Design and fabrication of blue-laser zero-gap directional coupler waveguide devices

Blue laser can be successfully integrated on a chip because of the modern advanced semiconductor fabrication technology, the range of wavelength for the application of integrated optics can be shrunk from 1550nm to blue-laser wavelength (473nm). Among them, optical communication system at blue-laser wavelength has been used for military and commercial application, and optical storage with high density can be realized. Thus, blue laser is of great potential for practical application in the near future. The study of optical devices at blue-laser wavelength is then important.ccuracy of fabrication is crucial for optical devices operating at short laser wavelengths owing to the need of narrower widths for single mode waveguides. In this work, the fabrication tolerances of directional coupler with various gaps are calculated. The results show that directional couplers without gaps are more tolerable than those with gaps.n experiment, zinc-and-nickel co-diffused single mode waveguides at blue-laser wavelength are used for the fabrication of proposed zero-gap directional couplers on a Z-cut lithium niobate substrate. The film thicknesses of diffused Zn and Ni are 450Å and 150Å, respectively. Experimental results show that the coupling length of the proposed directional coupler is 0.508mm for a waveguide of width 1.6μm. The measured operating voltage length product is 7.36V∙cm and the extinction ratio of signal output is 16.38dB, which are the best among those reported.xperimental results show the relative change of coupling ratio for 100 min test is as small as 1.89%, which indicates the photorefractive effect at blue-laser wavelength has no significant effect on the performance of the proposed directional coupler.