Abstract:Theoretical and experimental studies on the tilted fiber Bragg grating (TFBG) temperature and strain sensing characteristics are conducted. The TFBG is stuck to the surface of the beam along the axis direction. When the free end of the beam is forced, both the strain and temperature will induce wavelength shifts. The temperature characteristic of TFBG cladding modes is similar to that of the core mode while the strain characteristics of TFBG core mode and cladding modes are different. A novel me...

Abstract:In this paper, a ferroelectric polyvinylidene fluoride (PVDF)-coated porous polymer fiber based surface plasmon resonance (SPR)-like gas sensor is proposed theoretically in the terahertz (THz) region based on the total internal reflection (TIR). In such a sensor, the phase matching is achieved by changing the fiber parameters and the plasmon-like phenomenon at the interface between the ferroelectric polyvinylidene fluoride (PVDF) layer and the gaseous analyte is discussed. Using a fullvector finite-element method, the core-mode loss of the fiber is calculated to measure the resolution of the sensor. The amplitude resolution is demonstrated to be as low as 1.45 × 10⁻⁴ RIU, and the spectral resolution is 1.30 × 10⁻⁴ RIU in THz region, where RIU means the refractive index unit.

Abstract:The parity generators and the checkers are the most important circuits in communication systems. With the development of multi-valued logic (MVL), the proposed system with parity generators and checkers is the most required using the recently developed optoelectronic technology in the modified trinary number (MTN) system. This system also meets up the tremendous needs of speeds by exploiting the savart plates and spatial light modulators (SLM) in the optical tree architecture (OTA).

Abstract:Based on the Helmholtz equations, the full-vector finite element method (FEM) accompanied with the shifted iteration algorithm is used to analyze in-phase supermodes of a 19-core photonic crystal fiber. The effects of fiber structural parameters on the in-phase supermode field are also studied. The results indicate that the form of the fiber structure plays a key role on coupling of fiber cores, and the desired mode shapes which have the same amplitude in each core can be obtained by choosing the appropriate diameter of airhole. The results show a viable option for further achieving high-power laser output.

Abstract:A symmetric five-layer slab waveguide with anisotropic and dispersive left-handed material (LHM) in the core and righthanded material (RHM) in other layers is investigated. Through Maxwell’s equations and a transfer matrix method, the dispersion equations for the TE oscillating guided modes are obtained. Under consideration of two extremely anisotropic cases, some mode dispersion curves are plotted. The zero-order TE oscillating guided mode exists. Meanwhile, with the increase of mode number, their dispersion curves move to left or right, corresponding to positive or negative dielectric permittivity and magnetic permeability in the longitudinal direction. Besides, as the core thickness increases, mode dispersion properties change and three propagation properties appear: positive group velocity, negative group velocity and zero group velocity. The negative group velocity indicates the characteristics of the left-handed materials, and the zero group velocity implies that electromagnetic waves are trapped in the waveguide completely.

Abstract:An all-optical header extraction scheme based on the reflective semiconductor optical amplifier (RSOA) is presented, which can be used to process variable-length and bit-rate transparent packets. Through selecting the appropriate carrier-lifetime of the RSOA, the payload pulses obtain smaller gains than header pulses and are considered to be compressed. By using the reflective structure, the header pulses can acquire larger gains than the payload twice, and the contrast radio (CR) is improved. The simulation results show that the CRs can reach 22.8 dB and 18 dB for the packets with header pulses at the rates of 2.5 Gb/s and 10 Gb/s, respectively, and these values can be optimized through properly selecting the structure parameters, such as the small-signal gain and saturation energy.

Abstract:A novel design of bimorph deformable mirror (DM) is presented. Compared with the bilayer lead zirconium titanate (PZT) ceramic structure, the bilayer lead magnesium niobate (PMN) ceramic structure has greater surface displacement at the same thickness. The static simulation of the bilayer PMN bimorph deformable mirror with the finite element analysis (FEA) shows that the prototype has a stroke of above ± 23 μm, response time of 3 ms and nearly linear displacement characteristic with voltage rising. The results of simulation indicate that the bilayer PMN bimorph DM can satisfy the basic requirements of adaptive optics (AO) systems.

Abstract:For the surface plasmon resonance (SPR)-based optical fiber sensor with four-layer configuration (fiber core/metal/sensing layer/sample), the effects of different metals, different models (Lorentz-Drude model and Drude model) for the same metal, the thickness of metal layer, and the refractive index (RI) of sample on the transmitted spectra are investigated. The calculated results show that the real part of the refractive index of metal layer has the greatest effects on the sharp degree of the transmitted dip. Moreover, the dispersion function under four-layer configuration can be used to understand the relationship between the resonance wavelength and the thickness of metal layer.

Abstract:By using the proposed 3-D mode propagation analysis method and point-matching method, a polymer multimode interference (MMI) Mach-Zehnder interferometer (MZI) electro-optic (EO) switch is designed and optimized for enhancing the EO modulating efficiency and matching the impedance and the velocity. The designed switch possesses low driving voltages of ±1.375 V with a short EO active region length of 5 mm under 1550 nm wavelength, and the estimated cutoff switching frequency is up to 263 GHz due to the less mismatch between the lightwave velocity and microwave velocity. The 3-dB lightwave bandwidth is 60 nm, and within the wavelength range of 1520–1580 nm, the insertion loss and crosstalk are less than 6.71 and −30 dB, respectively.

Abstract:The band gap of two-dimensional (2D) photonic crystals with the square lattice of rotational square air columns made of GaAs and Ge is analyzed by the plane wave expansion method. The effects of dielectric refractive index and crystal structures on the absolute photonic band gap are investigated. The results show that the maximum absolute photonic band gap emerges when the square air columns are rotated for 30° and the filling ratio f of the medium is 0.3276. It is also noticed that absolute photonic band gaps appear when the refractive index of the medium (n) is 2.61. When n=3.70, the width of the absolute photonic bandgaps reaches the maximum.

Abstract:In this paper, the photonic band gap of photonic crystals with chiral and negative-index materials alternately is investigated. It is shown that this kind of photonic crystal exhibits very wide photonic band gap. The photonic crystals with a defect layer have a narrow defect mode in the band gap, which can be used as a very good filtering material by choosing the parameters of the defect layer properly.

Abstract:Because of the zero dispersion wavelength (ZDWL) random fluctuations, the gain and noise figures deteriorate in optical parametric amplifiers based on highly nonlinear fibers (HNLFs). The detrimental role of ZDWL fluctuations on the gain and noise performance in dual-pump fiber optical parametric amplifiers (FOPAs) is presented. Numerical investigations of noise figure (NF) for different fibers with random fluctuation are analyzed. The noise figures for different fibers are varying even if the random fluctuation is small. Through choosing HNLFs with low ZDWL fluctuation and large nonlinear coefficient, high-gain and low-noise performance can be obtained.

Abstract:The mechanism of a non-polarizing beam splitter (NPBS) with asymmetrical transfer coefficients causing the rotation of polarization direction is explained in principle, and the measurement nonlinear error caused by NPBS is analyzed based on Jones matrix theory. Theoretical calculations show that the nonlinear error changes periodically, and the error period and peak values increase with the deviation between transmissivities of p-polarization and s-polarization states. When the transmissivity of p-polarization is 53% and that of s-polarization is 48%, the maximum error reaches 2.7 nm. The imperfection of NPBS is one of the main error sources in simultaneous phase-shifting polarization interferometer, and its influence can not be neglected in the nanoscale ultra-precision measurement.

Abstract:A method based on morphological granulometric analysis for the speckle image is presented to estimate the scattering coefficient of the scattering media. It is experimentally demonstrated that the average granulometric size, derived from the successive opening operations, is approximately in inverse proportion to the scattering coefficient of the sample in a broad illumination. Furthermore, a theoretical model based on the spatial correlation function of the back scattered intensity for the experimental phenomenon is reported. The analysis demonstrates that the explicit theoretical relationship between average granulometric size of speckle and scattering coefficient is established, and the theoretical prediction is consistent with the experimental result.

Abstract:To improve the frequency stabilization of laser diode in the laser frequency scanned interferometric metrology, a modified method is proposed by using a fiber ring resonator. The theoretical analysis of this modified method is performed. Moreover, the Pound-Drever-Hall (PDH) technique is employed to obtain the frequency discrimination curve of a fiber ring resonator, whose finesse is 1260 and line-width is 270 kHz. The simulated results show that the curve has a steep slope near the resonant frequency, which proves the sensitivity of this system to the frequency deviation, so the modified method has great potential for the frequency stabilization of a laser diode.

Abstract:In the laser warning system, a non-mechanical scanning Fabry-Perot (F-P) type laser warning method and its crucial component-laser incident sensor design method are brought out, and the F-P etalon with the interferometric filter combination is adopted. For the incident laser pulse with a certain wavelength, the transmittance difference of the interferometric filters is independent with polarization of incident light, and descends almost linearly as the incident angle gets wider. A laser incident angle sensor experimental platform is built up, and the experiment is carried out with a given laser range finder. As the results indicate, when the incident angle is less than 5°, the transmittance difference measured by the laser angle sensor is significantly lower, and the deviation is more than 10%. While the incident angle is greater than 10°, the deviation is reduced significantly.

Abstract:A novel fiber grating vibration demodulation system, based on 2×2 and 3×3 couplers, is designed. Based on the phase unwrapping algorithm, the three-way asymmetrical output of the 3×3 coupler and demodulation state characteristics of the system when the vibration signal includes high harmonic waves are analyzed in simulations. The result shows that when the three-way output is asymmetrical, the maximum deviation of demodulation signal is 1.625%, and when the vibration signal includes high harmonic waves, the maximum deviation of demodulation signal is 0.9%. The corresponding experiment is conducted. The experimental result shows that the dynamic resolution of the system is 25.22 nɛ / $ \sqrt {Hz} $ \sqrt {Hz} when the vibration pitch is 5.5 Hz.

Abstract:A modified aperture-synthesis method is reported to improve the resolution of a reconstructed image in digital holography by a single hologram. A series of sub-holograms incoherently overlapped on a CCD are recorded as a single aperture-synthesized digital hologram. The angular division multiplexing is introduced to both the object and the reference path for holographic recording. The final super-resolved image is obtained by synthesizing the several reconstructed images. In the experiment, a two-dimensional transparent USAF resolution test target is used. The result demonstrates that the resolution of the reconstructed image is improved from 16.00 lp/mm to 22.64 lp/mm in the horizontal direction.

Abstract:With parametric down-conversion sources (PDCSs), the nonorthogonal decoy state protocol based on one vacuum and two weak decoy states is presented. The detection events on Bob’s side are divided into two groups depending on whether Alice gets a trigger or not: triggered components and nontriggered components. The triggered components are used to estimate the fractions and error rates of single-photon and two-photon pulses, and then the final secure key rate is deduced. Besides, both triggered and nontriggered components are used to deduce a more accurate value of the key generation rate. The simulation of the final key generation rate over transmission distance shows that the first method can obtain a key generation rate close to the theoretical limit of the infinite decoy state protocol, while the second method is better.