Low loss photonic components in high index bismuth borate glass by femtosecond laser direct writing

Single mode, low loss waveguides were fabricated in high index bismuth borate glass by femtosecond laser direct writing. A specific set of writing parameters leading to waveguides perfectly mode matched to standard single-mode fibers at 1.55 µm with an overall insertion loss of ~1 dB and with propagation loss below 0.2 dB/cm was identified. Photonic components such as Y-splitters and directional couplers were also demonstrated. A close agreement between their performances and theoretical predictions based upon the characterization of the waveguide properties is shown. Finally, the nonlinear refractive index of the waveguides has been measured to be 6.6 x 10/W by analyzing selfphase modulation of the propagating femtosecond laser pulse at the wavelength of 1.46 µm. Broadening of the transmitted light source as large as 500 nm was demonstrated through a waveguide with the length of 1.8 cm.