Writing low-loss waveguides in borosilicate (BK7) glass with a low-repetition-rate femtosecond laser

Borosilicate glass (BK7) is a widely-used material in integrated optics devices and in the optical communications industry. We report on laser-written waveguiding in BK7 glass using a low-repetition-rate (1 kHz) laser producing 40 fs pulses of 800 nm light. A 500 μm slit is used to write structures 100 μ m below the glass surface. These waveguides show strong guidance at 635 nm, with an index contrast of 3 × 10<SUP>-4</SUP> and a propagation loss of ~ 0.5 dB/cm. We measured the change in refractive index for a range of writing conditions as quantified in terms of energy dose; there is an energy dose window (&gt; 0.6 μJ μm<SUP>-3</SUP> and &lt; 1.5 μJ μm<SUP>-3</SUP>) within which the written structures show guidance