JPS61502220A - Hollow optical fiber waveguide and method for reducing transmission loss of hollow optical fiber - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Hollow optical fiber for mid-infrared region The present invention relates to a hollow optical fiber for low transmission loss for high-energy radiation in the mid-infrared region. In particular, it transmits energy from a carbon dioxide laser with a wavelength of 10.6 microns (μm). related to optical fibers such as transmission.

Recently, relatively cheap, compact, high-output gas lasers such as CO□ lasers have rapidly become available. have been put into practical use, especially in the fields of medicine, communications and industrial engineering. Its application is limited by the lack of suitably flexible transmission systems. Ru. For example, laser energy in the 10.6 μm wavelength range affects biological tissues. Related properties make CO2 lasers useful in medical applications, especially when lasers are highly accurate and efficient. Potentially extremely useful in the field of surgery that allows for controlled incisions. It is said that However, it is compact, flexible and controllable. CO□ lasers are mainly used in surgery because there is no available low-loss transmission system. Limited to direct surgery. Uses an articulated arm with a mirror attached to a mechanical joint. Although some endoscopic surgery has been performed, this method is very limited and impractical. do not have. A flexible material that is suitable for surgical applications and can transmit CO and laser energy with low loss. If flexible optical fibers can be obtained, the potential of Cog lasers in surgery will be enhanced. It is clear that this is indeed possible.

Ordinary optical fibers made of glass, like the inorganic materials in their base, are glass exhibits strong absorption properties at mid-infrared frequencies due to resonance effects in its molecular structure. , therefore it is virtually opaque to radiation in such frequency ranges and cannot be used. do not have. In contrast, for example, thallium promoter commonly called KR35 Optical fiber capable of transmitting in the mid-infrared region from certain alkali halides such as iodides have been fabricated, but with crystalline properties and high levels necessary to achieve good transmission rates. Due to the purity of these materials, it is very difficult to produce suitable fibers from these materials; It's expensive. Furthermore, KR35 is chemically toxic and has low chemical stability in terms of moisture resistance. It is highly susceptible to thermal degradation at relatively low temperatures, making it completely unsuitable for surgical applications.

To overcome the above problems, relatively low transmission of radiation in the relevant frequency range is required. Flexible hollow core waveguide so that loss is obtained through the hollow core of the fiber It has been proposed to produce optical fibers for mid-infrared transmission in the form of tubes. hollow circular metal waveguides, dielectric coated hollow metal waveguides, hollow glass waveguides, etc. Various proposals have been made regarding hollow core optical fiber waveguides as mentioned above. It is with this last type of hollow optical fiber waveguide that the present invention is particularly concerned.

The operation of hollow-core glass fiber waveguides is based on the absorption of oxidized glass at mid-infrared frequencies. The aggregation/dispersion characteristics (hereinafter referred to as the anomalous dispersion effect) are based on the complex refractive index (N=n− iK, where K is the attenuation or loss coefficient, which is related to the attenuation or absorption coefficient. Set the real part (n) to the entire wavelength range (for example, 7.5 to 9 μm in the case of silica glass). As a result, in that range, the angle from the core to the middle is larger than the critical angle. Based on the fact that radiation incident on the inner wall of an empty fiber is virtually totally internally reflected. ing.

Of course, the transmission loss at any given wavelength in a hollow optical fiber waveguide is above at that wavelength. It also depends on the values of n and K. A value of zero causes the attenuation rate of internally reflected radiation to be zero, but In reality, the value of is relatively large (as a result of making the refractive index n smaller than 1, the total internal reflection characteristic is applied to the fiber, it is practically impossible to achieve zero attenuation. death However, for any given glass, the maximum value of K is slightly longer than the minimum value of the refractive index. On the long side, generally speaking, the minimum transmission loss of a hollow fiber waveguide made of glass occurs at a wavelength slightly shorter than the minimum value of the refractive index.

Also, these values depend on the atomic weight and molecular structure of the glass, so forming the fiber The properties of the fiber glass have a large effect on the performance (transmission efficiency) of the fiber at a certain wavelength. have a strong influence.

The minimum refractive index of pure germanium oxide (GeO2) glass is It has also been found that the wavelength is very close to the length of 10.6 μm (943 cIo-'). (Ge O2) glass has extremely low transmission loss in the CO2 laser wavelength region. It is conceivable that it will be possible to manufacture hollow optical fiber waveguides with Fact, acid 80 mol% germanium oxide, 10 mol% zinc oxide and 10 mol% potassium oxide A hollow optical fiber made of glass and having its minimum transmission loss at 940 cm-' The American Journal of Applie d Physics, Vol. 53.1982. Published in pages 5484-549Q. τ.

This is described in the paper by Hidaka et al.

At least at the wavelength of interest, the transmission loss of hollow optical fiber wavelengths as described above should be avoided. According to the invention, glass based on germanium oxide at least the inner surface of the hollow glass fiber is made opaque and/or A hollow optical fiber waveguide with a thin germanium lining is provided.

The hollow fiber is heated at a temperature of 400 to 1300°C for up to 48 hours. Therefore, it is possible to make the glass opaque by changing the hollow fiber from a glassy state to a crystalline state. to a glass-ceramic state. Crystalline glass-ceramic molecular structure The presence of long-range transitional symmetries during construction suggests that the selection regulation is a spectral predictor of photoactivity. In the vector region, the reduction of molecules and electrons becomes more local and intense. this has a significant influence on the absorption-dispersion properties of the raw glass, and the refractive index (n) and extinction coefficient ( K), and therefore the target area, that is, the wavelength range of the CO2 laser of 943 cm. This further reduces transmission loss at wavelengths in the region.

Lead, titanium, phosphorus, cerium, zinc, lithium to accelerate the opacification process. aluminum, sodium, potassium, calcium, zirconium, barium, aluminum oxides of aluminum, magnesium, antimony, bismuth, and arsenic. Including at least one glass modifying and/or engraving agent in the glass composition Can be done.

A thin germanium lining in a hollow glass fiber waveguide provides a dielectric coating. Covered hollow metal waveguide (e.g. static plied Phystcs Letters+ 43(5) + M, Miya published September 1983, pp. 430-432 gi) as predicted and observed in the paper by et al. , the transmission loss of the hollow fiber, especially the bending loss, is reduced. The thickness of the lining is The fiber waveguide is made entirely of germanium to prevent optical effects as shown below. The germanium layer should be sufficiently thin to have a thickness of approximately 0.5 μm. available.

The germanium layer on the inner surface of the hollow glass fiber waveguide By exposing at least the inner surface to a reducing atmosphere, the germanium oxide of the glass is The fiber is heated to a suitable high temperature while allowing reduction to germanium on the inner surface of the fiber. It can be formed very easily and easily by heating. The reducing atmosphere contains hydrogen. It may be a mixture of 90% nitrogen and 10% hydrogen by volume. hollow light In addition to the glass on the inner surface of the IVA waveguide, the glass on the outer surface is also made of germanium. It is not important whether the fiber is reduced to Simply place it, but it ensures that a uniform germanium lining is created on the inside surface. Pump a reducing atmosphere through the heated hollow fiber core of the fiber to It is preferable to

The temperature at which the hollow optical fiber is heated for the reduction treatment is between 400 and 850°C, especially The temperature is preferably 650°C, and the reduction treatment is carried out on the inner surface of the hollow glass fiber or on the fiber. Advantageously, this is carried out simultaneously with the heat treatment which renders the whole opacified.

The composition of germanium oxide-based glass is 80% or more by weight of germanium oxide. 20% by weight of germanium oxide and 5 to 10% by weight of lead oxide. Preferably, as mentioned above, other small amounts (at least one type of alteration and/or nuclear Forming agents may also be included.

The invention will now be further explained by way of example and with reference to the accompanying drawings, in which: FIG.

Figure 1 shows the refractive index (n) of glassy germanium oxide versus wavelength in the mid-infrared region. Graph showing measured changes in extinction coefficient (K); Figure 2 is a graph similar to Figure 1, but with the refractive index of opaque germanium oxide and Graph showing changes in extinction coefficient; Figure 3 is made of vitreous germanium oxide and shows changes in pore diameter. is 0° for the wavelength in the mid-infrared region predicted for the hollow fiber waveguide of Tsuru. Graph showing changes in transmission rate; Figure 4 is the same graph as Figure 3, but now opaque. Graph showing the predicted transmission rate for a waveguide made of germanium oxide; Beauty Figure 5 shows (a) pore size of 0.5fl, 95% by weight of germanium oxide and 5% by weight of lead oxide. (b) a hollow optical fiber waveguide formed of glass consisting of %; Mid-infrared region experimentally determined for the same hollow optical fiber waveguide after transparentization. 3 is a graph showing a relative change in transmission rate with respect to wavelength at .

As is clear from Figure 1, the refractive index and extinction coefficient of pure germanium oxide glass is that in the CO□ laser wavelength range of 10.6um (943a++-') They are approximately 0.6 and 0.8, respectively. As mentioned above, the refractive index of less than 1 is If total internal reflection is provided in an empty optical fiber and the refractive index is further reduced at the target wavelength, the fiber The transmission rate of the fiber is further improved.

Figure 2 shows pure germanium oxide glass that has undergone a phase transformation from a glassy state to a crystalline state. It shows the measured values of the refractive index and extinction coefficient at the mid-infrared wavelength of 943 cm. The refractive index and extinction coefficient at -' are approximately 0.4 and 0.8, respectively.

We demonstrate the benefits of this phase transformation and the reduction of the refractive index in the wavelength range of CO2 lasers. Therefore, the transmission rate of the hollow optical fiber waveguide made of each material shown in Figure 1.2 is It was predicted by radiation optical calculation that the fiber waveguide has a circular cross section. required for this calculation The important parameters are the refractive index, extinction coefficient, and inner diameter of the hollow fiber waveguide (0.5 Iu). ) and wavelength. Figure 3 shows a hollow optical fiber made of vitreous germanium oxide. The transmission rate (transmission percentage per meter) for the wavelength predicted for the fiber is while the corresponding diagram for the same fiber after opaque glass is shown in Figure 4. The data is indicative. At a wavelength of 1066 μm (943 cm-'), the gel The predicted transmission for the manium glass fiber is 77% that of the opacified fiber. The ratio is 8%. Also, the predicted maximum transmission rate for glassy fiber is 925C111-' vs. 76% for the opacified fiber. m-' is 84%. This wavenumber range is within the tunable range of CO and lasers. be.

To further demonstrate the advantages of the present invention - by way of example - germanium oxide 95% by weight, acid Glass consisting of 5% lead oxide by weight is melted and drawn into a hollow fiber with an inner diameter of 0.50. After punching and forming, the spectral transmission properties of the fiber were measured at wavelengths in the mid-infrared region. Next The fiber is then heated in the furnace chamber for about 5 minutes to a temperature of about 700°C, during which time The fiber is made opacified and virtually completely converted to the glass-ceramic state of the crystal chamber. After that, the spectral transmission characteristics of the fiber were measured.

The results of these measurements are shown in FIG. From the same figure, the opaque glass fiber It can be seen that a significant increase in transmission rate has been achieved in the CO2 laser wavelength range. Ru.

Furthermore, as previously mentioned, the inner surface of the waveguide with or without glass opacification germanium oxide based by forming a thin layer of germanium on the surface. The present invention also aims to further improve the transmission rate of hollow optical fiber waveguides made of glass. Included within the scope of. Germanium is produced by reducing germanium oxide on the fiber surface. The possibility of forming a layer is to mix a piece of pure germanium oxide glass with 90% nitrogen and by heating to a temperature of 650°C in an atmosphere consisting of 10% hydrogen. It is. This means that a thin germanium layer on the glass surface forms relatively quickly. The layer thickness could be controlled by the processing time and temperature. Hollow optical GeO2 glass fiber for laser transmission with thin germanium surface layer Another advantage obtained by forming a layer is that the layer is sufficiently electrically conductive. within an electrical safety device designed to shut off the laser in the event of a fiber break. The advantage is that fibers can also be incorporated into the system.

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Claims (15)

[Claims] 1. Hollow glass fiber formed from germanium oxide based glass an opacified and/or thin germanium lining on at least the inner surface of the Hollow optical fiber waveguide with. 2. Processing of hollow optical fiber waveguides made of glass based on germanium oxide hollow fiber in a manner that reduces the transmission loss of the fiber at a given wavelength. A method of heating a fiber such that at least the inner surface of the fiber becomes opacified. 3. Claims that the fiber is heated at a temperature of 400 to 1300°C for up to 48 hours The method according to the second term of the scope. 4. At least the inner surface of the hollow fiber is exposed to a reducing atmosphere and the thin germanium Claim 2 or 3, wherein the inner lining of the pad is formed on the inner surface. How to put it on. 5. Processing of hollow optical fiber waveguides made of glass based on germanium oxide hollow fiber in a manner that reduces the transmission loss of the fiber at a given wavelength. At least the inner surface of the bar is exposed to a reducing atmosphere, and the thin germanium lining is A method of heating the fiber while allowing it to form on its internal surface. 6. 6. The method according to claim 4 or 5, wherein the reducing atmosphere contains hydrogen. 7. Claim 6, wherein the reducing atmosphere consists of 90% by volume of nitrogen and 10% by volume of hydrogen. How to put it on. 8. Claim 4, wherein the reducing atmosphere is pumped through the core of the hollow fiber. 7. The method according to any one of Items 7 to 7. 9. Claims 4 to 8, wherein the fiber is heated to a temperature of 400 to 850°C. The method according to any one of the above. 10. 10. The method of claim 9, wherein the fiber is heated to a temperature of 650<0>C. 11. Claims 4 to 1, wherein the germanium lining has a thickness of approximately 0.5 μm. The method according to any one of item 0. 12. A claim in which the fiber is heated so as to render the entire hollow glass fiber opaque. The method according to any one of items 2 to 11. 13. The composition of glass based on germanium oxide is 80% by weight or more. Any of claims 2 to 12 containing rumanium and 20% by weight or less of lead oxide. The method described in item 1. 14. The composition of the glass is 90-95% by weight of germanium oxide and 5-10% by weight. 14. The method of claim 13, comprising lead oxide. 15. The composition of the glass, which is based on germanium oxide, makes the glass opaque. Promotes lead, titanium, phosphorus, cerium, zinc, lithium, sodium, potassium , calcium, zirconium, barium, aluminum, magnesium, anti At least one type of glass modification selected from oxides of mono, bismuth, and arsenic and/or the forming agent according to any one of claims 2 to 14. the method of.