Abstract:A plasmonic refractive index sensor based on metal-insulator-metal (MIM) waveguide-coupled structure is proposed and demonstrated in this paper. The physical mechanism of the device is deduced, and the finite difference time domain (FDTD) method is employed to simulate and study its index sensing characteristics. Both analytic and simulated results show that the resonant wavelength of the sensor has a linear relationship with the refractive index of material under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of the resonant wavelength. The results show that the sensitivity of the sensor can exceed 1600 nm/RIU, and it can be used in chemical and biological detections.

Abstract:An up-tapered Mach-Zehnder interferometer (MZI) is proposed and demonstrated. By applying a modification setting of an existing program of the fusion splicer, two up-tapers are fabricated by pushing both sides of the fiber to the middle. It is found that the maximum extinction ratio reaches up to 20 dB. With the fiber length of 6.3–49 cm between the two up-tapers, the free spectral range (FSR) changes from 10.7 nm to 1.3 nm. Besides, the wavelength of maximum extinction ratio shifts to the shorter wavelength in the scope of tens of nanometers, while the elongation changes from 0% to 0.23%.

Abstract:Aiming at the problem that there isn’t any standardized calibration method for the performance index of surface plasmon resonance (SPR) sensor, the calibration method for key performance indices of SPR sensor is summarized and proposed based on the comparison of relative methods and definition of each index. Experimental data of sucrose solutions with various concentrations are obtained by the self-building SPR instrument, and then the calibration method is used to determine the performance indices, such as noise, drift, sensitivity, resolution, linearity, dynamic range and reproducibility. Experimental results show that the definition of indices is reasonable, and the calibration method is correct, which has great significance for performance evaluation of SPR sensor.

Abstract:A compact ammonia gas sensor with two gas chambers is proposed in this paper, whose core sensing device is a U-bending microring resonator. The waveguides of ring part and feedback part in this resonator are made of silicon on insulator (SOI) ridge waveguide covered with ZnO nanocrystals which are sensitive to ammonia gas. The sensor can measure two groups of gas samples simultaneously. By computer simulation, we obtain the clear sensitivity curves of two gas chambers in ammonia sensor when the gas concentration increases from 0 to 4‰. The gas concentrations in two chambers can be obtained from one output spectrum, which significantly reduces the material and time consumption.

Abstract:A 2×2 cross/bar polymer electro-optic (EO) routing switch is proposed, which is composed of two passive channel waveguides and two active EO polymer microrings with bending radius of only 13.76 μm. Detailed structure, theory and formulation are provided to characterize the output power of the switch. For obtaining fundamental mode propagation, small bending loss and phase-matching between channel waveguide and microring resonator (MRR) waveguide, the structural parameters are optimized under the wavelength of 1550 nm. Analyses and simulations on output power and output spectra indicate that a switching voltage of 5 V is desired to realize the exchange between cross state and bar state, the crosstalk under cross state and that under bar state are about ?28.8 dB and ?39.9 dB, respectively, and the insertion losses under these two states are about 2.42 dB and 0.13 dB, respectively. Compared with our four EO switches reported before, this device possesses ultra-compact size of 0.233 mm×0.233 mm as well as low crosstalk and insertion loss, and therefore it can serve as a good candidate for constructing large-scale optical routers or switching arrays in photonic network-on-chip (NoC).

Abstract:A surface plasmon resonance (SPR) sensor based on a multi-core photonic crystal fiber (PCF) is presented in this paper. There is only one analyte channel positioned in the center of the PCF cross section, rather than several closely arranged analyte channels around the central core. So the design of this sensor not only reduces the consumption of gold and samples, but also effectively avoids the interference between neighboring analyte channels. Optical field distributions of this fiber at different wavelengths and the sensing properties of this sensor are theoretically analyzed and discussed using finite element method (FEM). Simulation results confirm that both the thickness of metallic layer and the fiber structural parameters have significant effect on sensing performance. The amplitude sensitivity of the sensor is found to be 1.74×10^?5 RIU, and the spectral sensitivity is 3300 nm/RIU, corresponding to a resolution of 3.03×10^?5 RIU. Finally, in order to achieve PCF-SPR sensing characteristics, an experiment design scheme based on spectroscopic detection method is proposed.

Abstract:Blue phosphorescent organic light-emitting diodes (OLEDs) are fabricated by utilizing the hole transport-type host material of 1,3-bis(carbazol-9-yl)benzene (MCP) combined with the electron transport-type host material of 1,3-bis (triphenylsilyl) benzene (UGH3) with the ratios of 1:0, 8:2 and 6:4, and doping with blue phosphorescent dopant of bis(4,6-difluorophenylpyridinato-N,C2)picolinatoiridium (FIrpic). The device with an optimum concentration proportion of MCP:UGH3 of 8:2 exhibits the maximum current efficiency of 19.18 cd/A at luminance of 35.71 cd/m² with maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (0.1481, 0.2695), which is enhanced by 35.7% compared with that of 1:0 with (0.1498, 0.2738). The improvements are attributed to the effective carrier injection and transport in emitting layer (EML) because of mixed host materials. In addition, electron and exciton are confined in the EML, and 4,4′,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) and Di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC) have the high lowest unoccupied molecular orbital (LUMO) energy level and triplet exiton energy.

Abstract:A novel approach for the implementation of microwave photonic filter with positive and negative coefficients based on an unbalanced Mach-Zehnder modulator (MZM) is proposed. In the proposed filter, a microwave signal to be filtered is applied to an unbalanced MZM. Thanks to the unbalance between the two arms of the modulator, a π phase shift is obtained by adjusting the wavelength interval between the adjacent wavelengths, which leads to the generation of the positive and negative coefficients. The theoretical fundamentals of the design are described, which show that the required unbalanced MZM in the scheme can be well fabricated by the current technology, and the required other components, including the wavelength multiplexer, are also commercially available devices. An eight-tap microwave photonic filter with positive and negative coefficients is demonstrated. The tunability and reconfigurability of the eight-tap microwave photonic filter are also investigated to verify our approach.

Abstract:A novel dual-loop optoelectronic oscillator (OEO), which is constructed based on all optical signal processing, is proposed and analyzed. By inserting an erbium-doped fiber amplifier (EDFA) and a fiber Bragg grating (FBG) on the optical domain, the amplification and filter are implemented in the OEO loop. The performance of the OEO is improved without any electronic filter or electronic amplifier. A theoretical analysis is performed, and the generated microwave signal exhibits good performance with phase noise lower than ?120 dBc/Hz at 10 kHz and a high side-mode suppression ratio (SMSR).

Abstract:Ultraviolet (UV)-laser induced quantum well intermixing (QWI) technique can generate large multiple bandgap blue shifts in III-V quantum well semiconductor heterostructure. The application of the UV-laser QWI technique to fabricate multi-bandgap photonic devices based on compressively strained InGaAsP/InP quantum well laser microstructure is reported. We show that under certain UV-laser irradiation conditions, the photoluminescence (PL) intensity can be enhanced, and the full width at half maximum (FWHM) linewidth can be reduced. The blue shift of bandgap can reach as large as 145 nm, while the PL intensity is about 51% higher than that of the as-grown material. Experimental results of post growth wafer level processing for the fabrication of bandgap-shifted waveguides and laser diodes are presented.

Abstract:The use of Pr³⁺ co-doping for great enhancement of mid-infrared (mid-IR) emissions at 2.9 μm and 2.4 μm is investigated in the Ho³⁺/Pr³⁺ co-doped LiYF₄ crystals. With the introduction of Pr³⁺ ions, the fluorescence lifetime of Ho³⁺:⁵I₇ level is 2.15 ms for Ho³⁺/Pr³⁺co-doped crystal, and the lifetime for Ho³⁺ singly doped crystal is 17.70 ms, while the lifetime of Ho³⁺:⁵I₆ level decreases slightly from 2.11 ms for Ho³⁺:LiYF₄ to 1.83 ms for Ho³⁺/Pr³⁺:LiYF₄. It is also demonstrated that the introduction of Pr³⁺ greatly increases the mid-infrared emission of Ho³⁺:⁵I₆→⁵I₇ which depopulates the Ho³⁺:⁵I₇ level, while it has little influence on the Ho³⁺:⁵I₆ level, which is beneficial for greater population inversion and laser operation. The analysis on the decay curves of the 2.0 μm emissions in the framework of the Inokuti-Hirayama model indicates that the energy transfer from Ho³⁺ to Pr³⁺ is mainly from electric dipole-dipole interaction. The calculated efficiency of energy transfer from Ho³⁺:⁵I₇ to Pr³⁺:³F₂ level is 87.53% for Ho³⁺/Pr³⁺ (1.02%/0.22%) co-doped sample. Our results suggest that the Ho³⁺/Pr³⁺ co-doped LiYF₄ single crystals may have potential applications in mid-IR lasers.

Abstract:The high phonon energy oxide of B₂O₃ is introduced into the Er³⁺/Ce³⁺ co-doped tellurite-niobium glasses with composition of TeO₂-Nb₂O₅-ZnO-Na₂O. The absorption spectra, 1.53 μm band fluorescence spectra, fluorescence lifetime and Raman spectra of Er³⁺ in glass samples are measured together with the calculations of Judd-Ofelt spectroscopic parameter, stimulated emission and absorption cross-sections, which evaluate the effect of B₂O₃ on the 1.53 μm band spectroscopic properties of Er³⁺. It is shown that the introduction of an appropriate amount of B₂O₃ can further improve the 1.53 μm band fluorescence intensity through an enhanced phonon-assisted energy transfer (ET) between Er³⁺/Ce³⁺ ions. The results indicate that the prepared Er³⁺/Ce³⁺ co-doped tellurite-niobium glass with an appropriate amount of B₂O₃ is a potential gain medium for the 1.53 μm bandbroad erbium-doped fiber amplifier (EDFA).

Abstract:The preparation of nanometer aluminum nitrogen (AlN) films with uniform lattice arrangement is of great significance for the manufacture of high-frequency surface acoustic wave (SAW) device. We put forward the two-step growth method and the annealing treatment method for the deposition of (100) AlN thin films. The results show that when the sputtering pressure is 1.2 Pa and the ratio between N₂ and Ar is 12:8, the influence of lattice thermal mismatch and anti-phase is the smallest during the nucleation growth at low-temperature stage of (100) AlN/(100) Si films. The root-mean-square (RMS) surface roughness of AlN prepared by the two-step method is reduced from 6.4 nm to 2.1 nm compared with that by common deposition process.

Abstract:Hydrogenated silicon nitride (SiN _x :H) thin films are deposited on p-type silicon substrates by plasma enhanced chemical vapor deposition (PECVD) using a gas mixture of ammonia and silane at 230 °C. The chemical compositions and optical properties of these films, which are dealt at different annealing temperatures, are investigated by Fourier transform infrared (FTIR) absorption spectroscopy and photoluminescence (PL) spectroscopy, respectively. It is shown that the FTIR presents an asymmetric Si-N stretching mode, whose magnitude is enhanced and position is shifted towards higher frequencies gradually with the increase of the annealing temperature. Meanwhile, it is found that the PL peak shows red shift with its magnitude decreasing, and disappears at 1100 °C. The FTIR and PL spectra characteristics suggest that the light emission is attributed to the quantum confinement effect of the carriers inside silicon quantum dots embedded in SiN _x : H thin films.

Abstract:A novel construction method of quasi-cyclic low-density parity-check (QC-LDPC) code is proposed based on the finite field multiplicative group, which has easier construction, more flexible code-length code-rate adjustment and lower encoding/decoding complexity. Moreover, a regular QC-LDPC(5334,4962) code is constructed. The simulation results show that the constructed QC-LDPC(5334,4962) code can gain better error correction performance under the condition of the additive white Gaussian noise (AWGN) channel with iterative decoding sum-product algorithm (SPA). At the bit error rate (BER) of 10^?6, the net coding gain (NCG) of the constructed QC-LDPC(5334,4962) code is 1.8 dB, 0.9 dB and 0.2 dB more than that of the classic RS(255,239) code in ITU-T G.975, the LDPC(32640,30592) code in ITU-T G.975.1 and the SCG-LDPC(3969,3720) code constructed by the random method, respectively. So it is more suitable for optical communication systems.

Abstract:A network structure surface-enhanced Raman scattering (SERS)-active substrate is fabricated by adding Ag sol dropwise on adhesive tape. Scanning electron microscope (SEM) is employed to characterize the structure of the as-prepared substrate. The substrate shows great SERS enhancement ability and good uniformity by using p-aminothiophenol (PATP) as probe molecules. The detection of crystal violet (CV) in aqueous solution is demonstrated, and the detection limit is as low as 10^?12 M with the aid of the substrate. The results indicate that the proposed method is a potential approach for the fabrication of SERS substrates.

Abstract:Based on wide-band infrared (IR) light source and dual-channel pyroelectric detector with detection channel of 4.66 μm and reference channel of 3.95 μm, a differential mid-infrared (MIR) carbon monoxide (CO) detector is designed and implemented. In order to reduce the detection limit and improve the detection sensitivity, an open spherical mirror chamber is designed and fabricated according to the divergence angle of the light source. The CO detection system is established using the welded and debugged detection circuits, a series of CO gases with different concentrations are prepared, and gas concentration calibration experiment is carried out. Experimental results indicate that after the amplifying circuit, the signal-to-noise ratios (SNRs) of the two channels are 17.58 dB and 18.46 dB, respectively, and the detection error of this system is less than 9% in 0%–4% measuring range. The detection sensitivity in the low concentration range is approximately 0.05%. 6 h measurement on the 0 ppm sample gas shows that the fluctuation range is about ±0.02%, and the measurement standard deviation is about 0.89%.

Abstract:Combining heralded pair coherent state (HPCS) with passive decoy-state idea, a new method is presented for quantum key distribution (QKD). The weak coherent source (WCS) and heralded single photon source (HSPS) are the most common photon sources for state-of-the-art QKD. However, there is a prominent crossover between the maximum secure distance and the secure key generation rate if these two sources are applied in a practical decoy-state QKD. The method in this paper does not prepare decoy states actively. Therefore, it uses the same experimental setup as the conventional protocol, and there is no need for a hardware change, so its implementation is very easy. Furthermore, the method can obtain a longer secure transmission distance, and its key generation rate is higher than that of the passive decoy-state method with WCS or HSPS in the whole secure transmission distance. Thus, the limitation of the mentioned photo sources for QKD is broken through. So the method is universal in performance and implementation.

Abstract:Because of the circular symmetry of a completely coherent radially polarized beam, the azimuthal intensity component is zero when it is focused by a high numerical aperture (NA) objective. In this paper, we show that such a conclusion is not tenable under the illumination of partially coherent beam whose coherent property depends on the azimuthal angle. Taking the Gaussian Schell-model (GSM) beam for an example, the tight focusing property of a partially coherent beam is studied, and the intensity and its radial, azimuthal and longitudinal components are particularly researched. The results show that the percentage of the components on the total intensity depends on the correlation length of the partially coherent beam. The azimuthal intensity component is produced under the illumination of partially coherent beam.

Abstract:The eigenvector set of |φ(x, r ₁, r ₂)〉 with three compatible operators ( $\hat x_1 + \hat x_2 + \hat x_3$ , $\hat p_2 + \hat p_3 - 2\hat p_1$ and $\hat p_3 - \hat p_2$ ) is constructed by virtue of Radon transformation of the Wigner operator and the technique of integration within an ordered product (IWOP) of operators. Its entanglement property is then revealed by deriving its standard Schmidt decomposition. |φ(x, r ₁, r ₂)〉 makes up a new quantum mechanical representation. A new three-mode squeezing operator is found by using this entangled state representation.