Abstract

We present the design of an optical phase modulator using a PbSe-clad BaF₂ waveguide on a CaF₂ substrate. This materials combination is useful for integrated optical devices operating in the 3-5 µm wavelength range. The key property that controls the modulator is an induced change in the imaginary part of the PbSe permittivity ε_i. We have investigated the behavior of the TE modes over a wide range of ε_i for a free space wavelength of 3.4 µm. Our analysis shows that the TE₀ mode propagates discretely in the PbSe if ε_i <6.501. The discrete TE₀ mode converts continuously to a TE₁ mode propagating in the BaF₂ for an incremental change Δε_i. as small as 0.001. A phase modulator was designed for a PbSe cladding thickness of 0.026 µm, which coincides with the critical point where the discrete TE₀ mode converts to a continuous TE₁ mode for Δε = 0.001. Phase modulation is indicated by a large change in mode index value for a small induced change in the ε_i of the PbSe. The attenuation at this critical point remains relatively constant, even though a large phase change is produced.

© 1992 Optical Society of America