JP2000323770A - Plastic optical fiber and laser thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve durability of a plastic optical fiber used for an oscillating part of a plastic optical fiber laser. SOLUTION: A plastic fiber for an plastic optical fiber laser is formed by mixing light-activated medium into polymer material. The polymer material is obtained by copolymerizing first monomer material containing no hydroxy group and second monomer material containing hydroxy group, and further a ratio of the second monomer material to the first monomer material is 5 to 15 wt.%. As a result, durability for one to two hundred thousand shots level of the number of radiation of excitation pulse is obtained as against an conventional manner, in which output is significantly deteriorated by about hundreds of shots of excitation pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic optical fiber used for an oscillation section of a plastic optical fiber laser.

[0002]

2. Description of the Related Art Plastic optical fiber lasers (POF)
A laser) has an oscillating portion formed by doping (mixing) a photoactive medium in an optical waveguide having an optical fiber structure formed of a polymer material, and irradiating the oscillating portion with, for example, a pulse of excitation light. A pulsed laser oscillation is obtained (for example, "Plastic Optical Fiber Laser", edited by POF Consortium, Kyoritsu Shuppan, 1997). Therefore, it does not require sophisticated alignment adjustment like a Fabry-Perot cavity laser, and it does not require plastic optical fiber (POF).
When used as a signal light source for optical fiber communication using, it can be directly connected to POF, and since a variety of photoactive media can be used, it can be used in a wide range from near ultraviolet to far infrared. It has many advantages, such as the ability to arbitrarily select the oscillation wavelength. But PO
F lasers that can be used practically have not yet been obtained.

[0003]

A major factor that has not yet been obtained is a practical POF laser.
Generally, there is a problem of durability of a photoactive medium using an organic dye. That is, there is a problem that the organic dye is denatured by the excitation light and the output is reduced with time. For example, even the most durable case reported to date, the output is significantly reduced by about several hundred excitation pulses.

However, a POF laser can constitute a very simple laser head as described above. For this reason, the laser head can be made, for example, of a cartridge type so that the laser head can be easily replaced, so that durability for such a long time is not necessarily required. Although there is no clear standard for how much durability is actually required, it is generally considered that durability exceeding tens of thousands of excitation pulses is required at a minimum. That is, if the durability, which is about several hundreds of excitation pulses at present, can be increased to about tens of thousands, an important problem in practical use of a POF laser can be overcome. Therefore, an object of the present invention is to improve the durability of a POF laser, and more specifically, to improve the durability of a POF used in an oscillation section of the POF laser.

[0005]

Means for Solving the Problems The present inventor has proposed a laser P
Various experiments have been repeated in order to improve the durability of the OF. In the process, it has been found that the presence of hydroxyl groups (OH groups) in the polymer material of the POF greatly affects the durability. That is, the conventional general idea is to use a polymer material having no hydroxyl group as the polymer material in the POF. However, according to an experiment performed by the present inventor, the use of a polymer material having an appropriate amount of a hydroxyl group greatly increases durability. It has been found that it can be improved.

Although the reason why the hydroxyl group works to improve the durability is not always clear, the following mechanism of action can be estimated. The durability of the laser POF is related to the modification of the organic dye generally used as a photoactive medium by the excitation light as described above. This is related to the mechanism by which the organic dye emits light by the excitation light. That is, POF
The organic dye for laser emits light by excitation light at a photoactive site having a double bond or triple bond or a conjugated structure thereof. At the same time, the possibility that the photoactive site is destroyed by the excitation light is also a certain ratio, and this is a major factor in determining the durability.
From this, it can be seen that durability can be effectively improved if damage to the photoactive site by excitation light can be effectively suppressed. Generally, the stability of a photoactive site is affected by orbital electrons in the surrounding groups and molecules. It is considered that a hydroxyl group works particularly effectively as an atomic group affecting the stability of the photoactive site.
That is, the hydroxyl group effectively acts to enhance the stability of the photoactive site, which is the light emitting site of the photoactive medium, and as a result, the durability of the laser POF is improved.

In order to obtain an appropriate amount of a polymer material having a hydroxyl group, it is necessary to copolymerize a monomer material having no hydroxyl group with a monomer material having a hydroxyl group.
The monomer material having a hydroxyl group functions to assist the solubility of the organic dye in the monomer material having no hydroxyl group. For this reason, the organic dye can be more uniformly dispersed in the polymer material. In general, the higher the dispersion of the organic dye in the polymer material, the higher the laser oscillation efficiency, that is, the higher the efficiency of use of the organic dye, which is also considered to contribute to improvement in durability.

As described above, the hydroxyl group works to improve the durability. However, on the other hand, experiments have shown that an excess of hydroxyl groups in the polymer material makes it difficult to heat-draw the polymer material required for producing a laser POF. The specific degree is a general case where a monomer material having one hydroxyl group (second monomer material) is copolymerized with a monomer material having no hydroxyl group (first monomer material). The first of the second monomeric materials
The ratio to the monomer material was about 15 wt% at the maximum, and when it exceeded this, it was practically impossible to perform thermal stretching, and it was found that the favorable range of the thermal stretchability was about 10 wt%. Therefore, considering that the more hydroxyl groups are preferable in terms of durability, 5 to 15 w
It can be said that the ratio of t% is in the effective range. The reason why the thermal stretching becomes difficult due to the presence of an excessive hydroxyl group is presumed to be that crosslinking occurs in the polymer material due to the hydroxyl group, thereby hindering the thermal stretchability.

The present invention is based on the above findings, and is formed by mixing a photoactive medium into a polymer material.
Regarding the POF used in the oscillation section of the POF laser, the polymer material is obtained by copolymerization of a first monomer material having no hydroxyl group and a second monomer material having a hydroxyl group, and The ratio with respect to the first monomer material is set to 5 to 15 wt%.

The polymer material for the POF is required to have excellent transparency, and it is preferable to use a methacrylic acid type or an acrylic acid type. Particularly preferred is methyl methacrylate (methyl methacrylate; MMA), which is a typical transparent material of methacrylic acid, as a first monomer material and 2-hydroxyethyl methacrylate (2-hydroxyethyl methacrylate) as a second monomer material. ; HEMA)
Is used.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention, a step index type (SI type) having a uniform refractive index in a core portion and a refractive index in a core portion having, for example, a quadratic curve are described. A graded index type (GI type) forming a distribution is possible. More preferably, it is a GI type having a large effect of confining oscillation light.

Although various types of monomer materials can be used in practicing the present invention, it is preferable to use methacrylic acid type or acrylic acid type monomer materials in consideration of transparency, which is particularly important. Examples of these monomer materials include the following. Examples of the first monomer material having no hydroxyl group include methyl methacrylate (MMA), 2,2,2-trifluoroethyl methacrylate (3FMA), and benzyl methacrylate (B
zMA), ethyl methacrylate (EMA), n-butyl methacrylate (nBMA), n-propyl methacrylate (nPMA), n-hexyl methacrylate (nHM)
A), isopropyl methacrylate (iPMA), 1-phenylethyl methacrylate (1PhEMA), 2-phenylethyl methacrylate (2PhEMA). Examples of the second monomer material having a hydroxyl group include 2-hydroxyethyl methacrylate (HEMA) and 2-hydroxyethyl methacrylate.
Hydroxypropyl (HPMA), 2-hydroxyethyl acrylate (HEAA), 2-hydroxypropyl acrylate (HPAA).

Similarly, various photoactive media can be used. For example, a typical example of an organic dye that can be generally used as a photoactive medium is a dye generally called a laser dye. For example, Rhodamine
B, Rhodamine-based organic dyes such as Rhodamine 6G, Rhodamine 19 Perchlorate and coumarin-based organic dyes such as Coumarin 120 and Coumarin 2, or Oxazine 4 Perchlorate
Oxazine 170 Perchlorate and other oxaline-based organic dyes.
ostyril 124, Fluorescein, Cryptocyanine and the like can also be mentioned.

Many manufacturing methods are already known for PO type GI. For example, JP-A-4-97302
JP, JP-A-4-97303, WO93 / 08
488, JP-A-2-16504, JP-A-8-1
Examples thereof are disclosed in, for example, Japanese Patent Application Laid-Open No. 14714 and Japanese Patent Application Laid-Open No. 8-114715. Among these, WO93
/ 08488 can be used as a more preferable method. The method disclosed in WO 93/08488 is a method of forming a desired refractive index distribution by diffusing a substance (dopant) for the refractive index distribution by utilizing a polymerization process of a monomer. including.

[0015] The whole process is divided into a process for producing a preform and a process for obtaining a POF by hot stretching from the preform. The preform is produced by polymerizing a monomer in a cylindrical polymerization tube under the addition of a polymerization initiator and a chain transfer agent. A glass tube or a polymer tube is used for the polymerization tube. When a polymer tube is used, the polymer tube can be used as it is as a cladding layer. When a polymer tube is used, it can be made of a specific polymer material, that is, a polymer material having the same or a similar composition as the polymer material of the POF to be manufactured, so that the interfacial gel effect can be used. It is possible to form the refractive index distribution in a steeper form. That is, during the polymerization of the monomer, the polymer in the polymer tube swells with the monomer solution, whereby the polymerization proceeds preferentially at the interface between the polymer tube and the monomer solution, and as a result, the dopant is gathered at the center of the preform. This makes it possible to form a refractive index distribution with a steeper distribution.

In the case where the polymerization of the monomer in the polymerization tube is performed by thermal polymerization, the viscosity is increased to some extent by first preliminary heating for about several hours in a water bath or an oil bath at about 70 ° C., for example. Then, usually, the polymerization is carried out by heating at about 70 ° C. while rotating the polymerization tube at a speed of, for example, about 2000 rpm in a horizontal state. This rotation polymerization is usually performed over 15 hours or more.

When a preform having a desired thickness is obtained in this way, the preform is thermally stretched by a stretching apparatus to obtain POF. Heat stretching is usually heated to about 200 ° C., and several to several tens m
Per minute.

The POF obtained in this manner is incorporated into the oscillation section thereof as a structure as described in, for example, the above-mentioned "plastic optical fiber laser", and is used as a POF.
An OF laser can be formed.

[0019]

[Experimental Example 1] An experimental example relating to thermal stretchability will be described below. MMA is used as a first monomer material having no hydroxyl group, HEMA is used as a second monomer material having a hydroxyl group, triphenyl phosphate (TPP) is used as a dopant, and 1-butanethiol (nBM) is used as a chain transfer agent.
And t-butyl peroxyisopropyl carbonate (Pb-I) was used as a polymerization initiator. The composition of the monomer liquid for polymerization, polymerization conditions and hot stretching conditions are as follows.

Composition: MMA: HEMA = 85-95: 1
5-5 (weight ratio), TPP 20 wt%, nBM 0.15
wt%, Pb-I 0.3 wt%. Polymerization conditions: The monomer liquid having the above composition was filled in a glass tube and heated in a 90 ° C. oil bath for 27 hours. Then, in a dryer, 11
Heat treatment was performed at 0 ° C. for 46 hours. Thermal stretching conditions: 150
Stretching was attempted while raising the temperature from 240 ° C to 240 ° C in 5 ° C increments.

Experimental Results: As a result of testing the thermal stretchability while changing the ratio of MMA and HEMA by 3 points in the above range, good stretchability was obtained up to MMA: HEMA = 90: 10. It becomes difficult to stretch gradually,
The condition of MMA: HEMA = 85: 15 was the limit at which stretching was possible.

[0022]

[Experimental Example 2] An experimental example relating to durability will be described below. MMA is used for the first monomer material having no hydroxyl group, HEMA is used for the second monomer material having a hydroxyl group, and rhodamine B (2-
[6- (diethylamino) -3- (diethylamino) -3H-xanthen-9-y
l] benzoic acid) and rhodamine 6G (2- [6- (ethylamin
o) -3- (ethylamino) -2,7-dimethyl-3H-xanthen-9-yl] -et
hyl). The monomer composition and polymerization conditions are the same as those in the above-mentioned Experimental Example 1, and the amount of the organic dye added is 100 pp.
m. In addition, P using rhodamine 6G-added POF
In the case of an OF laser, 590 nm laser light is used as excitation light.
8 nm laser light was used as the excitation light.

Experimental results: In the case of POF to which rhodamine 6G was added, the half width was 6 nm, the conversion efficiency was 26%, and the number of irradiations of the excitation pulse until the conversion efficiency became half was 14000.
0 shots. On the other hand, in the case of rhodamine B-added POF, the half width is 8 nm, the conversion efficiency is 23%, and the number of excitation pulse irradiations until the conversion efficiency is reduced to half is 200000.
It was a departure.

Claims (4)

[Claims] 1. A plastic optical fiber which is formed by mixing a photoactive medium into a polymer material and is used for an oscillating portion of a plastic optical fiber laser, wherein the polymer material comprises a first monomer material having no hydroxyl group and a hydroxyl group. Wherein the ratio of the second monomer material to the first monomer material is 5 to 15 wt%, obtained by copolymerization with a second monomer material having . 2. The plastic optical fiber according to claim 1, wherein each of the first and second monomer materials is based on methacrylic acid or acrylic acid. 3. The plastic optical fiber according to claim 2, wherein the first monomer material is methyl methacrylate and the second monomer material is 2-hydroxyethyl methacrylate. 4. A plastic optical fiber laser using the plastic optical fiber according to claim 1 for an oscillation section.