JPH0255303A - Hollow optical waveguide and its production - Google Patents

Abstract

PURPOSE:To remove heating destruction due to coupling loss at an incident end and to transmit large power by forming the incident end of a hollow optical waveguide as a taper-like aperture having a specific expanding angle. CONSTITUTION:The expanding angle 2theta of the single end part of the hollow optical waveguide is formed as the taper-like aperture having the expanding angle 2theta=2lambda/Ka (0.4<=K<=0.65) (provided that 2a is the inner diameter of the hollow optical waveguide and lambda is the wavelength of a laser beam). In the case of producing the hollow optical waveguide, a conical body having a taper face with the expanding angle 2theta is heated and pressed against to the end part of a parent pipe 4 to form the optical waveguide. After forming a Ge dielectric thin film 7 and an external metallic layer 6 consisting of Ni or the like successively on the outside of the pipe 4, the pipe 4 is removed by etching. Since the incident end is shaped like a taper, the concentration of coupling loss can be suppressed and large power can be stably transmitted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hollow waveguide for transmitting optical power of a C02 laser or the like and a method for manufacturing the same.

[Conventional technology] Ch lasers, which can obtain high output with high efficiency, have begun to be used mainly for processing and medical purposes, and are also expanding their range of applications to isotope separation and gas concentration measurement. ,ing. However, compared to YAG lasers that can use low-loss, flexible silica-based optical fibers, CO2 lasers with a wavelength of 10.6 μI
In the case of two lasers, the unavailability of low-loss flexible waveguides has been a major obstacle in their application, and their realization has been long awaited. Currently, the most promising candidate is to coat the inner surface of the metal pipe with a dielectric material such as Ge or 2nSe, which has low loss in the 10.6 μl wavelength band, to increase the reflectance of the inner surface of the metal pipe and create a hollow This is a hollow metal waveguide with a dielectric interior that confines and transmits laser energy inside a pipe.

The method for manufacturing the waveguide will be explained below.

The base material pipe has a uniform outer diameter in the axial direction, and its material is A2 or polyimide. In the case of AQ, its outer surface must be mirror-finished using, for example, diamond base. Approximately 0.0% is applied to the outer surface of this base material pipe.
5μm thick Ge or about 0.8μm thick Zn5
e is formed by high frequency magnetron sputtering method. A metal thin film of Ag, Cu, Au, etc. is formed on the outer surface of this dielectric thin film. The thickness is equal to or greater than the skin depth at a wavelength of 10.6 .mu.l, and it is sufficient if it is approximately 300 .ANG. or greater.A Ni layer is formed on the surface of this metal thin film by bright plating in, for example, a Watt bath or a sulfamic acid bath. The thickness is determined from the mechanical strength of approximately 100
It is from μm to about 200 μm. Finally, the base material pipe is removed by etching to produce a dielectric-incorporated metal hollow waveguide.9 The etching solution contains about 10% Na in the case of M.
An OH solution or, in the case of polyimide, a mixture of hydrazine and ethylenediamine is used.

As shown in step 2, conventionally, to fabricate a dielectric-incorporated metal circular hollow waveguide, a dielectric and a metal layer are formed around a base material pipe, and the base material pipe is removed by etching or the like after I&.
The external method was used.

The base material pipe has a uniform outer shape in the axial direction,
Therefore! ! ! The inner shape of the remaining hollow waveguide is also axial.

It was like that.

[Problems to be solved by the invention] However, hollow waveguides fabricated using the conventional "external attachment method"
Since the internal shape of the waveguide is uniform in the transmission direction, mode confinement (1o
de conf 1nenent ) is different from that in air, coupling loss occurs, causing a concentrated heat generation temperature increase near the input end. Particularly in high power transmission, there was a risk that only the input end would be destroyed due to coupling loss.

An object of the present invention is to solve the problems of the prior art described above, eliminate local destruction of the waveguide due to coupling loss at the input end, and provide a structure of an optical power transmission device and a method for manufacturing the same, which can transmit large power. It's about doing.

[Means for Solving the Problems] A hollow optical waveguide of the present invention includes a dielectric thin film formed inside an external metal layer, and at least one end of the hollow optical waveguide has a divergence angle 2θ= 2λ, /Ka
r (0, 4≦K≦O, f35) However, 2a... The inner diameter of the hollow optical waveguide λ... It has a tapered aperture of the wavelength of the laser beam 9 As for its manufacturing method, In a method for manufacturing a hollow optical waveguide in which a dielectric thin film is formed inside at least an external metal layer, a divergence angle 2 θ = 2 λ, /Kar (0, 4≦K≦0.
65) However, 2a... Inner diameter of the hollow optical waveguide λ... A tapered surface of the wavelength of the laser beam is formed, a dielectric thin film is provided on the outside of the molded base material pipe, and an external metal layer is further provided on the outside of the formed base material pipe. After forming the base material pipe, the base material pipe is removed by etching.

The molded base material pipe itself may be formed by pressing a cone having a tapered surface with the spread angle 2θ against the heated end of the base material pipe, or by immersing the end of the base material pipe in a plating bath. However, a plating layer having a tapered surface with the spread angle 2θ may be formed by gradually slowing down the pulling speed during pulling.Furthermore, the end of the base material pipe may be placed in a plating bath. When repeating the dipping and pulling operations, the dipping region may be gradually limited to the tip, thereby forming a plating layer having a tapered surface with the spread angle 2θ.

[Function] The main point of the present invention is that in fabricating a hollow waveguide by the "external attaching method", one end of the base material pipe is set to the above-mentioned divergence angle 2θ=2.
λ, / K aπ is processed into a conical shape, and at the input end of the waveguide manufactured using this base material pipe, coupling with the incident laser beam is achieved by setting K = 0.4 to 0.65. Since the loss can be almost minimized, the mode confinement of the coupling part changes very slowly from the state in air, preventing the concentration of coupling loss at the input end of the hollow waveguide, and eliminating local destruction. <
L, this enables large power transmission.

For the base material pipe, materials such as ^Q, C++, Ni, polyimide, glass, etc. are used5.On the other hand, as the material for the cone for molding, the cone can be deformed even while heating the base material. To avoid any fear, it is preferable to use a material with a higher melting point than the base material.For example, when using 72 pipe (melting point 660°C) as the base material, the circle jif4c is C1'' (
melting point 1080℃), AU (melting point 960℃), Ni(
(melting point: 1455°C), etc. can be used.

Ge, 1nse, ZnS, etc. are used for the dielectric thin film, and Ni, Heg, Ct+, etc. are used for the metal layer. The dielectric thin film can be formed by sputtering, plating, or CVD.

[Example code] The illustrated embodiment will be described below.

Example 1 When fabricating a Ge/Ni hollow waveguide using 82 as the base material pipe, a CLI conical needle 3 having a conical body 1 and a support part 2 as shown in FIG. While rotating as shown in FIG. 2, the tip of the conical needle is pressed against one end of the AQHk material pipe 4 heated by the burner 5, and the one end is formed into a conical shape to form a tapered opening.

The shape of the conical body 1 of the conical needle 3 used here is as follows:
The inner conical shape of one end of the molded base material pipe 4 has a divergence angle 2θ=2λ, /Kar (0,4≦K≦0.65), however,
2a: Inner diameter λ of the hollow optical waveguide: A tapered aperture with the wavelength of the laser beam. That is, the same 2
It has a conical shape with a tapered surface of θ.

Next, using the molded base material pipe 4 thus obtained, a Ge dielectric film is formed on the outside by high frequency sputtering 1, and a metal layer is further formed by performing old plating. Next, the AQ, /Ge, /Ni pipes are immersed in caustic soda to etch only the AQ, /Ge, /Ni pipes. The Ge/Ni waveguide made in this way has a conical shape at one end as shown in Figure 3, and when coupled with a laser beam, the coupling loss is not concentrated near the input end, allowing high power transmission. 9 In general, the excitation efficiency of each mode excited in a circular hollow waveguide is determined by the ratio w of the waveguide radius a and the spot size W of the laser beam at the input end of the waveguide.
It varies greatly depending on 7/a. FIG. 5 shows the excitation efficiency of the HE mode excited in the circular hollow waveguide when a Gaussian beam is incident with no axis deviation in the lateral direction. As is clear from the figure, H of the circular hollow waveguide is generally
Among the E, modes, the mode with the lowest loss is the IIE mode, which is excited at maximum efficiency when w,/a=0.64.

Therefore, when you want the output beam to have a Gaussian distribution, or in a waveguide that is long enough to attenuate modes other than the HE mode, if the input beam satisfies w,/a = 0.64, then good. However, in relatively short waveguides or waveguides with low loss even in higher-order modes, such as waveguides intended for high power transmission, w, /a
If the beam diameter is smaller than 0.64, the power that protrudes outside the hollow region will be smaller, so the transmission capacity of the total power will be larger. The diameter is w7/a = 0.64 or less, generally 0.4
It is necessary to make f& suitable in the range of ~0.65. Furthermore, in order to maximize the excitation efficiency, the waveguide input end must be located at the beam waist of the light beam after passing through the lens, that is, the position where the spot size is the minimum value.

Although the pipe was heated in the above embodiment, a similar waveguide can be obtained by heating the conical needle without heating the pipe when forming the base material pipe.

Methods for creating the conical shape of the base material pipe include plating, casting, thermal spraying, cutting, etc. in addition to those described above.9 Example 2 Figure 4 is an example of plating, and 10 is a C, r electrode, 1
1 indicates a bathtub, and 12 indicates an electrolyte. Instead of using the conical needle of Example 1, one end of the AQ wire pipe 14 was closed with the sealing material 13 and immersed in the electrolytic solution (plating bath) 12 in the bath 11.
While pulling the base material pipe 14 through the connector 15 and using the pulley 9 for moving the sample up and down, and gradually slowing down the pulling speed, one end is plated with C and R in a conical shape of 20 mm, and the conical part 8 is plated. Forming 9 At that time, repeat the dipping and pulling up of one end of the base material pie 1. and a conical shape by gradually restricting the immersion area to the ends. Hereinafter, if this is used as a molded base material pipe and processed in the same manner, a hollow waveguide with characteristics similar to those of Example 1 can be obtained.9 Above Examples 1 and 2
In this example, only one end of the base material pipe was molded, but by making both ends conical instead of just one end, it is possible to obtain a hollow waveguide with low coupling loss (bidirectional low coupling loss) no matter which direction the incident beam is coupled. can.

Figure 6 shows the beam diameter of the incident beam W, /a=0.4~
This shows an example of a device that optimizes within the range of 0.65.
For convenience, the tapered state at the end of the optical waveguide is omitted.

A laser beam input optical system that uses at least a lens to input the laser beam emitted from the laser light source 22 into the hollow waveguide 21, and the lens L3 has a focal length M f
Laser light source 21! from 9 lenses L3 fixed on the laser light source 2 side from the hollow waveguide entrance end by 3! The l/lens L2 placed in the lens L2 and the lens L1 placed further on the side of the laser light source 2 from this lens L2 are 5 lenses whose positions can be varied by the moving stage of the pulse motor 3. The distance between the beam waist and the lens L1 is 745.9 1, depending on the change in +, Q+-f
l (EJ L, A I2 is L/7zu L+, distance 1 between 12, Q23 is distance to lenses L2 and L3, f+
I2 fa is lens L+, L2.

The focal length of L3 is automatically moved in the optical axis direction so as to maintain the following relationship. That is, when the beam diameter of the incident beam deviates from the optimum beam diameter, the distance Jt J + is changed.

This can be done by moving the laser light source 22, moving the hollow waveguide 21 and the entire incident optical system, or inserting a new appropriate lens on the laser light source 22 side of the lens L1, and adjusting the laser beam incident on the lens L1. The position of the waist may be changed, but in this case, the above equation must always be satisfied, and the pulse motor 3
7, change the position of lenses L+ and L2 9
The spot size of the beam 17 at the incident end of the hollow waveguide 1 is 0.4 to 0.6 of the waveguide radius of the hollow waveguide 1.
The beam diameter is varied so that it becomes 5 times as large.

By doing the following, the spot size of the incident beam can be changed arbitrarily over a wide range.92 Therefore, the spot size of the beam incident on the hollow waveguide 21 is set to i″1N.
7, efficient excitation is possible, and thermal damage to the input end can be suppressed, especially in waveguides for high power transmission.

[Effects of the Invention] As described above, according to the present invention, when optical power is transmitted through a hollow waveguide, local temperature rise at the coupling part and the resulting damage to the waveguide can be prevented, and large power can be transmitted. Stable transmission becomes possible. In other words, by making the input end of the base material pipe a conical waveguide whose mode confinement changes gradually with respect to the incident beam as described above, concentration of coupling loss can be avoided and loss can be guided.

Since it is dispersed throughout the wave path, damage to the input end due to heat due to coupling loss, which was a problem with conventional structures, is suppressed during large power transmission.

[Brief explanation of the drawing]

Fig. 1 is a side view of a conical needle used for forming the end of the base material pipe, Fig. 2 is a sectional view of the process of forming the end of the base material pipe using the conical needle, and Fig. 3 is a side view of a conical needle used for forming the end of the base material pipe. FIG. 4 is a perspective view of a hollow optical waveguide partially shown in the WI plane; FIG. 4 is a schematic diagram of forming a conical shape by plating the end of the base material; FIG.
The figure shows the excitation efficiency of the HE mode incident on the hollow waveguide, and FIG. 6 is a diagram illustrating the laser beam incidence optical system. In the figure, 1 is the CL1 cone, 2 is the support part, 3 is the conical needle, 4
is the base material ^ρ pipe, 5 is the burner, 6 is the old metal layer, 7 is Q
6 a dielectric layer, 8 a conical part formed by C plating, 9
10 is a Cr electrode, 11 is a bathtub,
12 is an electrolytic solution, and 13 is a sealing material. 14 is the base material ^ pipe, 15 is the connector. 9 Patent Applicant: Hitachi Cable Co., Ltd. Representative Patent Attorney Nobuo Kinutani Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1. In a hollow waveguide formed by forming a dielectric thin film inside an external metal layer, at least one end of the hollow optical waveguide has a divergence angle 2θ=2λ/Kaπ (0.4≦K≦ 0.65) However, 2
a: A hollow optical waveguide characterized by having a tapered aperture with an inner diameter λ of a wavelength of a laser beam. 2. In the manufacturing method of a hollow optical waveguide formed by forming a dielectric thin film inside an external metal layer, a spread angle 2θ=2λ/Kaπ (0.4≦K≦0.65) on the outer periphery of at least one end, provided that 2
a... Inner diameter of hollow optical waveguide λ... After providing a dielectric thin film on the outside of a molded base material pipe formed with a tapered surface of the wavelength of the laser beam, and further forming an external metal layer on the outside, A method for manufacturing a hollow optical waveguide, comprising removing the base material pipe by etching. 3. The method for manufacturing a hollow optical waveguide according to claim 2, wherein the molded base material pipe is formed by pressing a cone having a tapered surface with the spread angle of 2θ against an end of the heated base material pipe. 4. The formed base material pipe has a plating layer having a tapered surface with the spread angle 2θ by gradually slowing down the pulling speed when the end of the base material pipe is immersed in a plating bath and pulled up. 3. The method for manufacturing a hollow optical waveguide according to claim 2, wherein the hollow optical waveguide is formed by forming a hollow optical waveguide. 5. The formed base material pipe has the above-mentioned spread angle 2 by gradually limiting the immersion area to the tip when the end of the base material pipe is immersed in a plating bath and pulled up repeatedly.
3. The method of manufacturing a hollow optical waveguide according to claim 2, wherein a plating layer having a tapered surface of θ is formed.