Current situation of optical fiber technology used in optical network

The application of optical fiber in various optical networks determines the requirements of optical fiber technical performance. For short distance optical transmission networks, the emphasis is on multimode fibers that are suitable for laser transmission and wider mode bandwidth to support larger serial signal transmission capacity.

For long-distance submarine optical cable transmission system, in order to reduce the price of expensive fiber amplifier, we should consider using the fiber with large mode field diameter and negative dispersion to increase the transmission distance.

The focus of long-distance transmission system on land is to be able to transmit more wavelength, and each wavelength can be transmitted at high speed, but also to solve the dispersion problem of optical fiber, even if the dispersion value of the fiber with the wavelength of the change to reach the minimum value.

For the local area network and the circular feeder, because the transmission distance is relatively short, the focus of consideration is the optical network cost rather than the transmission cost. That is, to solve the problem of the up/down path in the optical fiber transmission system, it is necessary to minimize the cost of inserting/splitting wavelength.

Optical fiber for transmission

The application of optical fiber technology in transmission system is firstly realized by various optical networks. Up to now, the topology structure of all kinds of optical fiber transmission network can be divided into three kinds: Star shape, total shape and ring. Furthermore, from the layered mode of the network, the network can be divided into several layers from top to bottom, and each layer can be divided into several subnets. In other words, the network and network composed of each switching center and its transmission system can also be divided into several smaller subnets, so that the whole digital network can communicate effectively, and the All-digital Integrated Service Digital Network (ISDN) is the overall goal of the communication network. ADSL and CATV popularization, metropolitan Access system capacity is increasing, backbone network expansion of the main line requires different types of optical fiber to assume the responsibility of transmission.

Dispersion compensated fiber (DCF)

The optical fiber dispersion can widen the pulse and cause the error rate. This is a problem that must be avoided in communication network, and also a subject to be solved in long-distance transmission system. Generally speaking, the dispersion of optical fiber consists of material dispersion and waveguide structure dispersion, material dispersion depends on the dispersion of silica masterbatch and doping agent, and waveguide dispersion is usually a tendency that the effective refractive index of the mode changes with wavelength. Dispersion compensated optical fiber is a technique used to solve the dispersion management in the transmission system.

Non-dispersion shifted optical fiber (USF) is dominated by positive material dispersion, and it produces 0 dispersion near 1310nm after merging with small waveguide dispersion. The dispersion-shifted optical fiber (DSF) and the non-0 dispersion-shifted optical fiber (NZDSF) are used as technical means, intentionally, the refractive index distribution of optical fiber is designed to produce a waveguide dispersion which is comparable to material dispersion, so that the dispersion of the material and the dispersion of the waveguide are added, and the 0 dispersion wavelength of the DSF is moved to the vicinity of 1550nm. The 1550nm wavelength is the most widely used wavelength in the current communication network. In the submarine optical cable transmission system, the dispersion management is composed of two kinds of optical fibers, which are respectively positive dispersion and negative dispersive, which are integrated into the transmission system. With the increase of distance and capacity of transmission system, a large number of WDM and DWDM systems are put into use. In these systems, in order to compensate the dispersion, we developed the DCF which can work on the C-band and L-band, and the refractive index distribution of three packs of three layers. The dispersion value of SMF with dispersion compensation on C-band is 65ps/nm/km, and the effective area (APFF) is 28m2, and the loss is 0.225 0.265db/km.

Optical fiber for amplification

In the quartz fiber core layer doped with rare earth elements can be made into amplified optical fiber, such as erbium doped optical fiber (EDF), doped with thulium amplification fiber (TOF) and so on. Amplified optical fiber and traditional quartz fiber has good integration performance, but also has high output, wide bandwidth, low noise and many other advantages. Optical fiber amplifiers (such as EDFA) made of amplified optical fibers are the most widely used key devices in today's transmission systems. EDF's amplification bandwidth has been extended from the C-band (1530 1560nm) to the L-band (1570 1610), with an amplified bandwidth of up to 80nm. The latest research shows that EDF can also amplify light in S-band (1460 1530), and has produced an inductive Raman fiber amplifier, which is amplified on S-band.

For L-band (1530 1560nm) amplified optical fibers, double cladding fibers have been developed in the High Output field. One of the first cladding multimode transmission pump light, in the fiber core single mode cladding layer transmits the signal optical and doping the nail (Yb) as the photosensitive agent, in order to increase the absorption coefficient.

In solving the nonlinearity of optical fiber, the EYDF fiber was produced by using rare earth elements such as YB or La (lanthanum). This kind of fiber has almost no fwm. This is because YB ion and er ions have increased the distance between ER ions, which solves the concentration extinction caused by excessive concentration of EV ions, and also increases the doping of ER ions, increases the gain coefficient and thus reduces the nonlinearity.

For L-band (1570 1610nm) amplified optical fibers, EDF, developed by the Japanese Sumitomo Electrician, has been extended to the L-band using the C-band EDF, which requires a length of 1/3 short size EDF. The L-band three structure fiber amplifier (40GB/S) was successfully designed for high speed transmission with total dispersion of zero. The first segment of the amplifier is a conventional EDF with negative dispersion, while the second to third segment of the wavelength dispersion value of the short size EDF is positive.

For S-band (1460 1530nm) amplifier optical fiber, NEC uses a dual-wavelength pumping gs-td FA for long-distance transmission of 10.92tb/s, using 1440nm and 1560nm dual-wavelength lasers (LD) to achieve a 29% conversion rate NTT uses a single wave and 1440nm dual-channel pumped lasers to achieve a 42% conversion rate (Thulium-doped concentration of 6000ppm); Alcatel Company uses 1240 and 1400nm multi-wavelength Raman lasers to achieve 48% conversion rates, At the same time, using the 800nm Sapphire Laser and 1400nm multistage Raman laser Dual-wavelength pump to achieve the conversion rate of 50%, the latest report of Asahi Company in Japan to the bismuth (BI) group of oxide Glass as the matrix of S-band pump Amplification scheme. In short, the main technical issues to be solved are how to reduce the doping of phonon energy components and improve the quantum efficiency.

Optical fiber For the occurrence of Super continuous wave (SC)

The hyper-continuous wave is the time spectrum UWB phenomenon in the transparent medium for the strong light pulse transmission. As a new generation of multiple-load source is widely concerned by the industry. Ultra-wideband Light has been observed in optical fiber, semiconductor material, water and other kinds of materials since the Ultra wideband Light observed in Alfano and Shapiro in large capacity glass in 1970.

The SC light source using single mode fiber is an effective means to solve the technical problem by using the complex light source method.

1997, Nippon NTT developed a successful dual-cladding and 4-cladding refractive index distribution structure, the core by the length of the direction (longitudinal) of the cone-shaped distribution, with a convex dispersion characteristics of the fiber. 2000 also developed a successful use of SC light polarization-preserving fiber (PM-SC fiber).

The high nonlinear SC fiber mainly adopts the high closed structure of photonic crystal fiber and tapered core fiber, and the manufacturing technology of photonic crystal Fiber has made a new breakthrough, the future research direction is the low cost SC fiber manufacturing technology and how to apply it in the next generation network.

Optical fiber for optical devices

With the construction and expansion of a large number of optical communication networks, the consumption of active and passive devices is increasing. The most widely used fiber-optic devices, mainly optical fiber amplifier, fiber coupler, optical divide wave, fiber Bragg grating (FG), AWG and so on. These optical devices must be low loss, high reliability, easy to use and communication optical fiber for low loss coupling and connection can be applied to the communication network. Therefore, the development and production of FG used fiber and device coupling optical fiber (LP fiber).

FG is a GeO2, B2o3, P2O5 and other dopant in quartz fiber, which is formed by the change of the refractive index caused by the change of glass density due to ultraviolet light irradiation or chemical reaction with H2. The variation value of ultraviolet induced refractive index varies with the glass composition, so in order to improve photosensitive property and achieve long-term temperature stability of FG, we also study the problem of ultraviolet absorption by doping sn,sb and other heavy metals.

We have developed a variety of optical fiber to reduce the loss of FBG. such as waveguide structure multi-layer film embedded in optical fiber, in order to further reduce the loss, must make the cladding and core of the photosensitive characteristics as far as possible consistent. The loss value can be less than 0.1dB when the change of photosensitive characteristic is 10% and the refractive index change is 1 10-3.

The coupling fiber of optical devices is developed with the performance of AWG and PLC, and the high optical fiber with the MFD value of PLC has been developed, and the MfD of high value fiber of ordinary fiber is achieved by thermal diffusion expansion (TEC). The TEC method used in this new optical fiber can reduce the connection loss of the optical fiber from the original 1.5dB to the current 0.1dB below.

Polarization-Preserving fiber

Polarization-preserving fiber is the first optical fiber developed for coherent optical transmission. Since then, it has been used in fiber optic sensor technology field such as fiber optic gyroscope. In recent years, due to the increase of wavelength division multiplexing in DWDM transmission system and the development of high-speed, polarization-preserving fiber has been widely used. The most widely used is Panda optical fiber (PANDA).

Panda fiber is currently used in a large number of tail fiber, and other optical fiber devices connected to the system used in one.

Single-mode non-stripping optical fiber (SM-NSP) Single mode non-stripping optical fiber is a new type of optical fiber which still has the NSP polyester layer retained on the fiber cladding surface to protect the fiber's mechanical properties and high reliability even after the fiber is laminated.

SM-NSP Fiber has the same external diameter, eccentricity and non degree precision as conventional SM optical fiber. However, the mechanical strength of ASM-NSP fiber is much higher than that of SM, which has excellent reliability, and the successive tests show that both the SM-NSP fiber and the SM-NSP fiber are connected with the SM fiber, and the connection characteristics and the environment resistance are good. It can be widely used in transmission system, and is an ideal new wiring fiber.

Optical fiber for deep ultraviolet light transmission (DUV)

At present, one of the research topics of solid-state lasers and gas lasers is the laser oscillation technology in the field of deep ultraviolet light (250nm). In the field of solid-state lasers, the Clbo (cslib6o10) crystalline Nd:yag laser is used for four times times (=266NM), five times-fold (=213nm), and in the field of gas lasers, F2 (=157nm), KY2 (=148nm), AR2 (=126nm), The high wavelength =193nm of the epoxy resin laser with ARF is adopted.

Deep ultraviolet light is widely used in the field of semiconductor substrate surface treatment, DNA analysis and testing in the field of biochemistry, and the treatment of myopia in the medical field. The development of optical fiber for the transmission of deep ultraviolet light has also become a major technical issue of great concern to people.

From the loss spectra of DUV fiber, it can be seen that the transmission loss occurs when the wavelength is =200nm, and there are two peaks at 1240 and 1380nm, which we think is caused by the absorption of Oh's elastic vibration.

The same preform in the drawing process due to different drawing conditions, the loss spectral value is also different, in DUV drawing process (when <220nm) drawing speed is 0.5m/cent, the furnace temperature is 1780 ℃, the optical fiber loss value is smallest, the light uses the wavelength is 193nmArF laser source, the minimum transmittance rate is about 60%/m. The loss of optical fiber is increased with the speed of wire drawing, the increase of furnace temperature, the absorption at the 220nm wavelength is increased, this value is caused by E "center, which belongs to the defect of drawing process."