JP5836739B2 - Optical frequency measurement device - Google Patents

Description

The present invention relates to an optical frequency measurement device, at least either mode frequency and the offset frequency by a variable, continuous and dynamically variably controllable laser device the frequency of the optical frequency comb is light output The present invention relates to an optical frequency measuring device provided .

  Conventionally, there is a laser apparatus having an optical frequency comb generator that generates a plurality of spectral components (optical frequency combs) arranged in a comb shape on the frequency axis. The optical frequency comb is called a light ruler, and the mode frequency indicating the spectral interval of multiple spectral components arranged in a comb shape on the frequency axis and the zero when the arrangement of the multiple spectral components is extended to the frequency zero point. Once the offset frequency generated between the points is calibrated, it can be used as a frequency reference for the light to be measured. For this reason, various configurations for using the optical frequency comb as an optical ruler have been proposed.

  For example, in Patent Document 1, a first optical frequency comb generator and a second optical frequency comb generator are connected in series, and the output of the first optical frequency comb generator is further modulated by the second optical frequency comb generator. Yes. With such a configuration, it is possible to reduce the mode frequency while widening the generation range of the optical frequency comb output from the second optical frequency comb generator subsequent to the first optical frequency comb generator. ing. For this reason, in Patent Document 1, for example, it is possible to lower the frequency of the beat signal generated by the optical frequency comb and the measured light that are optically output for high-precision frequency measurement of the measured light.

JP 2006-293247 A

  However, in Patent Document 1, even if the mode frequency of the optical frequency comb output from the second optical frequency comb generator can be reduced, the position of each mode on the frequency axis cannot be changed continuously. For this reason, for example, when measuring the frequency of the measured light with high accuracy, it is sufficient to reduce the frequency of the beat signal generated by the optical frequency comb output from the second optical frequency comb generator and the measured light. There is a possibility that it will not be possible.

The present invention has been made to solve the above-mentioned problems, and at least one of the mode frequency and the offset frequency is made variable so that the frequency of the optical frequency comb to be output is continuously and dynamically controlled. It is an object of the present invention to provide an optical frequency measurement device including a possible laser device.

The invention according to claim 1 of the present application is an optical frequency measurement device including a laser device having first and second optical frequency comb generators that generate a plurality of spectral components arranged in a comb shape on the frequency axis, The first optical frequency comb generator performs a reference optical output based on a frequency reference, and the second optical frequency comb generator includes a mode frequency indicating at least spectral intervals of the plurality of spectral components and the plurality of spectra. It is possible to change any of the offset frequency generated between the zero point when the extended sequence of components to zero point frequency, and outputs its optical output as light output of the laser device, the first optical frequency A first photoelectric converter for detecting a first beat generated by optical heterodyne by mixing the optical output of the comb generator and the optical output of the second optical frequency comb generator; First processing for controlling the second optical frequency comb generator so that the frequency of the first beat signal output from the converter becomes a constant value and stabilizing the frequency of the optical output of the second optical frequency comb generator A second photoelectric converter for detecting a second beat generated by optical heterodyne by mixing the output light of the second optical frequency comb generator and the measured light of the measured laser light source; and the second photoelectric conversion The second beat signal output from the analyzer is analyzed, and the mode frequency and the offset frequency that can be changed are automatically changed, whereby the signal intensity, S / N ratio, and frequency of the second beat signal are changed. And the second processing control unit that obtains the optical frequency of the light to be measured based on the adjusted second beat signal .

  The invention according to claim 2 of the present application uses an atomic clock as the frequency reference.

In the invention according to claim 3 of the present application, the first processing control unit includes a counter for measuring the frequency of the first beat signal, and the frequency reference of the counter is synchronized with the output signal of the atomic clock.

In the invention according to claim 4 of the present application, at least one of the atomic clocks is calibrated by Coordinated Universal Time.

According to the present invention, by changing at least one of the mode frequency and the offset frequency, the frequency of the optical frequency comb output from the laser device can be continuously and dynamically controlled.

1 is a schematic diagram showing a schematic configuration of a laser apparatus according to a first embodiment of the present invention. Schematic diagram specifically showing the laser apparatus shown in FIG. Schematic diagram showing first and second optical frequency combs generated by first and second optical frequency comb generators (A) and (B) Schematic diagram showing an optical frequency measuring device to which the laser device shown in FIG. 2 is applied. The schematic diagram which shows the relationship between the 1st, 2nd optical frequency comb and to-be-measured light in the optical frequency measuring apparatus shown in FIG. The schematic diagram which shows the 2nd optical frequency comb which concerns on 2nd Embodiment of this invention. Schematic diagram showing the relationship between the first optical frequency comb and the measured light when the second optical frequency comb shown in FIG. 6 is used. The schematic diagram which shows the 2nd optical frequency comb which concerns on 3rd Embodiment of this invention. Schematic diagram showing the relationship between the first optical frequency comb and the measured light when the second optical frequency comb shown in FIG. 8 is used. Schematic diagram showing another optical frequency measuring device to which the laser device shown in FIG. 2 is applied.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The laser apparatus according to the first embodiment of the present invention will be described below with reference to FIGS.

  1 is a schematic diagram showing a schematic configuration of the laser device according to the first embodiment of the present invention, FIG. 2 is a schematic diagram specifically showing the laser device shown in FIG. 1, and FIG. Schematic diagrams (A) and (B) showing first and second optical frequency combs generated by the second optical frequency comb generator are shown.

  As shown in FIGS. 1 and 2, the laser apparatus 100 of the present embodiment schematically includes first and second optical frequency comb generators 102 and 106, a beam combiner (BC) 108, and a beam splitter (BS ) 110, a first photoelectric converter 112, and a first processing control unit 114.

  Each of the first and second optical frequency comb generators 102 and 106 generates ultrashort optical pulses at regular time intervals on the time axis. The amount of deviation of the optical electric field oscillation phase between the adjacent optical pulses is called carrier envelope phase offset (CEO). In addition, on the frequency axis, the first and second optical frequency comb generators 102 and 106 are each arranged in a comb shape at regular intervals over one octave as shown in FIGS. 3 (A) and 3 (B). Spectral components (modes) are generated. 3A and 3B, the vertical axis is signal intensity I and the horizontal axis is frequency f. These are referred to as first and second optical frequency combs, respectively. As shown in FIGS. 3A and 3B, the offset frequency fseo between the zero point when the arrangement is extended to the frequency zero point while maintaining the spectral interval (mode frequencies fsm, fvm) of these spectral components. fvceo is required. The offset frequencies fseo and fvceo are called carrier envelope offset frequencies fseo and fvceo, respectively, which correspond to the carrier envelope phase (CEP) in the frequency domain. The position on the frequency axis of each spectral component (each mode) of the first and second optical frequency combs is such that the mode frequencies fsm and fvm are changed by Δf, respectively, and the reference laser beam before and after the change. (The reference laser beam is not shown in the present embodiment, but may be provided in advance in the first and second optical frequency comb generators 102 and 106). May be introduced from the outside as appropriate).

  As shown in FIGS. 1 and 2, the first optical frequency comb generator 102 outputs a reference optical output based on the frequency reference (to the second optical frequency comb generator 106). That is, the first optical frequency comb generator 102 does not need to have frequency variability and is highly accurate, and the mode frequency fsm and the offset frequency fseo are fixed. For the first optical frequency comb generator 102, for example, a mode-locked (synchronized) laser (erbium-doped optical fiber amplifier doped with erbium in an optical fiber) and a band expanding fiber (highly nonlinear fiber) are used. Can do. An atomic clock 104 is used as a frequency reference for the first optical frequency comb generator 102. In other words, the frequency reference of the first optical frequency comb generator 102 is synchronized with the output signal of the atomic clock 104.

As shown in FIG. 2, the atomic clock 104 is a clock using absorption lines or emission lines in the spectrum of a specific atom or molecule such as cesium ( ¹³³ C _S ), for example, and outputs a frequency serving as a frequency reference. The atomic clock 104 is calibrated according to Coordinated Universal Time (UTC) synchronized with International Atomic Time (TAI). For this reason, the atomic clock 104 has extremely high accuracy (1 * 10 ⁻¹⁵ level) compared to the accuracy of a single atomic clock (1 * 10 ⁻¹² to 1 * 10 ⁻¹³ ). As the atomic clock 104, a more accurate (1 * 10 ⁻¹⁵ to 1 * 10 ⁻¹⁸ ) optical lattice clock or the like may be used. The Coordinated Universal Time (UTC) is leap with respect to the International Atomic Time (TAI), which is calculated based on the results of an intercomparison of about 300 atomic clocks around the world and the evaluation results of the primary frequency standards of several institutions. Second time adjustment, a time system in which the difference from universal time (determined from observations of UT1, Earth's rotation) is maintained within 0.9 seconds (Source: AIST Optical Frequency Com 2009/7 Announced on May 16 “National standard of length” is a new method-“Frequency” is improved by using optical frequency comb device-). For this reason, the first optical frequency comb generator 102 has the same accuracy as the atomic clock 104 calibrated by Coordinated Universal Time (UTC) and is extremely accurate.

  As shown in FIGS. 1 and 2, the second optical frequency comb generator 106 has a mode frequency setting function and an offset frequency setting function, and the mode frequency fvm and the offset frequency fvceo can be changed. Then, the second optical frequency comb generator 106 performs a stabilized optical output based on the optical output of the first optical frequency comb generator 102. That is, the second optical frequency comb generator 106 does not require excessive accuracy and stability as a single unit, but is based on the idea that they depend on the first optical frequency comb generator 102. As the second optical frequency comb generator 106, for example, a stabilized laser light source and a resonator in which the laser light is incident and a modulator such as an EOM can be used.

  As shown in FIGS. 1 and 2, the beam splitter 110 branches the light that has passed through the output light (second optical frequency comb) of the second optical frequency comb generator 106 into reflected light. The light transmitted through the beam splitter 110 is guided to the outside as output light of the laser device 100. That is, the optical output of the second optical frequency comb generator 106 is output as the optical output of the laser device 100 (if necessary, the optical output of the first optical frequency comb generator 102 is also output as the optical output of the laser device 100. May be output). On the other hand, the light reflected by the beam splitter 110 goes to the beam combiner 108.

  The beam combiner 108 superimposes the second optical frequency comb reflected and branched by the beam splitter 110 and the first optical frequency comb generated by the first optical frequency comb generator 102 as shown in FIGS. Mix). Then, a beat occurs between the second optical frequency comb and the first optical frequency comb due to the optical heterodyne. The beat is incident on the first photoelectric converter 112. Since the first and second optical frequency combs are mixed, many beats are generated.

  The first photoelectric converter 112 converts a beat into an electric signal (beat signal) as shown in FIGS. That is, the first photoelectric converter 112 detects the beat generated by the optical heterodyne by mixing the optical output of the first optical frequency comb generator 102 and the optical output of the second optical frequency comb generator 106. Here, the sensitivity of the first photoelectric converter 112 is higher as the beat has a lower frequency (similar to a general photoelectric converter). Therefore, the first photoelectric converter 112 can detect the lowest frequency beat (frequency fBmin (refer mainly to FIG. 5 described later)) among the many beats with an appropriate signal intensity (note that The frequency fBmin itself is observed from the frequency 0 Hz to the frequency fBmin on the frequency axis). That is, as is clear from FIG. 5, the detected beat (frequency fBmin or a frequency close thereto) is a frequency much lower than half the mode frequency fvm. For this reason, in other words, as the first photoelectric converter 112, a photoelectric converter having a narrow frequency band in which the sensitivity band (which does not require high-speed operation) is limited to a low frequency region can be used.

  As shown in FIG. 2, the first processing control unit 114 includes a signal conversion unit 116, a signal processing unit 118, and a control unit 120. The signal converter 116 removes and amplifies noise from the beat signal (frequency fBmin) output from the first photoelectric converter 112, for example, and outputs the result. The signal processing unit 118 includes a counter (not shown), for example. The atomic clock 104 is also used as a reference for the counter frequency. That is, the frequency reference of the counter is synchronized with the output signal of the atomic clock 104. The signal processing unit 118 measures the frequency fBmin of the output signal (beat signal) from the signal conversion unit 116 with a counter, and outputs the count value. For example, based on the count value output from the signal processing unit 118, the control unit 120 electrically and mechanically feedback-controls the second optical frequency comb generator 106 so that the count value becomes constant. Then, the control unit 120 stabilizes the output light of the second optical frequency comb generator 106. The frequency reference of the first optical frequency comb generator 102 is synchronized with the output signal of the atomic clock 104. At the same time, the frequency reference of the counter is also synchronized with the output signal of the atomic clock 104. Therefore, when the output light (frequency) of the second optical frequency comb generator 106 is stabilized (locked) according to the first optical frequency comb, the measurement value (measurement result) of the beat signal counter is the atomic clock. 104 is synchronized with the output signal.

  That is, the first processing control unit 114 controls the second optical frequency comb generator 106 so that the frequency fBmin of the beat signal output from the first photoelectric converter 112 becomes a constant value. Then, the optical output of the second optical frequency comb generator 106 is stabilized by the first processing control unit 114.

  Thus, in this embodiment, it has the 1st, 2nd optical frequency comb generator 102,106. However, in the present embodiment, these are not combined with each other, interfered with, or modulated, and the second optical frequency comb generator is based on the first optical frequency comb generator 102. The light output of 106 is stabilized. For this reason, the second optical frequency comb can be made as highly accurate and stable as the first optical frequency comb. Moreover, since the second optical frequency comb generator 106 can set the mode frequency fvm and the offset frequency fvceo, the laser device 100 continuously and dynamically varies the frequency of the second optical frequency comb that is the optical output. It is possible to control. That is, in the present embodiment, the position of each mode of the second optical frequency comb can be continuously changed on the frequency axis. That is, this embodiment uses a laser device (optical frequency comb generator) based on the idea of fixedly determining and using a mode frequency and an offset frequency as in the prior art, and uses a mode frequency fvm and an offset frequency fvceo. It can be said that the laser device (variable frequency optical frequency comb generator) capable of variably controlling the frequency continuously and dynamically by making it configurable (variable) has been revolutionized (advanced).

  At the same time, when the frequency is changed to about several tens of nanometers with a normal laser beam, the spectral line width is greatly deteriorated in this embodiment, compared with the case where the frequency is continuously changed. There is no degradation.

  In this embodiment, the first photoelectric converter 112 that detects the beat generated by the optical heterodyne by mixing the first optical frequency comb and the second optical frequency comb, and the beat output from the first photoelectric converter 112. A first processing control unit 114 that controls the second optical frequency comb generator 106 so that the frequency fBmin of the signal becomes a constant value, and the first processing control unit 114 controls the light of the second optical frequency comb generator 106. The output is stabilized. For this reason, the optical output of the second optical frequency comb generator 106 can be easily stabilized with the same degree of accuracy as the first optical frequency comb generator 102 with a simple configuration.

  In this embodiment, the atomic clock 104 is used as the frequency reference of the first optical frequency comb generator 102, and the frequency reference of the counter of the signal processing unit 118 is synchronized with the output signal of the atomic clock 104. The atomic clock 104 is calibrated by Coordinated Universal Time. For this reason, even if compared with the accuracy of a single atomic clock, the atomic clock of this embodiment can achieve a more accurate and stable frequency. That is, the optical output from the first optical frequency comb generator 102 is also highly accurate, and the beat signal can be measured with high accuracy. That is, the optical output of the second optical frequency comb generator 106 can be made extremely accurate.

  In the present embodiment, since the mode frequency fvm and the offset frequency fvceo can be changed, the frequency fBmin of the beat signal output from the first photoelectric converter 112 can be kept low. That is, the frequency sensitivity band for the beat of the first photoelectric converter 112 normally requires at least half of the mode frequency fvm, whereas in the present embodiment, even half of the mode frequency fvm is not required. For this reason, the first photoelectric converter 112 only needs to be sensitive to beats existing in the low frequency range, so that high-speed operation is not required. That is, the first photoelectric converter 112 can be suppressed at a low cost.

  That is, in the present embodiment, the mode frequency and the offset frequency are made variable so that the frequency of the second optical frequency comb output from the second optical frequency comb generator 106 is continuously and dynamically controlled. It becomes possible.

  An example when the optical frequency measuring device 130 is configured by the laser device 100 of the present embodiment will be described with reference to FIG.

  In addition to the laser device 100 described above, the optical frequency measurement device 130 includes a beam combiner 132, a second photoelectric converter 134, and a second processing control unit 135, as shown in FIG.

  As shown in FIG. 4, the beam combiner 132 mixes the output light (second optical frequency comb) of the second optical frequency comb generator 106 and the measured light (frequency fsub) from the measured laser light source OJ. Then, a beat (frequency fBsub) is generated between the second optical frequency comb and the light to be measured (frequency fsub) by optical heterodyne (FIG. 5). The beat (frequency fBsub) is incident on the second photoelectric converter 134.

  The second photoelectric converter 134 converts the beat into an electric signal (beat signal) as shown in FIG. That is, the second photoelectric converter 134 detects the beat generated by the optical heterodyne in which the light to be measured (frequency fsub) and the optical output of the second optical frequency comb generator 106 are mixed.

  As shown in FIG. 4, the second processing control unit 135 includes a signal analysis unit 136, an automatic adjustment value analysis unit 138, an fvm setting calculation unit 140, an fvceo setting calculation unit 142, an fvm control unit 144, and an fvceo control unit 146. Prepare.

  As shown in FIG. 4, the signal analysis unit 136 removes and amplifies the beat signal (frequency fBsub) output from the second photoelectric converter 134, and obtains a count value with a counter (not shown). May also use the atomic clock 104). Then, the signal analysis unit 136 obtains the frequency fBsub of the beat signal from the count value. Then, based on the position on the frequency axis of the mode of the second optical frequency comb mixed with the measured light (frequency fsub), the frequency fsub of the measured light is obtained.

  As shown in FIG. 4, the automatic adjustment value analysis unit 138 obtains an optimum beat signal (frequency fBsub) with respect to the frequency fsub of the light to be measured obtained by the signal analysis unit 136 by the second photoelectric converter 134. A second optical frequency comb is determined. That is, the automatic adjustment value analysis unit 138 automatically sets the position on the frequency axis of the mode of the second optical frequency comb mixed with the light to be measured (frequency fsub) so that an optimum beat signal (frequency fBsub) is obtained. To decide. Note that the optimum beat signal (frequency fBsub) here is newly determined, and is basically different from the beat signal (frequency fBsub) input to the signal analysis unit 136. The optimum beat signal is a signal output from the second photoelectric converter 134 having a high intensity and a high S / N ratio. Specifically, a signal whose frequency fBsub is as low as possible. desirable. When the frequency fBsub is too close to 0 Hz, a long period of fluctuation occurs in a short measurement time. For this reason, in the second photoelectric converter 134, for example, a corresponding high-pass filter or a DC cut circuit is provided in the amplifying section so that the frequency fBsub of the beat signal does not become too close to 0 Hz.

  As shown in FIG. 4, the fvm setting calculation unit 140 and the fvceo setting calculation unit 142 respectively have a mode frequency fvm from the position on the frequency axis of the mode of the second optical frequency comb obtained by the automatic adjustment value analysis unit 138. An offset frequency fvceo is obtained. At this time, between the fvm setting calculation unit 140 and the fvceo setting calculation unit 142 so that the frequency fBmin of the beat signal generated between the first optical frequency comb and the second optical frequency comb becomes an optimal beat signal, The mode frequency fvm and the offset frequency fvceo may be automatically adjusted. The optimal beat signal here means a signal having a high intensity and a high S / N ratio as a signal output from the first photoelectric converter 112, and specifically, its frequency fBmin is as much as possible. A low one is desirable. That is, the first photoelectric converter 112 has the same configuration as the second photoelectric converter 134, and the frequency fBmin of the beat signal is not too close to 0 Hz.

  As shown in FIG. 4, the fvm control unit 144 and the fvceo control unit 146 automatically convert the mode frequency fvm and the offset frequency fvceo obtained by the fvm setting calculation unit 140 and the fvceo setting calculation unit 142, respectively, into the second optical frequency comb. Set to generator 106.

  As described above, the second processing control unit 135 automatically adjusts the mode frequency fvm and the offset frequency fvceo of the second optical frequency comb, so that the second optical frequency comb (mode) and the light to be measured (the spectrum thereof) are obtained. Thus, an optimum beat signal (frequency fBsub) can be obtained. However, since this changes the second optical frequency comb (but not necessarily), the first processing control unit 114 performs feedback control so as to stabilize the second optical frequency comb with reference to the first optical frequency comb. I do.

  Here, when the control for stabilizing the second optical frequency comb is performed with reference to the first optical frequency comb, any mode of the first optical frequency comb is used as a reference. Stabilization control is performed using a beat with the mode of the second optical frequency comb closest to the mode of the first optical frequency comb as the reference. Of the beats generated by the first optical frequency comb and the second optical frequency comb, the beats having the lowest beat frequency, that is, the optimum beat signal are selected so as not to be the same as the previous one. That is, the mode of the first optical frequency comb that is the current reference is basically changed from the mode of the first optical frequency comb that is the previous reference. An optimum beat signal (frequency fBmin) can be obtained by the second optical frequency comb mode closest to the first optical frequency comb mode that is the current reference. In the first and second optical frequency combs, the accuracy is completely equivalent regardless of which mode is used as a reference. Thus, stable feedback control is continued without losing feedback control of the second optical frequency comb. Note that the mode of the second optical frequency comb is not necessarily the same as the previous mode (there may be the same case).

  Therefore, the optical frequency measuring device 130 performs control for stabilizing the second optical frequency comb based on the first optical frequency comb, and at the same time, beat signals (frequency fBsub) between the second optical frequency comb and the measured light. It is possible to perform control that makes the optimum.

  The frequency fBsub of the beat signal can be set to a stable and constant value (a constant frequency or a constant frequency and a low frequency) regardless of the frequency of the light to be measured, and the frequency measurement can be performed easily and with high accuracy. It can be carried out.

  Further, in the optical frequency measuring device 130, the frequency fBsub of the beat signal detected by the second photoelectric converter 134 can also be suppressed low. That is, the frequency sensitivity band of the second photoelectric converter 134 normally requires at least half of the mode frequency fvm, but here does not require even half of the mode frequency fvm. For this reason, the second photoelectric converter 134 only needs to be sensitive to beats existing in the low frequency range, so that high-speed operation is not required. That is, the second photoelectric converter 134 can also be reduced in cost.

  Further, in the optical frequency measuring device 130, the first optical frequency comb is regarded as a caliper main scale, the second optical frequency comb is regarded as a caliper vernier, and the number of modes of the first and second optical frequency combs is mutually determined. When it is slightly changed, the frequency fsub of the light to be measured can be measured with extremely high accuracy. Specifically, when the number of modes of the first and second optical frequency combs is slightly changed from each other in the same specific frequency range on the frequency axis (for example, as an example of “slightly changed”) The number of modes of the first optical frequency comb is 699, the number of modes of the second optical frequency comb is 700, etc.), and the first and second optical frequency combs are vernier functions of calipers, Similarly, it is possible to measure up to a minute frequency. Note that the specific frequency range is desirably the maximum range in which the mode can be reliably recognized without including the mode located at the end of the optical frequency comb.

  Although the present invention has been described with reference to the first embodiment, the present invention is not limited to the first embodiment. That is, it goes without saying that improvements and design changes can be made without departing from the scope of the present invention.

  In the first embodiment, the mode frequency fvm and the offset frequency fvceo can be changed, but the present invention is not limited to this. For example, the second embodiment shown in FIGS. 6 and 7 may be used. Note that the schematic configuration of the second embodiment is merely that the offset frequency fvceo is fixed in the same manner as the offset frequency fseo in the first embodiment, and therefore the symbols used for the other components are the same as those used in the first embodiment. Also, the frequencies fsub and fBsub in FIG. 7 indicate the frequency of the light to be measured and the frequency of the beat signal when the optical frequency measuring device is configured as shown in FIG.

  In the second embodiment, the offset frequency fseo and the offset frequency fvceo are equal, but the mode frequency fvm of the second optical frequency comb generator 106 is different from the mode frequency fsm of the first optical frequency comb generator 102. For this reason, as shown in FIG. 7, since a low frequency beat (such as fBmin) is always generated and detected by the first photoelectric converter 112, the frequency sensitivity band of the first photoelectric converter 112 is equal to the mode frequency fvm. Half is not needed. That is, as compared with the first embodiment, the components related to the setting of the offset frequency fvceo can be omitted, and the first photoelectric converter 112 can be reduced in cost.

  Or it may be like 3rd Embodiment shown in FIG. 8, FIG. Note that the schematic configuration of the third embodiment is merely that the mode frequency fvm is fixed in the same manner as the mode frequency fsm in the first embodiment, and therefore, the symbols used for the other components are the same as those used in the first embodiment.

  In the third embodiment, the mode frequency fsm and the mode frequency fvm are equal, but the offset frequency fvceo of the second optical frequency comb generator 106 and the offset frequency fseo of the first optical frequency comb generator 102 are different. . For this reason, as shown in FIG. 9, a low frequency beat (such as fBmin) is always generated and detected by the first photoelectric converter 112. Therefore, the frequency sensitivity band of the first photoelectric converter 112 is equal to the mode frequency fvm. Half is not needed. That is, as compared with the first embodiment, the components relating to the setting of the mode frequency fvm can be omitted, and the first photoelectric converter 112 can be reduced in cost.

  In the above embodiment, the first photoelectric converter 112 that detects the beat generated by the optical heterodyne by mixing the first optical frequency comb and the second optical frequency comb, and the beat output from the first photoelectric converter 112. A first processing control unit 114 that controls the second optical frequency comb generator 106 so that the frequency of the signal becomes a constant value, and the second optical frequency comb is stabilized by the first processing control unit 114 However, the present invention is not necessarily limited to this. For example, on the condition that the mode frequency or the offset frequency can be changed, the first optical frequency comb may be directly input to the second optical frequency comb generator to be stabilized.

  In the above embodiment, the atomic clock 104 is used as the frequency reference of the first optical frequency comb generator 102, and the frequency reference of the counter of the signal processing unit 118 is synchronized with the output signal of the atomic clock 104. Although the atomic clock 104 has been calibrated by Coordinated Universal Time, the present invention is not limited to this. For example, an atomic clock may be used for only one of the above two frequency references, or when an atomic clock is not used for the frequency reference of the first optical frequency comb generator, neither of them is used. May be. Also, atomic clocks may not be calibrated by Coordinated Universal Time.

  In the above embodiment, the accuracy is improved by directly connecting the atomic clock 104 to the first optical frequency comb generator 102, but the present invention is not limited to this. For example, an atomic clock may be provided outside a laser device (such as a GPS satellite), and an output from the atomic clock may be obtained via a GPS receiver provided in the laser device. In this case, since the atomic clock is not directly provided in the laser device, the cost of the laser device can be reduced as well as the size of the laser device.

  Moreover, in the said embodiment, although the zone | band which the 1st, 2nd optical frequency comb spreads was 1 octave or more, this invention is not limited to this. For example, the band over which the optical frequency comb extends may be smaller than one octave.

  In the above embodiment, the optical frequency measurement device 130 can automatically measure the frequency fsub of the light to be measured. However, the optical frequency measurement device 130 is, for example, another optical frequency measurement device 230 shown in FIG. There may be.

  In the optical frequency measuring device 230, the signal analysis unit 236 and the subsequent steps are performed manually. For this reason, in the optical frequency measuring device 230, the device configuration can be simplified as compared with the optical frequency measuring device 130, and cost reduction can be further promoted.

  Note that the light to be measured in the optical frequency measuring device is particularly intended for an optical frequency (wavelength) reference or a light source for interference measurement, and is measured based on an international standard or a national standard as described above. That is, the light to be measured is measured in a manner traceable to the national standard. For this reason, the optical frequency measurement device can also be understood as an optical frequency calibration device.

  Since the laser device of the present invention can continuously and dynamically variably control the frequency of a high-precision optical frequency comb, it constitutes a length master and measures the distance and the squareness as the length reference. It can be widely applied to long interferometers.

DESCRIPTION OF SYMBOLS 100 ... Laser apparatus 102, 202 ... 1st optical frequency comb generator 104, 204 ... Atomic clock 106, 206 ... 2nd optical frequency comb generator 108, 132, 208, 232 ... Beam combiner (BC)
110, 210 ... Beam splitter (BS)
112, 212 ... 1st photoelectric converter 114 ... 1st process control part 116, 216 ... Signal conversion part
118, 218 ... Signal processing unit 120, 220 ... Control unit 130, 230 ... Optical frequency measuring device 134, 234 ... Second photoelectric converter 135 ... Second processing control unit 136, 236 ... Signal analysis unit 138 ... Automatic adjustment value analysis Unit 140 ... fvm setting calculation unit 142 ... fvceo setting calculation unit 144 ... fvm control unit 146 ... fvceo control unit

Claims (4)

An optical frequency measurement device comprising a laser device having first and second optical frequency comb generators for generating a plurality of spectral components arranged in a comb shape on the frequency axis,
The first optical frequency comb generator performs a reference optical output based on a frequency reference,
The second optical frequency comb generator has an offset frequency generated between a mode frequency indicating a spectral interval of at least the plurality of spectral components and a zero point when the arrangement of the plurality of spectral components is extended to a frequency zero point. either it is changeable, and outputs its optical output as light output of the laser device,
A first photoelectric converter for detecting a first beat generated by optical heterodyne in which the optical output of the first optical frequency comb generator and the optical output of the second optical frequency comb generator are mixed;
The second optical frequency comb generator is controlled so that the frequency of the first beat signal output from the first photoelectric converter becomes a constant value, and the optical output frequency of the second optical frequency comb generator is stabilized. A first processing control unit,
A second photoelectric converter for detecting a second beat generated by optical heterodyne by mixing the output light of the second optical frequency comb generator and the measured light of the measured laser light source;
By analyzing the second beat signal output from the second photoelectric converter and automatically changing the mode frequency and the offset frequency that can be changed, the signal strength of the second beat signal, S / A second processing control unit that adjusts the N ratio and frequency, and obtains the optical frequency of the light under measurement based on the adjusted second beat signal;
Optical frequency measurement device according to claim Rukoto equipped with. 2. The optical frequency measuring device according to claim 1, wherein an atomic clock is used as the frequency reference. The optical frequency measurement device according to claim 2 , wherein the first processing control unit includes a counter that measures the frequency of the first beat signal, and the frequency reference of the counter is synchronized with an output signal of an atomic clock. . 4. The optical frequency measuring device according to claim 3 , wherein at least one of the atomic clocks is calibrated by Coordinated Universal Time.

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