Based on spin-flip model (SFM), the nonlinear dynamics of 1550 nm vertical-cavity surface-emitting lasers (VCSELs) subject to polarization-preserved optical feedback (PPOF) and orthogonal optical injection (OOI) are theoretically investigated. The results show that two linear polarization (LP) modes can be simultaneously stimulated and polarization switching (PS) can be observed, which is different from the case that only
Due to the short laser wavelength, almost all practical targets are rough. Surface elevations in rough targets will result in layovers in synthetic aperture ladar (SAL). High resolution SAL image with layovers will be different from the target picture taken by incoherent tools as digital camera. To investigate the layovers in SAL image, a simplified mathematical model is built by optics diffraction theory and a laboratory SAL is setup using 1550 nm tunable laser source. Layovers in SAL images, in both theoretical simulation and experimental demonstration, are carefully observed. Detailed results on various targets are illustrated.
This paper investigated characteristics of hybrid surface plasmon waveguiding modes in metal-clad Si/SiO2 waveguide. Mode characteristics are shown to be highly dependent on structure dimensions and polarization states. By controlling the structure dimensions, a compromise between propagation loss and field confinement can be made for the waveguiding modes. Here, the waveguide had been particularly designed to have very low loss, in which power is mainly confined in the high-index Si-core region to propagate. This waveguide showed excellent bending, isolation and coupling properties that is suitable for high-density integrated photonic circuits.
The influence of substrate temperature on microstructure, electrical and optical properties of in situ-textured zinc oxide (ZnO) films fabricated by metal organic chemical vapor deposition (MOVCD) had been investigated. Results indicated that the substrate temperature played a very important role on preparation of ZnO thin film. With the raising of temperature, firstly ZnO crystals were perpendicular to the substrate, then they were grown inclining toward the substrate, finally ZnO crystals grown in layers but not regular. Consequently, ZnO film surface morphology changed from smooth to a pyramid structure and then disappeared little by little. Moreover, it was also found in this study that ZnO film was characterized with high crystallinity, low resistivity (2.17 × 10-2) and high transmittance (>80%). These results suggested that ZnO thin film is suitable for front electrode of silicon thin film solar cell.
The objective assessment of image quality is important for image processing, which has been paid much attention to in recent years. However, there were few reports about objective quality assessment methods for geometrically distorted images. Different from the routine image degradation processing (for example, noise addition, contrast change and lossy compression), the geometric distortion results in the changes of the spatial relationship of image pixels, which makes the traditional quality assessment algorithms, such as mean square error (MSE) and peak signal to noise ratio (PSNR) failure to obtain expected assessment results. In this paper, a full reference image quality assessment algorithm is proposed specifically for the quality evaluation of geometrically distorted images. This assessment algorithm takes into account three key factors, such as distortion intensity, distortion change rate and line feature index for perceptual quality assessment of images. Experimental results in this study show that the proposed assessment algorithm not only is significantly better than those of the traditional objective assessment methods such as PSNR and structural similarity index measurement (SSIM), but also has significant correlation with human subjective assessment.
This paper reports a detailed theoretical investigation of strain effects on the performance of electroabsorption optical modulators based on the asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQWs) active layer. For this purpose, the electroabsorption coefficient was calculated over a range of AICD-SQWs strain from compressive to tensile strain. Then, the extinction ratio (ER) and insertion loss parameters were evaluated from calculated electroabsorption coefficient for transverse electric (TE) input light polarization. The results of the simulation suggest that the tensile strain from 0.05% to 0.2% strain in the wide quantum well has a significant impact on the ER and insertion loss as compared with compressive strain, whereas the compressive strain of the narrow quantum well from -0.5% to -0.7% strain has a more pronounced impact on the improvement of the ER and insertion loss as compared with tensile strain.
In this paper, a polymer electro-optic modulator has been designed and optimized using the full vectorial finite element method. For this purpose, the effects of magnesium oxide (MgO) and down cladding thicknesses, distance between two ground electrodes, hot electrode and modulator widths modulator on the key modulator parameters, such as microwave effective index
In this paper, a new structure of highly nonlinear low dispersion photonic crystal fiber (HN-PCF) by elliptical concentration of GeO2 in the PCF core has been proposed. Using finite difference time domain (FDTD) method, we have analyzed the dispersion properties and effective mode area in the HN-PCF. Simulative results show that the dispersion variation is within±0.65 ps/(nm?km) in C-band, especially 0.24 ps/(nm?km) in 1.55 μm wavelength. Effective area and nonlinear coefficient are 1.764 μm2 and 72.6 W-1?km-1 respectively at 1.55 μm wavelength. The proposed PCF demonstrates high nonlinear coefficient, ultra small effective mode area and nearly-zero flattened dispersion characteristics over C-band, which can have important application in all-optical wavelength conversion based on four wave mixing (FWM).
In this paper, a technique was numerically implemented to generate a frequency shift keying (FSK) radio-over-fiber (RoF) signal in optical domain. Due to the oscillator free generation of FSK signal, this scheme is highly stable with reduced complexity and extremely cost effective. The remote heterodyne detection method was used to detect the signal, where beating occurs to detect the FSK signal. With this scheme, it is able to efficiently generate FSK signal in the range of 60 and 75 GHz at 8 Gbit/s and effectively transmit it over 80 km link without degrading the signal shape and quality. The nonlinear threshold (NLT) point of the system has also been numerically analyzed to estimate the nonlinear tolerance of the system. Besides, the impact of transmission distance and polarization mode dispersion (PMD) was evaluated. Furthermore, the wavelength reuse for the uplink was implemented in the scheme by reusing the same wavelength for uplink that was used for signal generation at downlink. The whole process was performed in optical domain. Thus this scheme is very cost effective as the overall architecture of RoF system is simplified.
This paper has designed 2-channel dense wavelength division multiplexing (DWDM) chaotic system at the frequencies of 193.1 and 193.2 THz, respectively. The optical chaotic signals were produced by using the semiconductor laser that is numerically modeled by employing laser rate equations. These two channels were multiplexed and then propagated through single mode optical fiber (SMF) of 80 km length with dispersion compensating fiber of 16 km length. Erbium doped fiber amplifier (EDFA) was used to compensate the power losses in the SMF. In this paper, we investigated the effects of polarization mode dispersion (PMD) and nonlinearities especially stimulated Raman scattering (SRS) on 2 channel DWDM chaotic communication system by varying the length of the SMF and value of differential group delay (DGD).
The most important aim of nanotechnology development is to construct atomic-scale devices, and those atomic-scale devices are required to use some measurements that have ability to control and build in the range of these dimensions. A method based on super-heterodyne interferometers can be used to access the measurements in nano-scale. One of the most important limitations to increase the resolution of the displacement measurement is nonlinearity error. According to the base and measurement signals received by optical section of super-heterodyne interferometer, it is necessary for circuits to reconstruct and detect corresponding phase with target displacement. In this paper, we designed, simulated, and implemented the circuits required for electronic part of interferometer by complementary metal-oxide-semiconductor (CMOS) 0.5 μm technology. These circuits included cascade low-noise amplifiers (LNA) with 19.1 dB gain and 2.5 dB noise figure (NF) at 500 MHz frequency, band-pass filters with 500 MHz central frequency and 400 kHz bandwidth, double-balanced mixers with 233/0.6 μm ratio for metal-oxide-semiconductor field-effect transistors (MOSFETs), and low-pass filters with 300 kHz cutoff frequency. The experimental results show that the amplifiers have 19.41 dB gain and 2.7 dB noise factor, mixers have the ratio of radio frequency to local oscillator (RF/LO) range between 80 and 2500 MHz with intermediate frequency (IF) range between DC to 1000 MHz, and the digital phase measurement circuit based on the time-to-digital converter (TDC) has a nanosecond resolution.
Multi-threshold complementary metal-oxide-semiconductor (MTCMOS) is often used to reduce the leakage current in idle circuit. Ground bounce noise produced during a transition mode (sleep-to-active) is an important challenge in MTCMOS. In this paper, various noise-aware combinational MTCMOS circuit was used to evaluate the ground bounce noise. An intermediate mode was applied in the sleep-to-active mode transition to reduce the charge stored on virtual lines to real ground. The dependence of ground bounce noise on voltage, transistor size and temperature was investigated with different MTCMOS circuit technique. The peak amplitude of ground bounce noise was reduced up to 78.82%. The leakage current of the circuit was decreased up to 99.73% and the active power of the circuit was reduced up to 62.32%. Simulation of multiplier with different MTCMOS circuit techniques was performed on 45 nm CMOS technology.
In complementary metal oxide semiconductor (CMOS) nanoscale technology, power dissipation is becoming important metric. In this work low leakage voltage controlled ring oscillator circuit system was proposed for critical communication systems with high oscillation frequency. An ideal approach has been presented with substrate biasing technique for reduction of power consumption. The simulation have been completed using cadence virtuoso 45 nm standard CMOS technology at room temperature 27°C with supply voltage
In this paper, the photonic band gap (PBG) properties of two dimensional (2D) square lattice photonic crystal structures composed of rectangular cells were studied. The effect of refractive index, rectangles length and the ratio of width to length of the rectangles on the PBG properties of the structure with different configurations was investigated. It is found that the density of gaps in both modes (transverse electric (TE) and transverse magnetic (TM)) is high for structure composed of rectangular dielectric rods in air, while the density of the gaps is very low for structure composed of rectangular air pores in dielectric material.