Synchronous photoelastic modulator driving and detection

A method, comprising:

• generating an optical modulator driving signal with a controller frequency generator configured to produce a frequency signal at a selected frequency based on a clock signal of the controller;
• driving the optical modulator according to the optical modulator driving signal;
• synchronously detecting an optically modulated output from the optical modulator;
• and
• determining an optical modulation signal based on a mixing and demodulation of the frequency signal, clock signal, and the synchronously detected optically modulated output.

A method comprising:

• producing a direct digital synthesized high-low signal output at a predetermined optical modulator driving frequency;
• producing a high-low voltage signal corresponding to the high-low signal output with a voltage source;
• filtering the high-low voltage signal with a tank filter to produce a sinusoidal signal;
• and
• amplifying the sinusoidal signal with a high voltage transformer to produce an optical modulator driving signal;
• synchronously detecting an optical modulator output signal produced in response to the optical modulator driving signal;
• and
• determining an optical modulation signal by mixing the optical modulator output signal with frequency and clock signals associated with the digital synthesized high-low signal output, and then by demodulating the mixed signal.

An apparatus, comprising:

• an optical modulator;
• a controller having a frequency generator configured to produce a frequency signal at a selected frequency based on a clock signal of the controller, wherein the controller is configured to produce an optical modulator driving signal based on the frequency signal and to direct the optical modulator driving signal to the optical modulator to drive the optical modulator;
• and
• a detector optically coupled to the optical modulator and configured to receive an optically modulated output and to produce an optical modulator detection signal that includes an optical modulation signal;
• wherein the optical modulator comprises a photoelastic modulator (PEM) optical element, and a PEM transducer coupled to the PEM optical element and the controller and configured to drive the PEM with a PEM driving signal that corresponds to the optical modulator driving signal;
• wherein the optically modulated output corresponds to a PEM modulated output, the optical modulator detection signal corresponds to a PEM detection signal, and the optical modulation signal corresponds to a PEM modulation signal;
• a feedback filter coupled to the PEM transducer and configured to filter a return signal from the PEM transducer to produce a filtered return signal;
• and
• a phase comparator situated to receive the filtered return signal and configured to compare current and voltage signal components of the filtered return signal to determine a phase difference;
• wherein the controller is configured to receive the optical modulator detection signal and to extract the optical modulation signal from the optical modulator detection signal using the frequency signal and the clock signal.