Optical waveguiding through thermal boundary layer development over a microchannel walls

A single-liquid-core/liquid-clad optical waveguide whose refractive index changes thermally is proposed and numerically simulated. The waveguide consists of a large aspect ratio- microchannel heated on its both parallel flat walls. The steady state laminar Poiseuille flow of cold water which is introduced to the heated-microchannel forms a stable thermal boundary layer adjacent to the isothermal heated walls. Establishment of the thermal boundary layer causes the lateral refractive index gradient across the microchannel which is enough for waveguiding at and above a particular mass flow rate for a given wall temperature. The thermal boundary layer thickness which operates as a cladding region can be easily reconfigured by surface temperature and mass flow rate. The cutoff frequencies for TE mode of the optical waveguide were calculated at different mass flow rates and wall temperature through the microchannel.