Efficient coupling into inner photonic crystal waveguides (IPCW) is critical to the applications of PC in photonic integrated circuits. This paper discusses the highly efficient coupling from surface PCWs into IPCW based on all-PC structures by a modified taper at the interface. The introduction of the modified taper is aimed to compress gradually the extended field propagating at the surface as well as excite the surface mode at the modified oblique surface. Good matching of modal field profiles on the both sides of the interface is achieved by keeping the waveguide structures changeless. The numerical results based on finite-difference time-domain simulations show that the bandwidth for coupling efficiency >90% can be as broad as about 80 nm.
An ultracompact triplexer based on a shift of the cutoff frequency of the fundamental mode in a planar photonic crystal
waveguide with a triangular lattice of air holes is presented and optimized. Some defect holes are introduced to control
the beam propagation. The radii of the holes are changed to realize it. The numerical results obtained by the
finite-difference time-domain method show that the proposed triplexer with a total size 12 μm × 6.5 μm can separate
three specific wavelengths i.e. 1310, 1490 and 1550 nm with the extinction ratios higher than -18 dB.
A novel beam splitter is designed on the basis of the coupling characteristics between the waveguide and ring resonator
in two dimensional photonic crystals. By simply adjusting the effective refractive index of coupling dielectric rods in the
ring resonators symmetrically, inducing the redistribution of the power of the optical field, uniform or free splitting can
be achieved. The splitting properties of the beam splitter have been numerically studied using the finite difference time
domain (FDTD) method, uniform or free splitting can be achieved. It was shown that a small dimension, a large
separating angle, a high beam rate, and has been extended to have more light output channels in the beam splitter. These
features of the proposed heterostructure beam splitter make it a promising candidate in optical communications