Electro optic modulator (EOM) is a device that controls the power, phase, or polarization of optical signals through electrical signals. Its core principle is based on the linear electro-optic effect (Pockels effect). This effect is manifested as the applied electric field being proportional to the refractive index change of the nonlinear crystal, thereby achieving effective control of the optical signal.

Some modulators also use other electro-optic effects, such as electroabsorption modulators based on the Franz Keldysh effect, which achieve modulation through absorption changes. A typical electro-optic modulator structure includes a Pockels unit and auxiliary optical elements (such as polarizers). Its materials include inorganic crystals such as potassium dihydrogen phosphate (KDP) and lithium niobate (LiNbO), as well as special polarizing polymers. Different materials are suitable for different power and frequency requirements.

A phase modulator is the simplest electro-optic modulator that changes the phase delay of a laser beam through an electric field. The input polarization must be aligned with the crystal optical axis to maintain stable polarization state. This type of modulator is typically used for frequency monitoring and stabilization of optical resonators, or for achieving high modulation depth in situations where fixed frequency sine modulation is required. However, electro-optic modulators are limited in frequency modulation because they cannot support continuous linear changes in optical frequency. Polarization modulators change the polarization state of output light by adjusting the crystal direction or electric field direction and using voltage to control the wave plate characteristics. For example, when the input is linearly polarized light, the output may display elliptical polarization or a 90 ° rotation in the direction of linear polarization. By combining random driving signals, anti frequency effects can be achieved. Amplitude modulation is usually combined with a Pockels box and polarizer to affect the intensity of transmitted light by changing the polarization state. Another technical approach is to use a Mach Zehnder interferometer to convert phase modulation into amplitude modulation. Due to its phase stability advantage, this method has been widely applied in integrated optics.

In addition, electro-optic modulators can also be used as optical switches to achieve pulse selection or laser cavity dump functions through fast switching. Temperature drift is an issue that needs to be noted in modulator applications. The thermal effect may cause a shift in the operating point, which needs to be offset by automatic bias voltage compensation or the use of non thermal designs such as dual Pockels boxes or four crystal structures.