JPS627139B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber having good light transmission characteristics in the infrared wavelength range of 1 μm to 10 μm.

Conventionally, the following types of glasses are known as typical examples of optical glass fibers for transmitting infrared rays. Namely, (a) those composed of oxides of heavy metals such as GeO ₂ , Sb ₂ O ₅ and PbO, (b) compound glasses of Ge and As and chalcogens such as S, Se and Te, and (c) ZrF ₄ and others. There is fluorine compound glass that uses AlF ₃ as a mesh forming material.

Here, the optical fiber made of glass mentioned in (a) above is
There is a drawback that the wavelength band in which the optical loss is 1 dB/m or less in the infrared wavelength region is limited to about 2.5 μm or less. Furthermore, although the optical fiber made of the glass described in (c) above has a light transmission band that is somewhat wider on the longer wavelength side than that of the above-mentioned (a), it still has a transmission band of more than 1 dB/m in the wavelength region of about 4 μm or more. It is inevitable that this will result in a loss of light. On the other hand, some of the optical fibers using chalcogenide glass described in (2) above can transmit light well even in the wavelength range of 10 μm or more, and their optical loss can be sufficiently lower than that of other fibers. . However, from the point of view of actual use, optical fibers using chalcogenide glass have the disadvantage of extremely strong toxicity because their components include As, S, Se, Te, etc. In addition, chalcogenide deteriorates under outside air conditions such as moisture,
It has the disadvantage of poor long-term stability.

The present invention provides an optical fiber for infrared rays that eliminates the above-mentioned conventional drawbacks, and has a structure in which, in the cross section of the optical fiber, the center part is made of chalcogenide glass, and the peripheral part surrounding the center part is made of fluoride glass. By using chalcogenide glass in the center, remarkable infrared transmission performance is ensured, while in the periphery, fluoride glass, which has better infrared transmission than oxide glass, is used to transmit infrared rays. In addition to dealing with leakage to the periphery, the central part is prevented from being exposed and becomes harmful, ensuring low loss, harmlessness, and long-term reliability in a wide infrared wavelength range.

The present invention will be explained in detail below along with examples.

FIGS. 1a, b, and c show cross-sectional structures of optical fibers according to the present invention. In FIG. 1a, a central portion (core portion) 1 through which transmitted light mainly passes is made of chalcogenide glass, and a peripheral portion (cladding portion) surrounding the core portion is made of fluoride glass. In this example, As ₂ S ₃ is used as the chalcogenide glass, and BaF ₂ -GdF ₃ -ZrF ₄ glass is used as the fluoride glass.

Light in an optical fiber is mainly confined and propagated in the core, but some light also passes through the cladding. Especially in single mode optical fiber,
The normalized frequency defined by the core diameter 2a, the refractive index _n1 of the core, and _the refractive index _n2 of the cladding, V=2πa/ _λ√12-22 ^, determines the amount ^of light passing through the core and the cladding. There is. Here, λ is the wavelength of the propagated light. This situation is shown in FIG.

In a typical V=2.4 designed single mode optical fiber, approximately 20% of the transmitted optical power passes through the cladding. Therefore, it is understood that in order to increase the light transmittance, not only the core but also the cladding needs to have good optical transmittance properties.

FIGS. 1b and 1c show cross-sectional structures of optical fibers constructed from such a viewpoint. 1st
The example in Figure b is a multimode optical fiber in which the leakage of propagated light into the cladding part is relatively small, and the core part 1 is made of As ₂ S ₃ , and the outer periphery 1' is made of As 2 S 3.
Ms ₃₈ S ₆₂ , which has a lower refractive index than As ₂ S ₃ , is provided, and fluoride glass is provided as the outermost layer. Also the first
The example shown in FIG. 1C is a single mode optical fiber with a thick cladding portion, and the glass composition is the same as that in FIG. 1B.

FIG. 2 is a graph showing the light transmission characteristics of various chalcogenide glasses used in the core portion, and FIG. 3 is a graph showing an example of the light transmission characteristics of fluoride glasses arranged in the peripheral portion.

As is clear from Fig. 2, various chalcogenide glasses, such as As ₂ S ₃ , As ₃ Se ₇ , and GeS ₄ , all exhibit extremely low optical loss in the wavelength range of 2.0 to 5.5, and are highly sensitive to infrared light. It can be seen that the glass has suitable properties as a transmission glass. Further, as shown in FIG. 3, fluoride glass has smaller optical loss in the wavelength range of 2 to 5 μm than oxide glass.
From these two figures, it can be seen that good light transmission characteristics are obtained in an optical fiber in which the propagating light seeps not only into the core portion but also into the cladding portion.

As for the composition of chalcogenide glass, an example of a compound of arsenic and sulfur is shown here, but from the viewpoint of glass forming ability, possibility of wire drawing, and light transmittance, it is possible to use germanium, silicon, antimony, phosphorus, and tin. or two or more of the above elements including arsenic, selenium,
1 of the elements including tellurium and the above sulfur
Compound glasses with one or more elements can be used.

In addition, as a fluoride glass, the above-mentioned BaF ₂
In addition to −GdF ₃ −ZrF ₄ system, ZrF ₄ has La, Th, Al,
Glass doped with one or more of Cd, Tl, Y fluorides, and _AlF3 with Ca, Ba, Gd, Y, Sb,
Glass to which one or more of Tl and Cd fluorides are added can be used.

Next, an example of manufacturing an optical fiber according to the present invention will be shown below.

In advance, the composition was set to 33 mol% BaF ₂ −4 mol% GdF ₃ −
63 mol% ZrF ₄ inner diameter 10mmφ, outer diameter 14mmφ, length
A 200mm cylindrical glass pipe was made. next,
This was polished to obtain a smooth inner wall surface with no irregularities.

On the other hand, a rod having a core made of As ₂ S ₃ (core diameter 7 mm φ) and a cladding made of As ₃₈ S ₆₂ (clad diameter 9.8 mm φ) was prepared by a double casting method. Next, this chalcogenide glass rod was inserted into the fluoride glass pipe and integrated. The integrated glass body was then locally heated to about 320° C. and drawn to obtain an optical fiber having an outer diameter of 136 μm, a chalcogenite glass cladding diameter of 100 μm, and a core diameter of 70 μm. The refractive indices of the core, chalcogenide glass cladding, and fluoride glass cladding of the optical fiber were 2.41, 2.38, and 1.528, respectively. In addition, the light transmittance is 250dB/Km at a wavelength of 2.4μ, 3.4μ
It was 360dB/Km.

According to the optical fiber according to the present invention described above, it is possible to obtain good light transmission characteristics in the infrared wavelength range, and it is possible to obtain the advantage of excellent harmless weather resistance. In the above example, As ₂ S ₃ was used as the core glass, but by using AS-Se glass instead, it is also possible to achieve good light transmission characteristics up to a long wavelength range of about 10 μm. It is possible.

Furthermore, by using fluoride glass as the pipe material, the optical fiber according to the present invention can be easily drawn due to the similarity in coefficient of thermal expansion and softening point, and as a result, it retains the excellent infrared light transmittance of chalcogenide glass. It also has the great advantage of making it possible to realize optical fibers, which have been demonstrated for a long time. The optical fiber of the present invention can be used for communications, power transmission, infrared light sensing media, etc. as an optical transmission medium for information, power transmission, and infrared light sensing medium.
It can be applied to a wide range of fields such as medicine and image processing.

[Brief explanation of the drawing]

Fig. 1 is a, b, c sectional view of the optical fiber of the present invention, Fig. 2 is a graph of the light transmission characteristics of chalcogenide glass, Fig. 3 is a graph of the light transmission characteristics of fluoride glass, and Fig. 4 is a graph showing the relationship between the power density distribution and radius vector of a single mode optical fiber. In the figure, 1 is the core part of chalcogenide glass,
1' is a cladding portion of chalcogenide glass, and 2 is a cladding portion of fluoride glass.

Claims (1)

[Scope of Claims] 1. An infrared transmitting optical fiber characterized in that, in a cross section of the optical fiber, a central portion is made of chalcogenide glass, and a peripheral portion surrounding the central portion is made of fluoride glass. 2. In claim 1, the central glass contains one or more elements of arsenic, germanium, silicon, antimony, phosphorus, and tin, and one or more elements of sulfur, selenium, and tellurium. An infrared transmitting optical fiber characterized by being a chalcogenide glass in which the above elements are combined. 3 In claim 1, the peripheral glass is made of barium, gadolinium, lanthanum,
It is a fluoride glass consisting of a compound of one or more fluorides of thorium, aluminum, cadmium, thallium, or yttrium and zirconium fluoride, or a fluoride glass consisting of a compound of zirconium fluoride, or a fluoride of calcium, barium, gadolinium, yttrium, antimony, thallium, or cadmium. An infrared transmitting optical fiber characterized in that it is a fluoride glass made of a compound of one or more fluorides and aluminum fluoride.