Manufacture of three-dimensional optofluidic spot-size con-verters in fused silica using hybrid laser microfabrication

Spatially shaped fs laser-assisted chemical etching is first performed to form 3D hollow microchannels in glass, which are composed of embedded straight channels, tapered channels, and vertical channels connected with the glass surface.

Then, carbon dioxide laser-induced thermal reflow is carried out for internal polishing of the whole microchannels and sealing parts of vertical channels. Finally, 3D optofluidic spot-size converters (SSC) are formed by filling a liquid-core waveguide solution into laser-polished microchannels. With a fabricated SSC structure, the mode spot size of the optofluidic waveguide can be expanded from ~8 μm to ~23 μm with a conversion efficiency of ~84.1%.