WO2018159445A1 - Procédé de commande de peigne optique et dispositif de commande de peigne optique - Google Patents

Procédé de commande de peigne optique et dispositif de commande de peigne optique Download PDF

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Publication number
WO2018159445A1
WO2018159445A1 PCT/JP2018/006447 JP2018006447W WO2018159445A1 WO 2018159445 A1 WO2018159445 A1 WO 2018159445A1 JP 2018006447 W JP2018006447 W JP 2018006447W WO 2018159445 A1 WO2018159445 A1 WO 2018159445A1
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Prior art keywords
frequency
optical
optical comb
offset
comb
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PCT/JP2018/006447
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English (en)
Japanese (ja)
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薫 美濃島
彰文 浅原
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国立大学法人電気通信大学
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Priority to JP2019502930A priority Critical patent/JP6963322B2/ja
Publication of WO2018159445A1 publication Critical patent/WO2018159445A1/fr

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/365—Non-linear optics in an optical waveguide structure
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • G02F1/37—Non-linear optics for second-harmonic generation
    • 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
    • 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
    • H01S3/139—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the mutual position or the reflecting properties of the reflectors of the cavity, e.g. by controlling the cavity length

Definitions

  • the present invention relates to an optical comb control method and an optical comb control device.
  • Non-Patent Document 1 discloses a car lens mode-locked Ti: sapphire laser (Kerr-lens mode-locked Ti: sapphire laser). As disclosed in Non-Patent Document 1, an optical comb having a comb-like spectrum is widely used as a precise measure of time, space, and frequency.
  • the optical comb is a low-jitter coherent pulse train in the time domain, and is a comb-like spectrum that is accurately mode-resolved in the frequency domain.
  • the optical comb is used as a light source stabilized with high accuracy.
  • the offset frequency of the optical comb, the repetition frequency, the offset frequency difference when using two optical combs, and the repetition frequency difference are treated as fixed parameters.
  • the present inventor found that the difference in the relative carrier envelope phase (Carrier-Envelope offset Phase: CEP) between the two optical combs was made evenly little by little according to the offset frequency difference.
  • CEP Carrier-Envelope offset Phase
  • the present invention provides an optical comb control method and an optical comb control apparatus that actively utilize the degree of freedom of arbitrary control of relative CEP between two optical combs.
  • An optical comb control method includes a first frequency mode having a first frequency offset with respect to zero on a frequency axis and an integer of a first frequency interval with respect to the first frequency mode on the frequency axis.
  • the first frequency offset and the second frequency offset are set such that a difference between the first frequency offset and the second frequency offset satisfies the expression (1).
  • a difference from the second frequency offset may be set.
  • ⁇ f CEO represents the difference between the first frequency offset and the second frequency offset.
  • ⁇ f rep represents the difference between the first frequency interval and the second frequency interval.
  • K and N represent arbitrary natural numbers.
  • a difference between the first frequency offset and the second frequency offset may be set so as to satisfy Equation (2).
  • ⁇ f CEO represents the difference between the first frequency offset and the second frequency offset.
  • f rep represents the first frequency interval or the second frequency interval.
  • N is represented by an arbitrary natural number.
  • the difference between the first frequency offset and the second frequency offset may be set to satisfy the expression (3).
  • ⁇ f CEO is expressed by the first frequency offset and the second frequency offset.
  • f CEO represents the first frequency interval or the second frequency interval.
  • N represents an arbitrary natural number.
  • An optical comb control device includes a first frequency mode having a first frequency offset with respect to zero on a frequency axis and an integer of a first frequency interval with respect to the first frequency mode on the frequency axis. Controlling the first frequency offset and the first frequency interval in a first optical comb having a plurality of third frequency modes arranged at double intervals, and with respect to zero on the frequency axis A second frequency mode having a second frequency offset, and a plurality of fourth frequency modes arranged at intervals of an integer multiple of the second frequency interval with respect to the second frequency mode on the frequency axis.
  • a frequency control mechanism for controlling the second frequency offset and the second frequency interval in the second optical comb is provided.
  • the control mechanism includes the first frequency offset, the second frequency offset, the difference between the first frequency offset and the second frequency offset, the first frequency interval, the second frequency interval, and The first frequency offset, the second frequency offset, the first frequency interval, and the first frequency offset so that a difference between the first frequency interval and the second frequency interval is expressed by an integer ratio. Two frequency intervals can be controlled.
  • the relative CEP between the two optical combs can be arbitrarily controlled by controlling the offset frequency difference between the two optical combs.
  • FIG. 3 is a schematic diagram illustrating a relationship between waveforms of two optical combs Comb1 and Comb2 and interference signals in the first embodiment.
  • 6 is a graph showing a measurement result of an interference signal when an offset frequency difference ⁇ f CEO between two optical combs Comb1 and Comb2 is set to 0 in the first embodiment.
  • 6 is a graph showing a measurement result of an interference signal when an offset frequency difference ⁇ f CEO between two optical combs Comb1 and Comb2 is ⁇ f rep / 2 in Example 1.
  • 6 is a graph showing a measurement result of an interference signal when an offset frequency difference ⁇ f CEO between two optical combs Comb 1 and Comb 2 is ⁇ f rep / 3 in Example 1.
  • 6 is a graph showing an IGM obtained by averaging the differences of IGMs that are inverted with each other when the offset frequency difference ⁇ f CEO between two optical combs Comb 1 and Comb 2 is ⁇ f rep / 2 in Example 1.
  • FIG. In Example 2 it is the schematic which shows the structure of the apparatus for controlling offset frequency difference (DELTA) f CEO of the 0th-order diffracted light and 1st-order diffracted light of optical comb Comb1.
  • DELTA offset frequency difference
  • FIG. 11B is a graph showing the polarization state of the optical comb Comb1 and the measurement result of the intensity of interference light according to the relative change in CEP shown in FIG. 11A. It is a graph which shows the waveform of the interference light in the polarization state shown to FIG. 11B.
  • FIG. 11B is a graph showing the polarization state of the optical comb Comb1 and the measurement result of the intensity of interference light according to the relative change in CEP shown in FIG. 11A. It is a graph which shows the waveform of the interference light in the polarization state shown to FIG. 11B.
  • 11B is another graph showing the polarization state of the optical comb Comb1 and the measurement result of the intensity of the interference light according to the relative CEP change shown in FIG. 11A. It is a graph which shows the waveform of the interference light in the polarization state shown to FIG. 11D.
  • a mode-locked laser outputs a periodic pulse train in the time domain.
  • the pulse train output from the mode-locked laser can be illustrated by a function of an electric field (that is, carrier) oscillating at high speed and an envelope.
  • the propagation speed of the envelope and the group velocity v g, the propagation speed of the carrier and phase velocity v p, holds the relationship expressed by the equation (4) and (5).
  • n represents the refractive index of the medium through which the optical comb propagates.
  • ⁇ represents the center wavelength of the optical comb.
  • the phase shift (that is, the phase difference) is called a carrier-envelope offset phase (CEP).
  • CEP carrier-envelope offset phase
  • the relative CEP difference ⁇ CEP between adjacent pulse trains on the time axis is periodically shifted between pulses, and has a constant period TCEO .
  • T CEO the carrier envelope offset frequency of the frequency domain
  • the offset frequency corresponding to f CEO.
  • the longitudinal mode of the mode-locked laser is very uniformly distributed at intervals of the repetition frequency (frequency interval) f rep that is the reciprocal of the pulse repetition period T rep. is doing.
  • the relationship between the offset frequency f CEO and the repetition frequency f rep is expressed as shown in equation (6) using a relative CEP difference ⁇ CEP .
  • FIG. 1 schematically shows a waveform in the time domain and a spectrum in the frequency domain of each of the two optical combs Comb1 and Comb2.
  • the optical comb (first optical comb) Comb1 has an optical frequency mode (first frequency mode) FM1 having an offset frequency (first frequency offset) fCEO1 with respect to zero on the frequency axis.
  • a plurality of optical frequency modes (third optical frequency modes) FM3 arranged at intervals of an integral multiple of the repetition frequency (first frequency interval) f rep1 with respect to the optical frequency mode FM1 on the frequency axis.
  • the optical comb (second optical comb) Comb2 includes an optical frequency mode (second frequency mode) FM2 having an offset frequency (second frequency offset) f CEO2 with respect to zero on the frequency axis, and an optical frequency on the frequency axis.
  • An optical frequency mode (fourth optical frequency mode) FM4 arranged at intervals of an integer multiple of the repetition frequency (second frequency interval) f rep2 with respect to the mode FM2.
  • Expression (7) is established as a correspondence relationship between the offset frequency f CEO1 and the repetition frequency f rep1 in the optical comb Comb1.
  • the relationship of the equation (8) is established as a correspondence relationship between the offset frequency f CEO2 and the repetition frequency f rep2 in the optical comb Comb2.
  • ⁇ CEP1 represents a relative CEP of the optical comb Comb1.
  • ⁇ CEP2 represents the relative CEP of the optical comb Comb2.
  • the offset frequency f CEO1, f CEO2 the change amount of the CEP between pulses, i.e. relative CEPderutafai CEP1, is associated with ⁇ CEP2.
  • the offset frequency f CEO1, f CEO2 you can control the coherence of each pulse train of optical frequency comb COMB1, COMB2.
  • each waveform when the positions of the waveforms of the two optical combs Comb1 and Comb2 are aligned on the time axis is referred to as a first waveform.
  • the difference on the time axis between the second waveforms that have advanced on the time axis from the position of the first waveform of each of the two optical combs Comb 1 and Comb 2 is defined as a time difference ⁇ T rep .
  • the difference on the time axis between the third waveforms of the two optical combs Comb 1 and Comb 2 is the time difference (2 ⁇ ⁇ T rep ).
  • the difference on the time axis between the (M + 1) th waveforms of the two optical combs Comb1 and Comb2 is the time difference (M ⁇ ⁇ T rep ).
  • M represents an arbitrary natural number. That is, in the time domain, the waveforms of the two optical combs Comb1 and Comb2 are shifted evenly little by little according to the repetition frequency difference ⁇ f rep .
  • the repetition frequency difference ⁇ f rep is a frequency difference
  • the CEPs of the two optical combs Comb1 and Comb2 have a relative relationship at a common position on the time axis.
  • the first waveform CEP and the second waveform of each of the two optical combs Comb 1 and Comb 2 are used.
  • the phase difference between the waveform and CEP is ⁇ CEP1 and ⁇ CEP2 .
  • the phase difference between the first waveform CEP and the third waveform CEP of each of the two optical combs Comb1 and Comb2 is 2 ⁇ ⁇ CEP1 and 2 ⁇ ⁇ CEP2 .
  • the difference on the time axis between the (M + 1) -th waveforms of the two optical combs Comb1 and Comb2 is the time difference (M ⁇ ⁇ CEP1 ) and (M ⁇ ⁇ CEP2 ).
  • the relative CEP of the two optical combs Comb1 and Comb2 is shifted little by little according to the offset frequency difference ⁇ f CEO .
  • the offset frequency difference ⁇ f CEO is the frequency difference
  • the positions on the time axis of the pulse trains having the same waveform as the relative CEP relationship between the first pulse trains of the two optical combs Comb 1 and Comb 2 are aligned. That is, the relative CEP relationship between the two optical combs Comb1 and Comb2 changes with a period of (1 / ⁇ f CEO ).
  • the repetition frequency f rep and the offset frequency f CEO of the optical comb are important frequency parameters indicating the characteristics of the pulse train.
  • the repetition frequency difference ⁇ f rep and the offset frequency difference ⁇ f CEO are important frequency parameters indicating the characteristics of the pulse train. It is.
  • the offset frequency difference ⁇ f CEO has been treated as a fixed parameter.
  • the CEP can be arbitrarily controlled by controlling the offset frequency difference ⁇ f CEO .
  • the degree of freedom in controlling the offset frequency difference ⁇ f CEO is positively utilized.
  • the optical comb control method uses an optical comb Comb1 having an optical frequency mode FM1 and a plurality of optical frequency modes FM3, and an optical comb Comb2 having an optical frequency mode FM2 and a plurality of optical frequency modes FM4. And a control step of controlling the difference between the offset frequencies f CEO1 and f CEO2 (offset frequency difference, difference between the first frequency offset and the second frequency offset) ⁇ f CEO .
  • the offset frequency difference ⁇ f CEO is the difference between the offset frequencies f CEO1 and f CEO2 of the two optical combs Comb1 and Comb2.
  • the repetition frequencies f rep1 and f rep2 of the two optical combs Comb1 and Comb2 have a relative relationship with the offset frequencies f CEO1 and f CEO2 , respectively.
  • two offset frequency difference Delta] f CEO optical comb COMB1, COMB2, offset frequency f CEO1 optical comb COMB1, offset frequency f CEO2 optical comb COMB2, two optical comb COMB1 , Comb2 repetition frequency difference ⁇ f rep , optical comb Comb1 offset frequency f rep1 , optical comb Comb2 offset frequency f rep2 is preferably controlled so that the six parameters are expressed by an arbitrary integer ratio.
  • the relative relationship (predetermined condition) in which the above six parameters are represented by an arbitrary integer ratio is the control of four parameters of the offset frequencies f CEO1 and f CEO2 and the offset frequencies f rep1 and f rep2. It is preferable that
  • setting the above parameters other than the offset frequency difference Delta] f CEO to meet the offset frequency difference Delta] f CEO is (1) (3) at least one or more expression of expression from the equation. Can set the parameters other than the offset frequency difference Delta] f CEO to meet the offset frequency difference Delta] f CEO from (1) reacting a (3) any two equations of the type at the same time. Offset frequency difference Delta] f CEO may set the parameters other than the offset frequency difference Delta] f CEO to satisfy all the above-mentioned equation (1) (3).
  • optical Com control device First, an optical comb output mechanism used in an optical comb control apparatus applicable to the optical comb control method of the present invention will be described.
  • the optical comb output mechanism detects an interference signal between modes of two optical combs satisfying a predetermined relationship (so-called 1f-2f relationship) in the control step of the optical comb control method of the present invention.
  • This interference signal is a beat signal and is based on the frequency difference between the modes of the two optical combs.
  • the optical comb output mechanism is configured to be able to control the offset frequency and the repetition frequency by detecting an interference signal between modes of two optical combs.
  • the optical comb output mechanism 10 includes an optical comb light source 12, an optical interference unit 14, a beat signal detection unit 16, an offset frequency control unit 18, an optical comb output unit 20, and a repetition frequency control unit 22. ing.
  • the optical comb light source 12 is configured as a loop type fiber laser.
  • the optical comb light source 12 includes an erbium-doped optical fiber (EDF) 24 and a semiconductor laser (hereinafter referred to as pumping LD) 26 that pumps the EDF 24 by supplying pumping light to the EDF 24 via an optical coupler 25. And comprising.
  • the wave controller 28 is connected by the EDF 24.
  • the configuration of the optical comb light source 12 is not limited to the above configuration as long as it can emit the optical comb.
  • the optical comb emitted from the optical coupler 32 is supplied to the optical interference unit 14 and the optical comb output unit 20.
  • a polarization controller 38 and an EDF amplifier 40 are provided in order from the side closer to the optical coupler 32.
  • the EDF amplifier 40 includes an EDF 39, a pumping LD 41, and an optical coupler 43.
  • Each configuration up to the optical coupler 32 and the optical interference unit 14 and each configuration up to the optical coupler 32 and the output unit 20 are connected by an optical fiber 36.
  • a high-nonlinear optical fiber (HNLF) 42 is disposed between the EDF amplifier 40A and the optical interference unit 14.
  • the optical comb whose polarization is controlled and amplified by the polarization controller 38 ⁇ / b> A and the EDF amplifier 40 ⁇ / b> A is emitted by the HNLF 42 as a wider-band optical comb than before entering the HNLF 42.
  • the optical interference unit 14 includes, in order from the side closer to the optical comb light source 12, a fiber collimator 44, a condenser lens 46, a ⁇ / 2 wavelength plate 48, a periodically-poled lithium niobate (PPLN) 50, light A band pass filter 52 is provided.
  • the broadband optical comb emitted from the HNLF 42 enters the optical interference unit 14 and is focused on the PPLN 50.
  • second harmonic W S broadband optical comb is emitted. That is, the broadband optical comb component (2f) and the second harmonic component (2 ⁇ 1f) newly generated by the PPLN 50 are emitted from the PPLN 50 in an overlapping manner.
  • Equation (11) the frequency f B of the zeroth to n-th mode on the frequency axis is expressed as shown in Equation (11).
  • the frequency f S of the spectrum of the second harmonic wave W S is expressed as in equation (12).
  • the frequency f W of the 2n-th mode adjacent to the mode of the frequency f S in the broadband optical comb represented by the equation (12) on the low frequency side is represented by the equation (13).
  • the broadband optical comb and the second harmonic interfere with each other at the beat signal detector 16.
  • the beat signal detector 16 detects beat signals of a broadband optical comb and second harmonics.
  • the offset frequency difference f CEO is detected by detecting the beat signal between the spectrums of the frequencies represented by the equations (12) and (13).
  • the beat signals of the frequencies having the frequencies represented by the equations (12) and (13) are emitted to the beat signal detector 16 as interference light.
  • the beat signal detection unit 16 includes a photo detector 54.
  • the light emitted from the PPLN 50 is detected by the photodetector 54.
  • the intensity of the light emitted from the PPLN 50 is converted into the magnitude of an electric signal.
  • the electric signal output from the photodetector 54 is transmitted to the offset frequency control unit 18 through the electric cable 56 and is repeatedly transmitted to the frequency control unit 22 through the electric cable 58.
  • the offset frequency control unit 18 includes a high-frequency bandpass filter 61, a high-frequency amplifier 62, a function generator (FG) 64, a frequency converter (Double Balanced Mixer: DBM) 66, and a loop filter 68.
  • the high-frequency bandpass filter 61 extracts an offset frequency component from the electrical signal output from the photodetector 54.
  • the high frequency amplifier 62 amplifies the electric signal emitted from the high frequency band pass filter 61.
  • the FG 64 can transmit a reference signal of the frequency by setting a desired frequency.
  • the DBM 66 mixes the amplified electrical signal and the reference signal transmitted from the FG 64.
  • the loop filter 68 applies feedback to the current applied to the pumping LD 26 of the optical comb light source 12 in accordance with the mixed electric signal.
  • the offset frequency control unit 18 when the frequency of the reference signal transmitted from the FG 64 is changed, feedback is applied to the current applied to the excitation LD 26 of the optical comb light source 12 by the loop filter 68.
  • the applied current of the pumping LD 26 is changed, and the offset frequency f CEO of the optical comb emitted from the optical comb light source 12 is aligned with the frequency of the reference signal transmitted from the FG 64.
  • the offset frequency f CEO of the optical comb emitted from the optical comb light source 12 can be controlled by controlling the frequency of the reference signal transmitted from the FG 64.
  • the repetitive frequency control unit 22 includes a high frequency band pass filter 71, a high frequency amplifier 72, an FG 74, a DBM 76, and a loop filter 78.
  • the high-frequency bandpass filter 71 repeatedly extracts frequency components from the electrical signal output from the photodetector 54.
  • the high frequency amplifier 72 amplifies the electric signal from the high frequency band pass filter 71.
  • the FG 74 can transmit a reference signal of the frequency by setting a desired frequency.
  • the DBM 76 mixes the amplified electrical signal and the reference signal transmitted from the FG 74.
  • the loop filter 78 applies feedback to the voltage applied to the PZT element 30 of the optical comb light source 12 in accordance with the mixed electric signal.
  • the loop filter 78 applies feedback to the PZT element 30 of the optical comb light source 12 as described above.
  • the resonator length of the fiber laser of the optical comb light source 12 is changed, and the repetition frequency f rep of the optical comb emitted from the optical comb light source 12 is aligned with the frequency of the reference signal transmitted from the FG 74.
  • the repetition frequency f rep of the optical comb emitted from the optical comb light source 12 can be controlled by controlling the frequency of the reference signal transmitted from the FG 74.
  • the control device (optical comb control device) 100 of the present invention includes optical comb output mechanisms 10A and 10B, a frequency control mechanism 90, a continuous wave laser (hereinafter referred to as CW laser) 92, and a frequency.
  • a stabilizing mechanism 94 The optical comb output mechanism 10A is provided for emitting the optical comb Comb1, and the optical comb output mechanism 10B is provided for emitting the optical comb Comb2.
  • the frequency control mechanism 90 inputs a reference signal for controlling the offset frequency difference ⁇ f CEO to each of the optical comb output mechanisms 10A and 10B.
  • the CW laser 92 synchronizes the phases of the two optical combs Comb1 and Comb2.
  • the frequency stabilization mechanism 94 controls the beat signal between the continuous wave light (hereinafter, CW light) emitted from the CW laser 92 and each of the two optical combs Comb1 and Comb2.
  • FIG. 5 main parts such as the optical comb output unit 20 of the optical comb output mechanisms 10A and 10B, the FG 64 of the offset frequency control unit 18, the FG 74 of the repetition frequency control unit 22, and the PZT 12 are illustrated. Is omitted.
  • the control device 100 includes two FG 64 and FG 74 by providing two optical comb output mechanisms 10A and 10B. That is, the control apparatus 100 has two FGs 64 and FG74, each of which has a configuration capable of controlling a total of four parameters of the offset frequencies f CEO1 and f CEO2 and the repetition frequencies f rep1 and f rep2 of the two optical combs Comb1 and Comb2. And a frequency control mechanism 90 that transmits a reference signal to the two FGs 64.
  • the frequency stabilization mechanism 94 includes a frequency control mechanism 90 formed of a program or the like built in the computer, FGs 130 and 132, DBMs 108 and 118, and PID controllers 110 and 120.
  • the optical comb Comb1 emitted from the optical comb output unit 20 of the optical comb output mechanism 10A enters the optical coupler 104 via the optical coupler 102.
  • CW light emitted from the CW laser 92 enters the optical coupler 104 via the optical coupler 112.
  • the optical comb Comb1 and the CW light combined by the optical coupler 104 are received by a light receiving unit 106 such as a photodetector and converted into an electric signal.
  • the electrical signal emitted from the light receiving unit 106 is input to the DBM 108 and is combined with the reference signal from the FG 130.
  • An output from the DBM 108 is input to the PID controller 110.
  • the output from the PID controller 110 is fed back to the input current value to the CW laser 92.
  • the CW light emitted from the CW laser 92 enters the optical coupler 114 via the optical coupler 112.
  • the optical comb Comb2 emitted from the optical comb output unit 20 of the optical comb output mechanism 10B enters the optical coupler 114 via the optical coupler 122.
  • the optical comb Comb2 and the CW light combined by the optical coupler 114 are received by a light receiving unit 116 such as a photodetector and converted into an electric signal.
  • the electrical signal emitted from the light receiving unit 116 is input to the DBM 118 and is combined with the reference signal from the FG 132.
  • An output from the DBM 118 is input to the PID controller 120.
  • the output from the PID controller 110 is fed back to the displacement amount of the PZT 30 in the optical comb light source 12 of the optical comb output mechanism 10B.
  • the repetition frequency f rep1 and offset frequency f CEO1 of the optical comb Comb1 are stabilized according to the frequency of the reference signal transmitted from the FGs 64 and 74 of the optical comb output mechanism 10A according to the control procedure described with reference to FIG. Make it.
  • a beat signal between the optical comb Comb1 and the CW light output from the optical comb output unit 20 of the optical comb output mechanism 10A is detected.
  • the detected beat signal is stabilized with respect to the reference signal from the FG 130.
  • the frequency of the CW light is made to follow the repetition frequency f rep1 and the offset frequency f CEO1 of the optical comb Comb1.
  • the FG 64 of the optical comb output mechanism 10A issues a reference signal of the offset frequency f CEO1 of the optical comb Comb1.
  • the FG 74 of the optical comb output mechanism 10A generates a reference signal having a repetition frequency f rep1 of the optical comb Comb1.
  • the FG 132 emits a reference signal having a repetition frequency f rep2 of the optical comb Comb2.
  • the frequency control mechanism 90 includes six offset frequency differences ⁇ f CEO , offset frequency f CEO1 , offset frequency f CEO2 , repetition frequency difference ⁇ f rep , offset frequency f rep1 , and offset frequency f rep2 .
  • the four parameters of the offset frequencies f CEO1 and f CEO2 and the offset frequencies f rep1 and f rep2 are controlled so that a relative relationship (predetermined condition) expressed by an arbitrary integer ratio between the two parameters is established. That is, the control device 100 arbitrarily controls the offset frequency difference ⁇ f CEO between the two optical combs Comb1 and Comb2.
  • optical combs Comb1 and Comb2 having a desired offset frequency difference ⁇ f CEO and phase-controlled with each other are output from the optical comb output mechanisms 10A and 10B.
  • the CEP of the two optical combs Comb1 and Comb2 is arbitrarily set by actively controlling the offset frequency difference ⁇ f CEO between the two optical combs Comb1 and Comb2. Can be controlled.
  • arbitrary coherent modulation can be performed. Examples of applications that perform coherent modulation include, but are not limited to, coherent spectroscopy, coherent physical property analysis, and coherent time-resolved measurement.
  • the control device 100 of the present invention inputs a reference signal of an arbitrary frequency from the frequency control mechanism 90 to each of the FGs 64 and 74 of the optical comb output mechanism 10A, the FGs 130 and 132, and the FG 64 of the optical comb output mechanism 10B.
  • the optical combs Comb1 and Comb2 that are phase-controlled with each other can be generated.
  • the reference signal output from the FG 132 is indirectly input to the PZT 30 of the optical comb output mechanism 10B.
  • the optical comb control method and control apparatus according to the present invention can be applied in a wide field of performing arbitrary coherent modulation.
  • the control method of the optical comb of the present invention by positively controlling the offset frequency difference Delta] f CEO, it can control the relative phase of the optical comb COMB1, COMB2. Therefore, the optical comb control method and control apparatus of the present invention can be applied to highly efficient signal detection and signal control in observation of a phenomenon depending on relative CEP.
  • Phenomena that depend on relative CEP are, for example, interference and nonlinear optical phenomena.
  • the optical comb output mechanism 10 may be configured by using an acousto-optic device (Acoustic Optical Modulator: AOM) 120 shown in FIG.
  • AOM Acoustic Optical Modulator
  • a fiber collimator may be disposed on the input side of the optical comb output unit 20, and the AOM 120 may be disposed on the output side of the fiber collimator.
  • the AOM 120 is used, the frequency of the first-order diffracted light diffracted from the AOM 120 is shifted by the modulation frequency f AOM of the sound wave A applied to the AOM 120. Based on this principle, the offset frequency difference ⁇ f CEO can be positively controlled by appropriately setting the modulation frequency f AOM .
  • Example 1 As shown in FIG. 5, the optical comb Comb1 emitted from the optical comb output unit 20 of the optical comb output mechanism 10A of the control device 100 and the light emitted from the optical comb output unit 20 of the optical comb output mechanism 10B of the control device 100 Comb 2 was combined and interfered, and an interference signal (Interferogram: IGM) was received by high-speed detector 96.
  • the IGM received by the high-speed detector 96 is post-processed by the data processing unit 98 to visualize the IGM on a display (not shown).
  • the repetition frequency difference ⁇ f rep between the two optical combs Comb1 and Comb2 affects the period in which the IGM is detected.
  • the period in which IGM is detected corresponds to the interval on the time axis between plots of IGM shown in FIG.
  • the time period T IGM (1 / ⁇ f rep ) elapses from the plot of the IGM caused by the first waveform of the two optical combs Comb 1 and Comb 2 when the positions on the time axis are aligned, and the timing of the first waveform
  • the offset frequency difference ⁇ f CEO between the two optical combs Comb 1 and Comb 2 affects the phase of the IGM.
  • the phase of the IGM is indicated by the shape of the IGM waveform shown in FIG.
  • a spectrum including information such as optical characteristics of the sample S can be acquired.
  • the sample S is a semiconductor such as silicon or gallium arsenide.
  • the laser medium is, for example, Er: YAG, Nd: YAG, or the like.
  • Various information of the sample S can be obtained from optical characteristics included in the acquired spectrum.
  • the repetition frequency ⁇ f rep 120.6 Hz
  • the offset frequency ⁇ f CEO was controlled to be an inverse multiple of the integer of the repetition frequency difference ⁇ f rep
  • IGM was measured.
  • 8A, 8B, and 8C the upper graph shows the IGM after a predetermined time on the time axis, and the lower graph shows the IGM after the predetermined time on the page. It is displayed by shifting in the vertical direction.
  • FIG. 8C when the offset frequency ⁇ f CEO is set to ⁇ f rep / 3, it can be seen that the IGM waveform is repeated in three patterns as a predetermined time elapses, resulting in a phase shift of 2 ⁇ / 3. .
  • three patterns of IGM are illustrated by a solid line, a broken line, and an alternate long and short dash line, respectively.
  • N is an arbitrary natural number.
  • Example 2 As shown in FIG. 10A, in Example 2, an optical comb light source 110 in which relative CEP between pulse trains was stabilized was prepared.
  • the optical comb Comb1 emitted from the optical comb light source 110 was made incident on the AOM 120, and the offset frequency difference ⁇ f CEO between the 0th-order diffracted light and the first-order diffracted light of the optical comb Comb1 was controlled.
  • an optical comb light source 112 different from the optical comb light source 110 was prepared.
  • the center wavelength ⁇ of the optical comb light sources 110 and 112 was set to 1560 nm.
  • the repetition frequency f rep1 of the optical comb Comb 1 emitted from the optical comb light source 110 was set to 56.5 MHz.
  • the repetition frequency difference ⁇ f rep between the optical comb Comb1 and the optical comb Comb2 emitted from the optical comb light source 112 was set to 120.6 Hz.
  • a (1/4) wavelength plate 116 and a (1/2) wavelength plate 118 for converting the optical comb Comb1 into linearly polarized light in a predetermined direction are disposed in front of the direction in which the optical comb Comb1 is emitted from the optical comb light source 110. did. (1/2)
  • the AOM 120 is arranged in front of the emission direction of the optical comb Comb1 from the wave plate 118. From the AOM 120, the 0th order diffracted light (0 th shown in FIG. 10A) and the 1st order diffracted light (1 st shown in FIG. 10A) of the optical comb Comb1 are emitted at different angles in plan view. As shown in FIG.
  • Equation (14) by applying modulation to the AOM 120 at the frequency f AOM , the offset frequency difference ⁇ f CEO between the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1 is expressed as shown in Equation (14).
  • the optical path length changing unit 122 is disposed in front of the emission direction of the 0th-order diffracted light of the optical comb Comb1.
  • a (1/2) wavelength plate 124 is arranged in front of the emission direction of the first-order diffracted light of the optical comb Comb1. With this arrangement, the direction of linearly polarized light of the first-order diffracted light of the optical comb Comb1 was made orthogonal to the direction of linearly polarized light of the 0th-order diffracted light of the optical comb Comb1.
  • the zero-order diffracted light and the first-order diffracted light were combined by a polarizing beam splitter (PBS) 126 to generate a coherently controlled and polarization-modulated light pulse.
  • PBS polarizing beam splitter
  • the vibration direction of the pulse train of the 0th-order diffracted light of the optical comb Comb1 and the vibration direction of the pulse train of the 1st-order diffracted light are orthogonal to each other.
  • T in equation (15) represents time.
  • the wave plate 132 and the polarizing plate 134 were disposed.
  • the optical comb Comb2 having a predetermined linear polarization was combined with the 0th-order diffracted light and the first-order diffracted light of the optical comb Comb1 coherently controlled and polarization-modulated as described above by a beam splitter (Beam (Splitter: BS) 138.
  • Beam Splitter
  • the photodetector 140 detects the interference light of the two optical combs Comb 1 and Comb 2.
  • the optical comb Comb2 functions as a local oscillator (LO) signal.
  • the interference light received by the photo detector 140 is processed by a digitizer (data processing unit) 142 to visualize the interference light on a display (not shown).
  • An optical comb Comb2 emitted from the optical comb light source 112 and not passing through the (1/4) wave plate 130, the (1/2) wave plate 132, and the polarizing plate 134 is supplied to the digitizer 142 as a reference clock signal. I input it.
  • the timing of the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1 was matched.
  • the optical comb Comb1 when the direction of the linearly polarized light of the optical comb Comb2 as the LO signal is slanted to the right on the paper, the direction of the linearly polarized light of the optical comb Comb1 is slanted to the right on the paper.
  • the directions of the linearly polarized light of the optical comb Comb2 became the same as each other, and a strong interference signal was generated.
  • the optical comb Comb1 becomes counterclockwise or clockwise circularly polarized light on the paper, the optical comb Comb1 partially includes the linearly polarized light of the optical comb Comb2.
  • the optical comb Comb1 when the direction of the linearly polarized light of the optical comb Comb2 as the LO signal is slanted to the left on the paper, the direction of the linearly polarized light of the optical comb Comb1 is slanted to the left on the paper.
  • the directions of the linearly polarized light of the optical comb Comb2 became the same as each other, and a strong interference signal was generated.
  • the optical comb Comb1 becomes counterclockwise or clockwise circularly polarized light on the paper surface, the optical comb Comb1 partially includes the linearly polarized light of the optical comb Comb2.
  • the 0th-order diffracted light and the 1st-order diffracted light of Comb 1 were orthogonal to each other and overlapped spatially and temporally.
  • a polarization interference waveform modulated into linearly polarized light, elliptically polarized light, circularly polarized light, or the like was generated according to the desired conditions described above.
  • control device control device for optical comb
  • Comb1 ... optical comb (first optical comb) Comb2 ... optical comb (second optical comb) f CEO1
  • Offset frequency first frequency offset
  • f rep1 ... repetition frequency (first frequency interval) f CEO2 ... offset frequency (second frequency offset) f rep2 ... repetition frequency (second frequency interval) FM1 ... optical frequency mode (first frequency mode) FM3 ... optical frequency mode (third optical frequency mode) FM2 ...
  • Optical frequency mode (second frequency mode) FM4 ... optical frequency mode (fourth optical frequency mode)

Abstract

La présente invention concerne un procédé de commande de peigne optique qui comprend une étape de commande consistant à commander une différence entre un premier décalage de fréquence et un deuxième décalage de fréquence en utilisant : un premier peigne optique qui a un premier mode fréquentiel ayant le premier décalage de fréquence par rapport à zéro sur un axe de fréquence, et une pluralité de troisièmes modes fréquentiels agencés à un intervalle constitué d'un multiple entier d'un premier intervalle de fréquence par rapport au premier mode fréquentiel sur l'axe de fréquence ; et un deuxième peigne optique qui a un deuxième mode fréquentiel ayant le deuxième décalage de fréquence par rapport à zéro sur l'axe de fréquence, et une pluralité de quatrièmes modes fréquentiels agencés à un intervalle constitué d'un multiple entier d'un deuxième intervalle de fréquence par rapport au deuxième mode de fréquence sur l'axe de fréquence.
PCT/JP2018/006447 2017-02-28 2018-02-22 Procédé de commande de peigne optique et dispositif de commande de peigne optique WO2018159445A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013507005A (ja) * 2009-10-02 2013-02-28 イムラ アメリカ インコーポレイテッド モード同期レーザによる光信号処理
US20140185635A1 (en) * 2011-09-14 2014-07-03 Jonathan A. COX Methods and apparatus for broadband frequency comb stabilization
JP2015155984A (ja) * 2014-02-21 2015-08-27 日本電信電話株式会社 自己参照干渉装置

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2013507005A (ja) * 2009-10-02 2013-02-28 イムラ アメリカ インコーポレイテッド モード同期レーザによる光信号処理
US20140185635A1 (en) * 2011-09-14 2014-07-03 Jonathan A. COX Methods and apparatus for broadband frequency comb stabilization
JP2015155984A (ja) * 2014-02-21 2015-08-27 日本電信電話株式会社 自己参照干渉装置

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