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Abstract:

Abstract:A flat response silica-based arrayed waveguide grating (AWG) with 40-channels and 0.8 nm (100 GHz) channel spacing has been designed and fabricated using multimode interferometer (MMI) at the end of input waveguide. Proper width of MMI is theoretically optimized using beam propagation method (BPM). An AWG with a 16 μm width MMI is fabricated experimentally. The measurement results show that the 3 dB bandwidth is 0.62 nm, insertion loss (IS) ranges from 5.2 dB to 7.5 dB, and the crosstalk is less than —20 dB. The 3dB bandwidth, channel numbers and channel spacing of the AWG agree well with the simulation values. Supported by the National Natural Science Foundation of China (No. 60477035, No. 60507006) and The Ministry of Science and Technology “973” Plan (No. G2000036602)

Abstract:A novel large optical cavity laser diode, which consists of multi-active regions cascaded together through tunnel junctions, is proposed. After growing the epi-layers with LP-MOCVD system on GaAs substrate, the ridge waveguide laser structure is fabricated, and it shows a transverse divergence angle as low as 14.4°. This work was supported by special foundations for major state basic research project of China(G20000683-02)

Abstract:Based on super-molecule self-assembly and entropy-driven self-assembly mechanisms, the coupling agent was evolved into colloid spheres with average diameter of 2-2. 3 μm on the fiber Bragg grating (FBG) with silicon substrate, and the coupling mechanism among polymer, coupling agent and FBG was analyzed. The polymer coated FBG pressure sensors was capsulated by uniform coupling mode and self-assembly coupling mode of the coupling agent respectively, and their performance parameters were tested. It was shown, adopting the self-assembly coating of coupling agent and with the same other capsulated technologies, that the measuring range of the sensor expanded from 0.6 MPa to 1.6 MPa, the repeated times for coupling failure increased from 54 to 125 times and the pressure sensitivity coefficient enhanced from 1.09 to 2.98. By controlling the diameter of the spheres and the line density, the measuring range and the sensitivity of the FBG pressure sensors can be obviously improved. This work was supported by the National “863” Project of China (No. 2002AA313150).

Abstract:Based on couple wave equation and finite-difference time-domain (FDTD) algorithm, the strong couple characteristic of 2-D photonic crystal couplers is calculated. Theoretical analysis and numerical simulated results indicate that the energy in a 2-D photonic crystal coupler can not be totally transferred between two wave-guides. Compared with the result of weak coupling theory, our result is more accurate. Supported by the Youth Science and Technology Innovation Item Foundation of Fujian Province (2001J008)

Abstract:We demonstrate the fabrication and the application of an in-fiber triangular filter (T-filter) based on a linearly chirped and apodized fiber Bragg grating (FBG). The theoretical analysis shows that this type of FBG T-filter has a good response in the demodulation of a wavelength-matched FBG sensor. For the first time to our knowledge, such an FBG T-filter has been realized in our laboratory, and utilized to interrogate the signal of dynamic strain by a specially designed measurement scheme. Experimental results have proved that the system has a good performance in the measurement of dynamic strain. Because of its compactness and passiveness, such type of the device can be integrated as a portable demodulation module. This work is supported by the Science Foundation of Zhejiang Province, China (R104154)

Abstract:Because the general multi-wavelength UV-Visible absorbance detector cannot avoid the noise and drift resulting from the intensity fluctuation of the light source,a dual beam multi-wavelength UV-Visible detector based on CCD was designed. The ray of light source is divided into a signal ray and a reference ray by the beam splitter after it passes through the chopper. The signal ray shines into the sample cell. The signal ray passing through the sample cell falls onto a concave mirror which focuses it onto a slot that is imaged on one portion of COD by a concave grating. The reference ray is imaged on the other portion of COD by the concave grating after the slot. The signal spectrum, the reference spectrum and the dark current of COD can be measured on the same CCD under the cooperation of the optical system and accessorial circuits. The real-time compensation for the signal spectrum by using the reference spectrum and the dark current of OCD can effectively depress the noise and drift of the detector. The short-term noise is 10^-5 AU and the drift is 10^-1 AU/h.

Abstract:We propose a silica-core dispersion-decreasing Bragg fiber (DDBF) of mode effective area as large as 55 μm² for supercontinuum (SC) generation at the pump wavelength of 1060 nm. Using a fast and simple matrix method to model propagation in the DDBF, we have presented a general criterion to obtain the shortest length of the DDBF that would result in a broad SC spectrum. The proposed DDBF design should be amenable for reproducible fabrication through the well-developed MCVD fiber manufacturing technology and the concept has potential for realization as a practical device.

Abstract:Based on the Stokes signals of the spontaneous Raman backscattering, a demodulated method for the simultaneous distributed temperature measurement in an optical fiber is presented to improve the sensitivity of the sensor. The experimental system of Stokes temperature sensor is set up and 2 km of operating length, 1 m of distance resolution, accuracy of ±0.1°C are obtained.

Abstract:White organic light-emitting diodes were fabricated by using 4, 48-bis (2, 28-diphenylvinyl)-1, 18-biphenyl (DPVBi) as a dopant with a structure of ITO/4,4’-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (NPB, 50 nm)/NPB:DPVBi (molecular weight ratio 10:1,30 nm)/tris-(8-hydroxyquinoline)aluminum (Alq₃, 20 nm)/LiF(1 nm)/Al. A broad emissive band with four major peaks of 438, 464, 496 and 520 nm was obtained by electroluminescence spectra, of which 438 nm-, 464 nm- and 520 nm-peak come from emission of NPB, DPVBi and Alq₃, respectively, and 496 nm-one resulted from the emissive superposition of three materials above. The emission from DPVBi was attributed to the charge trapping from NPB. The emission region was transferred partly from Alq₃ to DPVBi-doped NPB by introducing the dopant DPVBi, which leads to emission of DPVBi and an enhanced emission from NPB. The maximum luminance and current efficiency were 4721 cd/m² at 22 V and 0.80 cd/A at 5V, respectively.

Abstract:A 1550 nm polarization-insensitive semiconductor optical amplifier (SOA) was fabricated with InGaAs tensile-strained bulk active region. Beam propagation method and planar wave expansion method are used to calculate the mode field profile and the mode reflectivity. For the SOA with a buried waveguide deviated 7⁰ from the normal direction of cleaved mirrors, the thickness tolerance of the mirror is 3% for keeping the reflectivity of TE mode and TM mode less than 10⁻⁴ simultaneously. For a SOA with a cavity length of 800 μm, the polarization sensitivity of amplified spontaneous emission spectra is less than 0.5 dB at an injection current of 250 mA, the corresponding fiber-to-fiber gain is 11.9 dB at 1550 nm with a 3 dB bandwidth of 63 nm, and the saturation output power is 5.6 dBm. The noise figure shows 8.8 and 7.8 dB at 1550 and 1570 nm, respectively. For a packaged SOA with a cavity length of 1000 μm, the fiber-to-fiber gain is 15 dB at an injection current of 190 mA.

Abstract:Er³⁺ / Yb³⁺ co-doped silica-alumina monolithic xerogels were prepared with the same concentration on 2 000 Er/Si ppm and 6 000 Al/Si ppm. The Yb/Si content was varied from 0 to 4 000 ppm Densification of the samples was achieved by thermal treatment in air at 950 °C for 120 hours with a heating rate 0.1 °C/min. Photoluminescence spectroscopy was used to obtain information about the effective excitation efficiency of Er³⁺ ions by co-doping with Yb³⁺ ions. The infrared-to-visible up-conversion luminescence has been investigated upon continuous wave excitation at 980 nm. The samples exhibit red, green and blue up-conversion emission. It is found that the intensity of up-conversion luminescence increases with increasing Yb³⁺ doping concentration. An opposite behavior is observed for the⁴l_13/2 luminescence of the Er³⁺ ions. This research is performed in the context of the Italy-Vietnam research project 6 BS 2 MAE 2006–2008. MIUR-FIRB RBNE012 N3X, PAT FAPVU2004–2006, MIUR-PRIN 2004–2006.

Abstract:In this paper,the effects of Ar ion bombardment during the electron beam evaporation deposition of the amorphous Si film were investigated. It was found that the bombardment increases the light absorption by two to eleven times and increases the conductance of the film by 3 000 times, This has never been reported before of amorphous Si with electron beam evaporation deposition.

Abstract:A new method based on UV photosensitivity is proposed to fabricate big scale two dimensional photonic crystal. The optical transmission properties of designed periodic structure are investigated by numerical analysis. The results show that the 2D photonic crystal fabricated by the new method has a desirable photonic bandgap of TE mode.

Abstract:Chromatic Dispersion (CD) monitoring technique based on narrow-band electrical power detecting is one of the cost-effective and simple CD monitoring techniques, while the performance of this method is debased by factors such as bandwidth and center frequency of the detected frequency band, self-phase modulation (SPM), light source chirps and optical fiber losses. The CD-electrical power curve is simulated to investigate the effects of the factors above mentioned. Theoretical analysis shows that in single-channeled fiber link, the effect of SPM is small enough (<-0.003%) to be ignored, while the chirps and the losses must be taken into account; the bandwidth of the detected frequency band would better be less than 2πX 1 GHz; the selected central frequency is related to the shape of the original pulse, a central frequency of 12 GHz is chosen in a 40 Gbit/s system, and 5GHz is chosen in a 10 Gbit/s system. A testing system is established. The experimental results agree well with the theoretical analysis. Supported by the National Natural Science Fund of China under contact No. 60377031 and No. 60577013, National Basic Research Program of China under contact No. 2003CB314907

Abstract:A hyperchaos-based watermarking algorithm is developed in the wavelet domain for images. The algorithm is based on discrete wavelet transform and combines the communication model with side information. We utilize a suitable scale factor to scale host image, then construct cosets for embedding digital watermarking according to scale version of the host image. Our scheme makes a tradeoff between imperceptibility and robustness,and achieves security. The extraction algorithm is a blind detection algorithm which retrieves the watermark without the original host image. In addition,we propose a new method for watermark encryption with hyperchaotic sequence. This method overcomes the drawback of small key space of chaotic sequence and improves the watermark security. Simulation results indicate that the algorithm is a well-balanced watermarking method that offers good robustness and imperceptibility.

Abstract:This paper addresses the use of fuzzy neural networks (FNN) for predicting the nonlinear network traffic. Through training the fuzzy neural networks with momentum back-propagation algorithm (MOBP) and choosing the appropriate activation function of output node, the traffic series can be well predicted by these structures. From the effective forecasting results obtained, it can be concluded that fuzzy neural networks can be well applicable for the traffic series prediction. In addition, the performance of the FNN was particularly discussed and analyzed in terms of prediction ability compared with solely neural networks. The effectiveness of the proposed FNN is demonstrated through the simulation. This work is supported in part by China Postdoctoral Foundation under grant (2005037529), Tianjin High Education Science Development Foundation under grant (20041325) and Education Ministry Doctoral Discipline Foundation of China under grant (2003005607).

Abstract:In this paper,an improved zerotree structure and a new coding procedure are adopted,which improve the reconstructed image qualities. Moreover, the lists in SPIHT are replaced by flag maps, and lifting scheme is adopted to realize wavelet transform, which lowers the memory requirements and speeds up the ceding process. Experimental results show that the algorithm is more effective and efficient compared with SPIHT.

Abstract:According to the Collins formula and its inverse diffraction computation, this paper presents an algorithm for reconstructing the object wavefront of a numerical holograph. To improve the quality of wavefront reconstruction, a technique of eliminating the zero-order diffraction light is introduced, which is achieved by subtraction of two intensities of the interference patterns. The computer simulation and image processing show that the method of eliminating the zero-order diffraction beam can be applied to the wavefront reconstruction of inverse diffraction computation. Supported by the Natural Science Foundation of Yunnan Province (2004F0025M)

Abstract:A method combining eigenface with different wavelet subbands for face recognition is proposed. Each training image is decomposed into multi-subbands for extracting their eigenvector sets and projection vectors. In the recognition process,the inner product distance between the projection vectors of the test image and that of the training image are calculated. The training image, corresponding to the maximum distance under the given threshold condition, is considered as the final result. The experimental results on the ORL and YALE face database show that,compared with the eigenface method directly on the image domain or on a single wavelet subband, the recognition accuracy using the proposed method is improved by 5% without influencing the recognition speed.

Abstract:Iris image segmentation is very important for an iris recognition system. There are always iris noises as eyelash,eyelid,reflection and pupil in iris images. The paper proposes a virtual method of segmentation. By locating and normalizing iris images with Gabor filter,we can acquire information of image texture in a series of frequencies and orientations. Iris noise regions are determined based on phase congruency by a group of Gabor filters whose kernels are suitable for edge detection. These regions are filled according to the characteristics of iris noise. The experimental results show that the proposed method can segment iris images effectively.

Abstract:Based on the Lyapunov stability theory,a new method for synchronization of hyperchaotic Rossler system with uncertain parameters is proposed. By this method, choosing appropriate control law and adaptive update law of uncertain parameters, all the errors of system variable synchronization and of uncertain param- eter track are asymptotically stable. The theoretical analysis and the numerical simulations prove the efffectiveness of the oroDosed method.

Abstract:Based on the charge discreteness, the property of quantum current and the effects of Coulomb blockade have been investigated for the mutual inductance coupled mesoscopic system with active source in external magnetic field. The relationships between quantum current and the conditions of Coulomb blockade in the coupled dual-ring system are given here.

Abstract:The multiphoton ionization of acetone-water clusters were detected at 355 nm laser wavelength by using the time of flight mass spectrometer (TOF-MS). The experiments show that all products are protonated. Three main products such as (CH₃COCH₃)_n-(H₂O)_n−2H⁺, (CH₃COCH₃)_n-(H₂O)_n−1 H⁺ and (CH₃COCH₃)_n−(H₂O)_nH⁺ are concluded from the results. In order to study the equilibrium structures of the (CH₃COCH₃)_n−(H₂O)_n−2H⁺, the ab-initio calculation is used on them. The experiment is even done when the volume rate of acetone to water is 1∶2.

Abstract:The fabrication and characterization of a laser ionization source for ion mobility spectrometer (IMS) is described with the calculated parameter of the drift tube. lons are created in alr at ambient pressure using laser ionization (λ=248 nm) with air as the drift gas. Mobility spectra for positive ions at different electric fields are obtained with the length of drift tube of 25 and 50 nm, respectively. The distribution of the electric field in the drift tube (50 nm) has also been investigated by SIMION simulation with the ion shutter closed and open respectively.

Abstract:Optoelectronics Letters is the companion journal to Journal of Optoelectronics .Laser （the core journal in Chinese）. The purpose of Optoelectronics Letters is reporting the new important results in the fields of optoelectronics Jphotonics in English to advance the international academic exchanges.