Fabry–Pe´rot enhancement of external electro-optic sampling

This paper describes the Fabry–Pe′rot enhancement of external electro-optic sampling. Previous reports of Fabry–Pe′rot enhancement have been exclusively on continuous wave systems. Using a picosecond dye laser and a standard electro-optic probe tip an increase is shown both in the sensitivity and the responsivity of the picosecond probing system. The results show that for a picosecond system considerable advantage can be gained by use of the Fabry–Pe′rot effect. This revised version was published online in June 2006 with corrections to the Cover Date.     

Influence of Light Polarization States on Sum—Frequency Generation in a Chiral Medium with a Two—Coupled—Oscillator Model

Sum-frequency generation (SFG) is investigated using the two-coupled-oscillator molecular model.The influence of the polarization states and angles of two incident beams on reflected and transmitted sum-frequency lights is discussed by considering the circular birefringence in a chiral medium.The different response of media with two kinds of enantiomers to polarization states of incident beams is also discussed.Furthermore,the relations between the SFG spectrum and the polarization states are studied.The theoretical result is consistent with a known experimental fact.     

Experimental study on the Stokes effect in disordered birefringent microstructure fibers

In this paper, a 120-fs pulse transmission experiment is carried out using disordered birefringent microstructure fibers with cladding ventages. Through this experiment, it is found for the first time that remarkable Stokes and anti-Stokes waves can also be produced when the central wavelength of the incident pulse is in the normal dispersion regime of the microstructure fiber. The generation of the two waves can be explained by the four-wave mixing phase matching theory. Properties of the two waves under the action of femtosecond laser pulses with different parameters are studied. The results show that the central wavelength of anti-Stokes waves and Stokes waves produced under the two orthogonal polarization states shift by 63 nm and 160 nm, respectively. The strengths and central positions of the two waves in birefringent fibers can be controlled by adjusting the phase match condition and the polarization directions of incident pulses.     

The design and preparation of a Fabry–Pérot polarizing filter

A novel single-cavity narrowband Fabry–Pe′rot(FP) polarizing filter at normal incidence,constructed from a sandwich structure with sculptured anisotropic space layer and symmetric isotropic HR mirrors,is designed and prepared.The optical performances of transmittance,phase shift,central wavelength,and bandwidth for two polarized states are analyzed with the characteristic matrix.The numerical studies accord reasonably well with the experimental results.It is demonstrated that the polarization state of the electromagnetic wave and phase shift can be modulated by employing an anisotropic space layer in the polarizing beam splitter system.The birefringence of the anisotropic space layer provides a sophisticated phase modulation by varying the incidence angles over a broad range to have a wide-angle phase shift.     

Reflected and transmitted powers of arbitrarily polarized plane waves at interface between chiral and achiral media

A study has been made on the reflected and transmitted powers generated when an arbitrarily polarized plane wave impinges at a planar interface separating an isotropic achiral medium(IAM) and an isotropic chiral medium(ICM). It follows that the theoretical formulas are derived for the normalized reflection and transmission powers from an IAM–ICM interface for an arbitrary polarized incident wave, and those at an ICM–IAM interface for right-hand circularly polarized(RCP) or left-hand circularly polarized(LCP) incident wave are also obtained. The behavior of the reflected and transmitted waves in different cases is studied, and the dependence of the reflection/transmission of the incident wave on the incident angle and the parameters of the media is investigated in detail. Our numerical results show that high transmission is exhibited under the impedance matching condition and the incident wave can be split into two waves of the same circular polarization state in the case of the ICM–IAM interface, which indicates that circular polarizing beam splitter is achieved.     

Linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces

In this Letter, we demonstrate a linear polarization conversion of transmitted terahertz wave with double-layer meta-grating surfaces, which integrated the frequency selectivity of a split ring resonator metasurface and the polarization selectivity of a metallic grating surface. Since the double-layer can reduce the loss, and the Fabry–Perot like resonant effect between the two layers can improve the conversion efficiency, this converter can rotate the incident y-polarized terahertz wave into an x-polarized transmitted wave with relatively low loss and high efficiency. Experimental results show that an average conversion efficiency exceeding 75% from 0.25 to 0.65 THz with the highest efficiency of 90% at 0.43 THz with only-2 dB loss has been achieved.     

Effective stimulated emission cross-sections determined by transient fluorescence amplification in a Fabry–Pe´rot resonator

The amplification of fluorescence light of an active medium in a Fabry-Pe′rot resonator, transversely pumped with picosecond pulses, is exploited to determine the effective stimulated emission cross-section spectrum, σem,eff(λ). A theory is presented for the ratio of amplified fluorescence output to spontaneous emission signal (resonator mirrors removed). The detection sensitivity is enhanced by the multi-pass amplification. Its dependence on the output mirror reflectivity and residual ground-state absorption in the emission region is analysed. As an example the effective stimulated emission cross-section spectrum of coumarin 2 in methanol is measured in the wavelength region 435nm to 610nm. This revised version was published online in November 2006 with corrections to the Cover Date.     

A tunable infrared plasmonic polarization filter with asymmetrical cross resonator

A tunable infrared plasmonic polarization filter is proposed and investigated in this paper. The filter is based on the sandwich absorption structure which consists of three layers. The top layer is an array of asymmetrical cross resonator.The middle and bottom layers are dielectric spacer and metal film respectively. By absorbing specific wavelength of the incident light perfectly, the reflection spectrum of the structure shows filter performance. The calculated results show that the absorption wavelength is strongly dependent on the length of branch of the asymmetrical cross resonator which is parallel to the light polarization and independent of the length of the vertical one. Therefore, the asymmetrical cross resonator filter structure opens the way for freely tuning the filtering wavelength for a different light polarization. We can fix a resonant wavelength(absorption wavelength) corresponding to one polarization and change the resonant wavelength for the other polarization by adjusting the corresponding branch length of the asymmetrical cross resonator, or change the two resonant wavelengths of both two polarizations at the same time.     

A Novel Nano-Grating Structure of Polarizing Beam Splitters

A metal wire nanograting is fabricated and used as a polarizing beam splitter that reflects TE polarization and transmits TM polarization. The metal wire nanograting is based on a fully optimized design structure that consists of not only the core nanowire metal grid but also the substrate nanograting. The substrate nanograting is designed to provide better performance for both TM and TE polarizations. We fabricate metal-stripe gratings on a glass substrate using nanoimprint lithography and reactive ion etching process. A detailed investigation of the polarization effect at 1550 nm wavelength is carried out with the theoretical analysis and experimental results. The polarizing beam splitter has uniform performance with wide variations in the incident angle （±25） and has high efficiency for both the reflected and the transmitted beams.     

Frequency-selective microwave polarization rotator using substrate-integrated waveguide cavities

A frequency selective polarization rotator that can rotate the polarization angle of an incident electromagnetic wave at the microwave frequency by 45 is presented. The polarization rotator is based on a two-dimensional periodic array of substrate integrated waveguide cavities, realizing the polarization rotation by coupling the input signal to the output wave through three metallic slots. Two layers of frequency selective surfaces are cascaded by substrate and form the polarization rotator. A vertical slot on the top layer is used to select the horizontal polarization from the incident wave, the vertical and the horizontal slots on the bottom layer are, respectively, used to obtain horizontally and vertically polarized outgoing waves. The two orthogonal outgoing waves are combined to result in the 45~ polarized wave. Both full wave simulation and experimental measurement are carried out, together validating the proposed method.     

Multi-band circular polarizer based on a twisted triple split-ring resonator

A multi-band circular polarizer using a twisted triple split-ring resonator（TSRR） is presented and studied numerically and experimentally. At four distinct resonant frequencies, the incident linearly polarized wave can be transformed into left/right-handed circularly polarized waves. Numerical simulation results show that a y-polarized wave can be converted into a right-handed circularly polarized wave at 5.738 GHz and 9.218 GHz, while a left-handed circularly polarized wave is produced at 7.292 GHz and 10.118 GHz. The experimental results are in agreement with the numerical results. The surface current distributions are investigated to illustrate the polarization transformation mechanism. Furthermore, the influences of the structure parameters of the circular polarizer on transmission spectra are discussed as well.     

Transmission Properties of One-Dimensional Photonic Crystals Containing Anisotropic Metamaterials

The transmission properties of one-dimensional photonie crystals （1DPCs） containing anisotropic metamaterials are theoretically studied. It is shown that the 1DPCs can possess a similar zero average index （zero-n） gaps, the edges of zero-~ gap are weakly dependent on the incident angles, scale length and the polarization of the electromagnetic wave. When an impurity is introduced, a defect mode appears inside the zeron gap with a very weak dependence on incident angles and sealing. It is found that in such photonic crystals, a transmitted Gaussian pulse with its carrier frequency lying in the lower gap edge, in the defect mode and in the bandgap, can experience a positive or negative group delay and hence a subluminal, ultra.slow or superluminal propagation with small distortions. These properties of the photonic crystals have potential applications in the transfer of information.     

Shaping of focal field with controllable amplitude,phase, and polarization

We propose a method for configuring the distribution of amplitude, phase, and polarization in the focal region of vector beams. The polarization and phase of incident beam is spatially tailored so that it can produce a focal field that has elaborately prescribed shapes. Our work focuses on the design of a special focus structure with two oval rings, wherein a phase gradient and polarization gradient exist in the inner and outer rings, respectively. The incident light yielding the desired focal field is determined based on an iterative scheme involving vectorial diffraction calculations and fast Fourier transforms. Simulations and experiments demonstrate the generation of a focal field with phase and polarization gradients, which may find applications in optical manipulation.     

Polarization effects during the interaction of counterpropagating waves in isotropic resonant media

Using the method of nonlinear polarization spectroscopy in the oppositely propagating laser beams of different power at a wavelength of 3.39 μm, we study, both theoretically and experimentally, the mechanisms of the formation of dichroism and birefringence during the interaction of arbitrarily polarized fields of resonant radiation with gaseous methane under conditions of low pressure of the gas in the cell and saturation of the operating transition F ₂ ⁽²⁾ by the field of a strong wave. Spectral forms of the polarization resonances of the test-wave intensity at the output of the polarization spectrometer are studied experimentally. Based on the vector theory of light interaction with matter, we present an exhaustive theoretical interpretation of the experimental data on the dependence of the polarization state of a weak wave on the intensity of a linearly or circularly polarized high-power counterpropagating wave. A new technique of measuring the induced nonlinear anisotropy for test-field waves and the macroscopic parameters of the resonant gas is developed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 72–93, January 2007.     

Controlling of the Polarization States of Electromagnetic Waves Using Epsilon-near-Zero Metamaterials

We demonstrate theoretically that the epsilon-near-zero materials can be utilized to control effectively the polarization conversion of an electromagnetic wave through reflection. The significant feature differing from all other means based on whatever natural materials or metamaterials is that for TM incident wave, the reflected phase is a constant, while for TE wave, the reflected phase is a linear function of the incident angle. The phase difference between them covers the range from-180° to 0°, and the polarization conversions from linear states to elliptical or circular states can be obtained by only adjusting the incident angle. Because no complex structures are employed, our proposal promises a simple approach for manipulating polarization conversion at both terahertz and optical frequencies.     

A linear-to-circular polarization converter based on I-shaped circular frequency selective surfaces

In this paper, a linear-to-circular polarization converter using a three-layer frequency selective surface based on Ishaped circular structure resonant is presented and investigated. Numerical simulations exhibit that when the normal ypolarized waves impinge on this device propagating towards +z direction, the two orthogonal components of the transmitted waves have a 90° phase difference as well as the nearly equal amplitudes at the resonant frequency of 7.04 GHz, which means that the left-hand circular polarization is realized in transmission. For validating the proposed design, a prototype which consists of 25 × 25 elements has been designed, manufactured and measured. The measured results are in good agreement with the simulated ones, showing that the polarization conversion transmission is over-3 dB in the frequency range of 5.22–8.08 GHz and the axial ratio is below 3 dB from 5.86 GHz to 7.34 GHz.     

Reflection and refraction of elastic wave at VTI-TTI media interface

We explore the physical phenomenon of acoustic waves induced at the interface between two different anisotropic rock media.Specifically,one medium is a transversely isotropic medium with a vertical axis of symmetry(VTI medium)and the other one is a transversely isotropic medium with a tilt axis of symmetry(TTI medium).By solving the Kelvin-Christoffel equation,an eighth-order polynomial is established for reflection and refraction angles,which is confirmed from SnelFs law.Three types of analytical expressions of the polarization coefficients of the induced waves are obtained corresponding to different incident angle regions.An effective algorithm has been developed for numerical analysis of the polarization coefficients.Applying characteristic anisotropic parameters reported in the literature,the influencing factors on reflection and refraction coefficients are analyzed,e.g.,the anisotropy,the tilt-angle of rock-layer,and the incident-angle.The calculated reflection and refraction coefficients have been rechecked for energy conservation.     

TeO2 single-crystal acoustooptic 2×2 switch for light beams of different wavelengths

The principles of acoustooptic switching of two light beams of different wavelengths by means of an acoustooptic interaction with two acoustic waves are examined. A version in which the acoustic waves form parallelograms and a version with strictly orthogonal propagation are considered. The latter version is the more attractive one when a TeO₂ single crystal is used as the acoustooptic cell. Experiments on the switching of two-color Ar laser radiation with wavelengths λ₁=0.5145 and λ₂=0.488 μm are carried out and demonstrate a high switching efficiency. On the whole, the experiment confirms the basic conclusions of the theory. Zh. Tekh. Fiz. 67, 66–71 (February 1997)     

A novel four-legged loaded element thick-screen frequency selective surface with a stable performance

<正>A thick-screen frequency selective surface(FSS) has not only a broad bandwidth but also the advantages of overcoming the multilayer FSS shortcoming of complex structure and low transmittance of centre frequency due to the cascade of FSSs,and this means it could potentially be applied in a stealth curved streamlined radome.However,there is an unsteadiness of centre frequency in a wide range of incident angles and another unsteadiness of polarization in a big incident angle.In order to solve these problems,in this paper we provide a novel four-legged loaded element thick-screen FSS.The structure is analysed and simulated using the mode matching method and moment method.The centre frequency,the transmittance of centre frequency,and bandwidth of the structure are investigated when some parameters including the polarization at a big incident angle and the incident angles of TE & TM waves are changed. The novel four-legged loaded element thick-screen FSS has better transmission properties with a better steadiness of polarization and incident angle independence.The novel structure of the four-legged loaded element thick-screen FSS provides a valuable reference for their application in a stealth curved streamlined radome.