JP2008010720A - Fiber laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fiber laser device which is compact and low in a power consumption. <P>SOLUTION: The fiber laser device comprises a fiber amplifier to which a rare-earth element is added, a seed light source for emitting a signal light by a pulse oscillation, an excitation light source for emitting an excited light, a first optical means which is connected to one end of the fiber amplifier for coinciding an optical path of the signal light from the seed light source with the optical path of the excited light, a second optical means connected to the other end of the fiber amplifier for separating the optical path of the signal light from the optical path of the excited light, and an optical resonance circuit which contains the first and second optical means and the fiber amplifier for oscillating the excited light consecutively. In a state that the excited light is consecutively oscillated in the fiber amplifier, the signal light is not amplified; and in a state that the excited light is stopped being oscillated consecutively, amplitude modulation pulse oscillation laser beams in which the signal light is amplified by the fiber amplifier are emitted to an external space via the second optical means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fiber laser device.

  A fiber laser device that emits fiber laser light toward an external space can be applied to various uses such as a lateral distance machine and a laser processing machine. In this case, a higher pulse laser beam output can be obtained by making the light from the pulsed YAG laser incident on the fiber amplifier.

  Wavelength conversion can be performed by making this pulsed laser light output incident on an optical parametric oscillator (OPO), and modulated pulsed laser light can be obtained by making it incident on various modulators. In this way, fiber laser devices corresponding to various applications can be realized.

Such a laser device has a technology disclosure example in which, for example, when laser light is emitted into a space, the optical axis of the laser light is quickly directed in a desired direction or an incident direction (Patent Document 1).
JP 2005-9956 A

  The present invention provides a fiber laser device that is small and has low power consumption.

  According to one aspect of the present invention, a fiber amplifier to which a rare earth element is added, a seed light source that emits signal light by pulse oscillation, an excitation light source that emits excitation light, and one end of the fiber amplifier are connected A first optical means for matching the optical paths of the signal light from the seed light source and the pumping light and the other end of the fiber amplifier, and separating the optical paths of the signal light and the pumping light. Second optical means, and an optical resonance circuit that includes the first and second optical means and the fiber amplifier, and oscillates the pumping light continuously, and the pumping light is in the fiber amplifier. Amplitude modulation in which the signal light is not amplified in a state where continuous wave oscillation is performed, and the signal light is amplified by the fiber amplifier in a state where the excitation light stops continuous wave oscillation Pulse fiber laser device oscillated laser light is characterized in that it is emitted to the outer space through the second optical means.

  According to the present invention, a small-sized and low power consumption fiber laser device is provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 are block diagrams of a fiber laser device according to a specific example of the present invention.
The pulse oscillation signal light from the seed light source 10 such as a YAG laser is reflected by the dichroic prism 18, converged by the lens 20, and enters one end of the fiber amplifier 14. After the excitation light from the excitation light source 40 that has passed through the dichroic prism 18 matches the optical path of the signal light from the seed light source 10, the light is made incident on one end of the fiber amplifier 14. When signal light having a wavelength of 2 μm, for example, enters the fiber amplifier 14 from the seed light source 10 in a state where the rare earth element added in the vicinity of the core of the fiber is activated by excitation light, the signal light is amplified by stimulated emission. .

  The amplified light and the excitation light are emitted from the other end of the fiber amplifier 14 and then converged by the lens 22, and the optical path is separated by the dichroic prism 26. That is, the dichroic prism 26 transmits the amplified light and reflects the excitation light. The outgoing light Pamp that has passed through the dichroic prism 26 is emitted to the external space by the optical parametric oscillator 30 as external outgoing light Pout that has been wavelength-converted to 3 to 5 μm, for example. The dichroic prism 26 reflects the excitation light from the second excitation light source 41 and matches the optical path of the signal light emitted from the other end of the fiber amplifier 14. However, the direction of travel is reversed. In this way, the excitation light from the excitation light source 41 enters from the other end of the fiber amplifier 14.

  In general, the YAG laser of the seed light source 10 generates a high peak light output by pulse oscillation. In this specific example, for example, pulse oscillation is performed at a repetition frequency of 15 kHz. Therefore, when amplitude modulation is not performed, the wavelength-converted pulsed laser beam output is emitted to the outside.

  Furthermore, in this specific example, mirrors 16 and 24 and their driving means 12 are provided as an optical resonant circuit. As shown in FIG. 1, the excitation light is CW-oscillated (ON state) by matching the optical axes of the continuous wave (CW) oscillation mirrors 16 and 24. Further, as shown in FIG. 2, the CW oscillation is stopped (OFF state) by tilting the optical axis of the mirror by the driving means 12 such as a piezo element.

  In general, since the fiber amplifier 14 has a high gain, CW oscillation occurs even in Fresnel reflection with a reflectance of several percent at both fiber end faces of the fiber amplifier 14. When CW oscillation occurs, excitation energy is consumed for CW oscillation and pulse amplification of the signal light stops. In order to prevent this, CW oscillation is prevented by making the both end surfaces of the fiber amplifier 14 into oblique cleaves having an angle of about 20 °, for example.

  In this specific example, pulse amplification is controlled by utilizing the point where CW oscillation is likely to occur in the fiber amplifier 14. In other words, the optical resonant circuit includes dichroic prisms 18 and 26, fiber amplifier 14, CW oscillation mirrors 16 and 24, and driving means 12 thereof. Then, the CW oscillation mirror 16 is displaced as shown in FIG. 2 by the driving means 12 such as a piezoelectric element utilizing a piezoelectric effect. In the OFF state where the optical axis of the mirror 16 is tilted and does not satisfy the CW oscillation condition, the excitation energy can pulse-amplify the signal light from the seed light source 10. That is, in the state shown in FIG. 2, the pulsed laser beam output Pout wavelength-converted by the optical parametric oscillator 30 is emitted to the outside. In order to create the OFF state, the optical axis of the CW oscillation mirror 24 may be tilted instead of tilting the optical axis of the CW oscillation mirror 16.

  On the other hand, as shown in FIG. 1, in the ON state in which the optical axes of the mirrors 16 and 24 coincide, the excitation light causes CW oscillation due to resonance between the CW oscillation mirror 24 and the CW oscillation mirror 16. Arise. For example, when the reflectivity of the mirror 24 is approximately 100% and the reflectivity of the mirror 16 is approximately 80%, an external light output Pp having a size of P1 is emitted from the CW oscillation mirror 16. At this time, the wavelength-converted laser beam output Pout is not output.

  FIG. 3 is a graph for explaining temporal changes in the ON / OFF state of CW oscillation, the pumping light external output Rp, and the amplified light output Pamp. During the ON state time shown in (a), the excitation light external output Pp of P1 is emitted as shown in (b). On the other hand, the CW oscillation is stopped as shown in FIG. Only during the time when the CW oscillation is stopped, the pulsed laser light from the seed light source 10 is amplified and transmitted through the dichroic prism 26 as shown in (c), and the amplified light output Pamp of size P2 is emitted.

When the period of the OFF state of the CW oscillation mirror 16 and _T h (sec), the repetition frequency _{f h (Hz) = 1 /} T h. The repetition frequency f _h is 2 kHz at maximum, which is lower than the pulse oscillation repetition of the seed light source 10.

  Thereafter, the amplified light is wavelength-converted to a laser beam of 3 to 5 μm by the optical parametric oscillator 30, and the wavelength-converted light output Pout is emitted to the external space. In the ON state, pulse amplification is not performed by CW oscillation, so that the amplified light output Pamp is small, becomes equal to or less than the threshold light input Pth of the optical parametric oscillator 30, and wavelength conversion is not performed.

FIG. 4 is a graph showing the wavelength-converted light output Pout on the time axis t (sec). That is, the time axis of FIG. 3C is partially enlarged. For example, signal light from the seed light source 10 is pulsed at a repetition frequency fs of 15kHz is pulsed amplified by the fiber amplifier 14 represents a further repeatedly undergo amplitude modulation frequency f _h. Thereafter, the optical parametric oscillator 30 converts the wavelength into 3 to 5 μm laser light, and a wavelength-converted light output Pout having a size P3 is emitted to the external space. As illustrated in FIG. 4, the emitted light is an amplitude-modulated pulsed laser beam having a wavelength of 3 to 5 μm. Repetition frequency f _h and the modulation width of the amplitude modulation can be controlled by driving means of the optical resonant circuit.

Next, returning to FIG. 1 and FIG. 2, supplementary explanation will be given regarding the components of this example.
The fiber amplifier 14 performs optical amplification by adding rare earth elements such as holmium (Ho), erbium (Er), and thulium (Tm) in the vicinity of the core of the fiber, and injecting and propagating excitation light and signal light. In this specific example, for example, by adding Tm, signal light having a wavelength of 2 μm of the seed light source is amplified by stimulated emission.

  The dichroic prisms 18 and 26 are optical means for reflecting or transmitting light of a specific wavelength by making the interference film a multilayer structure. For example, in FIGS. 1 and 2, the dichroic prism 18 reflects 2 μm signal light from the seed light source 10 and transmits 0.8 μm excitation light. On the other hand, the dichroic prism 26 transmits 2 μm signal light and reflects 0.8 μm excitation light.

  As the excitation light sources 40 and 41, for example, a semiconductor laser element made of AlGaAs having a peak wavelength of 0.8 μm band can be used. Since the CW light output of this semiconductor laser element can be 100 mW or more, it is suitable for excitation. In FIG. 1 and FIG. 2, the excitation light from the excitation light source 40 is bent by, for example, a mirror 42, passes through the dichroic prism 18, and enters the fiber amplifier 14. Similarly, the excitation light from the excitation light source 41 is bent by, for example, the mirror 43, further reflected by the dichroic prism 26, and enters the fiber amplifier 14. Further, the mirrors 42 and 43 transmit the oscillation light between the CW oscillation mirrors 16 and 24. For this reason, for example, a half mirror can be used as the mirrors 42 and 43. One excitation light source may be used, but two excitation light sources are more preferable because the excitation light intensity can be increased.

The optical parametric oscillator 30 is made of a bulk nonlinear crystal such as BaB ₂ O ₄ , LiB ₃ O ₅ , BiB ₃ O ₆ , LiNbO ₃ , KTiOPO ₄ , and performs wavelength conversion using the nonlinear optical effect. That is, in a nonlinear crystal arranged in an optical resonator formed by two mirrors, wavelength conversion is performed by dividing one high energy (high frequency) photon into two low energy photons. Is made.

FIG. 5 is a block diagram of a fiber laser device according to a comparative example.
In this comparative example, the pulse amplified light is modulated using a modulator 32 such as an EO (Electro-Optical) modulator or a movable chopper in the subsequent stage of the fiber amplifier 14. However, in either of these cases, the apparatus becomes undesirably large. Further, since a high voltage power supply is required to control the EO modulator, power consumption increases. The movable chopper is a mechanical modulation method using a large blade, and the control accuracy is inferior in controlling the repetition frequency. In addition, the excitation light source is abbreviate | omitted in this figure.

  On the other hand, this example does not require a high-voltage power source for the EO modulator or a mechanical drive device such as a movable chopper. As a result, power consumption can be reduced and the fiber laser device can be further downsized.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these specific examples. For example, those skilled in the art make various design changes with respect to fiber amplifiers, seed light sources, excitation light sources, CW oscillation mirrors, drive means, dichroic prisms, mirrors, optical parametric oscillators, lenses, etc. that constitute fiber laser devices, and modulation methods What has been done is included in the scope of the present invention without departing from the spirit of the present invention.

It is a block diagram of the fiber laser apparatus concerning the example of this invention. It is a block diagram of the fiber laser apparatus concerning the example of this invention. It is a graph explaining the time change of the ON-OFF state of CW oscillation, the excitation light external output, and the amplified light output. It is a graph explaining the time change of wavelength conversion light output. It is a block diagram of the fiber laser apparatus concerning a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Seed light source, 12 ... Drive means (piezo element), 14 ... Fiber amplifier, 16 ... CW oscillation mirror, 18 ... Dichroic prism, 24 ... CW oscillation mirror, 26 ... Dichroic prism, 30 ... Optical parametric oscillator, 40, 41 ... Excitation light source

Claims (4)

A fiber amplifier doped with rare earth elements;
A seed light source that emits signal light by pulse oscillation;
An excitation light source that emits excitation light;
A first optical means connected to one end of the fiber amplifier, for matching the optical paths of the signal light from the seed light source and the excitation light;
A second optical means connected to the other end of the fiber amplifier and separating an optical path between the signal light and the excitation light;
An optical resonant circuit that includes the first and second optical means and the fiber amplifier, and oscillates the excitation light continuously,
With
The signal light is not amplified when the pumping light is continuously wave oscillated in the fiber amplifier, and the signal light is amplified by the fiber amplifier when the pumping light is stopped from continuous wave oscillation. A fiber laser device characterized in that the amplitude-modulated pulsed laser beam is emitted to the external space through the second optical means. The optical resonant circuit includes: a first mirror; a second mirror having a lower reflectance than the first mirror; and a driving unit that displaces at least one of the optical axes of the first and second mirrors. Including
When the optical axes of the first and second mirrors coincide, the excitation light continues continuous wave oscillation in the fiber amplifier,
2. The fiber laser device according to claim 1, wherein when the optical axes of the first and second mirrors do not coincide with each other, continuous wave oscillation is stopped in the fiber amplifier.   The fiber laser device according to claim 2, wherein the driving unit includes a piezo element. An optical parametric oscillator that performs wavelength conversion of the amplitude-modulated pulsed laser light amplified from the signal light;
The first and second optical means are dichroic prisms or dichroic mirrors,
The seed light source comprises a YAG laser,
The excitation light source is a semiconductor laser element having a peak wavelength of 0.8 μm band,
The fiber laser device according to claim 1, wherein the rare earth element is thulium.

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