WO2010029663A1 - Laser à fibre optique à synchronisation des modes, et procédé d'oscillation d'un laser à impulsions utilisant un laser à fibre optique à synchronisation des modes - Google Patents

Laser à fibre optique à synchronisation des modes, et procédé d'oscillation d'un laser à impulsions utilisant un laser à fibre optique à synchronisation des modes Download PDF

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WO2010029663A1
WO2010029663A1 PCT/JP2009/002417 JP2009002417W WO2010029663A1 WO 2010029663 A1 WO2010029663 A1 WO 2010029663A1 JP 2009002417 W JP2009002417 W JP 2009002417W WO 2010029663 A1 WO2010029663 A1 WO 2010029663A1
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mode
wavelength
laser
fiber
locked
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PCT/JP2009/002417
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English (en)
Japanese (ja)
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浦田佳治
和田智之
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株式会社メガオプト
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Priority to JP2010528589A priority Critical patent/JP5341096B2/ja
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking
    • H01S3/1112—Passive mode locking
    • H01S3/1115—Passive mode locking using intracavity saturable absorbers
    • H01S3/1118—Semiconductor saturable absorbers, e.g. semiconductor saturable absorber mirrors [SESAMs]; Solid-state saturable absorbers, e.g. carbon nanotube [CNT] based
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
    • H01S3/067—Fibre lasers
    • H01S3/0675—Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/105—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length
    • H01S3/1055—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length one of the reflectors being constituted by a diffraction grating
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08018—Mode suppression
    • H01S3/08022—Longitudinal modes
    • H01S3/08031—Single-mode emission
    • H01S3/08036—Single-mode emission using intracavity dispersive, polarising or birefringent elements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/10038—Amplitude control
    • H01S3/10046—Pulse repetition rate control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/1062—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using a controlled passive interferometer, e.g. a Fabry-Perot etalon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
    • H01S3/1106—Mode locking
    • H01S3/1109—Active mode locking

Definitions

  • the present invention relates to a mode-locked fiber laser and a pulse laser light oscillation method using the mode-locked fiber laser, and more particularly, to a mode-locked fiber laser using a gain fiber in a laser resonator and a mode-locked fiber laser.
  • the present invention relates to an oscillation method of pulse laser light.
  • a mode-locked laser is known to be effective as means for generating pulsed laser light having a short pulse width of sub-picosecond or less, that is, pulse laser light by a short pulse train (pulse train) of sub-picosecond or less. .
  • Examples of processing objects that can be processed by such an ultrashort pulse laser beam include metal materials such as aluminum and iron, metal materials having a high melting point such as molybdenum and tungsten, and resin materials such as Teflon (registered trademark). And non-metallic materials such as glass and ceramics or biological materials.
  • examples of the types of processing methods for such a processing target include various types such as cutting, joining, and surface modification. Therefore, in processing performed using ultrashort pulse laser light, it is necessary to perform processing by setting optimum processing conditions in accordance with the material and processing method constituting the processing target.
  • the processing conditions when processing using ultrashort pulse laser light means the wavelength, pulse width, repetition frequency, output intensity of laser light, and the like. If these parameters, which are processing conditions, can be freely changed to those suitable for the material and processing method of the processing object, the processing can be performed under the optimum conditions for each processing.
  • a laser beam oscillated from the mode-locked laser although a pulse laser beam having a short pulse width can be obtained, there is a problem that it is generally difficult to change the pulse width condition. More specifically, since laser light that is mode-locked by the mode-locking element is pulse-oscillated at a repetition frequency corresponding to the resonator length, the repetition frequency is the value of the resonator length of the laser resonator.
  • the pulse train can be thinned out and extracted, the device configuration is complicated and the frequency obtained
  • the upper limit of is limited to the speed of the element, and is at most about 1 MHz.
  • the EO element requires a high voltage, so that there is a problem in the durability of the element.
  • a mode-locked laser is required to have a technique that can easily obtain a wider selection range of repetition frequencies while eliminating the complexity of the apparatus as much as possible.
  • An object of the present invention is to provide a mode-locked fiber laser capable of changing the repetition frequency of laser light that is pulse-oscillated in a wider range and a pulse laser light oscillation method using the mode-locked fiber laser.
  • the present invention provides a plurality of feedback elements having different reflection wavelengths, such as a fiber Bragg grating (FBG), in a laser resonator constituting a mode-locked fiber laser.
  • FBG fiber Bragg grating
  • the repetition frequency of the pulsed laser beam can be easily changed without significantly changing the conventional apparatus configuration. . Therefore, according to the present invention, since the resonator length is substantially changed by the selected feedback element by selecting the feedback element suitable for the wavelength of the oscillated laser beam, the configuration in the apparatus In addition, the repetition frequency of the pulsed laser beam can be changed without changing the arrangement positions of the constituent members.
  • a mode synchronization means is arranged on one end side of the gain fiber, and a plurality of feedbacks reflect light of different wavelengths with high reflectance on the other end side of the gain fiber.
  • An element is arranged, a resonator is constituted by the mode synchronization means and the feedback element, and a wavelength selection means for selecting a wavelength of laser light oscillated by the gain fiber is provided in the resonator. is there.
  • the plurality of feedback elements are arranged in series along the traveling direction of the light in the resonator, and the light in the resonator is directed in the traveling direction.
  • the plurality of feedback elements arranged in series along the line can be sequentially passed.
  • the feedback element is a fiber Bragg grating
  • the mode-locking means is a saturable absorbing element
  • the wavelength selecting means is a diffraction grating. It is what you have.
  • the feedback element is a fiber Bragg grating
  • the mode-locking means is a saturable absorber
  • the wavelength selecting means is a birefringent filter. Alternatively, it is a prism.
  • the present invention is the mode-locked fiber laser according to the present invention described above, and further, the one of the gain fibers between the one end side of the gain fiber and the wavelength selecting means in the resonator.
  • a collimating lens that converts the light emitted from the end of the light into parallel light, and a polarizing element or polarization preserving fiber into which the parallel light emitted from the collimating lens is incident.
  • the feedback element is a fiber Bragg grating
  • the mode-locking means is an AO mode-locking element
  • the wavelength selecting means is a diffraction grating, It is designed to be a birefringent filter or a prism.
  • the feedback element is a fiber Bragg grating
  • the mode-locking means and the wavelength selecting means are acousto-optic wavelength tunable filters. Is.
  • a dispersion correction optical element into which the diffracted light emitted from the acoustooptic wavelength tunable filter is incident is further provided.
  • the present invention is the mode-locked fiber laser according to the present invention described above, and further, between the one end portion side of the gain fiber in the resonator and the acoustooptic wavelength tunable filter, A collimating lens that converts the light emitted from the one end side into parallel light and a polarization controller that receives the parallel light emitted from the collimating lens are provided.
  • the present invention is a method for oscillating a pulsed laser beam using the mode-locked fiber laser according to the present invention described above, wherein the wavelength selecting means changes the wavelength of the laser beam to be pulsed out of the plurality of feedback elements.
  • One of the plurality of feedback elements that can reflect the wavelength selected by the wavelength selection means among the plurality of feedback elements and the mode are selected.
  • the laser light amplified with the synchronizing means and emitted from the gain fiber is pulsed from the resonator.
  • the present invention is configured as described above, the repetition frequency of pulsed laser light can be changed in a wider range without complicating the apparatus configuration as compared with the prior art. There is an excellent effect that it becomes possible.
  • FIG. 1 is an explanatory diagram of a conceptual configuration of a mode-locked fiber laser according to the first embodiment of the present invention.
  • FIG. 2 is an explanatory diagram showing, as a conceptual graph, the intensity and pulse period of laser light pulsed from a mode-locked fiber laser.
  • FIG. 2A shows a resonator length L 1 and a wavelength ⁇ 1 .
  • FIG. 2B is an explanatory diagram when the laser beam is amplified and pulsated, and FIG. 2B is an explanatory diagram when the laser beam having the resonator length L 2 and the wavelength ⁇ 2 is amplified and pulsated.
  • FIG. 1 is an explanatory diagram of a conceptual configuration of a mode-locked fiber laser according to the first embodiment of the present invention.
  • FIG. 2 is an explanatory diagram showing, as a conceptual graph, the intensity and pulse period of laser light pulsed from a mode-locked fiber laser.
  • FIG. 2A shows a resonator length L 1 and a wavelength
  • FIG. 2C is an explanatory diagram when a laser beam having a wavelength of ⁇ 3 is amplified and pulsed by a resonator length L 3 .
  • FIG. 3 is an explanatory diagram of a conceptual configuration of a mode-locked fiber laser according to the second embodiment of the present invention.
  • FIG. 4 is an explanatory diagram of a conceptual configuration of a modification of the mode-locked fiber laser according to the second embodiment of the present invention.
  • FIG. 5 is an explanatory diagram of a conceptual configuration of a modification of the mode-locked fiber laser according to the second embodiment of the present invention.
  • FIG. 6 is an explanatory diagram of a conceptual configuration of a modification of the mode-locked fiber laser according to the first embodiment of the present invention.
  • FIG. 7 is an explanatory diagram of a conceptual configuration of a modified example of the mode-locked fiber laser shown in FIG.
  • FIG. 8 is an explanatory diagram showing the setup of the mode-locked fiber laser according to the present invention used in the experiment conducted by the present inventor.
  • FIG. 9 is a graph showing the experimental results of the experiment conducted by the inventors of the present application, using a prism instead of the acousto-optic tunable filter, and changing the angle of the partially reflecting mirror as the output mirror. The oscillation spectrum when oscillating is shown.
  • A shows the case where the angle of the partially reflecting mirror is adjusted so as to select the short wavelength side
  • B shows the case where the angle of the partially reflecting mirror is adjusted so as to select the long wavelength side.
  • FIG. 10 is a graph showing in detail the peak near the oscillating wavelength of 1056 nm in the graph shown in FIG.
  • the horizontal axis represents wavelength (Wavelength) and the vertical axis represents intensity (Intensity).
  • FIG. 10 is a graph showing in detail the peak near the oscillating wavelength of 1056 nm in the graph shown in FIG.
  • the horizontal axis represents wavelength (Wavelength) and the vertical axis represents intensity (Intensity).
  • FIG. 11 shows the input / output characteristics at the wavelength of 1056 nm when the prism is inserted and when the acoustooptic wavelength tunable filter is inserted, that is, the current value of the pumping semiconductor laser light source and the mode-locked fiber in the setup shown in FIG. It is a graph which shows the input-output characteristic with the output power of the laser beam output as an emitted light from a laser.
  • the horizontal axis represents the current value (LD current) of the excitation semiconductor laser light source, and the vertical axis represents the output power (Output power).
  • FIG. 12 is a graph showing the relationship between the change in output power with respect to the RF frequency and the obtained wavelength. In the graph shown in FIG.
  • FIG. 13 is a graph showing a mode-locked pulse train as a waveform when the laser output is observed with a PIN photodiode under conditions where oscillation is stable at any one of the three wavelengths of 1056 nm, 1060 nm, and 1064 nm. It is.
  • the horizontal axis represents time (Time)
  • the vertical axis represents intensity (Intensity).
  • FIG. 14 is a photograph of the autocorrelator screen taken when the pulse width in mode synchronization was measured with an autocorrelator (APE, PulseCheck).
  • APE autocorrelator
  • FIG. 15 is a graph showing measurement results obtained by measuring spectral shapes at normal oscillation and mode-locked oscillation at 1060 nm.
  • the horizontal axis represents wavelength (Wavelength), and the vertical axis represents intensity (Intensity).
  • FIG. 16 shows the optical length of the laser resonator composed of the fiber Bragg grating (FBG1), the fiber Bragg grating (FBG2), the fiber Bragg grating (FBG3), and the partial reflection mirror as the output mirror, and the round trip time of light ( For RT time) and round trip frequency (RT freq.),
  • the refractive index of the silicate glass used in the fiber used in the experiment is 1.45, and the element placed in free space does not consider the effective length. It is a graph which shows the calculated value and experimental value in the case.
  • a fiber laser is solid in terms of mechanical stability. It has much better performance than a laser. However, it is physically impossible to change the length of a resonator operating at a single wavelength. For this reason, in the embodiments of the mode-locked fiber laser and the pulse laser light oscillation method using the mode-locked fiber laser according to the present invention, the reflection wavelengths are different inside the laser resonator constituting the mode-locked fiber laser. A plurality of feedback elements, for example, fiber Bragg gratings are inserted.
  • the fiber Bragg grating constituting the embodiment of the mode-locked fiber laser and the pulse laser beam oscillation method using the mode-locked fiber laser according to the present invention constitutes a feedback element corresponding to the resonator mirror in the solid-state laser.
  • the reflection band of the fiber Bragg grating is much narrower than that of the mirror. Specifically, it is difficult to create a steep reflection / transmission characteristic with a mirror, but according to a fiber Bragg grating, it is easy to create a characteristic with a reflection band of about 0.2 nm, and the surroundings Wavelength light is almost completely transmitted.
  • the embodiments of the mode-locked fiber laser and the pulse laser beam oscillation method using the mode-locked fiber laser according to the present invention are made by paying attention to the characteristics of the fiber Bragg grating described above, and reflect at different wavelengths.
  • the resonator length can be easily varied according to the resonance wavelength.
  • mode-locked oscillation is performed inside a resonator configured using a plurality of fiber Bragg gratings that reflect at different wavelengths, the fiber for a certain wavelength is changed by changing the wavelength while maintaining the state. It becomes possible to arbitrarily select a repetition frequency determined by the length of the resonator formed by the Bragg grating.
  • a high-speed and mechanically stable resonator configuration can be obtained.
  • a laser in which an acoustooptic wavelength tunable filter is inserted in a resonator is called a frequency-shifted feedback laser (Frequency-Shifted Feedback Laser: FSF Laser). Since synchronization is realized at the same time, there is another advantage that no element for mode synchronization needs to be applied.
  • FIG. 1 shows a conceptual configuration explanatory diagram of a mode-locked fiber laser 10 according to the first embodiment of the present invention.
  • This mode-locked fiber laser 10 has three fiber Bragg gratings (FBGs) 14 and 16 that are arranged so as to have different reflection wavelengths and to be adjacent to the saturable absorber 12 that is a mode-locking element as a mode-locking means.
  • FBGs fiber Bragg gratings
  • a coupler 20 that introduces excitation light, which is laser light generated by an excitation semiconductor laser light source 30 (described later), into a gain fiber 22 (described later), and an end portion of the coupler 20
  • a gain fiber 22 is connected to the optical fiber core and doped with a laser active medium and excited by pumping light generated by the pumping semiconductor laser light source 30 to output laser light, and an end 22b of the gain fiber 22 Connected and output from gain fiber 22 A coupler 24 for making light incident on a collimating lens 26 (described later), a collimating lens 26 arranged at the rear stage of the coupler 24 and making the laser light emitted from the coupler 24 parallel light, and the laser device 10 A diffraction grating 28 as a wavelength selection means that is disposed between the collimating lens 26 and the saturable absorber element 12 on the optical path of the laser beam and capable of diffracting laser light of a predetermined wavelength, and the saturable absorber element 12.
  • a condensing lens 34 that condenses the laser light emitted from the diffraction grating 28.
  • a plurality of fiber Bragg gratings can be arranged inside the mode-locked fiber laser 10 in the present invention, in the present embodiment, as described above, a series is provided along the light traveling direction. Three fiber Bragg gratings 14, 16, 18 are arranged (in series) so that light can sequentially pass through the three fiber Bragg gratings 14, 16, 18 arranged in series (series) along the traveling direction. Arranged.
  • the fiber Bragg grating 14 as one feedback element can reflect light with a narrow band wavelength with high reflectivity.
  • the fiber Bragg grating 14 has a reflectance of 30% with respect to the laser beam having the wavelength ⁇ 1 and other wavelengths. by having a transmittance of about 100% with respect to the laser beam, it is assumed it is possible to selectively reflect the laser beam having a wavelength lambda 1. Furthermore, the distance serving resonator length between the saturable absorber element 12 and the fiber Bragg grating 14 is assumed to be installed so that L 1.
  • the fiber Bragg grating 16 disposed adjacent to the fiber Bragg grating 14 can also reflect light of a narrow band wavelength with high reflectivity.
  • the fiber Bragg grating 16 has a reflectance of 30% with respect to the laser light having the wavelength ⁇ 2 and other wavelengths.
  • the distance serving resonator length between the saturable absorber element 12 and the fiber Bragg grating 16 is assumed to be installed so that L 2.
  • Such resonator length L 2 the distance L b between the fiber Bragg grating 16 and the diffraction grating 28, a distance which is the sum of the distance L d between the diffraction grating 28 and the saturable absorber element 12.
  • the fiber Bragg grating 18 disposed adjacent to the fiber Bragg grating 16 can also reflect light of a narrow band wavelength with high reflectivity.
  • the fiber Bragg grating 18 has a reflectance of 30% with respect to the laser light having the wavelength ⁇ 3 and other wavelengths. by having a transmittance of about 100% with respect to the laser beam, it is assumed it is possible to selectively reflect a laser beam having a wavelength lambda 3. Furthermore, the distance serving resonator length between the saturable absorber element 12 and the fiber Bragg grating 18 is assumed to be installed such that L 3.
  • the pumping light is generated by a pumping semiconductor laser light source 30 disposed outside the mode-locking fiber laser 10, and the pumping semiconductor laser light source 30 uses a gain substance. It is connected to the coupler 20 via a passive fiber 32 that does not have. That is, the excitation light generated by the excitation semiconductor laser light source 30 is incident on the coupler 20 disposed in the mode-locked fiber laser 10 via the passive fiber 32.
  • the diffraction grating 28 diffracts laser light having a predetermined wavelength in accordance with the angle at which the laser light is incident on the diffraction grating 28.
  • the diffraction grating 28 includes the diffraction grating 28.
  • a driving device 29 is connected as means for rotating. The driving device 29 can rotate the diffraction grating 28 in the direction of the arrow A under the control of a personal computer (not shown), whereby the angle at which laser light is incident on the diffraction grating 28. Can be set freely.
  • a broadband semiconductor saturable absorber mirror SESAM
  • SESAM broadband semiconductor saturable absorber mirror
  • the gain fiber 22 in this embodiment, ytterbium (Yb) is used as a gain medium, and a gain fiber having a wavelength range of 1000 nm to 1120 nm is used.
  • the excitation semiconductor laser light source 30 generates laser light having a wavelength of 975 nm as excitation light.
  • the diffraction grating 28 is a laser having a specific wavelength ⁇ ( ⁇ is a wavelength reflected by any one of the three fiber Bragg gratings 14, 16, and 18 used in the laser). It is assumed that it is rotated by the driving device 29 so that there is no loss with respect to only light.
  • the saturable absorbing element 12 performs a known shutter operation at the wavelength ⁇ and highly reflects light with the wavelength ⁇ .
  • the pumping light generated by the pumping semiconductor laser light source 30 enters the gain fiber 22 from the end 22 a of the gain fiber 22 through the passive fiber 32 and the coupler 20.
  • the pumping light excites the laser active medium of the gain fiber 22, but since the loss is small only for the wavelength ⁇ diffracted by the diffraction grating 28, any one of the fiber Bragg gratings 14, 16, 18 that reflects the wavelength ⁇ . And a saturable absorption element 12 functioning as a total reflection mirror, and a laser beam having a specific wavelength ⁇ is external to the mode-locked fiber laser 10 by the shutter operation of the saturable absorption element 12. The light is output in the form of pulses as outgoing light (see FIG. 1).
  • the wavelength of pulsed laser light is the wavelength ⁇ 1 that can be reflected by the fiber Bragg grating 14 among the wavelengths that can be reflected by the three fiber Bragg gratings.
  • the angle of the diffraction grating 28 is adjusted by driving the driving device 29 so that the diffraction grating 28 has an angle suitable for reducing the loss of only the laser beam having the wavelength ⁇ 1.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light.
  • Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain for wavelength lambda 1 of the light .
  • the laser resonator is configured between the saturable absorber element 12 and the three fiber Bragg gratings 14, 16, 18, but the diffraction grating 28 is kept in a state that does not give a loss only to the wavelength ⁇ 1 . In the resonator, only the light of wavelength ⁇ 1 generates a high gain, and laser oscillation can be performed only at this wavelength.
  • the diffraction grating 28 is only the light of wavelength lambda 1 are set so that the angle which is suitable for resonance at low loss, wavelengths other than the wavelength lambda 1 of the light Therefore, the laser light is reciprocated and amplified between the fiber Bragg grating 14 and the saturable absorbing element 12, and a pulse laser that is emitted to the outside of the mode-locked fiber laser 10 is lost. It will be output as light.
  • FIG. 2 is an explanatory diagram showing a conceptual graph of the intensity and pulse period of laser light pulse-oscillated from the mode-locked fiber laser 10.
  • FIG. 2 (a) illustrates a case where the pulse oscillation by amplifying the laser beam having a wavelength lambda 1 between the saturable absorber element 12 and the fiber Bragg grating 14 is shown.
  • the resonator length as the distance between the saturable absorbing element 12 and the fiber Bragg grating 14 is L. 1 .
  • f 1 c / 2L 1
  • FIG. 2A laser light having a certain intensity and pulse width is oscillated at a pulse period 2L 1 / c.
  • FIG. 2A the case of oscillating a pulse laser beam having a light intensity or a wider pulse period than the pulse oscillation shown in FIG. 2A will be described below.
  • the resonance is longer than the resonator length L 1 in the example shown in FIG. It is only necessary to increase the length of the instrument.
  • a fiber Bragg grating 16 suitable laser beam having a wavelength lambda 2 as a feedback element, it is sufficient to oscillate a laser beam having a wavelength lambda 2. That is, in place of the fiber Bragg grating 14, by the fiber Bragg grating 16 and the feedback element, the resonator length is the resonator length L 2, and the resonator length is longer than the resonator length L 1. For this reason, as a result, it becomes possible to obtain pulse oscillation different from the pulse period and light intensity shown in FIG.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light.
  • Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain for wavelength lambda 2 light .
  • the laser resonator is configured between the saturable absorber 12 and the three fiber Bragg gratings 14, 16, 18, but the diffraction grating 28 is kept in a state that does not give a loss only to the wavelength ⁇ 2 . In the resonator, only the light of wavelength ⁇ 2 generates a high gain, and laser oscillation can be performed only at this wavelength.
  • the diffraction grating 28 is only light of the wavelength lambda 2 is set to be an angle which is suitable for resonance at low loss, wavelengths other than the wavelength lambda 2 light Therefore, the laser beam is amplified by reciprocating between the fiber Bragg grating 16 and the saturable absorption element 12, and a pulse laser that is emitted to the outside of the mode-locked fiber laser 10 is lost. It will be output as light.
  • FIG. 2B shows an explanatory diagram when the laser beam having the wavelength ⁇ 2 is amplified between the saturable absorbing element 12 and the fiber Bragg grating 16 to cause pulse oscillation.
  • the pulse period 2L 2 / c at this time is wider than the pulse period 2L 1 / c in the case of the laser light having the wavelength ⁇ 1 shown in FIG. 2A, and the light intensity is It is stronger than the case of the laser beam having the wavelength ⁇ 1 shown in 2 (a).
  • FIGS. 2 (a) and 2 (b) the case of oscillating a pulse laser beam having a light intensity or a wider pulse period than the pulse oscillation shown in FIGS. 2 (a) and 2 (b) will be described below.
  • FIG. 2A and FIG. in which it may be longer resonator length than the cavity length L 1 and the resonator length L 2 of the embodiment shown in.
  • the fiber Bragg grating 18 which is suitable for a laser beam having a wavelength lambda 3 as a feedback element, it is sufficient to oscillate a laser beam having a wavelength lambda 3.
  • the resonator length is the resonator length L 3, and the more the resonator length L 1 and the resonator length L 2
  • the resonator length becomes longer. For this reason, as a result, it becomes possible to obtain pulse oscillation different from the pulse period and light intensity shown in FIG. 2 (a) and FIG. 2 (b).
  • the mode-locked fiber laser 10 is used to obtain pulsed laser light having the wavelength ⁇ 3 with the resonator length L 3 .
  • the diffraction grating 28, the diffraction grating 28 so that the angle suitable to become a low loss only for the laser beam of wavelength lambda 3, by driving the driving unit 29 to adjust the angle of the diffraction grating 28.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light. Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain to light having a wavelength lambda 3 .
  • the laser resonator is configured between the saturable absorber 12 and the three fiber Bragg gratings 14, 16, 18, but the diffraction grating 28 is kept in a state that does not give a loss only to the wavelength ⁇ 3 .
  • the resonator only light of wavelength ⁇ 3 generates a high gain, and laser oscillation can be performed only at this wavelength.
  • the diffraction grating 28 is only the light of wavelength lambda 3 is set to be an angle which is suitable for resonance at low loss, wavelengths other than the light of the wavelength lambda 3 Therefore, the laser light is reciprocated and amplified between the fiber Bragg grating 18 and the saturable absorbing element 12, and a pulse laser that is emitted to the outside of the mode-locked fiber laser 10 is lost. It will be output as light.
  • FIG. 2C shows an explanatory diagram when the laser beam having the wavelength ⁇ 3 is amplified between the saturable absorbing element 12 and the fiber Bragg grating 18 and is oscillated.
  • the pulse period 2L 3 / c at this time is the laser with the pulse period 2L 1 / c in the case of the laser light with the wavelength ⁇ 1 shown in FIG. 2A and the laser with the wavelength ⁇ 2 shown in FIG. It is wider than the pulse period 2L 2 / c in the case of light, and the light intensity is the case of the laser light having the wavelength ⁇ 1 shown in FIG. 2A and the wavelength ⁇ shown in FIG. It is stronger than the case of laser light of No. 2 .
  • the average light intensity of pulse oscillation does not change significantly as shown in FIGS.
  • the intensity increases in inverse proportion to the repetition frequency.
  • pulse oscillation is performed at a repetition frequency corresponding to the length of the resonator.
  • the mode-locked fiber laser 10 by installing a plurality of fiber Bragg gratings that reflect laser beams of different wavelengths, the wavelength of the laser light generated in the laser device is changed to a plurality of fiber Bragg gratings.
  • the pulse period and repetition frequency can be easily changed.
  • the length of the optical axis is proportional to the length of the gain fiber. Since it is possible to wind and arrange the fiber, it is possible to easily obtain a selection range of a wide repetition frequency.
  • FIG. 3 is an explanatory diagram of a conceptual configuration of a mode-locked fiber laser 100 according to the second embodiment of the present invention.
  • the mode-locked fiber laser 100 is capable of diffracting laser light having a predetermined wavelength instead of the diffraction grating 28.
  • a wavelength selection element 102 is provided.
  • the wavelength selection element 102 for example, a birefringence filter can be used.
  • the mode-locked fiber laser 100 is disposed between the collimating lens 26 and the saturable absorber 12 on the optical path of the mode-locked fiber laser device 100 and diffracts laser light having a predetermined wavelength.
  • the wavelength selection element 102 is provided as a wavelength selection means that can be configured to be disposed between the saturable absorption element 12 and the wavelength selection element 102 and collects the laser light emitted from the wavelength selection element 102.
  • the optical lens 34 is provided.
  • the three fiber Bragg gratings 14, 16, and 18 are disposed inside the mode-locked fiber laser 100 in the present invention as described above.
  • the distance serving resonator length between the saturable absorber element 12 and the fiber Bragg grating 14 is assumed to be installed so that L 1.
  • the distance serving resonator length between the fiber Bragg grating 16 which is positioned adjacent to the saturable absorption element 12 and the fiber Bragg grating 14 is assumed to be installed so that L 2.
  • the distance serving resonator length between the fiber Bragg grating 18 that is positioned adjacent to the saturable absorption element 12 and the fiber Bragg grating 16 is assumed to be installed such that L 3.
  • the wavelength selection element 102 reflects or transmits laser light having a predetermined wavelength according to the angle at which laser light is incident on the wavelength selection element 102.
  • a driving device 29 is connected as means for rotating the wavelength selection element 102.
  • the drive device 29 can rotate the wavelength selection element 102 in the direction of arrow B under the control of a personal computer (not shown), so that laser light is incident on the wavelength selection element 102. It is possible to freely set the angle.
  • the wavelength selection element 102 has a specific wavelength ⁇ ( ⁇ is a wavelength reflected by any one of the three fiber Bragg gratings 14, 16, and 18 used in the laser). It is assumed that it is rotated by the driving device 29 so that there is no loss with respect to only the laser beam.
  • the saturable absorbing element 12 performs a known shutter operation at the wavelength ⁇ and highly reflects light with the wavelength ⁇ .
  • the pumping light generated by the pumping semiconductor laser light source 30 enters the gain fiber 22 from the end 22 a of the gain fiber 22 through the passive fiber 32 and the coupler 20.
  • the pumping light excites the laser active medium of the gain fiber 22, but since the loss is small only for the wavelength ⁇ selected by the wavelength selection element 102, any one of the fiber Bragg gratings 14, 16 that reflects the wavelength ⁇ . , 18 and the saturable absorber element 12 functioning as a total reflection mirror, and a laser beam having a specific wavelength ⁇ is generated by the mode-locked fiber laser 100 by the shutter operation of the saturable absorber element 12. Is emitted in the form of pulses as outgoing light to the outside (see FIG. 3).
  • the wavelength of pulsed laser light is the wavelength ⁇ 1 that can be reflected by the fiber Bragg grating 14 among the wavelengths that can be reflected by the three fiber Bragg gratings.
  • the angle of the wavelength selection element 102 is adjusted by driving the driving device 29 so that the wavelength selection element 102 has an angle suitable for reducing the loss of only the laser beam having the wavelength ⁇ 1.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light.
  • Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain for wavelength lambda 1 of the light .
  • Laser resonator is constituted between the saturable absorber element 12 and three fiber Bragg gratings 14, 16, 18 Noto, are kept in a state of the wavelength selection element 102 does not cause losses only to the wavelength lambda 1 Therefore, in a resonator becomes possible to generate a gain only high light of a wavelength lambda 1, it only laser oscillation at this wavelength.
  • the wavelength selection element 102 because only the light of wavelength lambda 1 are set so that the angle which is suitable for resonance at low loss, the wavelength lambda 1 other than light Loss is increased with respect to light of a wavelength, so that the laser light is reciprocated and amplified between the fiber Bragg grating 14 and the saturable absorber element 12, and a pulse that is emitted to the outside of the mode-locked fiber laser 100. It will be output as laser light.
  • the mode-locked fiber laser 100 according to the present embodiment also has a certain intensity and pulse as shown in FIG. 2 (a).
  • the resonance is longer than the resonator length L 1 in the example shown in FIG. It is only necessary to increase the length of the instrument.
  • the mode-locked fiber laser 100 having the configuration described above, for example, a fiber Bragg grating 16 suitable laser beam having a wavelength lambda 2 as a feedback element, it is sufficient to oscillate a laser beam having a wavelength lambda 2. That is, in place of the fiber Bragg grating 14, by the fiber Bragg grating 16 and the feedback element, the resonator length is the resonator length L 2, and the resonator length is longer than the resonator length L 1. For this reason, as a result, it becomes possible to obtain pulse oscillation different from the pulse period and light intensity shown in FIG.
  • the wavelength selection element 102 so that the wavelength selection element 102 is an angle suitable for become low loss only for the laser beam of wavelength lambda 2, by driving the driving device 29 the angle of the wavelength selection element 102 adjust To do.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light. Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain for wavelength lambda 1 of the light .
  • Laser resonator is constituted between the saturable absorber element 12 and three fiber Bragg grating 14, 16, 18, are kept in a state of the wavelength selection element 102 does not cause losses only to the wavelength lambda 1 Therefore, in a resonator becomes possible to generate a gain only high light of a wavelength lambda 2, it can only lasing in this wavelength.
  • the wavelength selection element 102 because only light of the wavelength lambda 2 is set to be an angle which is suitable for resonance at low loss, the wavelength lambda 2 other than light Loss is increased with respect to light of a wavelength, so that the laser light is reciprocated and amplified between the fiber Bragg grating 16 and the saturable absorber element 12, and a pulse as light emitted to the outside of the mode-locked fiber laser 100. It will be output as laser light.
  • the mode-locked fiber laser 100 according to the present embodiment also has a certain intensity and pulse as shown in FIG.
  • f 2 c / 2L 2
  • a pulse period 2L 2 / c the case of oscillating a pulsed laser beam having a light intensity or a wider pulse period than the pulse oscillation shown in FIG. 2 (a) or (b) will be described below.
  • the example shown in FIG. 2 (a) or (b) is used. in which it may be longer resonator length than the cavity length L 1 or the resonator length L 2.
  • the mode-locked fiber laser 100 having the configuration described above, for example, a fiber Bragg grating 18 which is suitable for a laser beam having a wavelength lambda 3 as a feedback element, it is sufficient to oscillate a laser beam having a wavelength lambda 3. That is, in place of the fiber Bragg grating 14, or 16, by the fiber Bragg grating 18 and the feedback element, the resonator length is the resonator length L 3, and the long cavity length than the cavity length L 1 and L 2 become. Therefore, as a result, it becomes possible to obtain pulse oscillation different from the pulse period and light intensity shown in FIG.
  • the mode-locked fiber laser 100 is used to obtain pulsed laser light having the wavelength ⁇ 3 with the resonator length L 3 .
  • the angle of the wavelength selection element 102 is adjusted by driving the driving device 29 so that the wavelength selection element 102 has an angle suitable for reducing the loss of only the laser beam having the wavelength ⁇ 3.
  • the excitation semiconductor laser light source 30 is driven to oscillate laser light, and the laser light is incident on the coupler 20 through the passive fiber 32 as excitation light.
  • Excitation light incident on the coupler 20 is made incident from the coupler 20 to gain fiber 22 end 22a through the gain fiber 22 of gain fiber 22 excited generates a gain to light having a wavelength lambda 3 .
  • Laser resonator is constituted between the saturable absorber element 12 and three fiber Bragg grating 14, 16, 18, are kept in a state of the wavelength selection element 102 does not cause losses only in the wavelength lambda 3 Therefore, in a resonator becomes possible to generate a gain only high light of a wavelength lambda 3, it only laser oscillation at this wavelength.
  • the wavelength selection element 102 because only the light of wavelength lambda 3 is set to be an angle which is suitable for resonance at low loss, the wavelength lambda 3 other than light The loss increases with respect to the light of the wavelength.
  • the laser beam is reciprocated and amplified between the fiber Bragg grating 18 and the saturable absorber 12, and a pulse that is emitted to the outside of the mode-locked fiber laser 100. It will be output as laser light.
  • the mode-locked fiber laser 100 that is mode-locked and oscillated by the saturable absorption element 12 as the mode-locking means, pulse oscillation is performed at a repetition frequency corresponding to the length of the resonator.
  • the mode-locked fiber laser 100 by installing a plurality of fiber Bragg gratings that reflect laser beams of different wavelengths, the wavelength of the laser light generated in the laser device is changed to a plurality of fiber Bragg gratings. Since it is possible to change the resonator length without performing an operation such as changing the position of the constituent member of the laser device 100 by changing within the range of the wavelength that can be reflected, The pulse period and repetition frequency can be easily changed.
  • the length of the optical axis is proportional to the length of the gain fiber. Since it is possible to wind and arrange the fiber, it is possible to easily obtain a selection range of a wide repetition frequency.
  • each of the above-described embodiments can be modified as shown in the following (1) to (10).
  • the three fiber Bragg gratings 14, 16, and 18 having different reflection wavelengths are used.
  • the present invention is not limited to this.
  • the diffraction grating 28 is used as the wavelength selection means for selecting the wavelength of the laser beam, and the mode-locking according to the above-described second embodiment.
  • the wavelength selection element 102 such as a birefringence filter is used.
  • the present invention is not limited to this, and other dispersion elements such as a prism can be applied as wavelength selection means. It is.
  • the collimating lens 26 and the wavelength selection element 102 are disposed adjacent to each other. However, the present invention is not limited to this.
  • FIG. 4 is an explanatory diagram of a conceptual configuration of the mode-locked fiber laser 200.
  • the mode-locked fiber laser 200 includes a polarizing element or a polarization-preserving fiber indicated by reference numeral 202 between the collimating lens 26 and the wavelength selection element 102. Only is different. Describing in more detail with reference to FIG. 4, by using the polarizing element or polarization preserving fiber denoted by reference numeral 202 in FIG.
  • the parallel light emitted from the collimating lens 26 is incident on the polarizing element or polarization preserving fiber, and The laser beam is separated into each component, and it becomes possible to select the vertical component or the horizontal component of the laser beam and enter the wavelength selecting element 102.
  • a polarizing beam splitter can be used as the polarizing element.
  • the saturable absorbing element 12 and the fiber Bragg gratings 14, 16, and 18 constitute a resonator.
  • an AO (Acousto-Optic) mode locking element and a mirror can be used as mode locking means instead of the saturable absorbing element 12. More specifically, FIG.
  • FIG. 5 is a conceptual explanatory diagram illustrating the mode-locked fiber laser 300 using the above-described AO mode-locking element and mirror.
  • This mode-locked fiber laser 300 is different from the mode-locked fiber laser 100 according to the second embodiment only in that an AO mode-locking element 304 and a total reflection mirror 302 are provided instead of the saturable absorbing element 12. It is.
  • the pulse oscillation by the mode-locked fiber laser 300 having the AO mode synchronization element 304 becomes active mode synchronization that synchronizes the modes by an external control means (not shown) connected to the AO mode synchronization element 304.
  • the AO mode synchronization element 304 used in the mode synchronization fiber laser 300 is used in a conventional mode synchronization apparatus, and pulse oscillation using the mode synchronization fiber laser 300 having such an AO mode synchronization element 304 is used.
  • a wavelength selection element 102 such as a birefringence filter is used as the wavelength selection means for selecting the wavelength of the laser light, and the mode is used as the mode synchronization means.
  • FIG. 6 is a conceptual explanatory diagram illustrating a mode-locked fiber laser 400 using the above-described acousto-optic tunable filter (AOTF).
  • the mode-locked fiber laser 400 is diffracted by the acousto-optic wavelength tunable filter 404 and a point provided with an acousto-optic wavelength tunable filter 404 instead of the saturable absorber element 12 and the wavelength selection element 102.
  • the difference is that a total reflection mirror 402 is provided as an output mirror on which the incident light is incident and that n (where n is a positive integer) fiber Bragg gratings are provided.
  • n where n is a positive integer
  • an RF signal is supplied from an RF power source (not shown) to the acousto-optic wavelength tunable filter 404, whereby laser light having a wavelength corresponding to the frequency of the supplied RF signal is diffracted. Then, the diffracted light is reflected by the total reflection mirror 402 with a predetermined high reflectivity, amplified by reciprocating in the resonator, and totally reflected as pulse laser light that is emitted to the outside of the mode-locked fiber laser 400. It is output from the mirror 402.
  • the non-diffracted light that is not diffracted by the acoustooptic wavelength tunable filter 404 is not oscillated as a laser because it is removed outside the resonator without reciprocating the laser resonator. Accordingly, by appropriately controlling the frequency of the RF signal supplied to the acousto-optic wavelength tunable filter 404, only the diffracted light having an appropriate wavelength is reciprocated to the laser resonator and is output as a pulse to the outside of the mode-locked fiber laser 400. be able to. Then, by selecting an appropriate wavelength ⁇ , the pulse interval can be changed as in the first or second embodiment. Further, based on the configuration shown in FIG.
  • a mode-locked fiber laser having a configuration as shown in FIG. 8 to be described later may be constructed.
  • a pulse oscillation method using the mode-locked fiber laser 400 having such an acoustooptic wavelength tunable filter 404 for example, a known technique described in non-patent documents disclosed in the following (a) to (c) Therefore, the detailed description thereof will be omitted.
  • B C.I. C. Cutler, “Why Does Linear Phase Shift Cause Mode Locking?”, IEEE J.
  • a dispersion correction optical element such as a dispersion correction prism for correcting dispersion of diffracted light may be disposed between the acoustooptic wavelength tunable filter 404 and the total reflection mirror 402.
  • FIG. 7 shows a mode-locked fiber laser 500 including a dispersion correction prism as a dispersion correction optical element.
  • the mode-locked fiber laser 500 is different from the mode-locked fiber laser 400 only in that a dispersion correction prism 502 is provided between the total reflection mirror 402 and the acousto-optic wavelength variable filter 404.
  • the effects of the dispersion correction optical element such as the dispersion correction prism can be tuned when an acoustooptic wavelength tunable filter is used as a wavelength tuning element, as disclosed in, for example, Japanese Patent Laid-Open No. 9-172215.
  • the wavelength width is remarkably improved. More specifically, by disposing a dispersion correction optical element such as a dispersion correction prism between the total reflection mirror and the acoustooptic wavelength tunable filter, the angle incident on the total reflection mirror is vertical regardless of the wavelength. It becomes possible to become.
  • the dispersion correction optical element for example, a convex lens can be used in addition to the above-described prism, and an operation equivalent to that of the above-described prism can be realized by a convex lens. Therefore, the wavelength tuning width can be expanded as compared with the case where no dispersion correction optical element such as a dispersion correction prism is arranged.
  • the saturable absorption element 12 and the fiber Bragg gratings 14, 16, and 18 constitute a resonator, and the fiber Bragg gratings 14, 16, and 18 of the resonator are included.
  • a pulse laser beam which is emitted light, is output from the side.
  • the total reflection mirror 302 and the fiber Bragg gratings 14, 16, and 18 constitute a resonator, and light is emitted from the fiber Bragg gratings 14, 16, and 18 side of the resonator. It was configured to output pulsed laser light.
  • a resonator is constituted by the total reflection mirror 402 and n fiber Bragg gratings, and a pulse laser that is emitted from the n fiber Bragg grating sides of the resonator. It was configured to output light.
  • the mode-locked fiber lasers 300, 400, and 500 have a high reflectivity (for example, a reflectivity of 99.8% or higher), and are high with respect to a predetermined wavelength instead of the total reflection mirrors 302 and 402.
  • a partially reflecting mirror having a reflectance (for example, a reflectance of 80%) is used. If comprised in this way, a laser beam will be output in a pulse form as the emitted light to the exterior of a mode-locking fiber laser from the saturable absorption element 12 side or partial reflection mirror side of the resonator comprised.
  • a plurality of fiber Bragg gratings, saturable absorber elements 12, total reflection A laser output from the branch may be obtained by inserting a partial reflection splitter that reflects laser light at a certain ratio at an arbitrary point between the mirrors 302 and 402 or the partial reflection mirror. In this case, it is preferable to use a total reflection mirror rather than a partial reflection mirror.
  • the fiber Bragg grating is used as the feedback element.
  • the feedback element that can be used in the present invention is not limited to the fiber Bragg grating.
  • a band reflection device such as a fiber-coupled dielectric multilayer mirror or a volume grating can be used.
  • an experiment conducted by the inventors of the present invention using the mode-locked fiber laser 600 according to the present invention shown in FIG. 8 and the result thereof will be described.
  • the mode-locked fiber laser 600 shown in FIG. 8 the same or equivalent configuration as the mode-locked fiber laser 10, 100, 200, 300, 400, 500 described above is the same as the reference numeral used above. Detailed description of the configuration and operation will be omitted as appropriate by using reference numerals.
  • a polarization controller 604 composed of three wave plates between the collimating lens 26 and the acousto-optic wavelength tunable filter 404 located at the subsequent stage of the FC / APC connector 602. It differs from the mode-locked fiber laser 400 in that the passive fiber 32 is connected to the end of the fiber Bragg grating 18. Another difference is that the fiber Bragg gratings 14, 16, and 18 exhibit a high reflectance of 99.8% or more at the respective reflection center wavelengths, while the mirror disposed on the opposite side of the resonator has a wavelength around 1060 nm.
  • the partial reflection mirror 403 has a reflectance of 80% with respect to the wavelength.
  • the pumping semiconductor laser 30 is different from the mode-locked fiber laser 400 in that light is directly introduced into the gain fiber from the end of the fiber laser without using a coupler.
  • these differences may be considered as one of the variations in the functions provided by the present laser because they do not make a difference in nature with the mode-locked fiber laser 400.
  • a Yb-doped fiber is used as the gain fiber 22.
  • the resonator is an output mirror in which Yb-doped fiber is used as a gain medium, one of which is placed in free space via three fiber Bragg gratings 14, 16, and 18, and the other through FC / APC connector 602.
  • the collimator lens 26, the polarization controller 604 composed of three wave plates, and the acousto-optic wavelength tunable filter 404 are inserted in the free space portion after the FC / APC connector 602, respectively. Yes.
  • the fiber portions are all non-PM, and the polarization controller 604 holds the polarization between the acoustooptic wavelength tunable filter 404 and the partial reflection mirror 403 with a reflectance of 80% as a single linearly polarized light.
  • the partially reflecting mirror 403 having a reflectance of 80% is arranged so that a resonator is assembled with the diffracted light of the acoustooptic wavelength tunable filter 404, and the residual fluorescence that is not diffracted as non-diffracted light is generated by the resonator. Released to the outside.
  • an RF signal is supplied to an acousto-optic tunable filter 404 by an RF signal synthesizer 606.
  • a pumping semiconductor laser light source (Pump diode) 30 that emits laser light having a wavelength of 975 nm was used.
  • an FBG 1 serving as the fiber Bragg grating 14 was used with total reflection at a wavelength of 1064 nm and a reflection bandwidth of 0.2 to 0.6 nm.
  • the FBG2 that is the fiber Bragg grating 16 a fiber that totally reflects at a wavelength of 1060 nm and has a reflection bandwidth of 0.2 to 0.6 nm was used.
  • the fiber Bragg grating 18 FBG3 one having total reflection at a wavelength of 1056 nm and a reflection bandwidth of 0.2 to 0.6 nm was used.
  • the fiber Bragg gratings 14, 16, and 18 have almost no overlap between the reflection bands in terms of specifications.
  • the distance L between the FC / APC connector and the partial reflection mirror as the output mirror FS 220mm It was.
  • each of the fiber Bragg grating 14 (FBG1), the fiber Bragg grating 16 (FBG2), and the fiber Bragg grating 18 (FBG3) is oscillated by each fiber Bragg grating.
  • a prism was inserted instead of the acousto-optic tunable filter 404, and the wavelength was selected and oscillated by changing the angle of the partially reflecting mirror 403 having a reflectance of 80%.
  • the wavelength was selected and oscillated by changing the angle of the partially reflecting mirror 403 having a reflectance of 80%.
  • the peak considered to be resonance by the fiber Bragg grating between the wavelength 1056 nm on the short wavelength side and the wavelength 1064 nm on the long wavelength side can be selected, and oscillation can be performed independently.
  • Met the oscillation at the wavelength of 1060 nm was not reached.
  • FIG. 11 shows the input / output characteristics at a wavelength of 1056 nm when the prism is inserted and when the acoustooptic wavelength tunable filter 404 is inserted, that is, the current value of the pumping semiconductor laser light source 30 and the mode-locked fiber laser.
  • the input / output characteristics with the output power of the laser beam outputted as the emitted light from the are shown.
  • the diffraction efficiency is 90% or more.
  • it can be seen that diffraction with almost no loss is obtained in both the threshold value and the slope efficiency, which is comparable to that of the prism. Further, as shown in FIG.
  • the input / output characteristics changed linearly, and no influence such as saturation was observed in the experimental region.
  • the graph shown in FIG. 12 shows an output curve obtained by changing the RF frequency at the RF output power at which the diffraction efficiency is maximized.
  • the LD current value as the current value of the semiconductor laser light source 30 for excitation was 100 mA.
  • the acousto-optic tunable filter 404 diffracts short wavelength light on the high frequency side. From the results shown in the graph of FIG. 12, the curve indicated by D diffracts the wavelength of 1056 nm, and the curve indicated by E A wavelength of 1060 nm was diffracted, and in the curve indicated by F, a wavelength of 1064 nm was diffracted.
  • the resonator using the acousto-optic tunable filter 404 oscillation could be confirmed even at a wavelength of 1060 nm.
  • any two wavelengths did not oscillate at the same time, instability was observed in which output fluctuations appeared remarkably in terms of switching between the two wavelengths.
  • the center diffraction wavelength continuously changes with respect to the RF frequency.
  • the oscillation wavelength is almost determined by the reflection band of the fiber Bragg grating. It is easily assumed that the wavelength is a slight change within the band.
  • the acoustooptic wavelength tunable filter 404 has a wide diffraction wavelength width and the fiber laser has a large gain, it is considered that the output was obtained without interruption even when the RF frequency was changed at two adjacent wavelengths.
  • the peak for each wavelength in the graph shown in FIG. 12 seems to match the peak of the reflection band of each fiber Bragg grating.
  • the graph shown in FIG. 13 shows the waveform when the laser output is observed with a PIN photodiode under conditions where oscillation is stable at any of the three wavelengths of 1056 nm, 1060 nm, and 1064 nm. It is shown. It was observed that periodic short pulses, which are considered to be mode-locked, were generated at all wavelengths.
  • FIG. 13 shows the waveform when the laser output is observed with a PIN photodiode under conditions where oscillation is stable at any of the three wavelengths of 1056 nm, 1060 nm, and 1064 nm. It is shown. It was observed that periodic short pulse
  • FIG. 14 shows a photograph of the autocorrelator screen when the pulse width in mode synchronization is measured by an autocorrelator (APE, PulseCheck). The photograph shown in FIG.
  • FIG. 14 shows the measurement result of the pulse width of the mode-locking pulse at 1060 nm, and it was confirmed that the mode-oscillation had a pulse width of 24.6 ps when the mode-locking was achieved.
  • FIG. 15 shows a graph showing measurement results obtained by measuring the spectrum shapes at the time of normal oscillation and mode-locked oscillation at 1060 nm. . In this measurement, an optical spectrum analyzer (Advantest, Q8384) was used, and the resolution was set to 0.01 nm. The excitation current of the excitation semiconductor laser light source 30 was constant at 450 mA. FIG. 15 shows the measurement results under the above-described conditions.
  • the line width was about 0.03 nm when normal oscillation was performed, whereas the spectrum shape was obtained when mode-locked oscillation occurred. At the same time, the spectral width changed to about 0.2 nm. If the refractive index of the silicate glass used in the fiber used in the above experiment is 1.45, and the element placed in free space has a short effective length, it is not taken into account.
  • Fiber Bragg Grating 14 (FBG1), Fiber Bragg Grating 16 (FBG2) and Fiber Bragg Grating 18 (FBG3) and the output mirror part of 80% reflectivity, although there are some errors due to the fiber length defect at the stage
  • the optical length, the round trip time of light, and the round trip frequency of the laser resonator composed of the reflection mirror 403 are as shown in the table shown in FIG. 16, and are very close to the experimental results. From the above experimental results, using a composite oscillator in which a plurality of fiber Bragg gratings are arranged in series (series), by inserting a wavelength selective element and a mode-locking element, the mode-locked fiber laser according to the present invention repeatedly It has been shown that a frequency-tunable mode-locked laser can be realized.
  • the mode-locked fiber laser according to the present invention can easily be considered to have extremely high mechanical stability by using an acousto-optic tunable filter.
  • the repetition frequency completely reflects the optical length of the resonator, and mode locking of any repetition frequency can be performed by simply calculating the resonator length. A pulse can be generated.
  • the present invention can be used for precision processing technology using ultrashort pulse laser light, which is one of advanced laser processing.

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Abstract

Comparée à la technologie classique, la structure de dispositif d'un laser à fibre optique à synchronisation des modes n'est pas très compliquée, et la fréquence de répétition de la lumière laser pompée par impulsions peut varier sur une plage plus étendue. Des moyens de synchronisation des modes sont prévus à l'une des extrémités d'une fibre de gain, et une pluralité d'éléments de contre-réaction qui réfléchissent une lumière dans une longueur d'onde différente avec une capacité de réfléchissement élevée sont prévues à l'autre extrémité de la fibre de gain. Les moyens de synchronisation des modes et les éléments de contre-réaction composent un résonateur, et le résonateur possède des moyens de sélection de longueur d'onde qui sont aptes à sélectionner la longueur d'onde de la lumière laser pompée par la fibre de gain.
PCT/JP2009/002417 2008-09-09 2009-06-01 Laser à fibre optique à synchronisation des modes, et procédé d'oscillation d'un laser à impulsions utilisant un laser à fibre optique à synchronisation des modes WO2010029663A1 (fr)

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JP2013546201A (ja) * 2010-12-14 2013-12-26 コヒレント， インコーポレイテッド ショートパルスファイバーレーザー
JP2020128997A (ja) * 2012-06-01 2020-08-27 エヌケイティー フォトニクス アクティーゼルスカブＮｋｔ Ｐｈｏｔｏｎｉｃｓ Ａ／Ｓ 光学測定システム及び方法
US11154189B2 (en) 2012-06-01 2021-10-26 Nkt Photonics A/S Supercontinuum light source

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JPH0374888A (ja) * 1989-08-15 1991-03-29 Hamamatsu Photonics Kk レーザのパルス幅可変装置
JPH08213680A (ja) * 1994-10-21 1996-08-20 Aisin Seiki Co Ltd モードロックレーザー装置
JPH09172215A (ja) * 1995-12-19 1997-06-30 Rikagaku Kenkyusho 波長可変レーザーにおける波長選択方法および波長可変レーザーにおける波長選択可能なレーザー発振装置
JP2002502133A (ja) * 1998-01-30 2002-01-22 テクニオン リサーチ アンド ディベラップメント ファウンデイション リミテッド ファイバ光通信および波長分割多重化に特に有用な共振器共振周波数を使用する波長選択可能レーザシステム

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JPH0374888A (ja) * 1989-08-15 1991-03-29 Hamamatsu Photonics Kk レーザのパルス幅可変装置
JPH08213680A (ja) * 1994-10-21 1996-08-20 Aisin Seiki Co Ltd モードロックレーザー装置
JPH09172215A (ja) * 1995-12-19 1997-06-30 Rikagaku Kenkyusho 波長可変レーザーにおける波長選択方法および波長可変レーザーにおける波長選択可能なレーザー発振装置
JP2002502133A (ja) * 1998-01-30 2002-01-22 テクニオン リサーチ アンド ディベラップメント ファウンデイション リミテッド ファイバ光通信および波長分割多重化に特に有用な共振器共振周波数を使用する波長選択可能レーザシステム

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013546201A (ja) * 2010-12-14 2013-12-26 コヒレント， インコーポレイテッド ショートパルスファイバーレーザー
JP2020128997A (ja) * 2012-06-01 2020-08-27 エヌケイティー フォトニクス アクティーゼルスカブＮｋｔ Ｐｈｏｔｏｎｉｃｓ Ａ／Ｓ 光学測定システム及び方法
US11154189B2 (en) 2012-06-01 2021-10-26 Nkt Photonics A/S Supercontinuum light source
JP7275069B2 (ja) 2012-06-01 2023-05-17 エヌケイティー フォトニクス アクティーゼルスカブ 光学測定システム及び方法
US11800972B2 (en) 2012-06-01 2023-10-31 Nkt Photonics A/S Supercontinuum light source

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