Fiber Bragg Grating Production and Application Quartz-based optical fibers are doped with a small amount of germanium, and the refractive index of the core of the fiber will change permanently under the irradiation of strong ultraviolet light. This phenomenon of photosensitivity is caused by Ken Hill et al. In 1978 at the CommunicaTIons ResearchCenter in Canada (CRC) stumbled upon while working. Fiber grating (fiber graTIng) is to use this photosensitive effect to change the refractive index of a certain section of core in single-mode fiber to make it have the function of grating. The main function of the fiber grating is to filter. When the broadband optical signal passes through the fiber grating, the grating can effectively reflect the incident light whose wavelength meets the Bragg condition (Bragg CondiTIon: the refractive index change period is an integer multiple of 1/2 wavelength) , Lights of other wavelengths pass through without being affected by the grating. The operating wavelength of a fiber grating depends on the period of refractive index change, while the operating bandwidth and reflectivity depend on the length of the grating and the change in the refractive index of the fiber core; generally speaking, the longer the grating, the narrower the bandwidth and the reflectance The higher. Production of grating The manufacturing process of the grating is quite simple, just use the periodic or non-periodic strong ultraviolet light stripes to expose the single-mode fiber with a high germanium content, so that the refractive index of the core changes with the stripes; Exposure in a hydrogen environment can increase the sensitivity of light and reduce the time required for exposure. In the late 1980s, Bill Morey and Gerry Meltz of United Technologies Lab first used a spectroscope to split the ultraviolet laser beam into two beams, and then used a mirror to superimpose the two beams of light at the appropriate position, generating interference fringes to illuminate the fiber, making the fiber core become Raster. The advantage of this method is that the period of interference fringes can be easily changed to produce fiber gratings with different characteristics; however, due to the need for complex optical systems and excellent coherence ultraviolet lasers, the interference fringes are susceptible The impact of environmental vibration, the fringe period changes with the interference angle, the length of the grating is limited by the radius of the laser beam, etc., so this method is not suitable for mass production of fiber gratings. Ken Hill et al. Of CRC proposed a more suitable method for mass production in 1993: this method First, the appropriate two-dimensional pattern is etched on the quartz glass substrate by electron beam exposure. Make a phase mask with diffraction function, and then irradiate the mask with ultraviolet laser to allow the -1st and + 1st order diffracted lights to interfere with each other to produce light and dark stripes to expose the fiber; make fiber grating When it is necessary, just place the bare fiber on the photomask and illuminate the back side with ultraviolet laser. The advantage of this method is that it does not require complicated optical equipment and does not require high coherence of the light source. Once the phase mask is made, many of the same fiber gratings can be easily copied; however, the cost of manufacturing the phase mask is relatively high Gratings with high and different characteristics require different masks, etc. are the disadvantages of this method. When making a phase mask, if you choose an appropriate etching depth and shape, you can minimize the intensity of the 0th order diffracted light, improve the contrast of interference fringes and increase the reflectivity of the grating. Appropriate phase mask pattern design can produce periodic or non-periodic interference fringes, making gratings with different characteristics to suit different uses; in addition, due to the method of electron beam exposure etching can be made very fine ( During the production of distributed feedback (DFB) semiconductor lasers for long-distance communication, due to the amount of dopant and some geometric parameters cannot be accurately grasped, the laser wavelength produced will have some errors (current production technology can reach approximately Within 1nm of the target wavelength), this precision light source cannot meet the needs of some DWDM applications; to improve this situation, the grating can be used on the laser lead fiber, making the grating a reflector of the laser external cavity The External Cavity Diode Laser (ECDL), which constitutes an external cavity resonator, forces the laser to emit light according to the operating wavelength of the grating to achieve frequency selection and frequency stabilization. In addition, because the period of the grating can be changed by compressing, stretching, or changing the temperature, the emission wavelength of the laser can also be adjusted by these methods, which can greatly relax the specifications of the laser body, thus improving the production yield, And can make the laser wavelength error controlled within 0.1nm of the target wavelength. Stellar provides industrial motherboards, Android motherboards, Windows motherboards, and LCD module kits according to the different needs of customers. LCD kit includes: LCD panel, AD board, inverter board and backlight cable, OSD button and cable, LVDS cable, touch screen, optical bonding, industrial keyboard, etc. Indusrial Motherboard,Windows Motherboard,Android Mainboard,Pc Motherboard Shenzhen Hengstar Technology Co., Ltd. , https://www.angeltondal.com
The wavelength of 980nm pump laser in EDFA system and the stability of the wavelength are related to the performance of EDFA. The use of fiber grating can not only improve the performance of EDFA, but also reduce the requirements for pump laser, thus reducing production. the cost of. In addition, the non-periodic grating in the erbium-doped fiber can generate appropriate loss in the amplification bandwidth, flatten the gain curve, and greatly simplify the structure of the DWDM transmission system.
In the application of DWDM transmission system, in addition to filtering and frequency stabilization and frequency selection of the light source, the fiber grating can also be used as dispersion compensation for long-distance transmission. The optical fiber laid early had the smallest dispersion around the wavelength of 1310nm, but in order to cooperate with the use of EDFA, most of them are currently switched to the 1550nm band, but the problem of dispersion is also caused. One of the solutions is to add dispersion compensation at an appropriate distance If the period of the fiber grating is properly distributed, the dispersion effect opposite to that of the fiber will be produced, and the effect of compensating dispersion will be achieved.
In the application of optoelectronic components, fiber lasers can also use fiber grating technology: the ends of a section of erbium-doped fiber are made into a 1550nm grating, so that one of the gratings has a high reflectivity, and the other has a slightly lower reflectivity. After the pumped 980nm laser becomes a 1550nm fiber laser. Similar to the diode laser in the external cavity, the fiber grating laser can change the period of the grating by stretching or changing the temperature, thereby controlling the emission wavelength of the laser; the fiber for general communication can be elongated by about 1%. Therefore the tunable wavelength range reaches 10nm. Because the characteristics of fiber grating are related to the stress, tension or temperature of the fiber, the fiber grating can also be used as a sensing component; for example, the fiber grating is placed in the structure of a bridge or wing, and the change of its characteristics can be used Monitor the temperature, stress and other changes of the position of the grating in real time. It is expected that the application and development potential of fiber gratings in the future will be considerable.