Inscription of waveguides and power splitters in borosilicate glass using ultrashort laser pulses

We report on the use of a femtosecond fibre laser (1030 nm) to inscribe structures like waveguides and splitters inside borosilicate (BK7) glass. Inscription of two- and three-dimensional splitters (1 × 2, 1 × 4, 1 × 8) is accomplished by programing a translation stage so as to achieve smooth bends. We carry out optical characterization of these laser-written structures by measuring both spectral transmission and propagation loss. Single mode guidance with propagation loss of 0.65 dB/cm is measured at 1560 nm for straight waveguides inscribed at low incident energy of 450 nJ. The spectral transmission of our splitters in the optical communication window, 1300–1600 nm, compares very favorably with conventional optical fibre splitters. We find that the splitting ratio as a function of wavelength is significantly more constant over a wide wavelength range, 1200–1600 nm, than optical fibre splitters. We also present results on characterization for splitting ratio and insertion loss at 1550 nm.