What is the special structure of a tunable laser? They all contain three basic elements: a source diode with an active gain region and a resonant cavity; A regulating mechanism for changing and selecting wavelengths; And tools for stabilizing wavelength output. In addition to the VCSEL, the source diode is usually a variant of the Fabry Perot (FP) type; The regulating mechanism may be temperature control, current control or mechanical control, including micro-electro-mechanical systems (MEMS). The output wavelength stability is achieved by using some kind of wavelength locking device or etalon in the feedback control loop. There are many kinds of tunable lasers, which are generally developed by introducing wavelength tuning mechanism on the basis of various single wavelength lasers. There are already markets for some commodities in the world. In addition to the development of continuous-optical tunable lasers, other tunable lasers with integrated functions have also been reported, such as tunable lasers with monolithic integrated VCSEL and electro-absorption modulator, sampling grating Bragg reflectors and semiconductor optical amplifiers, electro-absorption modulator integrated lasers, etc.
Tunable high power laser pointer based on DBR and related DFB are one of the most common designs. Each uses an FP gain region and an additional diffraction grating. Diffraction gratings (often called Bragg gratings or Bragg reflectors) provide feedback for the oscillation of the optical signal and can be selected as a single mode or wavelength depending on the spacing of the gratings. In the DFB design, the grating is integrated into the active region of the diode; In the DBR design, the gratings are located in separate regions connected to the active region (see Figure 1), even though they are produced as a single chip. The wavelength of DFB and DBR can be changed by adjusting the refractive index of the resonant cavity semiconductor material. Refractive index affects the conditions under which a laser is emitted when a photon travels between two reflective surfaces. The refractive index can be changed by controlling the temperature or adjusting the current.