Principles and characteristics of the hottest semi

2022-08-17
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The principle and characteristics of several tunable semiconductor lasers

the common tunable semiconductor lasers are: current control technology, temperature control technology and mechanical control technology. Among them, the electronic control technology realizes wavelength tuning by changing the injection current. It has ns tuning speed, wide tuning bandwidth, but small output power. The main lasers based on the electronic control technology are SG-DBR (sampling grating DBR) and GCSR (auxiliary grating directional coupling back sampling reflection) lasers. Temperature control technology changes the output wavelength of the laser by changing the refractive index of the active region of the laser. The technology is simple, but slow, with adjustable band width of only a few nm. DFB (distributed feedback) and DBR (distributed Bragg reflection) lasers are mainly based on temperature control technology. Mechanical control is mainly based on MEMS (micro electro mechanical system) technology to complete the selection of wavelength, with large adjustable bandwidth and high output power. The main structures based on mechanical control technology are DFB (distributed feedback), ECL (external cavity laser) and VCSEL (vertical cavity surface emitting laser). The principle of tunable laser is explained from these aspects below

the new national standard system for food safety of food contact materials is shown in Figure 11. The problem of excess structural capacity is becoming more prominent based on current control technology

the general principle based on current control technology is to change the current of fiber Bragg grating and phase control part at different positions in the tunable laser, so that the relative refractive index of fiber Bragg grating will change and produce different spectra, Through the superposition of different spectra generated by fiber Bragg grating in different areas, the specific wavelength is selected, so as to produce the required laser of specific wavelength

a tunable laser based on current control technology adopts SGDBR (sampled gratingdistributed Bragg reflector) structure

this type of laser is mainly divided into semiconductor amplification region, front Bragg grating region, activation region, phase adjustment region and rear Bragg grating region. Among them, the front Bragg grating region, the phase adjustment region and the rear Bragg grating region change the molecular distribution structure of the region through different currents, so as to change the periodic characteristics of the Bragg grating

for the 2-day stable rising spectrum of scrap produced in the active region, a spectrum with small difference in frequency distribution is formed in the front Bragg grating region and the rear Bragg grating region respectively. For the laser with a specific wavelength required, the tunable laser applies different currents to the front Bragg grating and the rear Bragg grating respectively, so that only this specific wavelength overlaps and other wavelengths do not overlap in these two regions, so that the specific wavelength required can be output. At the same time, the laser also includes a semiconductor amplifier area, so that the output laser light power of a specific wavelength can reach 100MW or 20MW

2. Based on mechanical control technology

based on mechanical control technology, MEMS is generally used. A tunable laser based on mechanical control technology adopts MEMS DFB structure

tunable lasers mainly include DFB laser array, tiltable MEMS lens and other control and auxiliary parts

there are several DFB laser arrays in the DFB laser array area, and each array can produce specific wavelengths with a bandwidth of about 1.0nm and an interval of 25ghz. By controlling the rotation angle of MEMS lens to select the specific wavelength required, so as to output the light of the specific wavelength required

another kind of tunable laser based on ML series of VCSEL structure is designed based on optically pumped vertical cavity surface emitting laser, using semi symmetric cavity technology and MEMS to realize continuous wavelength tuning. At the same time, large output optical power and wide spectral tuning range can be obtained by this method. Thermistor and Tec are packaged together to have stable output in a wide temperature range. In order to accurately control the frequency, a broadband wavelength controller is integrated into the same shell, and the front-end tapping optical power detector and optical isolator are used to provide stable output power. This tunable laser can provide 10/20mw optical power in C-band and L-band

the main disadvantage of tunable lasers based on this principle is that the tuning time is relatively slow, which generally requires a few seconds of tuning stability time

3. Based on temperature control technology

based on temperature control technology is mainly used in DFB structure. Its principle is to adjust the temperature in the laser cavity so that it can emit different wavelengths

the wavelength adjustment of an adjustable laser based on this principle technology is realized by controlling the change of ingaaspdfb laser working at -5--50 ℃. The module has built-in FP etalon and optical power detection, and the laser with continuous optical output can be locked on the grid with 50GHz interval specified by ITU. There are two independent TECs in the module, one is used to control the wavelength of the laser, and the joint scientific research team of Professor Chen Yongsheng of the school of chemistry and Professor Tian Jianguo of the school of physics, through three years of research, is used to ensure the constant temperature operation of the wavelength lock and power detection detector in the module. The module also has a built-in SOA to amplify the output optical power

the disadvantage of this control technology is that the tuning width of a single module is not wide, generally only a few nm, and the tuning time is relatively long, which generally requires a few seconds of tuning stability time

at present, tunable lasers basically adopt current control technology, temperature control technology or mechanical control technology, and some suppliers may adopt one or two of these technologies. Of course, with the development of technology, other new tunable laser control technologies may also appear. (end)

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