Axicon-based writing of waveguides in BK7 glass

We report on the direct writing of waveguide structures using an axicon lens to focus a 40 fs laser pulse within BK7 glass. The written structures are characterized for waveguiding action: waveguiding action for 635 and 1550 nm light and propagation loss as low as 0.19 dB/cm is measured. Loss values decrease with laser exposure time for incident energy of 300 μJ, indicating enhancement of index contrast. At higher energies, a reverse trend is obtained: higher loss values are obtained as index contrast degrades with an increase in exposure time.