ABSTRACT
The quality factor of a partially coherent Airy beam in a turbulent atmosphere is investigated with the help of the extended Huygens-Fresnel integral formula and the Wigner distribution. From the numerical results, based on the analytical formula, we find that increasing the inner scale or decreasing the structure constant of the refractive index fluctuations of the turbulent atmosphere tends to decrease the quality factor of a partially coherent Airy beam in a turbulent atmosphere. Moreover, it is found that increasing the scale factor and wavelength or decreasing the coherent length of a partially coherent Airy beam can also be used to decrease the quality factor of a partially coherent Airy beam in a turbulent atmosphere. However, the quality factor of a partially coherent Airy beam in a turbulent atmosphere has a maximum when the exponential truncation factor of a partially coherent Airy beam is 0.63. Our results will be useful in long-distance free-space optical communications and laser defense.
ABSTRACT
Optical differential operation and image edge detection have shown some unique advantages, including faster operating speeds and lower power consumption, compared to a digital image processor. Here, we examine the origin of optical differentiator in the photonic spin Hall effect. We find that the optical differentiator in x direction is related to the beam divergence when the incident angle of the central wave vector meets Brewster's, while the optical differentiator in y direction is related to the cross polarization component. By eliminating the H-H or V-V polarization component, the H-V or V-H polarization component induced the spin-dependent splitting in the photonic spin Hall effect, which can be used for the one-dimensional optical differentiator in an arbitrary direction. Furthermore, we investigate the photonic spin Hall effect and double-peak profile near Brewster angle and predict that a perfect two-dimensional optical differentiator will become a reality.
ABSTRACT
A one-dimensional photonic crystal elliptical-hole tapered low-index-mode nanobeam cavity sensor fully encapsulated in a water environment is proposed. In the proposed structure, to confine the light in the low-index region and enhance the light-matter interaction, a tapered major axis of the elliptical hole away from the nanobeam cavities center is optimized. Through a three-dimensional finite-difference time-domain simulation, the results show that the low-index-mode of the middle geometry cell is confined in the photonic bandgap of two-sided cells. The highest quality factor of 6.04×105 is achieved when 13 tapered segments and 5 mirror segments are placed at both sides of the host waveguide. The proposed nanobeam structure theoretically possesses a sensitivity of 244.7 nm/RIU (refractive index unit) in a water environment. Moreover, an ultra-compact footprint of 6.4 µm×0.85 µm is achieved, which is only half of the size compared to the best value reported for the nanobeam structure. The results indicate that it is a promising sensor for excellent on-chip sensing with respect to the very small footprint.
ABSTRACT
The beam wander of a partially coherent Airy beam in oceanic turbulence is investigated with the help of the extended Huygens-Fresnel integral formula. Analytical expression for the second-order moment and the beam wander of a partially coherent Airy beam propagating in oceanic turbulence is derived. From the numerical results based on the analytical formula, we find that increasing the dissipation rate of turbulent kinetic energy or decreasing the dissipation rate of mean-square temperature and relative strength of temperature and salinity fluctuations of oceanic turbulence tends to decrease the wander effect of a partially coherent Airy beam. Moreover, it is found that increasing the transverse scale factor and wavelength or decreasing the coherent length and exponential truncation factor of a partially coherent Airy beam decreases beam wander in oceanic turbulence. Our results will be useful in optical underwater communications and laser defense.
