Overview of optical fiber communication technology

Overview of optical fiber communication technology

introduction

with the rapid popularization of the Internet and the rapid development of Broadband Integrated Services Digital (B-ISDN), people's demand for information has shown explosive growth, almost doubling every six months. Under this background, the construction of information superhighway has become a worldwide upsurge. As the core and pillar of the information superhighway, optical fiber communication technology has become the top priority. Many countries and regions have spared no effort to develop optical fiber communication technology and its industry, and the cause of optical fiber communication has achieved unprecedented development. In addition, because the production, transmission, exchange and application of information have a decisive impact on the national economy and national security, compared with other industries, optical fiber communication has more special significance. Optical fiber communication is a huge system engineering. Its various components are interdependent, promote each other and develop together. As far as the optical fiber communication technology itself is concerned, it should include the following main parts: optical fiber and cable technology, transmission technology, optical active components, optical passive components and optical network technology

progress of optical fiber and cable technology

the progress of optical fiber technology can be explained from two aspects: one is the optical fiber used in the communication system; Second, special optical fiber. There were only three transmission windows in the early optical fiber, namely 850nm (the first window), 1310nm (the second window) and 1550nm (the third window). In recent years, the fourth window (L-band), the fifth window (full wave fiber) and S-band window have been developed successively. Especially important is the full wave window without water peak. The great significance of the successful development of these windows lies in the wide optical frequency range from 1280nm to 1625nm, which can realize low loss and low dispersion transmission, and increase the transmission capacity by hundreds, thousands or even tens of thousands of times. This technological achievement will bring huge economic benefits. The other is the development and industrialization of special optical fiber, which is a very active field

special optical fibers are as follows:

1 Active optical fiber this kind of optical fiber mainly refers to the optical fiber doped with rare earth ions. For example, erbium doped (er3+), neodymium doped (nb3+), praseodymium doped (pr3+), ytterbium doped (yb3+), thulium doped (tm3+) and so on constitute laser active substances. This is the core material of optical fiber amplifier. Different doped fiber amplifiers are used in different working bands, such as erbium doped fiber amplifier (EDFA) is used near 1550nm (C and l bands); Praseodymium doped fiber amplifier (pdfA) is mainly used in 1310nm band; Thulium doped fiber amplifier (TDFA) is mainly used in S-band. These doped fiber amplifiers and Raman fiber amplifiers have brought revolutionary changes to the optical fiber communication technology. Its remarkable functions are: directly amplifying the optical signal and extending the transmission distance; Distribution loss compensation in optical fiber communication and CATV; In addition, it is an indispensable key component in wavelength division multiplexing (WDM) system and optical soliton communication system. It is precisely because of the fiber amplifier that the optical soliton transmission without repeater can be realized. With the fiber amplifier, not only the distance of WDM transmission can be greatly extended, but also the transmission performance can be optimized

2 Dispersion compensation fiber (DCF) the dispersion of conventional G.652 fiber near 1550 "nm wavelength is 17ps/nm? km。 When the rate exceeds 2.5gb/s, bit errors will occur as the transmission distance increases. If used in CATV system, the signal will be distorted. The main reason is that the accumulation of positive dispersion results in the aggravation of dispersion and the deterioration of transmission characteristics. In order to overcome this problem, the fiber with negative dispersion value must be used, that is, the anti dispersion fiber string is connected to the system to offset the positive dispersion value, so as to control the dispersion of the whole system. Here, the anti dispersion fiber is the so-called dispersion compensation fiber. At 1550nm, the dispersion value of the anti dispersion fiber is usually -50~200ps/nm? km。 In order to obtain such a high negative dispersion value, the core diameter must be made very small, and the relative refractive index difference must be made very large, which often leads to an increase in the attenuation of the optical fiber (0.5~1db/km). Dispersion compensation fiber uses fundamental mode waveguide dispersion to obtain high negative dispersion. Usually, the ratio of dispersion to attenuation is called quality factor. Of course, the larger the quality factor, the better. In order to compensate the dispersion of conventional single-mode fiber uniformly in the whole band, a "double compensation" fiber (ddcf) which can compensate both dispersion and dispersion slope has been developed recently. The characteristic of this fiber is that the dispersion slope ratio (RDE) is the same as that of conventional fiber, but the symbol is opposite, so it is more suitable for equalization compensation in the whole waveform

3. Fiber grating fiber grating is made by using the photosensitivity of fiber materials to produce periodic refractive index changes (i.e. grating) in the core of the fiber under the irradiation of ultraviolet light (usually referred to as ultraviolet "writing"). The germanium doped fiber is used. Under the cover of the phase mask, it is irradiated with ultraviolet light (in the hydrogen carrying atmosphere) to make the refractive index of the fiber core change periodically, and then it can be preserved for a long time after annealing. The manufacturing principle is shown in Figure 2. The phase mask in Figure 2 is actually a specially designed grating, and its positive and negative first-order diffracted light intersects to form interference fringes, thus gradually generating gratings in the fiber core. The grating period a is half of the template period. As we all know, the grating itself is a frequency selection device. Many important optical passive devices and optical active devices can be made by using fiber grating, such as hollow glass, vacuum glass, Low-E glass and coated glass, which play a certain role in building energy saving. For example: dispersion compensator, gain equalizer, optical add drop multiplexer, optical filter, optical wavelength multiplexer, optical mode or converter, optical pulse compressor, optical fiber sensor and fiber laser

4. Multi-core single-mode fiber (MCF) multi-core fiber is a single-mode fiber with a common outer cladding, containing multiple cores, and each core has its own inner cladding. The obvious advantage of this fiber is its low cost. The production cost of 4-core optical fiber is about 50% lower than that of ordinary optical fiber. In addition, this kind of optical fiber can improve the integrated density of cabling and reduce the construction cost. These are the major achievements of optical fiber technology in recent years. As for the achievements in optical cables, we believe that they are mainly reflected in the successful development and mass production of ribbon optical cables. This kind of optical cable is necessary for optical fiber access and local area. At present, there are more than 1000 optical cables, which effectively ensures the construction of access

progress of three optical active devices the research and development of optical active devices was originally the most active field, but due to the brilliant achievements made in previous years, today's activity space has been greatly reduced. At present, superlattice structure materials and quantum well devices have been fully mature, can be produced in large quantities, and have been fully commercialized, such as multi quantum well lasers (mqw-ld, mqw-dfbld)

in addition, major achievements have been made in the following areas

1 Integrated devices here mainly refer to the commercialization of optoelectronic integration (OEIC), such as the integration of distributed feedback laser (DFB-LD) and electric absorption modulator (eamd), i.e. dfb-ea; Integration of other transmitting devices, such as integration of DFB-LD and mqw-ld with MESFET or HBT or HEMT respectively; The integration of receiving devices mainly includes pin, metal? semiconductor? The metal detector is integrated with the preamplifier circuit of MESFET or HBT or HEMT respectively. Although these collections have been successful, they have not yet been commercialized

2 Vertical cavity surface emitting lasers (VCSELs) have attracted much attention due to their easy integration and high-density applications. Devices with this structure have achieved great success in short wavelength (algaas/gaas) and began to commercialize; The research and development work on long wavelength (ingaasf/inp) has already begun. At present, there are also a few commodities. It can be concluded that vertical cavity surface emitting lasers will play an important role in access and localization

3. The narrow-band response tunable integrated photon detector is getting smaller and smaller due to the channel spacing of DWDM optical network system, even to 0.1nm. Therefore, the half width of the detector response spectrum should basically meet this requirement. It just happens that the narrow-band detector has sharp response spectrum, which can meet this requirement. The resonant cavity enhancement (RCE) detector, which integrates the F-P cavity filter and the optical absorption active layer, can provide an important and comprehensive solution

4. The research on multi quantum well devices and integration (sige/si MQW) based on silicon-based heterogeneous materials is a hot spot. As we all know, silicon (SI) and germanium (GE) are simple band source materials with low luminous efficiency, which are not suitable for optoelectronic devices. However, the semiconductor technology of Si materials is very mature. Therefore, people imagine that the material can be modified by using the energy band tailoring project to achieve the purpose of making optoelectronic devices and their integration (mainly realizing optoelectronic integration, or OEIC) on the basis of silicon. Great achievements have been made in this regard. There are many innovations in theory, major breakthroughs in technology, and the device level is becoming more and more perfect

four optical passive devices

optical passive devices and optical active devices are also indispensable. Due to the development of optical fiber access and all-optical network, the development of optical passive devices is unprecedentedly popular. Conventional common devices have reached a certain industrial scale, and their varieties and performance have also been greatly expanded and improved. The so-called optical passive devices refer to optical energy consuming devices with various types and functions. Their main functions in optical communication systems and optical networks are: connecting optical waveguides or optical paths; Control the propagation direction of light; Control the distribution of optical power; Controlling the optical coupling between optical waveguides, between devices and between optical waveguides and devices; Wave combination and wave division; Up and down and cross connection of optical channel. Several early optical passive devices have been commercialized. Among them, the optical fiber movable connector has a considerable scale in terms of variety and output, which not only meets domestic needs, but also has a small amount of exports. Optical splitter (power divider), optical attenuator and optical isolator have been produced in small quantities. With the development of optical fiber communication technology, many optical passive devices have emerged, such as circulator, dispersion compensator, gain balancer, optical up-down multiplexer, optical cross connector, arrayed waveguide grating CAWG and so on. These are still in the research and development stage or trial production stage, and some can also provide a small amount of goods. According to the general law of the development of optical fiber communication technology, when optical fiber access is built on a large scale, the demand for optical passive devices is far greater than that for optical active devices. This is mainly due to the characteristics of access. The access market accounts for about one third of the entire communication market. Therefore, access products have a huge market and potential market

five optical multiplexing technologies

there are many types of optical multiplexing technologies, of which the most important are wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM). Optical multiplexing technology is the most active field of optical fiber communication technology. Its technological progress has greatly promoted the development of optical fiber communication and brought revolutionary changes to the transmission technology. The current commercial level of wavelength division multiplexing is 273 or more wavelengths, the research level is 1022 wavelengths (capable of transmitting 36.8 billion channels), the recent potential level is several thousand wavelengths, and the theoretical limit is about 15000 wavelengths (including optical polarization mode dispersion multiplexing, OPDM). According to light managemen in Toronto in may1999