Most often, thermoelectric coolers are used in systems where temperature control or refrigeration (sub-ambient cooling) is required. A classic use of TECs are for the temperature control of lasers in optical communication where the wavelength of the laser and the mechanical coupling of the laser to the fiber optic vary with temperature. For more general temperature control, systems can take advantage of a key aspect of TECs – they can be run in reverse to provide heating. Shown here in the lower right, an active solid-state solution can offer temperature control and allow for heating and cooling depending on the ambient conditions. All one has to do is provide electronic controls that can reverse the polarity of the DC power applied to the TECs. In many applications, the thermoelectric coolers replace vapor-compression systems for refrigeration. TEC systems have advantages of not using refrigerants, having low noise/vibration, and they typically have smaller overall systems.