Because the plastic optical fiber easy handling and processing, its diameter is large, one ram, fiber coupling and beam into high efficiency, therefore, as a short wave guide; Such as LAN, data line has been widely studied. All commercial plastic optical fiber is sl refractive index distribution. So. Even short distance optical communication, sl plastic optical fiber also can't cover in the near future the quick data lines and LAN, the need to all of the bandwidth, because the bandwidth of the s1 plastic optical fiber are only a few MHz/km.
In this article, introduces the copolymerization reaction method with a new interface gel successfully produced a kind of low loss and wide bandwidth Gl plastic optical fiber.
2. The GI plastic optical fiber production
Using the two kinds of monomer M - and Mz copolymerization interfacial gel copolymerization reaction process of preform diameter of 10 ram. This kind of precast them gradually reduce refractive index from the central shaft to the edge. Respectively in this paper, choose a vinegar (MMA) methyl propylene acid as M, monomer, tellurium benzene acetic acid b fat (VPAC) and PVC formic acid ester (VB) Mt. MMA, VPAC and VB refractive index were 1.49, as the starting jing. Butyl mercaptan as chain transfer agent. Will be filled with monomer mixture of PMMA tube in the 60-80 ℃ oven. Because single I4l ship towering walls of polymer tube slightly nitrate. Then on the inner wall of the tube to form a gel phase. This situation is roughly is shown in figure 1 (a). Here. Due to the gel effect as a result, the gel inside the polymerization speed than the speed of monomer liquid polymerization reaction, therefore, polymerization from the pipe wall.
Because of MMA monomer polymerization priority within the cylinder formed near the surface of the copolymer of refractive index is low. As can be seen: copolymer phase gradually thickening, and in the center of a monomer liquid polymer content (Pro) slightly increased.
DI and M. Priority compared to M, monomer polymerization, the monomer of the rest of the M monomer liquid is reduced, the percentage of so copolymer formed by the refractive index by the new increase, leads to the formation of a along the radial refractive index l brother degrees. In the end, until the center of the polymer tube shaft copolymer have been formed, to complete the polymerization condition is shown in figure l (c). Start with 70 "C temperature in the vacuum system of the top I Qian heat treatment for two days, and then in the 230-280 - C temperature heat drawing produce Gl optical fiber.
3. The GI fiber optical properties
Transverse interferometry was used to measure GI plastic optical fiber refractive index distribution. MMA - VPAC and MMA - VB refractive index distribution of the optical fiber is shown in figure 2. The n in the figure. And n is the central axis and distances from the center for r refractive index. Rp is the radius of the fiber, the pre the M/M. A 4.0 (wt/wt) is a 0.5 in BPO wt and nBw a 0.2 wt. In 70 'C temperature after 24 tj,. When make, normalization refractive index distribution of the optical fiber is almost the same as the preform. According to the difference of refractive index gradient refractive index, calculate the MMA - VPAC and MMA - VB the numerical aperture of the fiber is 0.18 and 0.22, respectively. With the spectrum analyzer (Advantest CO ModelTQ8345) measured by total GI optical fiber transmission attenuation spectrum. Figure 2 ql GI test result of plastic optical fiber is shown in figure 3, MM people VPAC and MMA - VB total optical fiber at 652 nm wavelength attenuation respectively is 143 db/db/km and 134 km. It is worth noting that these values are comparable to the commercial step of the refractive index of plastic optical fiber attenuation (100 ~ 300 db/km). GI and sI plastic optical fiber bandwidth measurement is as follows. - Ga person lP In laser diode (670 nm) wavelength: = = l0Mllz pulse into a 15 m long fiber (NA a 0.5) by taking the head (Model OO $a 01 / lamamatsuphotonics CO) detection of the output pulse. MMA in figure 2
A VB GI - VPAc and MM people optical fiber test result is shown in figure 4, can be compared with the commercial SI fiber. It is worth noting: by SI fiber output pulse is quite wide, by GI optical pulse is almost the same as the input pulse. According to the impulse response function. It SI 3 db bandwidth of the fibre optic is 6 ml ~ / km, and the first with the method of the experiment has proved that the bandwidth of the GI plastic optical fiber is better than ordinary SI plastic optical fiber. The two kinds of optical fiber attenuation.