According to the relative relationship between modulator and laser, laser modulation can be divided into internal modulation and external modulation.
1.Internal modulation means that the loaded modulation signal is carried out in the process of laser oscillation. The parameters of the oscillation are changed according to the law of the modulation signal, so as to achieve the purpose of changing the laser output characteristics and realizing the modulation. For example, the intensity of the output laser is modulated by directly controlling the laser pump source. The internal modulation can also be placed in the laser cavity, and the modulation element can be controlled by the signal to change the parameters of the resonator, so as to change the laser output characteristics and realize the modulation.
2. External modulation refers to the loading of modulation signal after the formation of laser, that is, the modulator is placed outside the laser cavity, and the modulation signal voltage is applied to the modulator, so that some physical characteristics of the modulator change phase and the modulation is obtained when the laser passes through it. Therefore, the external modulation is not to change the laser parameters but to change the parameters of the output laser (intensity, frequency, etc.). External modulation is one of the most important modulation methods.
According to the working mechanism, there are electro-optic modulation, acousto-optic modulation, magneto-optical modulation, and direct modulation (also known as power supply modulation).
According to the modulation object, it can be divided into amplitude modulation, frequency modulation, phase modulation, and intensity modulation.
Our normal lasers have a continuous wave (CW) normal working mode. For modulation mode, there are 2 kinds of methods: TTL or analog.
TTL modulation stands for transistor-transistor logic and describes a special display laser modulation used for laser sources. The laser source with TTL modulation cannot be dimmed, only the power can be turned on/off. Unable to achieve brightness adjustment.
"Analog modulation" defines the ability of the laser source to "dim" the output power of the laser beam, which means that the output power can be adjusted. The brightness can be controlled linearly to a large extent.