Photoelastic waveguides induced by a thin-film composite structure in InGaAsP/InP double heterostructures
This paper reports a photoelastic waveguide caused by a thin-film composite structure, which is composed of a 20 µm wide stripe window opened in a 110 nm thick W0.95Ni0.05 compressively strained thin film and a 4 µm wide W0.95Ni0.05 thin-film stripe located at the centre of the window. By calculating theoretically stress field profiles and dielectric constant variations induced by the thin-film composite structure in InGaAsP/InP double heterostructures, it is found that the increase of dielectric constant at 1 µm depth underneath the W0.95Ni0.05 thin-film stripe and the decrease of dielectric constant at the same depth underneath between the stripe edge and the window edge have maximal values of 0.0649 and 0.0622, respectively. The waveguide strength is determined to be 1.27 × 10−1–2.85 × 10−2 in the depth range 1.0 to 3.0 µm of the semiconductor. In comparison with an individual W0.95Ni0.05 thin-film stripe or narrow stripe window, the photoelastic waveguide caused by the W0.95Ni0.05 thin-film composite structure displays much better waveguide structural characteristics.