JPH0340361B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a synthetic resin optical transmission body, particularly a synthetic resin optical transmission body suitable for optical communication. Glass fibers for optical communications are broadly classified into single mode fibers and multimode fibers.
Single-mode fibers transmit only the fundamental mode, so they produce very little delay distortion of optical signals and are capable of extremely wide-band transmission. has the disadvantage of being relatively difficult. On the other hand, multimode fibers include clad fibers, in which the refractive index distribution changes stepwise, and convergent fibers, in which the refractive index gradually decreases from the central axis in the radial direction. The difference in group velocity between the fundamental mode and higher-order modes is large compared to the optical signal, and optical signals are subject to delay distortion, making broadband transmission difficult. Therefore, a layer with a refractive index lower than the core part is provided outside the core part, and a layer with a refractive index higher than the low refractive index layer is further provided outside the core part.
A proposal has been made for a clad fiber that has a type of mode filter effect in which high-order modes are radiated in this outermost layer and only low-order modes are propagated in the core, but essentially the refractive index is Since the distribution is step-like, it has the disadvantage that it is difficult to widen the band. On the other hand, in a focusing fiber, if the refractive index distribution is given by equation (1), there will be almost no difference in group velocity between modes. n=n ₀ (1-1/2Ar ² ) =n ₀ {1-1/2A'(r/rp) ² } (1) Here, n ₀ is the refractive index of the central axis, and n is the distance r from the central axis.
The refractive index of points at distances, A and A′ (≡Arp ² )
is the refractive index distribution constant and rp is the radius of the fiber.
If a layer with a continuously increasing refractive index is provided on the outside of such a fiber, higher-order modes will be emitted, resulting in a broadband property comparable to that of a single mode fiber. (W-type distribution fiber) The present invention satisfies the following conditions in order to obtain a plastic fiber having such a W-type distribution.
A monomer mixture of M ₁ , M ₂ and M ₃ is photocopolymerized in a cylindrical transparent container to obtain a polymer rod, which is then hot drawn to form a plastic fiber. Generally, in the copolymerization reaction of three types of monomers M ₁ , M ₂ , and M ₃ , the following nine types of growth reactions occur in competition. M ₁ ^* +M ₁ →M ₁ ^* (rate constant k ₁₁ ) M ₁ ^* +M ₂ →M ₂ ^* (〃 k ₁₂ ) M ₁ ^* +M ₃ →M ₃ ^* (〃 k ₁₃ ) M ₂ ^* +M ₁ →M ₁ ^* (〃k ₂₁ ) M ₂ ^* +M ₂ →M ₂ ^* (〃 k ₂₂ ) M ₂ ^* +M ₃ →M ₃ ^* (〃 k ₂₃ ) M ₃ ^* +M ₁ →M ₁ ^* (〃 k ₃₁ ) M ₃ ^* +M ₂ →M ₂ ^* (〃 k ₃₂ ) M ₃ ^* +M ₃ →M ₃ ^* (〃 k ₃₃ ) (2) The monomer reactivity ratio is defined by equation (3). r ₁₂ ≡k ₁₁ ／k ₁₂ r ₂₁ ≡k ₂₂ ／k ₂₁ r ₁₃ ≡k ₁₁ ／k ₁₃ r ₃₁ ≡k ₃₃ ／k ₃₁ r ₂₃ ≡k ₂₂ ／k ₂₃ r ₃₂ ≡k ₃₃ ／k ₃₂ (3 ) The conditions that the combination of monomers M ₁ , M ₂ , and M ₃ of the present invention must satisfy are (1) Regarding the reactivity ratio (r ₁₂ (M ₁ /M ₂ ) _n + 1)/{(M ₁ /M ₂ ) _n + r ₂₁ }＞1.1(4
) (r ₁₃ (M ₁ /M ₃ ) _n + 1)/{(M ₁ /M ₃ ) _n + r ₃₁ }＞1.1(5
) (r ₂₃ (M ₂ /M ₃ ) _n +1)/{(M ₂ /M ₃ ) _n +r ₃₂ }＞1.1(6
) Here, (Mi/Mj) _n is the mixing molar ratio of monomer Mi and monomer Mj. (2) Regarding the refractive index, n ₂ (refractive index of M ₂ homopolymer) < n ₃ (refractive index of M ₃ homopolymer) and n ₁ (refractive index of M ₁ homopolymer) > n ₂ . Condition (1) is that as the terpolymerization progresses, the initial monomer
M ₁ rapidly polymerizes, then monomer M ₂ polymerizes,
It shows that monomer M ₃ polymerizes most slowly. In other words, the copolymer formed at the initial stage of polymerization contains a large amount of monomer _M1 , but as the polymerization progresses, the content of _M1 rapidly decreases until the content of monomer _M2 decreases. To increase. As the polymerization progresses further, the content of M ₂ also decreases and the content of monomer M ₃ increases. Here, if condition (2) is satisfied, the refractive index of the copolymer produced as the polymerization progresses will initially decrease, and then increase when most of the M ₁ monomer is polymerized. become. The invention can be implemented as follows. First, a predetermined amount of monomers M ₁ , M ₂ , M ₃ are mixed,
A predetermined amount of a photopolymerization initiator (e.g. benzoyl peroxide (BPO), benzoin methyl ether, etc.) is dissolved in this, and this is heated to a predetermined inner diameter (e.g. about 2.9 mm).
A glass tube with one end closed is filled with the above-mentioned material and photopolymerized using the apparatus shown in FIG. A tubular ultraviolet lamp 1 is located at the center of the device, and cylindrical light-shielding plates 2 are attached to the upper and lower parts of the lamp 1. A mixture of these is irradiated.
Note that 11 indicates that the light from lamp 1 is separated by the distance between light shielding plates 2.
This is a brim-shaped light-shielding auxiliary plate designed to emit light to only 70mm. Ultraviolet intensity is silicon photocell 3
is being monitored. A plurality of glass tubes 4 filled with the monomer mixture are mounted on a support member 5 at a predetermined distance, for example, 10 cm from the ultraviolet lamp 1, and are rotated by a motor 6 at, for example, 40 RPM. First, the ultraviolet lamp 1 is placed at a position lower than the lower end of the glass tube 4, and the lamp 1 is moved at a constant speed V (mm/min) by the motor 7.
irradiate ultraviolet light while moving it upward. Air at a constant temperature is fed into the inside of the device from an inlet 8 by a fan 9 and is discharged from an outlet 10. Although the temperature rises due to the heat generated by the lamp 1, it remains at a temperature that is somewhat higher than the inlet air temperature. becomes constant. Photocopolymerization occurs from the bottom of the glass tube 4. The copolymer is deposited on the inner wall of the glass tube 4, and as the polymerization progresses, the deposited copolymer layer becomes thicker and solidifies to the center. As the lamp moves, the copolymerization location moves upwards in the glass tube. Although the volume shrinks during polymerization, no voids are created inside the polymer because the monomer mixture is always supplied from the unpolymerized portion at the top of the glass tube. The periphery inside the glass tube is occupied by a copolymer mainly composed of M ₁ produced at the initial stage of polymerization.
As we move towards the center, the _M2 content increases as it is occupied by the copolymer produced in the later stages of polymerization.
The refractive index initially decreases from the periphery toward the center. Since the M ₃ component increases from a certain point onward, the refractive index gradually increases. After a predetermined period of time, for example about 10 hours, from the start of irradiation, the glass tube 4 is removed from the apparatus and heated to, for example, 80° C. for 24 hours to polymerize as much of the remaining monomer as possible. Then, the glass tube 4 is crushed,
Take out the copolymer rod. The rod maintains a predetermined refractive index distribution over the entire rod except for the ends. By adjusting the type of monomer, charging ratio, and copolymerization conditions, the refractive index distribution near the central axis can be made into the distribution (square distribution) of formula (1). The obtained rod is heated and stretched to form a plastic fiber. 10 ^-3 to 10 ^-4 to remove trace amounts of volatile substances contained in the rod before heating and stretching the rod.
Place under reduced pressure of mmHg at 50°C for 3 to 4 days. Next, it is stretched using a hot stretching device whose principle is shown in FIG. That is, the above synthetic resin rod is attached to the support member 22 as a preform 21, and the speed
The film is lowered at a speed of V ₁ (mm/sec), passed through a constant temperature heater 23 at a constant temperature Td, and pulled and stretched by a lower drive roll 24 at a speed of V ₂ mm/sec. V ₂ /V ₁ is the stretching ratio. M ₁ is a methacrylate ester of an aromatic alcohol such as phenyl methacrylate or benzyl methacrylate; M ₂ is a methacrylate ester of an aliphatic alcohol such as methyl methacrylate, ethyl methacrylate, or fluoroethyl methacrylate; As M ₃ , vinyl esters of aromatic acids and halogen-containing fatty acids such as vinyl benzoate, vinyl phenyl acetate, and vinyl chloroacetate can be used. Examples of combinations of these monomers are shown in Table 1.

【table】

[Table] Example 1 Benzyl methacrylate, methyl methacrylate, and vinyl benzoate are used as M ₁ , M ₂ , and M ₃ , respectively. n ₁ = 1.57, n ₂ = 1.49, n ₃ = 1.58, r ₁₂ = 1.04,
r ₂₁ = 0.44, r ₁₃ = 7.64, r ₃₁ = 0.05, r ₃₂ = 8.52, r ₂₃
=8.52, satisfying the above formulas (4) to (6). Add benzoyl peroxide to 7 parts of M ₁ , M ₂ , M ₃ mixture.
Dissolve 0.21 part, UV lamp moving speed 0.8mm/min
Polymerization was performed to obtain the rods shown in the table below. In either case,

[Table] The refractive index continues to increase continuously from beyond the radius r _c to the periphery. Example number 1 rod had refractive indices of 1.52, 1.50, and 1.56 in the center, r _c , and periphery, respectively. These rods were used as preforms at 250℃.
A fiber with a diameter of 0.30 mm was obtained by hot stretching 100 times.
The A values (×10 ⁻³ mm) were 48.9, 110, and 120, respectively. Example 2 Benzyl methacrylate, vinyl acetate, and phenyl vinyl acetate are used as M ₁ , M ₂ , and M ₃ (one example of the group). n ₁ = 1.57, n ₂ = 1.47, n ₃ =
1.57, r ₁₂ = 20.6, r ₂₁ = 0.03, r ₁₃ = 20.7, r ₃₁ =
0.005, r ₂₃ = 1.74, r ₃₂ = 0.27, and the above (4) to (6)
satisfies the expression. 3 parts of benzoin methyl ether was dissolved in a mixture of 78 parts of M ₁ , 14 parts of M ₂ , and 8 parts of M ₃ and polymerized at a UV lamp moving speed of 0.6 mm/min. Obtained radius 1.5mm
The refractive index distribution of the rod was determined using the lateral interference fringe method (Otsuka,
As measured by Koike, Appl. Opt. 19 , 2866 (1980)), the refractive index is 1.5550 on the central axis and 0.52 on the radius.
The minimum value is 1.5537 at the position of mm, and it gradually increases toward the outside, and at the position of the radius of 1.10 mm.
It had a W-shaped refractive index distribution showing a value of 1.5562. This rod was used as a preform and was hot-stretched 100 times at 250°C to immediately obtain a 0.30 mm fiber.
The transmission loss of the He-Ne laser light was 900 dB/Km.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view showing an example of a manufacturing apparatus for carrying out the present invention, and FIG. 2 is a side view showing an example of carrying out the invention following the apparatus shown in FIG.

Claims (1)

[Claims] 1. The refractive index when the monomer Mi becomes a polymer.
ni, then at least two types of ni are different3
By maintaining a mixture of seed monomers Mi (i = 1, 2, 3) in a predetermined shape and applying locally non-uniform copolymerization conditions to the mixture of the predetermined shape, Initially, only a predetermined portion of the mixture locally forms a copolymer having a ratio of monomer components different from the mixing ratio, and then gradually copolymerizes from that portion to other portions. Synthetic resin light having a refractive index gradient, which creates a concentration gradient in which the monomer components gradually change from the predetermined part to other parts in the interior of the copolymerized object as In the method for producing a transmitter, the mixture of monomers Mi is a combination of monomers satisfying n ₁ > n ₂ and n ₃ > n ₂ and copolymerized in the order of M ₁ , M ₂ , and M ₃ . By selecting easy-to-use monomers and their mixing ratio, we can create a synthetic resin optical transmission body that has a refractive index gradient that gradually decreases radially outward from the central axis up to a certain point, and then increases. How to manufacture. 2 The mixture of the three types of monomers described above has a monomer reactivity ratio of Mj to Mi (i, j = 1, 2, 3)
is expressed as rij, and the mixing molar ratio of Mi and Mj is expressed as (Mi/Mj) _n , then the mixture of monomers is {r ₁₂ (M ₁ /M ₂ ) _n +1}/{(M ₁ / M _2n +r ₂₁ }＞1.1 {r ₁₃ (M ₁ /M ₃ ) _n +1}/{(M ₁ /M ₃ ) _n +r ₃₁ }＞1.1 {r ₂₃ (M ₂ /M ₃ ) _n +1}/{ A method for manufacturing a synthetic resin optical transmission body according to claim 1, which satisfies all of the following expressions: (M ₂ /M ₃ ) _n + r ₃₂ }>1.1.