ABSTRACT
A ring focus reflector is proposed for transmitting a perfect vortex (PV) beam, and the transmission characteristics of the PV beam with different topological charges in free space after passing through the reflector are studied. The reflector parameters can be determined by fitting the structural formula, and PV beams of different orders transmit with small spot sizes at the same time. The transmission trajectory calculated by the diffraction formula is consistent with the ray tracing results. The research results show that the reflector can achieve a high level of transmission efficiency of beams with different topological charges, which is conducive to the multiplexing of PV beams.
ABSTRACT
Dark hollow beams (DHBs) possess great potential for material processing, holography, and vortex beams, and thus designing a high-Q DHB cavity is significant for these applications. In this Letter, a method of designing and optimizing a high-Q DHB cavity based on a one-dimensional topological photonic crystal (TPhC) is proposed. Furthermore, how the structural parameters control the performance of the cavity is analyzed with the help of finite-element-method (FEM) simulation. According to the simulation results, the Q factor of the designed cavity can reach the order of 105 with only 19 periods of layers. It is critical to mention that, although increasing the layers can improve the average Q of the cavity, it will cause serious fluctuation of both the Q factor and the divergence angle of the output beam. The design method proposed in this Letter may not only help designers of future DHB lasers but also promote the applications of DHBs in various fields.
ABSTRACT
A method of designing negative curvature anti-resonant hollow-core fibers (NC-AR-HCFs) with bending resistance is proposed, by which the fundamental mode (FM) and higher-order mode (HOM) can be adjusted. An asymmetric double-ring negative curvature hollow-core fiber (ADR-NC-HCF) is proposed to verify the method. The ADR-NC-HCF achieves the FM loss of 0.8 dB/km at 1550 nm under the bending radius of 20 mm. The coupling relation between the modes in ADR-NC-HCFs is analyzed revealing the physical principle of the design method. Based on the principle, the fiber can be directionally optimized to achieve a lower loss of the FM or higher-order mode extinction ratio.
ABSTRACT
The efficiency of a hollow beam received by the Cassegrain antenna coupling into a single-mode fiber is low, and converting the hollow beam into a solid beam can remarkably improve the coupling efficiency. In this paper, shaping diffractive optical elements (DOEs) are designed through a modified Gerchberg-Saxton algorithm (MGS) with Fresnel diffraction. Further, the MGS algorithm can be applicable in the issue of circular symmetric beam shaping. The properties of the system with/without shaping DOEs are analyzed and compared. According to the simulation results, in consideration of the energy loss of the antenna, DOEs, and coupling lens, the total transmission efficiency of the receiving antenna system at 1550 nm wavelength can reach 77.81%. In addition, the system with shaping DOEs can better adapt for coupling lenses with different focal lengths, and the variation of the maximum coupling efficiency of the DOEs shaping system at different focal lengths studied in this paper is within 2.00%, which is 6.73% lower than that of the lens shaping system. The research results provide an idea of reverse design for improving a coupling system, which can also provide inspiration for other optical system designs.
ABSTRACT
To solve the serious loss problem for central energy of the Cassegrain antenna, this paper designs a beam-shaping system, named E-A system, to convert the elliptical divergent beam with astigmatism from a laser diode into an annular collimation beam. This E-A system, comprised only of lenses with quadratic surfaces, can simultaneously realize four functions, i.e., aberration correction, beam circularization, beam collimation, and dark hollow beam generation. By adjusting the parameters, the E-A system can be used to shape elliptical astigmatic beams with different parameters. Further, the E-A system can maintain good performance at wavelengths from 500 to 1647 nm. After considering various practical factors, the transmission efficiency of the entire transmitting system can be increased to 93.91% at a wavelength of 1550 nm.
ABSTRACT
Analyzing optical antenna systems through geometrical optics is quite popular for its convenience, which, however, may cause remarkable errors. This paper uses both geometrical optics and diffraction theory to analyze the performance of a traditional optical antenna system, and the results calculated through the two methods are carefully compared. Based on the comparison, it shows the situations in which geometric optics will cause significant errors. In addition, a parameter γ is defined to quickly determine whether geometrical optics is suitable for analyzing optical antenna systems under some situations. This paper can help engineers quickly choose the proper method for designing and analyzing optical antenna systems.
ABSTRACT
The low efficiency of coupling a hollow Gaussian beam into single-mode fiber terribly decreases the transmission efficiency of an optical communication system. In this paper, a coupling system containing a shaping lens and a coupling lens is designed based on the vector theory of refraction. The simulation results show that our coupling system can improve coupling efficiency to 81.45%, and the efficiency can still reach 74.73% even though chamfering and other factors are considered. This paper may not only provide engineers with a more efficient coupling system but also provide designers with ideas of hollow-solid (or solid-hollow) beam shaping systems.
ABSTRACT
In this paper, a reflector antenna design method is proposed to improve transmission efficiency and control output intensity distribution. Primary and secondary mirrors are constructed segment by segment using a numerical method according to the law of energy conservation, the vector theory of reflection, and Fermat's principle that the optical path length of each ray must be equal. To verify the effectiveness and practicability of this method, an example of an antenna with the prescribed intensity distribution of the output beam is given. The transmission efficiency of the antenna system designed by this method reaches 100% in theory. The effects of output intensity distribution and deviation on transmission efficiency were also analyzed. We believe that the results show that the proposed method is a highly efficient approach to the design of a freeform reflector antenna to improve transmission efficiency and control the output intensity distribution.
ABSTRACT
The ray transfer matrix method is widely used for analyzing beam-transmission properties and designing multi-pass systems. In this paper, a modified ray transfer matrix method is proposed for tracing an accurate non-sequential ray in three-dimensional space based on a vector reflection theory. The modified ray transfer matrix method can be utilized to analyze a ray transmitting between arbitrary surfaces, which is not confined to rotational symmetrical structures. There is no need to project rays onto two perpendicular planes, nor to introduce a paraxial approximation in our calculation. Since the length and angle of every ray can be calculated accurately, almost no deviation is accumulated in multi-pass system. The modified ray transfer matrix method can be applied in optical design, especially in the design of multi-pass cavities and multi-pass cells.
ABSTRACT
In this paper, the propagation properties of the Laguerre-Gaussian (LG) beam passing through Cassegrain antenna system in a turbulent atmosphere have been researched. The accurate analytical function for the diffraction field of LG beam passing through Cassegrain antenna, the average intensity, and the cross-talk among different orbital angular momentum (OAM) modes of LG beam passing through Cassegrain antenna in Kolmogorov turbulent have been derived. The simulation results show that LG beam with ring-like distribution is selected to enhance the emission efficiency of Cassegrain antenna. The cross-talk among different OAM modes can remarkably reduce through using Cassegrain antenna. The analysis process can also apply to accurately analyzing the propagation properties of other kinds of beams through different optical systems in turbulent atmosphere.
ABSTRACT
With the improvement of the transmission efficiency, the Cassegrain antenna can be widely used in space optical communication. In this paper, the Bessel-Gaussian (BG) beam is used to avoid the central energy loss of a Cassegrain antenna system. The intensity distribution and the phase distribution of the BG beam passing through a Cassegrain antenna are theoretically derived and simulated. At a wavelength of 1550 nm, this method can theoretically improve the transmission efficiency to approach 100% under the situation in which the obscuration ratio is nonzero, and the transmission efficiency can reach more than 80% when obscuration ratio is in the range of from 0 to 0.1252 with $l=4$l=4. The effects of on-axial defocusing on the light field and the transmission efficiency are studied. The method proposed in this paper can remarkably improve the transmission efficiency of a Cassegrain antenna in a practical and uncomplicated approach.
ABSTRACT
Central energy loss is a critical factor decreasing the transmission efficiency of a Cassegrain antenna. In this paper, a pair of conic lenses are designed and set in front of a Cassegrain antenna to improve the transmission efficiency of the antenna instead of designing a complicated antenna structure. On the basis of the analysis, the optimized conic lens pair can theoretically improve the transmission efficiency up to 100% at a wavelength of 1550 nm under ideal conditions. After several practical factors are considered, such as the dispersion of the material, the transmissivity and chamfering of the conic lens, and the reflectivity of the mirrors composing the Cassegrain antenna, the conic lens pair can still increase the transmission efficiency of the Cassegrain antenna up to 92.37% at a wavelength of 1550 nm. Compared with designing a complicated antenna, the method proposed here provides a more practical approach to improve the transmission efficiency of a Cassegrain antenna.
ABSTRACT
We propose a novel annular focus antenna with an off-axial parabolic primary mirror and slanting hyperbolic secondary mirror. Ray tracing based on three-dimensional vector reflection theory is utilized to design and analyze the structural parameters of the antenna. In ideal conditions, there is no geometric loss in theory and the transmitting efficiency increases by 24.54% compared with the conventional Cassegrain optical antenna. The transmitting efficiency is also calculated in the conditions of off-axial and on-axial defocus. The simulated results demonstrate that this design can increase transmission efficiency of the optical antenna effectively.
ABSTRACT
In this paper, an asymmetric large-mode-area photonic crystal fiber (LMA-PCF) with low bending loss at a smaller bending radius is designed. The finite-element method with a perfectly matched layer boundary is used to analyze the performance of the PCF. To achieve LMA-PCF with low bending loss, the air holes with double lattice constants and different sizes at the core are designed. Numerical results show that this structure can achieve low bending loss and LMA with a smaller bending radius at the wavelength of 1.55 µm. The effective mode area of the fundamental mode is larger than 1000 µm2 when the bending radius is ≥10 cm. The bending loss of the fundamental mode is just 0.0113 dB/m, and the difference between the fundamental and high-order modes of the bending loss is larger than 103 when the bending radius is 10 cm. Simulation results show this novel PCF can achieve LMA and have effective single-mode operation when the bending orientation angle ranges in ±110°. This novel photonic crystal has potential application in high-power fiber lasers.
ABSTRACT
In this work, a novel design of a high birefringence photonic crystal fiber (HB-PCF) with multimode and low confinement loss is proposed. To achieve high birefringence, the core is designed as an elliptical region, which is enclosed by twelve small holes. Based on this design, replacing the two circular holes at the top and bottom of the core region with two elliptical holes can further improve the birefringence. At the wavelength of 1.55 µm, the birefringence of the fundamental mode (LP01) and the second-order mode (LP11) are 1.70×10-2 and 1.85×10-2, respectively. Meanwhile, the confinement losses maintain on orders of 1×10-5 dB/km (LP01) and 1×10-1 dB/km (LP11). After the effective refractive indices of two types of the proposed HB-PCF are calculated by the finite element method, the birefringence, confinement loss, bending loss, dispersion, and nonlinear coefficient are studied. These results reveal that the HB-PCF might be applied for polarization-maintaining and nonlinear optics.
ABSTRACT
With the help of the vector theory of reflection and refraction, a novel emitting Cassegrain antenna with a semitransparent secondary mirror has been proposed and analyzed for a distant point source. Based on the absorptivity valued at 3.00% and the reflectivity valued at 0.10%, this new emitting antenna can increase the transmission efficiency from 63.65% to 93.85%. In addition, an off-axis parabolic receiving antenna corresponding to the emitting antenna is designed and the 3D ray-trace simulation result is given. According to the simulation result, this receiving antenna can nicely converge the rays from the emitting antenna.
ABSTRACT
An optical model with a hyperbola-parabola primary mirror added in the Cassegrain optical antenna, which can effectively improve the transmission efficiency, is proposed in this paper. The optimum parameters of a hyperbola-parabola primary mirror and a secondary mirror for the optical antenna system have been designed and analyzed in detail. The parabola-hyperbola primary structure optical antenna is obtained to improve the transmission efficiency of 10.60% in theory, and the simulation efficiency changed 9.359%. For different deflection angles to the receiving antenna with the emit antenna, the coupling efficiency curve of the optical antenna has been obtained.
