JPS645681B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a convergent optical transmission body having a refractive index distribution that continuously changes in the radial direction.

Conventionally, as described in Japanese Patent Publication No. 47-816, the above-mentioned focusing optical transmitters have conventionally been produced by changing the internal composition of glass fibers by ion-exchanging their oxides to change the refractive index. Manufactured by a method that causes change, or
As described in Publication No. 10056, it is manufactured by a method such as depositing material layers having gradually different components on the outer peripheral surface of a cylindrical starting member to give it a refractive index that changes stepwise in the radial direction. It had been. However, the former method requires a long time to impart a refractive index distribution within the glass by ion exchange, and the latter method has the disadvantage that the refractive index distribution becomes stepwise, resulting in a decrease in response as an image guide.

The present invention is a method for producing a focusing light transmitting body using a method different from conventional methods, and is a method for easily producing a flexible focusing light transmitting body by irradiating a photopolymerized plastic material with light. It provides:

Generally, a light-transmitting material with a certain absorption coefficient,
When irradiating light with a wavelength at which energy is absorbed by the material, the light is gradually absorbed by the material as it travels inside the material, as shown in Figure 1, and the light is absorbed in the direction in which the light travels. The amount of light produced differs, and its progress varies within the material as a function of wavelength, with shorter wavelengths being more easily absorbed.

The present invention utilizes the properties of a light-transmitting material having such a specific absorption coefficient. That is, in the present invention, a photopolymerized plastic material whose refractive index decreases as polymerization progresses is used as a light-transmitting material, and this is used as a thin rod-shaped preform member from the outer periphery of a cross section perpendicular to the central axis to the central axis. By irradiating light with uniform intensity towards the preform member and repeating this light irradiation with light of different wavelengths, the degree of photopolymerization within the member is changed and the refractive index is changed in the radial direction of the preform member. It is.

The photopolymerized plastic material is, for example, a plastic mainly composed of polycarbonate Z, whose refractive index decreases as the degree of polymerization increases, and which is supplemented with methyl acrylate, a sensitizer, a light absorption control agent, and a fogging agent. A homogeneous plastic made by dissolving the inhibitor is used and molded into a preform rod member as shown in FIG. Next, this preform rod member is spun into a perfect round thin rod shape as shown in FIG. 3 by using a heated drawing device.
This thin rod-shaped preform member is irradiated with light energy (hν ₁ ) of uniform intensity from the outer periphery of the cross section perpendicular to the central axis toward the central axis as shown in Fig. 4. -1).

Alternatively, when the preform member is stretched while being rotated, light is irradiated only from a specific direction. Similarly, the preform member being conveyed by rollers is irradiated with light of wavelengths that change continuously or intermittently in the axial direction of the preform member, in other words, with different energies (hν ₂ and hν ₃ ) (Figure 4-2). .
For example, when using plastic mainly composed of polycarbonate Z, as shown in Fig. 4-2, the preform member being conveyed by a pull-out roller is irradiated with light of wavelengths λ ₁ and λ ₂ as shown in Fig. 6. In this case, _{a mercury lamp (λ 1 =}
370 nm), N ₂ laser (λ _{2 =}
337 nm) for several tens of seconds each, although this varies depending on the power.

After the light irradiation, the methyl acrylate is removed and fixed onto a light-stable plastic member.

Note that light irradiation is not limited to only after the spinning process.
Spinning may be carried out after the preform rod (FIG. 2) is in the state.

In this way, the degree of photopolymerization of a preform member that is repeatedly irradiated with light of different wavelengths changes in its radial direction, that is, the degree of polymerization is higher as it approaches the surface, and the degree of polymerization decreases as it goes inside. The closer it is to the surface, the lower the refractive index becomes, and the closer it goes inside, the higher the refractive index becomes. This relationship is shown in FIG. This allows the member itself to function equivalent to a lens, that is, to function as a focusing light transmitter. As shown in FIG. 1, the amount of light absorbed by the irradiated polymer increases as the wavelength of the irradiated light becomes shorter _. n ₁ is determined in relation to the refractive index distribution by changing the irradiation order of light, the sensitive wavelength and irradiation intensity for photopolymerization, and by changing the composition of the preform member. Generally, the sensitive wavelength range for photopolymerization is in the ultraviolet region, and suitable light sources to be used include N ₂ laser and ultraviolet light.

According to the present invention as described above, since the refractive index distribution is imparted by light, there is less risk of condition changes caused by external factors such as heat, power consumption, pollution, etc. Further, the distortion of the distribution in the peripheral area is also reduced. Furthermore, since it is made of plastic, it has advantages such as being flexible and lightweight.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing that the attenuation of light intensity in a light-transmitting material depends on the wavelength, Fig. 2 is an external view of a preform rod made of a photopolymerized plastic material, and Fig. 3 is an illustration of the preform rod. An explanatory diagram when spinning a rod using a heated drawing device, Fig. 4 is an explanatory diagram showing the state of light irradiation to the preform member, and Fig. 5 is an explanatory diagram showing the refractive index distribution inside the preform member after light irradiation. , FIG. 6 is an explanatory diagram showing an example of light irradiation.

Claims (1)

[Claims] 1. A preform member made of a thin rod-shaped photopolymerized plastic material whose refractive index decreases as polymerization progresses, and the photosensitive wavelength of the member is applied from the outer periphery of a cross section perpendicular to the central axis of the member toward the central axis. 1. A method of manufacturing a convergent optical transmission body, comprising irradiating light of two or more different wavelengths within a range to impart a refractive index distribution in the radial direction of the member.