With Dense Wavelength Division Multiplexing (DWDM) technology, fiber amplification technology, including the development of erbium doped fiber amplifiers (EDFAs), distributed Raman fiber amplifiers (DRFAs), semiconductor amplifiers (SOA), and optical time division multiplexing (OTDM) technologies Widely used, fiber-optic communication technology is constantly developing toward higher-speed, larger-capacity communication systems, and advanced fiber-optic manufacturing technology can maintain stable and reliable transmission and sufficient margin, and meet the needs of optical communication for large broadband. And reduce nonlinear damage.
Multimode fiber
The center core of the multimode fiber is thicker (50 or 62.5 μm) and can transmit multiple modes of light. Commonly used multimode fibers are: 50/125μm (European standard), 62.5/125μm (US standard).
In recent years, the application of multimode fiber has grown rapidly. This is mainly because the world's fiber optic communication technology will gradually turn to deep development. The practical application of parallel optical interconnect components will also greatly promote the rapid growth of the short-range multimode fiber optic cable market, thus enabling multimode The market share of fiber optics continues to rise. With the establishment of Gigabit Ethernet, Ethernet will also upgrade from Gbps to 10Gbps ultra-high speed, and the 10Gbps Ethernet standard (IEEE802.3ae) was introduced in the first half of 2002. The continuous advancement of communication technology has greatly promoted the development of multimode fiber.
Full wave fiber
As the demand for fiber bandwidth continues to expand, the communications industry has been striving to find ways to eliminate the "water absorption peak." The manufacturing technology of All-Wave Fiber is essentially a specialized production process that eliminates the "water absorption peak" of OH ions as much as possible. It makes ordinary standard single-mode fiber at 1383 nm. The attenuation peak near is reduced to a low enough level. In 1998, Lucent developed a new fiber manufacturing technology that eliminates OH ions in fiberglass, so that fiber loss is completely controlled by the characteristics of the glass. The "water absorption peak" is basically "flattened". Therefore, the optical fiber can be used for optical communication in the entire wavelength range of 1280 to 1625 nm, and thus the problem of the full-wave optical fiber manufacturing technology is gradually solved. So far, many manufacturers have been able to produce full-wave fiber for communication, such as Lucent's All-wave fiber, Corning's SMF-28e fiber, Alcatel's ESMF-enhanced single-mode fiber, and Fujikura's LWPfiber fiber. Wait.
In April 2000, in order to adapt to the latest developments in fiber optic product technology, the ITU revised the G.652 single-mode fiber standard on a large scale and officially finalized it in October, corresponding to the IEC (International Electrotechnical Commission) classification number B1.3. ITU-T defines "full-wave fiber" as G.652c fiber, which is mainly applicable to the SDH transmission system specified by G.957 of ITU-T and the single-channel SDH transmission system with optical amplification specified by G.691 and up to STM-64 (10Gb/s) ITU-T G.692 optically amplified wavelength division multiplexing transmission system usually requires wavelength dispersion adjustment for high-rate transmission in the 1550 nm wavelength region.
Full-wave fiber will have a lot to do in the construction of metropolitan area networks. From the perspective of the network operator, with the full-wave fiber, the coarse wavelength division multiplexing technology can be used, and the channel spacing is about 20 nm, which can still provide a large bandwidth for the network, and at the same time, Filter and laser performance requirements are greatly reduced, which greatly reduces the construction costs of network operators. The emergence of full-wave fiber has made a variety of optical communication services more flexible. Because of the wide band for communication, we can divide the band of the full-wave fiber into different communication segments. use. It is foreseeable that this full-wave fiber will be widely used in the construction of metro networks in small and medium-sized cities in the future.
The desire of human beings to pursue high-speed, broadband communication networks is endless. Under the current situation that bandwidth demand has grown exponentially, full-wave fiber is receiving more and more attention from the industry. Its many advantages have been widely accepted by the communication industry.
Polymer fiber
At present, the main line of communication has realized the communication based on quartz fiber. However, in the access network and fiber-to-the-home (FTTH) project, quartz fiber has encountered great difficulties. Since the core of the quartz fiber is very thin (6-10 μm), the coupling and interconnection of the fiber are technically difficult. Because of the high precision alignment technology, it is a problem for access network users with short distance and many contacts. Since polymer optical fiber (POF) has a large core diameter (0.2 to 1.5 mm), it can use an inexpensive and simple injection molded connector, and has good toughness and flexibility, and has a large numerical aperture and can be used. An inexpensive laser source with a low-loss window in the visible region is suitable for access networks. Polymer fiber is the most promising transmission medium in FTTH engineering.
The polymer fiber is divided into two types: multimode step type SI-POF and multimode gradient type GI-POF. Due to the severe modal dispersion of the SIPOF, the transmission bandwidth is similar to that of the twisted copper wire, and is limited to 5MHz or less. The short communication distance can not meet the communication standard requirements of FDDI, SDH and B-ISDN, and the refractive index distribution of GIPOF core is parabolic, so the mode dispersion is greatly reduced, and the bandwidth of signal transmission can reach 2.5Gbps or more within 100m. In recent years, GIPOF has become the main direction of POF research. Recently, N.Tanio theoretically predicted that the theoretical loss limit of amorphous perfluoropolybutene vinyl ether at 1300 nm is 0.3 dB/km, and the loss at 500 nm can be as low as 0.15 dB/km, which is completely comparable. The loss of quartz fiber is comparable. G. Giorgio et al. reported that the data transmission rate of 100m perfluoro GI POF has reached 11 Gbps. Therefore, GI POF may become an ideal transmission medium for access networks, user networks, and the like.
Photonic crystal fiber
Photonic crystal fiber (PCF) was proposed by ST.J. Russell et al. in 1992. For quartz fiber, the structure of PCF is characterized by evenly arranging air holes in the axial direction. Thus, from the end face of the fiber, there is a two-dimensional periodic structure. If one of the holes is damaged and missing, Defects occur and light can be transmitted through it. Unlike ordinary single-mode fibers, PCF is known as a hollow fiber or a micro-structured fiber because it is composed of a single quartz material that periodically aligns air holes. PCF has special dispersion and nonlinear characteristics and will be widely used in the field of optical communication.
One of the striking features of PCF is that it is well-structured and has the ability to support single-mode transmission at all wavelengths, the so-called "endlessly-single-mode" feature, which has a good theory. Explanation. This needs to satisfy the condition that the air hole is sufficiently small, and the ratio of the air hole to the hole pitch must be no more than 0.2. A PCF with a large air hole will have the same multimode phenomenon in a short wavelength region as a normal fiber.
Another feature of PCF is its singular dispersion characteristics. Now people have successfully produced 850 nm optical solitons in PCF, and it is expected that the wavelength will be reduced in the future. PCF may play an important role in the future of ultra-wide WDM flat dispersion compensation.
The world's leading PCF product commercialization company, Denmark's CrystalFiberA/S, recently launched a new line of photonic crystal fiber products. One is a hollow "air-guiding Photonic Bandgap Fiber", which has a hollow core that uses air as a waveguide to allow light to travel in a particular band gap. The Other is "Double Clad High NA Yb Fiber", which can be used in fiber lasers or fiber amplifiers. In addition, because of its photosensitivity, it can also be used on it. Write the fiber grating.
Communication fiber problems
At present, there are still many problems in optical fiber communication applications to be solved. Such as dispersion and dispersion, finite dispersion and small dispersion slope, negative dispersion, polarization mode dispersion, nonlinearity, large area effective area bending loss, contradiction of comprehensive optimization, effective area and dispersion slope, negative dispersion and loss. But there are reasons to believe that with the continuous advancement of optical communication technology, these problems will find a suitable solution.
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