Semiconductor lasers are also called laser diodes (LDs). With the development of semiconductor physics, people imagined the invention of semiconductor lasers as early as the 1950s.

The semiconductor laser in the early 1960s was a homojunction laser, a semiconductor laser that could only work in the form of pulses. At the International Conference on Solid State Device Research held in July 1962, Keyes and Quist, two scholars at the Lincoln Laboratory of the Massachusetts Institute of Technology, reported the light emission phenomenon of gallium arsenide materials.

The second stage of semiconductor laser development is the heterostructure semiconductor laser, which is a laser composed of two thin layers of semiconductor materials with different band gaps, such as GaAs and GaAlAs. Single Heterojunction Injection Laser (SHLD) is a laser that uses the potential barrier provided by the heterojunction to confine the injected electrons in the P region of the GaAsP-N junction, thereby reducing the threshold current density.

In 1970, people invented the double heterojunction GaAs-GaAlAs (GaAs-GaAlAs) laser with a laser wavelength of 9000Å and continuous operation at room temperature. Among semiconductor laser devices, the electro-injection GaAs diode laser with double heterostructure is currently relatively mature, has better performance and is widely used.

Since the late 1970s, semiconductor lasers have obviously developed in two directions, one is information-based lasers for the purpose of transmitting information; the other is power-based lasers for the purpose of improving optical power. Driven by applications such as pumped solid-state lasers, high-power semiconductor lasers (continuous output power of more than 100W and pulsed output power of more than 5W, which can be called high-power semiconductor lasers) made breakthroughs in the 1990s. , which is marked by a significant increase in the output power of semiconductor lasers, the high-power semiconductor lasers of kilowatt-level in foreign countries have been commercialized, and the output of domestic sample devices has reached 600W.

In addition, there are high-power aluminum-free lasers, infrared semiconductor lasers and quantum cascade lasers, etc. Among them, the tunable semiconductor laser is to change the wavelength of the laser through external electric field, magnetic field, temperature, pressure, doping basin, etc., which can easily modulate the output beam.

In the late 1990s, surface-emitting lasers and vertical-cavity surface-emitting lasers developed rapidly.

At present, vertical cavity surface emitting lasers have been used in high-speed networks of Gigabit Ethernet. In order to meet the needs of broadband information transmission, high-speed information processing, large-capacity information storage, and small and high-precision military equipment in the 21st century, semiconductor lasers are used. The development trend is mainly towards high-speed broadband LD, high-power LD, short-wavelength LD, basin line and quantum dot lasers, mid-infrared LD and so on.

What is the wavelength of a semiconductor laser?

If it is the research of optical communication, the wavelength of the most commonly used semiconductor lasers is the 1550nm band, followed by 1310nm, and there are others such as 850nm and 980nm. Common parameters of semiconductor lasers can be divided into: wavelength, threshold current Ith, operating current Iop, vertical divergence angle, horizontal divergence angle ∥, monitoring current Im.

(1) Wavelength: that is, the working wavelength of the laser tube. The wavelengths of laser tubes that can be used as photoelectric switches are 635nm, 650nm, 670nm, and laser diodes are 690nm, 780nm, 810nm, 860nm, 980nm, etc.

(2) Threshold current Ith: that is, the current at which the laser tube starts to generate laser oscillation. For general low-power laser tubes, its value is about tens of milliamps, and the threshold current of laser tubes with strained multiple quantum well structures can be as low as 10mA. the following.

(3) Working current Iop: that is, the driving current when the laser tube reaches the rated output power. This value is more important for designing and debugging the laser driving circuit.

(4) Vertical divergence angle: the angle at which the light-emitting band of the laser diode opens in the direction of the vertical PN junction, generally around 15-40.

(5) Horizontal divergence angle∥: The angle at which the light-emitting band of the laser diode opens in the direction parallel to the PN junction, generally around 6~10.

(6) Monitoring current Im: that is, the current flowing through the PIN tube when the laser tube is at rated output power.