Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Design and analysis of broadband diffractive optical element for achromatic focusing
No full textThe achromatic diffractive optical element (DOE) was numerically studied. The light intensity distribution in the focal plane was studied by the vectorial diffraction theory, then the radially symmetric DOE to enable broadband achromatic focusing with low sidelobe intensity ratios and uniform central intensities were optimized by the simulated annealing (SA) algorithm. The plane wave with wavelength of 486nm, 588nm, and 656nm were used in our optimization and numerical research. Three DOEs with 60, 80, and 100 transition points were obtained. Numerical results shown that the sidelobe intensity suppression ratios of focal spots of these wavelengths are all less than 0.12, the principal peaks' intensities differences and spots' sizes differences of these focal spots are all less than 5% and 10%, respectively. The designed DOEs were polarization insensitive
High-density grating pair for displacement measurement
No full textA novel method of displacement measurement based on a high density grating pair is proposed. When a laser beam is incident normal to a closely placed high density grating pair, efficiencies of transmission diffraction orders will change periodically along with the relative displacement of the two gratings in the grating period direction. The period of efficiency changing is equal to the grating period, thus measurement of displacement in the grating period direction can be achieved by detecting the power of diffraction orders
Calibration of photoelastic modulator using direct current component
No full textInternational Science & Technology Cooperation Program of China [2016YFE0110600]; International Science & Technology Cooperation Program of Shanghai [16520710500]; Youth Innovation Promotion Association CASA method of calibrating the photoelastic modulator (PEM) using direct current component is proposed. The laser beam passes through a polarizer, the PEM to be calibrated and is then split into two sub-beams by a Wollaston prism. The two sub-beams are then detected by two detectors. The small peak retardation is independent of the fluctuation of the initial intensity. The calibration setup is compact. In experiments, a PEM was calibrated and the calibration error was less than 0.008 rad when the peak retardation changed in the range of 0.1 lambda-0.5 lambda
Fast modal decomposition for optical fibers using digital holography
No full textNational Natural Science Foundation of China [61377005]; Chinese Academy of Sciences [QYZDB-SSW-JSC002]Eigenmode decomposition of the light field at the output end of optical fibers can provide fundamental insights into the nature of electromagnetic-wave propagation through the fibers. Here we present a fast and complete modal decomposition technique for step-index optical fibers. The proposed technique employs digital holography to measure the light field at the output end of the multimode optical fiber, and utilizes the modal orthonormal property of the basis modes to calculate the modal coefficients of each mode. Optical experiments were carried out to demonstrate the proposed decomposition technique, showing that this approach is fast, accurate and cost-effective
Narrow-spectral-span spectral beam combining with a nonparallel double-grating structure
No full textShanghai Science and Technology Committee [16DZ2290102, 15JC1403500]; Chinese Academy of Sciences [QYZDJ-SSW-JSC014]; National Natural Science Foundation of China [61405216]We propose a nonparallel double-grating structure in a spectral-beam combining technique, where two gratings are placed nonparallel satisfying the Littrow mount in the focal region of the convergent lens. The most attractive advantage of this approach is that it will compress the spectral span into half of its original spectrum, which means the number of combined elements can be doubled in the gain range of diode lasers. Experimental results demonstrate that the CW output power of the combined beam is 30.9 W with a spectral span of 7.0 nm, compared with its original spectrum span of 13.6 nm, and the spectral beam combining efficiency is 70.5%. In consideration that a single grating could have a high efficiency of > 97% in a bandwidth of over ten nanometers, the efficiency loss of the grating pair should be less than 6%, which is acceptable for most applications, so this method of using double gratings should be highly interesting for practical applications when a nearly doubled number of diode lasers could be combined into one single laser compared with the previous single-grating methods
Efficient dual-mode up-conversion and down-shifting emission in -NaYF4:Yb3+,Er3+ microcrystals via ion exchange
No full textNational Natural Science Foundation of China [61405215, 61505232]We report efficient dual-mode up-conversion (UC) and down-shifting (DS) emission in a single Yb3+/Er3+-co-doped -NaYF4 microcrystals with controlled morphology and size via a simple Na+ ion-exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal-synthesized -NaYF4. Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er3+ and Yb3+ by several times in -NaYF4:Yb3+,Er3+ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er3+ and Yb3+ in visible and near-infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in -NaYF4:Yb3+,Er3+ are mainly ascribed to the dispersing of localized Yb3+ and Er3+ clusters during IEM
Enhanced 3 mu m luminescence properties based on effective energy transfer Yb3+ : F-2(5/2) -> Dy3+ : H-6(5/2) in fluoaluminate glass modified by TeO2
No full textNational Natural Science Foundation of China (NSFC) [51372235, 51401197, 51472225, 61605192]; South China University of Technology (Open Fund of the Guangdong Engineering Technology Research and Development Center of Special Optical Fiber Materials and Devices)Enhanced 3 mu m luminescence of Dy3+ based on the effective process of Yb3+: F-2(5/2). Dy3+: H-6(5/2) with a higher energy transfer coefficient of 7.36 x 10(-39) cm(6)/s in fluoaluminate glass modified by TeO2 was obtained. The energy transfer efficiency from Yb3+ to Dy3+ in Dy3+/ Yb3+ codoped glass was as high as 80%, indicating the effective energy transfer of Yb3+. The higher temperature of the glass transition (T g) and larger characteristic temperatures (Delta T; K gl) revealed better thermal properties of the prepared glasses compared with the traditional fluoaluminate glasses, which is of great benefit to fiber drawing. The lower hydroxyl content (15.7 ppm) indicated better fluorescence properties of the glass. It was noted that the longer lifetime of 572 mu s and higher emission cross section of 5.22 x 10(-21) cm(2) along with the bandwidth of 245 nm around 3 mu m proved potential applications in mid- IR laser materials of the present glass
Manipulating refractive index, homogeneity and spectroscopy of Yb3+-doped silica-core glass towards high-power large mode area photonic crystal fiber lasers
No full textNational Natural Science Foundation of China [61505232, 61405215]; Youth Innovation Promotion Association of the Chinese Academy of Sciences; National High Technology Research and Development Program of China [2016YFB0402201]Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb3+-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb3+/Al3+/F-/P5+-co-doped silica core-glass (YAFP), which is prepared by modified sol-gel method developed by our group and highly suitable for fabricating high power LMA PCF amplifiers. By controlling the doping combinations of Al3+/F-/P5+ in Yb3+-doped silica glass, it not only ensures low refractive index (RI) but also maintains the excellent optical homogeneity and spectroscopic properties of Yb3+. The spectroscopic properties of Yb3+ ions have not deteriorated by the co-doping of F- and P5+ in YAFP glass compared with that of Yb3+/Al3+ co-doped silica glass. A large-size (empty set 5 mm x 90 mm) YAFP silica-core glass rod with low average RI difference of 2.6 x 10(-4) (with respect to pure silica glass), and low radial and axial RI fluctuations of similar to 2 x 10(-4), was prepared. A LMA PCF with 50 mu m core diameter was obtained by stack-capillary-draw techniques using YAFP core glass. Its core NA is 0.027. An average amplified power of 97 W peaking at 1030 nm and light-light efficiency of 54% are achieved from a 6.5 m long PCF in the pulse amplification laser experiment. Meanwhile, quasi-single-mode transmission is obtained with laser beam quality factor M-2 of 1.4
MoS2/Carbon Nanotube Core-Shell Nanocomposites for Enhanced Nonlinear Optical Performance
No full textNational Natural Science Foundation of China [51302285, 61522510, 61675217]; External Cooperation Program of BIC, CAS [181231KYSB20130007]; "Strategic Priority Research Program" of CAS [XDB16030700]; Key Research Program of Frontier Science, CAS [QYZDB-SSW-JSC041]Nanocomposites of layered MoS2 and multi-walled carbon nanotubes (CNTs) with core-shell structure were prepared by a simple solvothermal method. The formation of MoS2 nanosheets on the surface of coaxial CNTs has been confirmed by scanning electron microscopy, transmission electron microscopy, absorption spectrum, Raman spectroscopy, and X-ray photoelectron spectroscopy. Enhanced thirdorder nonlinear optical performances were observed for both femtosecond and nanosecond laser pulses over a broad wavelength range from the visible to the near infrared, compared to those of MoS2 and CNTs alone. The enhancement can be ascribed to the strong coupling effect and the photoinduced charge transfer between MoS2 and CNTs. This work affords an efficient way to fabricate novel CNTs based nanocomposites for enhanced nonlinear lightmatter interaction. The versatile nonlinear properties imply a huge potential of the nanocomposites in the development of nanophotonic devices, such as mode-lockers, optical limiters, or optical switches
Passively Q-Switched Laser at 1.3 mu m With Few-Layered MoS2 Saturable Absorber
No full textNational Natural Science Foundation of China [61475088, 61475177, 51302285, 61522510]; Open Foundation of State Key laboratory of Crystal Material of Shandong University [KF1403]; Young Scholars Program of Shandong University [2015WLJH38]; External Cooperation Program of Bureau of International Co-operation Chinese Academy of Sciences [181231KYSB20130007]Solid-state passively Q-switched Nd: LuAG laser at 1.3 mu m with few layered MoS2 as saturable absorber has been experimentally realized and demonstrated. The shortest pulse width of 188 ns and pulse repetition rate of 73 kHz were obtained. The experimental results verified the broadband saturable absorption characteristics of MoS2 and indicated its ability to generate short pulses