Athermal waveguides for temperature-independent lightwave devices

The central waveguide of narrowband optical filters is quite sensitive to temperature. This is an obstacle to the broad use of optical frequency-division multiplexing (FDM) systems. Since this undesired characteristic is caused by the temperature dependence of optical path length in the filter, one can stabilize the filtering characteristics if such dependence is successfully eliminated. Thus, a temperature-independent optical waveguide (athermal waveguide), with an optical path length independent of temperature obtained by canceling out the positive dependence of ordinary optical materials with the negative temperature coefficient of the refractive index of some special materials like polymers, is proposed. The experimental result shows that the temperature dependence of optical path length is reduced to -7% of that of conventional glass waveguides.<>