Abstract
Linear modulators are useful for electromagnetic field sensing1 and as external modulators in communication and cable television systems2. Theoretically, a passively-biased modulator can be achieved with a difference in interferometer arm lengths, to give an intrinsic 90° phase bias angle. Fabrication tolerances result in error from 90° but can be corrected by using excimer laser ablation to phase-tune the angle3. Here we describe the thermal stability of modulator phase angle ϕ0 for dielectrically packaged devices, and we compare stability before and after ablation. The effect of humidity on the magnitude and stability of ϕ0 is investigated. Beaumont et al.4 showed that humidity significantly affects modulator stability under conditions of constant DC bias voltage. However, the interferometers studied were in Z-cut LiNbO3 with a silicon dioxide buffer layer. Many effects were thought to be due to a surface phenomenon associated with the SiO2. In our work we are concerned with X-cut LiNbO3 devices where no buffer layer is required. Such devices show no longterm drift, as opposed to those with SiO2 buffers5.
© 1995 Optical Society of America
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