With the rapid development of semiconductor physics and the subsequent invention of transistors, scientists conceived and invented semiconductor laser modules as early as 1950s. In the early 1960s, many groups competed to do research in this field. In theoretical analysis, Nikolai Basov of lebedev Institute of Physics has done the most outstanding work. At the international conference on solid-state device research held in July 1962, Keyes and Quist, two scholars in Lincoln Laboratory of Massachusetts Institute of Technology, reported the luminescence phenomenon of gallium arsenide, which aroused great interest of Hall, an engineer in General Electric Research Laboratory. He wrote down the relevant data on the train home after the meeting. After returning home, Hal immediately made a plan to develop semiconductor laser modules, and together with other researchers, after several weeks of struggle, their plan was successful. Semiconductor laser module, like crystal diode, is based on the p-n junction characteristics of materials, and its appearance is similar to the former. Therefore, the semiconductor laser module is usually called a diode laser or a laser diode. Early laser diodes had many practical limitations. For example, they can only work with microsecond pulses at a low temperature of 77 K. Bell Laboratories and the Ioffe Institute of Physics in Leningrad (now St. Petersburg) have spent more than eight years making continuous equipment that can work at room temperature. However, reliable semiconductor laser modules did not appear until the mid-1970s. Semiconductor laser module is very small, the smallest is only as big as a grain of rice. The working wavelength depends on the laser material and is generally 0.6 ~ 1.55 micron. Due to the needs of various applications, devices with shorter wavelengths are being developed. It is reported that the output of the laser with II ~ IV valence element compounds such as ZnSe has reached 0.46 micron at low temperature, while the output power of the room temperature continuous device with wavelength of 0.50 ~ 0.5 1 micron has reached 10 MW or more. But it has not been commercialized so far. Optical fiber communication is the most important and foreseeable application field of semiconductor lasers. On the one hand, it is a worldwide long-distance submarine optical fiber communication, on the other hand, it is a variety of regional networks. The latter includes high-speed computer network, avionics system, health communication network and high-definition closed-circuit television network. But at present, CD players are the biggest market for such devices. Other applications include high-speed printing, free-space optical communication, solid-state laser pumping source, laser indication and various medical applications. In the early 1960s, the semiconductor laser module was a homogeneous junction laser, which was made of a pn junction diode made of one material. Under the positive high current injection, electrons are continuously injected into the P region and holes are continuously injected into the N region. As a result, the distribution of carriers in the original pn junction depletion region reversed, because the migration speed of electrons was faster than that of holes, and radiation, recombination and fluorescence occurred in the active region. Laser occurs under certain conditions, and it is a semiconductor laser module that can only work in pulse form. The second stage of the development of semiconductor laser module is heterostructure semiconductor laser module, which consists of two thin layers of semiconductor materials with different band gaps, such as GaAs and Gaalas. First, a single heterostructure laser (1969) appeared. Single heterojunction body injection laser (SHLD) uses the potential barrier provided by heterojunction to confine the injected electrons to the P region of GaAsP-N junction, thus reducing the threshold current density, which is one order of magnitude lower than that of homogeneous junction laser, but it still cannot work continuously at room temperature. +0970 . 0970 . Aring； Double heterojunction GaAs- GaAs (As-Al-As) laser operating continuously at room temperature. With the birth of double heterojunction laser (DHL), the available bandwidth is continuously widened, and the linewidth and tuning performance are gradually improved. Its structural feature is that a thin layer of undoped material with narrow energy gap is grown between P-type and N-type materials, so the injected carriers are confined to this region. Therefore, the inversion of the number of carriers can be achieved by injecting less current. In the semiconductor laser module, the double heterostructure electrically injected GaAs diode laser is relatively mature, with good performance and wide application. With the research and development of heterojunction lasers, people think that if ultra-thin films (
General situation of development
brief introduction
Semiconductor laser module is also called laser diode [1](LD). In 1980s, people absorbed the latest achievements in the development of semiconductor physics, adopted novel structures such as quantum well (QW) and strained quantum well (SL-QW), introduced the latest technologies of refractive index modulation Bragg emitter and enhanced modulation Bragg emitter, and developed new crystal growth technologies such as MBE, MOCVD and CBE, which enabled the new epitaxial growth process to accurately control crystal growth, achieve the accuracy of atomic layer thickness, and grow high-quality quantum wells and. Therefore, the threshold current of the produced ld is significantly reduced, the conversion efficiency is greatly improved, the output power is doubled, and the service life is obviously prolonged.
Low power laser diode
Low-power LD applied in the field of information technology has developed rapidly. For example, distributed feedback (DFB) and dynamic single-mode LD used in optical fiber communication and optical switching systems, narrow linewidth tunable DFB-LD used in information processing technology fields such as optical disks, visible light wavelength (such as red light to blue-green light with wavelengths of 670nm, 650nm and 630nm) LD, quantum well surface emitting laser, ultrashort pulse LD and so on have all made substantial development. The development characteristics of these devices are: single frequency narrow linewidth, high speed, tunable, short wavelength and photoelectric monolithic integration.
High power laser diode
1983, the output power of LD with a single wavelength of 800nm has exceeded 100mW. By 1989, the continuous output of LD with a width of 0. 1mm has reached 3.7W, while the output of linear array LD with a wavelength of 1cm has reached 76W, and the conversion efficiency has reached 39%. 1992, Americans raised the index to a new height: 1cm linear array LD continuous wave output power reached 12 1W, and the conversion efficiency was 45%. At present, there are many high-power LD with output power of 120W, 1500W, 3kW, etc. It's already out. The rapid development of high-efficiency and high-power LD and its array also provides a strong condition for the rapid development of all-solid-state lasers, that is, solid-state lasers pumped by semiconductor lasers (LDP).
In recent years, in order to meet the requirements of EDFA and EDFL, high-power LD with wavelength of 980nm has also been greatly developed. In recent years, fiber grating frequency selective filtering has greatly improved its output stability and pumping efficiency.
Characteristics and scope of application
Semiconductor diode laser is the most important laser in practice. It is small in size and long in life, and can be pumped by simply injecting current. Its working voltage and current are compatible with integrated circuits, so it can be integrated with them on a single chip. In addition, current modulation can be directly performed at frequencies as high as GHz to obtain high-speed modulated laser output. Because of these advantages, semiconductor diode lasers have been widely used in laser communication, optical storage, optical gyro, laser printing, ranging and radar.