Brandt G B
Appl Opt. 1974 Jun 1;13(6):1359-62. doi: 10.1364/AO.13.001359.
An optical coupler has been developed whereby a birefringent prism or substrate is utilized to couple light into thin film optical waveguides. The coupler is designed so that the incident light, polarized as an extraordinary wave, passes through the birefringent material at such an angle that the index of refraction in the input medium is higher than that of the waveguide. In addition, the orientation of the birefringent material is chosen so that the reflected waves within the waveguide are incident on the input medium at such an angle that the medium index of refraction appears lower than that of the waveguide. In this way, the light is trapped within the waveguide and, when the light is incident at the appropriate angle, this light propagates in the waveguide as a single mode. Coupling takes place over the whole area common to the waveguide and input medium; thus, neither a sharp edge nor a trapped evanescent region are required to prevent the light coupled into the waveguide from leaking back into the coupling prism. The absence of a boundary makes it practical to couple wide beams of light into planar guides. Couplers made of calcite have been used to couple TM He-Ne laser light into multimode waveguides formed of liquids and optical cement.
已经开发出一种光耦合器，其中利用双折射棱镜或衬底将光耦合到薄膜光波导中。该耦合器的设计使得以异常波偏振的入射光以这样一种角度穿过双折射材料，即输入介质中的折射率高于波导的折射率。此外，选择双折射材料的取向，使得波导内的反射波以这样一种角度入射到输入介质上，即介质折射率显得低于波导的折射率。通过这种方式，光被限制在波导内，并且当光以适当角度入射时，该光在波导中作为单模传播。耦合发生在波导和输入介质的整个公共区域；因此，既不需要尖锐边缘也不需要捕获的倏逝区域来防止耦合到波导中的光泄漏回耦合棱镜。没有边界使得将宽光束耦合到平面波导中变得切实可行。由方解石制成的耦合器已被用于将TM氦氖激光耦合到由液体和光学胶形成的多模波导中。
