bi ltd

Birefringence Modulator: Configuration

Birefringence Modulator Operation

The unique 3-element design of the Beaglehole Instruments Birefringence Modulator eliminates variations in the modulation amplitude that plague traditional 2-element systems. It is therefore insensitive to temperature variations and other effects that influence the modulation amplitude. The high stability is achieved through an analog comparator circuit to keep the gauge voltage, and hence the modulation amplitude, at a constant level.

The 3-element design features a fused-silica optical element sandwiched between drive and gauge quartz transducers. The modulation is driven by an amplifier operating at the resonance frequency of 50 kHz (contact us about the availability of other frequencies). The modulation amplitude is controlled through an analog feedback circuit, which keeps the gauge voltage at a fixed ratio to the reference voltage. The reference can be adjusted with a front panel control, or remotely through an external voltage input for computer controlled operation.