Multiple light spots can be generated by modulating the spatial phase distribution of laser beam with a spatial light modulator (SLM). In this paper, we demonstrate the fabrication of three-dimensional 1 x 4 splitter waveguides inside a glass by focusing multiple light spots of femtosecond (fs) laser pulses, which can be controlled by switching spatial phase distributions on an SLM. In the conventional fs laser writing technique, a highly precise positioning of a substrate is essential for fabricating a branched waveguide in a splitter. Using the technique proposed in this paper, a continuously branched waveguide can be produced easily by translating a glass substrate only one time; therefore this technique can eliminate the need for a high precision in positioning of a substrate and save a fabrication time.
Multiple optical waveguides inside glass were drawn in parallel using multiple light spots, which were formed by focusing a spatially phasemodulated femtosecond laser pulse. Because the spatial phase distribution was modulated by a computer-generated hologram (CGH) on a liquid-crystal spatial light modulator (SLM), bent structures were formed in the drawn waveguides by changing the positions of the light spots by switching the CGHs when the waveguides were being drawn. We confirmed that a He-Ne laser beam can be guided through the fabricated waveguides, and we found that the propagation loss of the waveguides was determined by both the steps for changing the beam position and the number of times the CGHs were switched. We also explain the method we used to reduce the time required to calculate the CGHs used to create bent waveguides. #
The improved method for calculation of a phase hologram and its application to laser writing of waveguides with a spatial light modulator are presented. It was found that the amplitude and phase distributions of light spots generated by a phase hologram can be distorted compared to those of a focused single beam. The distortion of light spots could be reduced by adding a simple constraint, in which light intensities around a light spot should be as small as possible, to the conventional calculation method of a phase hologram. It was also demonstrated that the improved calculation method can be considered essential for laser writing of waveguides.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.