It is investigated the optical transmission properties of the Bragg microcavity sandwiched between Bragg reflectors which are composed of alternately arranged different dielectrics with positive and negative
refractive indices. The defect layer thickness, incident angle of incident wave, quasi-periodicity of the Bragg reflectors and dispersion of the negative-refractive-index dielectric all have influence on the transmission spectra. Comparison of optical bistable characteristics is presented for the following three nonlinear Bragg
microcavities. The first has Bragg reflectors with periodic structure containing non-dispersive negative-refractive-index dielectric; the second has the same structure as the first, however, the negative-refractive index dielectric is dispersive; the third also has periodic structure, however, where the Bragg reflectors are composed of alternately arranged dielectrics with different positive- refractive-indices. It is analyzed influence of the incident angle on the bistability of the nonlinear Bragg microcavity containing
In this paper, the propagation properties of the electromagnetic (EM) waves in one-dimension photonic crystals (PC) with nonlinear defects layer closed by periodic layered structures are reported. It is shown that in the presence of the nonlinearity, the transmission properties are strongly modulated by both the frequency and intensity, and the system exhibits bistability and multistability. Moreover, we find that both the switching-up and switching-down intensities of the bistable response can be made very low, when the intensity of the incident wave matches the defect mode of the structure. By use of the nonlinear finite-difference time-domain (NFDTD) method, we simulate the bistable threshold of the nonlinear photonic crystals with the kerr medium and the feasibility of making a switch utilizing such a structure. Bistable swithching with a low threshold intensity of 0.0007 kW/cm2 is obtained. The numerical experiments describenoptimal bistable switching in a nonlinear photonic crystal system. A photonic crystal enables the device to operate innsingle-mode fashion, as if it were effectively one-dimensional. This provides optimal control over the input and outputnand facilitates further large-scale optical integration.
We study the optical bistable properties in one-dimensional photonic crystal with symmetric structure (AB)N(D)M(BA)N, where A is high refractive index medium, B is low refractive index medium, D is defect layer, N is the number of layer periods at the left and right of the defect layer. M determines the thickness of the defect layer with Kerr medium. First, we analyze mechanisms producing bistability by the structure consisted of a nonlinear layer sandwiched between Bragg reflectors. Then by using the transfer matrix method, we calculate numerically the threshold value of the bistability switching in one-dimensional photonic crystals with structure (AB)N(D)M(BA)N. The investigations show that the number of layer periods (N) and the thickness of the defect layer (M) influence the threshold value of the bistability switching. We confirm the parameter of the bistability switching to produce the lower threshold value.
We present an analytical model and numerical experiments to describe optimal bistable switching involving photonic crystals nonlinear cavity. The involving photonic crystals nonlinear cavity is particularly suitable for large-scale all-optical integration. It is interesting to show that the refractive index of the system can be altered by the incident intensity when the incident frequency is tuned to the evanescent mode and the cavity contains a nonlinear Kerr medium. The response of this system to high-intensity incident waves is studied in detail. A cavity host a localized mode at 1.55 um with a Q of 4000 and a mode volume of 0.055 um3, we predict the onset of bistable reflection at incident powers of ~40 mW. The downstream reflections lead to hysteresis loops in the reflectivity that are topologically distinct from conventional Lorentzian-derived loops characteristic of isolated Fabry-Perot cavities. We provide a stability argument that reveals the unstable branches of these unique hysteresis loops, and we illustrate some of the rich bistable behaviors that can be engineered with such downstream sources, this fact may be used to obtain more flexibility in designing nonlinear devices.
On the basis of the investigation into organic thin films preparations and device, the Organic Light-Emitting Device (OLED) with mutual doped transitional layer was designed and fabricated, mutual doped layer of N,N’-bis-(1-naphthyl)-N,N’-diphenyl-1, 1’-biphenyl-4,4’-diamine (NPB) and aluminum tri(8-hydroxyquinoline)(Alq3) was used as emitting layer. Rate of NPB to Alq3 was 10:1 at anode to 1:10 at cathode. Light-emitting performance of the OLED was analyzed. Compared with conventional device in which Alq3 was used as emitting layer and blending device in which blending layer of NPB and Alq3 was used as emitting layer, the device performance of mutual doped transitional layer was evidently improved because of the interface and the waveguide effect were eliminated effectively.
We report on the properties of light transmission in one-dimension photonic crystals with defects of nonlinear dielectric material, photonic crystals have simple and complex period dielectric structure with multi-unit layer. In particular, we are interested in the transmittance of defect mode and the intensity enhancement factor of localized light. By the transfer-matrix method, we can calculate the electromagnetic waves transmission through a photonic crystal, the intensity enhancement factor of localized light can be obtained. The method calculated the transmission properties normal incident on a finite thickness slab of material. The numerical calculation shows that the transmission with defect layer of nonlinear dielectric material can induced to bring about change by the input intensity of light, and the change of the transmission shows the bistability. For simple and complex period dielectric in PC, if the threshold of input intensity be satisfied, the properties should be emerged easier. For complex period dielectric in PC, the transmission can show the property of complex results. When the total transmission is big, the bistability is also displayed. In addition, the character is seen to determine by the saturation absorption coefficient of the defect medium, the refractive index ratio and the number of layers.
The dispersion and self phase modulation is two important factors of the limit transmission distance in optical fiber communication. A novel method for measuring the dispersion slope of a long single-mode fiber was reported. By asymmetric modulation and Mach-Zehnder interferometer, the interferometer causes counter propagating wave to travel in test fiber with different propagation constants. We introduced the fast Fourier transform technique, the autocorrelation function is brought forward, and the information of the interference fringe is analysis with high speed so that the accuracy of signal is estimated. Successively, the experiment was performed on the test fiber to determine the nonlinear refractive index and self phase modulation, exact pulse bandwidth solution is presented. We found that
quantity was depends on the intensity of incidence light and the peak power, and the frequency spectrum is broadening clearly. The result shows that the intensity input and the peak power can affect the phase shift value.
A new reconstruction algorithm is presented, which transforms the plane image function into 2D Fourier series expansion and substitutes the projection vector of 2D Fourier series' orthogonal basic functions for that of the image function. By the minimum norm optimization criterion, the weighting coefficients are worked out and then the original image function can be obtained by inverse Fourier transformation. Computer simulations are made. The results show that the reconstruction time is less than one second and the maximum error can be less than 5%, the average error less than 1% by choosing proper approximation level.
In allusion to measuring the wavelength of plus laser using the FabryPerot etalon, we put forward a concrete method to detect and capture the plus signal: Firstly basing on the gray characteristic of the sequential images captured real-timely by image card and the trait of the interferogram, select the average gray-value of given region of image as the characteristic value, then acquire the characteristic value of each frame to draw the statistical histogram, calculate threshold based upon the statistical histogram through selecting reasonable algorithm. Secondly write callback program of image processing on the basis of the development library provided with the image card together to complete parallel image processing, image capturing and image processing at the same time. Judging whether this frame contains the plus information that we wanted through comparing the characteristic value with the predefined threshold, decide whether or not to give out the command of stopping capturing and freezing image. The key of this method is correctly calculating the threshold and redeveloping the user program of image card to complete parallel image processing.
Based on analyzed deficiency of traditional radar signal transmit system, advance optoelectronics technology and In- System Programmable (ISP) technology are used to realize general radar signal fiber transmit system. A special synchronous multiplex/demultiplex circuit is brought forward and realized with in-system programmable Large Scale Integrated (ispLSI). And Radar signal transmit quality is improved obviously.
The theory and experimental method of measuring flame temperature field with two-reference phase-shifting holographic interferometry and CT technique are studied in this paper. By recording the relative intensity distributions of three-step phase-shifting each view direction, we obtained the accurate phase distributions used to reconstruct the refractive index field. The cross section temperature field of a double-candle flame is measured, and the sources of experimental and other error are also discussed.