What is a phase modulator

What is a phase modulator

Phase modulator is an optical modulator that can control the phase of a laser beam. Common types of phase modulators are Pockels box-based electro-optic modulators and liquid crystal modulators, which can also take advantage of thermal fiber refractive index changes or length changes, or by stretching to change the length. Various phase modulators are used in the field of integrated optics, where the modulated light propagates in a waveguide.

Important properties of phase modulators include: The size of the phase modulation (which determines the modulation index and the relative power of the sideband) requires the drive voltage modulation bandwidth (modulation frequency range), the electro-optical modulator is in the GHz order, and the device using the thermal effect or liquid crystal material is far less than the operating bandwidth of the device aperture. Limits the beam radius of the modulated beam External dimensions of the device These properties vary greatly for different types of phase modulators. Therefore, different phase modulators need to be used in different practical applications.

Examples of phase modulator applications include: A phase modulator in the laser resonator of a single-frequency laser can be used for wavelength tuning, or active mode-locking (FM mode-locking) of the laser to phase the beam if it has a moderate modulation intensity, can be used in a laser frequency stabilization mechanism, for example, The Pell-Drever-Hall method requires phase modulators in many interferometer spectral measurement devices, usually using periodic drive signals. Some measurements require frequency combs, which are obtained by incident a single-frequency beam into the phase modulator. In this case, the phase modulation usually needs to be strong, so that you can get a lot of side bands. In the data transmitter of optical fiber communication system, the phase modulator can be used to decode the transmitted information. For example, the phase-shift keying method is used.