Nonperiodic Oscillation With Wavelength of Mode Guided in a Special Ti-Diffused $\hbox{LiNbO}_{3}$ Waveguide Structure

Abstract

We report an abnormal waveguiding phenomenon that the fundamental mode guided in strip waveguides of a special Ti-diffused LiNbO 3 waveguide structure, in which an array of 4-and 6-m-wide strip waveguides is embedded in a planar waveguide, nonperiodically oscillates with the wavelength along the waveguide width direction. The oscillation amplitude reaches $2 m. The oscillation results in a comb-like transmission spectrum at 1.5-m wavelength region. The phenomenon is abnormal as it displays the features of multimode interference (MMI), but the single-mode pattern was captured from the strip waveguide at the 1.5-m wavelength. Further numerical analysis for the waveguiding characteristics shows that the strip waveguide also supports a nearly cutoff higher order mode, in addition to the fundamental mode, allowing to explain the abnormal phenomenon: the MMI may take place in some regions of the strip waveguide and the observed singlemode pattern is because the higher order mode, which takes part in the MMI, is close to the cutoff.

Three-dimensional polarization-dependent full-wavelength beam splitter written by femtosecond laser in LiNbO3 crystal

“…Methods for fabricating optical waveguides in LiNbO 3 crystal include ion implantation, ion exchange [13,14], metal-ion diffusion [15,16], and femtosecond (fs) laser writing [17][18][19]. The latter is especially useful for three-dimensional (3D) processing of transparent materials since no masking is required [20][21][22][23][24].…”

Femtosecond laser writing of low-loss three-dimensional waveguide coupler in LiNbO3 crystal

“…These include use as switches, electro-optic modulators, multiplexers, frequency converters, and waveguide amplifiers, benefiting from the crystal's unique electro-optic, piezoelectric, acousto-optic, and nonlinear optical properties [8][9][10][11][12] . Traditional methods exist for the manufacture of a perpetual waveguide coupler in this material, e.g., titanium or zinc indiffusion [13,14] , dielectric periodic multilayers [15] , proton exchange [16] , and ion implantation combined with femtosecond laser ablation [17] . However, three-dimensional (3D) waveguide couplers are difficult to be fabricated by these techniques as they are all limited to the surface processing of samples.…”