What is a Semiconductor Laser?

Semiconductor lasers, also called laser diodes, are lasers that use semiconductor materials as a working substance. Due to the differences in material structure, the specific process of generating lasers of different types is more special. Commonly used working substances are gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS), and so on. There are three types of excitation methods: electric injection, electron beam excitation and optical pumping. Semiconductor laser devices can be classified into homojunctions, single heterojunctions, and double heterojunctions. The homojunction laser and the single heterojunction laser are mostly pulse devices at room temperature, while the double heterojunction laser can achieve continuous operation at room temperature.

A semiconductor laser

Semiconductor laser

The cavity of the laser can be divided into a resonant cavity and an external cavity. In the resonator, there are many types of laser losses, such as deflection loss. Fabry-Perot resonators have large deflection losses, while confocal cavities have smaller deflection losses, which are suitable for low-power continuous output lasers. Also, for example, the non-radiative transition loss of inverted particles (this kind of loss can be classified as white noise) and so on, all have large cavity length losses. The laser threshold current is just the current that can make the laser vibrate. The difference in the length of the resonant cavity can make the threshold current different. In semiconductor lasers, like

Scientists at Bell Labs, a research and development organization affiliated with Lucent Technologies, have successfully developed the world's first new semiconductor laser that can continuously and steadily emit light in the infrared wavelength range. The new device overcomes the shortcomings of the original broadband laser emission process and has broad potential applications in areas such as advanced fiber optic communications and photosensitive chemical detectors. The related manufacturing technology is expected to be the basis for high-performance semiconductor lasers for optical fibers in the future.

-A paper on the properties of new lasers was published in the journal Nature on February 21, 2002. Lead author of the article, Bell Labs physicist Claire Gmachl asserted: "UWB semiconductor lasers can be used to make highly sensitive universal detectors to detect traces of subtle pollution in the atmosphere. They can also be used to make new devices such as breath analyzers. Medical diagnostic tools. "

Semiconductor laser is a very convenient light source, which is compact, durable, portable and powerful. However, typical semiconductor lasers are usually narrow-band devices and can only emit monochromatic light at specific wavelengths. In contrast, ultra-wideband lasers have significant advantages and can simultaneously select wavelengths over a wider spectral range. Creating ultra-wideband lasers that can operate in a wide range of operating environments is a goal that scientists have long pursued.

-In order to develop a new type of laser, Bell Labs scientists used more than 650 types

Common parameters of semiconductor lasers can be divided into: wavelength, threshold current Ith, operating current Iop, vertical divergence angle , horizontal divergence angle , and monitoring current Im.

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

(2) Threshold current Ith: the current that the laser tube starts to oscillate. For general low-power laser tubes, the value is about tens of milliamps. The threshold current of a laser tube with a strained multiple quantum well structure can be as low as 10 mA. the following.

(3) Operating current Iop: the driving current when the laser tube reaches the rated output power. This value is useful for designing and debugging lasers.

The semiconductor lasers used in industrial laser equipment are generally 1064nm, 532nm, 355nm, and the power ranges from several watts to several kilowatts. Generally used in SMT template cutting, automotive sheet metal cutting, laser marking machine is 1064nm, 532nm is suitable for ceramic processing, glass processing and other fields. Wire, high frequency microwave circuit board processing and other fields.

Because semiconductor lasers have the advantages of simple structure, small size, long life, easy modulation, and low price, they are widely used in military fields, such as laser guidance and tracking, lidar, laser fuze, optical ranging, laser communication power, and laser simulation weapons , Laser sighting alarm, laser communication and laser gyroscope. Developed countries in the world attach great importance to the development of high-power semiconductor lasers and their military applications.

A laser diode is a type of laser device that uses semiconductor materials as a working substance. In addition to the common characteristics of lasers, it also has the following advantages:
(1) Small size and light weight;

(2) Low driving power and current;

(3) High efficiency and long working life;

(4) Can be directly electrically modulated;

(5) Easy to realize optoelectronic integration with various optoelectronic devices;

(6) Compatible with semiconductor manufacturing technology; can be mass produced. Because of these characteristics, semiconductor lasers have received extensive attention and research from various countries around the world since their introduction. It has become the world's fastest-growing, most widely used, the earliest type of laser out of the laboratory to achieve commercialization and the largest output value. After more than 40 years of development, semiconductor lasers have developed from the initial low temperature of 77K, pulse operation to continuous operation at room temperature, and the operating wavelength has expanded from the initial infrared and red light to blue-violet light; the threshold current has been reduced by the order of 10 ^ 5 A / cm2 To the order of 10 ^ 2 A / cm2; the working current is the smallest to the sub-mA order; the output power ranges from a few mW to the array device output power up to several kW; the structure develops from a homojunction to a single heterojunction, a double heterojunction, There are more than 270 forms such as quantum wells, quantum well arrays, distributed feedback, DFB, distributed Bragg reflection, and DBR. Production methods have evolved from diffusion to liquid phase epitaxy, LPE, gas phase epitaxy, VPE, metal organic compound deposition, MOCVD, molecular beam epitaxy, MBE, chemical beam epitaxy, CBE and other preparation processes.