JP3811476B2 - Hollow waveguide, laser light transmission method and laser light transmission device - Google Patents

Description

  The present invention relates to a light transmission medium in a wide wavelength band such as an infrared wavelength band that cannot be transmitted using a silica-based optical fiber as well as in the visible region, and includes medical, industrial processing, measurement, analysis, chemical The present invention relates to a flexible hollow waveguide suitable for various laser light transmissions useful in such fields.

Infrared light having a wavelength of 2 μm or more is used in various fields such as medical treatment, industrial processing, measurement, analysis, and chemistry. In particular, an Er-YAG laser with a wavelength of 2.94 μm, a CO laser with a 5 μm band, and a CO ₂ laser with a 10.6 μm band have high oscillation efficiency and high output, and also absorbs a large amount of water. Therefore, it is important as a medical treatment device and a light source for industrial processing.

  By the way, a conventional silica-based optical fiber used for communication has a high loss due to an increase in infrared absorption due to molecular vibration when a laser beam having a wavelength of 2 μm or more is used. For this reason, a quartz optical fiber cannot be used as a waveguide for transmitting these laser beams. Therefore, research and development of a new type of optical waveguide to be used in an infrared wavelength band having a wide application range is being actively conducted.

  Currently, research and development of infrared waveguides having a wavelength of 2 μm or more are roughly classified into so-called infrared fibers and hollow waveguides.

Infrared fiber materials are classified into heavy metal oxide glasses (GeO ₂ , GeO ₂ —Sb ₃ O ₃ etc.), chalcogenite glasses (As—S, As—Se etc.), and halides. Halides are further divided into halide glasses (ZnCl ₂ , CdF ₃ —BaF ₂ —ZrF ₄ etc.) and crystalline metal halides (KRS ₅ , AgCl, AgBr, KCl etc.).

  As for the hollow waveguide, various waveguides have been proposed and prototyped from the viewpoint of structure, material, and shape. For example, Patent Document 1 discloses a hollow waveguide using polyimide as a dielectric.

  Such a hollow waveguide is suitable for high-power transmission because it has less reflection in input / output and has a high cooling effect compared to a solid-type infrared optical fiber.

On the other hand, even in the ultraviolet region, there are important light sources in the field of laser chemistry such as excimer laser. However, a full-length optical fiber cannot be used as a transmission line because its loss increases rapidly due to Rayleigh scattering as the wavelength becomes shorter. Therefore, research and development of a transmission line in the ultraviolet region has hardly been conducted.
JP-A-8-36112

By the way, a solid type optical fiber used in the infrared wavelength band is generally disadvantageous for high power transmission because of its high refractive index and large reflection loss. In particular, the above conventional glassy optical fiber generally has a low melting point and softening point, and even a slight loss tends to damage the end face of the optical fiber. Further, most of the transmission region has a wavelength of 6 to 7 μm, and it is difficult to transmit the CO ₂ laser beam. Some crystalline infrared fibers have a transmission range up to 10.6 μm, which is the wavelength band of the CO ₂ laser, but many of them are plastically deformed by repeated bending and have high deliquescence. There is a problem with long-term reliability.

  On the other hand, in the hollow waveguide using the polyimide described in Patent Document 1 as a dielectric, transmission loss in the case of transmitting infrared laser light becomes a problem from the viewpoint of the water absorption rate of the dielectric. In particular, since the oscillation wavelength of 2.94 μm of the Er-YAG laser coincides with the wavelength of the maximum absorption peak of the laser beam by water, in the hollow waveguide using polyimide as a dielectric, the inclusion of a slight amount of moisture causes the waveguide to There was a problem that transmission loss increased.

  In the ultraviolet wavelength band, as described above, the loss of Rayleigh scattering increases sharply with short-wavelength optical fibers in the ultraviolet wavelength band, so there is almost no development of waveguides, but Rayleigh scattering is ignored. A hollow waveguide that can be formed is considered promising.

  Accordingly, an object of the present invention is to provide a hollow waveguide with a small transmission loss in a wavelength band of light in which a silica-based optical fiber cannot be used, particularly in an infrared wavelength band.

In order to achieve the above-mentioned object, the present invention provides a tubular member constituting a waveguide, and a cyclic olefin polymer which is embedded in the inner wall of the tubular member and is transparent in the ultraviolet region or the wavelength region of the infrared region having a wavelength of 2 μm or more. And a dielectric thin film having a water absorption of 0.01% or less.

  The cyclic olefin polymer is preferably an amorphous cyclic olefin polymer based on heat treatment of a polymer solution using norbornene, dicyclopentadiene, or tetracyclododecene as a raw material.

  The tubular member may be a metal pipe, and phosphor bronze or stainless steel can be used. Further, it may be a non-metallic pipe, and fluororesin or quartz glass can be used. The metal or non-metal pipe may have a configuration in which a metal thin film made of another metal material is provided on the inner wall, and gold, silver, molybdenum, or nickel may be coated as the metal thin film. In addition, visible light and infrared light having a wavelength of 2 μm or more can be superimposed or switched on the hollow waveguide thus configured, that is, a region surrounded by the tubular member. In addition, air, nitrogen, or carbon dioxide gas can be inserted into the hollow region of the tubular member.

  Since the hollow waveguide of the present invention has a low water absorption of 0.01% or less as the water absorption of the cyclic olefin polymer used as the dielectric thin film, the transmission loss when transmitting infrared laser light is small. Even at an oscillation wavelength of 2.94 μm of the Er-YAG laser, an increase in transmission loss of the waveguide due to moisture adsorption can be prevented.

  FIG. 1 shows a hollow waveguide 1 according to an embodiment of the present invention, in which a dielectric layer 3 made of a cyclic olefin polymer is formed on the inner wall of a metal pipe 2 and a hollow region 4 provided inside the dielectric layer 3. Have.

  The laser light entering the hollow waveguide 1 is propagated by repeating reflection at the boundary between the hollow region 4 and the dielectric layer 3 and at the boundary between the dielectric layer 3 and the metal pipe 2. In general, a metal material has a large absorption characteristic of laser light transmitted through a waveguide, so that laser energy does not penetrate deeply into the metal layer. Therefore, optically, it is sufficient that the thickness of the metal layer in contact with the dielectric layer 3B is not less than the skin depth.

  The metal pipe 2 is not only optically involved in transmission characteristics but also maintains the mechanical strength of the hollow waveguide 1. As the metal in contact with the dielectric layer 3, for example, the higher the complex refractive index, such as silver or gold, the lower the loss. While effective for reducing the loss of the waveguide, it is not practical considering economic and mechanical characteristics.

  Further, as the metal pipe 2, an inexpensive and thick metal pipe having a metal film made of another metal material on the inner wall may be used. Satisfying these conditions include phosphor bronze pipes with high thermal conductivity and excellent mechanical bending properties, and stainless steel pipes that can be obtained inexpensively with chemically stable and low inner wall surface roughness. There is. As the metal film formed on the inner wall of these metal pipes, gold, silver, copper having a particularly large absolute value of the complex refractive index, or molybdenum that is hard and hardly scratches is preferable.

Cyclic olefin polymers are transparent in a wide range from the ultraviolet region to the infrared region with a low refractive index. In the present invention, in particular, an amorphous cyclic olefin polymer using norbornene, dicyclopentadiene, or tetracyclododecene as a raw material is used. Such a cyclic olefin polymer has an absorption peak specific to the material in the infrared wavelength band, but exists discretely with respect to the wavelength. For example, an Er-YAG laser, a CO laser, a CO ₂ laser, etc. The oscillation wavelength of the laser light source, which is important, can be avoided.

  The cyclic olefin polymer has a larger absorption coefficient than germanium, zinc sulfide, and the like other than the wavelength band having the absorption peak specific to the material in the infrared region. However, unlike a solid optical fiber, the hollow waveguide concentrates most of the transmitted laser energy in the lossless hollow region 4 and is only slightly absorbed by the dielectric layer 3. The influence of a slight absorption loss on the transmission loss of the waveguide is extremely small.

  In the dielectric-incorporated metal hollow waveguide, the transmission loss is smaller as the refractive index of the dielectric thin film to be embedded is closer to √2. Since the refractive index of the cyclic olefin polymer material is about 1.45 to 1.55, a low-loss waveguide can be formed, and the allowable film thickness range of the thin film to be built is widened, so that the manufacture is facilitated.

  The cyclic olefin polymer has a higher heat resistance temperature than polymethyl methacrylate, which is widely used as an optical polymer, and the glass transition point of the polymethyl methacrylate is about 105 ° C., whereas the glass transition point of the cyclic olefin polymer is About 140 ° C. As described above, the laser energy propagating in the interior dielectric layer is small, but all absorbed laser energy is converted into thermal energy. Sex is an important property.

  Further, the water absorption rate of the cyclic olefin polymer is 0.01% or less, and the water absorption rate is lower than that of polycarbonate or polymethyl methacrylate of 0.2% or more. Transmission loss is small. In particular, since the oscillation wavelength of 2.94 μm of the Er-YAG laser coincides with the wavelength of the maximum absorption peak of the laser beam by water, the transmission loss of the waveguide increases due to the slight water content.

  In the hollow waveguide 1 of FIG. 1, a non-metal pipe coated with a metal film may be used instead of the metal pipe 2. As this non-metallic pipe, a fluororesin pipe or a quartz glass pipe is particularly preferable. The fluororesin pipe is excellent in flexibility and chemical resistance, the quartz glass pipe is excellent in heat resistance and chemical resistance, and the surface roughness of the inner wall is extremely small, so that transmission loss can be reduced. The mechanical strength of the glass pipe can be dramatically improved by applying a resin to the outer surface of the glass pipe.

  As the metal film to be coated on the inner wall of the non-metallic pipe described above, gold, silver, copper having a particularly large absolute value of the complex refractive index or molybdenum that is hard and hardly scratched is preferable as described above. Optically, these metal films are sufficient, but for example, the adhesion of the metal film can be enhanced by interposing a nickel layer between the non-metal pipe and these metal films. This nickel layer can be easily formed by flowing an electroless nickel plating solution into and discharging the non-metallic pipe.

  In the present invention, the thickness of the metal film coated on the inner wall of the metal pipe 2 is set to 50 μm or less. The thickness of the metal film is sufficient if it is equal to or greater than the skin depth.

  The hollow waveguide 1 can transmit visible light such as a He—Ne laser superimposed or switched inside. This is effective for safely irradiating an object with invisible laser light. In addition, a gas such as dried air, nitrogen, or carbon dioxide can be inserted into the waveguide. These dry gases not only prevent the entry of dust and moisture into the waveguide, but also cool the waveguide that generates heat based on the absorption of laser energy. When used in the medical field, it is necessary to inject the above-mentioned gas simultaneously with the irradiation of the laser beam to the affected area, and these gases can be introduced using the hollow structure of the waveguide.

  FIG. 2 shows an apparatus for manufacturing the hollow waveguide 1, and is composed of a cyclic olefin polymer coating apparatus shown in FIG. 2 (a) and a cyclic olefin polymer drying apparatus shown in FIG. 2 (b).

  The cyclic olefin polymer coating apparatus includes an injection container 13 containing a solution 14 in which an amorphous cyclic olefin polymer is dissolved in mesitylene, and an injection side pipe 17a connected to one end of a pipe 15 serving as a waveguide via a joint 18. The discharge pipe 17b is connected to the other end of the pipe 15 via the joint 18, and the liquid injection pump 16 is connected to the discharge pipe 17b.

  The solvent 14 is constituted by dissolving an amorphous cyclic olefin polymer in mesitylene or cyclohexane, and the concentration (solid content) is set to 8 to 10%. The pipe 15 is a quartz capillary having an inner diameter of 700 μm and an outer diameter of 800 μm, and an inner wall is coated with a silver thin film, and is wound in a coil shape in order to cope with an increase in length.

  The cyclic olefin polymer drying apparatus includes an electric furnace 19 that heat-treats the pipe 15 into which the polymer solution is injected, a vacuum pump 20 that reduces the internal pressure of the pipe 15, and a flow meter 21 that displays the flow rate of the gas inserted through the pipe 15. And pipes 22a, 22b, and 22c for connecting the pipe 15, the vacuum pump 20, and the flow meter 21.

  The dielectric interior process will be described below. First, the pipe 15 and the injection side pipe 17 a and the pipe 15 and the discharge side pipe 17 b are connected by the joint 18. Then, the tip of the injection side pipe 17 a is immersed in the solution 14 accommodated in the injection container 13, and the discharge side pipe 17 b is connected to the liquid injection pump 16.

  In this state, when the liquid injection pump 16 is operated, the solution 14 is sucked into the pipe 15 from the injection side pipe 17a, and the solution 14 is filled and discharged into the pipe 15, and a certain amount of solution is discharged to the inner wall of the pipe 15. 14 is applied.

  Next, the pipe 15 having the inner wall coated with the solution 14 is placed in an electric furnace 19, and the vacuum pump 20 is connected to one end via a pipe 22a, and the flow meter 21 is connected to the other end via a pipe 22b. Then, by heating the electric furnace 19 to a predetermined temperature, the mesitylene in the solution 14 is evaporated, and the cyclic olefin polymer is dried and solidified. Since the boiling point of mesitylene is 165 ° C., the heating temperature is set to a higher temperature.

At this time, a dry gas such as N ₂ gas or He gas is inserted into the pipe 15 so that the mesitylene is sufficiently dried. This dry gas is inserted through a pipe 22 c connected to the flow meter 21, and the flow rate is controlled based on the pointer of the flow meter 21. Thus, the application | coating process of the solution 14 and a drying process are performed repeatedly until the thin film of the cyclic olefin polymer built in the pipe 15 is built in desired thickness.

  When the thin film of the cyclic olefin polymer is loaded to a desired thickness, the temperature of the electric furnace 19 is set to 200 ° C., and the pipe 15 is heated for about 1 hour to be completely dried.

  In FIG. 2A, an injection pump is used as a method for applying the polymer solution, but the application method is not limited to this. For example, it is possible to immerse the capillary in the solution, then pull it up, and apply the uniform solution to the inner wall of the capillary using the gravity of the solution.

  FIG. 3 shows the loss-wavelength characteristics of a dielectric-incorporated metal hollow waveguide composed of a cyclic olefin polymer and a silver layer, and also shows the characteristics of a silver hollow waveguide that does not have a cyclic olefin polymer layer as a comparative example. Yes. The length of the waveguide is 1 m, and the inner diameter of the waveguide is 700 μm. The cyclic olefin polymer layer of the dielectric-embedded metal hollow waveguide is about 0.5 μm. As is apparent from the figure, it can be seen that the dielectric-incorporated metal hollow waveguide has a low loss in the vicinity of a wavelength of 5 μm and is suitable as a waveguide for CO laser light transmission that oscillates at a wavelength of 5.3 μm. The transmission loss of this dielectric-incorporated metal hollow waveguide depends on the film thickness of the dielectric inside, and the optimum film thickness is determined by the wavelength of the laser beam to be transmitted.

When a laser other than a CO laser, such as an Er-YAG laser, is used as the laser light source, it is necessary to set the film thickness of the cyclic olefin polymer to about 0.25 μm. In this case, the minimum loss wavelength of the waveguide Shifts to the short wavelength side and has a low loss in the vicinity of the oscillation wavelength of 2.94 μm of the Er-YAG laser. On the other hand, if laser light having a longer oscillation wavelength is transmitted, such as a CO ₂ laser having a longer oscillation wavelength, the film thickness of the cyclic olefin polymer to be incorporated must be set larger. Thus, a low-loss waveguide can be realized by appropriately setting the film thickness of the cyclic olefin polymer based on the oscillation wavelength of the laser light. The film thickness of the cyclic olefin polymer can be easily controlled in the manufacturing process of the hollow waveguide 1 by the solid content of the cyclic olefin polymer solution, the coating speed, the number of coatings, and the like.

  The cyclic olefin polymer used in the embodiment of the present invention has absorption loss inherent to the material in the infrared region. As is clear from FIG. 3, there is an absorption peak that appears to be caused by the CH group in the vicinity of a wavelength of 3.4 μm. In such a wavelength band where the absorption peak is large, a dielectric thin film is incorporated. However, the loss reduction of the waveguide cannot be realized.

On the other hand, no large absorption peak is observed in the oscillation wavelength bands of Er-YAG laser, CO laser, and CO ₂ laser, which are practically important light sources in the infrared region, and 2.94 μm, 5 μm, and 10.6 μm. Compared with a hollow waveguide, the loss of the waveguide can be reduced by incorporating a cyclic olefin polymer. By appropriately setting the film thickness of the dielectric layer made of cyclic olefin polymer material in this way with respect to the wavelength, low loss can be achieved over a wide wavelength range from ultraviolet to infrared, excluding the wavelength of the absorption peak unique to the material. A waveguide can be realized.

  As described above, much of the light transmitted through the waveguide propagates through the hollow region, but when the light propagates through the waveguide, the amount of light absorbed by the dielectric layer made of the cyclic olefin polymer material is Since it is slight, optical transmission can be performed with low loss, and excellent flexibility can be imparted by applying it to the meridian waveguide.

  In addition, a cyclic olefin polymer solution dissolved with a solvent flows into the hollow metal waveguide, and after discharging it, it is dried and solidified to easily form a dielectric layer of the cyclic olefin polymer on the inner wall of the metal waveguide. Can be decorated. The thickness of the dielectric layer can be arbitrarily and accurately controlled by the manufacturing conditions such as the number of filling, discharging and drying steps, the viscosity of the solution, the solid content, and the coating speed. In addition, this manufacturing method does not require an expensive manufacturing apparatus and can be applied to manufacturing a thin waveguide having excellent flexibility, and the length of the waveguide does not depend on the manufacturing apparatus, so that the length is increased. You can also.

It is explanatory drawing which shows the hollow waveguide of this invention. It is explanatory drawing which shows the coating device of (a) and a cyclic olefin polymer. (B) It is explanatory drawing which shows the drying apparatus of a cyclic olefin polymer. It is explanatory drawing which shows the transmission loss characteristic of a hollow waveguide.

Explanation of symbols

1, hollow waveguide 2, metal pipe 3, dielectric layer 4, hollow region 13, injection container 14, solution 15, pipe 16, injection pump 17a, injection side pipe 17b, discharge side pipe 18, joint 19, electric furnace 20, vacuum pump 21, flow meters 22a, 22b, 22c, piping

Claims (14)

A tubular member constituting a waveguide;
A dielectric thin film made of a cyclic olefin polymer that is embedded in the inner wall of the tubular member and is transparent in the ultraviolet region or in the wavelength region of the infrared region having a wavelength of 2 μm or more ,
And the hollow waveguide characterized by the water absorption being 0.01% or less.   The hollow waveguide according to claim 1, wherein the cyclic olefin polymer is an amorphous cyclic olefin polymer based on a heat treatment of a polymer solution using norbornene, dicyclopentadiene, or tetracyclododecene as a raw material.   The hollow waveguide according to claim 1, wherein the tubular member is a metal pipe.   The hollow waveguide according to claim 3, wherein the metal pipe is made of phosphor bronze or stainless steel.   The hollow waveguide according to any one of claims 3 and 4, wherein the metal pipe is provided with a metal thin film made of another metal material on an inner wall.   The hollow waveguide according to claim 5, wherein the metal thin film is made of gold, silver, molybdenum, or nickel.   The hollow waveguide according to claim 1, wherein the tubular member is a non-metallic pipe.   The hollow waveguide according to claim 7, wherein the non-metallic pipe is provided with a metal thin film made of at least one layer of metal material on an inner wall.   The hollow waveguide according to claim 8, wherein the metal thin film is made of gold, silver, molybdenum, or nickel.   The hollow waveguide according to claim 7, wherein the non-metallic pipe is made of fluororesin or quartz glass.   2. The hollow waveguide according to claim 1, wherein the hollow region surrounded by the tubular member is configured to superimpose or switch incident visible light and infrared light having a wavelength of 2 μm or more.   The hollow waveguide according to claim 1, wherein the hollow region surrounded by the tubular member is configured to allow air, nitrogen, or carbon dioxide gas to pass therethrough. A laser light transmission method comprising transmitting a laser beam in an infrared wavelength band having a wavelength of 2 μm or more from a laser light source through the hollow waveguide according to claim 1. A laser light transmission device comprising: a laser light source that oscillates laser light in an infrared wavelength band having a wavelength of 2 μm or more; and the hollow waveguide according to claim 1.

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