Resonant cavity enhanced waveguide transmission for broadband and high efficiency quarter-wave plate.

Existing transmission type optical quarter-wave plates based on metallic sub-wavelength structures can hardly realize transmission efficiency above 60%. And their working bandwidths are still very narrow. In this paper, we demonstrate a transmission type quarter-wave plate design with efficiency above 92% over a broad wavelength range (from 1260 nm to 1560 nm). The device proposed is based on a one-dimensional metal-insulator-metal waveguide array buried in silica. Phase difference between transmitted TE and TM components can be tuned continuously. At the same time, transmission efficiency can be kept above 90% in the same spectral range for both the TE and TM incidences. The broad bandwidth and remarkable efficiency are explained with the combination of low dispersion of waveguide modes and the resonant cavity enhanced transmission effect. To give a better understanding of the structure, we also propose a modified effective medium model. The optical response of the structure can be well reproduced with the semi-analytic effective medium model.