In this paper, a single elliptical patch antenna is proposed to generate double-deflection orbital angular momentum (OAM) vortex beams. The physical mechanism of an equivalent uniform elliptical array (UEA) is constructed and analyzed by using the theory of characteristic modes. The elliptical patch antenna can be fed with a 3dB directional coupler to generate the double-deflection vortex beams with single OAM mode or mixed OAM modes. The simulation and measurement results verify that the proposed single elliptical patch antenna is a simple, miniaturized, and multifunctional generator for OAM vortex beams.
We report on stable passively harmonic mode-locking dissipative pulses with high repetition rate and narrow bandwidth in 2µm Tm: CaYAlO4 laser. At the large intracavity intensity, the laser generated 1st-order to 5th-order passively harmonic solitons with fundamental repetition rate of ~198 MHz and 5th-order repetition rate up to 0.98 GHz, which was mainly caused by the peak power clamp effect. The solitons yielded a tunable central wavelength from 1940nm to 1950 nm, and a narrow optical spectrum bandwidth of 60 pm without any active optical filter. At low intracavity intensity, the laser operated on the typical SESAM-guided mode-locking mode, with the scaled output average power up to 1.15 W. To our knowledge, this is the first observation of passively harmonic mode locking in 2µm solid laser system, and the first Watt-level output average power in Tm: CYA mode locking laser.
In this paper, we propose a method to generate a high-order Bessel orbital angular momentum (OAM) vortex beam by using a single-layer reflective metasurface, which integrates the advantages of small size, high efficiency, insensitive polarization and stable incident angles. An offset-fed horn configuration is adopted to overcome the feed-blockage effect, and a subwavelength unit cell with rotational symmetry is designed to cover the reflection phase variation range of 360° in different incident angles. The metasurface is simulated, fabricated and measured at the center frequency of 10 GHz, and the results validate that a second-order Bessel OAM vortex beam can be generated effectively. By comparing the field distributions between the Bessel OAM vortex beam and the conventional OAM vortex beam, we find that the generated Bessel OAM vortex beam is obviously more convergent and has more stable field distributions. The single-layer reflective metasurface is simple and flexible to shape the wavefront to be a Bessel OAM vortex wave, which has the potential to be used in a wide range of applications. INDEX TERMS Bessel orbital angular momentum (OAM) vortex beam, high efficiency, insensitive polarization, single-layer reflective metasurface, stable incident angles
A continuous liquid level sensor (LLS) based on an in-fiber Michelson interferometer is proposed and experimentally demonstrated. The in-fiber Michelson interferometer is formed by a single long period grating (LPG) together with a reflective mirror at the end of the fiber. The portion between the mirror and LPG is immersed in the liquid to be measured as an LLS sensing probe, and the liquid level can be measured by monitoring the wavelength of interference fringes of the in-fiber Michelson interferometer. The experimental results show that the proposed LLS has a good sensing linearity and sensitivity.
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