Investigation of narrowband tunable filter based on multilayer waveguide structure

We propose a six-layer waveguide structure embedded in a single layer grating with a microcavity based on the guide mode resonance (GMR) effect, and realized a tunable notch filter in near infrared wavelength. The structure shows a very narrow filtering bandwidth and high tunable resonance absorption. The propagation characteristics are analyzed and calculated by using the finite-element method, and the reflection spectrum shows different properties under different structure parameters. The result of FWHM (full width at half maximum) is less than 0.001nm with a filtering resonance wavelength of 1550nm under a TM polarized incidence. The resonance wavelength is mainly controlled by the period of the grating layer; it shows a red shift from 1536.17nm to 1563.73nm under changing the period from 790nm to 810nm with 5nm interval. The filtering structure presents potential applications in optical communication, noise suppression and optical sensing.