WO2017204299A1 - Pulsed light source and pulsed light generating method - Google Patents

Pulsed light source and pulsed light generating method Download PDF

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Publication number
WO2017204299A1
WO2017204299A1 PCT/JP2017/019559 JP2017019559W WO2017204299A1 WO 2017204299 A1 WO2017204299 A1 WO 2017204299A1 JP 2017019559 W JP2017019559 W JP 2017019559W WO 2017204299 A1 WO2017204299 A1 WO 2017204299A1
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Prior art keywords
light source
resonator
pulse light
pulse
pump
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PCT/JP2017/019559
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French (fr)
Japanese (ja)
Inventor
ジイヨン セット
山下　真司
宇 王
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国立大学法人 東京大学
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Priority to JP2018519609A priority Critical patent/JP7043073B2/en
Publication of WO2017204299A1 publication Critical patent/WO2017204299A1/en

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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
    • H01S3/05—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
    • 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
    • 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
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/083—Ring 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
    • H01S3/09—Processes or apparatus for excitation, e.g. pumping
    • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
    • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
    • 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
    • H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
    • H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation

Definitions

  • the present invention relates to a pulse light source and a method for generating pulsed light.
  • REDFAs Rare earth doped fiber amplifiers
  • REDFA includes, for example, praseodymium ion (Pr 3+ ), neodymium ion (Nd 3+ ), holmium ion (Ho 3+ ), erbium ion (Er 3+ ), thulium ion (Tm 3+ ), or ytterbium ion (Yb 3+ ).
  • a REDFA containing thulium ions (Tm 3+ ) that is, a laser having a thulium-doped fiber amplifier (TDFA), can emit light having a wavelength of 2 ⁇ m.
  • the light in the wavelength band of 2 ⁇ m is expected to be applied to, for example, laser processing, LIDAR (Laser Imaging Detection And Ranging) or gas sensing.
  • LIDAR Laser Imaging Detection And Ranging
  • a laser having REDFA may generate pulsed light.
  • One method for generating pulsed light is mode synchronization. Furthermore, there are two types of mode synchronization, passive mode synchronization and active mode synchronization.
  • the pulse light source includes a resonator, a gain medium, and a saturable absorber.
  • the gain medium and the saturable absorber are between the two mirrors of the resonator.
  • the light loss of the saturable absorber is modulated by the intensity of light input to the saturable absorber, and specifically, the light loss decreases as the light intensity increases.
  • pulsed light can be generated by this loss modulation of the saturable absorber.
  • the pulsed light source includes a resonator, a gain medium, and an intensity modulator.
  • the gain medium and intensity modulator are between the two mirrors of the resonator.
  • the loss of the intensity modulator is modulated by a signal from the outside of the resonator.
  • pulsed light can be generated by this loss modulation of the intensity modulator.
  • the pulse light source in another example of active mode locking, includes a pump light source, a resonator, and a gain medium.
  • the pump light source is external to the resonator.
  • the gain medium is between the two mirrors of the resonator, and is TDFA in Non-Patent Documents 1 and 2.
  • Pulse light is supplied from the pump light source.
  • pulsed light is generated from the resonator by the pulsed light from the pump light.
  • pulse light may be supplied from a pump light source to a resonator as in active mode synchronization described in Non-Patent Documents 1 and 2.
  • the present inventor studied generating pulsed light by a new active mode synchronization different from the active mode synchronization described in Non-Patent Documents 1 and 2.
  • An object of the present invention is to generate pulsed light by a novel active mode synchronization in a pulsed light source having REDFA.
  • a resonator having a rare earth doped fiber amplifier having a rare earth doped fiber amplifier;
  • a pulse light source is provided in which the pump light is modulated by a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator.
  • a method for generating pulsed light comprising: A resonator having a rare earth-doped fiber amplifier and a pump light source capable of supplying pump light modulated with a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator are provided. To do; Supplying the pump light from the pump light source to the rare earth doped fiber amplifier; After the pump light is supplied from the pump light source to the rare earth doped fiber amplifier, the light is output from the resonator.
  • pulse light can be generated by a novel active mode synchronization in a pulse light source having REDFA.
  • FIG. 1 It is a figure which shows the measurement result of RF spectrum of the pulsed light output from the pulse light source which concerns on Example 1.
  • FIG. It is a figure which shows the measurement result of the autocorrelation of the pulsed light output from the pulse light source which concerns on Example 1.
  • FIG. It is a figure which shows the measurement result of the pulsed light output from the pulse light source which concerns on Example 2.
  • FIG. It is a figure which shows the measurement result of the optical spectrum of the pulsed light output from the pulse light source which concerns on Example 3.
  • FIG. It is a figure which shows the measurement result of the autocorrelation of the pulsed light output from the pulse light source which concerns on Example 3.
  • FIG. It is a figure which shows the measurement result of RF spectrum of the pulsed light output from the pulse light source which concerns on Example 3.
  • FIG. 1 is a diagram illustrating a pulse light source 10 according to the first embodiment.
  • the pulse light source 10 includes a pump light source 100, a resonator 200, and an output unit 300.
  • the resonator 200 includes a rare earth doped fiber amplifier (REDFA) 220.
  • the pump light source 100 supplies pump light to the REDFA 220.
  • the pump light is modulated by a modulation signal having a modulation frequency f mod substantially equal to an integral multiple of the basic resonance frequency f 1 of the resonator 200.
  • the modulation frequency f mod is 95% or more and 105% or less, preferably 99% or more and 101% or less, more preferably 100 ⁇ 0.1% of an integral multiple of the basic resonance frequency f 1 of the resonator 200. Is the frequency.
  • Pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • active mode synchronization with a repetition frequency equal to the modulation frequency f mod is realized. Details will be described below.
  • FIG. 2 is a diagram showing a first example of the pump light source 100 shown in FIG.
  • the pump light source 100 includes a pump laser 110, an optical amplifier 120, an electric signal generator 130, and a laser driver 140.
  • the pump laser 110 emits seed light having a wavelength that excites rare earth ions contained in the REDFA 220 (FIG. 1).
  • the seed light from the pump laser 110 is amplified by the optical amplifier 120.
  • the REDFA 220 (FIG. 1) contains thulium ions (Tm 3+ )
  • the wavelength of the seed light of the pump laser 110 is 1570 nm
  • the optical amplifier 120 is a C-band erbium doped fiber amplifier (EDFA).
  • the electrical signal generator 130 modulates the seed light of the pump laser 110 with a sine wave that oscillates at the modulation frequency f mod .
  • the electric signal generator 130 modulates the seed light of the pump laser 110 via the laser driver 140. In this way, the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod .
  • the electric signal generator 130 may modulate the seed light of the pump laser 110 with a rectangular wave that oscillates at the modulation frequency f mod .
  • the duty ratio T on / T mod of this rectangular wave may be 0.50 or may be different from 0.50.
  • the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod .
  • the degree of modulation by the electric signal generator 130 is preferably high to some extent, and is preferably 10% or more, for example. When the degree of modulation by the electric signal generator 130 is high to some extent, the pump light is sufficiently modulated. However, the degree of modulation by the electric signal generator 130 is not limited to the above example (10% or more).
  • FIG. 3 is a diagram showing a second example of the pump light source 100 shown in FIG.
  • the pump light source 100 may not include the optical amplifier 120 (FIG. 2).
  • the seed light (pump light) from the pump laser 110 is directly supplied to the resonator 200 without passing through the optical amplifier 120 (FIG. 2).
  • FIG. 4 is a diagram showing a third example of the pump light source 100 shown in FIG.
  • the seed light from the pump laser 110 may be modulated by a light intensity modulator 150 and an electric signal generator 130.
  • the laser driver 140 is a DC laser driver, for example, and does not modulate the seed light from the pump laser 110.
  • the light intensity modulator 150 is located between the pump laser 110 and the optical amplifier 120, and modulates the seed light from the pump laser 110 by a signal (for example, a sine wave or a rectangular wave) from the electric signal generator 130.
  • the pulse light source 10 includes a pump light source 100 and a resonator 200.
  • the resonator 200 includes an optical multiplexer 210, a REDFA 220, an isolator (ISO) 230, and an optical demultiplexer 240.
  • the optical multiplexer 210, the REDFA 220, the isolator 230, and the optical demultiplexer 240 are optically coupled to each other via an optical fiber.
  • the pump light source 100 is optically coupled to the optical multiplexer 210 of the resonator 200 via an optical fiber.
  • the output unit 300 is optically coupled to the optical demultiplexer 240 via an optical fiber.
  • the resonator 200 is a forward-excited ring resonator.
  • the pump light from the pump light source 100 passes through the optical multiplexer 210 between the front of the isolator 230 and the rear of the REDFA 220 in the forward direction of the isolator 230 (light propagation direction in the resonator 200). Have been supplied.
  • the pump light from the pump light source 100 is input to the REDFA 220 via the optical multiplexer 210.
  • the optical multiplexer 210 combines the pump light from the pump light source 100 and the light from the optical demultiplexer 240, and is specifically a WDM (Wavelength Division Multiplexing) coupler.
  • the rare earth ions contained in the REDFA 220 are excited by the pump light. Furthermore, light is emitted from the REDFA 220 when the excited rare earth ions transition to a low energy level.
  • Light from the REDFA 220 is input to the optical demultiplexer 240 via the isolator 230.
  • Part of the light from the isolator 230 is input to the optical multiplexer 210 via the optical demultiplexer 240 and further input to the REDFA 220 via the optical multiplexer 210.
  • Another part of the light from the isolator 230 is input to the output unit 300 via the optical demultiplexer 240 and further output to the outside of the pulse light source 10 via the output unit 300.
  • the optical demultiplexer 240 demultiplexes the light from the isolator 230 into two lights having the same wavelength, for example, 50:50, and is specifically an optical coupler.
  • the REDFA 220 functions as a gain medium for the resonator 200.
  • REDFA 220 includes glass fibers and rare earth ions doped into the glass fibers.
  • the rare earth ions contained in REDFA 220 include, for example, praseodymium ions (Pr 3+ ), neodymium ions (Nd 3+ ), holmium ions (Ho 3+ ), erbium ions (Er 3+ ), thulium ions (Tm 3+ ), and ytterbium ions (Yb 3+). At least one selected from the group consisting of:
  • the output unit 300 is, for example, an isolator.
  • the output unit 300 in the output unit 300 (isolator), light traveling from the resonator 200 toward the outside of the pulse light source 10 passes through the output unit 300, and light traveling from the outside of the pulse light source 10 toward the resonator 200 is blocked by the output unit 300. It is arranged so that.
  • the q-order resonance frequency f q of the resonator 200 is expressed by the following equation (1).
  • f q qc / (nL 1 ) (1)
  • c the speed of light
  • n the refractive index of the optical fiber of the resonator 200
  • L 1 the length of the resonator 200.
  • the resonance frequency f q is the basic resonance frequency f 1 .
  • pump light is supplied from the pump light source 100 to the REDFA 220 of the resonator 200.
  • the pump light is modulated by the modulation signal having the modulation frequency f mod substantially equal to the integral multiple of the basic resonance frequency f 1 of the resonator 200.
  • the present inventor examined, when the lifetime ⁇ of the upper level ( 3 F 4 ) of the rare earth ions contained in the REDFA 220 is somewhat shorter than the modulation signal repetition period T mod (T mod 1 / f mod ), Specifically, when the ratio tau / T mod lifetime tau for the repetition period T mod is for example, at 1 ⁇ 10 4 or less, equal to the modulation frequency f mod in Radio-frequency (RF) spectrum of the signal from the output unit 300 It became clear that a peak appeared in the frequency (for example, see FIG. 19 described later). Furthermore, it has been clarified that the intensity of the peak increases as the repetition period T mod increases (that is, the modulation frequency f mod decreases) when the lifetime ⁇ is constant. This result indicates that the peak is due to the modulation of the electric signal generator 130.
  • RF Radio-frequency
  • the lifetime ⁇ is about 8 ms to 10 ms for erbium ion (Er 3+ ), about 1 ms to 2 ms for ytterbium ion (Yb 3+ ), and erbium for thulium ion (Tm 3+ ). It is shorter than the lifetime of ions (Er 3+ ) and the lifetime of ytterbium ions (Yb 3+ ), specifically, approximately 400 ⁇ s or more and 500 ⁇ s or less.
  • the modulation frequency f mod is substantially equal to an integral multiple of the basic resonance frequency f 1 of the resonator 200. For this reason, mode synchronization of a repetition frequency equal to the modulation frequency f mod , specifically, Continuous Wave (CW) active mode synchronization is realized. For this reason, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • CW Continuous Wave
  • the modulation frequency f mod is 95% or more and 105% or less, preferably 99% or more and 101% or less, more preferably 100 ⁇ 0.1% of an integral multiple of the basic resonance frequency f 1 of the resonator 200. is there.
  • the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod substantially equal to the integral multiple of the basic resonance frequency f 1 of the resonator 200.
  • pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • pulsed light having a pulse width on the order of picoseconds (10 ⁇ 12 seconds), that is, ultrashort pulsed light can be generated.
  • the wavelength of the pulsed light generated from the pulsed light source 10 can be set to the near infrared wavelength.
  • the wavelength of the pulsed light can be in the 2 ⁇ m band
  • the wavelength of the pulsed light can be in the 1.5 ⁇ m band
  • the wavelength of the pulsed light can be in the 1 ⁇ m band.
  • FIG. 5 is a diagram showing a modification of FIG.
  • the resonator 200 may be a backward-pumped ring resonator.
  • the pump light from the pump light source 100 is between the front of the REDFA 220 and the rear of the isolator 230 in the forward direction of the isolator 230 (light propagation direction in the resonator 200). It is supplied via the optical multiplexer 210.
  • FIG. 6 is a diagram showing a pulse light source 10 according to the second embodiment, and corresponds to FIG. 1 of the first embodiment.
  • the pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
  • the resonator 200 is a linear resonator.
  • the resonator 200 includes a REDFA 220, a first reflective element 252 and a second reflective element 254.
  • the REDFA 220 is between the first reflective element 252 and the second reflective element 254.
  • the first reflective element 252 and the second reflective element 254 function as a mirror of the resonator 200.
  • the first reflective element 252 is a mirror or FBG (Fiber Bragg Grating).
  • the second reflective element 254 reflects a part of the light from the REDFA 220 and transmits the other part of the light from the REDFA 220. More specifically, the 2nd reflective element 254 is a mirror or FBG, for example.
  • Pump light from the pump light source 100 is supplied to the REDFA 220 via the optical multiplexer 210 between the first reflective element 252 and the REDFA 220.
  • Light from the resonator 200 is output to the outside of the pulse light source 10 via the second reflective element 254, the isolator 230, and the output unit 300.
  • the q-order resonance frequency f q of the resonator 200 is expressed by the following equation (2).
  • f q qc / (2nL 2 ) (2)
  • c is the speed of light
  • n is the refractive index of the optical fiber of the resonator 200
  • L 2 is the length of the resonator 200.
  • the resonance frequency f q is the basic resonance frequency f 1 .
  • the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200.
  • pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • FIG. 7 is a diagram showing a first modification of FIG.
  • the resonator 200 is a linear resonator.
  • the pump light from the pump light source 100 may be supplied via an optical multiplexer 210 between the REDFA 220 and the second reflective element 254.
  • FIG. 8 is a diagram showing a second modification of FIG.
  • the resonator 200 is a linear resonator.
  • the pump light from the pump light source 100 may be supplied to the REDFA 220 via the first reflective element 252.
  • the first reflecting element 252 functions as an element that reflects light of a specific wavelength, and specifically, transmits the pump light from the pump light source 100 and reflects the light emitted from the REDFA 220. More specifically, the first reflective element 252 is, for example, a multilayer film mirror or an FBG (Fiber Bragg Grating).
  • FIG. 9 is a diagram showing a pulse light source 10 according to the third embodiment, and corresponds to FIG. 1 of the first embodiment.
  • the pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
  • the resonator 200 is an 8-shaped resonator. Specifically, the resonator 200 has a first loop 202 and a second loop 204. The first loop 202 and the second loop 204 are optically coupled to each other via an optical demultiplexer 242 (specifically, an optical coupler).
  • the first loop 202 includes a REDFA 220 and a nonlinear fiber 260. Pump light from the pump light source 100 is supplied to the REDFA 220.
  • the second loop 204 includes an isolator 230 and an optical demultiplexer 240.
  • the optical demultiplexer 240 is optically coupled to the output unit 300 via an optical fiber.
  • the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200.
  • pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • FIG. 10 is a view showing a pulse light source 10 according to the fourth embodiment, and corresponds to FIG. 1 of the first embodiment.
  • the pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
  • the resonator 200 is a sigma resonator.
  • the resonator 200 includes a REDFA 220, an isolator 230, an optical demultiplexer 240, a reflecting element 256, and a PBS (Polarizing Beam Splitter) 270.
  • the REDFA 220 is between the reflective element 256 and the PBS 270. Pump light from the pump laser 110 is supplied to the REDFA 220.
  • the reflection element 256 is a Faraday mirror and reflects light so that the polarization direction of the reflected light is rotated by 90 ° from the polarization direction of the incident light.
  • the PBS 270, isolator 230, and optical demultiplexer 240 are optically coupled via a polarization maintaining fiber.
  • the isolator 230 is provided between the PBS 270 and the optical demultiplexer 240, and is provided so that the forward direction of the isolator 230 is the direction from the PBS 270 toward the optical demultiplexer 240.
  • the polarization maintaining fiber on the optical demultiplexer 240 side and the polarization maintaining fiber on the PBS 270 side are fused at the fusion part 280. Specifically, these polarization maintaining fibers are fused at the fusion part 280 so that the polarization direction on the optical demultiplexer 240 side and the polarization direction on the PBS 270 side are rotated by 90 °.
  • the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200.
  • pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
  • FIG. 11 is a diagram showing a pulse light source 10 according to the fifth embodiment, and corresponds to FIG. 5 of the first embodiment.
  • the pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
  • the resonator 200 is a ring resonator.
  • the resonator 200 may include a saturable absorber 292.
  • the saturable absorber 292 is located between the optical multiplexer 210 and the isolator 230.
  • the pump light from the pump light source 100 is an optical multiplexer between the front of the REDFA 220 and the rear of the isolator 230 in the forward direction of the isolator 230 (the propagation direction of light in the resonator 200). 210 is supplied.
  • FIG. 12 is a diagram showing a pulse light source 10 according to the sixth embodiment, and corresponds to FIG. 6 of the second embodiment.
  • the pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the second embodiment except for the following points.
  • the resonator 200 is a linear resonator. As shown in the figure, the resonator 200 may include a saturable absorbing mirror 294 instead of the first reflecting element 252 (FIG. 6). In the example shown in the drawing, the pump light from the pump light source 100 is supplied via the optical multiplexer 210 between the saturable absorption mirror 294 and the REDFA 220.
  • FIG. 13 is a diagram showing a laser processing apparatus according to the seventh embodiment.
  • the laser processing apparatus includes a pulse light source 10, a mirror 12, a lens 14, and a nozzle 16.
  • the laser processing apparatus is used for processing the object W.
  • the object W is, for example, an iron plate, a glass plate, or a plastic plate.
  • the pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments. Pulse light is output from the pulse light source 10.
  • the pulsed light is reflected by the mirror 12 and enters the lens 14.
  • the pulsed light is collected by the lens 14 and then passes through the nozzle 16 and is irradiated onto the object W.
  • the pulse width of the pulsed light irradiated from the pulse light source 10 onto the object W can be on the order of picoseconds (10 ⁇ 12 seconds) and can be very narrow. For this reason, the region irradiated with the pulsed light is removed in a short time. For this reason, it is possible to suppress the diffusion of heat around the area removed by the pulsed light.
  • the peak intensity of the pulsed light irradiated from the pulsed light source 10 to the object W is very large. For this reason, the probability that a multiphoton optical absorption process will occur in the object W increases. For this reason, in this embodiment, even if it is a case where the target object W consists of translucent materials like glass, the target object W can be processed.
  • FIG. 14 is a diagram illustrating an optical sensor according to the eighth embodiment.
  • the optical sensor is Laser Imaging Detection And Ranging (LIDAR), and includes a pulse light source 10 and a detector 20.
  • the pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments.
  • the detector 20 is specifically a CCD (Charge-Coupled Device) image sensor.
  • pulsed light is output from the pulsed light source 10 toward the object W.
  • the detector 20 detects the pulsed light reflected from the object W.
  • the optical sensor can calculate the distance from the pulse light source 10 to the object W based on the time from when the pulse light is output from the pulse light source 10 until the detector 20 detects the pulse light.
  • the optical sensor is mounted on a vehicle (for example, an automobile or a motorcycle).
  • a front or rear object W of the vehicle can be detected.
  • a light sensor is used for mapping. More specifically, for example, when an optical sensor is mounted on an airplane, the shape of the earth surface can be measured by mapping from the sky.
  • FIG. 15 is a diagram illustrating a medical device according to the ninth embodiment.
  • the medical device includes a pulse light source 10, a mirror 12, a lens 14, and a nozzle 16 in the same manner as the laser processing apparatus shown in FIG.
  • the pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments.
  • the object W is a living tissue, specifically, for example, skin. In the example shown in the figure, the pulsed light from the pulse light source 10 is applied to the object W in the same manner as in the example shown in FIG.
  • the pulse width of the pulsed light irradiated from the pulse light source 10 onto the object W can be on the order of picoseconds (10 ⁇ 12 seconds) and can be very narrow. For this reason, the region irradiated with the pulsed light is removed in a short time. For this reason, it is possible to suppress the diffusion of heat around the area removed by the pulsed light.
  • FIG. 16 is a diagram illustrating a gas sensor according to the tenth embodiment.
  • the gas sensor is used to analyze the gas G.
  • the gas sensor includes a pulse light source 10 and a detector 20.
  • the pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments.
  • the pulsed light from the pulsed light source 10 passes through the gas G and then reaches the detector 20.
  • the detector 20 detects the pulsed light from the pulse light source 10. Based on the detection result of the detector 20, the kind of gas contained in the gas G is analyzed. Specifically, light having a part of the wavelength of the pulsed light is absorbed in the gas G. Based on this wavelength, the type of gas contained in the gas G is analyzed.
  • Example 1 The pulse light source 10 shown in FIG. 1 was produced.
  • the pump light source 100 was as shown in FIG.
  • the pump laser 110 was a 1.57 ⁇ m wavelength laser.
  • the electric signal generator 130 modulated the seed laser with a sine wave having a modulation frequency f mod : 6.69850 MHz.
  • the degree of modulation by the electric signal generator 130 was 30%.
  • the optical amplifier 120 is an EDFA.
  • the optical multiplexer 210 is a WDM coupler.
  • the REDFA 220 was a thulium-doped fiber amplifier (TDFA) (OFS, TmDF200).
  • the optical demultiplexer 240 is a 50:50 optical coupler.
  • the length L 1 of the resonator 200 was 30.5 m, and the basic resonance frequency of the resonator 200 was 6.7 MHz.
  • the total dispersion of the resonator 200 was ⁇ 1.67 ps 2 .
  • FIG. 17 is a diagram showing the measurement result of the optical spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the optical spectrum was measured with an optical spectrum analyzer (OSA) (ANDO AQ6375) having a resolution of 0.05 nm.
  • OSA optical spectrum analyzer
  • the optical spectrum has a plurality of Kelly sidebands. This indicates that the pulse light source 10 generates a soliton pulse.
  • the spectral width is 0.9 nm.
  • FIG. 18 is a diagram illustrating a measurement result of the pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the pulsed light from the pulsed light source 10 was detected with an InGaAs photodetector (EOT ET-5000, 10 GHz) and measured with an oscilloscope (Agilent DSO1024A).
  • the pulsed light source 10 outputs pulsed light at a repetition frequency of 6.69850 MHz (that is, a frequency equal to the modulation frequency f mod ).
  • Continuous Wave (CW) active mode synchronization was confirmed.
  • FIG. 19 is a diagram illustrating a measurement result of the RF spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the RF spectrum was measured with an RF spectrum analyzer (Agilent E4440A) having a resolution of 1 kHz.
  • a peak with an SN ratio of 70 dB was measured at a frequency of 6.69850 MHz (that is, a frequency equal to the modulation frequency f mod ).
  • FIG. 20 is a diagram illustrating a measurement result of autocorrelation of pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the autocorrelation was measured with a background-free autocorrelator (Femtochrome FR-103HP).
  • the full width at half maximum of the autocorrelation was 8 ps.
  • the pulse width is 5 ps assuming that the waveform of the pulsed light is a hyperbolic secant distribution.
  • pulsed light having a pulse width of 5 ps and a spectral width of 0.9 nm was obtained by CW active mode synchronization.
  • the pulse light source 10 according to the second embodiment is the pulse according to the first embodiment except that the modulation frequency f mod is 13.3970 MHz (that is, the modulation frequency f mod of the first embodiment is twice as high as 6.698850 MHz). The same as the light source 10.
  • FIG. 21 is a diagram illustrating a measurement result of the pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the pulsed light source 10 outputs pulsed light at a repetition frequency of 13.3970 MHz (that is, a frequency equal to the modulation frequency f mod ).
  • f mod the modulation frequency
  • the pulse light source 10 according to the third embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
  • the pump laser 110 was a laser having a wavelength of 980 nm.
  • the seed laser was modulated at a modulation frequency f mod : 99.021 MHz.
  • the REDFA 220 was an erbium-doped fiber amplifier (EDFA).
  • the length L 1 of the resonator 200 was 2 km, and the basic resonance frequency of the resonator 200 was 99.021 kHz.
  • the total dispersion of the resonator 200 was ⁇ 0.31 ps 2 .
  • FIG. 22 is a diagram illustrating a measurement result of the optical spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment. Using Gaussian fitting, the spectral width was 2.26 nm.
  • FIG. 23 is a diagram illustrating a measurement result of autocorrelation of pulsed light output from the pulsed light source 10 according to the present embodiment.
  • the full width at half maximum of the autocorrelation was 1.18 ps, assuming that the waveform of the pulsed light is a hyperbolic secant distribution.
  • FIG. 24 is a diagram illustrating the measurement result of the RF spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment.
  • a peak with an SN ratio of 53 dB was measured at a frequency of 99.250 MHz (that is, a frequency substantially equal to the modulation frequency f mod ).

Abstract

This pulsed light source (10) is provided with: a pump light source (100); and a resonator (200). The resonator (200) has a rare-earth-doped fiber amplifier (REDFA) (220). The pump light source (100) provides pump light to the REDFA (220). The pump light is modulated by a modulation signal which has a modulation frequency fmod almost equivalent to an integer multiple of a fundamental resonance frequency f1 of the resonator (200). In detail, the modulation frequency fmod is a frequency of 95% to 105% of the integer multiple of the fundamental resonance frequency f1 of the resonator (200).

Description

パルス光源及びパルス光を発生させる方法Pulse light source and method for generating pulsed light
　本発明は、パルス光源及びパルス光を発生させる方法に関する。 The present invention relates to a pulse light source and a method for generating pulsed light.
　レーザの利得媒体として希土類ドープファイバ増幅器（ＲＥＤＦＡ）が用いられることがある。ＲＥＤＦＡは、例えば、プラセオジムイオン（Ｐｒ３＋）、ネオジムイオン（Ｎｄ３＋）、ホルミウムイオン（Ｈｏ３＋）、エルビウムイオン（Ｅｒ３＋）、ツリウムイオン（Ｔｍ３＋）又はイッテルビウムイオン（Ｙｂ３＋）を含んでいる。特にツリウムイオン（Ｔｍ３＋）を含むＲＥＤＦＡ、すなわちツリウムドープファイバ増幅器（ＴＤＦＡ）を有するレーザは、波長２μｍ帯の光を発することができる。波長２μｍ帯の光は、例えば、レーザ加工、ＬＩＤＡＲ（Ｌａｓｅｒ　Ｉｍａｇｉｎｇ　Ｄｅｔｅｃｔｉｏｎ　Ａｎｄ　Ｒａｎｇｉｎｇ）又はガスセンシングへの応用が期待されている。 Rare earth doped fiber amplifiers (REDFAs) may be used as laser gain media. REDFA includes, for example, praseodymium ion (Pr 3+ ), neodymium ion (Nd 3+ ), holmium ion (Ho 3+ ), erbium ion (Er 3+ ), thulium ion (Tm 3+ ), or ytterbium ion (Yb 3+ ). . In particular, a REDFA containing thulium ions (Tm 3+ ), that is, a laser having a thulium-doped fiber amplifier (TDFA), can emit light having a wavelength of 2 μm. The light in the wavelength band of 2 μm is expected to be applied to, for example, laser processing, LIDAR (Laser Imaging Detection And Ranging) or gas sensing.
　ＲＥＤＦＡを有するレーザでは、パルス光を発生させることがある。パルス光を発生させるための方法の一つとして、モード同期がある。さらに、モード同期には、受動モード同期及び能動モード同期の２種類の方法がある。 A laser having REDFA may generate pulsed light. One method for generating pulsed light is mode synchronization. Furthermore, there are two types of mode synchronization, passive mode synchronization and active mode synchronization.
　受動モード同期において、パルス光源は、共振器、利得媒体及び可飽和吸収体を備えている。利得媒体及び可飽和吸収体は、共振器の２枚のミラー間にある。可飽和吸収体の光損失は、可飽和吸収体に入力される光の強度によって変調し、具体的には、光の強度が高くなるほど光損失が低くなる。受動モード同期では、可飽和吸収体のこの損失変調によって、パルス光を発生させることができる。 In the passive mode synchronization, the pulse light source includes a resonator, a gain medium, and a saturable absorber. The gain medium and the saturable absorber are between the two mirrors of the resonator. The light loss of the saturable absorber is modulated by the intensity of light input to the saturable absorber, and specifically, the light loss decreases as the light intensity increases. In passive mode locking, pulsed light can be generated by this loss modulation of the saturable absorber.
　能動モード同期の一例において、パルス光源は、共振器、利得媒体及び強度変調器を備えている。利得媒体及び強度変調器は、共振器の２枚のミラー間にある。強度変調器の損失は、共振器の外部からの信号によって変調する。能動モード同期のこの例では、強度変調器のこの損失変調によって、パルス光を発生させることができる。 In an example of active mode synchronization, the pulsed light source includes a resonator, a gain medium, and an intensity modulator. The gain medium and intensity modulator are between the two mirrors of the resonator. The loss of the intensity modulator is modulated by a signal from the outside of the resonator. In this example of active mode locking, pulsed light can be generated by this loss modulation of the intensity modulator.
　非特許文献１，２に記載されているように、能動モード同期の他の例において、パルス光源は、ポンプ光源、共振器及び利得媒体を有している。ポンプ光源は、共振器の外部にある。利得媒体は、共振器の２枚のミラー間にあり、非特許文献１，２ではＴＤＦＡである。ポンプ光源からは、パルス光が供給される。非特許文献１，２の能動モード同期では、ポンプ光からのパルス光によって、共振器からパルス光が発生する。 As described in Non-Patent Documents 1 and 2, in another example of active mode locking, the pulse light source includes a pump light source, a resonator, and a gain medium. The pump light source is external to the resonator. The gain medium is between the two mirrors of the resonator, and is TDFA in Non-Patent Documents 1 and 2. Pulse light is supplied from the pump light source. In the active mode synchronization described in Non-Patent Documents 1 and 2, pulsed light is generated from the resonator by the pulsed light from the pump light.
　ＲＥＤＦＡを有するパルス光源では、非特許文献１，２に記載の能動モード同期のように、ポンプ光源から共振器にパルス光を供給することがある。これに対して、本発明者は、非特許文献１，２に記載の能動モード同期とは異なる新規な能動モード同期によってパルス光を発生させることを検討した。 In a pulse light source having a REDFA, pulse light may be supplied from a pump light source to a resonator as in active mode synchronization described in Non-Patent Documents 1 and 2. On the other hand, the present inventor studied generating pulsed light by a new active mode synchronization different from the active mode synchronization described in Non-Patent Documents 1 and 2.
　本発明の目的は、ＲＥＤＦＡを有するパルス光源において新規な能動モード同期によってパルス光を発生させることにある。 An object of the present invention is to generate pulsed light by a novel active mode synchronization in a pulsed light source having REDFA.
　本発明によれば、
　希土類ドープファイバ増幅器を有する共振器と、
　前記希土類ドープファイバ増幅器にポンプ光を供給するポンプ光源と、
を備え、
　前記ポンプ光は、前記共振器の基本共振周波数の整数倍の９５％以上１０５％以下の変調周波数を有する変調信号によって変調されているパルス光源が提供される。 According to the present invention,
A resonator having a rare earth doped fiber amplifier;
A pump light source for supplying pump light to the rare earth-doped fiber amplifier;
With
A pulse light source is provided in which the pump light is modulated by a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator.
　本発明によれば、以下の方法が提供される。
　パルス光を発生させる方法であって、以下を含む：
　希土類ドープファイバ増幅器を有する共振器と、前記共振器の基本共振周波数の整数倍の９５％以上１０５％以下の変調周波数を有する変調信号で変調されたポンプ光を供給可能なポンプ光源と、を準備すること；
　前記ポンプ光源から前記希土類ドープファイバ増幅器に前記ポンプ光を供給すること；
　前記ポンプ光源から前記希土類ドープファイバ増幅器に前記ポンプ光を供給した後、前記共振器から光を出力すること。 According to the present invention, the following method is provided.
A method for generating pulsed light comprising:
A resonator having a rare earth-doped fiber amplifier and a pump light source capable of supplying pump light modulated with a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator are provided. To do;
Supplying the pump light from the pump light source to the rare earth doped fiber amplifier;
After the pump light is supplied from the pump light source to the rare earth doped fiber amplifier, the light is output from the resonator.
　本発明によれば、ＲＥＤＦＡを有するパルス光源において新規な能動モード同期によってパルス光を発生させることができる。 According to the present invention, pulse light can be generated by a novel active mode synchronization in a pulse light source having REDFA.
　上述した目的、およびその他の目的、特徴および利点は、以下に述べる好適な実施の形態、およびそれに付随する以下の図面によってさらに明らかになる。 The above-described object and other objects, features, and advantages will be further clarified by a preferred embodiment described below and the following drawings attached thereto.
第１の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 1st Embodiment. 図１に示したポンプ光源の第１例を示す図である。It is a figure which shows the 1st example of the pump light source shown in FIG. 図１に示したポンプ光源の第２例を示す図である。It is a figure which shows the 2nd example of the pump light source shown in FIG. 図１に示したポンプ光源の第３例を示す図である。It is a figure which shows the 3rd example of the pump light source shown in FIG. 図１の変形例を示す図である。It is a figure which shows the modification of FIG. 第２の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 2nd Embodiment. 図６の第１の変形例を示す図である。It is a figure which shows the 1st modification of FIG. 図６の第２の変形例を示す図である。It is a figure which shows the 2nd modification of FIG. 第３の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 3rd Embodiment. 第４の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 4th Embodiment. 第５の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 5th Embodiment. 第６の実施形態に係るパルス光源を示す図である。It is a figure which shows the pulse light source which concerns on 6th Embodiment. 第７の実施形態に係るレーザ加工装置を示す図である。It is a figure which shows the laser processing apparatus which concerns on 7th Embodiment. 第８の実施形態に係る光センサを示す図である。It is a figure which shows the optical sensor which concerns on 8th Embodiment. 第９の実施形態に係る医療機器を示す図である。It is a figure which shows the medical device which concerns on 9th Embodiment. 第１０の実施形態に係るガスセンサを示す図である。It is a figure which shows the gas sensor which concerns on 10th Embodiment. 実施例１に係るパルス光源から出力されたパルス光の光スペクトルの測定結果を示す図である。It is a figure which shows the measurement result of the optical spectrum of the pulsed light output from the pulse light source which concerns on Example 1. FIG. 実施例１に係るパルス光源から出力されたパルス光の測定結果を示す図である。It is a figure which shows the measurement result of the pulsed light output from the pulse light source which concerns on Example 1. FIG. 実施例１に係るパルス光源から出力されたパルス光のＲＦスペクトルの測定結果を示す図である。It is a figure which shows the measurement result of RF spectrum of the pulsed light output from the pulse light source which concerns on Example 1. FIG. 実施例１に係るパルス光源から出力されたパルス光の自己相関の測定結果を示す図である。It is a figure which shows the measurement result of the autocorrelation of the pulsed light output from the pulse light source which concerns on Example 1. FIG. 実施例２に係るパルス光源から出力されたパルス光の測定結果を示す図である。It is a figure which shows the measurement result of the pulsed light output from the pulse light source which concerns on Example 2. FIG. 実施例３に係るパルス光源から出力されたパルス光の光スペクトルの測定結果を示す図である。It is a figure which shows the measurement result of the optical spectrum of the pulsed light output from the pulse light source which concerns on Example 3. FIG. 実施例３に係るパルス光源から出力されたパルス光の自己相関の測定結果を示す図である。It is a figure which shows the measurement result of the autocorrelation of the pulsed light output from the pulse light source which concerns on Example 3. FIG. 実施例３に係るパルス光源から出力されたパルス光のＲＦスペクトルの測定結果を示す図である。It is a figure which shows the measurement result of RF spectrum of the pulsed light output from the pulse light source which concerns on Example 3. FIG.
　以下、本発明の実施の形態について、図面を用いて説明する。尚、すべての図面において、同様な構成要素には同様の符号を付し、適宜説明を省略する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.
（第１の実施形態）
　図１は、第１の実施形態に係るパルス光源１０を示す図である。パルス光源１０は、ポンプ光源１００、共振器２００及び出力部３００を備えている。共振器２００は、希土類ドープファイバ増幅器（ＲＥＤＦＡ）２２０を有している。ポンプ光源１００は、ＲＥＤＦＡ２２０にポンプ光を供給している。ポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。具体的には、変調周波数ｆｍｏｄは、共振器２００の基本共振周波数ｆ１の整数倍の９５％以上１０５％以下、好ましくは９９％以上１０１％以下、より好ましくは１００±０．１％の周波数である。パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。このように、パルス光源１０では、変調周波数ｆｍｏｄと等しい繰り返し周波数の能動モード同期が実現されている。以下、詳細に説明する。 (First embodiment)
FIG. 1 is a diagram illustrating a pulse light source 10 according to the first embodiment. The pulse light source 10 includes a pump light source 100, a resonator 200, and an output unit 300. The resonator 200 includes a rare earth doped fiber amplifier (REDFA) 220. The pump light source 100 supplies pump light to the REDFA 220. The pump light is modulated by a modulation signal having a modulation frequency f mod substantially equal to an integral multiple of the basic resonance frequency f 1 of the resonator 200. Specifically, the modulation frequency f mod is 95% or more and 105% or less, preferably 99% or more and 101% or less, more preferably 100 ± 0.1% of an integral multiple of the basic resonance frequency f 1 of the resonator 200. Is the frequency. Pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod . Thus, in the pulse light source 10, active mode synchronization with a repetition frequency equal to the modulation frequency f mod is realized. Details will be described below.
　図２は、図１に示したポンプ光源１００の第１例を示す図である。ポンプ光源１００は、ポンプレーザ１１０、光増幅器１２０、電気信号発生器１３０及びレーザドライバ１４０を有している。 FIG. 2 is a diagram showing a first example of the pump light source 100 shown in FIG. The pump light source 100 includes a pump laser 110, an optical amplifier 120, an electric signal generator 130, and a laser driver 140.
　ポンプレーザ１１０は、ＲＥＤＦＡ２２０（図１）に含まれる希土類イオンを励起させる波長のシード光を発する。ポンプレーザ１１０からのシード光は、光増幅器１２０によって増幅される。例えば、ＲＥＤＦＡ２２０（図１）がツリウムイオン（Ｔｍ３＋）を含んでいる場合、ポンプレーザ１１０のシード光の波長は１５７０ｎｍであり、光増幅器１２０はＣ－バンドエルビウムドープファイバ増幅器（ＥＤＦＡ）である。 The pump laser 110 emits seed light having a wavelength that excites rare earth ions contained in the REDFA 220 (FIG. 1). The seed light from the pump laser 110 is amplified by the optical amplifier 120. For example, if the REDFA 220 (FIG. 1) contains thulium ions (Tm 3+ ), the wavelength of the seed light of the pump laser 110 is 1570 nm, and the optical amplifier 120 is a C-band erbium doped fiber amplifier (EDFA).
　一例において、電気信号発生器１３０は、変調周波数ｆｍｏｄで振動する正弦波によってポンプレーザ１１０のシード光を変調している。本図に示す例では、電気信号発生器１３０は、レーザドライバ１４０を介してポンプレーザ１１０のシード光を変調している。このようにして、ポンプ光源１００からのポンプ光は、変調周波数ｆｍｏｄの変調信号によって変調されている。 In one example, the electrical signal generator 130 modulates the seed light of the pump laser 110 with a sine wave that oscillates at the modulation frequency f mod . In the example shown in this figure, the electric signal generator 130 modulates the seed light of the pump laser 110 via the laser driver 140. In this way, the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod .
　その他の例において、電気信号発生器１３０は、変調周波数ｆｍｏｄで振動する矩形波によってポンプレーザ１１０のシード光を変調していてもよい。この例において、電気信号発生器１３０からの矩形波は、繰り返し周期Ｔｍｏｄ（Ｔｍｏｄ＝１／ｆｍｏｄ）及びオン時間Ｔｏｎを有している。この矩形波のデューティ比Ｔｏｎ／Ｔｍｏｄは、０．５０であってもよいし、又は０．５０とは異なっていてもよい。このようにして、ポンプ光源１００からのポンプ光は、変調周波数ｆｍｏｄの変調信号によって変調されている。 In another example, the electric signal generator 130 may modulate the seed light of the pump laser 110 with a rectangular wave that oscillates at the modulation frequency f mod . In this example, the rectangular wave from the electrical signal generator 130 has a repetition period T mod (T mod = 1 / f mod ) and an on time T on . The duty ratio T on / T mod of this rectangular wave may be 0.50 or may be different from 0.50. In this way, the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod .
　なお、電気信号発生器１３０による変調度は、ある程度高いことが好ましく、例えば、１０％以上であることが好ましい。電気信号発生器１３０による変調度がある程度高い場合、ポンプ光が充分に変調される。ただし、電気信号発生器１３０による変調度は、上記した例（１０％以上）に限定されるものではない。 It should be noted that the degree of modulation by the electric signal generator 130 is preferably high to some extent, and is preferably 10% or more, for example. When the degree of modulation by the electric signal generator 130 is high to some extent, the pump light is sufficiently modulated. However, the degree of modulation by the electric signal generator 130 is not limited to the above example (10% or more).
　図３は、図１に示したポンプ光源１００の第２例を示す図である。本図に示すように、ポンプ光源１００は、光増幅器１２０（図２）を有していなくてもよい。本図に示す例では、ポンプレーザ１１０からのシード光（ポンプ光）が光増幅器１２０（図２）を介さず共振器２００に直接供給される。 FIG. 3 is a diagram showing a second example of the pump light source 100 shown in FIG. As shown in the figure, the pump light source 100 may not include the optical amplifier 120 (FIG. 2). In the example shown in this figure, the seed light (pump light) from the pump laser 110 is directly supplied to the resonator 200 without passing through the optical amplifier 120 (FIG. 2).
　図４は、図１に示したポンプ光源１００の第３例を示す図である。本図に示すように、ポンプレーザ１１０からのシード光は、光強度変調器１５０及び電気信号発生器１３０によって変調されていてもよい。具体的には、本図に示す例において、レーザドライバ１４０は、例えば直流レーザドライバであり、ポンプレーザ１１０からのシード光を変調していない。光強度変調器１５０は、ポンプレーザ１１０と光増幅器１２０の間にあって、電気信号発生器１３０からの信号（例えば、正弦波又は矩形波）によってポンプレーザ１１０からのシード光を変調している。 FIG. 4 is a diagram showing a third example of the pump light source 100 shown in FIG. As shown in the figure, the seed light from the pump laser 110 may be modulated by a light intensity modulator 150 and an electric signal generator 130. Specifically, in the example shown in this figure, the laser driver 140 is a DC laser driver, for example, and does not modulate the seed light from the pump laser 110. The light intensity modulator 150 is located between the pump laser 110 and the optical amplifier 120, and modulates the seed light from the pump laser 110 by a signal (for example, a sine wave or a rectangular wave) from the electric signal generator 130.
　図１に戻る。パルス光源１０は、ポンプ光源１００及び共振器２００を備えている。共振器２００は、光合波器２１０、ＲＥＤＦＡ２２０、アイソレータ（ＩＳＯ）２３０及び光分波器２４０を有している。光合波器２１０、ＲＥＤＦＡ２２０、アイソレータ２３０及び光分波器２４０は、光ファイバを介して互いに光学的に結合している。ポンプ光源１００は、光ファイバを介して共振器２００の光合波器２１０に光学的に結合している。出力部３００は、光ファイバを介して光分波器２４０に光学的に結合している。 Return to Figure 1. The pulse light source 10 includes a pump light source 100 and a resonator 200. The resonator 200 includes an optical multiplexer 210, a REDFA 220, an isolator (ISO) 230, and an optical demultiplexer 240. The optical multiplexer 210, the REDFA 220, the isolator 230, and the optical demultiplexer 240 are optically coupled to each other via an optical fiber. The pump light source 100 is optically coupled to the optical multiplexer 210 of the resonator 200 via an optical fiber. The output unit 300 is optically coupled to the optical demultiplexer 240 via an optical fiber.
　本図に示す例において、共振器２００は、前方励起のリング共振器である。具体的には、ポンプ光源１００からのポンプ光は、アイソレータ２３０の順方向（共振器２００内での光の伝搬方向）においてアイソレータ２３０の前方とＲＥＤＦＡ２２０の後方の間で光合波器２１０を介して供給されている。 In the example shown in the figure, the resonator 200 is a forward-excited ring resonator. Specifically, the pump light from the pump light source 100 passes through the optical multiplexer 210 between the front of the isolator 230 and the rear of the REDFA 220 in the forward direction of the isolator 230 (light propagation direction in the resonator 200). Have been supplied.
　より具体的には、ポンプ光源１００からのポンプ光は、光合波器２１０を介してＲＥＤＦＡ２２０に入力される。光合波器２１０は、ポンプ光源１００からのポンプ光及び光分波器２４０からの光を合波しており、具体的にはＷＤＭ（Ｗａｖｅｌｅｎｇｔｈ　Ｄｉｖｉｓｉｏｎ　Ｍｕｌｔｉｐｌｅｘｉｎｇ）カプラである。ポンプ光によってＲＥＤＦＡ２２０に含まれる希土類イオンが励起する。さらに、励起した希土類イオンが低エネルギー準位に遷移することで、ＲＥＤＦＡ２２０から光が放出される。ＲＥＤＦＡ２２０からの光は、アイソレータ２３０を介して光分波器２４０に入力される。アイソレータ２３０からの光の一部は、光分波器２４０を介して光合波器２１０に入力され、さらに光合波器２１０を介してＲＥＤＦＡ２２０に入力される。アイソレータ２３０からの光の他の一部は、光分波器２４０を介して出力部３００に入力され、さらに出力部３００を介してパルス光源１０の外部に出力される。光分波器２４０は、アイソレータ２３０からの光を２つの同一波長の光に例えば５０：５０で分波しており、具体的には光カプラである。 More specifically, the pump light from the pump light source 100 is input to the REDFA 220 via the optical multiplexer 210. The optical multiplexer 210 combines the pump light from the pump light source 100 and the light from the optical demultiplexer 240, and is specifically a WDM (Wavelength Division Multiplexing) coupler. The rare earth ions contained in the REDFA 220 are excited by the pump light. Furthermore, light is emitted from the REDFA 220 when the excited rare earth ions transition to a low energy level. Light from the REDFA 220 is input to the optical demultiplexer 240 via the isolator 230. Part of the light from the isolator 230 is input to the optical multiplexer 210 via the optical demultiplexer 240 and further input to the REDFA 220 via the optical multiplexer 210. Another part of the light from the isolator 230 is input to the output unit 300 via the optical demultiplexer 240 and further output to the outside of the pulse light source 10 via the output unit 300. The optical demultiplexer 240 demultiplexes the light from the isolator 230 into two lights having the same wavelength, for example, 50:50, and is specifically an optical coupler.
　ＲＥＤＦＡ２２０は、共振器２００の利得媒体として機能している。例えば、ＲＥＤＦＡ２２０は、ガラスファイバ及びガラスファイバにドープされた希土類イオンを含んでいる。ＲＥＤＦＡ２２０に含まれる希土類イオンは、例えば、プラセオジムイオン（Ｐｒ３＋）、ネオジムイオン（Ｎｄ３＋）、ホルミウムイオン（Ｈｏ３＋）、エルビウムイオン（Ｅｒ３＋）、ツリウムイオン（Ｔｍ３＋）及びイッテルビウムイオン（Ｙｂ３＋）からなる群から選択される少なくとも１つである。 The REDFA 220 functions as a gain medium for the resonator 200. For example, REDFA 220 includes glass fibers and rare earth ions doped into the glass fibers. The rare earth ions contained in REDFA 220 include, for example, praseodymium ions (Pr 3+ ), neodymium ions (Nd 3+ ), holmium ions (Ho 3+ ), erbium ions (Er 3+ ), thulium ions (Tm 3+ ), and ytterbium ions (Yb 3+). At least one selected from the group consisting of:
　なお、出力部３００は、例えばアイソレータである。この場合、出力部３００（アイソレータ）は、共振器２００からパルス光源１０の外側に向かう光が出力部３００を透過し、パルス光源１０の外側から共振器２００に向かう光が出力部３００によって遮断されるように配置されている。 Note that the output unit 300 is, for example, an isolator. In this case, in the output unit 300 (isolator), light traveling from the resonator 200 toward the outside of the pulse light source 10 passes through the output unit 300, and light traveling from the outside of the pulse light source 10 toward the resonator 200 is blocked by the output unit 300. It is arranged so that.
　共振器２００のｑ次の共振周波数ｆｑは、以下の式（１）によって表される。
　　ｆｑ＝ｑｃ／（ｎＬ１）　　　（１）
ただし、ｃは光速、ｎは共振器２００の光ファイバの屈折率、Ｌ１は共振器２００の長さである。特にｑ＝１のとき、共振周波数ｆｑは、基本共振周波数ｆ１となる。 The q-order resonance frequency f q of the resonator 200 is expressed by the following equation (1).
f q = qc / (nL 1 ) (1)
However, c is the speed of light, n is the refractive index of the optical fiber of the resonator 200, and L 1 is the length of the resonator 200. In particular, when q = 1, the resonance frequency f q is the basic resonance frequency f 1 .
　次に、パルス光源１０の出力部３００からパルス光を出力する方法について説明する。まず、ポンプ光源１００から共振器２００のＲＥＤＦＡ２２０にポンプ光を供給する。上記したように、ポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。 Next, a method for outputting pulsed light from the output unit 300 of the pulsed light source 10 will be described. First, pump light is supplied from the pump light source 100 to the REDFA 220 of the resonator 200. As described above, the pump light is modulated by the modulation signal having the modulation frequency f mod substantially equal to the integral multiple of the basic resonance frequency f 1 of the resonator 200.
　本発明者が検討したところ、ＲＥＤＦＡ２２０に含まれる希土類イオンの上準位（３Ｆ４）の寿命τが変調信号の繰り返し周期Ｔｍｏｄ（Ｔｍｏｄ＝１／ｆｍｏｄ）に対してある程度短い場合、具体的には、繰り返し周期Ｔｍｏｄに対する寿命τの比τ／Ｔｍｏｄが例えば１×１０４以下である場合、出力部３００からの信号のＲａｄｉｏ－Ｆｒｅｑｕｅｎｃｙ（ＲＦ）スペクトルにおいて変調周波数ｆｍｏｄと等しい周波数にピークが出現するようになることが明らかとなった（例えば、後述する図１９を参照）。さらに、寿命τが一定の場合に繰り返し周期Ｔｍｏｄが長くなる（すなわち、変調周波数ｆｍｏｄが低くなる）ほど、当該ピークの強度は大きくなることが明らかとなった。この結果は、当該ピークが電気信号発生器１３０の変調に起因していることを示している。 When the present inventor examined, when the lifetime τ of the upper level ( 3 F 4 ) of the rare earth ions contained in the REDFA 220 is somewhat shorter than the modulation signal repetition period T mod (T mod = 1 / f mod ), Specifically, when the ratio tau / T mod lifetime tau for the repetition period T mod is for example, at 1 × 10 4 or less, equal to the modulation frequency f mod in Radio-frequency (RF) spectrum of the signal from the output unit 300 It became clear that a peak appeared in the frequency (for example, see FIG. 19 described later). Furthermore, it has been clarified that the intensity of the peak increases as the repetition period T mod increases (that is, the modulation frequency f mod decreases) when the lifetime τ is constant. This result indicates that the peak is due to the modulation of the electric signal generator 130.
　なお、寿命τは、エルビウムイオン（Ｅｒ３＋）については、おおよそ８ｍｓ以上１０ｍｓ以下であり、イッテルビウムイオン（Ｙｂ３＋）については、おおよそ１ｍｓ以上２ｍｓ以下であり、ツリウムイオン（Ｔｍ３＋）については、エルビウムイオン（Ｅｒ３＋）の寿命及びイッテルビウムイオン（Ｙｂ３＋）の寿命よりも短く、具体的にはおおよそ４００μｓ以上５００μｓ以下である。 The lifetime τ is about 8 ms to 10 ms for erbium ion (Er 3+ ), about 1 ms to 2 ms for ytterbium ion (Yb 3+ ), and erbium for thulium ion (Tm 3+ ). It is shorter than the lifetime of ions (Er 3+ ) and the lifetime of ytterbium ions (Yb 3+ ), specifically, approximately 400 μs or more and 500 μs or less.
　本図に示す例において、変調周波数ｆｍｏｄは、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい。このため、変調周波数ｆｍｏｄと等しい繰り返し周波数のモード同期、具体的にはＣｏｎｔｉｎｕｏｕｓ　Ｗａｖｅ（ＣＷ）能動モード同期が実現される。このため、パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。 In the example shown in this figure, the modulation frequency f mod is substantially equal to an integral multiple of the basic resonance frequency f 1 of the resonator 200. For this reason, mode synchronization of a repetition frequency equal to the modulation frequency f mod , specifically, Continuous Wave (CW) active mode synchronization is realized. For this reason, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
　なお、本発明者が検討したところ、変調周波数ｆｍｏｄと共振器２００の基本共振周波数ｆ１の整数倍の差が小さいほど、より良好なＣＷモード同期が実現されることが明らかとなった。このため、変調周波数ｆｍｏｄは、共振器２００の基本共振周波数ｆ１の整数倍の９５％以上１０５％以下、好ましくは９９％以上１０１％以下、より好ましくは１００±０．１％の周波数である。 As a result of studies by the present inventor, it has been clarified that better CW mode synchronization is realized as the difference between the integral frequency of the modulation frequency f mod and the basic resonance frequency f 1 of the resonator 200 is smaller. For this reason, the modulation frequency f mod is 95% or more and 105% or less, preferably 99% or more and 101% or less, more preferably 100 ± 0.1% of an integral multiple of the basic resonance frequency f 1 of the resonator 200. is there.
　以上、本実施形態によれば、ポンプ光源１００からのポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。これにより、パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。 As described above, according to the present embodiment, the pump light from the pump light source 100 is modulated by the modulation signal having the modulation frequency f mod substantially equal to the integral multiple of the basic resonance frequency f 1 of the resonator 200. As a result, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
　さらに、本実施形態によれば、例えば後述する図２０に示すように、ピコ秒（１０－１２秒）オーダのパルス幅を有するパルス光、すなわち超短パルス光を発生させることができる。 Furthermore, according to the present embodiment, for example, as shown in FIG. 20 described later, pulsed light having a pulse width on the order of picoseconds (10 −12 seconds), that is, ultrashort pulsed light can be generated.
　さらに、本実施形態によれば、パルス光源１０から発生するパルス光の波長を近赤外の波長にすることができる。具体的には、ＲＥＤＦＡ２２０がツリウムイオン（Ｔｍ３＋）を含んでいる場合、パルス光の波長は２μｍ帯にすることができ、ＲＥＤＦＡ２２０がエルビウムイオン（Ｅｒ３＋）を含んでいる場合、パルス光の波長は１．５μｍ帯にすることができ、ＲＥＤＦＡ２２０がイッテルビウムイオン（Ｙｂ３＋）を含んでいる場合、パルス光の波長は１μｍ帯にすることができる。 Furthermore, according to this embodiment, the wavelength of the pulsed light generated from the pulsed light source 10 can be set to the near infrared wavelength. Specifically, when the REDFA 220 contains thulium ions (Tm 3+ ), the wavelength of the pulsed light can be in the 2 μm band, and when the REDFA 220 contains erbium ions (Er 3+ ), the wavelength of the pulsed light Can be in the 1.5 μm band, and when the REDFA 220 contains ytterbium ions (Yb 3+ ), the wavelength of the pulsed light can be in the 1 μm band.
　図５は、図１の変形例を示す図である。本図に示すように、共振器２００は、後方励起のリング共振器であってもよい。具体的には、本図に示す例では、ポンプ光源１００からのポンプ光は、アイソレータ２３０の順方向（共振器２００内での光の伝搬方向）においてＲＥＤＦＡ２２０の前方とアイソレータ２３０の後方の間で光合波器２１０を介して供給されている。 FIG. 5 is a diagram showing a modification of FIG. As shown in the figure, the resonator 200 may be a backward-pumped ring resonator. Specifically, in the example shown in this figure, the pump light from the pump light source 100 is between the front of the REDFA 220 and the rear of the isolator 230 in the forward direction of the isolator 230 (light propagation direction in the resonator 200). It is supplied via the optical multiplexer 210.
（第２の実施形態）
　図６は、第２の実施形態に係るパルス光源１０を示す図であり、第１の実施形態の図１に対応する。本実施形態に係るパルス光源１０は、以下の点を除いて、第１の実施形態に係るパルス光源１０と同様である。 (Second Embodiment)
FIG. 6 is a diagram showing a pulse light source 10 according to the second embodiment, and corresponds to FIG. 1 of the first embodiment. The pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
　本図に示す例において、共振器２００は、リニア共振器である。共振器２００は、ＲＥＤＦＡ２２０、第１反射素子２５２及び第２反射素子２５４を有している。ＲＥＤＦＡ２２０は、第１反射素子２５２と第２反射素子２５４の間にある。第１反射素子２５２及び第２反射素子２５４は、共振器２００のミラーとして機能している。第１反射素子２５２は、ミラー又はＦＢＧ（Ｆｉｂｅｒ　Ｂｒａｇｇ　Ｇｒａｔｉｎｇ）である。第２反射素子２５４は、ＲＥＤＦＡ２２０からの光の一部を反射し、ＲＥＤＦＡ２２０からの光の他の一部を透過させる。より具体的には、第２反射素子２５４は、例えば、ミラー又はＦＢＧである。ポンプ光源１００からのポンプ光は、第１反射素子２５２とＲＥＤＦＡ２２０の間の光合波器２１０を介してＲＥＤＦＡ２２０に供給されている。共振器２００からの光は、第２反射素子２５４、アイソレータ２３０及び出力部３００を介してパルス光源１０の外部に出力される。 In the example shown in the figure, the resonator 200 is a linear resonator. The resonator 200 includes a REDFA 220, a first reflective element 252 and a second reflective element 254. The REDFA 220 is between the first reflective element 252 and the second reflective element 254. The first reflective element 252 and the second reflective element 254 function as a mirror of the resonator 200. The first reflective element 252 is a mirror or FBG (Fiber Bragg Grating). The second reflective element 254 reflects a part of the light from the REDFA 220 and transmits the other part of the light from the REDFA 220. More specifically, the 2nd reflective element 254 is a mirror or FBG, for example. Pump light from the pump light source 100 is supplied to the REDFA 220 via the optical multiplexer 210 between the first reflective element 252 and the REDFA 220. Light from the resonator 200 is output to the outside of the pulse light source 10 via the second reflective element 254, the isolator 230, and the output unit 300.
　共振器２００のｑ次の共振周波数ｆｑは、以下の式（２）によって表される。
　　ｆｑ＝ｑｃ／（２ｎＬ２）　　　（２）
ただし、ｃは光速、ｎは共振器２００の光ファイバの屈折率、Ｌ２は共振器２００の長さである。特にｑ＝１のとき、共振周波数ｆｑは、基本共振周波数ｆ１となる。 The q-order resonance frequency f q of the resonator 200 is expressed by the following equation (2).
f q = qc / (2nL 2 ) (2)
However, c is the speed of light, n is the refractive index of the optical fiber of the resonator 200, and L 2 is the length of the resonator 200. In particular, when q = 1, the resonance frequency f q is the basic resonance frequency f 1 .
　本実施形態においても、ポンプ光源１００からのポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。これにより、第１の実施形態と同様にして、パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。 Also in the present embodiment, the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200. As a result, similarly to the first embodiment, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
　図７は、図６の第１の変形例を示す図である。本図に示す例において、共振器２００は、リニア共振器である。本図に示すように、ポンプ光源１００からのポンプ光は、ＲＥＤＦＡ２２０と第２反射素子２５４の間の光合波器２１０を介して供給されていてもよい。 FIG. 7 is a diagram showing a first modification of FIG. In the example shown in this figure, the resonator 200 is a linear resonator. As shown in the figure, the pump light from the pump light source 100 may be supplied via an optical multiplexer 210 between the REDFA 220 and the second reflective element 254.
　図８は、図６の第２の変形例を示す図である。本図に示す例において、共振器２００は、リニア共振器である。本図に示すように、ポンプ光源１００からのポンプ光は、第１反射素子２５２を介してＲＥＤＦＡ２２０に供給されていてもよい。第１反射素子２５２は、特定の波長の光を反射する素子として機能しており、具体的には、ポンプ光源１００からのポンプ光を透過させ、ＲＥＤＦＡ２２０から放出された光を反射する。より具体的には、第１反射素子２５２は、例えば、多層膜ミラー又はＦＢＧ（Ｆｉｂｅｒ　Ｂｒａｇｇ　Ｇｒａｔｉｎｇ）である。 FIG. 8 is a diagram showing a second modification of FIG. In the example shown in this figure, the resonator 200 is a linear resonator. As shown in the figure, the pump light from the pump light source 100 may be supplied to the REDFA 220 via the first reflective element 252. The first reflecting element 252 functions as an element that reflects light of a specific wavelength, and specifically, transmits the pump light from the pump light source 100 and reflects the light emitted from the REDFA 220. More specifically, the first reflective element 252 is, for example, a multilayer film mirror or an FBG (Fiber Bragg Grating).
（第３の実施形態）
　図９は、第３の実施形態に係るパルス光源１０を示す図であり、第１の実施形態の図１に対応する。本実施形態に係るパルス光源１０は、以下の点を除いて、第１の実施形態に係るパルス光源１０と同様である。 (Third embodiment)
FIG. 9 is a diagram showing a pulse light source 10 according to the third embodiment, and corresponds to FIG. 1 of the first embodiment. The pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
　本図に示す例において、共振器２００は、８の字型共振器である。具体的には、共振器２００は、第１ループ２０２及び第２ループ２０４を有している。第１ループ２０２と第２ループ２０４は、光分波器２４２（具体的には、光カプラ）を介して互いに光学的に結合している。第１ループ２０２は、ＲＥＤＦＡ２２０及び非線形ファイバ２６０を有している。ポンプ光源１００からのポンプ光は、ＲＥＤＦＡ２２０に供給されている。第２ループ２０４は、アイソレータ２３０及び光分波器２４０を有している。光分波器２４０は、光ファイバを介して出力部３００に光学的に結合している。 In the example shown in the figure, the resonator 200 is an 8-shaped resonator. Specifically, the resonator 200 has a first loop 202 and a second loop 204. The first loop 202 and the second loop 204 are optically coupled to each other via an optical demultiplexer 242 (specifically, an optical coupler). The first loop 202 includes a REDFA 220 and a nonlinear fiber 260. Pump light from the pump light source 100 is supplied to the REDFA 220. The second loop 204 includes an isolator 230 and an optical demultiplexer 240. The optical demultiplexer 240 is optically coupled to the output unit 300 via an optical fiber.
　本図に示す例では、第２ループ２０４からの光が光分波器２４２に入力されると、この光は、第１ループ２０２のＲＥＤＦＡ２２０側に向かう光と第１ループ２０２の非線形ファイバ２６０側に向かう光に分離される。これら２つの光には、非線形ファイバ２６０において位相シフトが生じる。一方、光の伝搬方向に基づいて、これら２つの光では位相シフト差が生じる。これら２つの光が光分波器２４２において結合すると、位相シフト差に基づいて干渉が生じる。特定の干渉が生じている場合、光分波器２４２から第２ループ２０４に向かう光は、アイソレータ２３０の順方向に第２ループ２０４内を伝搬するようになる。 In the example shown in this figure, when light from the second loop 204 is input to the optical demultiplexer 242, this light is transmitted to the REDFA 220 side of the first loop 202 and to the nonlinear fiber 260 side of the first loop 202. It is separated by the light which goes to. These two lights cause a phase shift in the nonlinear fiber 260. On the other hand, a phase shift difference occurs between these two lights based on the light propagation direction. When these two lights are combined in the optical demultiplexer 242, interference occurs based on the phase shift difference. When specific interference occurs, the light traveling from the optical demultiplexer 242 toward the second loop 204 propagates in the second loop 204 in the forward direction of the isolator 230.
　本実施形態においても、ポンプ光源１００からのポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。これにより、第１の実施形態と同様にして、パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。 Also in the present embodiment, the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200. As a result, similarly to the first embodiment, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
（第４の実施形態）
　図１０は、第４の実施形態に係るパルス光源１０を示す図であり、第１の実施形態の図１に対応する。本実施形態に係るパルス光源１０は、以下の点を除いて、第１の実施形態に係るパルス光源１０と同様である。 (Fourth embodiment)
FIG. 10 is a view showing a pulse light source 10 according to the fourth embodiment, and corresponds to FIG. 1 of the first embodiment. The pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
　本図に示す例において、共振器２００は、シグマ型共振器である。共振器２００は、ＲＥＤＦＡ２２０、アイソレータ２３０、光分波器２４０、反射素子２５６及びＰＢＳ（Ｐｏｌａｒｉｚｉｎｇ　Ｂｅａｍ　Ｓｐｌｉｔｔｅｒ）２７０を有している。 In the example shown in the figure, the resonator 200 is a sigma resonator. The resonator 200 includes a REDFA 220, an isolator 230, an optical demultiplexer 240, a reflecting element 256, and a PBS (Polarizing Beam Splitter) 270.
　ＲＥＤＦＡ２２０は、反射素子２５６とＰＢＳ２７０の間にある。ポンプレーザ１１０からのポンプ光は、ＲＥＤＦＡ２２０に供給される。反射素子２５６は、ファラデーミラーであり、反射光の偏光方向が入射光の偏光方向から９０°回転するように光を反射する。 The REDFA 220 is between the reflective element 256 and the PBS 270. Pump light from the pump laser 110 is supplied to the REDFA 220. The reflection element 256 is a Faraday mirror and reflects light so that the polarization direction of the reflected light is rotated by 90 ° from the polarization direction of the incident light.
　ＰＢＳ２７０、アイソレータ２３０及び光分波器２４０は、偏波保持ファイバを介して光学的に結合している。アイソレータ２３０は、ＰＢＳ２７０と光分波器２４０の間にあり、アイソレータ２３０の順方向がＰＢＳ２７０から光分波器２４０に向かう方向になるように設けられている。光分波器２４０側の偏光保持ファイバとＰＢＳ２７０側の偏光保持ファイバは、融着部２８０において融着している。具体的には、光分波器２４０側の偏光方向とＰＢＳ２７０側の偏光方向が９０°回転するようにこれらの偏光保持ファイバは、融着部２８０において融着している。 PBS 270, isolator 230, and optical demultiplexer 240 are optically coupled via a polarization maintaining fiber. The isolator 230 is provided between the PBS 270 and the optical demultiplexer 240, and is provided so that the forward direction of the isolator 230 is the direction from the PBS 270 toward the optical demultiplexer 240. The polarization maintaining fiber on the optical demultiplexer 240 side and the polarization maintaining fiber on the PBS 270 side are fused at the fusion part 280. Specifically, these polarization maintaining fibers are fused at the fusion part 280 so that the polarization direction on the optical demultiplexer 240 side and the polarization direction on the PBS 270 side are rotated by 90 °.
　本実施形態においても、ポンプ光源１００からのポンプ光は、共振器２００の基本共振周波数ｆ１の整数倍とほぼ等しい変調周波数ｆｍｏｄを有する変調信号によって変調されている。これにより、第１の実施形態と同様にして、パルス光源１０の出力部３００からは、変調周波数ｆｍｏｄと等しい繰り返し周波数でパルス光が出力される。 Also in the present embodiment, the pump light from the pump light source 100 is modulated by a modulation signal having a modulation frequency f mod that is substantially equal to an integral multiple of the fundamental resonance frequency f 1 of the resonator 200. As a result, similarly to the first embodiment, pulse light is output from the output unit 300 of the pulse light source 10 at a repetition frequency equal to the modulation frequency f mod .
（第５の実施形態）
　図１１は、第５の実施形態に係るパルス光源１０を示す図であり、第１の実施形態の図５に対応する。本実施形態に係るパルス光源１０は、以下の点を除いて、第１の実施形態に係るパルス光源１０と同様である。 (Fifth embodiment)
FIG. 11 is a diagram showing a pulse light source 10 according to the fifth embodiment, and corresponds to FIG. 5 of the first embodiment. The pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
　本図に示す例において、共振器２００は、リング共振器である。本図に示すように、共振器２００は、可飽和吸収体２９２を有していてもよい。本図に示す例において、可飽和吸収体２９２は、光合波器２１０とアイソレータ２３０の間にある。なお、本図に示す例では、ポンプ光源１００からのポンプ光は、アイソレータ２３０の順方向（共振器２００内での光の伝搬方向）においてＲＥＤＦＡ２２０の前方とアイソレータ２３０の後方の間で光合波器２１０を介して供給されている。 In the example shown in the figure, the resonator 200 is a ring resonator. As shown in the figure, the resonator 200 may include a saturable absorber 292. In the example shown in this figure, the saturable absorber 292 is located between the optical multiplexer 210 and the isolator 230. In the example shown in the figure, the pump light from the pump light source 100 is an optical multiplexer between the front of the REDFA 220 and the rear of the isolator 230 in the forward direction of the isolator 230 (the propagation direction of light in the resonator 200). 210 is supplied.
（第６の実施形態）
　図１２は、第６の実施形態に係るパルス光源１０を示す図であり、第２の実施形態の図６に対応する。本実施形態に係るパルス光源１０は、以下の点を除いて、第２の実施形態に係るパルス光源１０と同様である。 (Sixth embodiment)
FIG. 12 is a diagram showing a pulse light source 10 according to the sixth embodiment, and corresponds to FIG. 6 of the second embodiment. The pulse light source 10 according to the present embodiment is the same as the pulse light source 10 according to the second embodiment except for the following points.
　本図に示す例において、共振器２００は、リニア共振器である。本図に示すように、共振器２００は、第１反射素子２５２（図６）に代えて可飽和吸収ミラー２９４を有していてもよい。なお、本図に示す例では、ポンプ光源１００からのポンプ光は、可飽和吸収ミラー２９４とＲＥＤＦＡ２２０の間で光合波器２１０を介して供給されている。 In the example shown in the figure, the resonator 200 is a linear resonator. As shown in the figure, the resonator 200 may include a saturable absorbing mirror 294 instead of the first reflecting element 252 (FIG. 6). In the example shown in the drawing, the pump light from the pump light source 100 is supplied via the optical multiplexer 210 between the saturable absorption mirror 294 and the REDFA 220.
（第７の実施形態）
　図１３は、第７の実施形態に係るレーザ加工装置を示す図である。レーザ加工装置は、パルス光源１０、ミラー１２、レンズ１４及びノズル１６を備えている。レーザ加工装置は、対象物Ｗを加工するために用いられる。対象物Ｗは、例えば、鉄板、ガラス板又はプラスチック板である。本実施形態に係るパルス光源１０は、第１の実施形態～第６の実施形態のいずれかに係るパルス光源１０である。パルス光源１０からはパルス光が出力される。パルス光は、ミラー１２で反射し、レンズ１４に入射する。パルス光は、レンズ１４によって集光され、その後、ノズル１６を通過して対象物Ｗに照射される。 (Seventh embodiment)
FIG. 13 is a diagram showing a laser processing apparatus according to the seventh embodiment. The laser processing apparatus includes a pulse light source 10, a mirror 12, a lens 14, and a nozzle 16. The laser processing apparatus is used for processing the object W. The object W is, for example, an iron plate, a glass plate, or a plastic plate. The pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments. Pulse light is output from the pulse light source 10. The pulsed light is reflected by the mirror 12 and enters the lens 14. The pulsed light is collected by the lens 14 and then passes through the nozzle 16 and is irradiated onto the object W.
　本実施形態において、パルス光源１０から対象物Ｗに照射されるパルス光のパルス幅は、ピコ秒（１０－１２秒）オーダにすることができ、非常に狭くすることができる。このため、パルス光が照射された領域は短時間で除去される。このため、パルス光によって除去された領域の周辺に熱が拡散することが抑制される。 In the present embodiment, the pulse width of the pulsed light irradiated from the pulse light source 10 onto the object W can be on the order of picoseconds (10 −12 seconds) and can be very narrow. For this reason, the region irradiated with the pulsed light is removed in a short time. For this reason, it is possible to suppress the diffusion of heat around the area removed by the pulsed light.
　さらに、本実施形態において、パルス光源１０から対象物Ｗに照射されるパルス光のピーク強度は、非常に大きい。このため、対象物Ｗにおいて多光子光学吸収過程が発生する確率が高くなる。このため、本実施形態では、対象物Ｗがガラスのような透光性材料からなる場合であっても、対象物Ｗを加工することができる。 Furthermore, in the present embodiment, the peak intensity of the pulsed light irradiated from the pulsed light source 10 to the object W is very large. For this reason, the probability that a multiphoton optical absorption process will occur in the object W increases. For this reason, in this embodiment, even if it is a case where the target object W consists of translucent materials like glass, the target object W can be processed.
（第８の実施形態）
　図１４は、第８の実施形態に係る光センサを示す図である。本図に示す例において、光センサは、Ｌａｓｅｒ　Ｉｍａｇｉｎｇ　Ｄｅｔｅｃｔｉｏｎ　Ａｎｄ　Ｒａｎｇｉｎｇ（ＬＩＤＡＲ）であり、パルス光源１０及び検出器２０を備えている。本実施形態に係るパルス光源１０は、第１の実施形態～第６の実施形態のいずれかに係るパルス光源１０である。検出器２０は、具体的にはＣＣＤ（Ｃｈａｒｇｅ－Ｃｏｕｐｌｅｄ　Ｄｅｖｉｃｅ）イメージセンサである。本図に示す例では、パルス光源１０から対象物Ｗに向かってパルス光が出力される。検出器２０は、対象物Ｗから反射したパルス光を検出する。光センサは、パルス光源１０からパルス光が出力されてから検出器２０でパルス光が検出されるまでの時間に基づいて、パルス光源１０から対象物Ｗまでの距離を算出することができる。 (Eighth embodiment)
FIG. 14 is a diagram illustrating an optical sensor according to the eighth embodiment. In the example shown in the figure, the optical sensor is Laser Imaging Detection And Ranging (LIDAR), and includes a pulse light source 10 and a detector 20. The pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments. The detector 20 is specifically a CCD (Charge-Coupled Device) image sensor. In the example shown in the figure, pulsed light is output from the pulsed light source 10 toward the object W. The detector 20 detects the pulsed light reflected from the object W. The optical sensor can calculate the distance from the pulse light source 10 to the object W based on the time from when the pulse light is output from the pulse light source 10 until the detector 20 detects the pulse light.
　一例において、光センサは、車両（例えば、自動車又はモータサイクル）に搭載される。この例においては、光センサを用いることにより、車両の例えば前方又は後方の対象物Ｗを検出することができる。 In one example, the optical sensor is mounted on a vehicle (for example, an automobile or a motorcycle). In this example, by using the optical sensor, for example, a front or rear object W of the vehicle can be detected.
　他の例において、光センサは、マッピングに用いられる。より具体的には、例えば、光センサを飛行機に搭載した場合、マッピングを空から行うことにより地球表面の形状を測定することができる。 In another example, a light sensor is used for mapping. More specifically, for example, when an optical sensor is mounted on an airplane, the shape of the earth surface can be measured by mapping from the sky.
（第９の実施形態）
　図１５は、第９の実施形態に係る医療機器を示す図である。医療機器は、図１３に示したレーザ加工装置と同様にして、パルス光源１０、ミラー１２、レンズ１４及びノズル１６を備えている。本実施形態に係るパルス光源１０は、第１の実施形態～第６の実施形態のいずれかに係るパルス光源１０である。対象物Ｗは、生体組織であり、具体的には例えば皮膚である。本図に示す例において、パルス光源１０からのパルス光は、図１３に示した例と同様にして、対象物Ｗに照射される。 (Ninth embodiment)
FIG. 15 is a diagram illustrating a medical device according to the ninth embodiment. The medical device includes a pulse light source 10, a mirror 12, a lens 14, and a nozzle 16 in the same manner as the laser processing apparatus shown in FIG. The pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments. The object W is a living tissue, specifically, for example, skin. In the example shown in the figure, the pulsed light from the pulse light source 10 is applied to the object W in the same manner as in the example shown in FIG.
　本実施形態において、パルス光源１０から対象物Ｗに照射されるパルス光のパルス幅は、ピコ秒（１０－１２秒）オーダにすることができ、非常に狭くすることができる。このため、パルス光が照射された領域は短時間で除去される。このため、パルス光によって除去された領域の周辺に熱が拡散することが抑制される。 In the present embodiment, the pulse width of the pulsed light irradiated from the pulse light source 10 onto the object W can be on the order of picoseconds (10 −12 seconds) and can be very narrow. For this reason, the region irradiated with the pulsed light is removed in a short time. For this reason, it is possible to suppress the diffusion of heat around the area removed by the pulsed light.
（第１０の実施形態）
　図１６は、第１０の実施形態に係るガスセンサを示す図である。本図に示す例において、ガスセンサは、ガスＧを分析するために用いられている。ガスセンサは、パルス光源１０及び検出器２０を備えている。本実施形態に係るパルス光源１０は、第１の実施形態～第６の実施形態のいずれかに係るパルス光源１０である。パルス光源１０からのパルス光は、ガスＧを通過し、その後、検出器２０に到達する。検出器２０は、パルス光源１０からのパルス光を検出する。検出器２０の検出結果に基づいて、ガスＧに含まれるガスの種類を分析する。具体的には、ガスＧ中においてパルス光の一部の波長の光が吸収される。この波長に基づいて、ガスＧに含まれるガスの種類を分析する。 (Tenth embodiment)
FIG. 16 is a diagram illustrating a gas sensor according to the tenth embodiment. In the example shown in this figure, the gas sensor is used to analyze the gas G. The gas sensor includes a pulse light source 10 and a detector 20. The pulse light source 10 according to this embodiment is the pulse light source 10 according to any one of the first to sixth embodiments. The pulsed light from the pulsed light source 10 passes through the gas G and then reaches the detector 20. The detector 20 detects the pulsed light from the pulse light source 10. Based on the detection result of the detector 20, the kind of gas contained in the gas G is analyzed. Specifically, light having a part of the wavelength of the pulsed light is absorbed in the gas G. Based on this wavelength, the type of gas contained in the gas G is analyzed.
（実施例１）
　図１に示したパルス光源１０を作製した。ポンプ光源１００は、図２に示すようにした。ポンプレーザ１１０は、波長１．５７μｍレーザとした。電気信号発生器１３０は、変調周波数ｆｍｏｄ：６．６９８５０ＭＨｚを有する正弦波によってシードレーザを変調した。電気信号発生器１３０による変調度は、３０％とした。光増幅器１２０は、ＥＤＦＡとした。光合波器２１０は、ＷＤＭカップラとした。ＲＥＤＦＡ２２０は、ツリウムドープファイバ増幅器（ＴＤＦＡ）（ＯＦＳ、ＴｍＤＦ２００）とした。光分波器２４０は、５０：５０光カプラとした。 Example 1
The pulse light source 10 shown in FIG. 1 was produced. The pump light source 100 was as shown in FIG. The pump laser 110 was a 1.57 μm wavelength laser. The electric signal generator 130 modulated the seed laser with a sine wave having a modulation frequency f mod : 6.69850 MHz. The degree of modulation by the electric signal generator 130 was 30%. The optical amplifier 120 is an EDFA. The optical multiplexer 210 is a WDM coupler. The REDFA 220 was a thulium-doped fiber amplifier (TDFA) (OFS, TmDF200). The optical demultiplexer 240 is a 50:50 optical coupler.
　共振器２００の長さＬ１は、３０．５ｍとし、共振器２００の基本共振周波数が６．７ＭＨｚとなるようにした。共振器２００の総分散は、－１．６７ｐｓ２であった。 The length L 1 of the resonator 200 was 30.5 m, and the basic resonance frequency of the resonator 200 was 6.7 MHz. The total dispersion of the resonator 200 was −1.67 ps 2 .
　図１７は、本実施例に係るパルス光源１０から出力されたパルス光の光スペクトルの測定結果を示す図である。本図に示す例において、光スペクトルは、分解能０．０５ｎｍの光スペクトルアナライザ（ＯＳＡ）（ＡＮＤＯ　ＡＱ６３７５）で測定した。本図に示すように、光スペクトルは、複数のＫｅｌｌｙサイドバンドを有している。このことは、パルス光源１０がソリトンパルスを発生させていることを示している。本図に示すように、スペクトル幅は０．９ｎｍである。 FIG. 17 is a diagram showing the measurement result of the optical spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment. In the example shown in this figure, the optical spectrum was measured with an optical spectrum analyzer (OSA) (ANDO AQ6375) having a resolution of 0.05 nm. As shown in the figure, the optical spectrum has a plurality of Kelly sidebands. This indicates that the pulse light source 10 generates a soliton pulse. As shown in the figure, the spectral width is 0.9 nm.
　図１８は、本実施例に係るパルス光源１０から出力されたパルス光の測定結果を示す図である。本図に示す例において、パルス光源１０からのパルス光は、ＩｎＧａＡｓフォトディテクタ（ＥＯＴ　ＥＴ－５０００、１０ＧＨｚ）で検知し、オシロスコープ（Ａｇｉｌｅｎｔ　ＤＳＯ１０２４Ａ）で測定した。本図に示すように、パルス光源１０からは、パルス光が繰り返し周波数６．６９８５０ＭＨｚ（すなわち、変調周波数ｆｍｏｄと等しい周波数）で出力されている。このように、本実施例に係るパルス光源１０では、Ｃｏｎｔｉｎｕｏｕｓ　Ｗａｖｅ（ＣＷ）能動モード同期が確認された。 FIG. 18 is a diagram illustrating a measurement result of the pulsed light output from the pulsed light source 10 according to the present embodiment. In the example shown in the figure, the pulsed light from the pulsed light source 10 was detected with an InGaAs photodetector (EOT ET-5000, 10 GHz) and measured with an oscilloscope (Agilent DSO1024A). As shown in this figure, the pulsed light source 10 outputs pulsed light at a repetition frequency of 6.69850 MHz (that is, a frequency equal to the modulation frequency f mod ). As described above, in the pulse light source 10 according to the present embodiment, Continuous Wave (CW) active mode synchronization was confirmed.
　図１９は、本実施例に係るパルス光源１０から出力されたパルス光のＲＦスペクトルの測定結果を示す図である。本図に示す例において、ＲＦスペクトルは、分解能１ｋＨｚのＲＦスペクトルアナライザ（Ａｇｉｌｅｎｔ　Ｅ４４４０Ａ）で測定した。本図に示すように、周波数６．６９８５０ＭＨｚ（すなわち、変調周波数ｆｍｏｄと等しい周波数）でＳＮ比７０ｄＢのピークが測定された。 FIG. 19 is a diagram illustrating a measurement result of the RF spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment. In the example shown in the figure, the RF spectrum was measured with an RF spectrum analyzer (Agilent E4440A) having a resolution of 1 kHz. As shown in this figure, a peak with an SN ratio of 70 dB was measured at a frequency of 6.69850 MHz (that is, a frequency equal to the modulation frequency f mod ).
　図２０は、本実施例に係るパルス光源１０から出力されたパルス光の自己相関の測定結果を示す図である。本図に示す例において、自己相関は、バックグラウンドフリーのオートコリレータ（Ｆｅｍｔｏｃｈｒｏｍｅ　ＦＲ－１０３ＨＰ）で測定した。本図に示すように、自己相関の半値全幅は８ｐｓであった。パルス光の波形は双曲線正割分布と仮定して、パルス幅は５ｐｓとなる。 FIG. 20 is a diagram illustrating a measurement result of autocorrelation of pulsed light output from the pulsed light source 10 according to the present embodiment. In the example shown in the figure, the autocorrelation was measured with a background-free autocorrelator (Femtochrome FR-103HP). As shown in the figure, the full width at half maximum of the autocorrelation was 8 ps. The pulse width is 5 ps assuming that the waveform of the pulsed light is a hyperbolic secant distribution.
　以上、本実施例によれば、ＣＷ能動モード同期によってパルス幅５ｐｓ及びスペクトル幅０．９ｎｍパルス光を得た。 As described above, according to this example, pulsed light having a pulse width of 5 ps and a spectral width of 0.9 nm was obtained by CW active mode synchronization.
（実施例２）
　実施例２に係るパルス光源１０は、変調周波数ｆｍｏｄが１３．３９７０ＭＨｚ（すなわち、実施例１の変調周波数ｆｍｏｄ：６．６９８５０ＭＨｚの２倍）である点を除いて、実施例１に係るパルス光源１０と同様である。 (Example 2)
The pulse light source 10 according to the second embodiment is the pulse according to the first embodiment except that the modulation frequency f mod is 13.3970 MHz (that is, the modulation frequency f mod of the first embodiment is twice as high as 6.698850 MHz). The same as the light source 10.
　図２１は、本実施例に係るパルス光源１０から出力されたパルス光の測定結果を示す図である。本図に示すように、パルス光源１０からは、パルス光が繰り返し周波数１３．３９７０ＭＨｚ（すなわち、変調周波数ｆｍｏｄと等しい周波数）で出力されている。このように、本実施例に係るパルス光源１０では、第二次高調波モード同期が確認された。 FIG. 21 is a diagram illustrating a measurement result of the pulsed light output from the pulsed light source 10 according to the present embodiment. As shown in this figure, the pulsed light source 10 outputs pulsed light at a repetition frequency of 13.3970 MHz (that is, a frequency equal to the modulation frequency f mod ). Thus, in the pulse light source 10 according to this example, second harmonic mode synchronization was confirmed.
（実施例３）
　実施例３に係るパルス光源１０は、以下の点を除いて、実施例１に係るパルス光源１０と同様である。 (Example 3)
The pulse light source 10 according to the third embodiment is the same as the pulse light source 10 according to the first embodiment except for the following points.
　ポンプレーザ１１０は、波長９８０ｎｍレーザとした。変調周波数ｆｍｏｄ：９９．０２１ＭＨｚでシードレーザを変調させた。ＲＥＤＦＡ２２０は、エルビウムドープファイバ増幅器（ＥＤＦＡ）とした。 The pump laser 110 was a laser having a wavelength of 980 nm. The seed laser was modulated at a modulation frequency f mod : 99.021 MHz. The REDFA 220 was an erbium-doped fiber amplifier (EDFA).
　共振器２００の長さＬ１は、２ｋｍとし、共振器２００の基本共振周波数が９９．０２１ｋＨｚとなるようにした。共振器２００の総分散は、－０．３１ｐｓ２であった。 The length L 1 of the resonator 200 was 2 km, and the basic resonance frequency of the resonator 200 was 99.021 kHz. The total dispersion of the resonator 200 was −0.31 ps 2 .
　図２２は、本実施例に係るパルス光源１０から出力されたパルス光の光スペクトルの測定結果を示す図である。ガウシアンフィッティングを用いると、スペクトル幅は２．２６ｎｍであった。 FIG. 22 is a diagram illustrating a measurement result of the optical spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment. Using Gaussian fitting, the spectral width was 2.26 nm.
　図２３は、本実施例に係るパルス光源１０から出力されたパルス光の自己相関の測定結果を示す図である。パルス光の波形は双曲線正割分布と仮定して、自己相関の半値全幅は１．１８ｐｓであった。 FIG. 23 is a diagram illustrating a measurement result of autocorrelation of pulsed light output from the pulsed light source 10 according to the present embodiment. The full width at half maximum of the autocorrelation was 1.18 ps, assuming that the waveform of the pulsed light is a hyperbolic secant distribution.
　図２４は、本実施例に係るパルス光源１０から出力されたパルス光のＲＦスペクトルの測定結果を示す図である。周波数９９．２５０ＭＨｚ（すなわち、変調周波数ｆｍｏｄとほぼ等しい周波数）でＳＮ比５３ｄＢのピークが測定された。 FIG. 24 is a diagram illustrating the measurement result of the RF spectrum of the pulsed light output from the pulsed light source 10 according to the present embodiment. A peak with an SN ratio of 53 dB was measured at a frequency of 99.250 MHz (that is, a frequency substantially equal to the modulation frequency f mod ).
　以上、図面を参照して本発明の実施形態について述べたが、これらは本発明の例示であり、上記以外の様々な構成を採用することもできる。 As described above, the embodiments of the present invention have been described with reference to the drawings. However, these are exemplifications of the present invention, and various configurations other than the above can be adopted.
　この出願は、２０１６年５月２７日に出願された日本出願特願２０１６－１０６８２８号を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2016-106828 filed on May 27, 2016, the entire disclosure of which is incorporated herein.

Claims (12)

  1. 　希土類ドープファイバ増幅器を有する共振器と、
    　前記希土類ドープファイバ増幅器にポンプ光を供給するポンプ光源と、
    を備え、
    　前記ポンプ光は、前記共振器の基本共振周波数の整数倍の９５％以上１０５％以下の変調周波数を有する変調信号によって変調されているパルス光源。     A resonator having a rare earth doped fiber amplifier;
    A pump light source for supplying pump light to the rare earth-doped fiber amplifier;
    With
    The pulse light source, wherein the pump light is modulated by a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator.
  2. 　請求項１に記載のパルス光源において、
    　前記共振器は、リング共振器であるパルス光源。     The pulse light source according to claim 1,
    The resonator is a pulse light source that is a ring resonator.
  3. 　請求項１に記載のパルス光源において、
    　前記共振器は、リニア共振器であるパルス光源。     The pulse light source according to claim 1,
    The resonator is a pulse light source that is a linear resonator.
  4. 　請求項１に記載のパルス光源において、
    　前記共振器は、８の字型共振器であるパルス光源。     The pulse light source according to claim 1,
    The resonator is a pulse light source which is an 8-shaped resonator.
  5. 　請求項１に記載のパルス光源において、
    　前記共振器は、シグマ型共振器であるパルス光源。     The pulse light source according to claim 1,
    The resonator is a pulsed light source that is a sigma type resonator.
  6. 　請求項１～５のいずれか一項に記載のパルス光源において、
    　前記希土類ドープファイバ増幅器に含まれる希土類イオンは、プラセオジムイオン、ネオジムイオン、ホルミウムイオン、エルビウムイオン、ツリウムイオン及びイッテルビウムイオンからなる群から選択される少なくとも１つであるパルス光源。     The pulse light source according to any one of claims 1 to 5,
    The rare earth ions contained in the rare earth doped fiber amplifier are at least one selected from the group consisting of praseodymium ions, neodymium ions, holmium ions, erbium ions, thulium ions and ytterbium ions.
  7. 　請求項６に記載のパルス光源において、
    　前記希土類イオンは、ツリウムイオンであるパルス光源。     The pulse light source according to claim 6,
    The pulsed light source, wherein the rare earth ions are thulium ions.
  8. 　請求項１～７のいずれか一項に記載のパルス光源において、
    　前記変調信号は、前記変調周波数で振動する正弦波であるパルス光源。     The pulse light source according to any one of claims 1 to 7,
    The pulsed light source, wherein the modulation signal is a sine wave that vibrates at the modulation frequency.
  9. 　請求項１～７のいずれか一項に記載のパルス光源において、
    　前記変調信号は、前記変調周波数で振動する基本波を含む矩形波であるパルス光源。     The pulse light source according to any one of claims 1 to 7,
    The pulse light source in which the modulation signal is a rectangular wave including a fundamental wave that vibrates at the modulation frequency.
  10. 　請求項９に記載のパルス光源において、
    　前記矩形波のデューティ比は、０．５０であるパルス光源。     The pulse light source according to claim 9,
    A pulse light source in which the duty ratio of the rectangular wave is 0.50.
  11. 　請求項９に記載のパルス光源において、
    　前記矩形波のデューティ比は、０．５０とは異なるパルス光源。     The pulse light source according to claim 9,
    A pulse light source in which the duty ratio of the rectangular wave is different from 0.50.
  12. 　パルス光を発生させる方法であって、以下を含む：
    　希土類ドープファイバ増幅器を有する共振器と、前記共振器の基本共振周波数の整数倍の９５％以上１０５％以下の変調周波数を有する変調信号で変調されたポンプ光を供給可能なポンプ光源と、を準備すること；
    　前記ポンプ光源から前記希土類ドープファイバ増幅器に前記ポンプ光を供給すること；
    　前記ポンプ光源から前記希土類ドープファイバ増幅器に前記ポンプ光を供給した後、前記共振器から光を出力すること。     A method for generating pulsed light comprising:
    A resonator having a rare earth-doped fiber amplifier and a pump light source capable of supplying pump light modulated with a modulation signal having a modulation frequency of 95% or more and 105% or less of an integral multiple of the basic resonance frequency of the resonator are provided. To do;
    Supplying the pump light from the pump light source to the rare earth doped fiber amplifier;
    After the pump light is supplied from the pump light source to the rare earth doped fiber amplifier, the light is output from the resonator.
PCT/JP2017/019559 2016-05-27 2017-05-25 Pulsed light source and pulsed light generating method WO2017204299A1 (en)

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