JPS61223805A - Plastic optical fiber - Google Patents

Abstract

PURPOSE:To obtain the titled fiber having an excellent optical transmission characteristic in a near infra-red range, and to lessen an increasement of a loss under a high temperature and a humidity conditions by using as a core component, the polymer contg. a specific fluorine substd. deuterium styrene unit as an essential repeating unit. CONSTITUTION:The core component composes of the polymer contg. the fluorine substd. deuterium styrene unit. shown by the formula as the essential repeating unit. The rate of depressing the refractive index by substituting with the fluorine atom is not large in the core component. Almost all materials which are used as a sheath component in the case of optical fiber that PMMA is used as the core component, are used as the sheath component. The extent of the selection of the sheath component is very wide. By substituted a hydrogen atom of an aromatic ring contd. in the styrene polymer with the fluorine atom and the heavy hydrogen atom, a hygroscopicity of the obtd. polymer is remarkably decreased. A vibration absorption strength of the O-H bonding due to the hygroscopicity reduces not only in the visible range but also in the near infra-red range.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a new plastic optical fiber, which has low loss particularly in the visible light region to near-infrared light region, and which has optical fiber conductivity based on the moisture absorption of the core component polymer. This invention relates to a plastic optical fiber with small fluctuations in optical loss.

(Background of the Invention) Conventionally, concentric cores have been produced in which a core is formed of a highly transparent synthetic polymer such as polystyrene or polymethyl methacrylate, and a sheath component is a synthetic polymer with a lower refractive index than the core component. - A plastic optical fiber that constitutes a composite fiber with a sheath structure and transmits the light incident on one end of the fiber by total internal reflection along the length of the fiber is well known. In forming the fiber, consideration must be given to minimizing factors that would increase the attenuation of the light by absorption or immersion as the light travels through the fiber.

Optical fibers using synthetic polymers have the advantage of being lighter and more flexible than conventionally known optical fibers made from inorganic glass, but they are more flexible than glass fibers. The disadvantage is that the transmitted light is highly attenuated.

It has been found that the cause of optical transmission loss in optical fibers is due to harmonics of infrared vibration absorption between carbon and hydrogen that constitute the synthetic polymer.

FIG. 1 shows the optical transmission characteristics of a plastic optical fiber manufactured by a conventionally known method and having a core made of polystyrene and a sheath made of ethylene-vinyl acetate copolymer. In the characteristics shown in Figure 1, the 7th overtone of infrared vibration absorption between aromatic and aliphatic carbon hydrogen is at wavelength 528 nm and 5
At 80n■, the 6th overtone appears at 605nm and 650n+a, and the 5th overtone appears at 715nm and 7B0nm. Here, the absorption intensity decreases by about one order of magnitude each time the order of overtone increases by one. However, due to these absorption paths, the optical transmission loss in the so-called loss window increases.
Although the minimum value of attenuation is 114 dB/+m at a wavelength of 650 nm and 129 dB/km at 624 nm, as it approaches the near-infrared region, it is 4004 B/km at 730 nm.
km, 370dB/km at 780rin,
Furthermore, on the long wavelength side, the optical loss value exceeds 1000 dB/km. Therefore, unless the vibrational absorption between carbon and hydrogen is reduced or eliminated in some way, the light transmittance will be excellent at around 850 nm or around 1.3 μm, where silica-based optical fiber is used. It turned out that plastic optical fibers could not be made.

As a method for this purpose, hydrogen is replaced with deuterium, and carbon-
One possible method is to eliminate vibrational absorption of hydrogen (C-H). Along with this, vibrational absorption between carbon and deuterium (C-D) appears, but according to the findings of the present inventors, infrared vibrational absorption between C-D is significantly more pronounced than that between C-H. Shifted to the longer wavelength side, for example in polymethyl methacrylate,
The 5th overtone of infrared vibration absorption that occurs in the visible to near-infrared light range is 740n- for C-H, while it is 990n for CD, and the 6th overtone is 622n for C-H. 250 to 28, such as 905 nm in CD
It is shifted to the higher wavelength side by about 0 nm. Furthermore, it has become clear that even for harmonics of the same order, the strength of C-0 vibration absorption is smaller than the strength of C-H vibration absorption.

In this way, by deuterating hydrogen in a synthetic polymer, it is possible to produce a plastic optical fiber having a window with extremely low loss, particularly in the visible light region to near-infrared light region.

As an example of replacing hydrogen in a synthetic polymer with deuterium, a plastic optical fiber with a core made of a resin made by deuterating methyl methacrylate and polymerizing it has already been proposed (for example, U.S. Pat. No. 4.13L 194). or the corresponding Japanese Patent Application Laid-Open No. 54-65556). In this example, perdeuterated methyl methacrylate is bulk-polymerized in the presence of a chain transfer agent and a polymerization initiator to obtain a core-type coalescence, and this core-type coalescence is made into a fiber.
7dB/km, 790nmi? 158dB/km
The value of is obtained. These loss values are 57% even if the loss values of conventional conventional methyl methacrylate polymers are best.
Considering that it is more than 220 dB/km at 0n, the loss has been reduced, and the visible wavelength has been expanded to the near-infrared light region, showing the effect of deuterated methyl methacrylate polymer. You could say that.

However, methyl methacrylate polymer has relatively high hygroscopicity, and even at room temperature, after 24 hours, 0.3~04Xywr1
．． :a meeting-m-*k rm by-”= ---
y--,.

Kurobedei 7 (Modern Plastic En
The same is true for deuterated polymers.

Vibration absorption between oxygen-hydrogen (0-H) bonds due to moisture absorption is a problem even in optical fibers made of inorganic glass, but in organic polymer compounds, the harmonics of O-H vibration absorption occur in the loss window. Wave effects are often present, and even the presence of a small amount of water degrades optical transmission properties, especially in the near-infrared region. For this reason, even if a low-loss plastic optical fiber was made by deuteration, there was a problem in that the light guiding performance fluctuated as the humidity of the usage environment changed (Po-
1y+m, I'reprints, Japan
, Vol B2. No, 4. (See P810°1983).

(Objective of the Invention) The present invention was made in view of the current situation, and its purpose is to provide extremely excellent optical transmission characteristics, especially in the near-infrared light region, and to reduce the effects of 0-H vibration absorption due to moisture absorption. Less low-loss plastic optical fiber) 71.
.

(Structure of the Invention) In order to achieve the above object, the plasti of the present invention (in the formula m
, n is m = 1-5, n = 0-4, m
The most important feature is that the core component is a polymer whose essential repeating unit is a fluorine-substituted deuterated styrene unit represented by +n = an integer satisfying 5. Conventionally, copolymers such as fluorinated methacrylates, in which the first component is a methacrylic acid ester whose side chain is partially substituted with fluorine, and the second component is styrene, have been proposed (Japanese Patent Application Laid-Open No. 1983-1999).
No. 116701), but these inventions differ greatly in that the influence of residual C--H bonds such as vinyl group hydrogen is large, and it is impossible to reduce the loss particularly in the near-infrared region.

The plastic optical fiber of the present invention essentially uses a polymer having a repeating unit represented by the above general formula (1) as a core component, and such a polymer can be obtained according to the general formula (1). The weight average molecular weight of such polymers is usually so,ooo to 200,000.

Specific examples of the fluorine-substituted deuterated styrene monomer in the present invention include the following.

Conventionally, in optical fibers with a polystyrene core, the refractive index of the core is relatively large at 1.59, and the Rayleigh scattering τ caused by fluctuations in the density of the polymer is as follows (2) and (3).
In the formula: Borckmann's constant, T: absolute temperature, λ. : wavelength in vacuum, βa: isothermal compressibility, ε: fusion rate, ρ: density, n: refractive index, so there is a problem that Rayleigh scattering due to density fluctuation increases due to the influence of the refractive index. Ta. However, as shown in equation (2), Rayleigh scattering is inversely proportional to the fourth power of the wavelength, so the value becomes smaller on the long wavelength side. Therefore, even in optical fibers with a polystyrene polymer as their core, it is possible to reduce the refractive index and reduce absorption loss in the near-infrared region. By replacing C with fluorine and deuterium, the refractive index of the polymer decreases and C
Based on the -H bond (molecular vibration absorption also disappears.

When a polymer with fluorine introduced into the molecule is used as the core of a plastic optical fiber, the refractive index of the fluorine-substituted polymer decreases, so depending on the method of introducing fluorine, Rayleigh scattering caused by density fluctuations of the polymer can be effectively suppressed. Even if it is possible to reduce the refractive index, there is a concern that it will be difficult to select a material with a lower refraction as the sheath material than that of the core type combination. However, in the core material of the plastic optical fiber according to the present invention, the degree of decrease in the refractive index itself due to the introduction of fluorine is not so great (the core material is made of a fluorine-substituted deuterated styrene monomer in which all hydrogens in the aromatic ring are fluorinated). Even polymers have a refractive index similar to that of polystyrene.
Almost all the materials currently used for the sheath materials of optical fibers with PMMA cores can be used as sheath materials for the cores of plastic optical fibers, and the range of choices is extremely wide.

On the other hand, by substituting the aromatic ring hydrogen of the styrene polymer with fluorine and deuterium, the hygroscopicity of the polymer is significantly reduced. Not only that, but it is also extremely small in the near-infrared light region. Conventionally, plastic optical fibers that have excellent light transmittance even in the near-infrared light region are made of deuterated PMMA.
The core tossuru also knows the power (A P L, V
ol, 42. No.

7, P2O3,198:(), This optical fiber has high hygroscopicity, so especially in the near-infrared light region, the absorption intensity based on OH groups fluctuates greatly due to moisture absorption and desorption, making it difficult to maintain stable light guiding properties. In contrast, the present invention provides absorption and
As mentioned above, it has the characteristic that extremely stable optical characteristics can be maintained even after dehumidification.

In the present invention, as the polymer serving as the core component, a polymer copolymerized with an appropriate comonomer can be used as long as the properties of the above-mentioned fluorine-substituted deuterated styrene are not impaired.

A preferred example of such a comonomer is a deuterated vinyl monomer. Particularly preferred as such deuterated vinyl monomer is persuterostyrene. Also preferred is fluorine-substituted deuterated a-methylstyrene.

Furthermore, styrene, a-methylstyrene, chlorostyrene, prolostyrene, bromostyrene or a,
Non-deuterated vinyl monomers such as styrene halo substitutes such as β, β-trifluorostyrene may also be used.

The amount of these comonomers to be used is not particularly limited as long as it does not impair the properties of the fluorine-substituted deuterated styrene, but it is generally less than 50 mol%, and even less than 20 mol%. In the case of non-deuterated vinyl monomers, the content is preferably 10 mol% or less.

Although a general vinyl monomer polymerization method can be used for producing the core component polymer in the present invention, it is particularly preferable to use a bulk polymerization method in order to obtain a low-loss optical fiber with little scattering loss. In this case, thermal bulk polymerization can be used, but by adding a small amount of catalyst and performing radical bulk polymerization, it becomes possible to shorten the polymerization time and obtain a suitable polymer. The radical polymerization initiator used here is
It is desirable that it can be easily distilled and purified under reduced pressure, but any substance that dissolves in the monomer and can be purified by filtration or the like can be used.

Such polymerization initiators include azo tert-octane,
Azo-tert-butane, azo-mibutane, azo-1
Examples thereof include alkylazo compounds such as 50-propane, azo-n-propane, and azo-Schifter's hexane, and organic peroxides such as di-tert-butyl peroxide, dicumyl peroxide, and cumene hydroxy peroxide.

Also usable are azo compounds such as azoisobutyrolonitrile, azobisschifftetrahexanecarbonitrile, and 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile.

On the other hand, in order to spin the resulting core-type aggregate, it is necessary to appropriately control the molecular weight, and it is desirable to use a chain transfer agent for this purpose that can be easily distilled and purified under reduced pressure conditions. Mercaptans are suitable as such chain transfer agents, and specific examples include primary mercaptans such as n-butyl and n-propyl, secondary mercaptans such as 5ee-butyl and isopropyl, tert-butyl and tert- Examples include tertiary mercaptans such as hexyl, and aromatic mercaptans such as phenyl mercaptan.

The sheath component used in the present invention has a refractive index lower than that of the core component, and may be any synthetic polymer having a refractive index lower by at least 0.5%, preferably 2%. Can be used. In particular, excellent light transmission properties can be obtained by using substantially amorphous polymers. Specific examples of the polymer of the soft sheath component include pinylidene fluoride-tetrafluorotetraethylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene ternary copolymer, or fluoroalkyl methacrylate polymer, etc. 2 with an alkyl chain
copolymers of fluoroalkyl methacrylates, copolymers of fluoroalkyl methacrylates and fluoroalkyl acrylates, mixtures of vinylidene fluoride-tetrafluoroethylene copolymers and fluoroalkyl methacrylate polymers or fluoroalkyl acrylate polymers, etc. can be mentioned. Any other material that can be used for the sheath material of optical fibers that generally have PMMA as the core,
Either can be used. By using these, it is possible to obtain a plastic optical fiber having excellent light transmittance, especially in the near infrared.

As for the spinning method, a conventionally known spinning method for vinyl polymers can be used. Examples include a method in which a core fiber is produced according to a conventional spinning method and then coated with a sheath polymer.

Hereinafter, the present invention will be explained in more detail with reference to Examples.
The present invention is not limited to these examples. A tungsten-halogen lamp was used as a light source for measuring the optical transmission characteristics of the optical fiber, and a diffraction grating spectrometer was used to determine the wavelength characteristics of the transmission attenuation rate. In addition, the optical fiber was left standing under high temperature and high humidity conditions, and the increase in loss value due to moisture absorption in the optical fiber was determined by measuring the transmission attenuation rate.

(Example) Monomer production example 21 g of Mg (0.86 Peng 01), 2340 mj of tetrahydrofuran (THF), bromobenzene-FS
When 54 g (0.22 mol) was added and heated after adding a catalytic amount of I2, the reaction started at about 60° C., and fading of 12 colors was observed. After that, most of the remaining bromobenzene-F used in the reaction was heated at 60 to 70°C for about 1 hour.
120 g (0.49 wmol) was added dropwise, and 65~
A Grignard reagent was prepared by reacting at 67° C. for about 1 hour and 30 minutes.

To the prepared Grignard reagent was added 1 g of acetaldehyde-d4(CD3CDO) 54 at 5±2°C.
(1,23 O1) was added dropwise over about 2 hours and reacted for 15 hours, and then treated with dilute hydrochloric acid at 20-30°C.
After extraction with n-hexane and drying with MgSO4, the solvent was evaporated under reduced pressure, and 151 g of the resulting residue was distilled under reduced pressure to obtain 1-(pentafluorophenyl)ethyl-d as a fraction 70-b.
109 g of 4-alcohol was obtained.

Next, 1-(pentafluorophenyl)ethyl--4-
Alcohol 250 g (1,18 mol), phosphorus pentoxide P2Ol 5164 g (1,161161),
3.5 g of p-tert-butylcatechol was combined and heated, and reacted at 140 ± 2°C for about 1 hour. After the reaction was completed,
The reactant was subjected to elementary distillation at a bath temperature of 160 DEG C. under reduced pressure (approximately 120 nHg) to obtain 190 g of a crude fraction, which was further distilled under reduced pressure to obtain 175 g of 70-b. The appearance is a colorless transparent liquid with a refractive index n
0 was 1.4465, and M'' (*/e) was 197.

11- In a closed system polymerization apparatus substantially free of oxygen, the following structural formula % tert-octane, as a chain transfer agent, o, o
After adding 1/l of n-butyl mercaptan and mixing thoroughly, bulk polymerization was carried out at 100°C for 20 hours, then the temperature was gradually raised to 120°C for 2 hours, and then to 140°C.
The polymerization was completed by treatment at 160° C. for 12 hours and 4 hours at 160° C. to obtain a core component polymer. The weight average molecular weight (measured by GPC using light scattering method) is about 500,000. On the other hand, a melt of tetrafluoropropyl methacrylate polymer was used as the sheath component, and as soon as the core component polymer was made into a fiber from an extruder, it was immediately coated to form a core-sheath structure, and the core 2 shown in FIG. An optical fiber with a diameter of 0.75 m and a sheath component of 3 and a film thickness of 0.05 m was obtained.

FIG. 2 shows the transmission attenuation wavelength characteristics of this optical fiber in the near-infrared region. As can be seen from Figure 2, the wavelength is 848.
175dB/km to nm, 373d to wavelength 942nm
B/km, a low loss window of 303 dB/km at a wavelength of 960 nm, 346 dB/km at a wavelength of 992 nm, and 530 dB/km at a wavelength of 1064 nIl was observed, and in the near-infrared light region, the conventional plus - + 5u - - J- al
+1la-p*kI)ke practice 1 tatami! 44'2! 5L-a
Aiva was obtained. This plastic optical fiber is
Under temperature and humidity conditions of 0° C. and 90% RH, the sample was left standing for two days and nights, then taken out, and the optical transmission characteristics were immediately measured.

The increase in loss due to moisture absorption in the above low loss window is at most 54
B/km or less, making it a plastic optical fiber with extremely low loss increase due to moisture absorption.

[In Example 1, a core was prepared in the same manner as in Example 1, except that vinylidene fluoride-tetrafluoroethylene copolymer was used as the sheath component and melt-spun with the core component polymer using a composite spinneret. An optical fiber having a diameter of 0.5 mm and a sheath component thickness of 0.05 mm was obtained.

This optical fiber has a minimum loss value of 227 at a wavelength of 786 nm.
dB/km, wavelength 844am, 960nm, 994
am to 241dB/km and 3824B/km, respectively.
, 4144B/km, and had extremely excellent characteristics as a plastic optical fiber for near-infrared light. Also, 60℃.

Based on moisture absorption after being left for 2 days under 90% RH conditions (the increase in loss was extremely small as in the examples) In Example 1, pentafluorophenyl group with the following structural formula was used as the core component. Richterostyrene monomer 90
A plastic optical fiber was produced in the same manner as in Example 1, except that a copolymer (weight average molecular weight: approximately 500,000) consisting of 10 mol % of styrene and 10 mol % of styrene was used. Similar to Example 1.2, this optical fiber also has excellent transparency in the near-infrared region, and has a minimum loss value of 230 at 794nwi.
4B/km was obtained. Also, similar to Examples 1 and 2,
The loss increase due to moisture absorption was also very low.

Article 1 0.01 o1/l of azo tert-butane as a polymerization initiator is added to persteromethyl methacrylate monomer in which all the hydrogens of methyl methacrylate are replaced with deuterium.
Add 0.03 x 01/J of n-butyl mercaptan as a chain transfer agent, mix thoroughly, and carry out bulk polymerization at 135°C for 12 hours in a closed polymerization apparatus substantially free of oxygen. Next, the temperature was gradually raised to increase the polymerization rate, and the polymerization was finally completed at 180° C. for 12 hours to obtain a core component polymer.

On the other hand, as a pod component, 30 mol% of IH, IH, 5B-octafluoropentyl methacrylate and IH, IH
, 3H-tetrafluoropropyl methacrylate in an amount of 70 mol %, the core component polymer was formed into a fiber using an extruder, and the core component polymer was immediately melt-coated with a sheath component copolymer to obtain a core-sheath structure. The obtained plastic optical fiber has a wavelength of 860 am and a wavelength of 480 d.
5 at B/km1780nm+? dB/km, 855nm
1064B/km, in the visible to near-infrared light range,
It has extremely good translucency. This optical fiber was left standing for two days and nights under the temperature and humidity conditions of 60°C and 90%RH, and then taken out.The optical transmission characteristics were immediately measured based on moisture absorption (loss increase was 25d at 6B0nm).
B/km, 100 at 780 nm, optical fibers whose core component is Persch-telometh 7-simethacrylate polymer have excellent initial light transmittance, but the light transmittance fluctuates due to changes in the humidity of the usage environment. Because it is extremely large, it is not suitable for use in the near-infrared region.

(Effects of the Invention) As explained above, the plastic optical fiber according to the present invention has extremely superior optical transmission characteristics, especially in the near-infrared light region, compared to conventional plastic optical fibers, and is resistant to exposure to high temperature and humidity conditions. However, since the increase in loss is extremely small, it has the advantage that it can be stably used as an optical signal transmission medium over distances of several hundred meters using a near-infrared light source.

In addition, it has low loss in the wavelength range of around 85 Onm and 1100 Ga or more, so it
Since it can be connected and used without electrical/optical conversion, it has the advantage of being able to construct an economical optical signal transmission system such as a local area network.

Moldings, films, sheets, etc. made of fluorine-substituted deuterated styrene units for use in the present invention are also useful.

For example, it can be effectively used in connectors, rectifiers, optical waveguides, etc.

[Brief explanation of drawings]

Figure 1 is a graph showing the measurement results of optical transmission characteristics in the visible light range of a conventional plastic optical fiber with a polystyrene core. 1 is a graph showing measurement results of optical transmission characteristics in the near-infrared region of a low-loss plastic optical fiber according to the invention. 1... Optical fiber, 2... Core part,
3...Saya part. Patent applicant Nippon Telegraph and Telephone Public Corporation Toshi Co., Ltd. Wavelength (8m)

Claims (1)

[Claims] In a plastic optical fiber having a core and sheath made of synthetic polymer, the core has a general formula ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (Here, m and n are m = 1 to 5, n =0~4, m+n=
1. A plastic optical fiber comprising a polymer having as an essential repeating unit a fluorine-substituted deuterated styrene unit represented by the formula (an integer satisfying 5).