Chinese Optics Letters
Search

2014, 12(2) Column

MORE

Chinese Optics Letters 第12卷 第2期

Author Affiliations
Abstract
We design two types of reflectors by using subwavelength high-index contrast gratings, which exhibit similar high focusing capabilities at normal incidence with a TE-polarized plane wave. One type has bars of different heights, whereas the other has bars of different depths. Both grating reflectors are designed to be approximately 22 \mu m in structural length and 10 \mu m in focal length, at an operating wavelength of 1.55 \mu m. Both achieve a full-width-half-maximum of 0.9 \mu m at the focal plane, which is fairly close to the diffraction limit. Their reflectance reach as high as 94% and 91%.
050.2770 Gratings 050.6624 Subwavelength structures 050.5080 Phase shift 230.4040 Mirrors 
Chinese Optics Letters
2014, 12(2): 020501
Author Affiliations
Abstract
We propose a polarization-insensitive and broadband subwavelength grating reflector based on a multilayer structure. The reflector has an overlapped high reflectivity (>99.5%) bandwidth of 248 nm between the TE and the TM polarizations, which is much higher than the previously reported results. We believe this subwavelength grating reflector can be applied to unpolarized devices.
050.1950 Diffraction gratings 050.5080 Phase shift 050.6624 Subwavelength structures 230.4170 Multilayers 
Chinese Optics Letters
2014, 12(2): 020502
Author Affiliations
Abstract
The laser source is an important element whose properties have influence on the output performance of single sideband (SSB) optical comb based on recirculating frequency shifter (RFS). The theoretical and experimental results show that the tone-to-noise ratio (TNR), flatness, and stability of optical comb improve using laser source with narrower linewidth. In order to obtain the optical comb with TNR larger than 42 dB and degree of stability (DOS) smaller than -6.7 dB, external cavity laser (ECL) with linewidth from 100 kHz to 1 MHz is a trade-off choice.
060.2330 Fiber optics communications 060.2630 Frequency modulation 140.3430 Laser theory 
Chinese Optics Letters
2014, 12(2): 020601
Author Affiliations
Abstract
A photonic generation of multi-frequency source based on the heterodyne of two phase-locked optical frequency combs (OFCs) is proposed and demonstrated. By applying an optical phase-locked loop, the phase noise induced by optical links is decreased by approximately 70, 66, and 35 dB at 0.01, 0.1, and 1.0 Hz offset frequencies, respectively. The proposed scheme provides 8 radio frequency signals, the frequencies of which span from 540 to 4040 MHz, with a 500-MHz interval. The number of generated signals can be readily scaled by using OFCs with broader bands, whereas the frequencies can be scaled by tuning the repetition rates of OFCs.
060.5625 Radio frequency photonics 350.4010 Microwaves 060.2330 Fiber optics communications 
Chinese Optics Letters
2014, 12(2): 020602
Author Affiliations
Abstract
We construct a dimethylsulfoxide (DMSO)-based photonic crystal fiber (PCF) temperature sensor with enhanced sensitivity. A solid-core PCF with large mode area is employed to supply the in-line Mach-Zehnder interference between the fundamental and cladding modes. Thus, temperature sensing can be realized because of the shift of interference spectrum at different temperatures.The DMSO solvent is infiltrated between the main sensor and a silica tube to increase the temperature sensitivity of the sensor. The obtained sensitivity (0.315 nm/oC) is one or two orders of magnitude higher than that of previously published results. The proposed sensor is adapted for high-temperature sensing.
060.0060 Fiber optics and optical communications 060.2370 Fiber optics sensors 060.5295 Photonic crystal fibers 060.2430 Fibers, single-mode 
Chinese Optics Letters
2014, 12(2): 020603
Author Affiliations
Abstract
A simple optical fiber cantilever vibration sensor consisting of two opposite aligned bare optical fibers sealed in a quartz capillary is presented.The fiber with the longer bare section is suspended in air and acts as a cantilever. By detecting the transmission power of the sensor directly, the environmental vibrational frequencies and amplitudes may be obtained. By adjusting the cantilever's natural deflection angle, the sensor can achieve high sensitivity, good response linearity, and a wide dynamic range. Coupling conditions are optimized to minimize temperature effects by simply setting an appropriate air gap between the bare fibers.
060.2370 Fiber optics sensors 280.4788 Optical sensing and sensors 120.7280 Vibration analysis 
Chinese Optics Letters
2014, 12(2): 020604
Author Affiliations
Abstract
A simple configuration for the generation of a switchable dual-wavelength fiber ring laser is presented. The proposed configuration employs a short twin-core photonic crystal fiber acting as a Mach–Zehnder interferometer at room temperature. A polarization controller is further utilized to enable switchable dualwavelength operation.
060.2330 Fiber optics communications 060.3510 Lasers, fiber 060.5295 Photonic crystal fibers 060.2370 Fiber optics sensors 
Chinese Optics Letters
2014, 12(2): 020605
Author Affiliations
Abstract
A phase retrieval method for dual-wavelength in-line digital holography is presented with double axially displaced holograms. A synthetic wavelength is used during iterative propagations to retrieve wrap-free phase distributions with a much extended measurement range. The simulation and experimental results demonstrate a better elimination of the twin image, a faster rate of convergence of the iterative routine and less number of wavelengths are compared with previously reported multiple-wavelength in-line holography.
090.1995 Digital holography 100.5070 Phase retrieval 100.3010 Image reconstruction techniques 
Chinese Optics Letters
2014, 12(2): 020901
Author Affiliations
Abstract
The laser cooling of ytterbium (Yb) atoms needs a 399-nm laser which operates on the strong 1S0 -1P1 transition and can be locked at the desired frequencies for different Yb isotopes. We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference. For unresolved fluorescence peaks, we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations; the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references. A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest, and a frequency stability of 304 kHz is achieved. This frequency-locked laser enables us to realize stable blue magneto-optic-traps (MOT) for all abundant Yb isotopes.
140.3425 Laser stabilization 300.6320 Spectroscopy, high-resolution 300.2530 Fluorescence, laser-induced 
Chinese Optics Letters
2014, 12(2): 021401
Author Affiliations
Abstract
We present a high-precision optical phase-locking based on wideband acousto-optical frequency shifting. Increasing the modulating bandwidth stabilizes the loop at a high loop gain, thus improving phase correction capability. An optical phase-locked loop with a wide control bandwidth is constructed. The closed-loop residual phase error is only 0.26o or smaller than \lambda/1000. The loop exhibits excellent correction capability for high-frequency noises. The correctable frequency range reaches 35 kHz when the noise amplitude is +(-)\lambda/2, and becomes even wider for smaller noise amplitudes.
140.0140 Lasers and laser optics 140.3298 Laser beam combining 140.3518 Lasers, frequency modulated 
Chinese Optics Letters
2014, 12(2): 021402
Author Affiliations
Abstract
A non-adiabatic microfiber coupler is fabricated by flame brushing technique and then theoretically and experimentally analyzed. The effective length of the microfiber coupler is determined by simulation, and a low-noise laser is demonstrated using various lengths of erbium-doped fiber (EDF) when incorporated in a laser setup. At 18.6-mW input pump power, the maximum output power of 20 \mu W and the lowest lasing threshold of 3.8 mW are obtained with a 90-cm-long EDF.
140.0140 Lasers and laser optics 060.0060 Fiber optics and optical communications 190.0190 Nonlinear optics 
Chinese Optics Letters
2014, 12(2): 021403
Author Affiliations
Abstract
A compact monolithic Nd:YAG non-planar ring laser with diffusion-bonded Cr4+:YAG is demonstrated, and high stable pulsed single-frequency laser at 1.06 \mu m is realized. Theoretical analysis and simulation results of pulsed laser parameters are illustrated. 14.96-kW maximum peak power, pulse-width of 4.8 ns is achieved for single-frequency operation.
140.3540 Lasers, Q-switched 140.3560 Lasers, ring 140.3570 Lasers, single-mode 
Chinese Optics Letters
2014, 12(2): 021404
Author Affiliations
Abstract
A passively Q-switched tunable Yb-doped double-clad fiber laser is demonstrated with graphene epitaxially grown on SiC. The spectral tuning of the Q-switched fiber laser is implemented by rotating a quartz plate filter inside the cavity. The central wavelength of the fiber laser can be continuously tuned from 1038.54 to 1056.22 nm. The maximum pulse energy of 0.65 \mu J is obtained at the pump power of 4.08 W, and the corresponding pulse duration and average output power are 1.60 \mu s and 35 mW, respectively.
140.3540 Lasers, Q-switched 140.3510 Lasers, fiber 140.3600 Lasers, tunable 140.3538 Lasers, pulsed 
Chinese Optics Letters
2014, 12(2): 021405
Author Affiliations
Abstract
Mid-infrared (MIR) emissions of 2.4 and 3.5 m from Tm3+:LiYF4 single crystals attributed to 3H4->3H5 and 3H5->3F4 transitions as well as MIR emissions of 4.2, 4.3, and 4.5 \mu m from Nd3+: LiYF4 lasers attributed to 4I15/2->4I13/2,4I13/2->4I11/2, and 4I11/2->4I9/2 transitions, respectively, are observed. LiYF4 single crystals possess high transmittance of over 85% in the 2.5-6 \mu m range. The large emission crosssections of Tm-doped crystals at 2.4 \mu m (1.9\times 10-20 cm2) and Nd-doped crystals at 4.2 \mu m (0.84\times 10-20cm2) as well as the high rare-earth doping concentrations, excellent optical transmission, and chemicalphysical properties of the resultant samples indicate that Nd3+ and Tm3+ singly doped crystals may be promising materials for application in MIR lasers.
160.3380 Laser materials 160.4760 Optical properties 160.5690 Rare-earth-doped materials 140.3380 Laser materials 
Chinese Optics Letters
2014, 12(2): 021601
Author Affiliations
Abstract
We theoretically study the light outcoupling efficiency of top-emitting organic light-emitting diode (OLED) with inverted structure and thin-film encapsulation. Thin-film optics is used to optimize the layer thickness to obtain high transmittance. Dipole mode is used to analyze the light outcoupling efficiency of the top-emitting OLED. Through this process, we can optimize the thin-film thickness with high transmittance and optimize the outcoupling efficiency of OLED. Compared with previous research, the current design method is a novel process.
230.0230 Optical devices 230.3670 Light-emitting diodes 250.5230 Photoluminescence 160.4890 Organic materials 
Chinese Optics Letters
2014, 12(2): 022301
Author Affiliations
Abstract
A numerical simulation is performed to study the far-field diffraction properties of planar diamond waveguides. The far-field intensity distributions of a planar air waveguide and a diamond waveguide with different distances are given by numerical calculations. In the experiment, the diffraction patterns on the screen with different distances are recorded using a He-Ne laser as the light source, wherein the laser beam is coupled with and propagates in the diamond waveguide. The simulation results are found to be consistent with the experimental ones.
230.7390 Waveguides, planar 070.7345 Wave propagation 220.2560 Propagating methods 260.6970 Total internal reflection 
Chinese Optics Letters
2014, 12(2): 022302
Author Affiliations
Abstract
A new method based on Maxwell's equations, ABCD ray matrices, and total internal reflection is proposed to theoretically analyze the characteristics of eigenmodes confined in nano-width rectangle resonators. Using this method, mode wavelengths and indices of transverse and longitudinal modes are obtained. Another method based on the finite difference time domain technique and Pad′e approximation is used to numerically calculate resonant wavelengths, mode field distributions and quality factors. The results of two methods show that the resonant wavelengths obtained from both methods are very close, and the maximum relative error is less than 2%. The mode indices of transverse and longitudinal modes obtained agree well with mode field distribution patterns calculated by finite difference time domain techniques.
230.5750 Resonators 230.7370 Waveguides 
Chinese Optics Letters
2014, 12(2): 022303
Author Affiliations
Abstract
A psychophysical experiment under constant stimuli is conducted on a CRT display to measure the visual suprathreshold color differences for five color centers recommended by CIE under the same five background colors. The performances of four CIELAB-based, three CIECAM02-based, and two OSA-UCS-based formulas are tested. Detailed analysis results indicate the existence of chromatic crispening effect. CIEDE2000 performs best for the gray center and gray background, whereas CAM02-LCD and CAM02-UCS have the best performance for non-neutral backgrounds. CAM02-LCD significantly outperforms all other formulas for all color centers under all background colors.
330.0330 Vision, color, and visual optics 330.1720 Color vision 330.5510 Psychophysics 
Chinese Optics Letters
2014, 12(2): 023301
Author Affiliations
Abstract
Traditional integral colorimeters use tungsten–halogen or xenon lamps for illumination, as well as correcting filters to make the instrument's spectral response meet the Luther condition. This structure causes the instruments to have relatively higher error and poor repeatability. Thus, this letter proposes a new measurement design that uses compound LEDs as the instrument's measurement light source. The new design adjusts the instrument's spectral response by modifying the spectra of the compound LEDs. A compound LED light source is designed for integral colorimeters, and an experiment is conducted to evaluate the performance of the integral colorimeter. Experiments show that the design effectively reduces the error of integral colorimeters.
330.1710 Color, measurement 040.5160 Photodetectors 120.6200 Spectrometers and spectroscopic instrumentation 
Chinese Optics Letters
2014, 12(2): 023302
Author Affiliations
Abstract
The computed tomography imaging of a local region inside a sample with a size larger than the field of view is particularly important for synchrotron X-ray imaging. In this letter, an improved algorithm is proposed to reconstruct the local structure inside a sample using almost completely local data. The algorithm significantly reduces the X-ray radiation dose and improves computational efficiency. Simulation results show that the new algorithm works well and has a higher reconstruction precision than previous methods, as confirmed by experimental results carried out at the Shanghai Synchrotron Radiation Facility.
340.7440 X-ray imaging 110.6960 Tomography 100.3010 Image reconstruction techniques 340.6720 Synchrotron radiation 
Chinese Optics Letters
2014, 12(2): 023401