The introduction

For the first time since 1986, when the dupont developed step refractive index (SI) plastic optical fiber (POF), has more than 30 years. Because of the POF transmission loss and lack of special commercial demand, slow progress for years. But since 1982 at Japan's keio university proposed gradient refractive index (GI) plastic optical fiber, in 1990 successfully developed the first high speed transmission GI POF and low loss in 1996 to develop the first total fluoride fiber, plastic optical fiber technology has made great development, the plastic optical fiber also has attracted much attention. Is expected in the next few years POF to apply a lot of optical communication field.

This paper will briefly introduce optical communication with plastic optical fiber

Structure, classification, preparation methods, main performance parameters, mechanical properties and thermal properties, development direction and the latest research progress and technical difficulties and the future research emphasis.

2 plastic optical fiber (POF)

2.1 the structure of POF

Used in optical communication of POF is circular cross section, generally divided into the fiber core and cladding and sheath of three layers. Fiber core radius is usually 125-490 mm, most of the light spread along the fiber core. Fiber core of low refractive index of cladding. Sheath or coated layers have the effect of mechanical optical fiber protection, with high strength, generally made from polyethylene, also can use polyvinyl chloride and chlorinated polyethylene production.

2.2 classification

From the perspective of dissemination, POF can be divided into single mode fiber and a multimode fiber. The former has a relatively small fiber core, it requires that the transmission light mode; The latter of the fiber core is quite big, enough to use the geometric ray tracing model analysis. If, in accordance with the actual use, POF can be divided into communication POF, high temperature resistant (hot) POF, lighting coarse diameter POF and medical like a bunch of POF, etc. And according to the fiber core material is different, can be divided into the polymethyl methacrylate POF POF (PMMA POF), polystyrene POF (PSPOF) and polycarbonate POF (PC POF) three.

2.3 preparation methods

The preparation of POF need two steps. First prepare a called preform solid cylindrical bar, length is about 0.5 ~ 1 m, diameter of a few millimeters. The preform structure will determine the fiber core and cladding refractive index distribution. The second step is, extrusion preform drawing out 500 meters to several kilometers of POF. Advanced production technology can be used to produce cheap, high quality, low loss of POF. At present, the production step refractive index (SI) POF mainly adopts molten study.this method, through the continuous extrusion or partial extrusion for optical fiber; While production of GI POF mainly adopts interfacial gel polymerization and diffusion method.

2.4 the main performance parameters

Against 2.4.1 attenuation

POF attenuation depends on the fiber core diameter, it along with the increase with the decrease of the fiber core diameter. In 570 nIn, diameter of 0.5 mm of PMMA

POF attenuation of 70 dB/km, 0.25 mm diameter PM - MA POF attenuation is 130 dB/km. This feature is due to the smaller diameter of fiber has a large number of geometric and structural defects. In addition, the decay also depends on the frequency spectrum width and numerical value of the light source used

Aperture (NA). Or the light source spectrum width of NA will cause attenuation increases For example, when NA was 0.1, PMMA POF attenuation only

NA for 70 dB/km, 0.65 when attenuation is 88 dB/km.

2.4.2 dispersion and bandwidth

Most of the optical fiber transmission system is digital, that is, information in the form of a pulse transmission through optical fiber. Pulse through the optical fiber transmission

When experience instantaneous bandwidth, called the instant dispersion, hereinafter referred to as dispersion. Dispersion can also affect communication, because it makes the signal waveform

The true. So can be observed in any of the optical fiber communication link, dispersion is the maximum bandwidth decided to transfer by optical fiber parameters. The factors affecting waveform distortion mainly have three: mode dispersion (also called mode dispersion), material dispersion and waveguide dispersion, the latter two dispersion can be combined together as dispersion dispersion or die. The bandwidth of the POF is one of the important performance parameters of the limited transmission rate.

The current methods to improve the POF bandwidth has two kinds: one is to change the structure of the fiber parameters; 2 it is to choose different refractive index profile structure. The former method is to step refractive index (SI) POF is the numerical aperture of the reduced from 0.5 to 0.3, to reduce mode dispersion, the optical fiber bandwidth increase by 7.5 MHz km to 12 MHz, km. The latter approach is to form of the refractive index distribution of POF by step type instead of the gradient type (GI), such doing can will die to minimize the delay, make POF's largest bandwidth up to 3.5 GHz, km.

2.4.3 numerical aperture (NA)

NA is a very important parameter of optical fiber, because it said fiber receives and the ability to guide light. Large numerical aperture of the optical fiber can receive more light. Compared with glass fiber, typical numerical aperture of POF is very large, about 0.5, then light coupled into the fiber.

In addition to numerical aperture decreasing fiber, they are used to implement the high transmission speed. Numerical aperture is smaller, the higher the bandwidth, because there are fewer mode transmission through optical fiber, the mode dispersion decreasing. As for the transmitter and detector, they also have their own numerical aperture, depends on the Angle of emission and receiving Angle. Particularly important is matching with the light source should make the numerical aperture of the fiber, so that the transmitted power coupled into the fiber effectively.

2.5 mechanical properties

Relevant personnel research the mechanical properties of POF. Research has focused on bending, stretching, or the attenuation of torsional stress. Plastic and glass fiber is different, POF, its young's modulus is almost two orders of magnitude lower than the silica fiber (PMMA POF is about 2.1 GPa). For this, according to the typical structure of optical fiber, even 1 mm diameter of POF is quite soft, also can be installed. Similarly, the smallest bending radius of POF

Also small, because plastic than quartz is softer and easier to bend. PCPOF got similar results, the young's modulus. 55-2.55

Within the scope of GPa. POF also depends on the transfer rate of some mechanical properties. For example, if the POF elongation reaches 10% of its length, the attenuation increases less than 0.1 dB. Other factors also can change the optical properties of POF, such as bending cycle will cause attenuation change, decay reaches a certain limit (1 mmPMMAPOF in bending radius of 5 0 mm, 1 after 000 times bending attenuation < 0.15 dB).

2.6 thermal performance

Because of POF is made of polymer, so it can generally work under the temperature of 80 ~ 100 ℃. Beyond this range, POF began to lose its robustness and transmission of light. Made of crosslinked polyethylene and polyolefin elastomer sheath, can make the job of POF temperature to 125 ℃, 135 ℃ even. On the other hand, the high temperature resistant performance depends largely on the humidity of POF. This feature is absorbed by the visible areas of strong OH a belt. Fluoride fiber do not absorb water, so their attenuation is affected by the humidity is not obvious. High bandwidth GI POF have high thermal stability at the same time, even under 85 ℃ ageing 10, 000 hours is not observed bandwidth distortion. 3 the development direction of POF and the latest research progress

The development direction of 3.1 POF

From the point of foreign research and development, the research focus of POF are mainly concentrated in the following aspects:

, reduce the loss of light;

, improve the bandwidth (by type SI to GI);

Improve the heat resistance.

Polycarbonate, silicon resin, crosslinking acrylic ester copolymer and can make the heat resistant up to 125 ~ 150 ℃.

3.2 the latest research progress of POF

POF attenuation and bandwidth in the latest practical progress as follows: the Japanese Asahi Glass company declared in July 2000, the company implemented at keio university in GI POF technology, adopts full fluorinated polymer Cytop manufacturing GI fiber, commodity name Lucina, attenuation of 25 ~ 50 dB/km,

Is 600 ~ 1 300 nm wavelength, transfer rate of 3 Gb/s, bandwidth is greater than 200 MHz, km, in a very wide wavelength window shows low attenuation. POF the latest practical progress in the aspect of heat resistance for: Japanese JSR and agms corporation jointly developed, heat-resisting transparent resin ARPON manufacturing SI POF, heat-resistant has amounted to 170 ℃.

4 technical difficulties and the future research emphasis

4.1 technical difficulties

At present in terms of technology, POF needs to solve two major problems. One is designing new pervious to light material and clad material. Plastic optical fiber as well as quartz optical fiber by the fiber core and cladding of two parts, to produce high quality fiber, both are very important. Optical fiber core requirements transparency and refractive index is higher, the better, while the cladding for refractive index is less than the core material, and the greater the difference between the two is, the better. Increase the refractive index of fiber core is more difficult, but reduce the cladding refractive index and potential can be dug, focuses on fluorinated polymer. The second problem is the technological conditions, the control of fiber core polymer molecular weight, uniformity, and improve the transparency of the new optical fiber technology, further improve the efficiency of light transmission, reduce the loss of light. Once the two problems solved satisfactorily, POF will replace silica fiber. At that time, it not only can be used for regular communication, but also for use under illumination, missile, rocket, large bombers cutting-edge fields such as radar and electronic countermeasures.

4.2 research emphasis in the future

Has now developed a variety of types with different properties of POF, to meet the requirements of different USES. By expanding the business, the POF will become an indispensable transmission medium for short distance high rate. POF inevitably compete with metal cable and become the core of the short distance high rate transmission channel. The research emphasis in the future in terms of POF is:

, increase the degree of visibility and recognition of POF;

, continue to reduce the POF attenuation;

, to improve the long-term stability of the GI POF,

The standardization of POF, a connector;

, reduce the cost of POF itself;

Into the corresponding standard.

5 conclusion

This paper briefly introduces the structure of optical communication in plastic optical fiber, classification, preparation methods, the main performance parameters and the research and the plastic optical fiber

Progress. With the progress of optical fiber technology, plastic optical fiber related peripheral technology, material technology, device technology research will be more in-depth, believe that there will be more practical, low cost products. In the future, should be in plastic optical fibers to improve performance, reduce costs, expand transmission distance, to reduce the transmission loss, etc to work hard, create new performance, to adapt to the needs of the development of high-speed communication.