Abstract:Whispering gallery mode (WGM)-enhanced nonlinear optical phenomena from crown-like nanostructure zinc oxide (ZnO) samples are observed. The samples are synthesized by vapor-phase transport method. The morphology and crystal structure are examined and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), and they are excited by femtosecond laser pulses with central wavelengths of 355 nm, 800 nm and 1150 nm, respectively. The typical stimulated emission presents a red shift compared with spontaneous emission, which is observed under the excitation of 355 nm with a relatively low threshold. The ultraviolet (UV) frequency up-conversion emission is obtained when the excitation pulse wavelengths are selected as 800 nm and 1150 nm, respectively. The peak position and the relationship between the emission intensity and excitation intensity demonstrate that the UV up-conversion photoluminescence (PL) is induced by two- and three-photon absorptions. The PL characteristics and their WGM-enhanced mechanism are investigated.

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Abstract:A band-pass microwave photonic filter (MPF) based on Lyot-Sagnac filter and two cascaded optical structures is demonstrated. In the experiment, a stabilized and tunable multi-wavelength optical source is obtained by slicing the broadband optical source (BOS) with a Lyot-Sagnac filter. A standard single-mode fiber (SMF) and a fiber ring resonator are cascaded to improve the mainlobe-to-sidelobe suppression ratio (MSSR) and Q-factor of the filter. The analysis shows that MSSR and Q-factor are improved by reducing the split ratio of the coupler or increasing the length of fiber in fiber ring resonator. The results have significant guidance for MPF design by choosing appropriate devices and parameters. Based on the analyses, a band-pass filter with MSSR of 53.54 dB and Q-factor of 4048 is achieved by choosing the split ratio of 0.01, the length of SMF of 30 km and the length of fiber in fiber ring resonator of 152.27 cm.

Abstract:An integration method of grating array with different periods and Fabry-Perot (FP) resonator with an all-dielectric singlecavity is proposed. It is based on the capacity of spatial separation of spectral component by the grating and band-pass characteristics of filter to achieve the multi-pass band filtering. The filtering response can be tuned by changing the period of the grating rather than the cavity length of the filter. Theoretically, the relationship of the grating period and the peak wavelength is obtained by using the transfer matrix method (TMM). The device is analyzed by adopting the finite-difference time-domain (FDTD) method. The filter array can cover the wavelengths ranging from 850 nm to 950 nm with the full-width at half-maximum (FWHM) of 11–28 nm, and is suitable for the integration of the micro-filter array and the detectors.

Abstract:A novel method is presented to enhance the resonant transmission contrast ratio in metal-insulator-metal (MIM) side-coupled-cavity waveguide. The finite difference time domain (FDTD) method is used to simulate and study the optical properties of the filter based on double side-coupled cavities structure with optofluidics pump system (OPS). This system provides a flexible way to change wavelength in the optical filter. In the numerical simulation, the resonant wavelengths from 1000 nm to 1550 nm are analyzed. We find that the double side-coupled cavities structure with OPS has higher on-resonance transmittance and better wavelength selectivity than the single side-coupled cavity structure with OPS.

Abstract:In this paper, an ultra compact cascaded microring filter consisting of two master rings with radius of 2.5 μm and two slave rings with radius of 1 μm is presented and studied theoretically. The filter with a very large free spectral range (FSR) of 206 nm, a deep extinction ratio of 23 dB, a high quality factor of 2.76×10⁵, and greatly suppressed spurious modes of less than 0.1 dB is achieved. The spectral responses of the filter are simulated by transfer matrix method, and the results show that this filter has a great potential of sensor application.

Abstract:In this paper, we propose and experimentally demonstrate an auto-bias control scheme for stabilizing a lithium niobate (LN) Mach-Zehnder modulator (MZM) at any operating point along the power transmission curve. It is based on that the bias drift would change the operating point and result in varying the output optical average power of the Mach-Zehnder modulator and its first and second derivatives. The ratio of the first to the second derivative of the output optical average power is used in the proposed scheme as the key parameter. The experimental results show that the output optical average power of the LN MZM hardly changes at the desired operating point, and the maximum deviation of output optical average power is less than ±4%.

Abstract:A new photolithography technique for 248 nm based on the interference of surface plasmon waves is proposed and demonstrated by using computer simulations. The basic structure consists of surface plasmon polariton (SPP) interference mask and multi-layer film superlens. Using the amplification effect of superlens on evanescent wave, the near field SPP interference pattern is imaged to the far field, and then is exposed on photo resist (PR). The simulation results based on finite difference time domain (FDTD) method show that the full width at half maximum (FWHM) of the interference pattern is about 19 nm when the p-polarization light from 248 nm source is vertically incident to the structure. Meanwhile, the focal depth is 150 nm for negative PR and 60 nm for positive PR, which is much greater than that in usual SPP photolithography.

Abstract:A fiber laser micro-nano sensor based on colloidal crystal structure is proposed in this paper. The fiber laser has stable frequency and narrow linewidth. It is realized by using an unpumped erbium-doped fiber (EDF) as the saturable absorber. The saturable absorber possesses the shape of taper. The laser threshold can be effectively reduced by the tapered saturable absorber. The tapered fiber coated with colloidal crystal as sensing unit is studied. The concentration of ethanol can be obtained from the detection of the output laser wavelength. It can be extensively used in chemical, medical and biological detections.

Abstract:To solve the cross-sensitivity to temperature of fiber Bragg grating (FBG) strain sensor, an effective method is firstly proposed for the discrimination of strain and temperature by using a single FBG adopting a special compensated structure, which is based on the thermal stress. The relationship of strain and temperature responses of FBG is analyzed theoretically. The experimental results are in agreement with the obtained theoretical analyses. This sensor structure has excellent characteristics, such as simple structure, easy manufacture and higher strain sensitivity.

Abstract:Based on the effect of total internal reflection (TIR) and photonic band gap, a new type of hexagonal-lattice hole-type silicon photonic crystal add-drop filter is proposed with a large circular hole as inner ring. The single mode operation is realized by compressing the two rows of photonic crystal above and below the line defect waveguide. Two-dimensional (2D) finite-difference time-domain (FDTD) method is then applied to investigate the impacts of side length of inner ring and coupling strength on its drop efficiency. It is also fairly compared with the traditional inner ring structure composed of hexagonal-lattice holes. The results show that the proposed structure can offer higher spectral selectivity than the traditional one. Two channel wavelengths of 1.425 μm and 1.45 μm can be simultaneously dropped at corresponding ports with drop efficiency of more than 90% and quality factor of 900 in the proposed configuration when the width of bus waveguide, the side length of inner ring and the coupling strength are 0.8 √3a, 4a and 0, respectively, where a is the lattice constant.

Abstract:An efficient light-trapping structure, which consists of the periodic Ag nanoparticles and a distributed Bragg reflector (DBR) with high reflectivity, is presented for the thin-film gallium arsenide (GaAs) solar cells. The effects of both Ag nanoparticles and DBR on the optical absorption of GaAs solar cells are theoretically investigated by using finite-difference time-domain (FDTD) method. The optimization process of parameters for the solar cell with both structures is analyzed systematically. The great absorption enhancement in GaAs layer is demonstrated, especially in the wavelength region near the GaAs band gap. It is observed that the superposition of the two effects excited by Ag nanoparticles and DBR results in the obvious absorption enhancement. By using cylindrical Ag nanoparticles and DBR together, the maximum enhancement factor of the solar cell is obtained as 4.83 in the simulation.

Abstract:Based on the normal pulsed laser ablation method, femtosecond pulsed laser deposition (fs-PLD) is adopted in vacuum for the production of TiO₂ nanoparticle-assembled films. We study the morphology and electronic characteristics of TiO₂ nanoparticle-assembled films deposited at different oxygen background gas pressures from high vacuum (～10^?4 Pa) to 100 Pa and different deposition time. Our results show that TiO₂ nanoparticle-assembled films obtained in high vacuum present both a mixture with rutile phase and anatase phase and a pure rutile phase. At the same time, there are more mesoporous structures in the film after annealing, which is beneficial for the enhancement of photocatalytic activity. In water splitting experiment, part of the TiO₂ nanoparticle-assembled films embedded with a small mass fraction of CdS nanoparticles (～5%) present an interesting photocurrent enhancement with a maximum value of ～0.2 mA/cm² under a solar simulator.

Abstract:The photoresponse and photoconductivity properties of micron-sized C₆₀ whiskers and sub-millimeter-sized C₆₀ clusters are successfully studied by the microfabrication technologies. According to the ultraviolet-visible-near infrared (UV-Vis-NIR) absorption spectroscopic study, a highly intense absorption is observed in the UV and visible light regions, which indicates probable applications in photoelectric devices. Furthermore, a large photocurrent is measured under the illumination of white light in nitrogen (N₂) atmosphere. The micron-sized C₆₀ whiskers and the sub-millimeter-sized C₆₀ clusters have different photoresponse curves under the same condition of measurement. A quick transformation of photoelectric response is detected in parallel multi-arranged micron-sized C₆₀ whiskers, but the recovery of the photocurrent of self-assembly sub-millimeter-sized C₆₀ clusters is much slower.

Abstract:Periodic triangle truncated pyramid arrays are successfully fabricated on the sapphire substrate by a low-cost and high-efficiency laser interference lithography (LIL) system. Through the combination of dry etching and wet etching techniques, the nano-scale patterned sapphire substrate (NPSS) with uniform size is prepared. The period of the patterns is 460 nm as designed to match the wavelength of blue light emitting diode (LED). By improving the stability of the LIL system and optimizing the process parameters, well-defined triangle truncated pyramid arrays can be achieved on the sapphire substrate with diameter of 50.8 mm. The deviation of the bottom width of the triangle truncated pyramid arrays is 6.8%, which is close to the industrial production level of 3%.

Abstract:To provide the differential quality of service (QoS) for different classes of packets and reduce the packet loss probability (PLP), a novel priority-based composite assembly scheme for optical burst switching (OBS) networks is proposed. The low and high packet classes are aggregated into a single burst simultaneously, and the highest-priority packets are placed in the middle, while the low-priority packets are at the tail and head of the burst. The priority is lowered gradually from the middle to the ends. Simulation results demonstrate that the proposed assembly strategy not only guarantees the integrity of the high-priority bursts, but also significantly reduces the average end-to-end delay of the bursts and the PLP of network. So it can adapt to the flexible network with QoS requirement.

Abstract:An effective mode selection is important for the multi-core photonic crystal fiber (PCF) to obtain good output. Talbot cavity is popular to lock the in-phase mode, but few satisfactory experimental results have been reported. In this paper, a dual-Talbot cavity with reflected mirrors on each side of PCF is designed to lock the in-phase mode. The design gains the advantage of in-phase mode against out-of-phase mode. What’s more, it can weaken the influence brought by the imperfect end facet of the fiber. The corresponding theoretical analyses and the experiment are taken. The experimental results suggest that the dual-Talbot cavity improves the capacity of mode selection.

Abstract:A novel hybrid switching architecture using optical circuit switching for intra-subnet communication and fiber channel (FC) for inter-subnet communication is proposed. The proposed scheme utilizes small-size arrayed waveguide grating routers (AWGRs) and legacy FC switches to construct the large-scale avionic network, thus has the potential of the lower latency, the satisfactory network bandwidth and the lower power consumption. The simulation results verify that the proposed architecture outperforms FC switched architecture in terms of real time performance and power consumption.

Abstract:Using three-layer vector field model, the dispersion characteristics and spectral response of long-period fiber gratings (LPFGs) with different cladding radii are analyzed. Both the numerical and experimental results demonstrate that LPFG’s resonant wavelengths shift towards much longer wavelength and the transmission depth is strengthened significantly by decreasing cladding radius. When the cladding radius is less than 20 μm, only a single resonant peak over a wavelength range of 600 nm (from 1200 nm to 1800 nm) is achieved, and the sensitivity of LPFG to external refractive index is enhanced significantly.

Abstract:The nematic liquid crystal (NLC) infiltrated photonic crystal fiber (PCF) used as a switch modulated by electric field is demonstrated. The switch consists of the infiltrated solid core PCF into which Bragg gratings are written. It is confirmed that the switch can achieve an accurate operation through measuring the reflected light with the change of electric field intensity from 1.4 kVrms/mm to 2.1 kVrms/mm. When the electric field intensity exceeds the threshold, the change of only 0.01 kVrms/mm can cause the wavelength shift of 1 nm. It is approved that the switch with such a structure provides a high sensitivity. The reflection peak is stabilized at about 15 dB which is high enough to separate from the factors such as system noise and error, and it can improve the control precision.

Abstract:A method for measuring the frequency stability of tunable laser is proposed by using confocal Fabry-Perot (F-P) interferometer. The F-P interferometer is used to get the output frequency of the laser as a reference, and the method eliminates the need of an independent optical source as a frequency reference. Using this technique, the frequency stability of the tunable external-cavity diode laser (ECDL) is measured to be 2.26×10^?9 with an integration time of 20 ms.

Abstract:For achieving the greatest sensitivity, numerical simulation is proposed to optimize the parameters of light force accelerometer (LFA). Firstly, the basic principle of the LFA is analyzed, and the mathematical model is established to describe the axial and radial optical trapping forces on microspheres in the fundamental mode Gaussian laser beam. Secondly, the axial and radial optical trapping forces applied on Mie spheres are simulated to obtain the optimal parameters of open-loop LFA. Results show that the sensitivity can reach 10³ μm/g. Finally, the LFA system is proposed based on the closed-loop scheme with dual beams. This can provide reference for the design and fabrication of LFA in future.