JP7015989B2 - Optical transmission equipment - Google Patents

Description

The present invention relates to an optical transmission device that condenses and incidents laser light on an optical fiber and transmits it.

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

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 wave combiner according to the prior art.

The laser beams 21 to 27 emitted from the LDs 1 to 7 arranged and fixed on the heat block 10 are condensed and incident on the multimode optical fiber 30 by the condenser lens 20. In the condenser lens 20, the collimator lens portion and the condenser lens portion are integrally formed of a common member, and by installing each of the LDs 1 to 7 at a predetermined position, an optical path B1 to 7 is formed and the fiber is formed. It is coupled to the core 30a. As a result, the laser beam obtained by adding the outputs of the LDs 1 to 7 is emitted from the optical fiber 30, and it is possible to irradiate the high output laser beam from the single fiber (see, for example, Patent Document 1).

Japanese Patent No. 4213402

However, in the conventional optical transmission device, the numerical aperture (NA (NA)) required at the time of emission is required because the core diameter of the fiber for combining the laser beam and the fiber for transmitting the laser beam to be finally used are the same. Light beyond the Numerical Aperture) cannot be coupled to the fiber.

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

Therefore, an object of the present invention is to provide an optical transmission device that solves the above problems, combines multiple light sources, and reduces the risk of condensing light on a fiber.

In order to solve the above problems, the optical transmission device according to the present invention includes a plurality of laser light sources, a combined wave fiber having a core diameter of Dcc and a numerical aperture of NAc for combining light, and light from the laser light source. A lens that condenses and incidents the combined light on the combined wave fiber, a transmission fiber having a core diameter of Dct and a numerical aperture of NAT for transmitting the combined light, and the transmission light emitted from the combined wave fiber. It is provided with a lens for condensing and incident light on the fiber , and Dcc ≧ Dct and NAc> NAT .

With the above configuration, the optical transmission device according to the present invention can reduce the risk of burning when condensing light on the fiber.

Configuration diagram of the optical transmission device according to the embodiment of the present invention Laser light propagation diagram until the emitted light from the laser light source enters the combined wave fiber Laser light propagation diagram until the outermost propagation component of the emitted light from the laser light source is incident on the combined wave fiber Explanatory drawing when the laser beam is incident on the combined wave fiber from the laser light source Explanatory diagram when laser light is emitted from the combined wave fiber Propagation diagram of laser beam from combined wave fiber to transmission fiber Explanatory drawing when laser light is emitted from transmission fiber Configuration diagram of the laser light combiner 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 designated by the same reference numerals, and thus description thereof may be omitted. Further, the X-axis, Y-axis, and Z-axis shown in the drawings are orthogonal to each other. Here, the Y-axis is the vertical direction corresponding to the top and bottom, and the coordinate axes in each figure are drawn so as to correspond to the direction of each field of view.

(Embodiment 1)
FIG. 1 shows a schematic configuration diagram of an optical transmission device according to an embodiment of the present invention. The optical transmission device is composed of a transmission fiber 107 selected to obtain a specified laser output characteristic, a combiner fiber 104 having a higher incident light characteristic than the transmission fiber 107, and a combiner fiber 104. It is provided with a condenser lens 106 for coupling the emitted light 105 to the transmission fiber 107, and a laser output unit 109 which is an optical system for condensing and incident a plurality of light sources on the combined wave fiber 104.

In FIG. 1, the laser light sources 100a and 100b are limited only by the laser characteristics finally used, and may be a laser light source including a semiconductor laser or a gain medium. Further, it can be applied to a multi-mode laser or a laser light source having a different wavelength, and the laser light sources 100a and 100b can combine waves even if they have different characteristics.

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

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

The laser light emitted from the laser light sources 100a and 100b is propagated as parallel light by passing through the collimating lenses 102a and 102b, respectively, and is condensed and incident on the combiner fiber 104 by the condenser lens 103. The laser beam is combined in the wave combining fiber 104, and by looping the fiber at this time, the wave can be combined with a short fiber length.

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

Next, the details of each part will be described.

FIG. 2 shows a laser beam propagation diagram until the laser beam emitted from the laser light sources 100a and 100b is incident on the wave combining 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 combiner fiber 104 is dc, and the condensing lens 103 to the combiner fiber 104. Assuming that the focal length of is f1, these relational expressions are shown as (Equation 1).

dc = (4 ・ f1 / D1) × BPP (1)

Since multi-mode laser light is used, in order to reduce the risk of burning to the combined wave fiber 104, the incident focusing diameter dc is set to 100 μm, and the focal length f1 = 100 mm of the condenser lens 103 is adopted. From 1), it can be seen that the incident beam diameter D1 to the condenser lens needs to be set to 16 mm.

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

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

The vertical axis of the combined wave fiber 104 with the incident end face and the angle formed by the incident light on the combined wave fiber 104 are θ1, the incident allowable outermost 110 of the combined wave fiber 104 and the outermost propagating component 111a of the emitted light 101a. Assuming that the distance at the time of parallel propagation of is xt1, (Equation 2) is derived from the calculation of geometrical optics.

tan θ1 ≧ xt1 / f1 (2)

In the present embodiment, since θ1 = arcSin (NAc), it can be seen that the distance xt1 at the time of parallel propagation should satisfy xt1 ≦ 29 mm. Therefore, a condenser lens 103 having an effective diameter of up to 58 mm may be selected.

FIG. 4 shows a state when the laser beam is incident on the combine wave fiber 104, and FIG. 5 shows a state when the laser beam is emitted from the combine wave fiber 104.

In FIG. 4, the emitted light 101a and 101b incident on the combined wave fiber 104 from the laser light sources 100a and 100b are condensed and incident at 100 μm, which is half of the core diameter of 200 μm of the combined wave fiber 104. This is to prevent the tail portion of the intensity distribution of the laser beam from damaging the clad 113.

In FIG. 5, the laser beam combined in the fiber is emitted as emitted light 105 from the core 112 of the combined wave fiber 104 as light having a single optical axis. The output is shown in relation to (Equation 3) because the total value of the laser light sources 100a and 100b is obtained and the BPP is stored.

BPP = θ2 ・ w (3)

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

From (Equation 3), it can be seen that the spread angle θ2 of the emitted light 105 can obtain an emission characteristic of 2.3 ° (NA = 0.04).

The shorter the fiber, the less the attenuation of light, but it is not completely combined and there is a risk that the NA will vary depending on the emission mode. Therefore, it is necessary to loop the fiber or intentionally arrange it with a curve so that the laser beam propagates through the entire core of the fiber.

FIG. 6 shows a propagation diagram of the laser beam from the combined wave 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 combined wave fiber 104 is set to an arbitrary condensing diameter by the condensing lens 106, and is coupled to the transmission fiber 107. Assuming that the focal length of the lens at this time is f2, the distance between the combiner fiber 104 and the condenser lens 106 is L2, and the distance between the condenser 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 emission beam diameter d2 from the combined wave fiber 104 and the condensing incident diameter d3 to the transmission fiber 107.

d3 / d2 = L3 / L2 (5)

In the present embodiment, the imaging ratio is set to 1/3 and the light collection diameter d3 = 67 μm is set in order to reduce the risk of burning when incident on the transmission fiber 107. At that time, considering that L2 is three times as large as L3 and the incident NA on the transmission fiber 107 needs to satisfy NAT = 0.2 (incident angle 11.5 °), the light is focused. Select the lens 106. It is shown that (Equation 6) should be satisfied with respect to the incident beam diameter to the condenser lens 106 by using the calculation of geometrical optics as in the case of the incident on the combined wave fiber 104.

L3 ・ tan11.5 ° ≦ L2 ・ tan2.3 ° (6)

For the condenser lens 106 of the present embodiment, it is possible to select, for example, f2 = 40 mm, which has an effective diameter larger than L2 · tan2.3 ° and satisfies (Equation 4) to (Equation 6) with respect to the focal length.

FIG. 7 shows the state of the emitted light from the transmission fiber 107. Since the light propagating through the transmission fiber 107 is incident with light having a single optical axis in the combined wave fiber 104, the light 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 represented by (Equation 7) as in (Equation 3).

BPP = θ3 ・ Wout (7)

However, depending on how the transmission fiber 107 is arranged, 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, the emission end face of the transmission fiber 107 may move, and the divergence angle may change each time the movement occurs. If the divergence angle changes, it will affect the power density at the processing point, so it is necessary to create a loop or intentionally curve it as in the case of the wave combine fiber.

The emitted light 108 basically has a total value of 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 0.5 dB / km and the loss due to an optical element is about 3%, if the length of the fiber is 10 m, the total loss is considered to be about 10%.

As described above, according to the optical 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 collimating lenses 102a and 102b, and is a condenser lens. By 103, the light is condensed and incident on the combined wave fiber 104 having a low risk of burning at the time of condensed incident, and is emitted as light having a single optical axis as it propagates through the combined wave fiber 104. The light emitted from the combined wave fiber 104 is condensed and incident on the transmission fiber 107 by the condenser lens 106, and the total output value of the input light is obtained.

In the present embodiment, a case where two multi-mode laser light sources are used and a multi-mode non-doped fiber is used for both the combined wave fiber and the transmission fiber has been described, but the laser light source is a combined wave fiber. As many as possible and the incident method can be used. It is also possible to obtain high output emitted light by combining the waves multiple times.

Further, regarding the laser light source, the present invention can be applied to a laser beam having arbitrary characteristics without any limitation in wavelength, mode, shape, beam quality, etc., and the wavelength characteristics and beam quality of each light source are different. But it can also be used. As for the fiber, any fiber can be used regardless of the material and the core type of the fiber, and by using the doped fiber, it can be used as an amplifier.

In addition, mode control can be performed by inserting a polarization control element or aperture before the incident of any of the fibers, so it is not only used for CW lasers but also for the generation mechanism of ultrashort pulse lasers. It can also be used as an amplification mechanism.

The optical transmission device of the present invention is useful in a laser processing machine, a laser welder, or the like because it emits light from a plurality of light sources in a combined wave with a low burnout risk.

100a, 100b Laser light source 101a, 101b Emission light 102a, 102b Collimating lens 103, 106 Condensing lens 104 Condensing fiber 105, 108 Emission light 107 Transmission fiber 109 Laser output unit 112, 116 core 113, 117 clad

Claims (1)

With multiple laser light sources
A fiber for combining waves having a core diameter of Dcc and a numerical aperture of NAc for combining light from the laser light source.
A condensing optical system that condenses and incidents light from the laser light source onto the combiner fiber,
A transmission fiber with a core diameter of Dct and a numerical aperture of NAT that transmits the combined light,
A condensing optical system for condensing and incident light emitted from the combined wave fiber onto the transmission fiber is provided .
Dcc ≧ Dct and NAc> NAT.
Optical transmission device.

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