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Band-dropping via coupled photonic crystal waveguides

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Abstract

We observe the dropping of electromagnetic waves having a specific frequency or a certain frequency band in two-dimensional dielectric photonic crystals. The single frequency is dropped via cavity-waveguide coupling. Tunability of the demultiplexing mode can be achieved by modifying the cavity properties. The band-dropping phenomenon is achieved by introducing interaction between an input planar, or coupled-cavity, waveguide and the output coupled-cavity waveguides (CCWs). The dropping band can be tuned by changing the coupling strength between the localized cavity modes of the output CCWs. We also calculate the transmission spectra and the field patterns by using the finite-difference-time-domain (FDTD)method. Calculated results agree well with the microwave measurements.

©2002 Optical Society of America

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Figures (5)

Fig. 1.
Fig. 1. Dropping of electromagnetic waves in two-dimensional photonic crystals. (a) Schematic drawing of a single-frequency dropping structure. A selected frequency can be dropped from the guided mode inside the waveguide due to coupling between the cavity and the waveguide mode. The tunability of the dropping frequency can be achieved by changing radius of the rods at the cavity sites. (b) The proposed band-demultiplexing structure. Photons having a certain frequency band inside the input waveguide can be filtered through the output coupled-cavity waveguides.
Fig. 2.
Fig. 2. Filtering of a selected frequency via cavity-planar waveguide coupling. [Left panel] (a) Calculated and (b) measured transmission spectra, A → C, corresponding to the single-frequency demultiplexing structures for various values of r c = 0 (blue line), r c = 0.32r 0 (green line), and r c = 048r 0 (red line). Tunability of the dropping frequencies can be achieved by changing radius of the rods at the cavity sites. The waveguide spectrum (black line, A → B) exhibits corresponding dips exactly at the resonance frequency of cavities. [Right panel] Calculated field pattern at the resonance frequency of the cavity C2. The electric field distribution clearly shows the filtering of cavity mode from the waveguide mode.
Fig. 3.
Fig. 3. Filtering of a selected frequency via cavity-coupled cavity waveguide coupling. [Left panel] (a) Calculated and (b) measured transmission spectra corresponding to the single-frequency demultiplexing structures for various values of r c =0 (blue line), r c = 0.32r 0 (green line), and r c = 048r 0 (red line). The black line represents the corresponding transmission spectrum of the coupled-cavity waveguide. [Right panel] Calculated field pattern at the resonance frequency of the cavity C2.
Fig. 4.
Fig. 4. Band-dropping from an input planar waveguide through output coupled-cavity waveguides. [Left panel] (a) Calculated (b) measured transmission spectra corresponding to the band-demultiplexing structure which contains two CCWs with the cavity rod radius r c = 0.32r 0 (blue line) and r c = 0.64r 0 (red line). [Right panel] Calculated field distribution for frequency f = 0.369c/a.
Fig. 5.
Fig. 5. Band-dropping from an input coupled-cavity waveguide through output coupled-cavity waveguides. [Left panel] (a) Calculated (b) measured transmission spectra corresponding to the band-demultiplexing structure which contains two CCWs with the cavity rod radius r c = 0.32r 0 (blue line) and r c = 0.64r 0 (red line). [Right panel] Calculated field distribution for frequency f = 0.363c/a.
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