A laser diode is a kind of laser generator. The working material is a semiconductor, which belongs to a solid-state laser. Most of the laser diodes are similar in structure to general diodes. A laser diode is essentially a semiconductor diode. According to whether the PN junction materials are the same, laser diodes can be divided into homojunction, single heterojunction (SH), double heterojunction (DH) and quantum well (QW) laser diodes. Quantum well laser diodes have the advantages of low threshold current and high output power, and are currently the mainstream products in the market.
Compared with lasers, laser diodes have the advantages of high efficiency, small size and long life. However, its output power is small (generally less than 2mW), its linearity is poor, and its monochromaticity is not very good, which greatly limits its application in cable TV systems, and cannot transmit multi-channel, high-performance analog signals. In the backhaul module of the bidirectional optical receiver, the quantum well laser diode is generally used as the light source for uplink emission.
The light-emitting principle of laser diodes
The crystal diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor, and a space charge layer is formed on both sides of the interface, and a self-built electric field is built. When there is no applied voltage, the diffusion current caused by the difference in carrier concentration on both sides of the p-n junction is equal to the drift current caused by the self-built electric field and is in an electrical equilibrium state.
When there is a forward voltage bias in the outside world, the mutual suppression of the external electric field and the self-built electric field increases the diffusion current of the carriers and causes the forward current.
When there is a reverse voltage bias outside, the external electric field and the self-built electric field are further strengthened, forming a reverse saturation current that is independent of the reverse bias voltage value within a certain reverse voltage range.