TEC stands for thermoelectric cooler, a miniature semiconductor solid-state temperature control element. Lasers in optical modules are highly sensitive to temperature; temperature fluctuations can easily cause problems such as wavelength shift, power instability, and signal degradation. It is a solid-state refrigeration technology based on the Peltier effect of thermoelectric materials, which can achieve temperature control on the surface of the TEC device by changing the. An electro–optic modulator (EOM) is an optical device in which a signal-controlled element exhibiting an electro–optic effect is used to modulate a beam of light. The side from which heat is removed becomes cold.