JPH0668006U - Optical fiber end face protector for high power lasers - Google Patents

Abstract

(57) [Abstract] [Purpose] An optical fiber end face protector for high-power lasers that prevents burnout of the optical fiber due to fluctuations in the focus position of the laser beam and prevents reflected light from entering the laser oscillator. provide. [Structure] At least the clad part 12 is provided on the end face of the optical fiber 10 having the core part 11 and the clad part 12.
Is provided to prevent heat loss of the cladding 12 due to laser beam irradiation. The protection member 1 is composed of four segments 1a to 1d, and each segment 1
Thermocouples 4a to 4d are provided on a to 1d. The protective member 1 has a tapered surface 2 extending from the opening 5 in a substantially conical shape.
Is provided to prevent reflected light from entering the laser oscillator. A highly reflective film is formed on the tapered surface 2 and the contact surface 8 between the protective member 1 and the optical fiber 10 to prevent a temperature rise due to laser beam irradiation.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an end face protection device used for protecting an end face of an optical fiber when a high power laser beam for laser processing is incident on the optical fiber.

[0002]

[Prior art]

 In an apparatus for laser processing, an optical fiber is often used to supply laser light to a laser processing nozzle or the like. In the optical fiber for supplying the laser light, it is necessary to accurately focus the laser beam on the core portion of the end face so as not to cause energy loss.

However, when the laser beam is used for a long time, the light collecting position of the optical fiber may gradually deviate from the core portion and the cladding portion may be irradiated with the laser beam.

Particularly, this tendency is remarkable immediately after the start of using the laser beam. When such a change in the focusing position occurs, the energy of the laser beam for processing is very large, and therefore the end face of the optical fiber is burnt by heat.

In order to prevent such burnout, various attempts have been made so far as shown below. That is, (1) As shown in FIG. 5, by covering the periphery of the end of the optical fiber 50 having the core part 51 and the clad part 52 with a metal member 53 having high thermal conductivity, heat generated by laser beam irradiation is dissipated. (2) Preventing burnout due to temperature rise of the optical fiber by coating the surface of the cladding with a surface-protecting member with high thermal conductivity (JP-A-58-58). 13 9102, JP-A-58-138587), and the like are known.

[0006]

[Problems to be solved by the device]

 However, in the above configuration (1), the focus position of the laser beam B deviates from the optical axis X as shown by B ′ in FIG. 5, and the incident laser beam directly irradiates the cladding portion 52 and the metal member 53. In that case, the metal member 53 cannot dissipate the heat of the cladding portion 52, and the end face of the optical fiber is burnt. Further, in the configuration of FIG. 5, there is a problem that the reflected light from the metal member 53 enters the laser oscillator again and the characteristics of the laser light change.

Further, according to the configuration of (2), the effect of heat radiation of the surface protection member can be expected in a portion other than the end face of the optical fiber, but it is generated in the end face of the optical fiber due to the variation of the focusing position of the laser beam. Large amounts of heat cannot be removed.

The present invention has been made in order to solve such a conventional problem, and an object of the present invention is to condense a laser beam incident on an optical fiber at the end face of the optical fiber. By providing an optical fiber end face protection device for a high-power laser, which can prevent the burning of the optical fiber when the position deviates from the core part, and the reflected light does not re-enter the laser oscillator. is there.

[0009]

[Means for Solving the Problems]

The optical fiber end face protector for a high power laser according to the present invention is an optical fiber end face protector for a high power laser, which is provided with a protective member that covers at least the clad portion at the end face of the optical fiber that emits the laser beam. The protection member has an opening having a diameter d _o centered on the optical axis at the end face of the optical fiber and satisfying a relationship of d _c ≧ d _o with respect to a diameter d _c of the core portion of the optical fiber. And an opening angle of not less than 2θ determined by the numerical aperture NA of the optical fiber, and a substantially conical taper surface having a highly reflective film formed on the surface thereof.

A high reflection film may be formed on the contact surface of the protective member with the optical fiber.

The protection member may be composed of a plurality of segments arranged around the optical fiber, and a temperature sensor may be provided in each segment.

Further, the protective member may be provided with a cooling pipe for circulating a refrigerant.

[0013]

[Action]

The optical fiber end face protection device for a high power laser having the above structure is used for the end face of an optical fiber for guiding a high power laser beam for laser processing to a processing nozzle or the like. This end face protection device has a protective member for protecting the end face of the optical fiber, and this protective member covers at least the clad portion at the end face of the optical fiber. That is, the protective member has an opening around the at optical axis on the end face of the optical fiber, the diameter d _o of the opening portion, the diameter d _c of the core portion of the optical fiber, d _c The relationship of ≧ d _o is satisfied. With this configuration, even if the focus position of the laser beam changes, the laser beam does not directly irradiate the clad part of the optical fiber, and therefore, burnout due to heat of the optical fiber can be prevented. it can.

Further, the protection member has a substantially conical tapered surface that gradually opens from the above-mentioned opening to the light source side of the laser beam, and the opening angle 2α of this tapered surface is the numerical aperture of the optical fiber. The angle is set to be 2θ or more determined by NA. With this configuration, even when the focus position of the laser beam deviates from the predetermined position, the reflected light from the protective member does not enter the laser oscillator again and change the characteristics of the laser light.

Further, a highly reflective film made of, for example, Au, Ag, Cu, Al, Mo, a dielectric multilayer film, or the like is formed on the surface of the tapered surface. With this configuration, even if the focus position of the laser beam changes, the tapered surface reflects the laser beam that directly irradiates the laser beam, so that the temperature rise of the protective member is small and heat loss does not occur in the optical fiber.

It is known that when a laser beam enters the optical fiber at an angle larger than the angle 2θ determined by the numerical aperture NA, the laser beam leaks out from a portion relatively close to the end face of the optical fiber. When such leaked light is generated, burnout occurs at the end of the optical fiber. In order to prevent this burning, in the present invention, a highly reflective film made of Au, Ag, Cu, Al, Mo, a dielectric multi-layer film or the like is formed on the contact surface between the protective member and the optical fiber. ing. With this configuration, the light leaked at the end of the optical fiber is reflected by the highly reflective film, and the temperature rise of the protective member is prevented.

Further, by forming the protective member by a plurality of segments arranged around the optical fiber and providing a temperature sensor in each segment, it is possible to detect the variation direction of the condensing position of the laser beam. That is, when the focus position of the laser beam moves on the optical axis and the laser beam spot becomes large, it is detected as an increase in the detection temperature of all the segments. Further, when the focus position of the laser beam deviates from the optical axis, only some of the temperature sensors provided in each segment detect the temperature rise. In this case, the direction of the segment in which the temperature sensor detecting the high temperature is provided is the moving direction of the focus position of the laser beam.

Further, in the configuration in which the cooling pipe for circulating the refrigerant is provided in the protective member, the temperature rise of the protective member is suppressed even when the laser beam irradiates the protective member due to the variation of the focusing position of the laser beam. The heat loss of the optical fiber does not occur.

[0019]

【Example】

 Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

FIG. 1 shows a cross-sectional structure of an optical fiber end face protection device for a high power laser according to a first embodiment of the present invention. The end face protection device of this embodiment has a protective member 1 that covers the end of an optical fiber 10 having a core part 11 and a clad part 12. Quartz is used for the optical fiber 10 in which the device of this embodiment is used, and Cu having high thermal conductivity is used for the protective member 1. Further, the protective member 1 is provided with an opening 5, and the end face 10a of the optical fiber 10 fixed to the opening 5 is irradiated with the laser beam B condensed through the condenser lens 6. ing. In this embodiment, the center of the optical fiber 10 and its end face 10a and the center of the condenser lens 6 are located on the optical axis X.

FIG. 2 shows a plan view of the protection member 1 viewed from the light source side of the laser beam B. As shown in the figure, the protection member 1 is composed of four segments 1a, 1b, 1c and 1d. Between each of the segments 1a to 1d, a metal such as SUS which is a low heat conductive material, or ceramics is used. .. are sandwiched in between. Each separation layer 7 is bonded to the metal material forming each segment. Each of the segments 1a, 1b, 1c and 1d is provided with a temperature measuring hole 3a, 3b, 3c and 3d, and each of the temperature measuring holes 3a to 3d is provided with a thermocouple 4a, 4b, 4c and 4d as a temperature sensor. It is provided.

Further, as shown in FIG. 2, an opening 5 is formed in the center of the protective member 1, and the center of this opening 5 coincides with the optical axis X shown in FIG. Here, the diameter d _o of the opening portion 5, when the diameter of the core portion 11 of optical fiber 10 and d _c, is set so as to satisfy the relation d _c ≧ d _o. That is, the protective member 1 covers at least the clad portion 12 of the optical fiber 10 on the end face 10a of the optical fiber 10 and also covers the peripheral portion of the core portion 11.

Further, as shown in FIG. 1, the protective member 1 has a tapered surface 2 which spreads from the opening 5 to the side of the incident laser beam B in a substantially conical shape, and the opening angle 2 of the tapered surface 2 is increased. α, that is, the angle formed by the tapered surface 2 in the cross section of the protective member 1 cut along a plane including the optical axis X is set to be 2 ° or more determined by the numerical aperture NA (= Sinθ) of the optical fiber 10. Has been done. In the case of the optical fiber 10 made of quartz, NA = 0.2, and therefore the opening angle 2α is 2α ≧ 2θ = 23 °.

Further, in the present embodiment, the highly reflective film made of Au is formed on the tapered surface 2. Further, a highly reflective film made of Au is also formed on the contact surface 8 between the protective member 1 and the optical fiber 10.

On the end face of the optical fiber 10 to which the end face protective device of this embodiment is attached, a laser having a Gaussian (bell-bell) optical energy distribution with the highest light intensity at the central portion as shown in FIG. Beam B is incident. When the laser beam B is focused at the position where the end face 10a and the optical axis X intersect, almost all of the laser beam B enters the optical fiber 10. However, when the focus position of the laser beam B moves on the optical axis X, or when it further deviates from the optical axis X, the laser beam B irradiates the tapered surface 2 of the protective member 1.

In the present embodiment, since the protection member 1 covers at least the cladding portion 12 on the end face 10 a of the optical fiber 10, the laser beam B causes the laser beam B to change even if the focus position of the laser beam B changes. The cladding portion 12 is not directly irradiated, and the burning of the optical fiber 10 due to heat does not occur. Moreover, since the coating of Au on the tapered surface 2 reflects the laser beam, the temperature rise of the protective member 1 is small, and the heat loss of the optical fiber 10 due to the temperature rise of the protective member 1 does not occur.

Further, since the protective member 1 has the substantially conical tapered surface 2 having the opening angle 2α of 2θ or more, even when the converging position of the laser beam B is changed, the protective member 1 is removed from the tapered surface 2 1. The reflected light does not enter the laser oscillator again and does not change the characteristics of the laser light.

Further, by coating the contact surface 8 of the protective member 1 with the optical fiber 10 with Au, the contact between the protective member 1 and the optical fiber 10 caused by the laser beam incident at an angle larger than the angle 2θ. Even if there is light leaking from the surface, the temperature rise of the protective member 1 due to this light leak is suppressed.

Further, in this embodiment, the change of the focusing position of the laser beam B is detected by the thermocouples 4a to 4d provided in the temperature measuring holes 3a to 3d of the respective segments 1a to 1d constituting the protection member 1. be able to. That is, when the focus position of the laser beam B moves on the optical axis X, the spot on the end face 10a becomes large, so that the temperature rise is detected in all the thermocouples 4a to 4d. Further, when the focus position of the laser beam B deviates from the optical axis X, only some of the thermocouples 4a to 4d detect the temperature rise. In this case, the direction of the segment provided with the thermocouple detecting the high temperature is the moving direction of the focus position of the laser beam B. By feeding back the detection result to the optical system for adjusting the laser beam B, the incident laser beam can be always kept in an appropriate state.

Although the thermocouples 4a to 4d are used as the temperature sensors in the present embodiment, piezoelectric elements for detecting elastic waves accompanying temperature rise may be used instead of them.

FIG. 4 shows a schematic cross-sectional structure of an optical fiber end face protection device for a high power laser according to a second embodiment of the present invention. In the end face protection device of this embodiment, the protection member 21 is provided with the fiber attachment portion 23 for attaching the end portion of the optical fiber 10. The optical fiber 10 is fixed in the mounting hole 24 of the fiber mounting portion 23 with screws 29, 29. Further, in this embodiment, the protection member 21 is not divided into a plurality of segments as in the first embodiment described above, but is formed integrally. Further, the protection member 21 is formed with a cooling pipe 27 for circulating cooling water as a refrigerant.

The protective member 21 includes a focusing surface 26 having an opening angle substantially equal to the conical shape of the laser beam B focused by the focusing lens 28, and a tapered surface having an opening angle larger than the opening angle of the focusing surface 26. 22 and 22. Also in the present embodiment, the opening angle 2α of the tapered surface 22 is equal to or more than the angle 2θ determined by the numerical aperture NA of the optical fiber 10. The focusing surface 26 and the tapered surface 22 are coated with Au.

Further, an opening 25 is formed in the center of the converging surface 26 of the protection member 21.

The center of the opening 25 coincides with the optical axis X. Also in the present embodiment, the diameter d _o of the opening 25 satisfies the relationship of d _c ≧ d _o with the diameter d _c of the core portion 11 of the optical fiber 10.

In the present embodiment, the light whose focusing position of the laser beam B has changed and cannot enter the opening 25 is reflected by the tapered surface 22 before reaching the end surface 10a. Therefore, the laser beam B does not directly irradiate the clad portion 12 of the optical fiber 10, and burnout due to heat of the optical fiber 10 does not occur. Further, since the cooling water circulates in the cooling pipe 27, the temperature rise of the protective member 21 due to the laser beam irradiation is suppressed.

Further, since the opening angle 2α of the tapered surface 22 is 2θ or more, even when the focus position of the laser beam B is changed, the reflected light from the tapered surface 2 is incident on the laser oscillator again. It does not change the characteristics of laser light.

[0037]

[Effect of device]

 In the optical fiber end face protection device for a high-power laser according to the present invention, the clad part at the end face of the optical fiber is covered with the protective member, so that the laser beam can be emitted even if the focus position of the laser beam fluctuates. It does not directly irradiate the cladding of the fiber, thus preventing thermal loss of the optical fiber.

Further, since the protective member has a substantially conical taper surface having an opening angle of 2θ or more determined by the numerical aperture NA of the optical fiber, this taper is generated even if the converging position of the laser beam changes. The characteristic change of the laser beam due to the reflected light from the surface does not occur.

Further, since a highly reflective film is formed on the surface of the tapered surface and the laser beam directly incident on this tapered surface is reflected, heat loss of the optical fiber due to the temperature rise of the protective member does not occur. In addition to this, by forming a high-reflection film on the contact surface between the protective member and the optical fiber, even if there is light leaking from near the end face of the optical fiber, the temperature rise of the protective member due to this light leak. Can be prevented.

Further, in the optical fiber end face protection device for a high power laser according to the present invention, the protection member is composed of a plurality of segments arranged around the optical fiber, and the temperature sensor provided in each segment causes the laser beam It is possible to detect the direction of variation of the focus position. It is possible to provide a stable laser beam by feeding back the detection result to the optical system of the laser beam.

Further, in the structure in which the cooling pipe for circulating the refrigerant is formed in the protective member, the temperature rise of the protective member is suppressed even when the laser beam irradiates the protective member, so that the heat loss of the optical fiber is prevented. Can be prevented.

[Brief description of drawings]

FIG. 1 is a sectional view showing a schematic configuration of an optical fiber end face protection device for a high power laser according to an embodiment of the present invention.

FIG. 2 is a plan view of a protection member of the end face protection device of FIG. 1 viewed from a light source side of a laser beam B.

FIG. 3 is a diagram showing a light energy distribution of an incident laser beam.

FIG. 4 is a cross-sectional view showing a schematic configuration of an optical fiber end face protection device for a high power laser according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conventional optical fiber that is end face protected.

[Explanation of symbols]

 1, 21 ... Protecting member 1a-1d ... Segment 2, 22 ... Tapered surface 3a-3d ... Temperature measurement hole 4a-4d ... Thermocouple 5, 25 ... Opening part 8 ... Contact surface 10 ... Optical fiber 10a ... End surface 11 ... Core Part 12 ... Clad part 26 ... Focusing surface 27 ... Cooling pipe

Claims (4)

[Scope of utility model registration request] 1. An optical fiber end face protection device for a high-power laser, comprising a protective member for covering at least a clad portion on an end face of an optical fiber on which a laser beam is incident, wherein the protective member is a member of the optical fiber. _Determined by an aperture having a diameter d _o centering on the optical axis at the end face and satisfying the relationship of d _c ≧ d _{o with} respect to the diameter d _c of the core of the optical fiber, and the numerical aperture NA of the optical fiber An optical fiber end face protection device for a high power laser, which has an opening angle of 2 ° or more and a substantially conical tapered surface having a highly reflective film formed on the surface thereof. 2. The optical fiber end face protection device for a high power laser according to claim 1, wherein a high reflection film is formed on a contact surface of the protection member with the optical fiber. 3. The protection member is composed of a plurality of segments arranged around the optical fiber, and each segment is provided with a temperature sensor. Optical fiber end face protector for high power lasers. 4. A cooling pipe for circulating a refrigerant is provided in the protection member.
An optical fiber end face protector for the high power laser described.