Abstract
Thin-film waveguide structures consisting of epitaxially grown low-carrier-concentration GaAs and having two distinct index profiles have been investigated with a 10.6-μm CO2 laser. Results of Schottky barrier and Hall measurements show that the carrier concentration of some of these films is less than 1012 cm−3, and the resistivity can be as high as 1.4 × 105 Ω-cm. Guided-wave modes were excited by means of a germanium prism or phase grating coupler. When the index difference Δn between the undoped film and the substrate is ≃0.3 (strong guide), a number of modes can be obtained with a typical angular full width at half maximum intensity Δθ1/2 of <0.5°. For guides having thickness greater than 20 μm, the measured losses are <1 dB/cm for N < 1013 cm−3 and 1.7 dB/cm for N = 4 × 1015 cm−3. Simultaneous excitation of two orthogonal guided-wave modes, i.e., TEm and TMm for m ≤ 2, is possible in this structure. For Δn ≃ 10−3 (weak guide) only one mode can be excited by means of a phase grating coupler with a typical Δθ1/2 of ≃3°. Measurements were also made of the transmission and cutoff characteristics of the TE and TM modes in weak guides as a function of the guide thickness that varied between 20 μ and 50 μ. Results indicate that optical transmission decreases rapidly as the thickness of the weak guide decreases toward the cutoff value.
© 1973 Optical Society of America
Full Article | PDF ArticleMore Like This
M. S. Chang, W. S. C. Chang, B. L. Sopori, H. R. Vann, M. W. Muller, M. G. Craford, D. Finn, W. O. Groves, and A. H. Herzog
Appl. Opt. 14(7) 1572-1578 (1975)
James F. Lotspeich
Appl. Opt. 13(11) 2529-2539 (1974)
A. Reisinger
Appl. Opt. 12(5) 1015-1025 (1973)