Laser Diodes (LD) are a type of laser generator whose working material is semiconductor and are solid-state lasers. Most laser diodes are similar in structure to general diodes. Since the laser diode is working, the energy conversion process of electrons only involves two energy levels, and there is no energy loss caused by the indirect band gap, so the efficiency is relatively high.
Technological progress has enabled lasers to enter various diversified markets as professional technical instruments. Laser diodes are the most widely used laser technology and are simple semiconductor devices. Over the past 30 years, the average power of the laser diode industry has increased significantly, while the average price per watt has declined exponentially. As a result, laser diodes are replacing some existing laser and non-laser technologies, while also enabling new optical technologies to become possible. Established application areas for laser diodes include data storage, data communications and optical pumping of solid-state lasers. In contrast, materials processing and optical sensing exemplify the rapid development of market segments with many emerging applications.
Laser diodes include single heterojunction (SH), double heterojunction (DH) and quantum well (QW) laser diodes. Quantum laser diodes have the advantages of low threshold current and high output power, and are mainstream products in the market. Compared with laser diodes, laser diodes have the advantages of high efficiency, small size, and long life. However, their output power is small, their linearity is poor, and their monochromaticity is not very good, which greatly limits their application in cable TV systems. Cannot transmit multi-channel, high-performance analog signals. In the backhaul module of a bidirectional optical receiver, quantum well laser diodes are generally used as light sources for uplink transmission.
A single laser emitter can provide a power output ranging from milliwatts to several watts. Each laser emitter can be used alone, combined into a laser diode strip for optical pumping of solid-state lasers, or integrated into a laser diode module. group to meet various application needs.
Laser diode is a semiconductor laser component widely used in optical fiber communication, medical treatment, display and radar detection. It has a simple structure, mature technology, high quality and low price, and is widely used in industrial production and scientific research.
The structure of laser diode mainly includes five parts: P-type region, N-type region, P-type reflection region, N-type reflection region and laser cavity. Among them, the P-type region and the N-type region form a PN junction, and the reflection region and the laser cavity are optical structures.
The P-type region and the N-type region are part of the main function of the laser diode and are also the determining factors of the laser diode's luminescence. The P-type region introduces positrons to the N-type region, and the N-type region introduces electrons to the P-type region. After the PN junction is generated, the positrons and electrons combine in the PN junction to send photons to achieve luminescence. In order to achieve rapid luminescence, the P-type region and the N-type region should have high-quality materials and delicate processing technology.
The main function of the P-type reflection region and the N-type reflection region is to reflect the laser so that the laser generates a standing wave ratio in the laser cavity. In laser diodes, the reflectivity of the P-type reflection area and the N-type reflection area is different. Generally, the reflectivity of the P-type reflection area is very low, and the reflectivity of the N-type reflection area is very high. Such a design can make the laser fully reflect and diffuse in the laser cavity, so as to achieve relatively stable single-mode fiber laser emission.
The laser cavity is the most important optical part of the laser diode, and its main function is to provide optical feedback amplification effect. The laser cavity is generally composed of reflectors, one of which is a half-reflector and the other is a high-reflector. The optical cavity formed between these two reflectors can realize the continuous reflection of light quanta in the laser cavity, thereby enhancing the amplification effect of the laser. By adjusting the reflectivity of the reflector and the length of the laser cavity, laser emission of different light wavelengths and output powers can be achieved.
In addition to the above structural features, the laser diode also includes several auxiliary structures, such as electrodes, substrates, windows, etc. This structure is not the core part of the laser diode, but it is also important for the performance and reliability of the laser diode.
The laser diode has a compact structure, but each part of it plays a vital role. Only when each part works in coordination can fast and relatively stable laser emission be achieved. With the continuous advancement of science and technology, the structure of laser diodes is also constantly being improved and perfected, providing better support for a wider range of applications.
Infrared lasers are generally used in distance measurement, lighting equipment, communications, simulated weapons, etc. The core of the laser is undoubtedly the laser diode, and the power of the laser diode determines the size of the pulse power.
The laser diode also has the structure of an ordinary diode, namely the N region, PN junction and P region. When a forward voltage is applied to the diode, the PN junction barrier will be weakened, forcing electrons to be injected from the N region through the PN junction into the P region, and holes to be injected from the P region through the PN junction into the N region. These unbalanced electrons and holes injected near the PN junction will recombine, thereby emitting photons.
However, these energetic photons are random in time and direction, unlike the "focusing" of lasers. As the saying goes, unity is strength. To make photons "unite" and produce coherent light with consistent direction and phase, two conditions must be met: 1. Enough electrons 2. Consistent direction.
Therefore, if a laser diode needs to emit a laser, it must be excited by a pulsed large current, and there must be an optical resonant cavity structure to ensure that the electrons have a consistent direction. This is the simple principle of a laser diode.
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