Ultralinear small-angle phase modulator

A DC electric field applied to a quartz plate resonator causes changes in the elastic constants which can lead to a change in the frequency of the resonator. This effect, known as the polarizing effect, has been shown to be extremely linear. A method for measuring the polarizing effect in high-Q SC-cut 5-MHz quartz resonators for small AC electric fields is introduced. This polarizing effect was used to make an ultralinear small angel phase modulator with low added phase noise. The second harmonic distortion was measured to be less than -17 dB relative to the fundamental in three different units, even though the modulation frequency was more than 20 times larger than the half-bandwidth of the resonators. The measurement techniques to verify this performance are discussed