Silicon nitride (Si3N4) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE0 mode at λ0 = 6328 Å have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si3N4 was separated from the substrate by a steam-oxide SiO2 buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.
© 1977 Optical Society of America
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