The wavelength response of a metal-coated 2. Coupled-Mode Analysis five-layer planar waveguide with a corrugated long-period grating is analyzed using the coupled-mode theory. TheWe consider an asymmetric five-layer planar waveguide phase-matching characteristics between the core mode and the * * * * cladding modes are discussed for the coating with different structure,rastsow indFg 1, twh cnsists oayguidin metals and the different thicknesses of the cladding layers. layer of refractive index n3, two cladding layers of Numerical results demonstrate that the rejection bands for the refractive indices n2 and n4 , and two thin metal films TE and TM polarizations can be well separated when both top and bottom surfaces of the waveguide are coated with of refractive indices n1 and n5 as the external layers, aluminum films and the thicknesses of the cladding layers are where n3 > n2, n4 Since the optical fields attenuate optimized.re nsid e the transvers ation, Key words Planar waveguide, long period grating, rapidly inside the metal films in the transverse direction, metal-coating, polarizer the two external layers may be assumed to extend to infinity [6] when each thickness is larger than 50 nm .
IntroductionThe thicknesses of the guiding and cladding layers are Long-period waveguide gratings (LPWGs) [1] have t3, t2, and t4 , respectively. A corrugated grating attracted increased attention because the waveguide with pitch A , length L , and corrugation depth 2h structure offers material and structural flexibility which is formed at the lower interface of the guiding layer. We allows the design of more compact and robust assume that the guiding layer supports only the integrated-optic devices [2]-[5], as compared with the fundamental TEO and TMO modes. The grating allows well-known long-period fiber gratings (LPFGs). It has light coupling between the fundamental TEo(TMo) been demonstrated experimentally that, superior to LPFGs fabricated in ordinary fibers, LPWGs can provide mode and the cladding TEr (TMm) modes at discrete wide wavelength tunability over the entire C + L band wavelengths, namely, the resonance wavelengths A, with high sensitivity [4]. The LPWGs has a polarization which are govered by the phase-matching condition dependence, which originates from the polarization effects in planar waveguides. Several works focusing on the elimination of polarization effects in LPWGs have x been reported [2],[4]. On the other hand, the polarization dependence of planar waveguides can be enhanced metl . nl [6],[7],[3] by incorporating metal layers into the planar I t4 n4 structure. The TM modes coupled to surface plasmons within the metal layers exhibit the propagation character-A [3 n3 istics which are quite different from those of the TE .2h modes. 2 n2In this paper, we present a theoretical analysis of a 0 m t LPWG with metal coating for realizing a large separation of transmission spectra for the TM mode and z=L TE mode. The proposed structure utilizes the resonant coupling between the core mode and the cladding mod...
