Design Of A New Structure Collimation System And Analysis Of Laser Beam Coupling

As a new type of light source in space communication,semiconductor lasers have the advantages of simple structure,small size,long life,and low price.However,due to the problem of its own structure,the active width of the semiconductor laser is much larger than the thickness,so that the divergence angle in the plane parallel to the junction plane and perpendicular to the junction plane is extremely asymmetric,and the far field presents a long and narrow elliptical spot with The initial astigmatism and poor beam quality seriously affect the application of semiconductor lasers.In this way,the output beam of the semiconductor laser must be subjected to the collimation of the optical collimation system before it can be practically used.The collimation of the laser beam includes the alignment,rounding and inherent astigmatism of the semiconductor laser beam.In recent years,many scholars and scientists at home and abroad have devoted themselves to the research of laser beam alignment and shaping technology,hoping to effectively improve the quality of the laser beam and the energy efficiency of the laser.The appearance of the freeform lens lens in the collimating and shaping system makes it possible to achieve a nearly perfect collimation effect.Therefore,in this paper,a collimation shaping system based on a freeform lens and a wedge lens is proposed.The system consists of a freeform lens and a wedge-shaped cylindrical lens.Among them,the front surface of the freeform surface lens is designed as a flat surface so that it can be attached to the surface of the semiconductor laser,and the back surface is a free-form surface.The freeform surface lens achieves the alignment of the laser beam and the correction of the initial astigmatism.The front surface of the wedge-shaped cylindrical lens coincides with the freeform surface,and the back surface is designed as a wedge surface with a certain inclination angle on the meridian plane.Therefore,the wedge-shaped cylindrical lens can be used to compress the light beam in the direction of the fast axis to realize the ellipse-circle of the light beam.Plastic surgery.The new collimation shaping system can achieve full collimation and rounding.Considering the processing difficulty of the freeform surface,we obtain an ellipsoidal lens by optimizing the parameters,instead of the freeform surface to achieve the laser beam collimation,the collimation effect is analyzed and verified by MATLAB simulation.The divergence angle is up to 10^-4rad.The advantages and characteristics of photonic crystal fibers over traditional optical fibers such as single-mode multimode fibers have been introduced.The use of photonic crystal fibers without cut-off single-mode transmission characteristics greatly improves the efficiency of spatial light-fiber coupling.The coupling efficiency of the most basic one-dimensional photonic crystal fiber-Bragg fiber was analyzed.By using the finite element method,the mode field of the photonic crystal fiber was calculated.According to the theory of pattern matching,using MATLAB simulation software to obtain the coupling efficiency of the Bragg fiber,we found that when the Bragg fiber core radius is different,the coupling efficiency will be different,indicating that by changing the air hole of the core or the cladding,Higher coupling efficiency can be achieved.