Phase shift and loss mechanism of optically excited E-planeelectron-hole plasma

This paper describes the phase shift and loss mechanism of an optically excited E-plane electron-hole plasma. The formulation based on the integral equation with rapidly convergent spectral Green's function plus a closed form spatial representation is presented. It includes the possible physical effects, among which are the injected light power level, the nonuniform distribution of the plasma and the end discontinuity effect. For GaAs as the inserted semiconductor, it is shown that an optically sensitive regime occurs, where the phase shift is highly influenced by the illumination level and where a peak of the optically induced loss exists. The regime is changed by the distribution profile of the excess carriers. It is also observed that at the high injection light power level, the optically excited plasma behaves like a metallic strip does. The field distributions at the optically excited plasma section are also presented, which support the field-displacement effects of the plasma     

Stabilisation of optically excited self-oscillation

A new experiment demonstrating the stabilisation of an optically driven self-oscillator is reported. The oscillation of the micromechanical silicon resonator is maintained by optical feedback provided by a Fabry-Perot interferometer formed between a semireflecting mirror and the surface of the silicon micromechanical resonator. The stabilisation of the oscillation is achieved by adjusting the frequency of the laser diode powering the system.<>     

Novel optically excited resonant pressure sensor

A novel pressure sensitive microresonator structure has been fabricated by anisotropic etching of silicon. An intensity modulated laser beam is focused onto the resonator and generates transverse vibrations, which are detected using optical heterodyne interferometric techniques. The pressure and temperature dependence of the resonant frequency of this structure is reported     

The amplification of far-infrared radiation on optically excited p-type germanium

The far-infrared spectrum of cyclotron resonance absorption in the valence band of p-type germanium has been calculated using 6 × 6 k*p Hamiltonian for degenerate valence band for magnetic field 20T and lattice temperature 77K. That has been shown that excitation by pulseCO ₂ laser radiation can lead to the amplification on light hole cyclotron resonance.     

Phase conjugation of single photons

Phase conjugation (PC) of extremely weak signals using a phase-conjugate mirror based on Mandelstam-Brillouin-enhanced four-wave mixing, coupled with an optical quantum amplifier, is considered. PC of a pulse with energy 4×10^-17 J is achieved. PC conditions for amplified superluminescence noise of the optical quantum amplifier are specified and the limiting parameters are estimated. It is shown experimentally that if the signal-to-noise ratio (S/N) is equal to unity, the energy of an input signal for which phase conjugation is possible corresponds to 30 photons per transverse mode     

Temperature dependence of resonant frequency in optically excited diaphragms

Silicon diaphragms of 4 ?m thickness, fabricated by anisotropic etching techniques, are coated with a thin layer of aluminium. An intensity-modulated laser beam focused on the diaphragm generates transverse vibrations which are detected interferometrically. The measured deflections, resonant frequencies and temperature dependence of resonant frequencies are reported.     

Dispersion characteristics of optically excited coplanarstriplines: pulse propagation

The propagation of optically excited picosecond electrical pulses on coplanar striplines is analyzed. A full-wave analysis method that includes dispersion and losses over terahertz bandwidths is outlined. Results of the full-wave analysis are interpreted in terms of the underlying physical phenomena. The full-wave analysis reveals the existence of peaks in the dispersion curve of the coplanar stripline. These are interpreted in terms of the onset and coupling of the substrate modes to the transmission line mode. Results of the full-wave analysis are in good agreement with those obtained by established theory. Pulse propagation is simulated using the dispersion and loss data obtained from the analysis and accounts for all the relevant mechanisms. Results of simulations are compared with previously published experimental data for normal as well as superconducting lines. It is demonstrated that the superconducting phenomena are not dominant, whereas modal dispersion and substrate losses dominate the evolution of the output pulse and must be included for accurate modeling of pulse propagation on coplanar striplines     

Gain and phase recovery of optically excited semiconductor optical amplifiers

An investigation of the recovery dynamics of semiconductor optical amplifiers (SOAs) explains why the ultrafast component of the gain recovery is largely absent in the phase response. The time-resolved gain and phase dynamics of a bulk GaInAs SOA are measured using a pump-probe technique and differences between the gain and phase recoveries are highlighted and explained using Kramers-Kronig analysis. These have important implications for optical signal processing.     

Dispersion characteristics of optically excited coplanarstriplines: comprehensive full-wave analysis

A comprehensive full-wave formulation to evaluate the dispersion and losses for coplanar striplines on substrates of finite and infinite thicknesses is presented. The loss mechanisms incorporated in the analysis are substrate losses and dielectric material losses. The method of N.K. Das and D.M. Pozar (1987) is generalized to include a complex propagation vector and can be used over a wide frequency range. A large range of line dimensions can also be handled, limits being set by the accuracy of the moment method. Metal losses can also be incorporated into this analysis by applying the appropriate boundary conditions for lossy metal. Analytically, the excitation of substrate modes is shown to correspond to the occurrence of the poles of the Green's function in the reaction integrals. Results of the full-wave analysis are in good agreement with those obtained by established theory     

光激、光拾硅微机械谐振传感器的进展

从基本工作原理着手阐述了光激、光拾硅微机械谐振式传感器,评述了近年来在光激、光拾方式下工作的硅微机械谐振式压力、温度传感器的进展,并就该领域未来的发展作了展望。     

Phase conjugation by four-wave mixing in single-mode fibers

We present an exact solution to the coupled-mode equations, governing four-wave mixing in single-mode fibers, under the perfect phase-matching condition. The solution accounts for pump depletion and fiber absorption. Optimum length of fiber is derived and phase conjugation efficiency is calculated and discussed. The calculated results are in good agreement with the reported experimental results     

Phase conjugation by degenerate four-wave mixing in absorbing media

A theory of degenerate four-wave mixing in absorbing media is developed in terms of a general nonlinear susceptibility. The predictions of the theory are examined in both high and low reflectivity regimes and the specific nonlinearity-inducing mechanisms of thermally induced refractive index changes, the Kerr effect, and saturable absorption are considered. Such a theory is of particular relevance to degenerate four-wave mixing experiments in the ultraviolet and the predictions of the theory are compared with results obtained from such experiments.     

Phase conjugation in saturable amplifiers by degenerate frequency mixing

Phase conjugation in staurable amplifiers by degenerate frequency mixing (DFM) is analyzed using numerical solutions for the appropriate equations. DFM reflectivities up to 10⁴are predicted with pump intensities considerably less than the saturation intensity. The results are compared to those for saturable absorbers. Effects of spontaneous emission in the amplifiers are also considered.     

Efficient computation of surface fields excited on adielectric-coated circular cylinder

An efficient method to evaluate the surface fields excited on an electrically large dielectric-coated circular cylinder is presented. The efficiency of the method results from the circumferentially propagating representation of the Green's function as well as its efficient numerical evaluation along a steepest descent path. The circumferentially propagating series representation of the appropriate Green's function is obtained from its radially propagating counterpart via Watson's transformation and then the path of integration is deformed to the steepest descent path on which the integrand decays most rapidly. Numerical results are presented that indicate that the representations obtained here are very efficient and valid even for arbitrary small separations of the source and field points. This work is especially useful in the moment-method analysis of conformal microstrip antennas where the mutual coupling effects are important     

光束相干驱动声子场提高SBS相位共轭保真度稳定性

光束相干引起的电致伸缩能驱动声子波，从而能加强受激布里渊散射（ＳＢＳ），提高相位共轭保真度稳定性。对折反池结构，采用２ｎｓ陡前沿的脉冲光泵浦，将双级钕玻璃放大器和ＳＢＳ池作为整体，测量了其相位共轭保真度。观测到输出激光的能量远场空间分布和相位共轭保真度稳定性在光束夹角θ５ｍｒａｄ时明显优于θ＞３０ｍｒａｄ。     

平面波导激励的对称型表面等离子体共振结构的研究

研究了一种平面波导激励的对称型表面等离子体共振（SPR）结构,该结构以一定厚度的介质两侧覆盖金属层为核心。理论分析表明,该结构的TM0模式为表面波。研究了一定波长下不同介质时金属膜间介质厚度与等效折射率之间自勺．关系。采用离子交换技术制备了多模平面波导,对其等效折射率进行了测试,采用平面波导激励对称结构的等离子体表面波...     

液相掺杂法可提高ZnO压敏电阻器的性能

用液相掺杂法制备的粉体制成了ＺｎＯ压敏电阻器。ＳＥＭ测试分析及密度测试结果证明,瓷片的微观结构得以改善,从而提高了ＺｎＯ压敏电阻器的性能,其中非线性系数达到６７,通流能力为传统法制作的ＺｎＯ压敏电阻器的２倍。     

Spin controlled optically pumped vertical cavity surface emitting laser

It is shown that the output polarisation of optically pumped vertical cavity surface emitting lasers (VCSELs) can be unambiguously controlled by the pump polarisation. The degree of the output polarisation is higher than that of the pump polarisation. It is concluded that the polarisation of VCSELs with spin polarised electrical pumping can be controlled even with low spin injection efficiencies.