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近年来,涡旋光束由于在囚禁和操控原子及其他微粒中的应用而引起了不少关注和研究。涡旋光束在光束的传播方向上有一个位相项e(ilθ),而且它拥有一个光束轨道角动量,如何从一个高斯基模变换到涡旋光束,已经提出了许多方法,比如在腔内放螺旋位相片直接产生,用计算机得到的位相片产生,用柱面镜或楔形镜产生光学涡旋。此外,在光纤中涡旋也能产生,比如可以使用光子晶体光纤作为一个非线性的两维光子晶体来产生光涡旋孤子。而在螺旋光纤中,纯的光学涡旋或者光学涡旋和TE及TM模式一起以高阶模形式出现,纯的模式在螺旋光纤传导中,会加上一个和内禀角动量以及螺旋立体角成比例的拓扑位相,而且HE和EH模式的x和y分量的分布模式在传输时也有旋转。1997年,E Abramochkin用一个图像旋转腔来产生一个涡旋激光束,在钝角三角形腔中用一个Dove棱镜来旋转光束,随着不同的棱镜旋转角度,可以得到不同的螺旋类型的激光光束。2003,Arlee V Smith在一个图像旋转腔的纳秒级光学参量振荡器里获得了涡旋光束,它的种子光和腔轴失调,在腔中形成了4个有着固定位相差的稳定模式,从而输出耦合成为一个涡旋光束。文中介绍用一种失调的多模光纤来做一个旋转腔,而把高斯基模光转换为一个涡旋光束的方法。在实验中,光源采用He-Ne的基模高斯光束,当激光束倾斜入射在光纤耦合器时,出射光场的模式会随输入位置和输入角而改变,在实验中用的是多模光纤,分别得到了顺时针和逆时针的涡旋光束,还的到了环状空心光束。用光强分布仪记录了光束的分布,得到了不同尺寸光纤纤芯的光强分布图;测量了光束转换耦合效率,结果是涡旋光束的耦合输出效率达到了80%以上;空心光束的耦合输出效率达到了50%以上。另外,对于失调耦合器下多模光纤产生光学涡旋的理论分析和研究也将进一步研究。由于这种方法产生的光束稳定性很好,不仅可以产生实验所需要的光束,还可以把这种光束传输到所需要的地方,因此,应用前景很广,如操控原子、微粒和细胞等,也是一种特殊的光镊。
In recent years, vortex beams have attracted a lot of attention and research due to their application in trapping and manipulating atoms and other particles. The vortex beam has a phase term e (ilθ) in the beam propagation direction and it possesses a beam trajectory angular momentum. Many methods have been proposed for how to transform from a Gaussian fundamental mode to a vortex beam Helical bit photos are generated directly from a computer generated bitmap and are optically edged with a cylindrical or wedge mirror. In addition, vortices can also be generated in optical fibers, such as the use of photonic crystal fibers as a nonlinear two-dimensional photonic crystal to produce optical vortex solitons. In helical fibers, pure optical vortices or optical vortices appear in high-order modes together with TE and TM modes. In pure helical fiber-optic mode, a pure mode is added with a third order proportional to the intrinsic angular momentum and helical solid angle And the distribution patterns of the x and y components of the HE and EH modes are also rotated during transmission. In 1997, E Abramochkin used an image rotation cavity to create a swirling laser beam. The Dove prism was used to rotate the beam in an obtuse triangular cavity. Different helical laser beams could be obtained with different prism rotation angles. In 2003, Arlee V Smith obtained a vortex beam in a nanosecond optical parametric oscillator of an image rotation cavity, whose seed light and cavity axis were out of phase, forming four stable modes with fixed phase differences in the cavity The output is coupled into a vortex beam. The article describes a method of using a mismatched multimode fiber to make a rotating cavity while converting Gaussian basis light into a vortex beam. In experiments, the He-Ne base-mode Gaussian beam is used as the light source. When the laser beam is obliquely incident on the fiber coupler, the mode of the outgoing light field changes with the input position and the input angle. In the experiment, multimode fiber , Respectively, have been clockwise and counterclockwise vortex beam, but also to the annular hollow beam. The distribution of the light beam is recorded by the light intensity profiler, and the light intensity distribution of the fiber cores with different sizes is obtained. The coupling efficiency of the light beam conversion is measured. As a result, the coupling output efficiency of the vortex beam reaches more than 80% Output efficiency reached 50% or more. In addition, theoretical analysis and research on the optical vortex generation of multimode fiber under the misaligned coupler will be further studied. Because of the good stability of the beam produced by this method, it can not only generate the beam needed for the experiment, but also transmit the beam to the required place. Therefore, the application prospect is very wide, such as manipulating atoms, particles and cells, It is also a special optical tweezers.