Observation of light-induced refractive index reduction in bulk glass and application to the formation of complex waveguides

We show that illuminating bulk Nd-doped Bk7 glass at 488 nm induces a decrease in refractive index of order 10-4. Using this index change we experimentally demonstrate that it is possible to use self-writing to enhance the divergence of a Gaussian beam. Here simulations with a Laguerre-Gaussian ‘donut’ writing beam show that a depressed-index ‘pipe’ structure can be created. We demonstrate that these complex waveguide structures can subsequently be used to guide light of different wavelengths