JP2004340690A - Light frequency measuring instrument and measuring method using multi-color mode-locked laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light frequency measuring instrument and a measuring method having a wide range of measurable wavelengths and used for finding a carrier envelope offset frequency f<SB>ceo</SB>with a high S/N. <P>SOLUTION: The range of measurable wavelengths can be widened because of using a multi-color mode-locked laser light source 1. Further, it is not necessary to generate higher harmonic wave by means of a nonlinear optical effect after enlarging a spectrum, since this instrument is of a non-f-2f self-reference type wherein a heterodyne interference beat is detected between the other monochromatic light wave (light comb) obtained by the multiplexing of a first multiplexing means 4 and enlarged light wave (light comb), which enables to find the f<SB>ceo</SB>with a high S/N. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for measuring the optical frequency of a laser with high accuracy. More specifically, the present invention relates to an optical frequency measurement technique using an optical comb (comb) having an ultrashort pulse output from a mode-locked laser as an “optical frequency ruler”.
[0002]
At the 17th International Metrology Meeting in 1983, the unit of length "m" was defined as follows in connection with the unit of time "s": "A meter is the length of the path that light travels through a vacuum in 1 / 299,792,458 of a second." This defines the light speed c as 299,792,458 m / s. Is equivalent to Between the wavelength λ, the frequency f, and the time t,
λ = c / f (1)
f = 1 / t (2)
In order to achieve the definition of the meter faithfully, it is achieved by measuring the optical frequency of the frequency-stabilized laser and dividing the light speed defined above to obtain the vacuum wavelength. You.
[0003]
[Prior art]
When an ultrashort pulse output with a repetition pulse interval of 1 / f _rep is schematically shown on the frequency axis, it becomes a comb-like shape shown by a solid line in FIG. 7 and is called an optical comb. In FIG. 7, f _ceo is called a carrier envelope offset (CEO) frequency. When the mode-locked laser and the CW laser to be measured are subjected to heterodyne interference, a beat as shown by a dotted line in FIG. 7 (δ is an offset from the solid line optical comb) is observed. The nth comb of the solid optical comb is
f (n) = nf _rep + f _ceo (3)
It is expressed as Similarly, the nth comb of the dotted optical comb is
f _cw (n) = nf _rep + f _ceo ± δ (4)
It is expressed as In equation (4), f _rep is known, and δ is obtained from FIG. 7. Therefore, if f _ceo is determined, the optical frequency f _cw of the measured CW laser is obtained. Note that there is an ambiguity between n and ± in equation (4), but this is removed by measuring the wavelength of the laser to be measured with a normal wavelength meter or the like.
[0004]
In conventional optical frequency measurement, f _ceo is obtained as follows (for example, see Non-Patent Document 1). The spectrum of a Ti: S (titanium: sapphire) laser having a wavelength of 778 nm is extended from 500 nm to 1100 nm, which is one octave or more, using a photonic crystal fiber (FCB), and Ti is spread over one octave as shown in FIG. : Optical comb of S laser was made. Then, the 2nth comb, one octave away from the nth,
f (2n) = 2nf _rep + f _ceo (3 ′)
It is expressed as On the other hand, a low-frequency portion is cut out and a second harmonic 2f (n) is generated by a second harmonic generation crystal (BBO). Then, when the beat frequency δ ₀ is observed by heterodyne interference (f−2f interference) between the 2n-th comb f (2n) and the second harmonic 2f (n), 2f (n) is obtained from the equation (3).
_{2f (n) = 2nf rep +} 2f ceo (5)
Is expressed as
δ ₀ = 2f (n) −f (2n) = f _ceo
And f _ceo is obtained. Such a method is called an f-2f self-referenced technique.
[0005]
That is, conventionally, the f-2f self-referencing technique, that is, the fundamental wave spectrum is extended to one octave or more, and then the second harmonic is generated to cause f-2f heterodyne interference. Expanding beyond the one octave required by the conventional f-2f self-referencing technology has the problem that a high-strength (high-power) optical comb cannot be made due to FCB loss. In addition, since the second harmonic is generated by cutting out from the fundamental wave, an optical comb having an even lower intensity is obtained. If the strength is low, f _ceo cannot be obtained with a high S / N. Further, in the conventional optical frequency measurement, since the optical comb has a wavelength of 500 nm to 1100 nm as described above, it is not possible to measure the optical frequency of a 1500 nm (1.5 μm) laser in the optical communication band.
[0006]
[Non-Patent Document 1] David J. Jones et al. , "Carrier-Envelope Phase Control of Femtosecond Mode-Locked Lasers and Direct Optical Frequency Synthesis", SIENCE, Vol. 288, 28 APRIL 2000, pp635-639
[0007]
[Problems to be solved by the invention]
As described above, the conventional optical frequency measurement requires an optical comb of one octave or more, cannot obtain f _ceo with a high S / N, and has a problem that the measurable wavelength range is narrow.
[0008]
The present invention has been made in view of the above-mentioned conventional optical frequency measurement technology, and has a wide measurable wavelength range, does not require an optical comb of one octave or more, and obtains f _ceo with a high S / N. It is an object of the present invention to provide an optical frequency measuring device and a measuring method which can perform the measurement.
[0009]
[Means for Solving the Problems]
An optical frequency measurement device according to the present invention includes a multicolor mode-locked laser light source that generates a plurality of lightwaves including a fundamental wave and a multiple of the fundamental wave, and the plurality of lightwaves generated from the multicolor modelocked laser light source. A wavelength separating element that separates each monochromatic light wave, and a spectrum extending unit that extends the spectrum of one monochromatic light wave of each monochromatic light wave separated by the wavelength separating element until it overlaps with the spectrum of the other monochromatic light wave, First multiplexing means for multiplexing the other monochromatic lightwave and the lightwave extended by the extension means; and a first multiplexing means for multiplexing the other monochromatic lightwave and the extended lightwave multiplexed by the first multiplexing means. A first detector for detecting a heterodyne interference beat, and a second multiplexer for multiplexing one of the monochromatic lightwaves separated by the wavelength separation element or a part of the expanded lightwave with a lightwave to be measured. And the second multiplexing means. One of the respective monochromatic light wave, or having, a second detector for detecting the heterodyne interference beat of a portion 該被 measuring light waves of the extended light waves.
[0010]
Since the multicolor mode-locked laser light source is used, the wavelength range that can be measured can be widened. Also, since the non-f-2f self-referencing type detects a heterodyne interference beat between the other monochromatic light wave multiplexed by the first multiplexing means and the expanded light wave, the harmonics are increased by the nonlinear optical effect after the spectrum is expanded. _Does not need to be generated, f _feo can be obtained with a high S / N, and the optical frequency can be measured with high accuracy.
[0011]
The multicolor mode-locked laser light source may include a passive mode-locked laser and a multiplying unit.
[0012]
Since an ultrashort pulse generated from a passive mode-locked laser is used as a fundamental wave and multiplied by a multiplication means, the light source can be made compact, and the optical frequency measuring device including the light source can be made compact and simple. Become.
[0013]
Passive mode-locked lasers can have erbium-doped fibers.
[0014]
By using an erbium-doped fiber as a laser medium, an ultrashort pulse having a wavelength of 1.5 μm is generated from a passive mode-locked laser, which is multiplied by a multiplication means as a fundamental wave. Spread to near red 1.5 μm.
[0015]
The multiplied wave may include a second harmonic and a light wave whose frequency is tripled, wherein the one monochromatic light wave is the second harmonic and the other monochromatic light wave is the tripled light wave. .
[0016]
One monochromatic light wave that expands the spectrum is a second harmonic, and the other monochromatic light wave that heterodynes with the extended second harmonic is a light wave whose frequency is tripled, so that one monochromatic light wave (light Comb) is overlapped with the other monochromatic lightwave (light comb) only by extending it by 0.5 octave, so that the intensity drop of the expanded lightwave is suppressed and f _seo can be obtained with a high S / N. become.
[0017]
The first multiplexing means may have a delay line for delaying one of the other monochromatic lightwave to be multiplexed and the lightwave expanded by the expansion means.
[0018]
By delaying the lightwaves to be multiplexed by the delay line, the timing of the two lightwaves to be multiplexed can be adjusted to increase the contrast of the heterodyne interference beat.
[0019]
The first multiplexing means may include a polarization adjusting element for adjusting the polarization of the other monochromatic lightwave to be multiplexed and the lightwave expanded by the expansion means, and a beam splitter.
[0020]
By combining one lightwave combined by the polarization adjusting element with p-polarized light and the other lightwave as s-polarized light with a beam splitter, the intensity of both light waves for heterodyne interference can be easily adjusted, and the contrast of the interference beat can be improved. Contribute.
[0021]
The first multiplexing unit may include an intensity adjustment unit that adjusts the polarization of the other combined monochromatic lightwave and the lightwave expanded by the expansion unit to adjust the intensity of both lightwaves.
[0022]
By making the intensities of both light waves equal in the intensity adjusting unit, the contrast of the heterodyne interference beat becomes high, and f _ceo can be obtained with a high S / N.
[0023]
Further, the first multiplexing means may include a single mode fiber.
[0024]
By passing the other combined monochromatic lightwave and the lightwave expanded by the expansion means through a single mode fiber, it is possible to ensure the superposition of both lightwaves and mode matching, and the contrast of the interference beat is increased, f _ceo can be obtained with a higher S / N.
[0025]
The second multiplexing means may include a polarization adjusting element and a beam splitter for adjusting the polarization of one of the monochromatic light waves to be multiplexed or a part of the expanded light wave and the light wave to be measured.
[0026]
The polarization adjusting element combines one lightwave to be p-polarized light and the other lightwave to be s-polarized light by a beam splitter, so that the intensity of both lightwaves for heterodyne interference can be easily adjusted, thereby improving the contrast of the interference beat. To contribute.
[0027]
In addition, the second multiplexing unit includes an intensity adjusting unit that adjusts the polarization of one of the multiplexed monochromatic lightwaves or a part of the expanded lightwave and the lightwave to be measured to adjust the intensity of both lightwaves. Can also be provided.
[0028]
By making the intensities of both light waves equal in the intensity adjusting section, the contrast of the heterodyne interference beat becomes high, and δ can be obtained with a high S / N.
[0029]
Further, the second multiplexing means may include a single mode fiber.
[0030]
By passing one of the combined monochromatic lightwaves, or a part of the expanded lightwave and the lightwave to be measured through a single mode fiber, it is possible to ensure superposition and mode matching of both lightwaves, The contrast of the interference beat is increased, and δ can be obtained with a higher S / N.
[0031]
BEST MODE FOR CARRYING OUT THE INVENTION
The multicolor mode-locked laser light source that generates a plurality of light waves including a fundamental wave and a multiplied wave may be any light source that generates a plurality of light waves including a fundamental wave and a multiplied wave of the fundamental wave. It is preferable that the passive mode-locked laser includes a mode-locked laser and a multiplying means, and the passive mode-locked laser includes an erbium-doped fiber. Since an ultrashort pulse having a wavelength of 1.5 μm is generated and is multiplied by a multiplication means as a fundamental wave (basic optical comb), the measurement wavelength range is widened from visible to near red 1.5 μm.
[0032]
As the multiplying means, a non-linear crystal such as ADP, KDP, LiNbO ₃ , BBO can be used.
[0033]
A wavelength separation element that separates multiple light waves (optical combs) generated from a multicolor mode-locked laser light source into each monochromatic light wave (optical comb) combines a two-color mirror, a diffraction grating, a beam splitter, and a bandpass filter. Can be used.
[0034]
A photonic crystal fiber or the like is used as spectrum expanding means for expanding the spectrum of one monochromatic light wave of each monochromatic light wave separated by the wavelength separating element until it overlaps the spectrum of the other monochromatic light wave.
[0035]
The first multiplexing means for multiplexing the other monochromatic lightwave and the lightwave expanded by the expansion means may be any fiber coupler or the like as long as it multiplexes both lightwaves. It is preferable to have a polarization adjusting element for adjusting the polarization of both light waves, a beam splitter, an intensity adjusting section for adjusting the polarization of the combined light wave to adjust the intensity of both light waves, and a single mode fiber. By delaying with a delay line, the timing of both light waves to be combined is adjusted, one light wave combined by the polarization adjusting element is set to p-polarized light, the other light wave is set to s-polarized light, and both light waves are combined by a beam splitter. Since the intensity of both light waves is made equal by the intensity adjusting unit and the two light waves are passed through a single mode fiber, superposition of both light waves and mode matching are ensured, so that the contrast of the heterodyne interference beat can be increased.
[0036]
As the second multiplexing means for multiplexing one of the monochromatic light waves separated by the wavelength separation element and the light wave to be measured, the same as the first multiplexing means described above can be used. However, the lightwave to be measured is generally a continuous wave laser, and the time difference between the two lightwaves multiplexed by the second multiplexing means does not matter, and the delay line may be omitted.
[0037]
The delay line may be configured by arranging a plurality of mirrors at a predetermined interval, or by arranging a mirror and a cat's eye prism at a predetermined interval. As the polarization adjusting element, a polarizer, a half-wave plate, or the like can be used, but a half-wave plate is preferable because the intensity is not lost. As the beam splitter, a half mirror, a polarizing beam splitter, or the like can be used, but a polarizing beam splitter is preferable because the intensity is not lost. As the intensity adjusting unit, a combination of a polarizer, a half-wave plate, and a polarizing beam splitter can be used.
[0038]
A first detector for detecting a heterodyne interference beat between the other monochromatic lightwave multiplexed by the first multiplexing means and the expanded lightwave, and one of the monochromatic lightwaves multiplexed by the second multiplexing means to receive A photodiode, an avalanche photodiode, PM, or the like can be used as the second detector that detects the heterodyne interference beat with the measurement light wave.
[0039]
【Example】
Embodiment 1 FIG. FIG. 1 is a configuration diagram of an optical frequency measurement device according to one embodiment of the present invention.
[0040]
The optical frequency measuring apparatus of this embodiment is a multi-color mode-locked laser light source that generates a fundamental wave (optical comb) of 1.5 μm, a second harmonic (optical comb) of 780 nm, and a sum frequency (optical comb) of 520 nm. 1, a wavelength separating element 2 for converting the three colors into a single color, a spectrum expanding means 3 for expanding the spectrum of the second harmonic of 780 nm, and a second element for multiplexing the sum frequency of 520 nm and the expanded second harmonic. (1) multiplexing means 4, a first detector 5 for detecting a heterodyne interference beat signal of a sum frequency and an extended second harmonic, and a second detector 5 for multiplexing a 1.5 μm fundamental wave and a lightwave to be measured. It has a multiplexing means 6 and a second detector 7 for detecting a heterodyne interference beat signal between the fundamental wave and the lightwave to be measured.
[0041]
The multicolor mode-locked laser light source 1 has a passive mode-locked fiber laser 11 using an erbium-doped fiber as a gain medium and a multiplying means 12, and the multiplying means 12 is composed of periodically polarized LiNbO ₃ . And generates a fundamental wave of about 50 mW, a second harmonic, and a sum frequency of 1 mW or less. The pulse width of the generated ultrashort pulse is 121 fs, and the pulse repetition period frep = 49.13 MHz.
[0042]
The wavelength separation element 2 includes two-color mirrors 21 and 22. The two-color mirror 21 separates (reflects) a fundamental wave of 1.5 μm, and the next two-color mirror 22 separates (reflects) a sum frequency of 520 nm. The second harmonic of 780 nm is transmitted from the two-color mirror 22.
[0043]
The spectrum extending means 3 is a photonic crystal fiber (PCF) having a length of 50 cm from Crystal Fiber. The PCF 3 is a polarization maintaining fiber having a core diameter of 1.8 μm. The second harmonic of 780 nm transmitted from the two-color mirror 22 is bent by the mirror 102, the polarization is adjusted by the half-wave plate 103, and the light is collected. The light is coupled to the incident end of the PCF 3 by the optical lens 106. The second harmonic (optical comb) whose spectrum has been extended by 0.5 octave to the shorter wavelength side after passing through the PCF 3 is collimated by the collimator lens 106 ′, and the spectrum of 550 nm or less is separated (reflected) by the two-color mirror 104. Is done. The light wave of 550 nm to 780 nm transmitted through the two-color mirror 104 is trapped by the optical trap 104.
[0044]
The first multiplexing unit 4 includes a delay line 41, polarization adjusting elements 42a and 42b, a beam splitter 43, an intensity adjusting unit 44, and a single mode fiber 45. The delay line 41 includes a cat's eye prism 411 and a mirror 412. The polarization adjustment elements 42a and 42b are 波長 wavelength plates, the beam splitter 43 is a polarization beam splitter, and the intensity adjustment unit 44 is a polarizer. The sum frequency of 520 nm separated (reflected) by the two-color mirror 22 is delayed by the delay line 41 so as to have an optical path length equal to the second harmonic of 780 nm, and adjusted to p-polarized light by the half-wave plate 42a. , Into the polarization beam splitter 43. On the other hand, the green portion of the second harmonic separated (reflected) by the two-color mirror 104 is adjusted to s-polarized light by the half-wave plate 42b, and is incident on the polarization beam splitter 43. The p-polarized light and the s-polarized light are multiplexed by the polarization beam splitter 43, and the p-polarized light and the s-polarized light are emitted to cause heterodyne interference. The p-polarized light and the s-polarized light emitted from the polarizing beam splitter 43 are linearly polarized by the polarizer 44 so that the p-polarized light component and the s-polarized light component are equal, bent by the mirror 102, and incident on the single mode fiber 45 by the condenser lens 106. At the end, the single mode fiber 45 reliably superimposes the sum frequency (p-polarized component) and the second harmonic (s-polarized component) and performs mode matching.
[0045]
The first detector 5 is a Si photodiode and receives the superimposed sum frequency (p-polarized component) and second harmonic (s-polarized component) emitted from the single mode fiber 45 of the first multiplexing means 4. .
[0046]
The second multiplexing unit 6 is equivalent to the first multiplexing unit 4 except for the delay line 41, and includes a polarization adjusting element 61a, 61b, a beam splitter 62, an intensity adjusting unit 63, a single mode fiber 64, Consists of The polarization adjustment elements 61a and 61b are 波長 wavelength plates, the beam splitter 62 is a polarization beam splitter, and the intensity adjustment unit 63 is a polarizer. The 1.5 μm fundamental wave (optical comb) separated (reflected) by the two-color mirror 21 is adjusted to p-polarized light by the 波長 wavelength plate 61 a and is incident on the polarization beam splitter 62. On the other hand, the lightwave to be measured input from the input port 101 is adjusted to s-polarized light by the half-wave plate 61b, and is input to the polarization beam splitter 62. The p-polarized light and the s-polarized light are multiplexed by the polarization beam splitter 62, and the p-polarized light and the s-polarized light are emitted to cause heterodyne interference. The p-polarized light and the s-polarized light emitted from the polarization beam splitter 62 are linearly polarized by the polarizer 63 so that the p-polarized component and the s-polarized component are equal, bent by the mirror 102, and incident on the single mode fiber 64 by the condenser lens 106. At the end, the superposition of the fundamental wave (p-polarized component) and the measured light wave (s-polarized component) and the mode matching are reliably performed by the single mode fiber 64.
[0047]
The second detector 7 receives the superimposed fundamental wave (p-polarized component) and the lightwave to be measured (s-polarized component) emitted from the single mode fiber 64 of the second multiplexing means 4 with a Si photodiode.
[0048]
The optical frequency of an external resonator type continuous wave semiconductor laser having a wavelength of 1.5 μm was measured by the optical frequency measuring apparatus of the present embodiment. FIGS. 2 and 3 show the results of measurement when a 1.5 μm light wave to be measured is incident from the input port 101, FIG. 2 shows the beat signal spectrum obtained by analyzing the output of the first detector 5 with a spectrum analyzer, and FIG. 2 is a beat signal spectrum obtained by analyzing the output of the detector 7 with a spectrum analyzer.
[0049]
It can be seen from FIG. 2 that f _ceo = 17.4 MHz, and from FIG. 3 that δ _1.5 = 18.7 MHz. Therefore, if only an integer n is determined using a normal wavelength meter or the like, f _1.5 is determined from equation (4). That is, the optical frequency measuring apparatus of the present embodiment measures the optical frequency with high accuracy because the f _ceo is not obtained by the f-2f self-referencing type as in the conventional case, and the spectrum only needs to be extended by 0.5 octave. We were able to.
[0050]
Embodiment 2. FIG. FIG. 4 is a configuration diagram of the optical frequency measurement device according to the second embodiment of the present invention. Although the optical frequency measuring device of the first embodiment can measure only the optical communication wavelength band of 1.5 μm, the measuring device of the second embodiment also has an optical frequency of 520 nm to 780 nm in the visible wavelength region in addition to 1.5 μm. It is one that can be measured. Therefore, two pairs (6 ′ and 7 ′, 6 ″ and 7 ″) of the second multiplexing unit 6 and the second detector 7 of the first embodiment (FIG. 1) are further provided.
[0051]
In FIG. 4, the same components as those in the first embodiment are denoted by the same reference numerals as those in FIG. In order to measure an optical frequency of 520 nm to 550 nm, the second harmonic (from the sum frequency (p-polarized component) and the second harmonic (s-polarized component) emitted from the polarization beam splitter 43 of the first multiplexing means 4 is used. It is necessary to separate the s-polarized light component), and the intensity adjusting unit 44 of the first embodiment includes a half-wave plate 441 and a polarizing beam splitter 442. In order to measure an optical frequency of 550 nm to 780 nm, the optical trap 105 of the first embodiment (FIG. 1) is replaced with a mirror 102 and a light wave (optical comb) of 550 nm to 780 nm transmitted through a two-color mirror 104 is used as a second light. The light is incident on the multiplexing means 6 '.
[0052]
The optical frequency of the external-cavity continuous-wave semiconductor laser having a wavelength of 780 nm and the optical frequency of a frequency-stabilized YAG laser having a wavelength of 532 nm were measured by the optical frequency measuring apparatus of this embodiment. FIGS. 5 and 6 show the results of measuring a lightwave to be measured of 780 nm from the input port 101 ′ and a lightwave of 532 nm from the input port 101 ″, and FIG. 5 shows the spectrum of the output of the second detector 7 ′. 6 is a beat signal spectrum analyzed by an analyzer, and FIG. 6 is a beat signal spectrum obtained by analyzing the output of the second detector 7 ″ by a spectrum analyzer.
[0053]
From FIG. 5, δ ₇₈₀ = 19.8 MHz, and from FIG. 6, δ ₅₃₂ = 16.5 MHz. If only an integer n is determined using a normal wavelength meter or the like, f ₇₈₀ and f ₅₃₂ can be obtained from equation (4).
[0054]
As described above, the single optical frequency measuring device of the second embodiment can measure the optical frequency from 520 nm visible light to 1.5 μm near infrared light.
[0055]
【The invention's effect】
As described above, the optical frequency measuring device of the present invention uses the multicolor mode-locked laser light source, so that the measurable wavelength range can be widened. Also, since the non-f-2f self-referencing type detects a heterodyne interference beat between the other monochromatic light wave multiplexed by the first multiplexing means and the expanded light wave, the harmonics are increased by the nonlinear optical effect after the spectrum is expanded. _Does not need to be generated, f _feo can be obtained with a high S / N, and the optical frequency can be measured with high accuracy.
[0056]
Further, since the multicolor mode-locked laser light source can have a passive mode-locked laser and a multiplying unit, an ultrashort pulse generated from the passive mode-locked laser is used as a fundamental wave, and the fundamental wave is used by the multiplying unit. Since the multiplication is performed, the light source can be made compact, and the optical frequency measurement device including the light source can be made small and simple.
[0057]
Further, since the passive mode-locked laser can have an erbium-doped fiber, an ultrashort pulse having a wavelength of 1.5 μm is generated from the passive mode-locked laser. Because the frequency is multiplied, the measurement wavelength range extends from visible to near red 1.5 μm.
[0058]
The multiplied wave includes a second harmonic and a light wave whose frequency is tripled, wherein the one monochromatic light wave is the second harmonic wave and the other monochromatic light wave is the triple light wave. . One monochromatic lightwave that expands the spectrum is the second harmonic, and the other monochromatic lightwave that heterodynes with the expanded second harmonic is a lightwave whose frequency is tripled. Since only the extension by 0.5 octaves overlaps with the other monochromatic light wave, a decrease in the intensity of the expanded light wave is suppressed, and f _seo can be obtained with a high S / N.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical frequency measurement device using a multicolor mode-locked laser according to a first embodiment.
FIG. 2 is a beat signal spectrum for _obtaining a carrier envelope offset frequency f _ceo observed by the optical frequency measurement device of the first embodiment.
FIG. 3 is a beat signal spectrum for obtaining an offset frequency δ _1.5 of a measured light wave having a wavelength of 1.5 μm, which is observed by the optical frequency measuring device of the first embodiment.
FIG. 4 is a schematic configuration diagram of an optical frequency measurement device using a multicolor mode-locked laser according to a second embodiment.
FIG. 5 is a beat signal spectrum for obtaining an offset frequency δ ₇₈₀ of a measured light wave having a wavelength of 780 nm, which is observed by the optical frequency measuring device of the second embodiment.
FIG. 6 is a beat signal spectrum for obtaining an offset frequency δ ₅₃₂ of a measured light wave having a wavelength of 532 nm, which is observed by the optical frequency measuring device of the second embodiment.
FIG. 7: Observation of f _{ceo in} the conventional self-reference type [Explanation of symbols]
1 Multicolor mode-locked laser light source 2 Wavelength separation element 3 ·········· Spectrum expansion means 4 ······ First multiplexing means 5 ··· ..First detectors 6, 6 ', 6 "... second combining means 7, 7', 7" ... ················································ Multiplication means 41 delay lines 42a, 42b, 61a, 61b, 61'a, 61'b, 61''a, 61''b polarization adjusting element 43,62,62 ', 62''... beam splitters 44,63,63', 6 '' ............ strength adjusting portions 45,64,64 ', 64''............ single mode fiber

Claims (21)

A multicolor mode-locked laser light source that generates a plurality of light waves including a fundamental wave and a multiple of the fundamental wave,
A wavelength separation element that separates the plurality of light waves generated from the multicolor mode-locked laser light source into respective monochromatic light waves,
Spectrum extending means for extending the spectrum of one monochromatic light wave of each monochromatic light wave separated by the wavelength separating element until overlapping with the spectrum of the other monochromatic light wave,
First multiplexing means for multiplexing the other monochromatic lightwave and the lightwave extended by the extension means;
A first detector for detecting a heterodyne interference beat between the other monochromatic lightwave multiplexed by the first multiplexing means and the extended lightwave;
Second multiplexing means for multiplexing one of the monochromatic lightwaves separated by the wavelength separation element, or a part of the expanded lightwave and the lightwave to be measured,
A second detector for detecting a heterodyne interference beat between one of the monochromatic light waves or a part of the expanded light wave and the light wave to be measured, multiplexed by the second multiplexing means;
And a carrier envelope offset (CEO) frequency f _ceo is obtained from the interference beat detected by the first detector, and an offset frequency δ is obtained from the interference beat detected by the second detector. An optical frequency measuring device for measuring an optical frequency of an optical wave. The optical frequency measuring apparatus according to claim 1, wherein the multicolor mode-locked laser light source includes a passive mode-locked laser and a multiplying unit. The optical frequency measurement device according to claim 2, wherein the passive mode-locked laser includes an erbium-doped fiber. The multiplied wave includes a second harmonic and a light wave whose frequency is tripled, wherein the one monochromatic light wave is the second harmonic and the other monochromatic light wave is the tripled light wave. The optical frequency measurement device according to claim 1. 5. The device according to claim 1, wherein the first multiplexing unit includes a delay line that delays one of the other monochromatic lightwave to be multiplexed and the lightwave expanded by the expansion unit. 6. An optical frequency measurement device according to the item. The first multiplexing means has a polarization adjusting element for adjusting the polarization of the other monochromatic lightwave to be multiplexed and the lightwave expanded by the expansion means, and a beam splitter. 6. The optical frequency measurement device according to any one of 5. The first multiplexing unit has an intensity adjusting unit that adjusts the polarization of the other monochromatic lightwave combined with the lightwave expanded by the expansion unit to adjust the intensity of both lightwaves. The optical frequency measurement device according to claim 1. The said 1st multiplexing means has a single mode fiber which ensures the superposition and mode matching of the other monochromatic lightwave multiplexed and the lightwave expanded by the expansion means. 8. The optical frequency measurement device according to any one of items 7 to 7. The second multiplexing unit may include a polarization adjusting element and a beam splitter that adjust polarization of one of the monochromatic light waves to be multiplexed or a part of the extended light wave and the light wave to be measured. The optical frequency measurement device according to any one of claims 1 to 8, wherein The second multiplexing means adjusts the polarization of one of the multiplexed monochromatic lightwaves or a part of the expanded lightwave and the lightwave to be measured to adjust the intensity of both lightwaves. The optical frequency measurement device according to any one of claims 1 to 9, further comprising a unit. The second multiplexing unit includes a single mode fiber that ensures superposition and mode matching of one of the multiplexed monochromatic lightwaves or a part of the extended lightwave and the lightwave to be measured. The optical frequency measurement device according to any one of claims 1 to 10, wherein: Generating a plurality of light waves including a fundamental wave and a multiplied wave of the fundamental wave;
Separating the plurality of light waves into monochromatic light waves;
Extending 3 the spectrum of one monochromatic lightwave of each monochromatic lightwave until it overlaps the spectrum of the other monochromatic lightwave;
Combining the other monochromatic lightwave and the lightwave extended in step 3 to cause heterodyne interference;
Detecting a heterodyne interference beat between the other monochromatic lightwave and the extended lightwave to determine a carrier envelope offset frequency _fceo of a frequency spectrum of each monochromatic lightwave;
Step 6 of combining one of the monochromatic light waves or a part of the expanded light wave with the light wave to be measured to cause heterodyne interference,
A heterodyne interference beat between one of the monochromatic lightwaves or a part of the expanded lightwave and the lightwave to be measured is detected to determine an offset frequency δ, and the frequency of the lightwave to be measured is measured using the f _ceo. Step 7 to do
An optical frequency measurement method, comprising: 13. The optical frequency measuring method according to claim 12, wherein the step 1 includes a sub-step 11 for generating a fundamental wave and a sub-step 12 for multiplying the fundamental wave by a nonlinear optical effect. The fundamental wave includes a light wave having a wavelength of 1.5 μm, the multiplied wave includes a second harmonic having a wavelength of 780 nm and a sum frequency having a wavelength of 520 nm, and the one monochromatic light wave includes the second harmonic. 14. The optical frequency measuring method according to claim 12, wherein the other monochromatic light wave is the sum frequency. The method according to any one of claims 12 to 14, wherein the step (4) includes a sub-step (41) for delaying one of the other monochromatic light wave to be multiplexed and the light wave extended in the step (3). The described optical frequency measurement method. 16. The method according to claim 12, wherein the step (4) comprises a sub-step (42) for adjusting a polarization of the other monochromatic light wave to be multiplexed and the light wave expanded in the step (3). The described optical frequency measurement method. 13. The method as claimed in claim 12, wherein the step (4) includes a sub-step (43) of adjusting the polarization of the combined monochromatic light wave and the light wave expanded in the step (3) to adjust the intensity of both light waves. 17. The optical frequency measurement method according to any one of items 16 to 16. 18. The method according to claim 12, wherein the step (4) includes a sub-step (44) for ensuring superposition and mode matching of the combined other monochromatic light wave and the light wave extended in the step (3). The optical frequency measurement method according to claim 1. 13. The method according to claim 12, wherein the step (6) includes a sub-step (61) of adjusting a polarization of one of the monochromatic light waves to be combined or a part of the extended light wave and the light wave to be measured. 19. The optical frequency measurement method according to any one of items 18 to 18. Step 6 includes a sub-step 62 of adjusting the polarization of one of the multiplexed monochromatic lightwaves or a part of the extended lightwave and the lightwave to be measured to adjust the intensity of both lightwaves. 20. The optical frequency measurement method according to claim 12, wherein: 21. The method according to claim 12, wherein the step (6) includes a sub-step (63) for ensuring superposition and mode matching of one of the multiplexed monochromatic light waves and the light wave to be measured. The optical frequency measurement method according to the paragraph.

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