The properties of the linear chirped fiber grating (CFG) which is used in the true time delay unit of the optical beamforming networks (OBFNs) are studied intensively through theoretical analyses and numerical calculations. It is concluded that the dispersion of the CFG is equal to 1/(3Gc), where G is the chirp coefficient of CFG and c is the light speed. Based on this relationship, a simplified designing process of a CFG which satisfies the requirements of the OBFN is given. The simulation results are coincident with the theoretical conclusions.
Sputtering deposition coatings offer significant advantages on electron beam (EB) deposition, including high packing density, environmental stability and extremely low losses. But the inherent high compressive stress affects its application in high power laser system. This paper describes the technical feasibility of high damage threshold laser mirrors deposited by a novel remote plasma sputtering technique. This technique is based on generating intensive plasma remotely from the target and then magnetically steering the plasma to the target to realize the full uniform sputtering. The pseudo-independence between target voltage and target current provides us very flexible parameters tuning, especially for the films stress control. Deposition conditions are optimized to yield fully oxidized and low compressive stress single layer HfO2 and SiO2. The high damage threshold of 43.8 J/cm2 for HfO2/SiO2 laser mirrors at 1064 nm is obtained. For the first time the remote plasma sputtering is successfully applied in depositing laser mirrors with high performance.
We report the plasmon-enhanced polymer bulk-heterojunction solar cells with Ag nanoparticles (AgNPs) obtained via chemical method. Here, the AgNPs films with different particle densities are introduced between the poly (3,4-ethylene dioxythiophene) poly (styrenesulfonate) (PEDOT: PSS) buffer layer and the poly (3-hexythiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT: PCBM) layer. By improving the optical absorption of the active layer owing to the localized surface plasmons, the power conversion efficiency of the solar cells is increased compared with the control device. It is shown that the efficiency of the device increases with the density of AgNPs. For the device employing higher density, the resulted power conversion efficiency is found to increase from 2.89% to 3.38%, enhanced by 16.96%.
Using nanosecond pulse near-infrared and mid-infrared laser pulses as the pump source, we obtain terahertz wave sources via four-wave difference frequency mixing. From the coupled wave theory, we analyze the four-wave mixing process of GaSe crystal and alkali metal vapor in detail, get the analytical expression of terahertz wave output power, and discuss the conditions for achieving phase matching. By adjusting the pump frequency, the third-order nonlinear polarization of alkali metal vapor is resonance-enhanced. This program offers a new type of high-power terahertz radiation source.
In this paper, a model of photonic crystal temperature sensor based on crystal microcavity in a straight photonic crystal waveguide is proposed. The transmission characteristics of light in the sensor under different temperatures are simulated by using finite-difference time-domain (FDTD) method. The thermal expansion and thermal-optic effects of silicon are taken into account. The results show that the resonant wavelength of microcavity increases linearly as the temperature rising. The wavelength shift along with temperature is 6.6 pm /°C.
In this paper, a polymer electro-optic modulator is designed and simulated using the full vectorial finite element method. First order edge elements are used in finite element implementation, and the finite element technique is used to obtain modulator response thoroughly. From the numerical analysis, frequency dispersions of modulator’s important parameters, such as microwave effective index nm, microwave characteristic impedance ZC and microwave loss α, are extracted. Our design exhibits electrical bandwidth of 260 GHz and drive voltage of about 2.8 V·cm in this frequency.
The dependence of color points of white light on the composition of borophosphate glasses co-doped with europium (Eu) and terbium (Tb) has been investigated in terms of valence change of rare earth ions. Under ultraviolet (UV) excitation, the white light is observed to be from a combination of 4f65d → 4f7 band transition emission at 425 nm for Eu2+, 5D0 → 7FJ (J=1, 2) line-emissions at 593 nm and 611 nm for Eu3+, and 5D4 → 7F5 band transition emission at 545 nm for Tb3+. By varying the glass composition, the resultant emission color can be tuned efficiently. Eventually, the optimized white light with commission international de I’Eclairage (CIE) coordinate of (0.3382, 0.2763) and the correlate color temperature (CCT) at 5010 K are achieved.
Polycrystalline ZnO films are prepared using radio frequency magnetron sputtering on glass substrates which are sputteretched for different time. Both the size of ZnO grains and the root-mean-square (RMS) roughness decrease, as the sputteretching time of the substrate increases. More Zn atoms are bound to O atoms in the films, and the defect concentration is decreased with increasing sputter-etching time of substrate. Meanwhile, the crystallinity and c-axis orientation are improved at longer sputter-etching time of the substrate. The Raman peaks at 99 cm−1, 438 cm−1 and 589 cm−1 are identified as E2(low), E2(high) and E1(LO) modes, respectively, and the position of E1(LO) peak blue shifts at longer sputter-etching time. The transmittances of the films, which are deposited on the substrate and etched for 10 min and 20 min, are higher in the visible region than that of the films deposited under longer sputter-etching time of 30 min. The bandgap increases from 3.23 eV to 3.27 eV with the increase of the sputter-etching time of substrate.
A tunable photonic crystal filter with a twisted nematic liquid crystal layer is proposed. The defect modes spectra with varying incident angles are discussed in detail by 4×4 matrix method. The results show that the defect modes are mainly decided by the applied voltage when the incident angle is smaller than 8°. As the incident angle further increases, the band gap and the defect modes shift toward the shorter wavelength side, and the changes of the two modes are different. In the lower voltage range, the defect modes can be tuned not only by the applied voltage but also by the incident angle. In the higher voltage range, the defect modes can be further tuned by varying incident angle and the different modes can be separated from each other by a big incident angle.
In this paper, a new millimeter-wave (mm-wave) wavelength division multiplexing (WDM) system based on radio-over-fiber (ROF) technology is proposed. In this approach a multi-wavelength light source is obtained by supercontinuum (SC) technique, and mm-wave signals are obtained by using optical heterodyning method. We experimentally demonstrate the generation of optical carriers for 6-WDM channels, obtain 40 GHz mm-wave signals by employing optical heterodyne technique, and successfully achieve low error rate transmission of 2.5 Gbit/s in WDM channels over a distance of 25 km in a G.652 fiber. The experimental results verify that the proposed solution is feasible and cost effective.
The paper studies a kind of improved photonic crystal fiber gratings fabricated by CO2 laser heating method. The effective refractive index of cladding induced by periodic air hole deformation is computed using multipole method, and the relationship between the effective refractive index and the collapse of air-holes is discussed, thereby the modulation expression of effective refractive index is obtained. The grating transmission characteristics are simulated. The results indicate that with the diameter of air-holes increasing from 3.3 μm to 3.7 μm, the resonance wavelength shows blue-shift, the resonance peak intensifies, and the bandwidth becomes narrow. As the collapse degree of cladding enhances, the resonance wavelength shows red-shift, the transmission increases, and the bandwidth tends to narrow.
Influence induced by Raman effect on the noise characteristics of a depleted and lossy dual pump fiber optical parametric amplifier (FOPA) is investigated. Taking the Raman effect into account, the modified coupled amplitude equations are firstly built, then the influences of Raman effect on the Stokes and anti-Stokes wavelengths with different initial signal powers are further analyzed. Besides, the effect on the FOPA gain is also shown with the same initial signal power and constant noise figure (NF).
To meet the requirement of high tracking angular accuracy for the acquisition, tracking, and pointing (ATP) subsystem of the free-space optical communication, and provide the basis for the further optical communication between maritime mobile platforms, the experimental system, which executing part for the fine tracking is voice coil motor with high frequency and good performance for error compensation, is established, and the whole system can be controlled by personal computer. A series of experiments has been done for the simulation target of different uniform speed, and the data of tracking error for fine tracking and coarse tracking are collected, analyzed and evaluateds separately, and the real-time optical power of communication laser is also collected. The result shows that standard deviation for ATP system tracking error increases with the increase of target speed, while the range of tracking error appears to be no order. Furthermore, communication link can be hold for a long time.
By introducing orthogonal frequency division multiplexing (OFDM) technology, a visible light communication (VLC) system using a 5×5 white LED array is studied in this paper. The OFDM transmitter and receiver are modeled through MATLAB/Simulink tool. The electrical-optical-electrical (EOE) response of the VLC channel, which is also the response of the detector, is derived based on Lambert’s lighting model. Then the modeling on the overall OFDM/VLC system is established by combining the above three models together. The effects of the factors which include the digital modulation, Reed-Solomon (RS) coding, pilot form, pilot ratio (PR) and communication distance on the bit error rate (BER) of the system are discussed. The results show that through the use of RS coding, block pilot, quadrate phase shift keying (QPSK) modulation and a suitable pilot ratio about 1/3, under the communication rate about 550 kbit/s, the BER can be dropped to below 10–5, and the communication distance can reach 0.9 m.
A novel distributed optical fiber vibration sensing system based on polarization detection is proposed and demonstrated. A Faraday rotator mirror is employed at the end of the system, which eliminates the slow polarization variation of signal light and only responses to rapid polarization change caused by external vibration interference. Based on the sensing signal characteristics, the location of polarization disturbance point can be detected accurately. Experiments on polarization controller simulation and actual vibration detection show that a higher localization accuracy better than 1% is successfully obtained in 13.8 km, 21.2 km and 35.8 km sensing fibers systems.
In this paper, we demonstrate the acetylehe (C2H2) sensor with high sensitivity using a hollow-core photonic bandgap fiber (HC-PCF). Experiments for measuring C2H2 concentrations in gas mixture are performed. Using a 2 m-long HC-PCF as gas cell, the spectrum of acetylene at ν1+ν3 band has been measured, and the P11-branch has been selected for the purpose of sensing. A minimum detectivity of 143 parts per million by volume (ppmv) for the system configuration is estimated.
A new on-line remote particle analysis system based on image processing has been developed to measure microparticles. The system is composed of particle collector sensor (PCS), particle image sensor (PIS), image remote transmit module and image processing system. Then some details of image processing are discussed. The main advantage of this system is more convenient in particle sample collection and particle image acquisition. The particle size can be obtained using the system with a deviation abot less than 1 μm, and the particle number can be obtained without deviation. The developed system is also convenient and versatile for other analyses of microparticle for academic and industrial application.
In this paper, we describe the basic principles and system design of continuous wave cavity ring-down spectroscopy (CWCRDS). We also particularly study the nature and the behavior of a novel method to detune a laser and apply it to a cavity ring-down spectroscopy experiment. Both simulations and experiments are completed on the relation between the transmission characteristic and different reflectivities, as well as scanning speed. Output electric field equation is deduced. It has been investigated that how photons are coupled to the cavity and how to accumulate the intensity and leak out of the cavity as a function of time. It is noted that both accumulation of intensity and decay times decrease, and the oscillation amplitude increases as the reflectivity increases. Relative intensity increases with decreasing scanning velocity. Additionally, the simulations show that a non-detuned cavity displays the transmitted signals which are highly dependent on the mirror reflectivity and piezoelectric translator (PZT) modulation speed. Simulations also display that the laser switching off is different from detuning.
The field entropy of the system with two moving atoms interacting with the coherent state is investigated by means of the full quantum theory. Under the different initial states with two atoms, the influences of the light field intensity and the atomic motion on the field entropy are discussed. The results indicate that the motion of the atoms leads to strict periodicity in the field entropy evolution. When the two atoms are in the Bell state |β11〉 initially, the system is in a completely disentangled state. For the atoms initially at other Bell states, the field periodically entangles with the atoms.
Based on the definition of second order moment and the approximate three-dimensional analytical formula for probe detected laser beam passing through a cat-eye optical lens with center shelter and oblique detector, the analytical expression of the encirclement power ratio of the cat-eye effect reflected light under far-field condition has been deduced. Variable laws of light intensity at the return place and encirclement power ratio are performed by numerical calculation, and are analyzed physically. The results show that the light intensity at the return place decreases monotonically with the increases of the diameter, incidence angle, tilted angle of the detector and the center shelter ratio, but the relationships between these parameters and the encirclement power ratio are all nonmonotonic. The reasonable choice of the focal shift size would result in the largest light intensity at the return place and the largest erirclenent power ratio.