We investigate theoretically the dependence of the extinction ratio, metal layer thickness and buffer thickness of a short length plasmonic polarizer on the buffer layer index. The polarizer section consists of a thin metal layer above the single mode dielectric waveguide separated by a low index dielectric buffer layer. Strong coupling between the surface plasmon polariton (SPP) mode and the guided mode takes place when their phase constants are matched. The SPP mode being of TM type, interacts with the guided TM mode and is completely absorbed by metal film due to resonant coupling between the two modes. The TE guided mode does not couple to the SPP mode and is passed un-attenuated through the polarizer. The buffer layer thickness can be optimized to maximize the TM mode attenuation and reduce the TE losses, which provides a large extinction ratio. Since the polarizer is based on the interference of the SPP mode and the waveguide mode, a periodic coupling of the field takes place between these two modes. It is shown that for properly optimized layer thicknesses, an extinction ratio exceeding 200 dB can be achieved for various buffer layer indices. Effect of buffer layer index on the polarizer length is also presented.

我们在理论上研究了消光比，金属层厚度和短长度等离激元偏振器的缓冲厚度对缓冲层折射率的依赖性。偏振器部分由单模介电波导上方的薄金属层组成，该薄金属层被低折射率介电缓冲层隔开。当它们的相位常数匹配时，表面等离子体激元（SPP）模式和引导模式之间会发生强耦合。SPP模式为TM类型，与引导的TM模式相互作用，并且由于两种模式之间的共振耦合而被金属膜完全吸收。TE引导模式不会耦合到SPP模式，并且会以不衰减的方式通过偏振器。可以优化缓冲层的厚度，以最大化TM模式的衰减并减少TE损耗，消光比大。由于偏振器基于SPP模式和波导模式的干扰，因此在这两种模式之间会发生场的周期性耦合。结果表明，对于适当优化的层厚度，对于各种缓冲层折射率可以达到超过200 dB的消光比。还介绍了缓冲层折射率对偏振片长度的影响。