JPS58199737A - Optical fiber and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an optical fiber capable of transmitting light having wavelengths in a region ranging from the near ultraviolet region to the intermediate infrared region with small loss, by sticking a molten mixture of cesium bromide with cesium iodide to the outside of a core fiber of cesium iodide and by solidifying the mixture. CONSTITUTION:A core fiber 4 of cesium iodide is manufactured by the stepanov method or other method. A molten mixture 2 consisting of 2-57mol% cesium bromide and the balance cesium iodide is prepared and charged into a crucible 1. The mixture 2 is allowed to flow out from a circular slit 3 positioned at the tip of the crucible 1 in contact with the fiber 4 at a prescribed flow rate, and the mixture 2 is stuck to the outside of the fiber 4 while drawing the fiber 4 downward with rollers 5 at a prescribed rate. The coat of the stuck mixture is solidified by cooling with water-cooled pipes 6 to form a clad. Thus, the desired optical fiber is obtd.

Description

[Detailed Description of the Invention] 1. Technical Field of the Invention] The present invention relates to an optical fiber and a method for manufacturing the same, and more specifically, to an optical fiber that can transmit light with wavelengths from near ultraviolet to mid-infrared with low loss. 7. [Technical background of the invention and related points] Regarding AIPA and its method of use] In recent years, research and development of various laser beams has been actively conducted. For example, the wavelength of 10 μm known from carbon dioxide laser Mid-infrared laser light having a relatively high output of several watts or more is applied to laser beam processing, medical laser scalpels, etc., and is in practical use in some cases.

Optical fibers used to transmit such laser light have good flexibility, are capable of transmitting high-power mid-infrared laser light, etc., have little leakage, and have low loss. Materials that can transmit laser light are required, and their development is desired.

Optical fibers are usually made of a central part (core) with a high refractive index for transmitting laser beams, etc., and a layer (cladding) with a low refractive index that surrounds this and prevents light from leaking from the core. The core material of the mid-infrared optical 7-eyeper with such a structure is potassium (K), rubidium (Rh), silver (Ag), cesium (Cs), thallium (TQ), etc. Compounds of monovalent metals with relatively high atomic numbers and herogen group elements such as bromine (Br) and iodine (I) are used. Basic research has revealed that it can be used as an optical fiber with sufficiently low transmission loss for the above-mentioned applications.

However, among these low-loss halides, thallium halide is toxic and requires careful handling, while silver halide is sensitive to visible light and gradually loses its transparency. have. Also, cesium bromide (
Alkali metal halides other than CsBr (CsBr) and cesium iodide (CsI) have a problem of low flexibility due to their tendency to open. Therefore, CsBr or Cs
There is a need for an optical fiber having I as a core material and a method for manufacturing the same.

A hot extrusion method is known as a method for processing the above-mentioned core material consisting of a valent metal halide into a polycrystalline fiber. Further, as a manufacturing method that further develops this method and performs cladding processing, a method has been proposed in which a composite preform in which a rod-shaped core material is covered with a cylindrical cladding material is hot-extruded. However, the hot extrusion processing method for composite preforms described above has a problem in that it is difficult to control the interface between the core and the clad to a constant diameter.

On the other hand, a core material consisting of a -valent metal halide was
The methods for processing into eye-shaped single crystals are usually the Stepper 77 method, the reverse Stepparts 7 method, and the EFG method (Edge-D
efined, Film-Fed Growth), or methods similar to these are known.

These methods produce a single crystal core fiber from a monovalent metal halide melt as a raw material. Unlike a polycrystalline core fiber, such a single-crystal core fiber does not have a grain boundary phase that causes scattering loss, so the core material made of a -valent metal halide is inherently It has the advantage that it can be used without impairing its high infrared transmittance.

In order to put such a core fiber into practical use, it is necessary to cover the outer periphery of the core with a cladding material having low loss and high flexibility, and process it into an optical fiber structure. During coating processing, if irregular variations occur in the dimensions and shape at the interface between the core and cladding, transmission loss called structural loss increases, so in order to obtain a low-loss optical fiber, the interface between the core and cladding must be smooth. Therefore, the Clara F processing technology that can produce products with high dimensional accuracy is required. However, such a rad processing technique has not been obtained for single crystal fibers, and a specific cladding material suitable for single crystal fibers is not yet known.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems and to transmit light with wavelengths from near ultraviolet to mid-infrared with low loss.
An object of the present invention is to provide an AIPA and a method for manufacturing the same.

[Summary of the Invention] The optical fiber of the present invention is characterized in that the core is made of cesium iodide and the cladding is made of cesium iodide. be.

Cesium iodide (Cs
I) The fiber is made of monocrystalline or polycrystalline cesium bromide (CsBr) and cesium iodide (CsI) ip used as the cladding material of the present invention.
r 2 to 57 moles and the balance consists of CsI, preferably 47 to 57 moles of CsBr and the balance consists of CsI. If the CsBr content is less than 2 mol, the difference in refractive index with the core is too small and the function as a cladding is insufficient, while if it exceeds 57 mol, problems occur during manufacturing.

The club F in the optical fiber of the present invention contains a trace amount of a halide of an alkaline earth metal element in addition to CsBr and CsI, and is fast. Examples of the halides include calcium (Ca), strontium A (Sr
), /(Compounds of alkaline earth metal elements such as lithium (Bs) and halogen group elements such as fluorine (F), chlorine (J), bromine (Br), iodine CI) Can be mentioned.

The method for producing an optical fiber of the present invention involves adhering a melted mixture consisting of 2 to 57 moles of cesium bromide and the remainder cesium iodide to the outer periphery of a core 7 eyeglass made of cesium iodide, and then solidifying it by cooling. It is characterized by encouraging people.

Below, the manufacturing method of the present invention will be explained in more detail.

In the present invention, the production of CsI core fiber usually consists of
Any method used for fiber AM can be adopted.

Examples of such methods include, for example, the Stepper 77 method, the reverse Stepparts 7 method, the EFG method, a single crystal 7 IPA production method similar to these, and a single crystal 7 IPA production method by hot extrusion. Single crystal or polycrystalline CsI obtained by the method of
The core fiber is then coated with a melt mixture of CsBr and CsI using, for example, an apparatus such as that shown in FIG. In FIG. 1, CsBr is added to the crucible 1.
A mixture melt 2 consisting of CsI and CsI is poured out in a predetermined flow pattern from an annular slit 3 located at the tip of the Luppo 1 and in contact with the CsI core fiber 4. The CsI core fiber 4 attached to the outer periphery of the fiber 4 is pulled down by a roller 5 at a predetermined speed, and the attached coating solution is cooled by a water-cooled pipe 6 located between the crucible 1 and the roller 5. It solidifies and becomes cladding. At this time, it is preferable to provide a heater 7 around the outer periphery of the crucible 1 to maintain the mixture melt at a temperature higher than its liquidus temperature to prevent the solid phase from precipitating from the melt. Furthermore, in the apparatus shown in FIG. 1, for example, by connecting the CsI core 7 eyeper 1111a to a device such as the reverse stepper 77 method, it is possible to continuously perform core fiber manufacturing and craft processing. is possible.

According to the optical 7-eyeper am method of the present invention, a fiber with good adhesion between the core fiber and the cladding can be obtained. Furthermore, since the thermal expansion coefficients of CsI and CsBr match fairly well as shown in FIG. 2, the residual strain is small even after cooling to room temperature.

The composition of the mixture melt consisting of CsBr and CsI used in the present invention is such that CsBr is 2 to 57 moles and the balance is CsI, preferably CsBr and CsI.
is composed of 47 to 57 moles and the remainder is CsI. If the content of C + sBr is less than 2 mol, the formed fiber will not function properly and the light will leak thickly, whereas if it exceeds 57 mol, the melt will not be applied to the core fiber. Sometimes, the core 7 eyer partially melts and the interface with the cladding fluctuates unstablely, or the core 7 eyer melts, making it impossible to manufacture the optical 7 eyer.

The relationship between the core fiber melting phenomenon and the melt composition is based on the phase diagram of the CsBr-C5I system shown in Figure 3.
This will be explained in detail below.

In FIG. 3, the vertical axis represents temperature (C), and the horizontal axis represents CsBr content (in moles).

In FIG. 3, the CsBr content X is X, = 52
The liquidus line a and the solidus line a match at the point of mole.

The solid point is the so-called congruent melting point (CongruentMe
lting point (also translated as harmonic melting point)
This is the point at which the liquidus temperature takes the minimum value Tc.

First, consider the case where the CsBr content is less than 52 moles. In this range, as the CsBr content X increases, the liquidus temperature and solidus temperature of the CsBr-Cs component system decrease.

Now, CsBr-C when the CsBr-containing @XQ melt maintains thermodynamic equilibrium at its liquidus temperature TQC.
If the CsBr content of the 5I solid solution is Xs molar, then
As shown in Fig. 3, when a TeC melt with a CsBr content of χ1 moles is attached to a CsI core 7 eyepah, where s is given by the intersection of the horizontal line corresponding to T = TiC and the in-phase band, Although an ion exchange reaction occurs between the core 7 eyeper and the melt, the CsBr content on the core fiber surface does not exceed the equilibrium value Xs. Therefore,...Core 7 Aiper Decay Surface...

The in-phase temperature of TiC is also
Because it is dangerous to appear lower, Core 7 Aipah exists in a stable manner as it melts. The core fiber is CsBr
During cladding processing by coating the -C5I mixture melt, the paper is constantly pulled down by rollers or the like at an appropriate speed.

Then, since it is cooled by a water-cooled pipe or the like, the wettability of the melt adhering to the core 7 eyeper gradually decreases, and the CsBr
-C5I solid solution crystals are precipitated and solidified, and a cladding is formed while maintaining the dimensional accuracy and smoothness of the core 7 eyeper.

On the other hand, when the CsBr content of the melt is 52 moles 10 more,
That is, as the CsBr content increases, CsBr-C
If the liquidus temperature and solidus temperature of the component system rise in s, the following will occur. That is, in FIG. 3, Cs of the melt
Br content is Xl'% (XI'>Xc) (
7) If the liquidus temperature at the time is 'rg'c, then the CsBr content Xs' of the CsBr-C5I solid solution that maintains thermodynamic equilibrium at the temperature of the melt satisfies the following inequality (1). .

Xe <XQ'< When it is attached to IPA, an ion exchange reaction progresses and it is removed. In the process, Xsf changes from the initial point containing no CsBr to the concentration Xc at the matching melting point.
At the same time, the liquidus temperature of the surface layer becomes Tc.
Descend at Ct. Since the TCC is lower than the melt temperature T/ll', the core 7 IPA melts from the surface as the ion exchange reaction progresses. If the melting rate is high, the core 7 is removed before the cladding cools and solidifies in the cladding process described above
In cases where the eye pad is fused, even if the eye pad is not fused, the surface of the eye pad is subject to heterogeneous erosion due to melting, resulting in structural loss and increased transmission loss.

WII! of the Hikari 7 Aipa of the present invention as described above. According to the method, cooling of the melt starts almost at the same time as the melt is applied to the core 7 eyeper, so an ion exchange reaction occurs between the core fiber surface and the melt, and the melting of the core fiber surface progresses. This is a short period of time, approximately several tens of seconds or less. The study based on the above phase diagram assumes that the core 7 eyelid and the melt contact each other for a sufficiently long time at the same temperature. Therefore, in the manufacturing method of the present invention, since cooling is started continuously, Cs
Even if a melt containing a large amount of Br is used, there is no problem as long as the melting on the surface of the core 7 eyeper is negligible. For these reasons, the composition of the CsBr-C5I mixture melt is such that the upper limit of the CsBr content is 57 moles. If the melt has a II composition within this range, the temperature may be higher than the liquidus temperature within a range of not exceeding 10C; The liquid contains Cs
In addition to Br and C5I, a trace amount of a halide of an alkaline earth metal element may also be contained. Examples of the above-mentioned halide include the above-mentioned Shitayoni, Ca, 8r, Ba
! 9 alkaline earth metal elements and F, (J, Br,
Examples include compounds of helogen group elements such as I.

The cladding of the optical fiber of the present invention has a composition in which the composition of the melt forming the vertical fiber is approximately the same as that of the melt except for the interface between the core fiber and the cladding, which has a CsBr content of 5. Due to the growth of crystals, there is no segregation and there is high homogeneity.

Furthermore, when the CsBr content is less than the above range, the homogeneity of the cladding is slightly reduced due to ion exchange reactions on the core fiber surface. However, an optical fiber having a cladding having a composition in this range has an approximate effective numerical aperture in a wide range of 008 to 0.35, as shown in FIG. Therefore, when this optical 7-eyeper is incorporated into a system, the degree of freedom in selecting optical characteristics is increased. On the other hand, when the cladding is formed using a melt with a CsBr content of less than 2 mol%, the effective numerical aperture of the optical 7-eyeper is less than 0.07, so the optical 7-eyeper Structural loss increases when bending.

Furthermore, since the difference between the liquidus temperature of the melt and the melting point of the CsI core fiber is 4C or less, cladding processing becomes difficult and practicality is lost.

〔Effect of the invention〕

The optical fiber of the present invention has CsI and Cs without cleavability.
Since the core and cladding are composed of I-CsBr II solution, it has high flexibility.

In addition, by selecting the CsBr content of the cladding from the range of 2 to 57 mol, the numerical aperture of the Hikari 7 Aiper can be adjusted to α08.
This is a book that can be set arbitrarily between 035 and 035.

The optical fiber of the present invention has good adhesion between the core fiber and the cladding, and the cladding is formed around the core fiber with high dimensional accuracy and smoothness. Since the cladding is highly homogeneous without segregation, the structural loss of the optical fiber is reduced. Furthermore, by forming the rad in this manner, the optical 7 eyer of the present invention reduces local concentration of distortion that occurs when the optical 7 eyer is whitened, and has increased flexibility. By using such an optical 7-eyeper, it is possible to transmit light with wavelengths from near ultraviolet to mid-infrared with low loss.

WI of the light 7 Aipa of the present invention! The method is such that it is possible to easily obtain an optical 7-iper having the above-mentioned characteristics.

[Brief explanation of the drawing]

FIG. 1 is an example of a conceptual diagram showing the method for manufacturing an optical fiber of the present invention, FIG. 2 is a diagram showing the relationship between the thermal expansion coefficients and temperature of CsBr and CsI, and FIG. 3 is a diagram showing the relationship between the thermal expansion coefficients of CsBr and CsI and the temperature The phase diagram and FIG. It is a figure which shows the relationship between the number of side ports and Clara F composition. 1... Crucible, 2... CsB. 1 compound melt consisting of r and CsI, 3... annular slit, 4... Cs
I core 7 eyepa, 5...roller, 6...water cooling pipe,
7... Heater. r- Maki・1: (= Shi shouting ← ν斗り￥

Claims (1)

[Claims] (1) Core made of cesium iodide and cesium bromide 2
Hikari 7 Aipah is characterized in that it is composed of a cladding consisting of cesium iodide and the remainder being cesium iodide. {2} The optical fiber according to claim 1, wherein Clara F is composed of 4 full 5 fumol of cesium bromide and the balance is cesium iodide. (3) The optical fiber according to claim 1, wherein the cladding contains a trace amount of a halide of an alkaline earth metal element. (4) A light beam characterized by layering a melted mixture of 2 5 fumoles of cesium bromide and the remainder cesium iodide on the outer periphery of a core 7 IPA made of cesium iodide, and then cooling and solidifying it. Fiber manufacturing method. (5) The light 7 according to claim 4, wherein the melt consists of 4 full 5 fumoles of cesium bromide and the remainder is cesium iodide.
Aipa's II* method. (6) The method for manufacturing an optical fiber according to claim 4, wherein the melt contains a trace amount of a halide of an alkaline earth metal element. (7) The method for manufacturing an optical fiber according to claim 4 or 6, wherein the temperature of the melt is within the range of TT+10C, where TC is the liquidus temperature of the mixture.