Chinese Optics Letters
Search

2014, 12(9) Column

MORE

Chinese Optics Letters 第12卷 第9期

Author Affiliations
Abstract
National Laboratory of Solid State Microstructures and School of Physics, Nanjing University, Nanjing 210093, China
We propose a method for configuring the distribution of amplitude, phase, and polarization in the focal region of vector beams. The polarization and phase of incident beam is spatially tailored so that it can produce a focal field that has elaborately prescribed shapes. Our work focuses on the design of a special focus structure with two oval rings, wherein a phase gradient and polarization gradient exist in the inner and outer rings, respectively. The incident light yielding the desired focal field is determined based on an iterative scheme involving vectorial diffraction calculations and fast Fourier transforms. Simulations and experiments demonstrate the generation of a focal field with phase and polarization gradients, which may find applications in optical manipulation.
050.1960 Diffraction theory 260.5430 Polarization 120.5060 Phase modulation 
Chinese Optics Letters
2014, 12(9): 090501
Author Affiliations
Abstract
We present a liquid refractive index (RI) sensor based on step-index multimode polymer optical fiber with a micro-hole drilled by the femtosecond laser. The experimental results show that in the RI operation range of 1.333–1.473, the sensor has a good linear loss (dB) response to the liquid RI in the micro-holes and a high sensitivity of 18 dB/RIU approximately. The experimental results are explained with the mode of the refraction loss caused by the hole–core interface and connection loss caused by the gap of the holes. The sensor has many advantages including high sensitivity and low cost.
060.2370 Fiber optics sensors 060.2310 Fiber optics 060.2300 Fiber measurements 
Chinese Optics Letters
2014, 12(9): 090601
Author Affiliations
Abstract
Optical spatial modulation (OSM) is a multiple-transmitter technique that can provide higher data rates with low system complexity as compared with single-input single-output systems. Orthogonal frequency division multiplexing (OFDM) is widely implemented to achieve better spectral efficiency in wireless channels. Asymmetrically clipped optical OFDM (O-OFDM) and DC-biased O-OFDM are two well-known O-OFDM techniques suitable for intensity-modulation direct-detection optical systems. In this work, sample indexed spatial OFDM (SIS-OFDM) is proposed to combine OSM and O-OFDM in a novel way and achieve significant performance gain. By assigning time-domain samples of the O-OFDM transmit symbol to different transmitters, SIS-OFDM achieves much better spectral efficiency and reduces computational complexity at the transmitter as compared with previous work that combines OSM with O-OFDM in the frequency domain. We also consider the impact of optical source biasing on overall performance, and the relative performance of imaging receiver (ImR) versus non-imaging receiver (NImR) design for our proposed SIS-OFDM technique. Results indicate that for an Ntx × Nrx multiple-input multiple-output configuration where Ntx = Nrx = 4, SIS-OFDM using ImR can achieve up to 135 dB of signal-to-noise ratio gain over comparable system using a NImR. Also, using Nsc number of O-OFDM subcarriers provides up to Nsc × log2(Ntx) additional bits per symbol of spectral efficiency over techniques that combine OSM and O-OFDM in the frequency domain.
060.4080 Modulation 060.4230 Multiplexing 060.4510 Optical communications 060.2605 Free-space optical communication 
Chinese Optics Letters
2014, 12(9): 090602
Author Affiliations
Abstract
1 School of Electronics and Information Engineering, Foshan University, Foshan 528000, China
2 Wuhan National Laboratory for Optoelectronics and School of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
3 School of Electrical and Information Engineering, The University of Sydney, Sydney, NSW 2006, Australia
We propose a return-to-zero on-off keying (RZ-OOK) to non-return-to-zero (NRZ) OOK conversion scheme based on a single custom-designed fiber Bragg grating (FBG). The custom-made FBG is designed and syn-thesized using discrete layer-peeling algorithm. It is shown that such a FBG can replace the combination of interferometer and the cascaded filter that are invariably employed together in the reported schemes for -RZ-OOK to NRZ-OOK format conversion. Simulation results show that the input 20-Gb/s RZ-OOK signals with different duty cycles can be converted into NRZ-OOK signals with high Q-factor.
060.3735 Fiber Bragg gratings 060.2340 Fiber optics components 060.4080 Modulation 
Chinese Optics Letters
2014, 12(9): 090603
Author Affiliations
Abstract
College of Physics, Jilin University, Changchun 130012, P. R. China
We study the theoretical and experimental effects of hole quantity and inter–inter-hole spacing on insertion loss for using femtosecond laser to make bend-sensitive multi-hole plastic optical fiber (POF), and also analyze the mechanism of bending loss in multi-hole POF. A force sensor based on bending loss of the multi-hole POF is fabricated. The measurement ranges from 0 to 65 N, and the maximum output change exceeds 15.51 dB with good linearity and repeatability, and the sensitivity is 0.24 dB/N.
060.2370 Fiber optics sensors 060.2310 Fiber optics 
Chinese Optics Letters
2014, 12(9): 090604
Author Affiliations
Abstract
1 Department of Control Engineering, Naval Aeronautical and Astronautical University, Yantai 264001, China
2 Navy Unit 91404, Qinhuangdao 066001, China
3 National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150080, China
Broadband mid-infrared (IR) supercontinuum laser is generated in standard single-mode fiber-28 directly pumped by a 2054 nm nanosecond Q-switched Tm,Ho:YVO4 laser. The average output powers of 0.53 W in the ~1.95–2.5 μm spectral band and 0.65 W in the ~1.97–2.45 μm spectral band are achieved at pulse rate frequencies of 7 and 10 kHz, and the corresponding optic-to-optic conversion efficiencies are 34.6% and 42.4% by considering the coupling efficiency. The output spectra have extremely high flatness in the range 2060–2400 and 2060–2360 nm with negligible intensity variation (<2%), respectively. The output pulse shape is not split, and pulse width is reduced from 29 to ~15.4 ns. The beam quality factor M2 is 1.06, measured using traveling knife-edge method, and the laser beam spot is also monitored by an IR vidicon camera.
060.2390 Fiber optics, infrared 060.2430 Fibers, single-mode 060.4370 Nonlinear optics, fibers 
Chinese Optics Letters
2014, 12(9): 090605
Author Affiliations
Abstract
College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
An optical microfiber phase modulator (OMPM) directly driven with low-power light is presented. Phase modulation response of OMPM is theoretically analyzed. A 10-mm optical microfiber (OM), tapered from conventional single-mode fiber, is inserted in one arm of a Michelson fiber interferometer. To drive the OMPM, 980-nm wavelength light with sinusoidal intensity modulation is injected into the interferometer. The OMPM response properties are measured and p-phase modulation amplitude can be obtained with only 7.5-mW average power light at 1-kHz modulation frequency. The OMPMs shown in this study have advantages of simple structure, potential compact size, and low-power-driven light.
060.2430 Fibers, single-mode 120.5060 Phase modulation 250.4110 Modulators 
Chinese Optics Letters
2014, 12(9): 090606
Author Affiliations
Abstract
A monostatic strip-map mode interferometric synthetic aperture ladar (SAL) is reported. Using a chirped laser of about 5 mW at 1550 nm wavelength as the illumination source and two cross-track receiving apertures with a baseline of 1.6 mm, the ladar can generate both well-focused two-dimensional SAL images without adopting phase error removing techniques and three-dimensional images by interferometric SAL techniques. Detailed results are illustrated for retro-reflective or diffusive targets at a distance of 2.4 m.
110.6880 Three-dimensional image acquisition 280.4788 Optical sensing and sensors 280.3640 Lidar 110.0110 Imaging systems 
Chinese Optics Letters
2014, 12(9): 091101
Author Affiliations
Abstract
Key Laboratory of Space Laser Communication and Detection Technology, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
In a two-stage optical parametric amplifier based on KTiOAO4 crystals, we apply beam-overlapping technique to nanosecond signal pulse amplification, which results in high conversion efficiency and good beam quality. A signal pulse energy of 66 mJ at 1.572 μm wavelength is generated with 220 mJ of pump pulse input. A maxi-mum gain of 66 and a maximum pump depletion of as high as 44% are determined. The spectral linewidth of the amplified signal pulse is around 50 MHz, and the beam quality factor of M.2 is less than 2.3.
140.3280 Laser amplifiers 190.4410 Nonlinear optics, parametric processes 
Chinese Optics Letters
2014, 12(9): 091401
Author Affiliations
Abstract
Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Science, Beijing 100083, China
We report the fabrication of widely tunable ridge waveguide distributed Bragg reflector (DBR) lasers with InGaAsP butt-joint as grating material. The shape of the butt–joint interface is found to have significant effect on the properties of the lasers. It is shown that irregular mode jumps during wavelength tuning can be avoided by a V-shaped butt–joint interface. From the fabricated device, 23 channels with 0.8 nm spacing and greater than 35 dB side mode suppression ratios are obtained. The different tuning characteristics of the ridge waveguide and the previously reported buried ridge stripe DBR lasers are discussed. Combined with the wide tuning range and the simple structure, the ridge waveguide DBR lasers are promising for use in wavelength division multiplexing passive optical networks (WDM-PONs).
230.1480 Bragg reflectors 140.3600 Lasers, tunable 230.7370 Waveguides 230.0250 Optoelectronics 
Chinese Optics Letters
2014, 12(9): 091402
Author Affiliations
Abstract
College of OptoElectric Science and Engineering, National University of Defense Technology, Changsha, Hunan 410073, China
A model of steady-state rate equations including amplified spontaneous emission for long-wavelength ytterbi-um-doped fiber laser is set up, which provides design principle for a practical laser system. We demonstrate a diode-pumped all-fiber Yb-doped fiber laser at 1150 nm with an output power of 33.6 W, the optical efficiency is 60%.
140.3510 Lasers, fiber 060.3510 Lasers, fiber 
Chinese Optics Letters
2014, 12(9): 091403
Author Affiliations
Abstract
1 Department of Electrical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia
2 Department of Electrical Engineering, Universiti Teknologi Malaysia, Kuala Lumpur 54100, Malaysia
We propose a Q-switched Er-doped fiber laser (EDFL) with a threshold pumping power as low as 7.4 mW, and demonstrate using graphene polyvinyl alcohol (PVA) thin film as a passive saturable absorber (SA). The SA is fabricated from graphene flakes, which is synthesized by electrochemical exfoliation of graphite at room temperature in 1% sodium dodecyl sulfate aqueous solution. The flakes are mixed with PVA solution to produce a thin film, which is then sandwiched between two ferrules to form a SA and integrated in the EDFL ring cavity to generate a stable Q-switched pulse train. The pulse train operates at 1560 nm with a threshold pump power of 7.4 mW. At maximum 1480 nm pump power of 33.0 mW, the EDFL generates an optical pulse train with a repetition rate of 27.0 kHz and pulse width of 3.56 μs. The maximum pulse energy of 39.4 nJ is obtained at a pump power of 14.9 mW. This laser can be used as a simple and low-cost light source for metrology, environmental sensing, and biomedical diagnostics.
060.3510 Lasers, fiber 320.7090 Ultrafast lasers 060.2410 Fibers, erbium 
Chinese Optics Letters
2014, 12(9): 091404
Author Affiliations
Abstract
We synthesize continuous solid solutions with monophasic zircon-type structure of vanadates of formula YxBi0.95-xVO4:0.05Dy3+ (x = 0–0.95) using a combined method of co-precipitation and hydrothermal synthesis. The X-ray diffractometer patterns confirm the formation of a solid solution of YxBi0.95-xVO4:0.05Dy3+, and the results show that all the samples have monophasic zircon-type structure. The absorption spectra of the prepared phosphors show a blue-shift of the fundamental absorption band edge with increasing Y3+ content. An intense tunable characteristic emission of Dy3+ is observed with the increasing ratio of Y/Bi. Finally, the mechanism of luminescence of Dy3+ in the YxBi0.95-xVO4:0.05Dy3+ (x = 0–0.95) solid solution is analyzed and discussed.
160.0160 Materials 230.0230 Optical devices 300.0300 Spectroscopy 
Chinese Optics Letters
2014, 12(9): 091601
Author Affiliations
Abstract
1 Department of Applied Physics, Chongqing University, Chongqing 401331, China
2 Chongqing Key Laboratory on Optoelectronic Functional Materials, Chongqing Normal University, Chongqing 401331, China
The electronic and optical properties, including band structure, density of states (DOS), absorption rate, refractive index, and dielectric function, of anatase TiO2 codoped with N and first transition elements are investigated using the plane wave pseudopotential method based on the density functional theory. The calculation results show that TiO2 codoping with N and first transition elements (Sc, V, Cr, Mn, and Fe) lead to significant reduction of conduction band relative to the Fermi level, reduction of band gap width, formation of new donor, and acceptor impurity levels below the conduction band and above the valence band, and cause some redshifts of optical absorption band edge with the amount of redshift decrease in the following order: N–Fe > N–Cr > N–Mn. Further, the synergistic effect of shallow donor and acceptor levels enhances light excitation for effective separation of electron–hole pairs and enhancement of light absorption ability, thereby increasing the TiO2 photocatalytic properties. This study reveals that the visible-light absorption ability of the codoped anatase TiO2 decreases in the order of N–Fe > N–Cr > N–Mn > N–Sc > N–V > N, and does not monotonically follow the dopant atomic number. Especially, in N–Cr codoped TiO2, the 4s atomic orbit of Cr is not completely filled, which hybridized with the p electronic orbit most probably acts as photo-generated electron trap centers resulting in higher photocatalytic activity than that of N–Mn codoped TiO2.
160.6990 Transition-metal-doped materials 160.4760 Optical properties 
Chinese Optics Letters
2014, 12(9): 091602
Author Affiliations
Abstract
1 Key Laboratory of Advanced Process Control for Light Industry (Ministry of Education), Department of Electronic Engineering, Jiangnan University, Wuxi 214122, Jiangsu, China
2 The 38th Research Institute of China Electronics Technology Group Corporation, Hefei 230088, China
We study the performance of GaN-based p–i–n ultraviolet (UV) photodetectors (PDs) with a 60 nm thin p-type contact layer grown on patterned sapphire substrate (PSS). The PDs on PSS exhibit a low dark current of ~2 pA under a bias of -5 V, a large UV/visible rejection ratio of ~7×103, and a high-quantum efficiency of ~40% at 365 nm under zero bias. The average quantum efficiency of the PDs still remains above 20% in the deep-UV region from 280 to 360 nm. In addition, the noise characteristics of the PDs are also discussed, and the corresponding specific detectivities limited by the thermal noise and the low-frequency 1/f noise are calculated.
230.0250 Optoelectronics 230.5160 Photodetectors 230.5440 Polarization-selective devices 
Chinese Optics Letters
2014, 12(9): 092301
Author Affiliations
Abstract
We design and fabricate compact, low loss, and high port-count optical power splitters of 1 × 128 and2 × 128 using silica-based planar lightwave circuit (PLC) technology on 6 inch quartz substrate. PLC tech-nology is mainly based on plasma enhanced chemical vapor deposition, photolithography, and etching. The measured results show that the insertion loss, uniformity, and wavelength-dependent loss of 1 × 128 and 2 × 128 optical power splitters are less than 23, 1.43, and 0.92 dB and 23.3, 1.8, and 1.3 dB, respectively, in the wavelength range from 1.26 to 1.65 mm. The polarization-dependent losses are less than 0.16 and 0.2 dB, respectively, in the wavelengths of 1.31, 1.49, and 1.55 mm.
230.7370 Waveguides 230.1360 Beam splitters 230.7390 Waveguides, planar 
Chinese Optics Letters
2014, 12(9): 092302
Author Affiliations
Abstract
Laboratory of Optical Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
High-sensitivity and broad bandwidth photo-detector devices are important for both fundamental studies and high-technology applications. Here, by using three-dimensional (3D) finite-difference time-domain simulation, we design an optimized 3D multilayer gold nano-antenna to enhance the nearinfrared (NIR) absorption of germanium nanoparticles. The key ingredient is the simultaneous presence of multiple plasmonic resonance modes with strong light-harvesting effect that encompass a broad bandwidth of germanium absorption band. The simulation results show more than two orders of magnitude enhanced absorption efficiency of germanium around 1550 nm. The design opens up a promising way to build high-sensitivity and broad bandwidth NIR photo-detectors.
240.6680 Surface plasmons 230.5750 Resonators 220.2740 Geometric optical design 290.5850 Scattering, particles 
Chinese Optics Letters
2014, 12(9): 092401
Author Affiliations
Abstract
State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876, China
We propose and analyze a long-range dielectric-loaded surface plasmon polariton (SPP) waveguide based on graded-index ridge over server millimeter distances. Then the influence of the dielectric thickness and the ridge refractive index on propagation length and mode width is discussed and simulated with the finite ele-ment method. The result shows that the SPP can propagate as long as 3.42 mm, as well as the mode width keeping as 1.64 mm, a better one compared with the fixed refractive index. Considering its nanoscale dimen-sion and outstanding performance, the structure is easily realized when connected with electrodes.
240.6680 Surface plasmons 160.4236 Nanomaterials 230.7370 Waveguides 
Chinese Optics Letters
2014, 12(9): 092402
Author Affiliations
Abstract
1 Department of Physics, East China University of Science and Technology, Shanghai 200237, China
2 Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
We demonstrate a method for further reducing the cavity linewidth by the application of a small longitudinal magnetic field on the Rb cell. Because of the magnetic field multiple electromagnetically induced transparencies (EITs) are observed. The center EIT linewidth is measured as a function of the magnetic field. By utilizing the center EIT we narrow the cavity linewidth to 2 MHz which is half of the cavity linewidth without magnetic field.
270.1670 Coherent optical effects 300.3700 Linewidth 260.2030 Dispersion 020.7490 Zeeman effect 
Chinese Optics Letters
2014, 12(9): 092701
Keding Yan 1,2,3Shouyu Wang 1,2,3Shu Jiang 4Liang Xue 5[ ... ]Zhenhua Li 1,2,3
Author Affiliations
Abstract
1 Department of Information Physics &
2 Engineering, Nanjing University of Science &
3 Technology, Nanjing 210094, China
4 704 Institute, China Shipbuilding Industry Corporation, Shanghai 200031, China
5 College of Electronic and Information Engineering, Shanghai University of Electric Power, Shanghai 200090, China
6 China North Vehicle Research Institute, Beijing 100072, China
7 Xi'an Modern Control Technology Institute, Xi'an 710065, China
A new criterion for target detection and identification is proposed to realize metal/dielectric identification and recognition based on Mueller matrix analysis. By using randomly rough surfaces as targets, numerical calculations are used to prove the robustness and accuracy of the criterion. Moreover, to the best of our knowledge, this is the first time to successfully explain the criterion by theoretical analysis. We believe the work provides an important reference for polarization imaging in laser radar and remote sensing, and so on.
290.5880 Scattering, rough surfaces 240.5770 Roughness 290.0290 Scattering 240.0240 Optics at surfaces 
Chinese Optics Letters
2014, 12(9): 092901
Author Affiliations
Abstract
1 Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei 230026, China
2 Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
In inertial confinement fusion, the laser–plasma interaction (LPI) happens when the high-energy laser irradi-ates on the target where the scattered light share generated from the stimulated Raman scattering (SRS) effect is difficult to suppress. We propose a method using fence pulses (FPs) to suppress the backward SRS by inhibiting the growth of the intensity of electron plasma waves. Based on our simulation, the FPs can weaken SRS effect in the LPI effectively.
290.1350 Backscattering 290.5910 Scattering, stimulated Raman 
Chinese Optics Letters
2014, 12(9): 092902
Author Affiliations
Abstract
1 School of Materials and Metallurgy, Northeastern University, Shenyang 110819, China
2 Engineering Research Center for Process Technology of Nonferrous Metallurgy, Ministry of Education, Shenyang 110819, China
We study ionic structure of KNO3–NaNO2 melts under air atmosphere by using Raman spectroscopy. Molar fraction of NO3- and NO2- is obtained and thermal stability of this kind of melts system is then analyzed. The results show that when the temperature is increased to a certain value, equilibrium between the decom-position of NO3- and the oxidation of NO2- exists in KNO3–NaNO2 melts. When temperature is higher than 644 K, the molar fraction of NO3- decreases a little with temperature increasing for the melts in which the initial fraction of KNO3 is 90 wt%, but for the melts in which the initial fraction of KNO3 is 10–80 wt%, the molar fraction of NO3- increases with temperature, and the increasing rate is slower for a higher initial frac-tion of KNO3. Molar fraction of NO3- increment increases linearly with initial fraction of NaNO2. The sample in which the initial fractions of NaNO2 are 11.3 and 14.5 wt% under air atmosphere shows the best thermal stability at 762 and 880 K, respectively.
300.6450 Spectroscopy, Raman 290.5860 Scattering, Raman 
Chinese Optics Letters
2014, 12(9): 093001
Author Affiliations
Abstract
1 CAS Key Laboratory of Materials for Energy Conversion, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
2 Inorganic Materials Analysis and Testing Center, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050, China
Highly conducting ZnO:Al (AZO) films are normally prepared through substrate heating and post-annealing in reducing atmosphere, which is deleterious to maintain the high transparency of films and the overall so-lar cell performance. Here we fabricate AZO films through one-step sputtering at room temperature using oxygen-deficient targets prepared via double crucible method. The best-performed AZO film achieves a low resistivity of 4.4 × 10-4 . cm, a high haze factor of 35.0%, and optimizes the efficiency of Cu (In, Ga)Se2 solar cell with a high value of 14.15%. This letter demonstrates that oxygen deficiency can induce high surface texture, conductivity, and boost solar cell performance.
000.1570 Chemistry 040.5350 Photovoltaic 160.4670 Optical materials 240.0310 Thin films 
Chinese Optics Letters
2014, 12(9): 093101
Shengzhen Yi 1,2,3Baozhong Mu 1,2Xin Wang 1,2Li Jiang 1,2[ ... ]Sizu Fu 4
Author Affiliations
Abstract
1 MOE Key Laboratory of Advanced Micro-Structured Materials, Shanghai 200092, China
2 School of Physics Sciences and Engineering, Tongji University, Shanghai 200092, China
3 School of Aerospace Engineering and Applied Mechanics, Tongji University, Shanghai 200092, China
4 Shanghai Institute of Laser Plasma, CAEP, Shanghai 201800, China
A four-channel Kirkpatrick–Baez microscope working at multiple energy bands is developed for multiframe X-ray imaging diagnostics at the Shenguang-II laser facility. The response to the multiple energy bands is realized by coating the double-periodic multilayers on the reflected surfaces of the microscope. Because of the limited size of the microstrips in the X-ray framing camera, the image separation is controlled by the conical angle of the reference cores during microscope assembly. This study describes the optical and multilayer design, assembly, and alignment of the developed microscope. The microscope achieves a spatial resolution of 4–5 mm in the laboratory and 10–20 mm at Shenguang-II laser facility within a 300 mm field of view. The versatile nature of the developed microscope enables the multiple microscopes currently installed in the laser facility to be replaced with a single, multipurpose microscope.
340.7440 X-ray imaging 310.6845 Thin film devices and applications 340.7470 X-ray mirrors 
Chinese Optics Letters
2014, 12(9): 093401