Optical waveguides([1,2]) are structures that confine and guide light waves. They are important in a range of applications: communication lines, photonic sensors (bio-,([3]) chemo-,([4,5]) and fluoro-sensors([6])), and components of optical devices([7]) such as couplers, splitters, and interferometers. In particular, channel waveguides([8]) allow high integration density, unambiguous sensing held, and spatial multiplexing in optical systems. These channel (or strip) waveguides are fabricated by dry etching,([9,10]) localized ion exchange,([11]) laser-densification of sol-gel films,([12]) direct laser writing,([13]) and conventional photolithographic techniques.([14-16])