An integrated optical phase modulator using a PbSe-clad BaF2 waveguide

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.