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(a) Schematic of waveguide constructed in a triangular-lattice PC slab. The width of the waveguide , as well as the radius of air holes in the first and second row ( and ), are the three crucial parameters to optimize the width of the transmission windows. (b) and (c) are SEM pictures of original and optimized waveguides.
Calculated modal dispersion relation of (a) the original waveguide and (b) an optimized waveguide. The band width of the waveguide modes (within the dashed boxes) is 22 nm in the original waveguide. After optimization it is significantly broadened to 74 nm.
(a) Schematic configuration of an optical filter consisting of the and waveguides serving as the input and output channels, and the microcavity made from three missing air holes serving as the resonant coupler. (b) Calculated transmission spectrum at the output channel in the linear scale. (c) Infrared imaging of the output signal observed in experiment for a practical sample. A bright spot appears at the end of the output channel when the input wavelength coincides with the resonant wavelength and disappears when it is at off-resonance.
Transmission spectra of the four-channel filter simulated by the 2D FDTD method. The amplified picture of spectrum in the inset indicates the details at the resonance. Each channel has only one resonant peak, which appears at 1550, 1551.5, 1553, and 1556 nm, respectively.
SEM image of the fabricated four-channel filter. Four cavities are located on the two sides of the input waveguide. The parameters of the waveguide are and .
Experimental transmission spectra of the four-channel filter in linear scale. The inset picture illustrates two groups of end points (air-hole centers) of the cavity marked with “a, b” and “c, d.” Black arrows indicate the moving direction of these air holes.
Structural parameters of the four-channel filter.
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