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Chinese Optics Letters 第13卷 第3期

Author Affiliations
Abstract
State Key Laboratory of Advanced Optical Communication Systems and Networks, Peking University, Beijing 100871, China
The characteristic equation of orbital angular momentum modes in a ring fiber is derived. By solving the equation with the graphical method, mode distribution in a ring fiber can be precisely determined for arbitrary fiber parameters without relying on simulation of the vector field. This will provide a useful method to determine the separation between quasi-degenerate modes in a ring fiber.
050.4865 Optical vortices 060.2270 Fiber characterization 060.2310 Fiber optics 
Chinese Optics Letters
2015, 13(3): 030501
Author Affiliations
Abstract
Institute of Opto-Electronics Technology, Beihang University, Beijing 100191, China
We propose a method for the real-time measurement of the reflection at both splicing points between a photonic bandgap fiber coil and conventional fiber during the process of fusion splicing in a photonic bandgap fiber optical gyroscope (PBFOG), using the interference among the secondary waves, which arise from the fusion splicing points and the mirror face produced by intentionally cutting the bear end of the coupler. The method is theoretically proven and experimentally verified in a practical PBFOG, and it is significant for inline examination of the fusion splicing quality and evaluation of the PBFOG performance.
060.2310 Fiber optics 060.5295 Photonic crystal fibers 
Chinese Optics Letters
2015, 13(3): 030601
Author Affiliations
Abstract
1 Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia
2 Photonics Research Center, University of Malaya, Kuala Lumpur 50603, Malaysia
3 Department of Electrical and Computer Engineering, International Islamic University Malaysia, Jalan Gombak, Kuala Lumpur 50603, Malaysia
4 Fiber Optics and Photonics Division, Central Glass & Ceramic Research Institute, CSIR, Kolkata, India
We propose and demonstrate a passively mode-locked fiber laser operating at 1951.8 nm using a commercial thulium-doped fiber (TDF) laser, a homemade double-clad thulium–ytterbium co-doped fiber (TYDF) as the gain media, and a multi-walled carbon nanotube (MWCNT) based saturable absorber (SA). We prepare the MWCNT composite by mixing a homogeneous solution of MWCNTs with a diluted polyvinyl alcohol (PVA) polymer solution and then drying it at room temperature to form a film. The film is placed between two fiber connectors as a SA before it is integrated into a laser ring cavity. The cavity consists of a 2 m long TDF pumped by a 800 nm laser diode and a 15 m long homemade TYDF pumped by a 905 nm multimode laser diode. A stable mode-locking pulse with a repetition rate of 34.6 MHz and a pulse width of 10.79 ps is obtained when the 905 nm multimode pump power reaches 1.8–2.2 W, while the single-mode 800 nm pump power is fixed at 141.5 mW at all times. To the best of our knowledge, this is the first reported mode-locked fiber laser using a MWCNT-based SA.
060.3510 Lasers, fiber 320.7090 Ultrafast lasers 
Chinese Optics Letters
2015, 13(3): 030602
Author Affiliations
Abstract
Center for Quantum Science and Technology, Jiangxi Normal University, Nanchang 330022, China
In this Letter, a new fractional entangling transformation (FrET) is proposed, which is generated in the entangled state representation by a unitary operator exp{iθ(ab +a b)} where a(b) is the Bosonic annihilate operator. The operator is actually an entangled one in quantum optics and differs evidently from the separable operator, exp{iθ(a a+b b)}, of complex fractional Fourier transformation. The additivity property is proved by employing the entangled state representation and quantum mechanical version of the FrET. As an application, the FrET of a two-mode number state is derived directly by using the quantum version of the FrET, which is related to Hermite polynomials.
270.0270 Quantum optics 070.2575 Fractional Fourier transforms 
Chinese Optics Letters
2015, 13(3): 030801
Author Affiliations
Abstract
1 Department of Physics, Fudan University, Shanghai 210433, China
2 Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Laser-driven ultrafast X-ray sources are widely used for diagnostic radiography. However, there is a large divergence of fast electrons when they are generated by an intense short-pulse laser interacting with a foil target. We design a nanowire array target to achieve a more compact point X-ray source. Fast electrons are confined and guided by the nanowire array structure in order to generate a Kα source with a small spot size. In our work, the smallest measured source size is comparable to the laser spot size, while the conversion efficiency can reach 2.4×10 4.
100.0100 Image processing 340.0340 X-ray optics 
Chinese Optics Letters
2015, 13(3): 031001
Author Affiliations
Abstract
1 Department of Optometry, Eulji University, 553, Sanseong-daero, Sujeong-gu, Seongnam-si, Gyonggi-do, South Korea
2 Department of Electrical, Electronic, and Control Engineering, Hankyong National University, Kyonggi-do 456-749, South Korea
We propose a novel method of slice image reconstruction with controllable spatial filtering by using the correlation of periodic delta-function arrays (PDFAs) with elemental images in computational integral imaging. The multiple PDFAs, whose spatial periods correspond to object’s depths with the elemental image array (EIA), can generate a set of spatially filtered EIAs for multiple object depths compared with the conventional method for the depth of a single object. We analyze a controllable spatial filtering effect by the proposed method. To show the feasibility of the proposed method, we carry out preliminary experiments for multiple objects and present the results.
110.6880 Three-dimensional image acquisition 110.4190 Multiple imaging 
Chinese Optics Letters
2015, 13(3): 031101
Author Affiliations
Abstract
1 College of Photonic and Electronic Engineering, Fujian Normal University, Fuzhou 350007, China
2 Department of Physics and Electronic Information Engineering, Minjiang University, Fuzhou 350108, China
A tunable dual-band infrared polarization filter is proposed and investigated. Based on the perfect absorption characteristic of the metal-dielectric-metal sandwich structure, the reflection spectrum performs as a filter. The filter consists of three layers. The top layer is a compound metal nano-structure array comprised of rectangular strips. The middle and bottom layers are a dielectric spacer and metal film, respectively. The calculated results show that the filter properties are closely related to the polarization of the incident light. Different dual-band wavelengths are filtered while the incident light has different polarizations, which are parallel or vertical to the x axis. Moreover, it is found that the resonant wavelength strongly depends on the length of the rectangular strip (which causes the resonant effect) and is independent of other strips. Therefore, the filter wavelengths can be tuned freely by adjusting the length of the corresponding rectangular strip. In addition, the calculated results show that all of the intensities at the filter wavelengths are closed to zero, which implies that the filter exhibits good filtering performance.
130.0130 Integrated optics 130.7408 Wavelength filtering devices 130.3990 Micro-optical devices 
Chinese Optics Letters
2015, 13(3): 031301
Author Affiliations
Abstract
1 Institute of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications (BUPT); State Key Laboratory of Information Photonics and Optical Communications (BUPT), Beijing 100876, China
2 Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
We fabricate a GaAs-based InGaAs/InGaAsP multiple quantum wells (MQWs) laser at 1.55 μm. Using two-step growth method and thermal cyclic annealing, a thin low-temperature InP layer and a thick InP buffer layer are grown on GaAs substrates by low-pressure metal organic chemical vapor deposition technology. Then, high-quality MQWs laser structures are grown on the InP buffer layer. Under quasi-continuous wave (QCW) condition, a threshold current of 476 mA and slope efficiency of 0.15 mW/mA are achieved for a broad area device with 50 μm wide strip and 500 μm long cavity at room-temperature. The peak wavelength of emission spectrum is 1549.5 nm at 700 mA. The device is operating for more than 2000 h at room-temperature and 600 mA.
140.0140 Lasers and laser optics 160.6000 Semiconductor materials 140.5960 Semiconductor lasers 
Chinese Optics Letters
2015, 13(3): 031401
Author Affiliations
Abstract
1 School of Science, Changchun University of Science and Technology, Changchun 130022, China
2 State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun 130033, China
This Letter proposes a method to balance the gain and loss of the orthogonally polarized emissions of dual wavelengths in a solid laser cavity. By adjusting the tilt angle of the uncoated glass plate inserted into the cavity, the gain and loss of the orthogonally polarized emission lines with small intervals can be balanced to equalize the oscillation thresholds of the orthogonally polarized dual wavelengths. We select the birefringent crystal Nd:LiYF (Nd:YLF) as the gain media, and theoretically analyze the simultaneous oscillation conditions of dual wavelengths with π- and σ-polarized emissions from a four-level transition (F3/24I11/24 and F3/24I13/24) in Nd3+. A simple linear cavity structure is adopted in the experiment, and stable CW orthogonally polarized dual-wavelength laser outputs of 1047, and 1053, 1321, and 1313 nm are obtained.
140.3580 Lasers, solid-state 140.2020 Diode lasers 140.3430 Laser theory 140.3410 Laser resonators 
Chinese Optics Letters
2015, 13(3): 031402
Author Affiliations
Abstract
1 Anhui Provincial Key Laboratory of Photonic Devices and Materials, Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
2 Beijing Aerospace Control Instrument Research Institute, Beijing 100854, China
A compact and stable all-normal-dispersion mode-locked ring fiber laser with the repetition rate of 312 MHz is obtained with a wavelength-division multiplexing isolator. The compressed pulse is nearly transform-limited and the pulse width is 118 fs. It exhibits an optical efficiency of 50% and the maximum output power is about 205 mW with a 410 mW pump.
140.3510 Lasers, fiber 140.3560 Lasers, ring 140.3615 Lasers, ytterbium 
Chinese Optics Letters
2015, 13(3): 031403
Author Affiliations
Abstract
1 State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
2 Graduate University of the Chinese Academy of Sciences, Beijing 100049, China
3 Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117576, Singapore
Anisotropic dewetting polydimethylsiloxane (PDMS) surfaces, which consist of groove-like micro/nanostructures (so-called hierarchical structures), are fabricated using an ultrashort pulsed laser. The contact angles (CAs) are measured parallel to the microgrooves, which are always larger than those measured perpendicular to the microgrooves, exhibiting a superhydrophobic anisotropy of approximately 4° on these fabricated PDMS surfaces at optimized parameters. These pulsed-laser irradiated surfaces exhibit enhanced hydrophobicity with CAs that increase from 116° to 156° while preserving the anisotropic dewetting. Additionally, the wettability of the surfaces with different morphologies is investigated. The temporal evolution of the wettability of the pulsed-laser irradiated PDMS surface is also observed within the first few hours after pulsed laser irradiation.
140.3390 Laser materials processing 140.3538 Lasers, pulsed 160.1435 Biomaterials 160.4236 Nanomaterials 
Chinese Optics Letters
2015, 13(3): 031404
Author Affiliations
Abstract
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
We report a simple Nd:YAG laser that emits radially polarized beam with helical wavefront. The laser cavity consists of a piece of laser crystal and a plane output coupler, and there is no additional polarization component inside it. The pump light is converted into annular profile through de-focal coupling into a multi-mode fiber. For the continuous-wave (CW) operation, the laser emits radially polarized vortex beam, and it is observed that the helical wavefront of the laser beam is switched from right handedness to left handedness when the output coupler is tilted slightly. For the Q-switched operation under the insertion of a Cr4+:YAG saturable absorber inside the cavity, we obtain radially polarized outputs with left-handedness helical wavefront. By tilting the laser crystal slightly, the laser output switches to azimuthal polarization at pump power larger than 4.5 W and left-handedness helical wavefront of laser beam is preserved.
140.3580 Lasers, solid-state 140.3540 Lasers, Q-switched 140.3530 Lasers, neodymium 140.3480 Lasers, diode-pumped 140.3410 Laser resonators 
Chinese Optics Letters
2015, 13(3): 031405
Author Affiliations
Abstract
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Stray light in high-power laser facilities not only decreases the gain capacity of the main amplifier, but can also cause permanent damage to optical components, greatly threatening the safety operation of the SG-III. This Letter reports a technique for quickly pinpointing the source of stray light in the main amplification optical path of the SG-III. The achieved results indicate that the accuracy of our method is up to 1 m in an optical path of 100 m. The judging method is effective for examining and removing harmful stray light in the SG-III laser facility and it can be promoted in huge laser facilities of this kind.
140.3330 Laser damage 290.2648 Stray light 290.2745 Ghost reflections 
Chinese Optics Letters
2015, 13(3): 031406
Author Affiliations
Abstract
Faculty of Physics and Optoelectronic Engineering, Institute for Nanophysics and Rare-Earth Luminescence, Xiangtan University, Xiangtan 411105, China
Li+-doped HoPO4 powders with a pure tetragonal phase are successfully synthesized by the co-precipitation method. It exhibits an obvious color change under sunlight and tri-phosphor fluorescent light illumination. The introduction of Li+ ions into HoPO4 can further enhance its photochromic property effectively. The doped Li+ ions induce changes in the crystal structure. The spectral characteristics and thus photochromic properties of HoPO4 are explored. The improved HoPO4 powder, when used as a photochromic material, has wide-ranging prospects in security, decoration, and other applications.
160.5690 Rare-earth-doped materials 300.1030 Absorption 330.1720 Color vision 
Chinese Optics Letters
2015, 13(3): 031601
Author Affiliations
Abstract
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Tb3Ga5O12 (TGG) is an excellent material for magneto-optical applications, and is the key component in Faraday isolators (FIs). The preparation process of transparent TGG ceramics is experimentally studied. The optical quality and the microstructure of the samples are investigated. The results show that the transmittance of the sample sintered at 1550°C is close to 72% in the region of 500–1500 nm. The Verdet constant at 632.8 nm measured at room temperature is 125.01 rad T 1 m 1, which is almost the same as that of a single crystal.
160.3820 Magneto-optical materials 140.3380 Laser materials 160.4670 Optical materials 
Chinese Optics Letters
2015, 13(3): 031602
Author Affiliations
Abstract
Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
A real-time monitoring system is set up based on a computer, dynamic interferometer, beam expanding system, and a beam reflecting system. The stability and repeatability of the monitoring system is verified. A workpiece and a glass monitoring plate are placed in the same ring. The surface figure of the workpiece, monitored by the monitoring plate, synchronizes with the surface of the glass monitoring plate in terms of peak–valley and power. The influence of the reflection and transmission surface are discussed in theory and a numeral deviation in online and offline testing data is quantitatively analyzed. The new method provides a quick and easy real-time method to characterize changes to the optical surface during polishing.
220.4610 Optical fabrication 220.5450 Polishing 120.4820 Optical systems 120.6650 Surface measurements, figure 
Chinese Optics Letters
2015, 13(3): 032201
Author Affiliations
Abstract
1 Department of Green Energy and Semiconductor Engineering, Hoseo University, Asan 330-713, South Korea
2 Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S4L8, Canada
In this Letter, blue phosphorescence organic light-emitting diodes (PHOLEDs) employ structures for electron and/or hole confinement; 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene is used as a hole confinement layer and tris-(phenylpyrazole)iridium [Ir(ppz)3] is utilized for an electron confinement layer (ECL). The electrical and optical properties of the fabricated blue PHOLEDs with various carrier-confinement structures are analyzed. Structures with a large energy offset between the carrier confinement and emitting layers enhance the charge-carrier balance in the emitting region, resulting from the effective carrier confinement. The maximum external quantum efficiency of the blue PHOLEDs with the double-ECLs is 24.02% at 1500 cd/m2 and its luminous efficiency is 43.76 cd/A, which is 70.47% improved compared to the device without a carrier-confinement layer.
230.3670 Light-emitting diodes 230.0230 Optical devices 230.4170 Multilayers 230.4205 Multiple quantum well (MQW) modulators 230.5590 Quantum-well, -wire and -dot devices 
Chinese Optics Letters
2015, 13(3): 032301
Author Affiliations
Abstract
1 Institute of Polymer Optoelectronic Materials and Devices, South China University of Technology, Guangzhou 510640, China
2 State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China
A novel structure, called a “freeform surface,” is integrated into a direct type light-emitting diode backlight. By applying the Taguchi method, the performance of this backlight is optimized. The Taguchi experiments are configured in L9(34) orthogonal arrays and are simulated via LightTool analysis software. After that, the influence of the design parameters on the luminance and uniformity are separately evaluated by analysis of variance (ANOVA). Next, the parameters are optimized, and a new backlight structure with desirable performance is designed at last. LightTool simulation shows that this new type of backlight is just 15 mm thick and has 310.3 nits luminance and 83.5% uniformity.
230.3670 Light-emitting diodes 220.2945 Illumination design 
Chinese Optics Letters
2015, 13(3): 032302
Author Affiliations
Abstract
College of Optoelectric Science and Engineering, National University of Defence Technology, Changsha 410073, China
A Closed Cavity measuring platform is built on the basis of a 1000 W-class direct current (DC)-discharge drived continuous-wave (CW) HF/DF chemical laser. On this platform, the absorption coefficients of optical thin films coated on the surfaces of monocrystalline silicon substrates, at the wavelength of 3.6–4.1 μm, is measured, when the power density on the surfaces of optical thin films reaches about 3.16 kW/cm2. The measuring principle and structure of the Closed Cavity is introduced. The temperature curves and balanced temperature rises of the film-substrate systems under test measured through the experiment is presented in this Letter. The experiments show high reliability, good repeatability and strong practicality. The Closed Cavity measuring platform is applicable for not only absorption measurement but other performance measurement of optical thin films under high power density.
310.6860 Thin films, optical properties 140.3070 Infrared and far-infrared lasers 140.3330 Laser damage 140.3460 Lasers 
Chinese Optics Letters
2015, 13(3): 033101
Author Affiliations
Abstract
State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
Filamentation-induced water condensation and snow formation are investigated using laser pulses with different chirps and pulse widths. Chirped pulses result in the laser filamentation with different spatial lengths and intensities, which has a great impact on airflow motion and snow formation. The experiments show that snow formation mainly relates to the filament intensity distribution. Negative chirped pulses produce a greater amount of snow because of higher intensity inside the filaments as compared with the positive chirped pulses.
320.0320 Ultrafast optics 190.0190 Nonlinear optics 140.0140 Lasers and laser optics 
Chinese Optics Letters
2015, 13(3): 033201