We compute the radiation losses of a rectangular dielectric waveguide (integrated optics channel waveguide) that is tapered so that its wider cross-sectional dimension increases by roughly a factor of three while its narrow dimension remains constant. As the waveguide widens its refractive index decreases to ensure that the waveguide supports only one guided mode. The taper is approximated by a discontinuous staircase curve. A rectangular waveguide taper of 2-μm thickness, tapering from 3- to 10-μm width through fourteen steps of 0.25-μm height, has a minimum loss (at 0.6328-μm wavelength) of 0.13 dB for a 200-μm taper length.
© 1980 Optical Society of America
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