We report on the fabrication of symmetric waveguides in bulk poly(methyl methacrylate) (PMMA) by femtosecond laser pulses. A waveguide with a circular transverse profile can be obtained by using a slit beam shaping method. The refractive index in the core increases by up to 4.6 × 10-4 and the waveguide works as single-mode waveguide at a wavelength of 632.8 nm. This writing technique is applied to the fabrication of a directional coupler to split a coupled beam with a 1:1 splitting ratio at 632.8 nm.
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