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Chinese Optics Letters 第13卷 第10期

Author Affiliations
Abstract
1 CAS Key Laboratory of Time and Frequency Primary Standards, National Time Service Center, Xi’an 710600, China
2 University of Chinese Academy of Sciences, Beijing 100049, China
We report experiments on the observation of the S01 P03 transition spectrum of Sr88 in the Lamb-Dicke regime. After going through a two-stage magneto-optical trap (MOT), Sr88 cold atoms with number of about 1×105 and a longitudinal temperature of 8.4 μK are loaded into a one-dimensional (1D) optical lattice, which is realized with a semiconductor laser at 813.4 nm. Using the magnetic field-inducing P13 state mixing into P03 state, the spectroscopy of the S01 P03 transition with a linewidth of 180 Hz is detected.
020.7010 Laser trapping 140.3320 Laser cooling 020.1335 Atom optics 020.3320 Laser cooling 
Chinese Optics Letters
2015, 13(10): 100201
Author Affiliations
Abstract
1 Institute of Optoelectronics Technology, China Jiliang University, Hangzhou 310018, China
2 School of Electronic and Optical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
Using the first-principles method based on the density functional theory (DFT), the work function of seven different GaN (0001) (1×1) surface models is calculated. The calculation results show that the optimal ratio of Cs to O for activation is between 31 and 41. Then, Cs/O activation and stability testing experiments on reflection-mode negative electron affinity GaN photocathodes are performed. The surface model [GaN (Mg): Cs] Cs-O after being activated with cesium and oxygen is used. The experiment results illustrate that the adsorption of O contained in the residual gas increases the surface potential barrier and the reduction of the effective dipole quantity is the basic cause of the quantum efficiency decay.
040.7190 Ultraviolet 160.1890 Detector materials 230.0040 Detectors 260.7210 Ultraviolet, vacuum 
Chinese Optics Letters
2015, 13(10): 100401
Author Affiliations
Abstract
College of Mechatronic Engineering and Automation, National University of Defense Technology, Changsha 410073, China
A symmetrical heterodyne grating interferometer with both a short period and high signal-to-noise ratio is proposed. It possesses good immunity to environmental disturbances and can simultaneously achieve high resolution and stability. The experimental results show that the standard deviation of 24.67 nm can be realized for the long range of 10 mm. The measurement resolution of better than 2 nm is achieved with the theoretical resolution of 12 pm. Additionally, system stability at less than ±1.5 nm is obtained in just over 10 min. The measurement errors, including cosine error, nonlinear error and non-common path error, are discussed as well.
050.1950 Diffraction gratings 120.3180 Interferometry 120.3930 Metrological instrumentation 
Chinese Optics Letters
2015, 13(10): 100501
Author Affiliations
Abstract
1 Institute of Modern Optics, Nankai University, Tianjin 300071, China
2 Institute of Photonics Technology, Jinan University, Guangzhou 510632, China
3 Institute of Micro & Nano Optics, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, .China
We propose and demonstrate free-space optical data links based on coaxial sidelobe-modified optical vortices (CSMOVs). In contrast to the optical communication systems based on amplitude, frequency, or phase detection, the proposed scheme uses the radii ratio between the principle ring and the first sidelobe of the CSMOV. Therefore, the demand of stringent alignment and/or accurate phase matching is released. We design and optimize a composite computer-generated hologram to generate a CSMOV with four topological charges (TCs). Extracted from the images captured by a CCD camera, the radii ratio between the principle ring and the first sidelobe of different TCs are consistent with the theoretical values.
050.4865 Optical vortices 060.4510 Optical communications 090.2890 Holographic optical elements 
Chinese Optics Letters
2015, 13(10): 100502
Author Affiliations
Abstract
1 National Engineering Laboratory for Fiber Optic Sensing Technology, Wuhan University of Technology, Wuhan 430070, China
2 Key Laboratory of Fiber Optic Sensing Technology and Information Processing, Ministry of Education, Wuhan University of Technology, Wuhan 430070, China
3 School of Science, Wuhan University of Technology, Wuhan 430070, China
4 Wuhan Institute of Marine Electric Propulsion, CSIC, Wuhan 430070, China
In this Letter, a sensor consisting of a fiber Bragg grating (FBG) and a fiber Fabry–Perot interferometer (FFPI) sensor is developed to measure the coefficient of thermal expansion (CTE) and the thermo-optical coefficient (TOC) of a silica-based optical fiber at cryogenic temperatures. The FFPI is fabricated by welding together two acid-etched fibers. The temperature performance of the FFPI-FBG hybrid sensor is studied in the temperature range of 30–273 K. The CTE and TOC of the optical fiber at cryogenic temperatures are derived analytically and verified by experiments.
060.2300 Fiber measurements 060.2370 Fiber optics sensors 060.2400 Fiber properties 
Chinese Optics Letters
2015, 13(10): 100601
Author Affiliations
Abstract
Key Laboratory for Information Science of Electromagnetic Waves (MoE), Fudan University, Shanghai 200433, China
We propose a two-cascaded, constant-resistance, symmetrical bridged-T amplitude equalizer for a high-speed visible light communication (VLC) system. With the pre-equalization circuit, the 3 dB bandwidth of the VLC system can be extended from 12 to 235 MHz using a commercially available phosphorescent white light-emitting diode (LED), a blue filter, and a low-cost PIN photodiode. The data rate is 1.20 Gbit/s, exploiting 16-quadrature amplitude modulation-orthogonal frequency-division multiplexing with a 300 MHz modulation bandwidth over 50 cm of free-space transmission under the pre-forward error correction limit of 3.8×10 3. To our knowledge, this is the highest 3 dB bandwidth and the highest data rate ever achieved by using a pre-equalization circuit and white LED in a VLC system.
060.2605 Free-space optical communication 060.4080 Modulation 070.4340 Nonlinear optical signal processing 
Chinese Optics Letters
2015, 13(10): 100602
Author Affiliations
Abstract
1 Shanghai Key Laboratory of All Solid-state Laser and Applied Techniques, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2 University of Chinese Academy of Sciences, Beijing 100049, China
3 Shanghai Synet Optics Technology Corporation, Shanghai 200135, China
4 Bandweaver Technologies Co. Ltd., Shanghai 201203, China
A novel distributed passive vehicle tracking technology is proposed and demonstrated. This technology is based on a phase-sensitive optical time domain reflectometer (Φ-OTDR) that can sense and locate vibrations. Two algorithms, dynamic frequency-space image and 2D digital sliding filtering, are proposed to distinguish a car’s moving signals from severe environmental noises and disturbances. This technology is proved effective by field experiments for tracking a single car and multiple cars. This work provides a new distributed passive way for real-time vehicle tracking and this technology will be extremely important for traffic controlling and public safety in modern society.
060.2370 Fiber optics sensors 230.0250 Optoelectronics 290.5870 Scattering, Rayleigh 
Chinese Optics Letters
2015, 13(10): 100603
Author Affiliations
Abstract
1 State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China
2 School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
In this Letter, we develop the Stokes space-based method for modulation format identification by combing power spectral density and a cluster analysis to identify quadrature amplitude modulation (QAM) and phase-shift keying (PSK) signals. Fuzzy c-means and hierarchical clustering algorithms are used for the cluster analysis. Simulations are conducted for binary PSK, quadrature PSK, 8PSK, 16-QAM, and 32-QAM signals. The results demonstrate that the proposed technique can effectively classify all these modulation formats, and that the method is superior in lowering the threshold of the optical signal-to-noise ratio. Meanwhile, the proposed method is insensitive to phase offset and laser phase noise.
060.1660 Coherent communications 060.2330 Fiber optics communications 060.4510 Optical communications 
Chinese Optics Letters
2015, 13(10): 100604
Author Affiliations
Abstract
1 State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China
2 Engineering and Surface Metrology Laboratory, National Institute of Standards, Tersa St., El haram, El Giza, Egypt
3 Division of Mechanical System Engineering, Chonbuk National University, Jeonju 561-756, Republic of Korea
We present a Fizeau interferometer using a microscopic objective as a tool for surface contouring without the need for a numerical lens for reconstruction. The interferometer is associated with a telescope system to feature the object with collimated light. The experiment is conducted on two objects possessing different step heights. The phase maps from the captured off-axis holograms are calculated numerically, which allows us to deduce the contours of the objects. The great advantages of the presented technique are that it can be done in real time and there is no need for numerical lenses for micro-objects reconstruction.
070.6110 Spatial filtering 100.5090 Phase-only filters 170.0180 Microscopy 180.0180 Microscopy 
Chinese Optics Letters
2015, 13(10): 100701
Author Affiliations
Abstract
University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China
Photoacoustic imaging with a synthetic aperture focusing technique (SAFT) is an effective method to improve the lateral resolution for out-of-focus regions in scanning microscopy systems, which commonly require a decent motorized scanning stage for a lateral scan of a transducer to obtain a cross-sectional image. In this study, we propose and test a photoacoustic imaging system with a scanning mirror-based SAFT (SM-SAFT) for simple and fast data acquisition, without the need for a physical scan of the transducer. Photoacoustic images of hair phantoms acquired by SM-SAFT are demonstrated, serving as a proof-of-concept experiment to show the feasibility and potential of the proposed approach.
110.5120 Photoacoutic imaging 180.5810 Scanning microscopy 110.6880 Three-dimensional image acquisition 
Chinese Optics Letters
2015, 13(10): 101101
Author Affiliations
Abstract
1 Ultra-Precision Optoelectronic Instrument Engineering Center, Harbin Institute of Technology, Harbin 150001, China
2 Postdoctoral Research Station of Optical Engineering, Harbin Institute of Technology, Harbin 150001, China
A beam combination setup for a dual-frequency laser with orthogonal linear polarization is proposed. It consists of two polarizing beam splitters (PBSs) whose polarization axes are orthogonal to each other. A theoretical analysis demonstrates that a combined dual-frequency laser beam with this setup strictly meets orthogonal linear relation. The experimental results show that compared with the conventional setup, the ellipticity and nonorthogonality of the combined dual-frequency laser beam are significantly reduced.
120.0120 Instrumentation, measurement, and metrology 120.3180 Interferometry 140.3298 Laser beam combining 280.3420 Laser sensors 
Chinese Optics Letters
2015, 13(10): 101201
Author Affiliations
Abstract
School of Optical Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
A method for isochromatic determination in three-fringe photoelasticity is presented. It combines the phase-shifting method with cubic polynomial curve-fitting technology to eliminate the errors caused by color repetition. We perform a demonstration of the method on a circular disc subjected to compressive loading and an injection-molded cover with residual stresses. The test results compare well with the theoretical results.
120.0120 Instrumentation, measurement, and metrology 120.5050 Phase measurement 
Chinese Optics Letters
2015, 13(10): 101202
Author Affiliations
Abstract
1 Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
2 Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
We demonstrate a large-mode-volume transverse-electric-polarized λ/4 shifted distributed feedback (DFB) cavity on silicon-on-insulator (SOI). A 2.86 mm-long DFB cavity with sidewall corrugation on the ridge is fabricated on a silicon rib waveguide. The cavity structure is designed to enlarge both the longitudinal and transversal mode profiles of the cavity to enclose more luminescent media. Design strategies are verified by both finite difference time domain simulation and experiments. A linewidth of 69 pm and an extinction ratio of 15 dB is obtained, indicating not only the well confinement of the longitudinal mode, but also its well stretching to the cavity ends. The mode volume is 75.39 μm3.
130.0130 Integrated optics 130.7408 Wavelength filtering devices 
Chinese Optics Letters
2015, 13(10): 101301
Author Affiliations
Abstract
1 Key Laboratory of Opto-electronic Information and Technical Science, College of Precision Instrument and Opto-electronics Engineering, Tianjin University, Tianjin 300072, China
2 Department of Applied Physics, Tianjin University, Tianjin 300072, China
We experimentally and numerically demonstrate the generation of square pulses without any wave-breaking in a fiber ring laser. A segment of nonzero dispersion-shifted fiber is used to increase the laser cavity length and to optimize the parameters of the laser cavity. In the experiment, the pulse width can be tuned in a wide range from 13.5 to 119.5 ns without wave-breaking while the peak power remains almost constant. The maximum single-pulse energy is up to 65.58 nJ at a pump power of 508 mW. Numerical results are in good agreement with the experimental results. Numerical results also reveal the role of cavity length and nonlinearity in generating a square pulse without pulse breakup.
060.3510 Lasers, fiber 140.3560 Lasers, ring 140.3600 Lasers, tunable 140.4050 Mode-locked lasers 
Chinese Optics Letters
2015, 13(10): 101401
Author Affiliations
Abstract
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China
In this Letter, we demonstrate a diode-pumped electro-optical cavity-dumped Tm:YAP laser for the first time to our knowledge. A pulse width of 7.1 ns is achieved at a wavelength of 1996.9 nm. A maximum output power of 3.02 W is obtained with a pump power of 58.8 W at a repetition rate of 100 kHz and a high-voltage time of 1000 ns, corresponding to an overall optical-to-optical conversion efficiency of 5.2%. In addition, we study the effect of repetition rate and high-voltage time on the output power characteristics of a cavity-dumped Tm:YAP laser.
140.3460 Lasers 140.3480 Lasers, diode-pumped 140.3580 Lasers, solid-state 
Chinese Optics Letters
2015, 13(10): 101402
Author Affiliations
Abstract
1 School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054, China
2 School of Information and Communication, Guilin University of Electronic Technology, Guilin 541004, China
A polarization-insensitive, square split-ring resonator (SSRR) is simulated and experimented. By investigating the influence of the asymmetrical arm width in typical SSRRs, we find that the variation of the arm width enables a blue shift of the resonance frequency for the 0° polarized wave and a red shift of the resonance frequency for the 90° polarized wave. Thus, the resonance frequency for the 0° polarized wave and the resonance frequency for the 90° polarized wave will be identical by asymmetrically adjusting the arm width of the SSRR. Two modified, split-ring resonators (MSRRs) that are insensitive to the polarization with asymmetrical arm widths are designed, fabricated, and tested. Excellent agreement between the simulations and experiments for the MSRRs demonstrates the polarization insensitivity with asymmetrical arm widths. This work opens new opportunities for the investigation of polarization-insensitive, split-ring resonator metamaterials and will broaden the applications of split-ring resonators in various terahertz devices.
350.2450 Filters, absorption 160.3918 Metamaterials 040.2235 Far infrared or terahertz 
Chinese Optics Letters
2015, 13(10): 101601
Author Affiliations
Abstract
Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, China
Zinc strontium phosphate glasses doped with different trivalent praseodymium ion (Pr3+) concentrations are presented and their photoluminescence properties are investigated upon 442 nm excitation. With the Pr3+ concentration decreasing, the orange emission of Pr3+ (D21 HJ3) is enhanced steadily at the cost of its blue emission (P1,03 H43). Monochromic orange emission of Pr3+ ions is obtained when the Pr3+ doping is reduced to 0.05 mol.%. The mechanism controlling the monochromatic characteristic of Pr3+ emissions is supposed to be associated with the phonon-aided nonradiative relaxation process of Pr3+: Pj3250.5230 Photoluminescence 160.2750 Glass and other amorphous materials 160.5690 Rare-earth-doped materials 300.2140 Emission 
Chinese Optics Letters
2015, 13(10): 101602
Author Affiliations
Abstract
1 College of Physics and Energy, Fujian Normal University, Fuzhou 350007, China
2 College of Photonic and Electronic Engineering, Fujian Normal University, Fuzhou 350007, China
In this Letter, we discuss Raman–Nath acousto-optic diffraction, and a new model of Raman–Nath acousto-optic diffraction is presented. The model is based on the individual and simultaneous occurrences of phase-grating diffraction and the Doppler effect and optical phase modulation and photon–phonon scattering. We find that the optical phase modulation can cause temporal and spatial fluctuations of the diffracted light power escaping from the acoustic field.
170.5120 Photoacoustic imaging 290.1350 Backscattering 290.4210 Multiple scattering 290.7050 Turbid media 
Chinese Optics Letters
2015, 13(10): 101701
Author Affiliations
Abstract
1 State Key Laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, China
2 Department of Applied Physics, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
3 Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
4 General Research Institute for Nonferrous Metals, Beijing 100088, China
In this Letter, silver (Ag) hierarchical nanostructures grown on black silicon (BS) are used as the catalyst and a surface-enhanced Raman scattering (SERS) detector integrated in a microfluid. The BS is fabricated via femtosecond laser ablation in an atmosphere of sulfur hexafluoride, and then hydrogenated with hydrofluoric acid. As formed, the BS substrate directly acts as a reducing template to grow silver hierarchical nano-structures. Particularly, Ag-BS composite micro/nano-structures can be in-situ constructed in silicon-based microchannels. These structures simultaneously serve as integrated catalytic reactors and a SERS substrate for sensing. The sensitivity is tested to be as low as 10 8 mol/L using Rhodamine 6G.
240.6695 Surface-enhanced Raman scattering 160.3380 Laser materials 
Chinese Optics Letters
2015, 13(10): 102401
Author Affiliations
Abstract
1 Department of Physics, Sichuan Normal University, Chengdu 610068, China
2 Department of Physics, Zhejiang University, Hangzhou 310027, China
The far-zone scattered spectral density of a light wave on the scattering from a collection of particles is investigated, and the relationship between the character of the collection and the distribution of the scattered spectral density is discussed. It is shown that both the number of particles and their locations in the collection play roles in the distribution of the far-zone scattered spectral density. This phenomenon may provide a potential method to reconstruct the structure character of a collection of particles from measurements of the far-zone scattered spectral density.
290.2558 Forward scattering 290.5850 Scattering, particles 
Chinese Optics Letters
2015, 13(10): 102901
Author Affiliations
Abstract
1 Department of Optical Science and Engineering, Fudan University, Shanghai Ultra-Precision Optical Manufacturing Engineering Center, Shanghai 200433, China
2 Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education), Shanghai 200433, China
3 College of Physical Science and Engineering, Tongji University, Shanghai 200092, China
4 Department of Medical Physics, Weifang Medical University, Shandong 261053, China
A number of zinc oxide (ZnO) films are deposited on silicon substrates using the magnetron sputtering method. After undergoing thermal treatment under different conditions, those films exhibit hexagonal wurtzite structures and different photoluminescent characteristics. Besides the notable ultraviolet emission, which is related to the free exciton effect, a distinct blue fluorescence around 475 nm is found in some special samples. The blue photoluminescence emission of the ZnO film is believed to be caused by oxygen vacancies.
310.6860 Thin films, optical properties 310.1860 Deposition and fabrication 300.6280 Spectroscopy, fluorescence and luminescence 260.3800 Luminescence 
Chinese Optics Letters
2015, 13(10): 103101