JP4699131B2 - Optical fiber laser, optical fiber amplifier, MOPA optical fiber laser - Google Patents

Description

  The present invention relates to an optical fiber laser and an optical fiber amplifier using a rare earth-doped optical fiber, and in particular, a component such as a pumping light source is damaged by light (ASE) which is once emitted from the laser light and returned to the rare earth-doped optical fiber. The present invention relates to an optical fiber laser, an optical fiber amplifier, and a MOPA type optical fiber laser that can prevent the occurrence of the damage and improve safety and lifetime.

  Laser light is used in various fields such as processing machines, medical equipment, and measuring instruments. In the field of processing machines, laser light is excellent in condensing performance, and a very small beam spot with high power density can be obtained, so that precision processing is possible, laser processing is non-contact processing, and laser light Because it is possible to process materials with high hardness that can be absorbed, the applications are expanding rapidly. In particular, an optical fiber laser using a rare earth-doped optical fiber as a laser medium has features such as higher efficiency than a conventional solid-state laser, a compact apparatus, and the same lasing medium and propagation medium. An extremely high output kW class optical fiber laser has been developed.

  In order to realize the high output as described above in an optical fiber laser, it is important how much pumping light can be introduced into the rare earth-doped optical fiber. In the case of a normal rare earth-doped optical fiber, core excitation is performed by introducing excitation light into the core. However, since the core diameter is as small as several μm to 10 μm, it is difficult to introduce much excitation light. Therefore, when constructing an optical fiber laser, clad pumping using an optical fiber having a double clad structure (rare earth-doped double clad optical fiber) is often used. The optical fiber having a double clad structure has a two-layer structure in which a clad surrounding a core is a first clad and a second clad covering the outer periphery thereof. The first clad not only functions as a clad for the core but also the first clad. The cladding itself also functions as a core with the second cladding as a cladding. In addition, since the first cladding usually has a diameter of 100 μm or more, it becomes possible to inject a large amount of excitation light relatively easily.

  As means for introducing pump light into the first cladding, (1) a method in which pump light is mainly incident from the end face of the rare earth-doped double clad fiber, and (2) pump light is incident from the side surface of the rare earth-doped double clad fiber. Broadly divided into methods.

  (1) As a method for making excitation light incident from the end face of the rare earth-doped double clad fiber, there is a method using an optical coupler as described in Patent Document 1, for example. A configuration example of an optical fiber laser 100 using the optical coupler disclosed herein is shown in FIG. In this optical fiber laser 100, the optical coupler 103 has seven pumping ports 102 made of a multimode optical fiber and one output port 104 formed by melting and stretching them to be integrated. An excitation light source 101 is connected to each excitation port 102, and excitation light emitted from the excitation light source 101 is emitted from the emission port 104. For example, if the output of each excitation light source 101 is 3 W, a total of 21 W excitation power can be obtained. This excitation light is incident on the rare earth-doped double clad fiber 105. The diameter of the exit port 104 of the optical coupler 103 is equal to or less than the diameter of the first cladding of the rare earth-doped double clad fiber 105, and the numerical aperture of the exit port 104 is the first of the rare earth doped double clad fiber 105. If it is smaller than the numerical aperture of the clad, it becomes possible to make the excitation light emitted from the emission port 104 enter the first clad of the rare earth-doped double clad fiber 105 with low loss.

  Moreover, (2) As a method of making excitation light incident from the side surface of the rare earth-doped double clad fiber, for example, Patent Document 2 discloses. A configuration example of an optical fiber laser 110 using the optical coupler disclosed herein is shown in FIG. In this optical fiber laser 110, the first coupler is exposed in the optical coupler 111 portion by processing a part of the side surface of the rare earth-doped double clad fiber 105, and the end surface is obliquely polished in that portion. A plurality of excitation ports 102 are joined at an appropriate angle. The angle of the junction is such that the light emitted from the excitation port 102 and incident on the first cladding of the rare earth-doped double clad fiber 105 can be totally reflected at the boundary surface between the first cladding and the second cladding. The excitation light emitted from the excitation light source connected to 102 can be incident on the first cladding of the rare earth-doped double cladding fiber 105. Further, by providing a plurality of optical couplers 111 in the longitudinal direction of the rare earth-doped double clad fiber 105, a large amount of excitation light can be incident on the rare earth doped double clad fiber 105.

  The excitation light introduced into the first clad of the rare earth-doped double clad fiber by the method (1) or (2) crosses the core while propagating in the first clad. Absorbed by the added rare earth ions. The rare earth ions that have absorbed the excitation light emit spontaneous emission light having a wavelength different from that of the excitation light, and the spontaneous emission light that propagates through the core is amplified while propagating and output as ASE (Amplified Spontaneous Emission). Is done.

  On the other hand, fiber grading is provided at both ends of the rare earth-doped double clad fiber 105. The fiber grading provided on the laser emission side is an output coupler 107, which has the property of reflecting light of a part of the spontaneous emission light emitted from the rare earth-doped double clad fiber 105, The reflectivity is not 100% but has an appropriate reflectivity so that a desired output can be obtained. The fiber grading provided at the other end is a high reflection mirror 106, which has the same reflection wavelength as that of the output coupler 107, but its reflectance is almost 100%, and what is the excitation light wavelength? It does not even work. The highly reflective mirror 106 and the output coupler 107 constitute a resonator, and the ASE emitted from the rare earth-doped double clad fiber 105 is reflected by this mirror and reciprocates in the resonator, so that the rare earth doped double clad fiber The laser beam is amplified every time it passes through 105, and eventually oscillates. A part of the laser beam passes through the output coupler 107 and is output as laser beam through the isolator 108.

  However, since the number of excitation ports is limited in the configuration of FIG. 1, the laser output power obtained is limited. Therefore, as shown in FIG. 3, the laser light output from the optical fiber laser 100 may be further introduced into the optical fiber amplifier 200 and amplified to increase the output. Such a system is generally called a MOPA (Master Oscillator Power Amplifier) system. In FIG. 3, an optical fiber laser 100 is used as an MO (Master Oscillator), and an optical fiber amplifier 200 is used as a PA (Power Amplifier). Yes. This optical fiber amplifier 200 includes a plurality of pumping light sources 201, an optical coupler 203 that bundles pumping ports 102 of these pumping light sources 201 and enters one end side of the rare earth-doped double clad fiber 205, and a rare earth-doped double clad fiber 205. And an isolator 208 connected to the other end. The pumping light source 201, the rare earth-doped double clad fiber 205, and the isolator 208 can be the same as those used in the optical fiber laser 100. The optical coupler 203 is obtained by replacing one of the pumping ports 102 of the optical coupler 103 used in the optical fiber laser 100 with a signal port 202, and a single mode fiber is used for the signal port 202. Laser light emitted from the optical fiber laser 100 enters from the signal port 202 and enters the core of the rare earth-doped double clad fiber 205 through the optical coupler 203. On the other hand, an excitation light source 201 is connected to each excitation port 102, and excitation light is incident on the first cladding of the rare earth-doped double clad fiber 205 via the optical coupler 203. The excitation light incident on the first cladding of the rare earth-doped double clad fiber 205 is absorbed by the rare earth ions added to the core, and stimulated emission is generated to amplify and output the laser light propagating in the core. .

Such a MOPA system is also effective in the configuration shown in FIG. 2, but in the configuration shown in FIG. 2, high output can be achieved by connecting a plurality of optical fiber lasers 110.
US Pat. No. 5,864,644 US Patent Application Publication No. 20040047553

  In the conventional optical fiber laser shown in FIGS. 1 to 3, once emitted laser light returns for some reason as reflected light (for example, a laser used for processing is reflected light from an object to be processed during processing). In this case, the intensity of the returned light is temporarily reduced by the isolators 108 and 208, but is amplified when a part of the transmitted laser light passes through the rare earth-doped double clad fibers 105 and 205. The amplified reflected light may have the same intensity as the output laser light, and when the return light is generated by scattering such as Rayleigh scattering or Brillouin scattering, the return light is added with rare earth. The laser beam is amplified while passing through the double clad fibers 105 and 205 and may have the same intensity as the laser beam. Such high-intensity laser beam is incident on the optical couplers 103 and 203.

  In the case of the optical fiber laser 100 shown in FIG. 1, the reflected light that has been amplified and entered the optical coupler 103 is almost evenly distributed to each pumping port 102 and reaches each pumping light source 101. Deals damage. On the other hand, in the case of the optical fiber laser shown in FIG. 3, most of the reflected light incident on the optical coupler 203 propagates through the signal port and enters the optical fiber laser 100. Damage the excitation light source. Further, a part of the reflected light leaks from the core due to the connection loss between the rare earth-doped double clad fiber 205 and the optical coupler 203 and reaches the pumping light source 201, thereby causing fatal damage to the pumping light source 201. In particular, in the case of pulse oscillation, even if the average power is low, the peak value of the pulse has a very high power, so that the possibility of damaging the excitation light sources 101 and 201 is very high.

  In general, when light having a wavelength different from the wavelength of light emitted from the excitation light sources 101 and 201 is incident, damage may be caused even when only a few percent of the output power is incident.

  In the optical fiber laser 100 shown in FIG. 1, the laser light is almost reflected by the high reflection mirror 106, but the light of other wavelengths is not reflected at all. Therefore, the ASE light generated separately from the laser light is not reflected by the high reflection mirror 106 but is incident on the excitation light source 101 via the optical coupler 103 and may damage the excitation light source 101. there were.

  Further, in the case of the MOPA type optical fiber laser shown in FIG. 3, only the optical fiber amplifier 200 operates in a state in which the optical fiber laser 100 does not output laser light or the output is lowered in operation. In some cases, it was in a state of being. In such a situation, high-strength ASE is emitted from the rare earth-doped double clad fiber 205 in the optical fiber amplifier 200 in both directions of the optical fiber, and the pump light source 201 is also damaged through the optical coupler 203. There was a case to give.

  The present invention has been made in view of the above circumstances, and it is possible to prevent components such as an excitation light source from being damaged by the ASE that is once amplified and returned to the rare-earth-doped optical fiber, thereby improving safety and life. An object is to provide an optical fiber laser, an optical fiber amplifier, and a MOPA optical fiber laser.

  In order to achieve the above object, the present invention provides at least a rare earth-doped optical fiber that is a laser medium, a plurality of pumping light sources that optically pump the rare earth-doped optical fiber, and a pumping light from each pumping light source. In an optical fiber laser that performs laser oscillation by entering pump light into a rare earth-doped optical fiber, the optical coupler is configured to transmit return light from the rare earth-doped optical fiber toward the pump light source. A monitor port through which a part is propagated is provided, and the intensity of the return light propagating through the monitor port is measured, and when the light intensity exceeds a predetermined value, the output of the excitation light source is reduced to amplify the return light. An optical fiber laser is provided, which is provided with excitation light source control means for preventing the above.

  In the optical fiber laser according to the present invention, the excitation light source control means is connected to the monitor port and measures the intensity of the return light, and inputs a light intensity signal from the photodetector. A determination circuit that emits an abnormal signal when the intensity of light received at a light intensity exceeds a certain intensity, and connected to the determination circuit to emit a drive signal to the excitation light source to emit light when no abnormal signal is received. It is preferable to have an excitation light source drive circuit that shuts down the drive signal at the time.

  In the optical fiber laser of the present invention, the rare earth-doped optical fiber includes a core doped with one or more selected from the group consisting of Yb, Er, Ho, and Tm, a first cladding surrounding the core, and the core A rare earth-doped double clad fiber having a second clad provided outside the first clad is preferable.

  In the optical fiber laser of the present invention, a high reflection mirror that transmits the pump light but reflects the laser light generated by the laser oscillation is provided on the pump light incident side of the rare earth-doped optical fiber. It is preferable that an output coupler that reflects and partially transmits laser light generated by laser oscillation is provided on the output side, and a resonator is configured between the high reflection mirror and the output coupler.

  The present invention also includes at least a rare earth-doped optical fiber that is an optical amplifying medium, a plurality of pumping light sources that optically pump the rare earth-doped optical fiber, and a combination of pumping light and signal light from each pumping light source that is incident on the rare earth-doped optical fiber. In the optical fiber amplifier that amplifies and outputs the signal light in a rare earth-doped optical fiber, the optical coupler includes a return light that travels from the rare earth-doped optical fiber to the pumping light source side. A monitor port through which the light is propagated, and the intensity of the return light propagating through the monitor port is measured. When the light intensity exceeds a predetermined value, the output of the excitation light source is reduced to amplify the return light. An optical fiber amplifier is provided, which is provided with a pumping light source control means for preventing.

  In the optical fiber amplifier of the present invention, the excitation light source control means is connected to the monitor port and measures the intensity of the return light, and inputs a light intensity signal from the light detector. A determination circuit that emits an abnormal signal when the intensity of light received at a light intensity exceeds a certain intensity, and connected to the determination circuit to emit a drive signal to the excitation light source to emit light when no abnormal signal is received. It is preferable to have an excitation light source drive circuit that shuts down the drive signal at the time.

  In the optical fiber amplifier of the present invention, the rare earth-doped optical fiber includes a core doped with one or more selected from the group consisting of Yb, Er, Ho, and Tm, a first cladding surrounding the core, and the core A rare earth-doped double clad fiber having a second clad provided outside the first clad is preferable.

  The present invention also includes an optical fiber laser that oscillates by entering pump light into a rare earth-doped optical fiber, at least a rare earth-doped optical fiber that is a laser medium, and a plurality of pump light sources that optically pump the rare-earth doped optical fiber, An optical coupler that combines the excitation light from each excitation light source and the laser light emitted from the optical fiber laser and enters the rare earth-doped optical fiber, and amplifies and outputs the laser light emitted from the optical fiber laser In the MOPA optical fiber laser, the optical coupler is provided with a monitor port through which a part of the return light from the rare earth-doped optical fiber toward the pumping light source is propagated, and the intensity of the return light propagating through the monitor port is set. Excitation light source control means is provided to prevent amplification of return light by measuring and reducing the output of the excitation light source when the light intensity exceeds a predetermined value. Providing MOPA fiber optic laser, characterized in that.

  In the MOPA optical fiber laser of the present invention, the excitation light source control means inputs a light intensity signal from the light detector connected to the monitor port and measuring the intensity of the return light, A determination circuit that emits an abnormal signal when the intensity of light received by the detector exceeds a certain intensity, and is connected to the determination circuit and emits a drive signal to the excitation light source to emit light when not receiving the abnormal signal. It is preferable to have an excitation light source drive circuit that shuts down the drive signal when it is received.

  In the MOPA optical fiber laser of the present invention, the rare earth-doped optical fiber includes a core doped with one or more selected from the group consisting of Yb, Er, Ho, and Tm, and a first cladding surrounding the core And a rare earth-doped double clad fiber having a second clad provided outside the first clad.

  In the MOPA-type optical fiber laser of the present invention, an optical coupler provided at a signal port connecting the output side of the optical fiber laser and the optical coupler to branch a part of the laser light output from the optical fiber laser, When a second light detector connected to the branch port of the optical coupler and a light intensity signal from the second light detector are input, and the light intensity received by the second light detector is lower than a certain intensity It is good also as a structure provided with the 2nd determination circuit which emits an abnormal signal with respect to the said excitation light source drive circuit.

  In the MOPA type optical fiber laser of the present invention, a part of the laser light output from the optical fiber laser provided at the signal port connecting the output side of the optical fiber laser and the optical coupler is branched to the first branch port. And an optical coupler for branching return light from the optical coupler to the optical fiber laser to a second branch port, a second photodetector connected to the first branch port, and a second detector A second determination circuit that inputs a light intensity signal from a light detector and emits an abnormal signal to the excitation light source drive circuit when the light intensity received by the second light detector is lower than a certain intensity; A third photodetector connected to the second branch port, and a third detector for emitting an abnormal signal to the excitation light source driving circuit when the intensity of light received by the third photodetector is greater than a certain intensity. Judgment circuit It may be kicked configuration.

  In the MOPA optical fiber laser of the present invention, it is preferable that the excitation light source drive circuit is configured not to emit a drive signal when the optical fiber laser is not output.

  According to the present invention, an optical fiber laser that can prevent components such as a pumping light source from being damaged by ASE that has been amplified after the emitted laser light is returned to the rare earth-doped optical fiber, and has improved safety and life, An optical fiber amplifier and a MOPA optical fiber laser can be provided.

[First Embodiment]
A first embodiment of the present invention is shown in FIG.
The optical fiber laser 300 of this embodiment includes a rare earth-doped double clad fiber 105 that is a laser medium, a plurality of pump light sources 101 that optically pump the fiber, and a pump port 102 from each pump light source 101. An optical coupler 103 that is coupled with the pumping light, and a monitor port 302 that is provided in the optical coupler 103 and transmits a part of the return light from the rare earth-doped double clad fiber 105 toward the pumping light source 101; A photodetector 301 connected to the monitor port 302 for measuring the intensity of the return light and a light intensity signal 351 from the photodetector 301 are input, and the light intensity received by the photodetector 301 is greater than a certain intensity. Then, a determination circuit 310 that emits an abnormal signal 352 is connected to the determination circuit 310, and the abnormal signal 352 is Only in the absence emit light emits a drive signal 350 to the excitation light source 101 is configured by a pump light source drive circuit 311 having a function of shutting down the drive signal 350 at the time of receiving the abnormal signal 352.

  The rare earth-doped double clad fiber 105 includes a core added with one or more selected from the group consisting of Yb, Er, Ho, and Tm, a first clad surrounding the core, A second cladding provided on the outside.

The rare earth-doped double clad fiber 105 is provided with a high reflection mirror 106 that transmits excitation light but reflects laser light generated by laser oscillation on the excitation light incident side of the rare earth-doped double clad fiber 105, and is generated by laser oscillation on the laser output side. An output coupler 107 that reflects and partially transmits the laser light is provided, and a resonator is configured between the high reflection mirror 106 and the output coupler 107.
An isolator 108 is provided on the output side of the rare earth-doped double clad fiber 105.

The coupling method of the excitation port 102 and the rare earth-doped double clad fiber 105 by the optical coupler 103 may be either the end-face incidence method or the side-face incidence method, or may be used in combination.
A laser diode (LD) or the like is preferably used as the excitation light source 101, but is not limited thereto.

  For example, a photodetector 301 having a function of receiving an ASE propagating through the monitor port 302 and outputting an electric signal having a higher voltage as the received light intensity increases is used in the optical communication field or the like. It can be appropriately selected from conventionally known photodetectors. When the photodetector 301 receives ASE propagating through the monitor port 302, it outputs a light intensity signal 351 corresponding to the received light intensity, and the light intensity signal is sent to the determination circuit 310.

  The excitation light source drive circuit 311 outputs a drive signal 350 that determines the drive current of the excitation light source 101. The excitation light source 101 receives the drive signal 350 and outputs excitation light with a predetermined power. At the time of laser oscillation, a drive signal 350 is sent to the excitation light source so that a laser output with a desired intensity can be obtained.

  When the excitation light source 101 receives the drive signal 350 and outputs the excitation light, laser transmission is started, and the ASE emitted from the rare earth-doped double clad fiber 105 passes through the high reflection mirror 106, and the optical coupler 103 and the excitation port 102. And the excitation light source 101 is reached.

  In the present embodiment, a monitor port 302 and a photodetector 301 are provided in order to monitor the light intensity incident on such an excitation light source 101. Since light (ASE) having the same intensity as that of the excitation port 102 propagates to the monitor port 302, the light intensity incident on the photodetector 301 connected to the monitor port 302 is observed to enter the excitation light source 101. You can know the light intensity.

  As described above, the excitation light source 101 is damaged when laser light or ASE having an intensity higher than a certain level is incident on the excitation light source 101. Therefore, when such intensity light is incident on the excitation light source 101, or such intensity It is necessary to stop the laser oscillation immediately before reaching.

  Therefore, in the determination circuit 310, the light intensity signal 351 sent from the photodetector 301 is compared with a predetermined determination level, and when the level of the light intensity signal 351 reaches the determination level, an abnormal signal is detected. 352 is output. For example, the determination level is set to a level slightly lower than the level of the electric signal output when the photodetector receives the light intensity at which the excitation light source 101 is damaged. That is, when the intensity of light received by the photodetector 301 is greater than a certain intensity, an abnormal signal 352 is output.

  The abnormal signal 352 output from the determination circuit 310 is sent to the excitation light source drive circuit 311. The excitation light source drive circuit 311 immediately shuts down the drive signal 350 when receiving the abnormal signal 352. When the drive signal 350 is shut down, no excitation light is emitted from the excitation light source 101 and laser oscillation is stopped, so that no ASE is incident on the excitation light source 101, and the excitation light source 101 is prevented from being damaged. Can do.

[Second Embodiment]
A second embodiment of the present invention is shown in FIG.
This embodiment is a case where a MOPA type optical fiber laser is configured, and includes an optical fiber laser 100 that is an MO, an optical fiber amplifier 400 that is a PA, a determination circuit 410, and a pumping light source driving circuit 411. Yes. The optical fiber amplifier 400 includes a rare earth-doped double clad fiber 205 as a laser medium, a plurality of pumping light sources 201 for optically pumping the fiber, pumping ports 102 from the pumping light sources 201 and laser light emitted from the optical fiber laser 100. And an optical coupler 203 that couples the signal port 202 propagating to the rare earth-doped double clad fiber 205 to amplify and output the laser beam output from the optical fiber laser 100. Further, in the optical fiber amplifier 400, one of the excitation ports 102 is used as a monitor port 402, and a photodetector 401 is connected to the monitor port 402. The light intensity signal 451 measured by the photodetector 401 is input to the determination circuit 410, and the determination circuit 410 is connected so that the abnormal signal 452 can be output to the excitation light source drive circuit 411.

The rare earth-doped double clad fiber 205 includes a core doped with one or more selected from the group consisting of Yb, Er, Ho, and Tm, a first clad surrounding the core, A second cladding provided on the outside.
An isolator 208 is provided on the output side of the rare earth-doped double clad fiber 205.

The coupling method of the excitation port 102 and signal port 202 by the optical coupler 203 and the rare earth-doped double clad fiber 205 may be either an end-face incidence method or a side-incidence method, or may be used in combination.
A laser diode (LD) or the like is preferably used as the excitation light source 201, but is not limited thereto.

  The excitation light source drive circuit 411 outputs a first drive signal 350 that determines the drive current of the excitation light source of the optical fiber laser 100, and the excitation light source 101 of the optical fiber laser 100 outputs the first drive signal 350. The pumping light having a predetermined power is received and the second driving signal 450 for determining the driving current of the pumping light source 201 is output, and the pumping light source 201 of the optical fiber amplifier 400 receives the second driving signal 450. The pumping light with a predetermined power is output.

  The optical fiber laser 100 starts laser oscillation upon receiving the first drive signal 350, and the laser light is incident on the rare earth-doped double clad fiber 205 of the optical fiber amplifier 400 via the signal port 202 and the optical coupler 203. . On the other hand, the optical fiber amplifier 400 receives the second drive signal 450, and pumping light is output from the pumping light source 201, and this pumping light is incident on the rare earth-doped double clad fiber 205 via the optical coupler 203. The rare earth ions added to the core of the rare earth doped double clad fiber 205 are excited. Accordingly, the laser light output from the optical fiber laser 100 and incident on the optical fiber amplifier 400 is amplified by the rare earth-doped double clad fiber 205 and output as high-intensity laser light.

  However, as described above, when the laser beam once output is reflected and returned for some reason, it passes through the rare-earth-doped double clad fiber 205 although the intensity once decreases when passing through the isolator 208. Is amplified again. The intensity of the amplified reflected light may be equal to the intensity of the output laser light, and such high-intensity laser light enters the optical coupler 203. Most of the laser light incident on the optical coupler 203 is incident on the optical fiber laser 100 via the signal port 202, and the remaining laser light is distributed almost evenly to each pumping port 102 to reach the pumping light source 201. In some cases, fatal damage may be given to the excitation light source 201.

  The MOPA optical fiber laser of the present embodiment is provided with a monitor port 402 and a photodetector 401 in order to monitor the light intensity incident on such an excitation light source 201. Since light having the same intensity as that of the excitation port 102 propagates to the monitor port 402, the light intensity incident on the excitation light source 201 is observed by observing the light intensity incident on the photodetector 401 connected to the monitor port 402. Can know.

  For example, a light detector 401 having a function of receiving an ASE propagating through the monitor port 402 and outputting an electric signal having a higher voltage as the received light intensity increases is used. It can be appropriately selected from conventionally known photodetectors. When the light detector 401 receives ASE propagating through the monitor port 402, it outputs a light intensity signal 451 corresponding to the received light intensity, and the light intensity signal 451 is sent to the determination circuit 410.

  Similar to the determination circuit 310 shown in FIG. 4, the determination circuit 410 outputs an abnormal signal 452 when the light intensity signal 451 corresponding to the light intensity output from the photodetector 401 reaches the determination level. That is, when the light intensity received by the light detector 401 becomes greater than a certain intensity, an abnormal signal 452 is output.

  Upon receiving the abnormal signal 452, the excitation light source driving circuit 404 shuts down the second driving signal 450 immediately. When the second drive signal 450 is shut down, the pumping light emitted from the pumping light source 201 disappears, and the optical fiber amplifier 400 does not amplify the laser light output from the optical fiber laser 100. Accordingly, the laser light output from the optical fiber laser 100 is propagated in the optical fiber amplifier 400 while reducing its intensity due to the loss of each component, and is output as laser light. Even if all of the laser light returns to the optical fiber amplifier 400 as reflected light, most of the laser light is blocked by the isolator 208. Since the slightly transmitted reflected light is not amplified by the rare earth-doped double clad fiber 205, the excitation light source 201 is not damaged.

  Even if the second drive signal 450 is shut down, the laser is output because the optical fiber laser 100 continues to oscillate. If this laser output has a dangerous intensity, a means for stopping the output of the excitation light source of the optical fiber laser 100 may be provided separately.

[Third Embodiment]
A third embodiment of the present invention is shown in FIG.
This embodiment is a case where a MOPA type optical fiber laser is configured, and the basic configuration is the same as the optical fiber laser of the second embodiment shown in FIG. A certain optical fiber amplifier 400, a determination circuit 410, and a pumping light source driving circuit 511 are provided.

  As described above, in the case of the optical fiber laser of the MOPA system, the optical fiber laser 100 does not output laser light or the output is reduced due to failure or control of the optical fiber laser 100. In some cases, only the fiber amplifiers 200 and 400 are in operation. In such a situation, high-strength ASE is emitted in both directions of the optical fiber from the rare earth-doped double clad fiber 205 in the optical fiber amplifiers 200 and 400, and the pump port 102 is also passed through the optical coupler 203. In some cases, the excitation light source 201 may be damaged.

  In order to avoid this, in the present embodiment, in addition to the configuration of the MOPA type optical fiber laser shown in FIG. 5, a laser output from the optical fiber laser 100 between the optical fiber laser 100 and the optical fiber amplifier 400. An optical coupler 520 for branching a part of the light is provided, and a second photodetector 501 and a second determination circuit 510 for receiving the branched laser light are newly provided.

  A part of the output of the laser light from the optical fiber laser 100 is branched by the optical coupler 520, and the branched light is input to the second photodetector 501. As the second photodetector 501, for example, one having a function of outputting an electric signal having a higher voltage as the received light intensity is increased, and is appropriately selected from conventionally known photodetectors in the optical communication field or the like. And can be used. When the second photodetector 501 receives the laser beam branched by the optical coupler 520, the second photodetector 501 outputs a light intensity signal 551 corresponding to the received light intensity, and the light intensity signal 551 is output from the second determination circuit 510. Sent to.

  The second determination circuit 510 compares the light intensity signal 551 sent from the second photodetector 501 with a predetermined determination level, and when the level of the light intensity signal 551 reaches the determination level. The abnormal signal 552 is output to the excitation light source driving circuit 511.

  The determination level is, for example, based on the level of an electric signal output when the second photodetector 501 receives light when the laser output of the optical fiber laser 100 decreases to a light intensity that damages the excitation light source 201. Also set to a slightly higher level. That is, when the laser output of the optical fiber laser 100 decreases to a certain light intensity, the abnormal signal 552 is output from the second determination circuit 510. Upon receiving this abnormal signal 552, the excitation light source drive circuit 511 immediately shuts down the drive signal 550. When the drive signal 550 is shut down, no pump light is emitted from the pump light source 201, so that no ASE is generated from the rare earth-doped double clad fiber 205, and damage to the pump light source 201 can be avoided.

  On the other hand, when there is no output from the optical fiber laser 100 or when the output is reduced, the intensity of the ASE emitted from the rare earth-doped double clad fiber 205 is higher than when the optical fiber laser 100 is operating normally. When the intensity of ASE increases, the intensity of light incident on the excitation light source 201 via the optical coupler 203 increases, and the excitation light source 201 is damaged. Therefore, the intensity of light propagating through the monitor port 402 is monitored, and the pumping light source 201 can be prevented from being damaged by the same operation principle as that of the second embodiment. That is, when the intensity of light received by the light detector 401 becomes greater than a certain intensity, an abnormal signal 452 is output, and when the excitation light source drive circuit 511 receives this abnormal signal 452, the drive signal 550 is immediately shut down. When the laser drive signal 550 is shut down, the pumping light emitted from the pumping light source 201 disappears, so that no ASE is generated from the rare earth-doped double clad fiber 205, and the pumping light source 201 can be prevented from being damaged. .

  Here, the excitation light source driving circuit 511 shuts down the driving signal 550 when receiving either the abnormal signal 452 or the abnormal signal 552.

  In operation, when the excitation light source 201 of the optical fiber amplifier 400 outputs the excitation light before the optical fiber laser 100 outputs the laser light (that is, the excitation light source of the optical fiber laser 100 outputs the excitation light), Again, since high-intensity ASE is generated from the rare earth-doped double clad fiber 205, the excitation light source 201 may be damaged. Therefore, it is preferable to perform control so that the drive signal 550 is output after the drive signal 350 is output by a control circuit (not shown), or when the drive signal 350 is not output, the drive signal 550 is not output.

[Fourth Embodiment]
A third embodiment of the present invention is shown in FIG.
This embodiment is a case where a MOPA system optical fiber laser is configured, and the basic configuration is the same as that of the optical fiber laser of the third embodiment shown in FIG. 6, but the output from the optical fiber laser 100 in FIG. An optical coupler 520 for branching a part of the laser light to be output, an optical fiber laser from the first branch port 621 for branching a part of the laser light output from the optical fiber laser 100 and the optical fiber amplifier 400 A part of the light incident on 100 is also replaced with an optical coupler 620 having a second branch port 622 for branching. Further, when the third branching port is connected to the third photodetector 601 and the light intensity signal 651 from the third photodetector 601 is input to the third determination circuit 610, there is an abnormality. The third determination circuit 610 outputs an abnormal signal 652 to the excitation light source drive circuit 511.

  As described above, in the MOPA type optical fiber laser as shown in FIG. 7, when the light reflected once for some reason returns, this return light passes through the isolator 208. Although the intensity once decreases, it is amplified again by passing through the rare earth-doped double clad fiber 205. There is a possibility that the intensity of the amplified reflected light is equivalent to the intensity of the output laser light. Then, most of the amplified reflected light is incident on the optical fiber laser 100 through the signal port 202 and damages the optical components and the excitation light source of the optical fiber laser 100.

  In order to avoid this, in this embodiment, the optical coupler 620 is provided between the optical fiber laser 100 and the optical fiber amplifier 400, and the second branch port 622 is connected from the optical fiber amplifier 400 to the optical fiber laser 100. A part of the incident light is output, and the third optical detector 601 is connected to the second branch port 622 so that the optical fiber amplifier 400 enters the optical fiber laser 100. The light intensity can be monitored.

  As the third photodetector 601, for example, one having a function of outputting an electric signal having a higher voltage as the received light intensity is increased, and is appropriately selected from conventionally known photodetectors in the optical communication field or the like. And can be used. When the third photodetector 601 receives the laser beam branched by the optical coupler 620, the third photodetector 601 outputs a light intensity signal 651 corresponding to the received light intensity, and the light intensity signal 651 is output from the third determination circuit 610. Sent to.

  The third determination circuit 610 compares the light intensity signal 651 transmitted from the third photodetector 601 with a predetermined determination level, and when the level of the light intensity signal 651 reaches the determination level. The abnormal signal 652 is output to the excitation light source driving circuit 511.

  For example, the determination level is set to a level slightly lower than the level of the electrical signal output when the photodetector receives the light intensity at which the optical component or the excitation light source of the optical fiber laser 100 is damaged. That is, when the intensity of light received by the third photodetector 601 becomes greater than a certain intensity, an abnormal signal 652 is output.

  The abnormal signal 652 output from the third determination circuit 610 is sent to the excitation light source driving circuit 511. Upon receiving the abnormal signal 652, the excitation light source driving circuit 511 immediately shuts down the driving signal 550. When the drive signal 550 is shut down, amplification by the rare earth-doped optical fiber 205 is not performed, so that even if the reflected light returns, the intensity of the reflected light reaching the optical coupler 203 becomes very low. Therefore, it is possible to avoid damage to the optical components of the optical fiber laser 100 and the excitation light source.

  The excitation light source drive circuit 511 shuts down the drive signal 550 if any one of the abnormal signals 452, 552, 652 is input.

It is a block diagram which shows the conventional optical fiber laser. It is a block diagram which shows another conventional optical fiber laser. It is a block diagram which shows the conventional optical fiber laser of a MOPA system. It is a block diagram which shows 1st Embodiment of this invention. It is a block diagram which shows 2nd Embodiment of this invention. It is a block diagram which shows 3rd Embodiment of this invention. It is a block diagram which shows 4th Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100,110,300 ... Optical fiber laser, 101, 201 ... Excitation light source, 102 ... Excitation port, 103, 111, 203 ... Optical coupler, 104 ... Outlet port, 105, 205 ... Rare earth addition double clad fiber (rare earth addition light) Fiber), 106 ... high reflection mirror, 107 ... output coupler, 108, 208 ... isolator, 202 ... signal port, 301, 401, 501, 601 ... photodetector, 302 ... monitor port, 310, 410, 510, 610 ... Determination circuit, 311, 411, 511... Excitation light source drive circuit, 350, 450, 550... Drive signal, 351, 451, 551, 651 ... light intensity signal, 352, 452, 552, 652, abnormal signal, 520, 620. Optical coupler.

Claims (13)

A rare earth-doped optical fiber that is at least a laser medium, a plurality of pumping light sources that optically pump the rare earth-doped optical fiber, and an optical coupler that combines the pumping light from each pumping light source and enters the rare earth-doped optical fiber, In an optical fiber laser that oscillates by entering pump light into a rare earth-doped optical fiber
The optical coupler is provided with a monitor port through which a part of the return light traveling from the rare earth-doped optical fiber toward the pumping light source is propagated, and the intensity of the return light propagating through the monitor port is measured. An optical fiber laser, characterized in that an excitation light source control means is provided for reducing the output of the excitation light source to prevent amplification of return light when a predetermined value is exceeded.   A light detector connected to the monitor port for measuring the intensity of the return light; a light intensity signal received from the light detector; and a light intensity received by the light detector. A determination circuit that emits an abnormal signal when it becomes larger, and an excitation that is connected to the determination circuit, emits a drive signal to the excitation light source to emit light when not receiving the abnormal signal, and shuts down the drive signal when the abnormal signal is received The optical fiber laser according to claim 1, further comprising a light source driving circuit.   The rare earth-doped optical fiber is provided on one or more cores selected from the group consisting of Yb, Er, Ho, and Tm, a first clad surrounding the core, and an outer side of the first clad. 3. The optical fiber laser according to claim 1, wherein the optical fiber laser is a rare earth-doped double clad fiber having a second cladding.   A high-reflection mirror is provided on the excitation light incident side of the rare earth-doped optical fiber to reflect the laser light generated by laser oscillation but to the laser output side of the rare earth-doped optical fiber. The light according to claim 1, wherein an output coupler that substantially reflects and partially transmits the laser beam is provided, and a resonator is configured between the high-reflection mirror and the output coupler. Fiber laser. A rare earth-doped optical fiber that is at least an optical amplifying medium; a plurality of pumping light sources that optically pump the rare earth-doped optical fiber; In an optical fiber amplifier that amplifies and outputs the signal light in a rare earth-doped optical fiber,
The optical coupler is provided with a monitor port through which a part of the return light traveling from the rare earth-doped optical fiber toward the pumping light source is propagated, and the intensity of the return light propagating through the monitor port is measured. An optical fiber amplifier characterized in that pumping light source control means for reducing the output of the pumping light source to prevent amplification of return light when a predetermined value is exceeded is provided.   A light detector connected to the monitor port for measuring the intensity of the return light; a light intensity signal received from the light detector; and a light intensity received by the light detector. A determination circuit that emits an abnormal signal when it becomes larger, and an excitation that is connected to the determination circuit, emits a drive signal to the excitation light source to emit light when not receiving the abnormal signal, and shuts down the drive signal when the abnormal signal is received 6. The optical fiber amplifier according to claim 5, further comprising a light source driving circuit.   The rare earth-doped optical fiber is provided on one or more cores selected from the group consisting of Yb, Er, Ho, and Tm, a first clad surrounding the core, and an outer side of the first clad. 7. The optical fiber amplifier according to claim 5, wherein the optical fiber amplifier is a rare earth-doped double clad fiber having a second clad. An optical fiber laser that oscillates by entering pump light into a rare earth-doped optical fiber, at least a rare earth-doped optical fiber that is a laser medium, a plurality of pump light sources that optically pump the rare earth-doped optical fiber, A MOPA optical fiber laser having an optical coupler that combines pumping light and laser light emitted from the optical fiber laser and enters the rare-earth-doped optical fiber, and amplifies and outputs the laser light emitted from the optical fiber laser In
The optical coupler is provided with a monitor port through which a part of the return light traveling from the rare earth-doped optical fiber toward the pumping light source is propagated, and the intensity of the return light propagating through the monitor port is measured. A MOPA type optical fiber laser characterized in that pumping light source control means is provided for reducing amplification of return light by reducing the output of the pumping light source when a predetermined value is exceeded.   A light detector connected to the monitor port for measuring the intensity of the return light; a light intensity signal received from the light detector; and a light intensity received by the light detector. A determination circuit that emits an abnormal signal when it becomes larger, and an excitation that is connected to the determination circuit, emits a drive signal to the excitation light source to emit light when not receiving the abnormal signal, and shuts down the drive signal when the abnormal signal is received 9. The MOPA optical fiber laser according to claim 8, further comprising a light source driving circuit.   The rare earth-doped optical fiber is provided on one or more cores selected from the group consisting of Yb, Er, Ho, and Tm, a first clad surrounding the core, and an outer side of the first clad. 10. The MOPA optical fiber laser according to claim 8, wherein the MOPA optical fiber laser is a rare earth-doped double clad fiber having a second cladding. An optical coupler provided at a signal port connecting the output side of the optical fiber laser and the optical coupler and branching a part of the laser light output from the optical fiber laser, and a first coupler connected to the branch port of the optical coupler When the light intensity signal from the second light detector and the second light detector is input and the light intensity received by the second light detector becomes lower than a certain intensity, an abnormal signal is output to the excitation light source drive circuit. The MOPA type optical fiber laser according to claim 9 or 10 , further comprising a second determination circuit that emits light. A part of the laser light output from the optical fiber laser provided at a signal port connecting the output side of the optical fiber laser and the optical coupler is branched to a first branch port, and the light is output from the optical coupler. An optical coupler for branching return light directed to the fiber laser to a second branch port, a second photodetector connected to the first branch port, and a light intensity signal from the second photodetector are input. When the intensity of light received by the second photodetector becomes lower than a certain intensity, a second determination circuit that issues an abnormal signal to the excitation light source driving circuit and a second determination port connected to the second branch port And a third determination circuit for generating an abnormal signal to the excitation light source driving circuit when the intensity of light received by the third photodetector is greater than a certain intensity. claim 9-11 noise and A MOPA optical fiber laser as described above. The MOPA system according to any one of claims 9 to 12, wherein the pumping light source driving circuit is configured not to emit a driving signal when the optical fiber laser is not output. Fiber optic laser.

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