Diode-pumped CW and passively Q-switched lasers of Nd:GdLuAG mixed garnet at 1123 nm were demonstrated. The maximum average output power of CW operation was 4.13 W. For Q-switched operation, the average output power was 800 mW, the corresponding single pulse energy was 133.8 μJ. The Nd:GdLuAG laser emitting at 1123 nm was obtained for the first time to the best of our knowledge, which proves that the Nd:GdLuAG mixed garnet has a better ability of energy storage than Nd:YAG in 1123 nm oscillation.
A 4-element wavelength division multiplexed linear array of asymmetric distributed feedback fiber lasers (DFB-FL), pumped at 1480nm is reported. A very desirable feature of asymmetric DFB-FL is unidirectionality, and relevant principle is presented. Larger output powers are obtained from shorter ends of all the four asymmetric DFB-FLs which are fabricated in our laboratory by phase mask moving method. This obvious advantage has important applications to design sensor array. And furthermore, many experiments are completed to confirm it. Output flatness of the sensor array system presents a good performance with the applications of asymmetric DFB-FLs.
In trace water vapor direct absorption spectroscopy, the absorption signal is buried in noise and up and downs of the light intensity, an effective signal extraction method is vital. In the basis of double-beam differential absorption, division method in voltage and an approach based on balanced ratiometer detection (BRD) were studied. Voltage division has an excellent stability to temperature variation, mechanical extrusion and fiber bend loss. As to the BRD method, it has an outstanding self-adjusting capability and it can also avoid an excess phase difference caused by current-to-voltage converting circuit, thus this method has a high sensitivity. Furthermore, a so called dual-peak method based on the differential value of two adjacent absorption lines is introduced, the differential value proved has a linear relation with water vapor concentration, and this method provides a way to measure the concentration at high pressure. In addition, the influence of water vapor inside the optical components has been discussed.
KEYWORDS: Absorption, Modulation, Temperature metrology, Signal to noise ratio, Wavelength tuning, Dielectrics, Absorption filters, Directed energy weapons, Absorption spectroscopy, Data processing
Two measuring methods of wide absorption spectrum by DFB-LDs are presented in detecting water vapor absorption line. One is subsection scanning method, it takes advantage of wide spectrum tuning range by temperature modulation and fast spectrum tuning speed by current modulation, specifically, this method is realized by dividing a target spectral region into several sections which corresponding to specific temperature of DFB-LD, and scanning every section by current modulation for hundreds times and average the data to raise SNR, combining all sections to get the whole spectrum. An accuracy of 10 ppmv had been obtained in the measurement of water vapor with a 10-cm path length by this method. Another is data fitting method, based on absorption line-shape function, the absorption line can be described by fitting with partial measured data. The fitting absorption line is fitted well with the measured data, and the square of correlation coefficient (R-square) is no less than 0.99.
A novel temperature demodulation method which eliminates the impact of Rayleigh scattering on Raman distributed temperature sensors (RDTS) using anti-Stokes light only is presented. This method utilizes two sections of reference fiber which are placed into temperature control chambers with different temperatures, such that the impact caused by the variation of laser’ power and the Rayleigh scattering is eliminated by the two reference temperatures. In the experiment, the temperature error caused by the Rayleigh scattering was decreased by 0.6℃ and 1.7℃ at 30℃ and 50℃compared with conventional method respectively.
The mode competition mechanism in concentric 4-core and 7-core fiber lasers with large mode area single mode (SM)
fiber as in-phase supermode selection component is presented. The coupling coefficient between the fundamental mode
in large mode area SM fiber and each supermode in mutlicore fiber is discussed. For individual supermode in multicore
fiber, the coupling coefficient is optimized as a function of the core radius of SM fiber as well as the distance between
multicore fiber and SM fiber. The optimization results demonstrate that only two supermodes are involved in
concentric-type fiber lasing - in-phase and anti-phase supermode, owing to the negligible coupling coefficients of the
other supermodes. Furthermore, to achieve the best in-phase supermode selection, the core radius of SM fiber will be
optimized for maximum coupling coefficient difference between in-phase supermode and anti-phase supermodes. The
numerical results illustrate that in-phase supermode always dominate the output and is the highest when the distance
equals zero. Compared to conventional multicore fiber lasers with Talbot cavity, this all-fiber configuration based on
large mode area SM fiber has higher-order supermodes more efficiently suppressed and high-brightness output may be
achieved.
Photonic crystal (PhC) is a new class of material which has a periodic modulation of dielectric constant. PhC will exhibit superprism effect, negative refraction and self-collimating ultra-low group velocity due to the anomalous dispersion of PhC . We can utilize the characters of photonic bandgap(PBG), defect band, pass band and band edge to control the propagation of the light .This research was to investigate the refraction and superprism effect of photonic crystals .The study background and the basic theories of photonic crystals were introduced. The refraction of photonic crystals and superprism effect were discussed with the correlating knowledge and the computing methods. A new theory of light refraction at the surface of a photonic crystal was put forward and simulated. The simulating results of this application for negative refraction and superprism effect were demonstrated by some simulating figures. These may bring about important potential applications in some areas.
Keywords: photonic crystal, superprism effect, simulation
Using soft lithography technology, the 2D photonic crystal superprism structures
with a triangle array of air holes on the polymer slab were designed, simulated and
fabricated successfully. The profile of the molded structures with 450nm in diameter
and 900nm in lattice constant was obtained and observed by SEM. By means of
optical experiment and measurement, when the input incident angle varied from 15°
to 11°, we observed the beam propagation angle change from positive to negative and
the superprism effect was demonstrated effectively at near-infrared wavelength
1550nm.
An analysis of superprism effect in low index contrast polymer photonic crystal is presented. It
shows extremely sensitivity to the wavelength and angle of the incident light due to the strong
anisotropy of photonic band structures. Two-dimensional (2-D) polymer photonic crystals with
triangular lattice structure were fabricated by soft lithography using elastomeric
polydimethylsiloxane (PDMS) templates. Dense two dimensional photonic crystal superprism
structures with feature sizes of 150-500nm and aspect ratios of up to 1.25 were successfully
replicated by soft lithography. Large field size and easy fabrication are two major advantages when
compared with other imprint technology. Atomic Force Microscopy images showed that the molded
structures had high fidelity to the masters. Such an effective, low cost, and high throughput soft
lithography technique could find wide use in making photonic crystal based nanostructures.
Photonic crystal based superprism offers a new way to design new optical components for beam steering and DWDM application. 3D photonic crystals are especially attractive as they could offer more control of the light beam based on the needs. A polygonal prism based holographic fabrication method has been demonstrated for a three-dimensional face-centered-cubic (FCC)-type submicron polymer photonic crystal using SU8 as the photo-sensitive material. Therefore antivibration equipment and complicated optical alignment system are not needed and the requirement for the coherence of the laser source is relaxed compared with the traditional holographic setup. By changing the top-cut prism structure, the polarization of the laser beam, the exposure and development conditions we can achieve different kinds of triclinic or orthorhombic photonic crystals on demand. Special fabrication treatments have been introduced to ensure the survivability of the fabricated large area (cm2) nano-structures. Scanning electron microscopy and diffraction results proved the good uniformity of the fabricated structures. With the proper design of the refraction prism we have achieved a partial bandgap for S+C band (1460-1565nm) in the [111] direction. The transmission and reflection spectra obtained by Fourier transform infrared spectroscopy (FTIR) are in good agreement with simulated band structure. The superprism effects around 1550nm wavelength for the fabricated 3D polymer photonic crystal have been theoretically calculated and such effects can be used for beam steering purpose.
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