval only. The amount of AM was always less than the threshold for detecting AM alone. The FM thresholds depended significantly on the magnitude of the coexisting AM. For low modulation rates (4, 16, and 64 Hz), the FM thresholds did not depend significantly on the relative phase of modulation for the FM and AM. For a high modulation rate (256 Hz) strong effects of modulator phase were observed. These phase effects are as predicted by the model proposed by Hartmann and Hnath [Acustica 50, 297-312 (1982)], which assumes that detection of modulation at modulation frequencies higher than the critical modulation frequency is based on detection of the lower sideband in the modulated signal's spectrum. In the second experiment, psychometric functions were measured for the detection of AM alone and FM alone, using modulation rates of 4 and 16 Hz. Results showed that, for each type of modulation, d' is approximately a linear function of the square of the modulation index. Application of this finding to the results of experiment 1 suggested that, at low modulation rates, FM and AM are not detected by completely independent mechanisms. In the third experiment, psychometric functions were again measured for the detection of AM alone and FM alone, using a 10-Hz modulation rate. Detectability was then measured for combined AM and FM, with modulation depths selected so that each type of modulation would be equally detectable if presented alone. Significant effects of relative modulator phase were found when detectability was relatively high. These effects were not correctly predicted by either a single-band excitation-pattern model or a multiple-band excitation-pattern model. However, the detectability of the combined AM and FM was better than would be predicted if the two types of modulation were coded completely independently. 相似文献
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Closed form solutions for a simultaneously AM and high-harmonic FM mode locked laser system is presented. Analytical expressions
for the pulsewidth and pulsewidth-bandwidth products are derived in terms of the system parameters. The analysis predicts
production of 17 ps duration pulses in a Nd:YAG laser mode locked with AM and FM modulators driven at 80 MHz and 1.76 GHz
for 1 W modulator input power. The predicted values of the pulsewidth-bandwidth product lie between the values corresponding
to the pure AM and FM mode locking values. 相似文献
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介绍了铌酸锂调制器在1550nm有线电视(CATV)外调制发射机中的功能及其结构,调制器集成了高频相位调制器、模拟强度调制器和无源3dB耦合器在同一芯片上。分析了CATV调制器的关键技术和解决方案,采用了新颖的非平行电极、磨凹芯片背面的结构和阻抗变换方案。设计制作的模拟强度调制器获得了优于±0.5dB平坦的响应和小于-20dB的电反射。基于工艺容差和BPM软件模拟优化设计的3dB耦合器使器件得到大于30 dB的开关消光比。 相似文献
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We present full phase stabilization of an amplified Yb:fiber femtosecond frequency comb using an intracavity electro-optic modulator and an acousto-optic modulator. These transducers provide high servo bandwidths of 580 kHz and 250 kHz for f(rep) and f(ceo), producing a robust and low phase noise fiber frequency comb. The comb was self-referenced with an f-2f interferometer and phase locked to an ultrastable optical reference used for the JILA Sr optical clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors (over 1 mHz-1 MHz), respectively. Alternatively, the comb was locked to two optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of integrated phase errors, respectively. 相似文献
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Bryan J. O'Regan 《Optics Communications》2011,284(24):5650-5654
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Guina M Vainionpää A Harkonen A Orsila L Lyytikäinen J Okhotnikov OG 《Optics letters》2003,28(1):43-45
We propose and demonstrate a reflection-type optical modulator, with surface-normal architecture, that exploits the optical saturation of absorption in semiconductor quantum wells. The modulation section of the modulator, which is composed of quantum wells placed within a Fabry-Perot cavity, is optically controlled by an intensity-modulated beam generated by an in-plane laser integrated monolithically on the same wafer and grown in a single epitaxial step. The modulation section and the in-plane laser share the same medium; therefore, efficient coupling between the control beam and the signal beam is achieved. The device was successfully used for active mode locking of an erbium-doped fiber laser. 相似文献
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利用波导调制器实现连续可调任意整形激光脉冲 总被引:7,自引:1,他引:6
目前,惯性约束聚变激光驱动哭有级的发展方向是以稳定性好的激光二极管取代原来的闪光灯泵浦,以集成光学和光纤技术取代原来的块状光学调制器进行激光脉冲的整形工艺。本文从实验上研究了以激光二极管泵浦的固体激光器作为光源,以波导调制器作为整形器件的激光脉冲的整形和频谱展工技术,获得了初步的实验结果。 相似文献
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TU Tao ZHA Kaide YANG Jianliang 《Chinese Journal of Lasers》2000,9(4):343-348
1 Introduction CurentlythestudyofopticalCATVtechnologyhasmainlyfocusedontransmitters.TherearetwotypesofopticalCATVtransmitters:directlymodulatedandexternallymodulated .Inadditiontothedifficultyinincreasingopticalpower,opticallinkreflectioncanimpairtran… 相似文献
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Edwards DR Lee J Andrews J Wong A 《The Journal of the Acoustical Society of America》2008,123(5):EL111-EL115
A previous study by [J. Lee, G. Long, and C. Jeung, J. Acoust. Soc. Am. 119, S3332 (2006)] found that information at the onset or offset of modulation could be utilized for improved amplitude modulation (AM) depth discrimination in a continuous carrier condition (carrier presented 250 ms earlier and later than the modulator). In this study, the relative contribution of information at the onset or offset of the modulation was examined with an onset-fringe carrier condition (carrier begins 250 ms earlier than the modulator) and an offset-fringe condition (carrier ends 250 ms later than the modulator). The results suggest that modulation information at the onset might be utilized more than at the offset. 相似文献
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Ravi Pant David Marpaung Irina V. Kabakova Blair Morrison Christopher G. Poulton Benjamin J. Eggleton 《Laser \u0026amp; Photonics Reviews》2014,8(5):653-666
Demonstration of continuously tunable delay, low‐noise lasers, dynamically controlled gratings, and optical phase shifting using the stimulated Brillouin scattering (SBS) process has lead to the emergence of SBS as a promising technology for microwave photonics. On‐chip realization of SBS enables photonic integration of microwave photonic signal processing and offers significantly enhanced performance and improved efficiency. On‐chip stimulated Brillouin scattering is reviewed in the context of slow‐light based tunable delay, low‐noise narrow linewidth lasers and filtering for integrated microwave photonics. A discussion on key material and device properties, necessary to enable on‐chip Brillouin scattering using both the single‐pass and resonator geometry, is presented along with an outlook for photonic integration of microwave signal processing and generation in other platforms. 相似文献
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We propose a new method to separate different orders of an all-fiber passive Q-switching stimulated Brillouin scattering(SBS) laser. We use two fiber Bragg gratings connected by two circulators for the filtering. We obtain a stabilized pulse laser and measure the pulse width of different orders. The first order of SBS has a central wavelength of 1549.75 nm, an average output power of 9 mW, and a pulse width of 400 ns. The pulse width of SBS is reduced by the higher-order signals with the larger fluctuations. 相似文献
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We propose a novel compact and integrated optical modulator, which consists of p–i–n silicon photonic crystals with triangular lattice and a line defect waveguide. The device operation is based on a dynamic shift of the photonic band gap (PBG), which induced change in the silicon refractive index by the free carrier injection. We have numerically analyzed and investigated its light modulation performance by using plane wave expansion (PWE) method and finite-difference time-domain method. With small size, rapid response time and high extinct ratio, the designed optical modulator can be used in photonic integrated circuits. 相似文献
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Gockel H Carlyon RP Deeks JM 《The Journal of the Acoustical Society of America》2002,112(6):2975-2984
The effect on modulation detection interference (MDI) of timing of gating of the modulation of target and interferer, with synchronously gated carriers, was investigated in three experiments. In a two-interval, two-alternative forced choice adaptive procedure, listeners had to detect 15 Hz sinusoidal amplitude modulation (AM) or frequency modulation (FM) imposed for 200 ms in the temporal center of a 600 ms target sinusoidal carrier. In the first experiment, 15 Hz sinusoidal FM was imposed in phase on both target and interferer carriers. Thresholds were lower for nonoverlapping than for synchronous modulation of target and interferer, but MDI still occurred for the former. Thresholds were significantly higher when the modulators were gated synchronously than when the interferer modulator was gated on before and off after that of the target. This contrasts with the findings of Oxenham and Dau [J. Acoust. Soc. Am. 110, 402-408 (2001)], who reported no effect of modulation asynchrony on AM detection thresholds, using a narrowband noise modulator. Using FM, experiment 2 showed that for temporally overlapping modulation of target and interferer, modulator asynchrony had no significant effect when the interferer was modulated by a narrowband noise. Experiment 3 showed that, for AM, synchronous gating of modulation of the target and interferer produced lower thresholds than asynchronous gating, especially for sinusoidal modulation of the interferer. Results are discussed in terms of specific cues available for periodic modulation, and differences between perceptual grouping on the basis of common AM and FM. 相似文献