Phase matched optical dielectric waveguide using the artificial anisotropic structure

Birefringent material in a thin film dielectric waveguide is used to realize phase matching of the waves with different polarizations. However, this method cannot be used exclusively due to lattice mismatch as happens in a mode conversion type isolator. This paper proposes an artificial anisotropic waveguide realizing phase matching with isotropic dielectric materials only. the structure is a slab waveguide loaded with dielectric strips parallel to the wave propagation direction. This structure can equalize the phase velocities of the Ex and Ey modes. A numerical analysis based on the mode matching technique is used to obtain the phase match condition. the effect of an artificial anisotropy is confirmed in a waveguide fabricated in experiments. A waveguide is realized in which difference of the propagation constants of the Ex and Ey modes is extremely small. It is believed possible that a thin film optical isolator can be reproduced with this waveguide.