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31.
32.
This paper presents a multicarrier communication system which transmits information on independent subcarriers to achieve an increased data rate. For this system, a passive-phase conjugation (PPC) based receiver structure is assessed by processing data collected in sea trials. Based on temporal diversity (pulse compression) exploited by PPC processing, an adaptive multichannel decision feedback equalizer is used to remove intersymbol interference, where spatial diversity is exploited by adaptive multichannel combination. The digital phase-locked loop (DPLL) technique is implemented for carrier-phase tracking. In the scenario of low input signal-to-noise ratios (SNRs), the receiver structure achieved superior performance using a common DPLL. In a depth-fluctuated environment, two sea experiments were conducted over ranges of 2 km and 4 km, respectively, and this communication system was assessed with a data rate of 4 kbps. In terms of mean square error, output SNR and bit error rate, this receiver structure has demonstrated its performance for the multicarrier communication system. 相似文献
33.
Passive time reversal exploits underwater acoustic channels’ spatial and temporal diversity. It can refocus multipath propagated signal at the receiver and can be realized simply by the passive phase conjugation (PPC) method. By the temporal focusing, time delay spread caused by multipath propagation is mitigated for spectral efficient coherent communications. However, the PPC method is unable to eliminate multipath and is limited by channel variations. An adaptive equalizer is therefore needed to compensate residual multipath after refocusing and to track channel temporal variations. Spatial diversity is obtained by using a vertical receiving array. In this paper we used 4-hydrophone array and demonstrated that the adaptive decision feedback equalization in conjunction with PPC significantly decreased the bit error rate. 相似文献
34.
为了分析半球谐振陀螺仪非敏感轴X、Y轴存在比力输入时,对输出角速率解算精度的影响,首先,利用环形谐振子的动力学方程,得到了径向振动方程。然后,分析了存在比力输入时,谐振子唇沿中心将偏移激励器和位移传感器所确定的圆心,并根据闭环检测原理,推导了陀螺仪解算角速率误差的表达式,仿真计算了相对偏移量对输出结果的影响程度。最后,利用分度头进行了非敏感轴的多位置翻滚试验,验证了输出中存在与非敏感轴比力输入有关的误差。 相似文献
35.
基于自再现原理,利用菲涅耳-基尔霍夫衍射积分方程,引入腔镜失调、激光介质上的增益分布以及光阑口径,采用本征矢量法分析了大口径平凹腔薄片激光器的本征模式,并计算了相应的光束质量因子M2.建立了千瓦级薄片激光系统和光纤扫描光斑诊断装置,开展了高功率激光输出特性研究.结果表明,在大口径高功率平凹腔中多个本征模式可同时起振,获... 相似文献
36.
通过将单回路镜像对称开口金属环结构印制在高介电常数基板上,实现了一种金属含量比传统负折射材料更少,"双负"通带比全介质负折射材料更宽的负折射材料.分析了高介电常数基板产生负介电常数以及"双负"通带形成的机理,通过仿真实验分析了影响"双负"通带的因素.通过制作样品验证了这一机理实现"双负"的可行性,理论分析与实验结果都表明这种方法可实现较宽频段内的"双负"通带.
关键词:
负折射材料
负介电常数
负磁导率
介质谐振器原理 相似文献
37.
38.
Yoshiteru Amemiya Tomohiro Tokunaga Yuichiro Tanushi Shin Yokoyama 《Optical Review》2009,16(3):247-251
Electric-field drive optical modulators using a Si ring resonator were fabricated on silicon-on-insulator (SOI) wafers. The
fabricated resonators consisted of Si waveguides with width and thickness of 1.0 and 0.3 μm, respectively. In order to induce
the linear electro-optic (EO) effect in the Si core layer, the strain was applied by covering the layer with Si3N4 film (0.26 μm thick) deposited by low pressure chemical vapor deposition (LPCVD) at 750 °C. The vertical electric-field was
applied to the Si waveguide through the top and bottom cladding layers, and the optical output from the drop port at the resonance
wavelength was measured. At a wavelength of 1501.6 nm, the optical modulation of 33% was obtained at 200V (electric-field
at the silicon surface ∼3 × 105 V/cm, nearly the breakdown field). The resonance wavelength was shifted toward the short wavelength side by applying both
positive and negative voltages, this shift was explained by carrier concentration modulation. The linear EO effect in the
Si core layer was not observed, presumably because the strain in the Si core layer was too small. 相似文献
39.
Implementing of photonic sampling and quantizing analog-to-digital converters (ADCs) enable us to extract a single binary word from optical signals without need for extra electronic assisting parts. This would enormously increase the sampling and quantizing time as well as decreasing the consumed power. To this end, based on the concept of successive approximation method, a 4-bit full-optical ADC that operates using the intensity-dependent Kerr-like nonlinearity in a two dimensional photonic crystal (2DPhC) platform is proposed. The Silicon (Si) nanocrystal is chosen because of the suitable nonlinear material characteristic. An optical limiter is used for the clamping and quantization of each successive levels that represent the ADC bits. In the proposal, an energy efficient optical ADC circuit is implemented by controlling the system parameters such as ring-to-waveguide coupling coefficients, the ring’s nonlinear refractive index, and the ring’s length. The performance of the ADC structure is verified by the simulation using finite difference time domain (FDTD) method. 相似文献
40.