Tunable diode lasers come in various forms, each with unique characteristics and mechanisms for tuning the wavelength. The two most common types are External Cavity Diode Lasers (ECDLs) and Distributed Feedback (DFB) lasers. Diode lasers, also known as semiconductor lasers, operate by passing an electric current through a semiconductor material. This process generates light, which is then amplified to produce a coherent laser beam. The specific wavelength of the laser depends on the band gap of the semiconductor. This is the 3-dB frequency of the direct-modulation input located at the laser head.