Radial Radiation Laser And Its Application In Optical Antenna Systems

Reflective system without chromatic aberration is widely used as transmitting antenna and receiving antenna in free space optical communication where multiwavelength transmission is always required.When Gauss beam transmits along the axis,the majority of energy concentrates on the axis.However,the beam reflected by the central part of the secondary mirror will pass though the aperture of the primary mirror and cannot be transmitted resulting in huge energy loss which has significant influence on long-distance free space optical communication.Taking advantages of radial radiation laser can avoid central energy loss and remarkably improve the transmission efficiency of optical antenna system so that radial radiation laser possesses high application value in free space optical communication.The main research fruits in this paper can be concluded into four parts as follow.In this paper,Bragg fiber with micro-notch is proposed.This kind of fiber can be jointed with an axially-emitting Bragg fiber laser so that the axial beam can be changed into radial beam.This notched fiber possesses several advantages such as no complicate cladding design and no extra optical shaping system.How the width and depth of the notch control the output beam is analyzed in this paper.The results show that when appropriate width is selected the output beam can propagate perpendicular to the fiber cladding and the output beam has Guasslike distribution.Besides the width of the notch has influence on the divergence angle of the output beam.The minimum divergence angle?full angle?measured is 41.73°.After analyzing the relation between the output energy and the depth of the notch,it can be found that the nature of the output beam is the leakage mode of the Bragg fiber.Furthermore,it is also demonstrated that the phase of the input light can control the phase of the output light.According to the property of the radial radiation beam from the notched fiber,this fiber is suggested to be applied to designing optical antenna array.Since the subelement comprising of a notched fiber and a parabolic mirror has no central energy loss,it can acheive 100%transmission efficiency if the absorption loss and the diffraction loss are not taken into account.The transmitting light can be well-collimated.In this paper,a high-Q fiber cavity for radial radiation laser with one-dimensional topological photonic crystal.The fiber cladding is designed and analyzed on the basis of the theory of Bragg reflection and the band theory of one-dimensional photonic crystal.After that,the performance of the fiber cavity is studied with the help of finite element method.The process of designing,modeling and analyzing is described in detail.The simulation results show that the cavity proposed in this paper works at the wavelength of 1544.9 nm with the pump light at the wavelength of 980 nm,and the output beam from the cavity can propagate along a certain direction.The radial radiation cavity proposed in this paper has three advantages:?1?The confine loss of the pump light is low,and the pump light can illuminate the gain medium more uniformly;?2?The cavity has a high Q-factor at the order of 10⁸,and it is proved that the Q-factor can be further improved by increasing the number of the period of the fiber cladding;?3?Only common materials?Si,SiO₂ and Er-doped SiO₂?are selected to build the cavity.Moreover,the method of using one-dimensional topological photonic crystal to design high-Q cavity for radial radiation laser is concluded into 5 steps.This method can also be applied to designing a cavity for optofluidic laser or quantum dot laser.In this paper,the properties of one-dimension photonic crystal,one-dimension topological photonic crystal,and the proposed cavity under thermal condition are studied.The simulation results show that,when only linear thermal expansion and thermo-optic effect are considered,the increase of the temperature can cause the red shift and the widening of the high reflectivity band of one-dimension photonic crystal,and the value of the red shift and the widening have linear relation with temperature.Besides,the increase of the temperature can cause the red shift of the transmission peak and the decrease of the full width at half maxima of transmission peak of one-dimension topological photonic crystal,and the value of the red shift and decrease have linear relation with temperature.Moreover,the increase of the temperature can cause red shift of the transmission peak and decrease of the full width at half maxima and the maxima of transmission peak of the proposed cavity.The value of the red shift has linear relation with temperature,but the decrease of the full width at half maxima and the decrease of the maxima of the transmission peak both have nonlinear relation with temperature.Because the full width at half maxima deceases and the central wavelength red shifts with the temperature increasing,the Q-factor of the proposed cavity also increases with the temperature.In this paper,the design method of single-reflection optical antenna based on radial radiation source is proposed.Two kinds of optical antenna are designed:standard parabolic optical antenna designed with point source model and off-axis parabolic optical antenna designed with ring source model.These two antennas can achieve the collimation and expansion of the input beam through a single reflection so that the secondary mirror can be removed,which not only simplifies the structure but also fundamentally avoids central energy loss.The transmission efficiency can reach 100%if the absorption loss and the diffraction loss are not taken into account,and the transmitting light can be well-collimated.After giving the surface equations of the mirror of the two antennas,their transmission performances are analyzed using a ring light source model.After that,the performance of the antenna when the light source has axially offset and off-axis offset is analyzed,and the method to suppress the reduction of the antenna performance caused by the offset is given.In a word,the research fruits proposed in this paper help the previous radial radiation laser to get rid of their shortages like bad directivity and low Q-factor so that the radial radiation laser proposed in this paper can be applied to optimizing the design of optical antenna with higher transmission efficiency.