JPH0813692B2 - Chalcogenide glass fiber with core-clad structure - Google Patents

Description

TECHNICAL FIELD The present invention relates to a chalcogenide glass fiber having a core-clad structure excellent in light transmittance.

[Prior art] Chalcogenide glass is sulfur (S), selenium (S)
e), a glass containing tellurium (Te) as a main component,
It is an optical material with excellent infrared transparency, chemical stability, and heat resistance. Chalcogenide glass is partly used for infrared transmission windows and filters, but this glass molded into fiber can only be applied to the information transmission waveguide that has already been put to practical use with silica glass. Without
It can also be used as a waveguide for energy transmission such as CO laser and carbon dioxide laser, and for radiation thermometer.

When the chalcogenide glass fiber is used for energy transfer of a carbon dioxide gas laser or a radiation thermometer in a low temperature region, the Te concentration in the glass is preferably high. However, in general, as the Te concentration increases, the heat resistance of the glass deteriorates and the glass tends to crystallize, which makes spinning difficult. As a glass with high Te concentration and excellent heat resistance, GeSeTe
Glass is known. Unclad fiber of GeSeTe glass is 10.6 μm (lasing wavelength of carbon dioxide laser)
The present inventors previously confirmed that the loss at 1.5 dB / m or less was obtained (J. Non. Cryst. Sol. 95 & 96 (1987) 641). GeS
In order to put the eTe glass fiber into practical use, it is necessary to make the fiber have a core-clad structure, but an example of producing a fiber having a core-clad structure with this glass has not yet been reported.

[Problems to be Solved by the Invention] First, the present inventors first put a core rod of chalcogenide glass and a clad tube vertically in a cylindrical crucible having a nozzle at a lower portion thereof, and locally localize only the vicinity of the nozzle of the crucible. We proposed a method of continuously drawing the glass in the crucible while heating it (see Japanese Patent Application No. 63-38474). According to this method, a low-loss chalcogenide glass fiber having good adhesion at the interface between the core and the clad can be produced. However, even with this method, GeSeTe
It is difficult to form a core-clad structure from glass, and there is a problem that the cladding glass is likely to devitrify particularly near the interface between the cladding glass and the crucible.

[Means for Solving the Problems] The chalcogenide glass fiber having a core-clad structure according to the present invention is characterized in that both the core glass and the clad glass having a lower refractive index than the core glass contain tellurium. And More specifically, the core glass of the present invention is composed of three elements germanium, selenium and tellurium, while the cladding glass is composed of four elements germanium, arsenic, selenium and tellurium. The composition of the core glass composed of three elements is Ge: 20 to 35 at%, Se: 12 to 30 at%, Te: 40 to 6
5at% range, preferably Ge: 24-33at%, Se: 15
It is in the range of ~ 25at% and Te: 47-61at%. When the composition of the core glass deviates from the above range, crystallization becomes easy,
Spinning becomes difficult. The composition of the clad glass composed of four elements is Ge: 5 to 30 at%, As: 10 to 45 at%, Se: 8
~ 40at%, Te: 15-45at%, preferably Ge:
8-22at%, As: 12-41at%, Se: 10-37at%, Te: 20-40
It is in the range of at%. If the composition of the clad glass deviates from the above range, the expansion coefficient and the spinning temperature will be greatly different from those of the core glass, so that the fiber having the core-clad structure cannot be obtained by spinning with the core glass. Further, in the clad glass of the present invention, the quantitative specifications for germanium, arsenic and tellurium are also requirements for keeping the refractive index of the clad glass lower than that of the core glass, and any of Ge, As and Te. If the at% (atomic percentage) exceeds the upper limit of the above-defined range, the refractive index of the cladding glass becomes higher than that of the core glass, and light cannot be transmitted.

EXAMPLES Next, the present invention will be described in more detail based on examples.

Example 1 A core rod having a composition of Ge: 30at%, Se: 20at%, Te: 50at% was prepared by using Ge: 15at%, As: 20at%, Se: 35at%, Te: 30.
It was inserted into a clad tube having a composition of at%, and this was placed vertically in a crucible having a nozzle at the bottom, and the inside of the crucible was replaced with argon gas. After a while
Only the vicinity of the crucible nozzle was heated until the viscosity of the cladding tube and core rod reached 10 ⁶ poise. As a result, the clad tube and the core rod are fused to each other, and the fused clad glass adheres to the entire inner surface of the nozzle. In this state, the clad tube was pressurized with a pressure of 1.5 kg / cm ² , and at the same time, the gap between the clad tube and the core rod was reduced to 10 ^-2 torr. By this operation, the clad tube and the core rod were completely integrated, and a fiber having a core diameter of 340 μm and a clad diameter of 450 μm could be continuously spun from the crucible nozzle. The resulting fiber was immediately coated with resin and then wound on a drum. The transmission loss of this fiber is shown in FIG. The minimum loss was 0.4 dB / m near 8.2 μm, and the transmission loss was 1.7 dB / m at 10.6 μm, which is the oscillation wavelength of the carbon dioxide laser. The minimum bending radius of this fiber was 15 mm or less.

Examples 2 to 3 Using core rods and clad tubes having the compositions shown in Table 1, a core diameter of 340 μm was obtained in the same manner as in Example 1.
A fiber having a diameter of m and a clad diameter of 450 μm was continuously spun. The transmission loss of the obtained fiber is shown in FIGS. 2 and 3. The minimum loss is 0.2 dB / m with the fiber of Example 2.
(7.3 μm) was achieved. The transmission loss at 10.6 μm, which is the oscillation wavelength of the carbon dioxide laser, is 1.8 dB / m for both the fibers of Examples 2 and 3, and the minimum bending radius is 15 m for both.
m or less.

Comparative Example A core rod having a composition of Ge: 27at%, Se: 18at%, Te: 55at% was inserted into a clad tube having a composition of Ge: 27at%, Se: 23at%, Te: 50at%, and implemented. A fiber having a core diameter of 340 μm and a clad diameter of 450 μm was continuously spun in the same manner as in Example 1. The transmission loss of the obtained fiber is shown in FIG. The minimum loss of this fiber is 1d
Although it was B / m (8.5 μm), precipitation of fine crystals was observed on the clad surface of the fiber a few minutes after the start of spinning, the mechanical strength of the fiber was very low, and the minimum bending radius was
It was over 100 mm.

[Effects of the Invention] According to the present invention, a chalcogenide glass fiber having a core-clad structure, which has excellent heat resistance despite a high tellurium content and has a transmission loss comparable to that of an unclad fiber, is obtained. be able to.

[Brief description of drawings]

1 to 3 show transmission loss spectra of the core-clad type fibers obtained in Examples 1 to 3, and FIG. 4 shows transmission loss spectra of the core-clad type fibers obtained in Comparative Example.

Claims (2)

[Claims] 1. A core glass is composed of three elements germanium (Ge), selenium (Se) and tellurium (Te), and a cladding glass is composed of four elements germanium, arsenic (As), Se and Te. A chalcogenide glass having a core-clad structure characterized by the above. 2. The composition of the core glass is Ge: 20-35 at%, Se: 12
~ 30at%, Te: 40 ~ 65at%, clad glass composition is Ge: 5 ~ 30at%, As: 10 ~ 45at%, Se: 8 ~ 40at%
%, Te: 15-45 at% in range, chalcogenide glass having a core-clad structure according to claim 1.