JP2019096655A - Optical transmission device - Google Patents

Abstract

To provide an optical transmission device capable of solving a problem a risk of fiber burnout when multiple light sources are included, since laser light with high focusing intensity is radiated to the incident end face of the fiber at the time when focusing the light on a fiber with a small core diameter.SOLUTION: The optical transmission device includes: a plurality of laser light sources; a coupling fiber for coupling light from the laser light sources; a set of focusing optics for focusing the light from laser light sources to the coupling fiber; a transmission fiber for transmitting the coupled light; and a set of focusing optics for focusing the light emitted from the coupling fiber to enter into the transmission fiber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical transmission apparatus which condenses laser light on an optical fiber and transmits it.

  In recent years, techniques for transmitting high-power laser light to an optical fiber for processing are widely accepted. Among them, with the increase in efficiency and output of a laser diode (hereinafter referred to as LD), there is a demand for a technology for using light from the LD directly for processing.

  An example of the prior art for this problem will be described with reference to the drawings. FIG. 8 is a block diagram of a multiplexing apparatus according to the prior art.

  The laser beams 21 to 27 emitted from the LDs 1 to 7 arrayed and fixed on the heat block 10 are condensed and incident on the multimode optical fiber 30 by the condensing lens 20. In the condenser lens 20, the collimator lens part and the condenser lens part are integrally formed from a common member, and by installing the respective LDs 1 to 7 at predetermined positions, optical paths B1 to B7 are formed, and It is coupled to the core 30a. As a result, laser light in which the outputs of the LDs 1 to 7 are summed is emitted from the optical fiber 30, and it is possible to irradiate high-power laser light from a single fiber (see, for example, Patent Document 1).

Patent No. 4213402

  However, in the conventional optical transmission device, the core diameter of the fiber for multiplexing the laser light and the core diameter of the fiber for transmitting the laser light to be used finally are the same, so the numerical aperture (NA Optical (Numerical Aperture) can not be coupled to the fiber.

  In addition, very delicate adjustment is required, and the adjustment is further complicated when a plurality of light sources are provided. In addition, at the time of focusing on a fiber with a small core diameter, a laser beam having a high focusing intensity is irradiated to the incident end face of the fiber, so the risk of burning out of the fiber becomes a problem.

  An object of the present invention is to solve the above problems and to provide an optical transmission apparatus which multiplexes multiple light sources and reduces the risk at the time of focusing on a fiber.

In order to solve the above-mentioned subject, the optical transmission device concerning the present invention is a plurality of laser light sources,
A combining fiber for combining light, a lens for condensing and entering the light from the laser light source onto the combining fiber, a transmission fiber for transmitting the combined light, and a combining fiber And a lens for condensing and entering the light into the transmission optical fiber.
It is preferable to use a fiber that has a sufficient degree of light concentration conditions as the coupling fiber compared to the transmission fiber. Further, it is preferable that at least one of the core diameter and the incident NA of the multiplexing fiber and the transmission fiber be different.

  According to the above-described configuration, the light transmission device according to the present invention can reduce the risk of burnout at the time of focusing on a fiber.

Configuration diagram of an optical transmission apparatus according to an embodiment of the present invention Laser light propagation diagram until the light emitted from the laser light source is incident on the multiplexing fiber Laser light propagation diagram until the outermost propagation component of the light emitted from the laser light source is incident on the multiplexing fiber Explanatory drawing when a laser beam injects into the fiber for multiplexing from a laser light source Explanatory view when laser light is emitted from the multiplexing fiber Propagation of laser light from the multiplexing fiber to the transmission fiber Explanatory view when laser light is emitted from the transmission fiber Configuration diagram of the laser beam multiplexing apparatus in the prior art

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same components are denoted by the same reference numerals, and the description may be omitted. Further, the X-axis, the Y-axis and the Z-axis shown in the drawing are directions orthogonal to each other. Here, the Y-axis is the vertical direction corresponding to the upper and lower sides, and the coordinate axes of each drawing are drawn so as to correspond to the directions of the respective fields of view.

Embodiment 1
FIG. 1 is a schematic diagram of an optical transmission apparatus according to an embodiment of the present invention. The optical transmission apparatus includes a transmission fiber 107 selected to obtain a prescribed laser output characteristic, a multiplexing fiber 104 having a greater tolerance in incident light characteristics than the transmission fiber 107, and a multiplexing fiber 104. The condensing lens 106 for coupling the emitted light 105 to the transmission fiber 107, and the laser output unit 109 which is an optical system that condenses and causes a plurality of light sources to be incident on the multiplexing fiber 104.

  In FIG. 1, the laser light sources 100a and 100b are limited only by the laser characteristics to be finally used, and may be a laser light source provided with a semiconductor laser or a gain medium. Also, multi-mode lasers and laser light sources having different wavelengths can be applied, and the laser light sources 100a and 100b can be combined even if they have different characteristics.

  In an optical fiber, multiplexing can be performed regardless of ion doping. When ion-doped one is used, it can be used for wavelength conversion or amplifier, and by installing a polarization control element or a mode control mechanism between the multiplexing fiber 104 and the transmission fiber 107, tuning can be performed. It can also be expected to be used in application fields using a pulse laser.

  In the present embodiment, two laser light sources are installed in the laser output unit 109, and a circular multimode laser with the same wavelength of 1 μm and BPP (Beam Parameter Products) = 4 mm · mrad is output at 1 kW. The coupling fiber 104 has a core diameter of 200 μm, a numerical aperture NAc = 0.3, and the transmission fiber 107 has a core diameter of 100 μm, and a numerical aperture NAt = 0.2, both of which are silica fibers without ion doping.

The laser light emitted from the laser light sources 100 a and 100 b is propagated as parallel light by passing through the respective collimating lenses 102 a and 102 b, and is condensed and incident on the multiplexing fiber 104 by the condensing lens 103. The laser beams are multiplexed in the multiplexing fiber 104. By looping the fibers at this time, multiplexing can be performed with a short fiber length.

  The combined outgoing light 105 is emitted from the multiplexing fiber 104 with a single optical axis, and is condensed and incident on the transmission fiber 107 by the condensing lens 106. The light propagating through the transmission fiber 107 is output as the outgoing light 108, and basically the same as the output sum value of the laser light sources 100a and 100b except for the absorption loss by the fiber and the energy transition to the higher mode. Beam quality can be obtained.

  Next, the details of each part will be described.

  FIG. 2 shows a laser light propagation diagram until the laser light emitted from the laser light sources 100 a and 100 b is incident on the multiplexing fiber 104.

  The incident beam diameter of the laser light emitted from the laser light sources 100a and 100b to the condensing lens 103 is D1, the incident condensing diameter to the multiplexing fiber 104 is dc, and the condensing lens 103 to the multiplexing fiber 104 Assuming that the focal length of f is f1, these relational expressions are expressed as (Expression 1).

    dc = (4 · f1 / D1) × BPP (1)

  Since multimode laser light is used, the incident condensing diameter dc is set to 100 μm and focal length f1 of the condensing lens 103 is set to 100 mm in order to reduce the risk of burnout to the multiplexing fiber 104. 1) It can be seen that the incident beam diameter D1 to the condenser lens needs to be set to 16 mm.

  In addition, in order for all the laser light incident in the fiber to propagate, it is necessary to satisfy the specified NA (Numerical Aperture) of the fiber, and if the conditions are satisfied, the inter-beam distance L1 can be set arbitrarily and three or more It is also possible to combine the light from the light sources of

  FIG. 3 shows a laser light propagation diagram until the outermost propagation component of the emitted light 101 a from the laser light source 100 a is incident on the multiplexing fiber 104.

  The vertical axis between the incident end face of the multiplexing fiber 104 and the angle formed by the incident light to the multiplexing fiber 104 is θ1, and the outermost allowable component 110a of the incident permissible outermost portion 110 of the multiplexing fiber 104 and the emitted light 101a Assuming that the distance of parallel propagation of xt is xt1, Equation 2 is derived from the calculation of geometrical optics.

    tan θ1 ≧ xt1 / f1 (2)

  In this embodiment, since θ1 = arcSin (NAc), it can be understood that the distance xt1 in parallel propagation should satisfy xt1 ≦ 29 mm. Therefore, what has an effective diameter of the condensing lens 103 up to 58 mm may be selected.

  FIG. 4 shows a state when laser light is incident on the multiplexing fiber 104, and FIG. 5 shows a state when laser light is emitted from the multiplexing fiber 104.

In FIG. 4, the outgoing lights 101a and 101b from the laser light sources 100a and 100b to be incident on the multiplexing fiber 104 are focused at 100 μm which is half the core diameter of 200 μm of the multiplexing fiber 104. This is to prevent the tail portion of the intensity distribution of the laser light from damaging the cladding 113.

  In FIG. 5, the laser light multiplexed in the fiber is emitted as the emitted light 105 from the core 112 of the multiplexing fiber 104 as light having a single optical axis. The output is represented by the relationship of (Equation 3) because the sum of the laser light sources 100a and 100b is obtained and BPP is stored.

    BPP = θ2 · w (3)

  θ2 is the spread angle of light emitted from the multiplexing fiber 104, w is the beam waist radius, and when the laser intensity is spread uniformly in the fiber, light is emitted from the entire core and the core diameter is 200 μm Therefore, the diameter (2 · W) of the beam waist is also 200 μm.

  It can be understood from (Equation 3) that an outgoing characteristic of 2.3 ° (NA = 0.04) can be obtained for the spread angle θ2 of the outgoing light 105.

  The shorter the fiber, the lower the light attenuation, but there is a possibility that the NA will not be completely multiplexed and the NA will be different for each emission mode. Therefore, it is necessary to loop the fiber, or to arrange it by intentionally curving, so that the laser light propagates through the entire core of the fiber.

  FIG. 6 shows a propagation diagram of laser light from the multiplexing fiber 104 to the transmission fiber 107. The transmission fiber 107 has a core 116 and a cladding 117.

  The light 114 emitted from the multiplexing fiber 104 is set to an arbitrary condensing diameter by the condensing lens 106 and coupled to the transmission fiber 107. Assuming that the focal length of the lens at this time is f2, the distance between the multiplexing fiber 104 and the focusing lens 106 is L2, and the distance between the focusing lens 106 and the transmission fiber 107 is L3 (Equation 4) Shown in the relationship.

    1 / L2 + 1 / L3 = 1 / f2 (4)

  Further, the relationship of the imaging system can be expressed by Equation 5 using the outgoing beam diameter d2 from the multiplexing fiber 104 and the condensed incident diameter d3 on the transmission fiber 107.

    d3 / d2 = L3 / L2 (5)

  In the present embodiment, in order to reduce the risk of burnout at the time of incidence on the transmission fiber 107, the imaging ratio is set to 1/3, and the focusing diameter d3 is set to 67 μm. At that time, in addition to L2 being three times L3, in consideration of the fact that the incident NA to the transmission fiber 107 needs to satisfy NAt = 0.2 (incident angle 11.5 °), The lens 106 is selected. It is shown that the equation (6) should be satisfied for the incident beam diameter to the condenser lens 106 using calculation of geometrical optics as in the case of incidence to the coupling fiber 104.

    L 3 · tan 11.5 ° ≦ L 2 · tan 2.3 ° (6)

  For the condenser lens 106 of the present embodiment, for example, f2 = 40 mm, which has an effective diameter larger than L2 · tan 2.3 ° and satisfies (Expression 4) to (Expression 6) regarding the focal length, can be selected.

FIG. 7 shows the state of light emitted from the transmission fiber 107. As shown in FIG. The light propagating through the transmission fiber 107 is such that the light having a single optical axis is incident on the multiplexing fiber 104, so the light 108 emitted from the transmission fiber 107 also has a single optical axis. Is output. At that time, since the beam quality is preserved, BPP = 4 mm · mrad does not change, and is expressed by (Expression 7) as in (Expression 3).

    BPP = θ3 · Wout (7)

  However, depending on how the transmission fiber 107 is disposed, the beam waist radius Wout at the time of emission may be small, and the spread angle θ3 may be large. When used for processing, there is a movement of the output end face of the transmission fiber 107, and there is a possibility that the spread angle may change with each movement. Since the change of the spread angle affects the power density of the processing point, it is necessary to make a loop or to intentionally arrange in a curve, like the multiplexing fiber.

  The outgoing light 108 basically has a total value 2 kW of the output values of the laser light sources 100a and 100b, but it is necessary to consider the loss of the fiber. Since the loss of a 1 μm band laser of a general silica fiber is about 0.5 dB / km and the loss due to an optical element is about 3%, the total loss is considered to be about 10% when the fiber length is 10 m.

  As described above, according to the light transmission device of the present embodiment, the light emitted from the laser light sources 100a and 100b is propagated as parallel light by passing through the collimator lenses 102a and 102b, and the light collecting lens By 103, the light is condensed and incident on the multiplexing fiber 104 with a low risk of burnout at the time of condensing incidence, and is emitted as light having a single optical axis along with the propagation in the multiplexing fiber 104. The light emitted from the multiplexing fiber 104 is condensed and incident on the transmission fiber 107 by the condensing lens 106, and the output sum value of the input light is obtained.

  In the present embodiment, two multi-mode laser light sources are used, and a multimode non-doped fiber is used for both the multiplexing fiber and the transmission fiber. However, the laser light source is not limited to the multiplexing fiber. It is possible to use the number and the incidence method as long as the incident NA of In addition, it is also possible to obtain high-power output light by combining multiple times.

  Further, as to the laser light source, there is no limitation in wavelength, mode, shape, beam quality and the like, and the present invention can be applied to laser light of any characteristics, and the wavelength characteristics and beam quality of each light source are different. But it can also be used. Also in the fiber, an arbitrary one can be used regardless of the material or the core form of the fiber, and it can be used as an amplifier by using the doped fiber.

  In addition, since it is possible to perform mode control by inserting a polarization control element or an aperture before the incidence of any of the fibers, the generation mechanism of the ultrashort pulse laser instead of using only for the CW laser It can also be used as an amplification mechanism.

  The light transmission device according to the present invention is useful in a laser processing machine, a laser welding machine, etc. because it combines and emits light from a plurality of light sources with a low risk of burnout.

100a, 100b Laser light source 101a, 101b Emitted light 102a, 102b Collimator lens 103, 106 Condensing lens 104 Coupling fiber 105, 108 Emitting light 107 Transmission fiber 109 Laser output part 112, 116 Core 113, 117 Clad

Claims (3)

With multiple laser light sources,
A multiplexing fiber for multiplexing light from the laser light source;
A condensing optical system that condenses and makes light from the laser light source incident on the multiplexing fiber;
A transmission fiber for transmitting the multiplexed light;
An optical transmission device, comprising: a condensing optical system that condenses and makes light emitted from the multiplexing fiber enter the transmission fiber. The optical transmission device according to claim 1, wherein the multiplexing fiber is a fiber having a sufficient light concentration condition compared to the transmission fiber. The optical transmission device according to claim 1, wherein the multiplexing fiber and the transmission fiber have different core diameters or numerical apertures, or both of the core diameter and the numerical aperture.

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