JPWO2018159445A1 - Optical comb control method and optical comb control device - Google Patents

Abstract

An optical comb control method to which the present invention is applied includes a first frequency mode having a first frequency offset with respect to zero on a frequency axis and a first frequency interval for the first frequency mode on the frequency axis. A first optical comb having a plurality of third frequency modes arranged at an integer multiple of an interval, a second frequency mode having a second frequency offset with respect to zero in the frequency axis, and the frequency axis And a second optical comb having a plurality of fourth frequency modes arranged at intervals of an integral multiple of a second frequency interval with respect to the second frequency mode, using the first frequency A control step of controlling a difference between the offset and the second frequency offset.

Description

  The present invention relates to an optical comb control method and an optical comb control device. Priority is claimed on Japanese Patent Application No. 2017-037766 filed on Feb. 28, 2017, the content of which is incorporated herein by reference.

  Light having a spectrum in which optical frequency modes are precisely distributed on the frequency axis at equal intervals is called an optical comb or an optical frequency comb. In this specification, the optical frequency mode may be simply described as “frequency mode”. The optical comb is emitted from an ultrashort pulse laser such as a mode-locked laser. As an example of a mode-locked laser emitting an optical comb, Non-Patent Document 1 discloses a 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.

Steven T. Cundiff and Jun Ye, "Colloquium: Femtosecond optical frequency combs," REVIEWS OF MODERN PHYSICS, VOLUME 75, JANUARY (2003).

  The optical comb is a low-jitter coherent pulse train in the time domain, and is a comb-like spectrum accurately mode-decomposed in the frequency domain. As disclosed in Non-Patent Document 1, an optical comb is used as a light source stabilized with high precision. However, conventionally, the offset frequency and the repetition frequency of the optical comb and the offset frequency difference and the repetition frequency difference when two optical combs are used have been treated as fixed parameters.

  As shown in FIG. 2, the present inventor has found that the difference in the relative carrier envelope phase (Carrier-Envelope offset Phase: CEP) between two optical combs gradually and gradually becomes smaller in accordance with the offset frequency difference as time advances. Attention was paid to the essence of the deviation and the essence that the period of the relative CEP difference is represented by the reciprocal of the offset frequency difference as shown in FIG. The present inventor has obtained a new finding that the relative CEP can be arbitrarily controlled by controlling the offset frequency difference based on the essence of the optical comb, and completed the present invention.

  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 the relative CEP between two optical combs.

  The method of controlling an optical comb according to the present invention comprises an integer of a first frequency mode having a first frequency offset with respect to zero on the frequency axis and a first frequency interval for the first frequency mode on the frequency axis. A first optical comb having a plurality of third frequency modes arranged at double intervals, a second frequency mode having a second frequency offset with respect to zero on the frequency axis, and With a second optical comb having a plurality of fourth frequency modes arranged at intervals of an integral multiple of the second frequency interval with respect to the second frequency mode, using the first frequency offset and A control step of controlling a difference from the second frequency offset.

  In the control method for an optical comb according to the present invention, in the control step, the first frequency offset and the second frequency offset are set so that a difference between the first frequency offset and the second frequency offset satisfies Expression (1). A difference from the second frequency offset may be set.

In the equation (1), Δf _CEO represents a difference between the first frequency offset and the second frequency offset. Δf _rep represents the difference between the first frequency interval and the second frequency interval. K and N represent arbitrary natural numbers.

  In the optical comb control method according to the present invention, in the control step, a difference between the first frequency offset and the second frequency offset may be set so as to satisfy Expression (2).

In the equation (2), Δf _CEO represents a 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.

  In the optical comb control method according to the present invention, in the control step, a difference between the first frequency offset and the second frequency offset may be set so as to satisfy Expression (3).

In the equation (3), Δf _CEO is represented 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.

  The control device of the optical comb according to the present invention 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. And controlling the first frequency offset and the first frequency interval in the first optical comb having a plurality of third frequency modes arranged at double intervals, and with respect to zero in the frequency axis. A second frequency mode having a second frequency offset, and a plurality of fourth frequency modes arranged at an integer multiple of a 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; The control mechanism is 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 second frequency difference so that the difference between the first frequency interval and the second frequency interval is represented by an integer ratio to each other. The two frequency intervals can be controlled.

  According to the present invention, by controlling the offset frequency difference between two optical combs, the relative CEP between the two optical combs can be arbitrarily controlled.

It is a schematic diagram of two optical combs Comb1 and Comb2 in each area of a time domain and a frequency domain. It is a schematic diagram which shows the relative relationship of the repetition period of the pulse train of two optical combs Comb1 and Comb2 in a time domain. It is a schematic diagram which shows the relative relationship of the phase of the pulse train of two optical combs Comb1 and Comb2 in a time domain. It is the schematic which shows an example of the optical comb output mechanism comprised so that the offset frequency and repetition frequency of an optical comb can be controlled. It is a schematic diagram showing one embodiment of a control device of an optical comb concerning the present invention. It is a schematic diagram which shows the optical behavior of the acousto-optic element for controlling the offset frequency of an optical comb. FIG. 3 is a schematic diagram illustrating a relationship between waveforms of two optical combs Comb1 and Comb2 and an interference signal according to the first embodiment. 6 is a graph illustrating a measurement result of an interference signal when an offset frequency difference Δf _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 Δf _CEO between two optical combs Comb1 and Comb2 is set to Δf _rep / 2 in the first embodiment. 7 is a graph illustrating a measurement result of an interference signal when an offset frequency difference Δf _CEO between two optical combs Comb1 and Comb2 is set to Δf _rep / 3 in the first embodiment. 5 is a graph illustrating an IGM obtained by averaging the IGMs that are mutually inverted with each other when an offset frequency difference Δf _CEO between two optical combs Comb1 and Comb2 is set to Δf _rep / 2 in the first embodiment. FIG. 11 is a schematic diagram illustrating a configuration of an apparatus for controlling an offset frequency difference Δf _CEO between a 0th-order diffracted light and a 1st-order diffracted light of the optical comb Comb1 in the second embodiment. FIG. 10B is a schematic diagram showing the spectra of the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1 in the acousto-optic element of the device shown in FIG. 10A. It is a figure which shows the relative CEP of the 0th-order diffraction light and the 1st-order diffraction light of the optical comb Comb1. 9 is a graph showing the relationship between elapsed time and relative CEP in Example 2. FIG. 11B is a graph showing the polarization state of the optical comb Comb1 and the measurement results of the intensity of the interference light according to the change in the relative CEP shown in FIG. 11A. 11B is a graph illustrating a waveform of the interference light in the polarization state illustrated in FIG. 11B. FIG. 11B is another graph showing a polarization state of the optical comb Comb1 and a measurement result of the intensity of the interference light according to a change in the relative CEP shown in FIG. 11A. 11D is a graph illustrating a waveform of the interference light in the polarization state illustrated in FIG. 11D.

  Hereinafter, an embodiment of an optical comb control method and an optical comb control device according to the present invention will be described with reference to the drawings. Note that the length, width, thickness ratio, and the like of each component in the drawings referred to in the following description are schematic.

The mode-locked laser outputs a pulse train that is periodic in the time domain. The pulse train output from a mode-locked laser can be illustrated by a function of a rapidly oscillating electric field (ie, carrier) and 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).

  In the equation (4), n represents the refractive index of the medium through which the optical comb propagates. λ represents the center wavelength of the optical comb.

Since the group velocity v _g and the phase velocity v _p are different, the envelope of the pulse gradually deviates from the peak part of the carrier as time advances. The phase shift (ie, phase difference) is called a carrier-envelope offset phase (CEP). The difference Δφ _CEP of the relative CEP between adjacent pulse trains on the time axis is periodically shifted between the pulses, and has a constant period T _CEO . The reciprocal of the period T _CEO corresponds to a carrier envelope offset frequency (also simply referred to as an offset frequency) f _CEO in the frequency domain. When the optical comb output from the mode-locked laser is observed in the frequency domain, the longitudinal mode of the mode-locked laser is very uniformly distributed at intervals of a repetition frequency (frequency interval) f _rep which is the reciprocal of the pulse repetition period T _rep. are doing. The relationship between the offset frequency f _CEO and the repetition frequency f _rep is expressed by Expression (6) using a relative CEP difference Δφ _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. As shown in FIG. 1, the optical comb (first optical comb) Comb1 has an optical frequency mode (first frequency mode) FM1 having an offset frequency (first frequency offset) f _CEO1 with respect to zero on the frequency axis. And 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 has an optical frequency mode (second frequency mode) FM2 having an offset frequency (second frequency offset) f _CEO2 with respect to zero in the frequency axis, and an optical frequency in the frequency axis. A plurality of optical frequency modes (fourth optical frequency mode) _FM4 are arranged at intervals of an integral multiple of the repetition frequency (second frequency interval) f _rep2 with respect to the mode FM2.

From Expression (6), Expression (7) holds as the correspondence between the offset frequency f _CEO1 and the repetition frequency f _rep1 in the optical comb Comb1.

Similarly, from the equation (6), the relation of the equation (8) is established as the correspondence between the offset frequency f _CEO2 and the repetition frequency f _rep2 in the optical comb Comb2.

In the equation (7), Δφ _CEP1 represents a relative CEP of the optical comb Comb1. In the equation (8), Δφ _CEP2 indicates a relative CEP of the optical comb Comb2.

(7) and (8) As shown in equation, the offset frequency _{f CEO1, f CEO2} the change amount of the CEP between pulses, i.e. relative CEPderutafai _CEP1, is associated with Δφ _CEP2. In other words, by controlling the offset frequencies f _CEO1 and f _CEO2 , the coherence of each pulse train of the optical combs Comb1 and Comb2 can be controlled.

2 and 3 schematically show waveforms when the two optical combs Comb1 and Comb2 are viewed on a common time axis. As shown in FIG. 2, each waveform when the positions of the two optical combs Comb1 and Comb2 on the time axis are aligned is referred to as a first waveform. The difference on the time axis between the second waveforms advanced on the time axis from the position of the first waveform of each of the two optical combs Comb1 and Comb2 is defined as a time difference ΔT _rep . The difference on the time axis between the third waveforms of the two optical combs Comb1 and Comb2 is a time difference (2 × ΔT _rep ). That is, the difference on the time axis between the (M + 1) -th waveforms of the two optical combs Comb1 and Comb2 is a time difference (M × ΔT _rep ). M represents an arbitrary natural number. That is, in the time domain, the waveforms of the two optical combs Comb1 and Comb2 slightly and evenly shift according to the repetition frequency difference Δf _rep . The repetition frequency difference Δf _rep is the frequency difference | f _rep1 −f _rep2 |.

When the time (1 / Δf _rep ) elapses from the position on the time axis of the first waveform of the two optical combs Comb1 and Comb2, the positions on the time axis of the waveforms of the two optical combs Comb1 and Comb2 are aligned again. In other words, the timing of each pulse of the two optical combs Comb1 and Comb2 changes at a period of (1 / Δf _rep ). The waveform after the time (1 / Δf _rep ) has elapsed from the position on the time axis of the first waveform is the (M + 2) th waveform of the optical comb Comb1 and the (M + 1) th waveform of the optical comb Comb2, respectively. Then, the relationship of the expressions (9) and (10) is established.

On the other hand, the respective CEPs of the two optical combs Comb1 and Comb2 have a relative relationship at a common position on the time axis. As shown in FIG. 3, when each waveform having a relative relationship (that is, a difference in CEP) is the first waveform, the CEP of the first waveform of each of the two optical combs Comb1 and Comb2 and the second waveform The phase differences between the waveform and CEP are Δφ _CEP1 and Δφ _CEP2 . The phase differences between the first waveform CEP and the third waveform CEP of the two optical combs Comb1 and Comb2 are 2 × Δφ _CEP1 and 2 × Δφ _CEP2 . That is, the difference on the time axis between the (M + 1) -th waveforms of the two optical combs Comb1 and Comb2 is a time difference (M × Δφ _CEP1 ) and (M × Δφ _CEP2 ). That is, in the time domain, the relative CEP of the two optical combs Comb1 and Comb2 slightly and evenly shifts according to the offset frequency difference Δf _CEO . The offset frequency difference Δf _CEO is a frequency difference | f _CEO1 −f _CEO2 |).

Therefore, after a lapse of time (1 / Δf _CEO ) from the position on the time axis of the first waveform of each of the two optical combs Comb1 and Comb2, the difference between the phase difference Δφ _CEP1 and the phase difference Δφ _CEP2 becomes 2π. Become. At this time, a pulse train having the same relationship as the CEP relationship between the waveforms of the first pulse trains of the two optical combs Comb1 and Comb2 appears. In FIG. 3, it is assumed that the repetition frequency difference Δf _rep between the two optical combs Comb1 and Comb2 is 0 for easy explanation. Therefore, 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 Comb1 and Comb2 are aligned. That is, the relative CEP relationship between the two optical combs Comb1 and Comb2 changes at a period of (1 / Δf _CEO ).

(Optical comb control method)
As described above, the repetition frequency f _rep and offset frequency f _CEO of the optical comb are important frequency parameters indicating the characteristics of the pulse train. Considering the relative relationship between the two optical combs, in addition to the repetition frequency f _rep and the offset frequency f _CEO of each optical comb, the repetition frequency difference Δf _rep and the offset frequency difference Δf _CEO are important frequency parameters indicating the characteristics of the pulse train. It is. Conventionally, the offset frequency difference Δf _CEO has been treated as a fixed parameter. However, the CEP can be arbitrarily controlled by controlling the offset frequency difference Δf _CEO . In the present invention, the degree of freedom in controlling the offset frequency difference Δf _CEO is positively utilized.

An optical comb control method according to the present invention 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 (offset frequency difference, difference between the first frequency offset and the second frequency offset) Δf _CEO between the offset frequencies f _CEO1 and f _CEO2 .

The offset frequency difference Δf _CEO is a difference between the offset frequencies f _CEO1 and f _CEO2 of the two optical combs Comb1 and Comb2. As shown in the equations (7) and (8), the repetition frequencies f _rep1 and f _rep2 of the two optical combs Comb 1 and Comb 2 have a relative relationship to the offset frequencies f _CEO1 and f _CEO2 , respectively. Therefore, in order to control the offset frequency difference Delta] f _CEO, 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 , it is preferable to control each parameter to the repetition frequency difference Delta] f _rep of COMB2, offset frequency _{f rep1} optical comb COMB1, six parameters between the offset frequency _{f rep2} optical comb COMB2 is represented by any integer ratio . Specifically, the relative relationship (predetermined condition) in which the above-mentioned six parameters are expressed by an arbitrary integer ratio is the control of the four parameters of the offset frequencies f _CEO1 and f _CEO2 and the offset frequencies f _rep1 and f _rep2. Is preferably satisfied.

For example, 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 comb control device)
First, an optical comb output mechanism used in an optical comb control device applicable to the optical comb control method of the present invention will be described. The optical comb output mechanism detects an interference signal between two optical comb modes satisfying a predetermined relationship (a 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 control an offset frequency and a repetition frequency by detecting an interference signal between two optical comb modes.

  As shown in FIG. 4, 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 is a semiconductor laser (hereinafter, referred to as an excitation LD) 26 that excites the EDF 24 by supplying excitation light to the EDF 24 via an erbium-doped optical fiber (EDF) 24 and an optical coupler 25. And. An optical isolator 34, an optical coupler 32, a piezo (PZT) element 30 capable of changing the resonator length of the above-described fiber laser along an emission direction of the light from the EDF 24 (clockwise direction on the paper surface of FIG. 4), and a polarization Wave controllers 28 are connected by EDF 24. The configuration of the optical comb light source 12 is not limited to the above-described configuration as long as the optical comb light can be emitted.

  The optical comb emitted from the optical coupler 32 is supplied to the optical interference unit 14 and the optical comb output unit 20. Between the optical coupler 32 and 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 pump LD 41, and an optical coupler 43. The components up to the optical coupler 32 and the optical interference unit 14 and the components 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 arranged between the EDF amplifier 40A and the optical interference unit 14. The optical comb whose polarization is controlled and amplified by the polarization controller 38A and the EDF amplifier 40A is output by the HNLF 42 as an optical comb having a wider band than before entering the HNLF 42.

The optical interference unit 14 includes a fiber collimator 44, a condenser lens 46, a λ / 2 wavelength plate 48, a periodically-poled lithium niobate (PPLN) 50, and a light, in order from the side closer to the optical comb light source 12. 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. From PPLN50, second harmonic _{W S} broadband optical comb is emitted. In other words, a broadband optical comb component (2f) and a second harmonic component (2 × 1f) newly generated by the PPLN 50 are emitted from the PPLN 50 in an overlapping manner.

Frequency f _B from zero on the frequency axis of the n-th mode in a wideband optical comb can be expressed as (11).

  N in Expression (11) is an arbitrary natural number.

With respect to the frequency of the n-th mode of the wide band optical comb frequency f _S of the spectrum of the second harmonic wave W _S is expressed by the equation (12).

(12) the frequency f _W of the 2n-th mode adjacent low-frequency side to a mode of the frequency f _S of the broadband optical comb of the formula is expressed as equation (13).

The broadband optical comb and the second harmonic interfere in the beat signal detector 16. The beat signal detector 16 detects a beat signal between the optical comb and the second harmonic in a wide band. The offset frequency difference f _CEO is detected by detecting a beat signal between the spectrums of the frequencies represented by the equations (12) and (13). In other words, the beat signal between the spectrums of the frequencies represented by the equations (12) and (13) is emitted to the beat signal detection unit 16 as interference light. The beat signal detection unit 16 is configured by a photo detector 54. Light emitted from PPLN 50 is detected by photodetector 54. The intensity of light emitted from the PPLN 50 is converted into a magnitude of an electric signal.

  The electric signal output from the photodetector 54 is transmitted to the offset frequency control unit 18 via the electric cable 56 and transmitted to the frequency control unit 22 repeatedly via the electric cable 58.

  The offset frequency control unit 18 includes a high-frequency band-pass 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 band-pass filter 61 extracts an offset frequency component from the electric signal output from the photo detector 54. The high frequency amplifier 62 amplifies the electric signal output from the high frequency band pass filter 61. The FG 64 can transmit a reference signal of a desired frequency by setting the desired frequency. The DBM 66 mixes the amplified electric signal with the reference signal transmitted from the FG 64. The loop filter 68 feeds back the current applied to the excitation LD 26 of the optical comb light source 12 according to the mixed electric signal.

In the offset frequency controller 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 current applied to the excitation LD 26 is changed, and the offset frequency f _{CEO of the} optical comb emitted from the optical comb light source 12 is made equal to the frequency of the reference signal transmitted from the FG 64. In other words, by controlling 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.

  The repetition 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 extracts a repetition frequency component from the electric 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 a desired frequency by setting the desired frequency. The DBM 76 mixes the amplified electric signal with the reference signal transmitted from the FG 74. The loop filter 78 feeds back a voltage applied to the PZT element 30 of the optical comb light source 12 according to the mixed electric signal.

In the repetition frequency control unit 22, when the frequency of the reference signal transmitted from the FG 74 is changed, feedback is applied to the PZT element 30 of the optical comb light source 12 by the loop filter 78 as described above. Thereby, 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 becomes equal to the frequency of the reference signal transmitted from the FG 74. In other words, 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.

  Next, the configuration and control procedure of the optical comb control device of the present invention will be described.

As shown in FIG. 5, the control device (optical comb control device) 100 of the present invention includes an optical comb output mechanism 10A, 10B, a frequency control mechanism 90, a continuous wave laser (hereinafter, CW laser) 92, a frequency And 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 Δf _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 stabilizing mechanism 94 controls a 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 illustrates main parts such as the optical comb output unit 20 of each 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, the PZT 12, and the like. Is omitted.

The control device 100 includes two optical comb output mechanisms 10A and 10B, and thus includes two FG64 and two FG74, respectively. That is, the control device 100 is configured to be able to control a total of four parameters of the offset frequencies f _CEO1 and f _CEO2 of the two optical combs Comb1 and Comb2 and the repetition frequencies f _rep1 and f _rep2 , so that the FG 64 and the FG 74 are each two. And a frequency control mechanism 90 for transmitting a reference signal to the two FGs 64.

  The frequency stabilization mechanism 94 includes a frequency control mechanism 90 including a program or the like built in a 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. The 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 electric 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. The 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 also 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 electric 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. The 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 of the PZT 30 in the optical comb light source 12 of the optical comb output mechanism 10B.

Next, an example of a control procedure of the offset frequency difference Δf _CEO using the control device 100 will be described.

First, the repetition frequency f _rep1 and the 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. To make

Next, 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. According to such a procedure, the frequency of the CW light follows the repetition frequency f _rep1 and the offset frequency f _CEO1 of the optical comb Comb1.

Next, according to the control procedure described with reference to FIG. 4, the offset frequency f _CEO2 of the optical comb Comb2 output from the optical comb output unit 20 of the optical comb output mechanism 10B is stabilized, and then the CW light and the optical A beat signal with the comb Comb2 is detected, and the detected beat signal is stabilized with respect to the reference signal from the FG 118. By such a procedure, the repetition frequency f _rep2 of the optical comb Comb2 is made to follow the frequency of the CW light. As a result, Comb2 follows optical comb Comb1, and a dual-comb light source with phase synchronization can be obtained.

The FG 64 of the optical comb output mechanism 10A emits a reference signal of the offset frequency f _CEO1 of the optical comb Comb1. The FG 74 of the optical comb output mechanism 10A emits a reference signal having a repetition frequency f _rep1 of the optical comb Comb1. The FG 132 _issues a reference signal having a repetition frequency f _rep2 of the optical comb Comb2. By controlling each setting of FG64, FG64, and FG132 by the frequency control mechanism 90, an arbitrary repetition frequency difference or offset frequency difference can be obtained. In order to control the offset frequency difference Δf _CEO , the frequency control mechanism 90 controls the offset frequency difference Δf _CEO , the offset frequency f _CEO1 , the offset frequency f _CEO2 , the repetition frequency difference Δf _rep , the offset frequency f _rep1 , and the 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) in which the two parameters are expressed by an arbitrary integer ratio is satisfied. That is, the control device 100 arbitrarily controls the offset frequency difference Δf _CEO between the two optical combs Comb1 and Comb2.

According to the above control procedure, the optical combs Comb1 and Comb2 having the desired offset frequency difference Δf _CEO and having their phases controlled are output from the optical comb output mechanisms 10A and 10B.

As described above, in the optical comb control method of the present invention, the CEP of the two optical combs Comb1 and Comb2 can be arbitrarily set by actively controlling the offset frequency difference Δf _CEO between the two optical combs Comb1 and Comb2. Can control. According to the optical comb control method of the present invention, it is possible to appropriately control the correspondence between important parameters that determine the characteristics of the pulse train of the optical comb, and therefore, it is possible to perform arbitrary coherent modulation. Examples of applications for performing 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, the FGs 130 and 132 of the optical comb output mechanism 10A, and the FG 64 of the optical comb output mechanism 10B. The optical combs Comb1 and Comb2 whose phases are controlled with each other can be generated. As described above, the reference signal output from the FG 132 is indirectly input to the PZT 30 of the optical comb output mechanism 10B.

INDUSTRIAL APPLICABILITY The control method and control apparatus for an optical comb according to the present invention can be applied in a wide field of performing arbitrary coherent modulation. In the optical comb control method of the present invention, the relative phase of the optical combs Comb1 and Comb2 can be controlled by positively controlling the offset frequency difference Δf _CEO . Therefore, the optical comb control method and control device of the present invention can be applied to highly efficient signal detection and signal control in observing a phenomenon dependent on relative CEP. The phenomenon depending on the relative CEP is, for example, interference, a nonlinear optical phenomenon, or the like.

  The preferred embodiments of the present invention have been described above in detail. The present invention is not limited to the embodiments described above, and may be appropriately modified and changed within the scope of the present invention described in the appended claims.

As an example, the optical comb output mechanism 10 may be configured using an Acoustic Optical Modulator (AOM) 120 shown in FIG. In the optical comb output mechanism 10 shown in FIG. 4, a fiber collimator may be arranged on the input side of the optical comb output unit 20, and the AOM 120 may be arranged on the output side of the fiber collimator. When 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. By appropriately setting the modulation frequency f _AOM based on this principle, the offset frequency difference Δf _CEO can be positively controlled.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(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. Comb2 was caused to interfere with the comb, and an interference signal (Interferogram: IGM) was received by the high-speed detector 96. The IGM received by the high-speed detector 96 was post-processed by the data processing unit 98 to visualize the IGM on a display (not shown).

As shown in FIG. 7, the repetition frequency difference Δf _rep between the two optical combs Comb1 and Comb2 affects the period in which the IGM is detected. The period in which the IGM is detected corresponds to the interval on the time axis between the IGM plots shown in FIG. A plot of the IGM caused by the first waveforms of the two optical combs Comb1 and Comb2 when the positions on the time axis are aligned, and a time period T _IGM = (1 / Δf _rep ) elapses from the timing of the first waveform. The plots of the IGM resulting from the (M + 2) th waveform of the optical comb Comb1 and the (M + 1) th waveform of the optical comb Comb2 overlap. The offset frequency difference Δf _CEO between the two optical combs Comb1 and Comb2 affects the phase of the IGM. The phase of the IGM is represented by the waveform of the IGM shown in FIG.

  By performing Fourier analysis on the IGM, for example, by disposing the sample S or the laser medium in front of the emission direction of the optical comb Comb1, a spectrum including information such as the optical characteristics of the sample S can be obtained. 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 the optical characteristics included in the acquired spectrum.

In the present example, the repetition frequency Δf _rep = 120.6 Hz, the offset frequency Δf _CEO was controlled to be the reciprocal multiple of an integer of the repetition frequency difference Δf _rep , and the IGM was measured. In each of FIGS. 8A, 8B, and 8C, the upper graph shows the IGM after the lapse of a predetermined time on the time axis, and the lower graph shows the IGM after the lapse of the predetermined time. Are shifted vertically.

As shown in FIG. 8A, when the offset frequency Δf _CEO is set to 0, the waveform of the IGM does not change over time, and the offset frequency difference Δf _CEO between the two optical combs Comb1 and Comb2 changes to the IGM waveform. It clearly shows the effect.

As shown in FIG. 8B, when the offset frequency Δf _CEO is set to (Δf _rep / 2), the waveform of the IGM is inverted when a predetermined time has elapsed, and a phase shift of 2π / 2 = π occurs. Understand. By controlling so that a phase shift of π occurs in the IGM and by taking a difference average between the IGMs that are continuously obtained and have distributions that are inverted from each other, as shown in FIG. Bias and the like can be canceled. From the measurement results shown in FIGS. 8B and 9, it was confirmed that by controlling the offset frequency Δf _{CEO to} be (Δf _rep / 2), it is possible to detect an IGM that is robust to environmental changes.

As shown in FIG. 8C, when the offset frequency Δf _CEO is set to Δf _rep / 3, the waveform of the IGM is repeated in three patterns as the predetermined time elapses, and a phase shift of 2π / 3 occurs. . In FIG. 8C, three patterns of the IGM are illustrated by a solid line, a broken line, and an alternate long and short dash line, respectively.

As shown in FIGS. 8A to 8C, by controlling the offset frequency Δf _{CEO to} be (1 / N) of the repetition frequency difference Δ _rep , a phase shift of (2π / N) is generated for each IGM, We confirmed that coherent waveform control was possible. N is an arbitrary natural number.

(Example 2)
As shown in FIG. 10A, in Example 2, an optical comb light source 110 in which the relative CEP between pulse trains was stabilized was prepared. The optical comb Comb1 emitted from the optical comb light source 110 was incident on the AOM 120, and the offset frequency difference Δf _CEO between the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1 was controlled. Further, an optical comb light source 112 different from the optical comb light source 110 was prepared to perform so-called dual comb spectroscopy. The center wavelength λ of the optical comb light sources 110 and 112 was 1560 nm. The repetition frequency f _rep1 of the optical comb Comb1 emitted from the optical comb light source 110 was _set to 56.5 MHz. The repetition frequency difference Δf _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 emission direction of the optical comb Comb1 from the optical comb light source 110. did. The AOM 120 was disposed in front of the emission direction of the optical comb Comb1 from the (1/2) wavelength plate 118. From AOM120, 0-order diffracted light of the optical comb Comb1 and ^{0 th} shown in (FIG. 10A)) 1-order diffracted light ^{(1 st} shown in FIG. 10A) is emitted at different angles in plan view. As shown in FIG. 10B, by modulating the _AOM 120 at the frequency f _AOM , the offset frequency difference Δf _CEO between the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1 is expressed by Expression (14).

As shown in FIG. 10A, an optical path length changing unit 122 is arranged in front of the emission direction of the 0th-order diffracted light from the optical comb Comb1. A (1/2) wavelength plate 124 is arranged in front of the direction of emission of the first-order diffracted light from the optical comb Comb1. With this arrangement, the direction of the linearly polarized light of the first-order diffracted light of the optical comb Comb1 is made orthogonal to the direction of the linearly polarized light of the 0th-order diffracted light of the optical comb Comb1. The 0th-order diffracted light and the 1st-order diffracted light were combined by a polarizing beam splitter (PBS) 126 to generate a coherently controlled and polarization-modulated light pulse. As shown in FIG. 10C, in the optical pulse subjected to the coherent control and the polarization modulation, the oscillation direction of the pulse train of the 0th-order diffracted light of the optical comb Comb1 is orthogonal to the oscillation direction of the pulse train of the 1st-order diffracted light. Relative CEP between 0-order diffracted light and 1-order diffracted light of the optical comb Comb1: Δφ _CEP' occurs, (15) holds.

  In equation (15), t represents time.

  As shown in FIG. 10A, a (1/4) wave plate 130, (1/1) for converting the optical comb Comb2 into linearly polarized light in a predetermined direction ahead of the emission direction of the optical comb Comb2 from the optical comb light source 112. 2) The wave plate 132 and the polarizing plate 134 were arranged. The optical comb Comb2 having a predetermined linear polarization was combined with the 0th-order diffracted light and the 1st-order diffracted light of the optical comb Comb1, which was coherently controlled and polarization-modulated as described above, by the beam splitter (BS) 138. Interference light between the two optical combs Comb1 and Comb2 was detected by the photodetector 140. In this configuration, the optical comb Comb2 functions as a local oscillator (LO) signal. The interference light received by the photodetector 140 was processed by a digitizer (data processing unit) 142 to visualize the interference light on a display (not shown). An optical comb Comb 2 emitted from the optical comb light source 112 and not passing through the (１ ／) wavelength plate 130, the (１ ／) wavelength 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 adjusted using the optical path length changing unit 122. As shown in FIG. 11A, the relative CEP between 0-order diffracted light and 1-order diffracted light of the optical comb COMB1: the Δφ _CEP', was varied under the conditions of _{Δf CEO = (Δf rep / 4} ).

  As shown in FIG. 11B and FIG. 11C, when the direction of the linearly polarized light of the optical comb Comb2 as the LO signal is obliquely rightward and downward on the paper, the direction of the linearly polarized light of the optical comb Comb1 is obliquely downward and rightward on the paper. At this time, the directions of the linearly polarized light of the optical comb Comb2 were the same as each other, and a strong interference signal was generated. When the optical comb Comb1 becomes left-handed or right-handed circularly polarized light on the paper, the optical comb Comb1 partially includes the linearly polarized light of the optical comb Comb2. At this time, a weaker interference signal was generated as compared with the case where the direction of the linearly polarized light of the optical comb Comb1 was obliquely downward and rightward on the paper. When the direction of the linearly polarized light of the optical comb Comb1 is obliquely downward and to the left and is orthogonal to the direction of the linearly polarized light of the optical comb Comb2, the optical combs Comb1 and Comb2 do not interfere with each other, and the interference signal is smaller than in other cases. It became very weak.

  As shown in FIG. 11D and FIG. 11E, when the direction of the linearly polarized light of the optical comb Comb2 as the LO signal is obliquely leftward down on the paper, the direction of the linearly polarized light of the optical comb Comb1 is obliquely downwardly left on the paper. At this time, the directions of the linearly polarized light of the optical comb Comb2 were the same as each other, and a strong interference signal was generated. When the optical comb Comb1 becomes the left-handed or right-handed circularly polarized light on the paper, the optical comb Comb1 partially includes the linearly-polarized light of the optical comb Comb2. At this time, a weaker interference signal was generated as compared with the case where the direction of the linearly polarized light of the optical comb Comb1 was obliquely leftward and downward on the paper. When the optical comb Comb1 is obliquely downward to the right and orthogonal to the direction of the linearly polarized light of the optical comb Comb2, the optical combs Comb1 and Comb2 do not interfere with each other, and a very weak interference signal is generated as compared with other cases. .

As can be seen from the results shown in FIGS. 11A to 11E, the offset frequency difference Δf _CEO between the 0th-order diffracted light and the 1st-order diffracted light of Comb1 is set to a desired condition (in this embodiment, Δf _CEO = Δf _rep / 4). In the present embodiment, the 0th-order diffracted light and the 1st-order diffracted light of Comb1 are orthogonal to each other, and are superimposed spatially and temporally. At this time, a polarization interference waveform modulated into linearly polarized light, elliptically polarized light, circularly polarized light, or the like was generated according to the above-described desired conditions. By applying the present invention, it has been confirmed that high-speed modulation and coherent detection of relative CEP by polarization interference can be performed.

90 frequency control mechanism 100 control device (optical comb control device)
Comb 1 ... 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)

［００１０］
（１）式において、Δｆ_ＣＥＯは前記第一の周波数オフセットと前記第二の周[0002]
The return frequency, the offset frequency difference when using two optical combs, and the repetition frequency difference were treated as fixed parameters.
[0005]
As shown in FIG. 2, the inventor of the present invention has found that the difference between the relative carrier envelope phases (Carrier-Envelope offset Set: CEP) of the two optical combs is gradually and evenly smaller in accordance with the offset frequency difference as time advances. Attention was paid to the essence of the deviation and the essence that the period of the relative CEP difference is represented by the reciprocal of the offset frequency difference as shown in FIG. The present inventor has obtained a new finding that the relative CEP can be arbitrarily controlled by controlling the offset frequency difference based on the essence of the optical comb, and completed the present invention.
[0006]
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 the relative CEP between two optical combs.
Means for solving the problem [0007]
The method of controlling an optical comb according to the present invention comprises an integer of a first frequency mode having a first frequency offset with respect to zero on the frequency axis and a first frequency interval for the first frequency mode on the frequency axis. A first optical comb having a plurality of third frequency modes arranged at double intervals, a second frequency mode having a second frequency offset with respect to zero on the frequency axis, and A second optical comb having a plurality of fourth frequency modes arranged at an integer multiple of the second frequency interval with respect to a second frequency mode, using 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 interval and the second With frequency spacing The first frequency offset, the second frequency offset, the first frequency interval, and the first frequency offset by controlling the second frequency interval, so that is represented by an integer ratio to each other And a control step of controlling a difference between the first frequency offset and the second frequency offset.
[0008]
In the control method for an optical comb according to the present invention, in the control step, a difference between the first frequency offset and the second frequency offset may be set so as to satisfy Expression (1).
[0009]
[Equation 1]

[0010]
In the equation (1), Δf _CEO is the first frequency offset and the second frequency offset.

［００１３］
（２）式において、Δｆ_ＣＥＯは前記第一の周波数オフセットと前記第二の周波数オフセットとの差を表す。ｆ_ｒｅｐは前記第一の周波数間隔または前記第二の周波数間隔を表す。Ｎは任意の自然数で表す。
［００１４］
本発明の光コムの制御方法では、前記制御工程において、前記第一の周波数オフセットと前記第二の周波数オフセットとの差を（３）式を満たすように限定してもよい。
［００１５］
［数３］

［００１６］
（３）式において、Δｆ_ＣＥＯは前記第一の周波数オフセットと前記第二の周波数オフセットとの差を表す。ｆ_ＣＥＯは前記第一の周波数オフセットまたは前記第二の周波数オフセットを表す。Ｎは任意の自然数を表す。
［００１７］
本発明の光コムの制御装置は、周波数軸で零に対して第一の周波数オフセットを有する第一の周波数モードと前記周波数軸で前記第一の周波数モードに対して第一の周波数間隔の整数倍の間隔をあけて並ぶ複数の第三の周波数モードとを有する第一の光コムにおける前記第一の周波数オフセット及び前記第一の周波数間隔とを制御すると共に、前記周波数軸で零に対して第二の周波数オフセットを有する第二の周波数モードと前記周波数軸で前記第二の周波数モードに対して第二の周波数間隔の整数倍の間隔をあけて並ぶ複数の[0003]
Indicates the difference from the wave number offset. Δf _rep represents the difference between the first frequency interval and the second frequency interval. K and N represent arbitrary natural numbers.
[0011]
In the optical comb control method according to the present invention, in the control step, a difference between the first frequency offset and the second frequency offset may be set so as to satisfy Expression (2).
[0012]
[Equation 2]

[0013]
In the equation (2), Δf _CEO represents a 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.
[0014]
In the optical comb control method according to the present invention, in the control step, a difference between the first frequency offset and the second frequency offset may be limited so as to satisfy Expression (3).
[0015]
[Equation 3]

[0016]
In the equation (3), Δf _CEO represents a difference between the first frequency offset and the second frequency offset. f _CEO represents the first frequency offset or the second frequency offset. N represents an arbitrary natural number.
[0017]
The control device of the optical comb according to the present invention 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 the first optical comb having a plurality of third frequency modes arranged at double intervals, and zero with respect to zero in the frequency axis. A plurality of second frequency modes having a second frequency offset and a plurality of lines arranged at intervals of an integral multiple of a second frequency interval with respect to the second frequency mode on the frequency axis.

[0004]
A frequency control mechanism for controlling the second frequency offset and the second frequency interval in a second optical comb having a fourth frequency mode. The frequency control mechanism, 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 The first frequency offset, the second frequency offset, the first frequency interval, and the difference between the first frequency interval and the second frequency interval are represented by an integer ratio to each other. The second frequency interval is configured to be controllable.
Effect of the Invention [0018]
According to the present invention, by controlling the offset frequency difference between two optical combs, the relative CEP between the two optical combs can be arbitrarily controlled.
BRIEF DESCRIPTION OF THE DRAWINGS [0019]
FIG. 1 is a schematic diagram of two optical combs Comb1 and Comb2 in each of a time domain and a frequency domain.
FIG. 2 is a schematic diagram showing a relative relationship between repetition periods of pulse trains of two optical combs Comb1 and Comb2 in a time domain.
FIG. 3 is a schematic diagram showing a relative relationship between phases of pulse trains of two optical combs Comb1 and Comb2 in a time domain.
FIG. 4 is a schematic diagram showing an example of an optical comb output mechanism configured to be able to control an offset frequency and a repetition frequency of the optical comb.
FIG. 5 is a schematic view showing an embodiment of an optical comb control device according to the present invention.
FIG. 6 is a schematic diagram showing an optical behavior of an acousto-optic device for controlling an offset frequency of an optical comb.
FIG. 7 is a schematic diagram showing a relationship between waveforms of two optical combs Comb1 and Comb2 and an interference signal according to the first embodiment.
FIG. 8A is a graph showing a measurement result of an interference signal when an offset frequency difference Δf _CEO between two optical combs Comb1 and Comb2 is set to 0 in the first embodiment.
[FIG. 8B] Offset of two optical combs Comb1 and Comb2 in the first embodiment

[0011]
f _CEO2, as the repetition frequency difference Delta] f _rep of the two optical comb COMB1, COMB2, offset frequency _{f rep1} optical comb COMB1, six parameters between the offset frequency _{f rep2} optical comb COMB2 is represented by any integer ratio It is preferable to control each parameter. Specifically, the relative relationship (predetermined condition) in which the above-mentioned six parameters are expressed by an arbitrary integer ratio is the control of the four parameters of the offset frequencies f _CEO1 and f _CEO2 and the repetition frequencies f _rep1 and f _rep2. Is preferably satisfied.
[0043]
For example, 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 △ f _CEO may set the parameters other than the offset frequency difference Delta] f _CEO to satisfy all the above-mentioned equation (1) (3).
[0044]
(Optical comb control device)
First, an optical comb output mechanism used in an optical comb control device applicable to the optical comb control method of the present invention will be described. The optical comb output mechanism detects an interference signal between two optical comb modes satisfying a predetermined relationship (a 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 control an offset frequency and a repetition frequency by detecting an interference signal between two optical comb modes.
[0045]
As shown in FIG. 4, 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.
[0046]
The optical comb light source 12 is configured as a loop type fiber laser. The optical comb light source 12 is an erbium-doped optical fiber (ED).

Claims (5)

A first frequency mode having a first frequency offset with respect to zero on a frequency axis and a plurality of second frequencies arranged at intervals of an integral multiple of a first frequency interval with respect to the first frequency mode on the frequency axis. A first optical comb having three frequency modes;
A plurality of second frequency modes having a second frequency offset with respect to zero on the frequency axis and a plurality of the second frequency modes on the frequency axis arranged at an integer multiple of a second frequency interval. And a second optical comb having a fourth frequency mode,
A control method for an optical comb, comprising a control step of controlling a difference between the first frequency offset and the second frequency offset. In the control step,
The optical comb control method according to claim 1, wherein a difference between the first frequency offset and the second frequency offset is set so as to satisfy Expression (1).

In the equation (1), Δf _CEO represents a difference between the first frequency offset and the second frequency offset. Δf _rep represents the difference between the first frequency interval and the second frequency interval. K and N represent arbitrary natural numbers. In the control step,
The optical comb control method according to claim 1 or 2, wherein a difference between the first frequency offset and the second frequency offset is set so as to satisfy Expression (2).

In the equation (2), Δf _CEO represents a difference between the first frequency offset and the second frequency offset. f _rep represents the first frequency interval or the second frequency interval. N represents an arbitrary natural number. In the control step,
4. The optical comb according to claim 1, wherein a difference between the first frequency offset and the second frequency offset is set so as to satisfy Equation (3). 5. Control method.

In the equation (3), Δf _CEO represents a difference between 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. A first frequency mode having a first frequency offset with respect to zero on a frequency axis and a plurality of second frequencies arranged at intervals of an integral multiple 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 the first optical comb having three frequency modes, and
A plurality of second frequency modes having a second frequency offset with respect to zero on the frequency axis and a plurality of the second frequency modes on the frequency axis arranged at an integer multiple of a second frequency interval. A frequency control mechanism for controlling the second frequency offset and the second frequency interval in the second optical comb having a fourth frequency mode,
The control mechanism, 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, The first frequency offset, the second frequency offset, the first frequency interval, and the difference between the first frequency interval and the second frequency interval are represented by an integer ratio to each other. A control device for an optical comb, wherein the control device is configured to control a second frequency interval.

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