Answer: The most important optical device in a cable TV optical transmitter is a semiconductor laser. In fact, it is a laser diode (Laser Diode, LD). Of course, some do not use a laser diode, but use a semiconductor light-emitting diode (Light Emitting Diode). Diode, LED).

The function of the optical transmitter is to convert the electrical signal into an optical signal, which is achieved by changing the power injected into the laser through an external circuit. The bias circuit it sets can provide the best bias working power supply for the laser. Different bias currents will result in different power outputs of the lasers. To ensure stable output optical power, an automatic control circuit for optical power and laser temperature should be designed. , such as the use of microcomputer to achieve the best working state of automatic control of the optical transmitter.

Lasers are widely used as optical oscillators (ie, light-emitting devices), which rely on the interaction between the energy state of the laser medium material and the light.

In order to make the laser work, there must be a certain amount of current. There is a certain relationship between the size of this current and the light intensity. When the current is increased, the light intensity increases sharply, which indicates that the laser has started to work, which makes the laser start to work. The current is called the threshold current. The smaller it is, the better, because it can already make the laser work. If you continue to increase the threshold current, the output saturation area will be formed. After the current in the saturation area reaches a certain value, it will make the transmission signal The quality of the laser diode is degraded or even damaged. For the power required for optical fiber transmission, there are several megawatts of output power in the linear region to meet the requirements of long-distance transmission of signals and information. In addition to the amount of light intensity, the transmission quality of light is also related to problems such as spectrum and noise.

The multi-wavelength spectrum is not suitable for the transmission of high-quality analog signals. Even if it works in a single-mode mode, its emission line has a width. The narrower the width, the purer the light wave becomes, and the more time-coherent it becomes. That is, light waves with good coherence. Light waves with good coherence do not need lenses and other devices to condense it into small light spots, and are more suitable for the incidence of optical fibers.