WO2015045266A1 - Measurement device - Google Patents

Abstract

The present invention expands the measurement band of a measurement device having a spectroscopic optical system, simplifies a control system for the measurement device, and reduces the cost of the measurement device. Provided is a measurement device for measuring the transmission characteristics or reflection characteristics of a sample to be measured, wherein: the measurement device is provided with a frequency comb light source for outputting comb light including a plurality of light modes having a constant frequency interval, a spectroscopic optical system that receives the comb light and decomposes the plurality of light modes in the comb light into individual frequencies, and a photodetector for detecting the intensity of at least one light mode from among the plurality of light modes extracted from the spectroscopic optical system; a single light mode having the intensity thereof detected by the photodetector passes through or is reflected by the sample to be measured, which is disposed between the comb light source output and the photodetector input; and the frequency interval between the comb light modes is larger than the optical frequency resolution of the spectroscopic optical system.

Description

measuring device

The present invention relates to a measuring apparatus.

FIG. 25 shows a conventional measuring apparatus 1400 provided with a frequency comb light source. Using the measurement apparatus 1400, the optical frequency response characteristic of the sample 1420 to be measured can be measured. The measurement apparatus 1400 includes a frequency comb light source 1402 whose mode light interval is on the order of 10 GHz, an interleaver 1408 that generates a plurality of low density frequency comb lights, and a low density frequency comb light emitted from the interleaver 1408. An optical switch 1410 to be selected, an EDFA (optical amplifier) 1412 that amplifies the light emitted from the optical switch 1410, and a variable optical filter 1414 that extracts one mode light out of the light emitted from the optical amplifier 1412 are provided.

In the measurement apparatus 1400, one mode light (frequency f _m ) transmitted through the variable optical filter 1414 is swept by the frequency shifter 1416 on the optical frequency axis by a frequency f on the order of MHz. The one mode light thus swept passes through the sample to be measured 1420 and enters the high-speed photodetector 1422. In addition to the swept one mode light, the light emitted from the variable wavelength laser 1430 is also incident on the high-speed photodetector 1422. The output of the high-speed photodetector 1422 is output to the optical power meter 1428 through the electric amplifier 1424 and the low-pass filter 1426. Thereby, the swept one mode light is optically heterodyne detected by the light emitted from the variable wavelength laser 1430.

In the measuring apparatus 1400, one mode light out of the comb light output from the frequency comb light source 1402 is taken out and changed by frequency sweeping in the order of MHz by the frequency shifter 1416. Therefore, the incident light on the sample 1420 to be measured can be controlled on the order of MHz. Further, since the mode interval is widened by using one or two interleavers 1408, one mode light can be selected even for a comb light source having a mode interval smaller than the resolution of the variable optical filter 1414. Furthermore, the intensity and frequency of light transmitted through the sample 1420 to be measured can be measured by optical heterodyne detection. Therefore, the measuring apparatus 1400 has a resolution on the order of MHz with respect to the response characteristics of the sample 1420 to be measured with respect to the optical frequency (see, for example, Patent Document 1).
[Prior art documents]
[Patent Literature]
[Patent Document 1] JP 2011-017649 A

However, in the measuring apparatus 1400, an interleaver 1408, an optical switch 1410, and a variable optical filter 1414 are used to widen the mode interval of comb light and extract only one mode light. Further, in order to make the mode interval larger than the resolution of the variable optical filter 1414, the interleaver 1408 is used in one or two stages. An optical amplifier (EDFA) 1412 is necessary to compensate for the loss of these components. Since the usable wavelength band of these components is 1520 to 1570 nm which is a communication wavelength band, there is a problem that the measurement band is limited to this wavelength band. Also, one low density frequency comb light must be sequentially selected by the optical switch 1410 from the low density frequency comb light distributed by the interleaver 1408. Therefore, there is a problem that measurement takes time. Furthermore, since the measuring apparatus 1400 requires a wavelength tunable laser for optical heterodyne detection, there is a problem that the control system of the measuring apparatus is complicated and the measuring apparatus is expensive.

In the first aspect of the present invention, a measurement apparatus for measuring transmission characteristics or reflection characteristics of a sample to be measured, a frequency comb light source that outputs comb light including a plurality of mode lights having a constant frequency interval; Spectral optical system that receives comb light and frequency-resolves each mode light of the comb light one by one, and light detection that detects the intensity of at least one mode light out of the plurality of mode lights extracted from the spectroscopic optical system A mode light whose intensity is detected by the photodetector is transmitted or reflected from a sample to be measured disposed between the output of the comb light source and the input of the photodetector, and the mode of the comb light The spacing frequency provides a measuring device that is greater than the optical frequency resolution of the spectroscopic optical system.

According to a second aspect of the present invention, there is provided a measuring apparatus for measuring transmission characteristics or reflection characteristics of a sample to be measured by heterodyne detection, wherein the comb light source outputs comb light including a plurality of mode lights having different frequencies, The comb light source includes a dual comb light receiver that is combined and inputted with two types of comb light that are output from the comb light source and become comb light having different mode interval frequencies, and the comb light source includes a plurality of adjacent modes in the comb light. A pulse light source that outputs an optical pulse that has the same interval as the mode interval frequency, which is the frequency interval of light, and includes a smaller number of mode lights than the comb light, and a frequency band in which the mode light exists from the optical pulse The band expanding unit that generates the expanded comb light based on the optical pulse and the frequency of the optical pulse output from the pulse light source are shifted in a range narrower than the mode interval frequency. And a frequency shifter that collectively shifts the frequency of each mode light of the comb light, the pulse light source is a continuous wave laser that outputs continuous light, and the frequency of the continuous light according to the mode interval frequency. A first optical modulator and a second optical modulator that generate seed-comb light including a plurality of mode lights by modulating the frequency, and adjusting the phase and amplitude of each mode light in the seed-comb light; An optical pulse synthesizing unit that synthesizes the pulses, the continuous light is branched into two, and is incident on the first optical modulator and the second optical modulator, respectively, and the first optical modulator interval frequency generates a seed com light comb light f _1, the second optical modulator, the mode spacing frequency generates a seed com light comb light f _2, the difference between f ₁ and f ₂ are , smaller than either of _{f 1} and _{f 2,} the mode spacing frequency of _{f 1} comb light One or both of the called mode interval frequency comb light f ₂ is, are transmitted through or reflected by the measured sample, the mode spacing frequency is comb light and the mode spacing frequency of f ₁ multiplexing and comb light f ₂ And a measuring device that is incident on the dual comb receiver.

According to a third aspect of the present invention, there is provided a measuring apparatus for measuring an emission spectrum of a light source to be measured by heterodyne detection, a comb light source that outputs comb light including a plurality of mode lights having different frequencies, and the comb light is input. And a spectroscopic optical system that extracts only one designated mode light out of a plurality of mode lights in the comb light, and a single mode light extracted from the spectroscopic optical system and the measured light of the measured light source are combined. And a photodetector for detecting the intensity of the emitted light, and a mode interval frequency which is a frequency interval between adjacent mode lights in the comb light is larger than the optical frequency resolution of the spectroscopic optical system.

According to a fourth aspect of the present invention, there is provided a measuring apparatus for measuring an emission spectrum of a light source to be measured by heterodyne detection, a comb light source that outputs comb light including a plurality of mode lights having different frequencies, the comb light, There is provided a measuring apparatus including a photodetector for detecting the intensity of light combined with light to be measured from a measurement light source, and an electric spectrum analyzer to which an output of the photodetector is input.

Note that the above summary of the invention does not enumerate all the necessary features of the present invention. In addition, a sub-combination of these feature groups can also be an invention.

It is a figure showing measuring device 100 in a 1st embodiment. It is a figure which shows the mode light of the comb disperse | distributed and imaged on the surface of the output slit 58 in FIG. It is a figure which shows the measuring apparatus 105 which is a modification of 1st Embodiment. It is a figure which shows the measuring apparatus 200 in 2nd Embodiment. It is a figure which shows that the SSB modulator 14 shifts the frequency of one laser beam. 3 is a diagram illustrating comb light that is frequency-shifted by an SSB modulator 14. FIG. It is a figure which shows the frequency comb light source 10 which has the short pulse light source 12 using the optical pulse synthesizer 24. FIG. It is a figure which shows the frequency comb light source 10 which has the short pulse light source 12 using the dispersion | distribution provision device 21. FIG. It is a figure which shows the measuring apparatus 300 in 3rd Embodiment. It is a figure which shows the measuring apparatus 400 in 4th Embodiment. It is a figure which shows the measuring apparatus 500 in 5th Embodiment. It is a figure which shows the change of the spectrum in the case of the dual comb spectroscopy using two paths. It is a figure which shows the measuring apparatus 550 which is a modification of 5th Embodiment. It is a figure which shows a mode that the SSB modulator 34-2 shifts comb light on an optical frequency axis. It is a figure which shows the measuring apparatus 600 in 6th Embodiment. It is a figure which shows the measuring apparatus 700 in 7th Embodiment. It is a figure which shows the change of the spectrum in the case of the dual comb spectroscopy using one path | route. It is a figure which shows the measuring apparatus 800 in 8th Embodiment. It is a figure which shows the principle of the optical frequency measurement in 8th Embodiment. It is a figure which shows the measuring apparatus 900 in 9th Embodiment. It is a figure which shows the measuring apparatus 1000 in 10th Embodiment. It is a figure which shows the measuring device 1100 and measuring device 1106 in 11th Embodiment. This is a measuring apparatus including a white lamp 1204 and a spectroscopic optical system 1220. It is a measuring apparatus provided with a wavelength variable laser light source. It is the conventional measuring device provided with a frequency comb light source.

Hereinafter, the present invention will be described through embodiments of the invention. However, the following embodiments do not limit the invention according to the claims. In addition, not all the combinations of features described in the embodiments are essential for the solving means of the invention.

FIG. 1 is a diagram showing a measuring apparatus 100 according to the first embodiment. The measuring apparatus 100 measures the transmission characteristic or reflection characteristic of the sample 40 to be measured. The measuring apparatus 100 includes a frequency comb light source 10, a spectroscopic optical system 50, a single photoelectric conversion element 60 as a photodetector, an AD converter 70, a drive circuit 80, and a processor 90 as a control unit.

The light emitted from the frequency comb light source 10 is input to the sample to be measured 40 via the collimating lens 35. Light output from the sample to be measured 40 is input to the spectroscopic optical system 50 via the collimating lens 45. The light output from the spectroscopic optical system 50 is input to a single photoelectric conversion element 60. The single photoelectric conversion element 60 is, for example, a photodiode. When a single photoelectric conversion element 60 is used, the output of the single photoelectric conversion element 60 is input to the processor 90 via the AD converter 70. The processor 90 takes in a signal output from the AD converter 70 and sends a control signal to the drive circuit. The drive circuit 80 controls the rotation angle of the diffraction grating 55 in the spectroscopic optical system 50 based on the control signal.

The frequency comb light source 10 outputs comb light called super continuum light. The frequency comb light source 10 outputs a short pulse light source 12 as a pulse light source, an EDFA (Erbium-Doped Optical Fiber Amplifier) 16 that amplifies the light intensity of the light pulse of the short pulse light source 12, and an EDFA 16 And a HNLF (Highly-Nonlinear Fiber) 18 as a band expanding unit that expands the optical frequency band of the optical pulse to be transmitted.

The short pulse light source 12 generates a light pulse. The frequency comb light source 10 generates comb light having a mode interval frequency equal to the repetition frequency of the optical pulse output from the short pulse light source 12. In this specification, the mode interval frequency refers to a frequency interval between a plurality of adjacent mode lights in the comb light. In this example, if the repetition frequency of the optical pulse output from the short pulse light source 12 is 12.5 GHz, the frequency interval of the plurality of mode lights is 12.5 GHz. The optical pulse is an optical pulse having a center wavelength of 1.55 μm and a spread of about 10 nm in the wavelength band. The light pulse output from the short pulse light source 12 is input to the EDFA 16.

The EDFA 16 amplifies the light intensity of the light pulse output from the short pulse light source 12. The light pulse emitted from the EDFA 16 is input to the HNLF 18.

The HNLF 18 generates comb light called supercontinuum light having a mode interval frequency equal to the repetition frequency of the optical pulse. Comb light in which the frequency band in which mode light exists is expanded from the optical pulse is generated based on the optical pulse. For example, the HNLF 18 expands an optical pulse having a spread of about 10 nm in the wavelength band to about several hundred nm. Accordingly, the HNLF 18 outputs comb light including a plurality of mode lights having different frequencies in a wavelength band (frequency band) wider than the input optical pulse. The HNLF 18 may be a silica-based optical fiber to which GeO ₂ or the like is added, or a photonic crystal fiber in which holes are periodically arranged in a cross section. Comb light emitted from the HNLF 18 enters the spectroscopic optical system 50 via the collimator lens 45.

The comb light transmitted through the sample to be measured is input to the spectroscopic optical system 50 (transmission optical system). Note that comb light reflected from the sample to be measured may be input to the spectroscopic optical system 50 (reflection optical system). In the case of a reflective optical system, the light emitted from the collimating lens 35 is reflected by the mirror 42 and input to the sample 40 to be measured. Then, the light reflected from the measurement sample 40 is input to the collimating lens 45 through the mirror 42.

The spectroscopic optical system 50 receives comb light transmitted through the sample to be measured or comb light reflected from the sample to be measured, and extracts only one designated mode light from a plurality of mode lights in the comb light. The spectroscopic optical system 50 outputs an incident slit 52 to which comb light is input, a collimator lens 54 to which light transmitted through the incident slit 52 is input, a diffraction grating 55 that diffracts the comb light transmitted through the collimator lens 54, and a lens 56. And an exit slit 58 that transmits the transmitted light. The diffracted comb light forms an image of the mode light spectrum on the surface of the exit slit 58 via the lens 56.

Of the spectrum of mode light imaged on the surface of the exit slit 58, only one mode light determined according to the angle of the diffraction grating 55 passes through the exit slit 58 and exits to the single photoelectric conversion element 60. To do.

Also, the mode interval frequency in the comb light is strictly determined at the stage where the comb light is generated. Therefore, by adjusting the rotation angle of the diffraction grating 55, one mode light can be acquired via the exit slit 58, and the frequency of the mode light is strictly determined. Thereby, by adjusting the rotation angle of the diffraction grating 55, it is possible to measure the optical frequency response characteristic for each mode frequency interval for the sample to be measured.

The single photoelectric conversion element 60 detects the intensity of one mode light extracted from the spectroscopic optical system 50. The one mode light is light that is transmitted or reflected through the measurement sample 40 arranged between the output of the frequency comb light source 10 and the input of the single photoelectric conversion element 60. The single photoelectric conversion element 60 converts the intensity of one mode light emitted from the emission slit 58 into an analog electric signal according to time. The analog electric signal is converted by the AD converter 70 into a digital electric signal. The digital electric signal is input to the processor 90 as a light intensity signal.

The processor 90 receives the light intensity signal and controls the drive circuit 80. The processor 90 has information on the rotation angle of the diffraction grating 55 in advance. Therefore, the processor 90 has in advance information on the frequency of one mode light emitted from the exit slit 58 based on the information on the rotation angle. The processor 90 knows the frequency spectrum obtained from the spectroscopic optical system 50 based on the frequency information of the one mode light and the light intensity signal obtained from the AD converter 70.

The processor 90 further designates the mode light extracted from the spectroscopic optical system 50 after the measurement using one mode light from the spectroscopic optical system 50 is completed. For example, the processor 90 may specify mode light having a frequency that is higher or lower than one mode light that has already been observed.

The processor 90 transmits a control signal for controlling the rotation angle of the diffraction grating 55 to the drive circuit 80 in order to sequentially extract only one mode light among the plurality of mode lights in the comb light. The drive circuit 80 receives the control signal and adjusts the rotation angle of the diffraction grating 55. The rotation angle of the diffraction grating 55 may be an angle of the incident light surface of the diffraction grating 55 with respect to the parallel light emitted from the collimating lens 54.

The comb light used in this example can be a near infrared band having a wavelength band of 1.2 to 1.8 μm, for example. That is, the wavelength band of the measuring device can be expanded as compared with the conventional measuring device. Further, in the measuring apparatus 100 of this example, a wavelength tunable laser for optical heterodyne detection is not necessary. Therefore, the control system is simplified as compared with the conventional measuring apparatus. Therefore, the measuring device itself can be manufactured at a low cost.

FIG. 2 is a view showing the mode light of the comb that is split and imaged on the surface of the exit slit 58 in FIG. The relationship between the frequency interval of the comb light and the optical frequency resolution of the spectroscopic optical system 50 is shown. The sharp spectrum is the original spectrum of the mode light of the optical comb. The spectrum that is gentler than that of the mode light is a spectrum of the mode light that has been expanded to the resolution by the spectroscopic optical system 50.

The light diffracted by the diffraction grating 55 is emitted at an angle corresponding to the frequency. The exit slit 58 allows light in a predetermined frequency range to pass through the light diffracted by the diffraction grating 55. In this example, the optical frequency resolution of the spectroscopic optical system 50 indicates the width of the frequency range through which the exit slit 58 passes light. By rotating the diffraction grating 55 relative to the exit slit 58, the frequency of light passing through the exit slit 58 changes.

The comb light is diffracted by the diffraction grating 55, and the spectrum of the mode light is developed on the exit slit surface. If the mode interval frequency is not greater than the optical frequency resolution of the spectroscopic optical system 50, only one mode light cannot be extracted from the exit slit 58. For example, the mode interval frequency is at least twice the optical frequency resolution of the spectroscopic optical system 50. Desirably, the mode interval of the mode light is 3 to 4 times the optical frequency resolution of the spectroscopic optical system 50.

In this example, the mode interval of mode light is 12.5 GHz. In general, in a high-performance spectroscope, the optical frequency resolution of the spectroscopic optical system 50 including the diffraction grating 55, the entrance slit 52, and the exit slit 58 is about 4 GHz for light having a wavelength of 1500 nm. Therefore, the mode interval frequency of the mode light in this example is about three times the optical frequency resolution of the spectroscopic optical system 50. Therefore, even with the spectroscopic optical system 50 of the present example having an optical frequency resolution of about 4 GHz, a plurality of mode lights in the comb light can be extracted independently.

FIG. 3 is a diagram showing a measuring apparatus 105 which is a modification of the first embodiment. In this example, an image sensor 62 is used as the photodetector instead of the single photoelectric conversion element 60. The output of the image sensor 62 is processed by the image processing circuit 72 and output to the processor 90. In this example, unlike the example of the first embodiment (FIG. 1), the exit slit 58 is not used.

The image sensor 62 has a plurality of photoelectric conversion elements arranged in an array. The spectra of the plurality of mode lights emitted from the diffraction grating 55 are incident on different photoelectric conversion elements in the image sensor 62, respectively. Accordingly, the image sensor 62 detects in parallel the intensity of the plurality of mode lights output from the spectroscopic optical system 50 as analog electric signals. The image processing circuit 72 converts analog electrical signals detected in parallel by the image sensor 62 into digital electrical signals and outputs them to the processor 90. Note that the image sensor 62 may have both the photoelectric conversion function of the image sensor 62 and the analog-digital conversion function of the image processing circuit 72.

In this example, the intensity of each mode light can be measured without the exit slit 58. Further, since the exit slit 58 is not used, the diffraction grating 55 may be fixed. Therefore, in this example, the drive circuit 80 for driving the diffraction grating 55 may not be provided, but a drive circuit may be provided for rotating the diffraction grating for coarse adjustment. Therefore, compared with the first embodiment (FIG. 1), the configuration can be simplified. Moreover, since the spectrum of several mode light can be acquired simultaneously, measurement speed can be raised.

FIG. 4 is a diagram showing a measuring apparatus 200 according to the second embodiment. The frequency comb light source 10 in the second embodiment includes an SSB (Single Side Band) modulator 14 (single sideband optical modulator) as a frequency shifter between the short pulse light source 12 and the EDFA 16, and the SSB modulator. 14 is different from the first embodiment in that a signal generator 15 that inputs a modulation signal to 14 and a pulse compressor 17 between the EDFA 16 and the HNLF 18 are provided. Further, the point that the processor 90 controls the frequency of the SSB modulator 14 is also different from the first embodiment.

If the repetition frequency is 12.5 GHz, for example, the light pulse generated in the short pulse light source 12 includes a plurality of mode lights having mode intervals equal to the frequency. 4A is a schematic diagram of a light pulse emitted from the short pulse light source 12 (for example, the half width is 4 ps). The upper side is an intensity spectrum (the horizontal axis indicates the optical frequency, the vertical axis indicates the light intensity), and the lower side. The side is a time waveform (the horizontal axis represents time, and the vertical axis represents light intensity). The light pulse generated in the short pulse light source 12 enters the SSB modulator 14.

The SSB modulator 14 collectively shifts the spectrum of the optical pulse output from the short pulse light source 12 by the sine wave signal output from the signal generator 15. Since the SSB modulator 14 uses the signal generator 15 having an extremely high frequency accuracy of 1 Hz or less, a frequency shift on the order of MHz can be realized with high accuracy.

FIG. 4B is a schematic diagram of an optical pulse emitted from the SSB modulator 14. The upper intensity spectrum (the horizontal axis indicates the optical frequency and the vertical axis indicates the optical intensity) shows a state in which they are collectively shifted by Δf. Although only the intensity spectrum is schematically shown here, the phase spectrum is also shifted by Δf at the same time. The lower side is a time waveform (time is on the horizontal axis and light intensity is on the vertical axis), and shows how the time waveform of the optical pulse is retained after emission from the SSB modulator. The time waveform of the optical pulse is held at a half width of 4 ps. The optical pulse whose center frequency is shifted by Δf in the SSB modulator 14 enters the HNLF 18 via the EDFA 16.

The HNLF 18 generates comb light based on the optical pulse whose center frequency is shifted. The comb light is comb light having the same mode interval frequency as the input pulse in a wider frequency band than the input optical pulse. However, the comb light reflects that the intensity / phase spectrum of the optical pulse has been shifted by Δf on the frequency axis by the SSB modulator 14, and all of the plurality of mode lights are shifted by Δf on the frequency axis.

Conventionally, it has been confirmed that the monochromatic continuous light is frequency-shifted by using the SSB modulator 14 for the monochromatic continuous light (also in Patent Document 1, the monochromatic light that has passed through the variable optical filter 1414 has been confirmed. This phenomenon is used for continuous light).

FIG. 5 is a diagram showing that the SSB modulator 14 shifts the frequency of one laser beam. The laser light having the optical frequency f ₀ is swept by the frequency f in the positive direction on the frequency axis in accordance with the frequency f of the voltage applied from the signal generator 15 to the SSB modulator 14.

Returning to the explanation of FIG. It was first confirmed by the inventors of the present application that the SSB modulator 14 not only changes the amplitude of the picosecond pulse but also the phase spectrum and does not change the time waveform of the optical pulse. Note that the SSB modulator 14 has wavelength dependency. Therefore, it is desirable that the SSB modulator 14 be disposed immediately after the short pulse light source 12 before the wavelength band of the optical pulse is expanded. If the SSB modulator 14 is disposed after the pulse compressor 17 or the HNLF 18, the wavelength band of the optical pulse has already been expanded, so that the spectrum can be shifted well due to the wavelength dependence of the SSB modulator 14. Can not.

The processor 90 shifts the range of the optical frequency taken out by the spectroscopic optical system 50 according to the shift amount in the SSB modulator 14. For example, the processor 90 controls the frequency shift amount of each mode light by controlling the frequency of the signal generator 15 in the order of MHz, and adjusts the rotation angle of the diffraction grating 55 according to the frequency shift amount.

The processor 90 adjusts the rotation angle of the diffraction grating 55 so as to coincide with the frequency of the mode light to be measured whose center is shifted to the optical frequency range taken out by the spectroscopic optical system 50. For example, the processor 90 adjusts the rotation angle of the diffraction grating 55 so that the shifted mode light to be measured passes through the center of the exit slit 58. Thereby, one of the shifted mode lights can be detected by the single photoelectric conversion element 60. Therefore, the measurement of the response characteristic of the optical frequency can be realized with high resolution on the order of MHz. In the second embodiment using the optical frequency shifter, it is needless to say that the image sensor 62 may be disposed instead of the single photoelectric conversion element 60 and the exit slit 58 may be omitted.

FIG. 6 is a diagram illustrating comb light that is frequency-shifted by the SSB modulator 14. Each of a plurality of mode lights (..., F _m−1 , f _m , f _{m + 1} ...) Included in the comb light has a frequency axis according to the frequency f of the voltage applied from the signal generator 15 to the SSB modulator 14. It is swept by the frequency f in the upper positive direction. In this example, mode light of the optical frequency f _m which is swept by the frequency f is taken out from the spectroscopic optical system 50. The processor 90 controls the frequency f of the voltage applied to the SSB modulator 14 by controlling the signal generator 15.

FIG. 7 is a diagram showing a frequency comb light source 10 having a short pulse light source 12 using an optical pulse synthesizer 24. In this example, an optical pulse synthesizer 24 is used as the optical pulse synthesizer. The frequency comb light source 10 includes a short pulse light source 12, an EDFA 16 into which an optical pulse emitted from the short pulse light source 12 is incident, a pulse compressor 17 that compresses the pulse width of the optical pulse emitted from the EDFA 16, and a pulse compressor 17 HNLF18 which expands the optical frequency band of the light emitted from the.

The short pulse light source 12 includes a frequency stabilization laser 20 as a continuous wave laser, an optical modulator 22 that generates seed comb light from continuous light, and an optical pulse synthesizer 24 that synthesizes an optical pulse based on the seed comb light. Have. The frequency stabilizing laser 20 outputs continuous light whose oscillation frequency is constant for a long time (for example, a frequency fluctuation of 1 MHz or less per day). The frequency stabilized laser has a constant single optical frequency as shown in FIG. 7 (a-1) and is continuously output in time as shown in FIG. 7 (b-1). .

The optical modulator 22 modulates the frequency of continuous light with a frequency corresponding to the repetition frequency of the optical pulse to be generated, and generates a plurality of sidebands. Here, a single optical frequency of continuous light oscillated from the frequency stabilized laser 20 and a sideband group generated from the single optical frequency are collectively referred to as seed comb light. The optical modulator 22 receives RF modulation from the signal generator 23 and modulates continuous light. The light modulator 22 may be a LiNbO ₃ (LN) light modulator that is a dielectric crystal.

The optical modulator 22 of this example generates approximately 30 sidebands having a frequency interval of 12.5 GHz by, for example, a 12.5 GHz sine wave signal generated by the signal generator 23 (FIG. 7 (a-2)). ). These sideband waves become seed comb light. The modulated light is not continuous light but has a temporally discontinuous waveform (FIG. 7 (b-2)).

The optical circulator 25 outputs the light input from the optical modulator 22 to the optical pulse synthesizer 24. The optical pulse synthesizer 24 adjusts the phase and amplitude of each mode light in the seed comb light input from the optical modulator 22. The optical pulse synthesizer 24 includes an arrayed waveguide grating 26, an intensity modulator 27, a phase modulator 28, a current controller 29, and a mirror 30. The arrayed waveguide grating 26 guides light to the intensity modulator 27.

Each mode light of the seed comb light is demultiplexed into different channel waveguides by the arrayed waveguide grating 26. The intensity modulator 27 and the phase modulator 28 installed for each channel adjust the phase and amplitude of each mode light to synthesize an optical pulse (FIG. 7 (a-3)). Regarding this optical pulse synthesizer 24, there is Non-Patent Document 1. The synthesized optical pulse is output to the EDFA 16 via the optical circulator 25 (Non-patent Document 1: H. Tsuda, Y. Tanaka, T. Shioda, and T. Kurokawa: “Analog and digital optical pulses.” arrayed-waveguided grafting for high-speed optical signal processing, "IEEE J. Lightwave Technol., Vol. 26, No. 6, pp. 670-677," 670-677.

Thereby, in this example, an optical pulse having a repetition frequency of 12.5 GHz (pulse interval 80 ps) is synthesized (FIG. 7B-3). The optical pulse synthesized by the optical pulse synthesizer 24 is input to the pulse compressor 17 through the EDFA 16.

The pulse compressor 17 increases the light intensity peak of the light pulse by compressing the pulse width of the light pulse. The optical pulse subjected to pulse compression is input to the HNLF 18.

The HNLF 18 generates comb light in which the frequency band in which mode light exists is expanded from the optical pulse (FIG. 7 (a-4)). Note that the mode interval frequency of the comb light is maintained at 12.5 GHz which is the same as the mode interval frequency of the seed comb light.

FIG. 8 is a diagram showing the frequency comb light source 10 having the short pulse light source 12 using the dispersion applicator 21. In this example, a dispersion applicator 21 is used instead of the optical pulse synthesizer 24 as the optical pulse synthesizer. The dispersion applicator 21 has a large absolute value of dispersion at the center wavelength of the optical pulse to be synthesized. For example, a standard single mode fiber can be used in the vicinity of a wavelength of 1.55 μm. . Even if the dispersion applicator 21 is used, it is possible to synthesize optical pulses based on continuous light as in the optical pulse synthesizer 24. Compared with the case where an optical pulse synthesizer is used, although the quality (for example, FT product) of the synthesized optical pulse is somewhat inferior, there is an advantage that the device configuration is simple and the cost is low and the operation is simple.

FIG. 9 is a diagram illustrating a measuring apparatus 300 according to the third embodiment. FM spectroscopy can be performed by the measuring apparatus 300. The measurement apparatus 300 basically has a configuration in which the frequency comb light source 10 of the measurement apparatus 100 in the first embodiment is the frequency comb light source 10 of FIG. However, the difference is that a phase modulator 31, a signal generator 32, a phase adjuster 120, and a lock-in detector 110 are provided.

The short pulse light source 12 of this example has a phase modulator 31 between the frequency stabilized laser 20 and the optical modulator 22. A modulation voltage in the order of MHz is applied to the phase modulator 31 from the signal generator 32. The phase modulator 31 phase-modulates the frequency of the continuous light of the frequency stabilized laser 20 with a frequency smaller than the mode interval frequency. In this example, the modulation frequency of the phase modulator 31 is smaller than the modulation frequency of the optical modulator 22. The phase modulator 31 generates first-order double sideband light in the single frequency continuous light oscillated by the frequency stabilized laser 20 (FIG. 9A-1), and inputs the light to the optical modulator 22. To do.

That is, in this example, only the phase of the continuous wave light emitted from the frequency stabilized laser 20 is phase-modulated by the phase modulator 31, and the modes of all frequency combs can be phase-modulated in the same manner.

The optical modulator 22 modulates the light input from the phase modulator 31 to generate seed comb light. Each mode of the seed comb light has a first-order both-side band (FIG. 9 (a-2)). A sine wave signal generated by the signal generator 32 is input to the phase modulator 31. At the same time, the phase of the sine wave signal generated by the signal generator 32 is adjusted by the phase adjuster 120 and input to the lock-in detector 110.

One mode light shallowly phase-modulated by the phase modulator 31 is taken out by the spectroscopic optical system 50 and is incident on a single photoelectric conversion element 60 as a photodetector. The processor 90 as a control unit takes in a signal output from the lock-in detector 110 and sends a control signal to the drive circuit 80. The drive circuit 80 controls the rotation angle of the diffraction grating 55 in the spectroscopic optical system 50 based on the control signal. The light intensity detected by the single photoelectric conversion element 60 includes a component that varies at the same frequency as the modulation signal in the phase modulator 31. The component includes a quadrature component whose phase is shifted by π / 2 from the modulation signal and an in-phase component having the same phase as the modulation signal (SIN component and COS component).

The amplitudes of these SIN component and COS component include phase and amplitude information, respectively. Each of the SIN component and the COS component of the synthesized wave is detected by the lock-in detector 110 using the modulation signal in the phase modulator 31. The lock-in detector 110 detects the SIN component and the COS component using the modulation signal from the phase modulator 31 and the signal obtained by changing the phase of the modulation signal by π / 2. Thereby, changes in amplitude and phase can be detected. In this example, the comb light phase-modulated by the phase modulator 31 passes through the sample to be measured 40 and the spectroscopic optical system 50 and is then converted into an electric signal by a single photoelectric conversion element 60. Double balance detection is performed by the modulation signal, and minute changes in absorption and phase are detected.

FIG. 10 is a diagram showing a measuring apparatus 400 according to the fourth embodiment. The measuring apparatus 400 is used for dual comb spectroscopy using two optical paths. The dual comb light receiver 150 of the measuring apparatus 400 detects the optical frequency response characteristics of the sample 40 to be measured by heterodyne detection of the signal light transmitted or reflected by the sample 40 to be measured and the reference light.

The frequency comb light source 10 of the measuring apparatus 400 is basically the same as the frequency comb light source 10 shown in FIG. However, the difference is that the output from the frequency stabilized laser 20 is branched by the branching coupler 33, one of which is signal light transmitted through the sample to be measured 40 and the other is reference light.

The optical modulator 22 of this example includes a first optical modulator 22-1 and a second optical modulator 22-2 to which continuous light from the frequency stabilized laser 20 is branched and input. The first optical modulator 22-1, the modulation voltage of the frequency _{f 1} is given. On the other hand, the second optical modulator 22-2, the modulation voltage of the frequency _{f 2} is given. Thus, the first optical modulator 22-1, the mode spacing frequency to produce a seed comb light f _1. The second optical modulator 22-2, the mode spacing frequency to produce a seed comb light f _2.

In this example, the difference between _{f 1} and _{f 2} is sufficiently smaller than any of the _{f 1} and _{f 2.} Specifically, _{f 1} is 12.5 GHz. On the other hand, _{f 2} is (12.5 + δf) GHz, also delta] f is typically set to several kHz ~ Number 10 MHz.

In the measurement, the upper limit of the number of sampling points is determined by the ratio of δf and f ₁ or the ratio of δf and f ₂ . Therefore, the number of sampling points can be increased by setting δf sufficiently smaller than f ₁ or f ₂ . Thereby, the measurement band can be widened.

The seed comb light whose mode interval frequency is f _{1 and} the seed comb light whose mode interval frequency is f ₂ are EDFAs 16-1 and 16-2, pulse compressors 17-1 and 17-2, and HNLFs 18-1 and 18 respectively. Through -2, the comb light having a mode interval frequency of f ₁ and the seed comb light having a mode interval frequency of f ₂ are obtained.

The optical pulse synthesizer 24 of this example corresponds to the first optical modulator 22-1 and the second optical modulator 22-2, and the first optical pulse synthesizer 24-1 as a first optical pulse synthesizer. And a second optical pulse synthesizer 24-2 as a second optical pulse synthesis unit. The first optical pulse synthesizer 24-1, the mode spacing frequency from the first optical modulator 22-1 seed comb light f ₁ is input. Similarly, seed comb light having a mode interval frequency of f ₂ is input from the second optical modulator 22-2 to the second optical pulse synthesizer 24-2.

The HNLF 18 serving as the band expanding unit includes the HNLF 18-1 serving as the first band expanding unit and the second band expanding unit corresponding to the first optical pulse synthesizer 24-1 and the second optical pulse synthesizer 24-2. Includes HNLF18-2. HNLFs 18-1 and 18-2 generate comb light having a mode interval frequency of f ₁ and comb light having a mode interval frequency of f ₂ , respectively.

The comb light having a mode interval frequency of f ₁ is transmitted or reflected through the sample to be measured 40 and becomes signal light. Comb light having a mode interval frequency of f ₂ passes through the mirror 42 and becomes reference light. The comb light having a mode interval frequency of f _{1 and} the comb light having a mode interval frequency of f ₂ transmitted through or reflected by the sample to be measured 40 is combined by the combining mirror 36 and is incident on the spectroscopic optical system 50. The combined light is split by the spectroscopic optical system 50 and subjected to heterodyne detection by the single photoelectric conversion element 60. The frequency of the Nth signal mode light from the center frequency f _C of the comb light (equal to the oscillation frequency of the frequency stabilized laser 20) is f _C + N · f ₁ . The frequency of the Nth reference mode light is f _C + N · (f ₁ + δf). If the frequency difference N · δf between the two is set smaller than f ₁ , the N-th signal mode light and reference mode light are selected by the spectroscopic optical system and are incident on a single photoelectric conversion element 60. Therefore, if the maximum band of the single photoelectric conversion element 60 is set to f1, a heterodyne signal between the two can be obtained. Thereby, the optical frequency response characteristic of the sample 40 to be measured is detected.

In this example, since the optical combs of the signal light and the reference light are generated independently from one frequency stabilized laser 20, the modes of the two optical combs are synchronized and stable. In addition, before the reference light is detected by the dual-com light receiver 150, the signal light and the reference light are combined to enable highly sensitive detection. That is, even if the intensity of the signal light is attenuated by absorption, highly sensitive detection can be performed by heterodyne detection with strong reference light. In this specification, when it is simply described as comb light having a mode interval frequency of f ₁ or f ₂ , the comb light is transmitted through the measured sample 40 or is reflected from the measured sample 40. It is not limited to light.

Also in this example, an SSB modulator 34 may be further provided between the optical pulse synthesizer 24 and the pulse compressor 17 as in the first embodiment. Specifically, the SSB modulator 34 includes a seed comb light with a mode interval frequency f ₁ output from the optical pulse synthesizer 24-1 and a seed with a mode interval frequency f ₂ output from the optical pulse synthesizer 24-2. The comb light may be frequency swept on the optical frequency axis. As a result, spectrum measurement can be performed with a higher resolution than when the SSB modulator 34 is not used. Similarly to the second embodiment (FIG. 4), the processor 90 as a control unit controls the diffraction grating 55 and the SSB modulator 34 in the spectroscopic optical system 50, and includes a single photoelectric conversion element 60. An output signal may be acquired.

FIG. 11 is a diagram showing a measuring apparatus 500 according to the fifth embodiment. The measurement apparatus 500 is used for dual-comb spectroscopy using two optical paths, like the measurement apparatus 400. The dual comb light receiver 160 of the measuring apparatus 500 measures the light transmission characteristic or light reflection characteristic of the sample to be measured 40 by heterodyne detection using the signal light that transmits or reflects the sample to be measured 40 and the reference light.

However, the dual-com light receiver 160 of the measuring apparatus 500 is different from the spectroscopic optical system 50 and the single photoelectric conversion element 60 in that it has a single photoelectric conversion element 60 and an electric spectrum analyzer 130. Different from 150. That is, the comb light having a mode interval frequency of f ₁ transmitted through or reflected by the sample to be measured and the comb light having a mode interval frequency of f ₂ are combined and first input to a single photoelectric conversion element 60. The output of the single photoelectric conversion element 60 is input to the electric spectrum analyzer 130.

Measurement apparatus 500 is different from measurement apparatus 400 in that variable wavelength filter 19 is provided between HNLF 18-2 and multiplexing mirror 36. By using a variable wavelength filter 19 to filter a portion of the mode spacing frequency f ₂ of the comb beam not used for measurement (reference light).

According to the dual comb spectroscopy of this example, the mode spacing frequency f ₁ of the comb beam (signal light) and mode spacing frequency f ₂ of the comb beam (refer to light) heterodyne detection. That is, the electrical spectrum analyzer 130 detects the spectrum of the electrical signal subjected to heterodyne detection. Therefore, the optical frequency response characteristic of the sample 40 to be measured can be detected by the electric spectrum analyzer 130 in the microwave wavelength band. Furthermore, a single photoelectric conversion element 60 is sufficient to realize high resolution spectroscopy of around several MHz. Further, since the measurement wavelength band can be widened in one measurement, a large amount of information can be acquired by one measurement.

FIG. 12 is a diagram showing a change in spectrum in the case of dual comb spectroscopy using two paths. FIG. 12 (a-1) shows comb light having a mode interval frequency f ₁ output from the HNLF 18-1. Figure 12 (b-1) shows a comb light _{f 2} is the mode spacing frequency output from HNLF18-2. As described above, since f ₂ is larger than f ₁ by δf, the comb light whose mode interval frequency is f ₂ is the central mode light (thick line) derived from the comb light having the mode interval frequency f ₁ and continuous light. And a frequency difference of 0, δf, 2δf, 3δf.

FIG. 12A-2 shows comb light having a mode interval frequency of f ₁ after passing through the sample 40 to be measured. FIG. 12B-2 shows comb light having a mode interval frequency of f ₂ after passing through the variable wavelength filter 19. The comb light having a mode interval frequency of f ₁ is transmitted through the sample to be measured 40, and the light intensity of the specific mode light is attenuated. The comb light having the attenuated information and the mode interval frequency f ₁ becomes signal light indicating the optical frequency response characteristic of the sample 40 to be measured. Note that a spectrum having a frequency lower than that of the central mode light (thick line) may be filtered when not used for measurement.

Figure 12 (a-3) includes a comb light mode interval frequency f ₁ after passing through the sample to be measured 40 (signal light) and the mode interval frequency f ₂ of the comb beam (reference light), but combined The spectrum combined by the mirror 36 and heterodyne detected is shown. The spectrum can be measured by the dual comb light receiver 150 having the spectroscopic optical system 50 or the dual comb light receiver 160 having the electric spectrum analyzer 130.

As described above, δf is a frequency (order of microwaves in the wavelength band) sufficiently smaller than 12.5 GHz. Therefore, δf, 2δf, 3δf... Can also be detected by the electric spectrum analyzer 130.

FIG. 13 is a diagram illustrating a measuring apparatus 550 that is a modification of the fifth embodiment. In this example, the dual comb light receiver 160 includes a single photoelectric conversion element 60 and a digitizer 140. The digitizer 140 sequentially AD-converts analog signals that change over time and records them as digital signals. Further, instead of the first optical pulse synthesizer 24-1 and the second optical pulse synthesizer 24-2, the first dispersion imparting device 21-1 and the second dispersion imparting device 21-2 are used as the optical pulse synthesis unit. Have Further, an SSB modulator 34-2 as a frequency shifter is provided between the first dispersion applicator 21-1 and the pulse compressor 17-1. An SSB modulator 34-1 is provided between the frequency stabilizing laser 20 and the branch coupler 33. The above points are different from the measurement apparatus 500 of the fifth embodiment. Similar to the fifth embodiment, the SSB modulator 34-1 can sweep two comb lights having mode interval frequencies f ₁ and f ₂ on the optical frequency axis.

FIG. 14 is a diagram showing how the SSB modulator 34-2 shifts the comb light on the optical frequency axis. The upper left part of FIG. 14 shows comb light having a mode interval frequency of f ₁ output from the first dispersion imparting device 21-1 of FIG. The lower left part of FIG. 14 shows comb light having a mode interval frequency of f ₂ output from the second dispersion applicator 21-1 of FIG. Com light mode interval frequency f _2, the mode spacing frequency coincides with the optical frequency f ₀ with respect to comb light f _1. The comb light having the mode interval frequency f ₂ has a frequency difference of 0, δf, 2δf, 3δf... From the optical frequency f _{0 with} respect to the comb light having the mode interval frequency f ₁ .

The left-pointing arrow in the upper left part of FIG. 14 represents the direction in which the comb light whose mode interval frequency is f ₁ is frequency-shifted. In this example, the comb light whose mode interval frequency is f ₁ is frequency shifted by 4δf in the low frequency direction. The upper right part of FIG. 14 shows comb light having a mode interval frequency f ₁ shifted by the SSB modulator 34-2. Also, the right lower part of FIG. 14, the mode spacing frequency indicates the comb light f _2.

As described above, the SSB modulator 34-2 can select only the comb light having a mode interval frequency of f ₁ on the optical frequency axis and select a mode in which the two comb lights coincide with each other. As a result, the two comb light modes can be matched in accordance with the wavelength range to be measured.

FIG. 15 is a diagram showing a measuring apparatus 600 according to the sixth embodiment. The measuring apparatus 600 is used for dual comb spectroscopy using one optical path. The measurement apparatus 600 is the same as the measurement apparatus in the fourth embodiment in that the light output from the optical modulators 22-1 and 22-2 is combined by the branch coupler 33 before being input to the optical pulse synthesizer 24. Different from the device 400. Other points are the same as those of the measuring apparatus 400. Similarly to the second embodiment (FIG. 4), the processor 90 as a control unit controls the diffraction grating 55 and the SSB modulator 34 in the spectroscopic optical system 50, and includes a single photoelectric conversion element 60. An output signal may be acquired.

FIG. 16 is a diagram illustrating a measuring apparatus 700 according to the seventh embodiment. The measuring apparatus 700 is used for dual comb spectroscopy using one optical path. The measurement apparatus 700 is the same as the measurement apparatus according to the fifth embodiment in that the light output from the optical modulators 22-1 and 22-2 is combined by the branch coupler 33 before being input to the optical pulse synthesizer 24. Different from the device 500. Other points are the same as those of the measuring apparatus 500.

Dual comb spectroscopy (sixth and seventh embodiments) using one optical path has lower detection sensitivity than dual comb spectroscopy (fourth and fifth embodiments) using two paths. However, the number of component parts of the device can be reduced and the configuration of the device can be simplified as compared to dual-comb spectroscopy using two paths. Therefore, when higher accuracy than dual comb spectroscopy using two paths is not required, dual comb spectroscopy using one path can also be used.

FIG. 17 is a diagram showing a change in spectrum in the case of dual comb spectroscopy using one path. FIG. 17A-1 shows comb light with a mode interval frequency f ₁ output from the HNLF 18. Figure 17 (b-1) also shows the comb beam mode interval frequency output is _{f 2} from HNLF18. The comb light having the mode interval frequency f _{1 and} the comb light having the mode interval frequency f ₁ are multiplexed by the branch coupler 33 before being input to the optical pulse synthesizer 24. It is shown separately in two.

As described above, _{f 2} is greater by δf than _{f 1.} Therefore, the comb light with the mode interval frequency f ₂ is 0, δf, 2δf, 3δf from the position where the comb light with the mode interval frequency f ₁ matches the central mode light (bold line) derived from continuous light. Has a frequency difference of.

FIG. 17A-2 shows comb light having a mode interval frequency of f ₁ after passing through the sample 40 to be measured. FIG. 17B-2 shows comb light having a mode interval frequency of f ₂ after passing through the sample 40 to be measured. The comb light having a mode interval frequency of f _{1 and} the comb light having a mode interval frequency of f ₂ are transmitted through the sample to be measured 40 and the light intensity of the specific mode light is attenuated. Note that a spectrum having a frequency lower than that of the central mode light (thick line) may be filtered when not used for measurement.

Figure 17 (a-3) shows the spectrum mode spacing frequency after passing through the measurement sample 40 is the comb light and the mode spacing frequency of f ₁ and comb light f _2, were synthesized. FIG. 17 (a-4) shows a state in which heterodyne detection is performed by correcting the spectral intensity. As described above, in dual comb spectroscopy using a single path, if the transmitted light intensity of the sample to be measured 40 is Is, the output of the electric spectrum analyzer 130 is proportional to the square of Is. Therefore, for the purpose of obtaining the transmitted light intensity Is of the sample 40 to be measured, the square root of the spectrum intensity is calculated and corrected. The corrected spectrum can be measured by either the dual comb light receiver 150 having the spectroscopic optical system 50 or the dual comb light receiver 160 having the electric spectrum analyzer 130.

In dual comb spectroscopy (fourth and fifth embodiments) using two paths and dual comb spectroscopy (sixth and seventh embodiments) using one optical path, the same frequency stabilized laser 20 Is the light source. Therefore, it is not necessary to separately provide a heterodyne laser. In addition, even if fluctuation occurs in the output frequency of the frequency stabilization laser 20, the frequency difference (δf) between the two combs to be observed is not affected by performing heterodyne detection using the same light source. Therefore, even if there is a fluctuation in the output frequency of the frequency stabilization laser 20, the accuracy of heterodyne detection can be ensured.

FIG. 18 is a diagram showing a measuring apparatus 800 according to the eighth embodiment. The measuring device 800 measures the emission spectrum of the light source 38 to be measured by heterodyne detection. That is, the measuring apparatus 800 measures the emission spectrum of the light under measurement output from the light source under measurement 38. The measuring apparatus 800 is substantially the same as the measuring apparatus 200 in the second embodiment except that the sample to be measured 40 is not provided between the collimating lenses 35 and 45.

The measuring apparatus 800 includes a frequency comb light source 10, a multiplexing mirror 36, a light source 38 to be measured, and a spectroscopic optical system 50. The frequency comb light source 10 outputs comb light including a plurality of mode lights having different frequencies. The frequency comb light source 10 includes the short pulse light source 12 using the optical pulse synthesizer 24 described in FIG. 7 as the short pulse light source 12 of the measuring apparatus 200 in the second embodiment.

The comb light output from the HNLF 18 is combined with the measured light output from the measured light source 38 at the multiplexing mirror 36 after passing through the collimating lens 35. The combined light is output to the spectroscopic optical system 50 through the collimating lens 45.

The spectroscopic optical system 50 may be the same as the spectroscopic optical system 50 described in the first to third embodiments. The spectroscopic optical system 50 receives comb light, and extracts only one designated mode light from a plurality of mode lights in the comb light. Note that the mode interval frequency, which is the frequency interval between adjacent mode lights in the comb light, is larger than the optical frequency resolution of the spectroscopic optical system 50.

A single photoelectric conversion element 60 as a photodetector detects the intensity of light obtained by combining one mode light extracted from the spectroscopic optical system 50 and light to be measured from the light source to be measured. The intensity of the combined light is converted into an electric signal by a single photoelectric conversion element 60, and output to an AD converter 70 through a BPF (Band Pass Filter) 65. As described above, the optical frequency output from the exit slit 58 is predetermined according to the rotation angle of the diffraction grating 55.

The BPF 65 passes only an electric signal having a frequency f in a range of f ₀ <f <f ₀ + Δf. Therefore, the frequency band of the heterodyne signal detected by the single photoelectric conversion element 60 is limited to the above range by the BPF 65 and transmitted to the AD converter 70. The center frequency f ₀ of the transmission frequency width (Δf) of the BPF 65 is a frequency sufficiently smaller than half of the interval between adjacent comb lights. For example, the center frequency f ₀ may be a value sufficiently smaller than 6.25 (= 12.5 / 2) GHz.

Thereby, when the heterodyne signal generated from one mode light and the light to be measured matches the transmission frequency band of the BPF 65, the measuring apparatus 800 can measure the light intensity signal and the frequency of the optical beat. If the light intensity and optical frequency of the one mode light are known, the light intensity and optical frequency of the light to be measured can be calculated from the light intensity and optical frequency of the light to be measured of the beat signal.

The AD converter 70 outputs the light intensity signal to the processor 90 as a control unit. The processor 90 may control the frequency of the voltage applied to the SSB modulator 14 and the rotation angle of the diffraction grating 55 based on the light intensity signal and the optical frequency (that is, the observed optical frequency spectrum). For example, the processor 90 may sweep the mode light by controlling the SSB modulator 14 after observing the optical frequency spectrum once. The processor 90 once observes the optical frequency spectrum and then changes the rotation angle of the diffraction grating 55 to specify that the spectroscopic optical system 50 takes out the mode light having an optical frequency different from the mode light used for the observation. You can do it.

FIG. 19 is a diagram showing the principle of optical frequency measurement in the eighth embodiment. As shown in FIG. 19A, the spectrum of the optical comb has a plurality of different mode lights. As shown in FIG. 19B, the spectroscopic optical system 50 has a transmission bandwidth including one mode light. The BPF 65 has a transmission bandwidth with a frequency width (Δf) narrower than the frequency resolution width of the spectroscopic optical system 50.

As shown in FIG. 19C, the transmission frequency band of the BPF 65 is in the range of f ₀ <f <f ₀ + Δf. The frequency f ₀ has a frequency sufficiently smaller than half of the interval between adjacent comb lights. As shown in FIG. 19D, when the frequency of the optical beat of one mode light and the light to be measured matches the transmission frequency of the BPF 65, the measuring apparatus 800 can measure the light intensity signal. On the other hand, when the frequency of the optical beat does not match the transmission frequency of the BPF 65, the light intensity signal is not measured.

FIG. 20 is a diagram showing a measuring apparatus 900 according to the ninth embodiment. The measurement apparatus 900 of the present example is that the measurement light described above is obtained by performing heterodyne detection between the mode light and the measured light of the measured light source 38 after the mode light of the comb light is separated by the spectroscopic optical system 50. Different from the device 800. Other configurations are the same as those of the measurement apparatus 800 described above.

FIG. 21 is a diagram showing a measuring apparatus 1000 according to the tenth embodiment. The measuring apparatus 1000 measures the emission spectrum of the light source to be measured by heterodyne detection. Compared with the measurement apparatus 800 of the eighth embodiment, the measurement apparatus 1000 includes a spectroscopic optical system 50 and a single photoelectric conversion element 60, and a single photoelectric conversion element 60 and an electric spectrum analyzer 130 as a photodetector. Basically different in that it is replaced with. Since the measuring apparatus 1000 detects a beat signal in the order of microwaves in the wavelength band by heterodyne detection, instead of the spectroscopic optical system 50, the measurement light 1000 is obtained by combining the comb light and the measured light of the measured light source 38. A single photoelectric conversion element 60 for detecting the intensity and an electric spectrum analyzer 130 to which the output of the photodetector is input are provided. Also with this configuration, heterodyne detection can be performed.

FIG. 22 is a diagram showing a measuring apparatus 1100 according to the eleventh embodiment. The measuring apparatus 1100 can convert the wavelength band of the optical frequency comb light source in the near infrared region (1.2 to 1.8 μm) to the wavelength band in the mid infrared region (2.0 to 5.0 μm). Thereby, in the mid-infrared wavelength band, the transmission characteristic or reflection characteristic of the sample 40 to be measured, or the emission spectrum of the light to be measured from the light source 38 to be measured can be measured. Further, when measuring transmission characteristics or reflection characteristics or measuring emission spectrum, the wavelength band of light is converted from the mid-infrared region to the near-infrared region.

The measuring apparatus 1100 includes a near-infrared frequency comb light source 10, a first wavelength conversion unit 1102, a second wavelength conversion unit 1104, a spectroscopic optical system 50, and a single photoelectric conversion element 60 as a photodetector. The frequency comb light source 10, the spectroscopic optical system 50, and the single photoelectric conversion element 60 are as described above in the first to tenth embodiments. The first wavelength conversion unit 1102 and the second wavelength conversion unit 1104 are provided between the frequency comb light source 10 and the spectroscopic optical system 50.

The first wavelength conversion unit 1102 includes a polarization inversion device 172 and pump light 170. The polarization inversion device 172 is a nonlinear optical crystal having optical anisotropy. The polarization inversion device 172 may be a PPLN (Periodically poled lithium niobate). The pump light 170 is a laser light whose frequency is stabilized. The pump light 170 may be a laser light having a wavelength of 0.98 μm.

The first wavelength conversion unit 1102 converts the near-infrared wavelength band comb light output from the optical frequency comb light source 10 into a mid-infrared wavelength band that is longer than the near-infrared wavelength band. Convert to The first wavelength conversion unit 1102 combines the comb light (center wavelength λ ₁ ) in the near-infrared wavelength band and the pump light 170 (wavelength λ ₂ ) by the combining mirror 36, and inputs the combined light to the polarization inverting device 172. To do. The polarization inversion device 172 generates light having a wavelength λ ₃ that satisfies 1 / λ ₃ = 1 / λ ₂ −1 / λ ₁ (Equation 1) by generating a difference frequency. Difference frequency generation means that when light having two wavelengths λ ₁ and λ ₂ (λ ₂ <λ ₁ ) is incident on a nonlinear optical crystal, light having a wavelength λ ₃ longer than both λ ₁ and λ ₂ This is a phenomenon that occurs.

For example, the polarization inversion device 172 uses a comb light (center wavelength λ ₁ = 1.5 μm) in the near-infrared wavelength band and a pump light 170 (wavelength λ ₂ = 0.98 μm) in the mid-infrared wavelength band. Comb light (center wavelength λ ₃ = 2.8 μm) is generated. The frequency interval of the mode light in the comb light in the mid-infrared wavelength band is the same frequency interval as the comb light in the near-infrared wavelength band (center wavelength λ ₁ = 1.5 μm).

The comb light in the mid-infrared wavelength band output from the polarization inversion device 172 is input to the sample 40 to be measured. In addition, although this example demonstrates the case where the transmission characteristic of the to-be-measured sample 40 is measured, as demonstrated in 1st Embodiment, you may change a structure so that a reflection characteristic may be measured. Further, like the measuring apparatus 1106, the comb light in the mid-infrared wavelength band output from the polarization inverting device 172 and the measured light output from the measured light source 38 are multiplexed by the multiplexing mirror 36, The spectrum of the light to be measured may be measured.

The second wavelength conversion unit 1104 transmits or reflects the comb light converted into the mid-infrared wavelength band in the first wavelength conversion unit 1102 through the sample to be measured 40, and then the comb in the near-infrared wavelength band. Convert back to light. The second wavelength conversion unit 1104 multiplexes the comb light (wavelength λ ₁ ′) and the pump light (wavelength λ ₂ ′) in the mid-infrared wavelength band by the multiplexing mirror 36 and inputs it to the polarization inversion device 172. To do. The polarization inversion device 172 generates light having a wavelength λ ₃ ′ that satisfies 1 / λ ₃ ′ = 1 / λ ₂ ′ −1 / λ ₁ ′ (Equation 1) by generating a difference frequency. Note that the frequency interval of the mode light in the comb light in the near-infrared wavelength band is the same frequency interval as the comb light of the optical frequency comb light source 10.

In this example, the wavelength band is converted from the near infrared region to the mid infrared region, and then the wavelength band is converted again from the mid infrared region to the near infrared region. Accordingly, the near-infrared spectroscopic optical system 50 can be used as it is without using the mid-infrared spectroscopic optical system 50 separately. The mid-infrared photodetector has low sensitivity and high noise. However, in this example, the wavelength band is reconverted from the mid-infrared to the near-infrared. Therefore, compared with the case where light is detected in the mid-infrared wavelength band, it is possible to increase the sensitivity of light detection and reduce noise.

Also, in this example, the optical comb in the near-infrared wavelength band can be converted into an optical comb in the mid-infrared wavelength band useful for gas analysis by generating a difference frequency. Furthermore, by reconverting the comb light in the mid-infrared wavelength band into the near-infrared wavelength band, it is possible to detect optical frequency response characteristics with high sensitivity and low noise.

In this example, the measurement apparatuses 1100 and 1106 having the spectroscopic optical system 50 have been described. However, the spectroscopic optical system 50 and the single photoelectric conversion element 60 may be replaced with a photodetector and an electric spectrum analyzer. In this case, the first wavelength conversion unit and the second wavelength conversion unit are provided between the comb light source and the photodetector. As a result, the measured light of the measured light source 38 can be heterodyne detected.
(Comparative Example 1)

FIG. 23 shows a measuring apparatus 1200 including a white lamp 1204 and a spectroscopic optical system 1220. As the white lamp 1204, a tungsten lamp having a spectrum that continuously spreads from the visible to the infrared region is used. The light from the white lamp 1204 is converted into a parallel beam by the collimator lens 1206 and output from the light source 1202 to the sample 1210 to be measured. The light transmitted through the sample 1210 to be measured is output to the spectroscopic optical system 1220.

A diffraction grating 1222 is used for the spectroscopic optical system 1220. By applying light to the diffraction grating 1222 to disperse the light and passing through the slit 1224, monochromatic light having a target wavelength is obtained. A photodetector 1230 such as a photomultiplier tube or a photodiode is provided behind the slit 1224 to detect monochromatic light.

The measuring device 1200 uses a white lamp 1204 as a light source, so the wavelength band is wide, but the resolution is determined by the diffraction grating of the spectroscopic optical system 1220, and is generally about several GHz. Further, since the light source is a tungsten lamp, the light intensity is also weak. Furthermore, calibration with a reference light source is required to obtain frequency accuracy.
(Comparative Example 2)

FIG. 24 shows a measuring apparatus 1300 provided with a wavelength tunable laser light source. As the wavelength tunable laser 1304, an external resonator type semiconductor laser is generally used. The wavelength tunable laser 1304 can sweep the wavelength every mode interval (generally, about 1 pm = about 100 MHz). The wavelength tunable laser 1304 has a simple configuration in which the laser beam transmitted through the sample to be measured 1310 is detected by the photodetector 1324. Since the wavelength is detected by a wavelength meter incorporated in the wavelength tunable laser 1304, a spectroscopic optical system is unnecessary.

In the measuring apparatus 1300, the wavelength is swept using the wavelength tunable laser 1304, so that a high resolution of about 10 to 100 MHz can be obtained. However, since the variable wavelength range of the laser is at most 100 nm, there is a problem that the measurement band is narrow (about 100 nm). In addition, calibration with a reference light source is required to obtain frequency accuracy.
(Comparative Example 3)

Other than that, there is an FM spectrometer. FM spectroscopy is a laser spectroscopy technique proposed in 1980, but it has extremely high sensitivity and high resolution, so it can observe spectra of atoms and molecules. In FM spectroscopy, sidebands are generated in laser light by phase modulation, and heterodyne detection is performed between the sidebands and a carrier wave. By using a double balance mixer after the photodetector, both absorption and phase can be detected with high sensitivity. By using a frequency-stabilized semiconductor laser as the light source, a high resolution of 0.1 MHz can be obtained (reference document: GC Bjorkund, “Frequency-Modulation Spectroscopy”, Opt. Lett., 5, p.15, 1980.).

The FM spectrometer can obtain extremely high sensitivity and high resolution (0.1 MHz) by phase modulation of the laser. However, since a frequency-stabilized semiconductor laser is used, the measurement wavelength range is an extremely narrow wavelength range (about 1 nm). Therefore, in order to measure at different wavelengths depending on the sample to be measured, it is necessary to prepare lasers with different oscillation wavelengths.
(Comparative Example 4)

In addition, there is a dual-comb spectrometer. Dual comb spectroscopy was reported by NIST (USA) in 2008 as a measurement result of the HCN absorption spectrum using two femtosecond lasers (optical comb at 100 MHz interval, δf = 4 kHz) (reference document I). Codington et al., “Coherent Multiheterodyne spectroscopic using stabilized optimistic combs” Phys. Rev. Lett. (100, 013902 (2008)).

Dual comb spectroscopy can obtain a high resolution spectrum of about 100 MHz with only one photodetector by using an electric spectrum analyzer. However, in the proposed dual comb spectroscopy, it is necessary to synchronize the modes of the two femtosecond lasers and the mode interval of the lasers, so that measurement is not easy. Moreover, the frequency band which can be measured at a time is narrow.

Table 1 below summarizes the comparison results between the present application and Comparative Examples 1 to 4 and the multi-GHz comb light source described in Background Art.

The measuring device described in the present application can be widely used in fields such as medical / life science, industrial chemistry, and medicine / food.

Medical and biological applications (blood glucose concentration measurement, etc.).
For example, regarding diabetes (about 7 million people in Japan), quantitative analysis of glucose concentration in blood can be performed non-invasively, and a great effect can be expected for treatment or prevention. Until now, research on non-invasive analysis technology using light has been promoted in Japan and abroad for more than 20 years, but it has not been put into practical use. The main reason is that the spectrum analysis of broadband, high resolution, and high light intensity is undeveloped.

Gas Analysis _(CO 2, CO, NO _x, etc.).
In a chemical plant or the like, a spectroscopic analysis technique is mainstream in order to manage gas leakage or mixing ratio. In order to cope with various gases, a high-intensity light source is required from the near infrared to the middle infrared.

Optical communications (modulation spectrum measurement, light source line spectrum measurement, etc.).
In the field of optical communications, research to allocate frequency channels with high density over a wide wavelength range of 1.2 μm to 1.8 μm has been advancing due to the depletion of frequency resources, and modulation signal analysis in the order of MHz over a wide frequency band is required. .

Physical properties research (precision measurement of atomic and molecular energy levels, isotope separation).
In the field of physical property research, frequency accuracy with MHz accuracy is required for precise measurement of atomic and molecular energy rankings or for isotope separation.

As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. It will be apparent to those skilled in the art that various modifications or improvements can be added to the above embodiment. It is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

The execution order of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the description, and the drawings is particularly “before” or “prior”. It should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the description, and the drawings, even if it is described using “first”, “next”, etc. for the sake of convenience, this means that it is essential to carry out in this order. is not.

10 frequency comb light source, 12 short pulse light source, 14 SSB modulator, 15 signal generator, 16 EDFA, 17 pulse compressor, 18 HNLF, 19 variable wavelength filter, 20 frequency stabilized laser, 21 dispersion applicator, 22 light modulation , 23 signal generator, 24 optical pulse synthesizer, 25 optical circulator, 26 array waveguide grating, 27 intensity modulator, 28 phase modulator, 29 current controller, 30 mirror, 31 phase modulator, 32 signal generator, 33 branch coupler, 34 SSB modulator, 35 collimating lens, 36 combining mirror, 38 measured light source, 40 measured sample, 42 mirror, 45 collimating lens, 50 spectroscopic optical system, 52 entrance slit, 54 collimating lens, 55 diffraction Lattice, 56 lenses, 58 Firing slit, 60 single photoelectric conversion element, 62 image sensor, 65 BPF, 70 AD converter, 72 image processing circuit, 80 drive circuit, 90 processor, 100 measuring device, 105 measuring device, 110 lock-in detector, 120 phase Adjuster, 130 Electrical spectrum analyzer, 140 Digitizer, 150 Dual comb light receiver, 160 Dual comb light receiver, 170 Pump light, 172 Polarization inversion device, 200 measuring device, 300 measuring device, 400 measuring device, 500 measuring device, 550 measurement Device, 600 measuring device, 700 measuring device, 800 measuring device, 900 measuring device, 1000 measuring device, 1100 measuring device, 1102 first wavelength converting unit, 1104 second wavelength converting unit, 1106 measuring device 1200 measuring device, 1202 light source, 1204 white lamp, 1206 collimating lens, 1210 sample to be measured, 1220 spectroscopic optical system, 1222 diffraction grating, 1224 slit, 1230 photodetector, 1300 measuring device, 1304 wavelength tunable laser, 1310 device to be measured Sample, 1324 photodetector, 1400 measuring device, 1402 frequency comb light source, 1408 interleaver, 1410 optical switch, 1412 EDFA, 1414 variable optical filter, 1416 frequency shifter, 1420 sample to be measured, 1422 high-speed photodetector, 1424 electrical amplifier , 1426 low-pass filter, 1428 optical power meter, 1430 variable wavelength laser

Claims (18)

1. A measuring device for measuring transmission characteristics or reflection characteristics of a sample to be measured,
   A frequency comb light source that outputs comb light including a plurality of mode lights having a constant frequency interval;
   A spectroscopic optical system that receives the comb light and frequency-resolves the plurality of mode lights in the comb light one by one;
   A photodetector for detecting the intensity of at least one mode light out of the plurality of mode lights extracted from the spectroscopic optical system;
   The one mode light whose intensity is detected by the photodetector transmits or reflects the sample to be measured disposed between the output of the comb light source and the input of the photodetector,
   A measuring apparatus in which a mode interval frequency of the comb light is larger than an optical frequency resolution of the spectroscopic optical system.
2. The measuring apparatus according to claim 1, wherein the mode interval frequency is at least twice the optical frequency resolution of the spectroscopic optical system.
3. The spectroscopic optical system has an exit slit that extracts only one designated mode light among the plurality of mode lights,
   The photodetector has a single photoelectric conversion element that detects the intensity of the one mode light emitted from the exit slit.
   The measuring apparatus according to claim 1 or 2.
4. 3. The measuring apparatus according to claim 1, wherein the photodetector includes an image sensor that detects the plurality of mode lights frequency-resolved by the spectroscopic optical system in parallel.
5. The comb light source is
   A pulse light source that outputs an optical pulse having the same repetition frequency as the mode interval frequency;
   A frequency shifter that shifts the frequency of the spectrum of the optical pulse output from the pulse light source;
   The measurement apparatus according to any one of claims 1 to 4, further comprising: a band expanding unit that generates the comb light obtained by expanding the frequency band of the optical pulse based on the optical pulse.
6. The measurement apparatus according to claim 5, further comprising a control unit having a control function of shifting a range of an optical frequency taken out by the spectroscopic optical system in accordance with a shift amount in the frequency shifter.
7. The pulse light source is
   A continuous wave laser that outputs continuous light of a single frequency;
   An optical modulator that modulates the frequency of the continuous light with a frequency according to the mode interval frequency to generate seed comb light including a plurality of mode lights;
   The measuring apparatus according to claim 5, further comprising: an optical pulse synthesizing unit that adjusts a phase and an amplitude of each mode light in the seed comb light and synthesizes an optical pulse.
8. A phase modulator that phase-modulates the frequency of the continuous light at a frequency smaller than the mode interval frequency, generates first-order double sideband light in each mode light, and inputs the light to the optical modulator;
   A signal generator for inputting a signal to the phase modulator;
   A lock-in detector for receiving an output of the photodetector and a signal in which a signal of the signal generator is phase-adjusted;
   The spectroscopic optical system simultaneously takes out one designated mode light and the first-order both sideband light of the mode light and enters the photodetector.
   The measurement apparatus according to claim 7, wherein an electrical signal output from the photodetector is sent to the lock-in detector, phase-sensitive detection is performed using a modulation signal, and two orthogonal signals are extracted.
9. The optical modulator includes a first optical modulator and a second optical modulator into which the continuous light is branched and input,
   The first optical modulator generates the seed comb light of the comb light having the mode interval frequency of f ₁ , and the second optical modulator generates the seed light of the comb light having the mode interval frequency of f _2. Generating the seed comb light,
   the difference between f ₁ and _{f 2} is smaller than any of the _{f 1} and _{f 2,}
   One or both of the comb light having the mode interval frequency of f _{1 and} the comb light having the mode interval frequency of f ₂ are transmitted or reflected through the sample to be measured.
   The measurement apparatus according to claim 7, wherein the comb light having the mode interval frequency of f _{1 and} the comb light having the mode interval frequency of f ₂ are combined and incident on the spectroscopic optical system.
10. The optical pulse synthesis unit includes a first optical pulse synthesis unit and a second optical pulse synthesis unit corresponding to the first optical modulator and the second optical modulator,
    The measurement apparatus according to claim 9, wherein the band expanding unit includes a first band expanding unit and a second band expanding unit corresponding to the first optical pulse combining unit and the second optical pulse combining unit.
11. A measuring device for measuring transmission characteristics or reflection characteristics of a sample to be measured by heterodyne detection,
    A comb light source that outputs comb light including a plurality of mode lights having different frequencies;
    Two types of comb light that is output from the comb light source and becomes comb light of different mode interval frequencies, and a dual comb light receiver that is combined and input,
    The comb light source is
    A pulse light source that outputs a light pulse having a mode interval frequency that is a frequency interval of a plurality of mode lights adjacent to each other in the comb light and that includes a smaller number of mode lights than the comb light;
    A band expanding unit for generating the comb light, which is obtained by expanding the frequency band in which the mode light exists, from the optical pulse, based on the optical pulse;
    A frequency shifter that collectively shifts the frequency of each mode light of the comb light by shifting the frequency of the optical pulse output by the pulse light source in a range narrower than the mode interval frequency;
    The pulse light source is
    A continuous wave laser that outputs continuous light;
    A first optical modulator and a second optical modulator that modulate the frequency of the continuous light at a frequency corresponding to the mode interval frequency to generate seed comb light including a plurality of mode lights;
    An optical pulse synthesis unit that synthesizes an optical pulse by adjusting the phase and amplitude of each mode light in the seed comb light,
    Including
    The continuous light is split into two, and is incident on the first optical modulator and the second optical modulator, respectively.
    The first optical modulator generates the seed comb light of the comb light having the mode interval frequency of f ₁ , and the second optical modulator generates the seed light of the comb light having the mode interval frequency of f _2. Generating the seed comb light,
    the difference between f ₁ and _{f 2} is smaller than any of the _{f 1} and _{f 2,}
    One or both of the comb light having the mode interval frequency of f _{1 and} the comb light having the mode interval frequency of f ₂ are transmitted or reflected through the sample to be measured.
    The measuring device in which the comb light having the mode interval frequency of f _{1 and} the comb light having the mode interval frequency of f ₂ are combined and incident on the dual comb light receiver.
12. The optical pulse synthesizer includes a first optical pulse synthesizer and a second optical pulse synthesizer corresponding to the first optical modulator and the second optical modulator,
    The measuring apparatus according to claim 11, wherein the band expanding unit includes a first band expanding unit and a second band expanding unit corresponding to the first optical pulse synthesizer and the second optical pulse synthesizer.
13. The measurement apparatus according to claim 8, further comprising an optical frequency shifter between the optical pulse synthesis unit and the band expansion unit.
14. The optical pulse combining unit includes a first dispersion applicator and a second dispersion applicator corresponding to the first optical modulator and the second optical modulator,
    The band expanding unit includes a first band expanding unit and a second band expanding unit corresponding to the first dispersion applicator and the second dispersion applicator,
    The dual comb receiver is
    A photoelectric conversion element to which comb light having different mode interval frequencies is combined and input;
    A digitizer to which an output from the photoelectric conversion element is input;
    The measuring device is
    A frequency shifter provided between the first dispersion applicator and the first band expanding unit;
    A branch coupler that branches the output from the continuous wave laser to the first optical modulator and the second optical modulator, and another frequency shifter provided between the continuous wave laser;
    The measuring apparatus according to claim 11.
15. A measuring device for measuring an emission spectrum of a light source to be measured by heterodyne detection,
    A comb light source that outputs comb light including a plurality of mode lights having different frequencies;
    A spectroscopic optical system that receives the comb light and extracts only one mode light of the plurality of mode lights in the comb light;
    A photodetector for detecting the intensity of the combined light of the one mode light extracted from the spectroscopic optical system and the measured light of the measured light source;
    A measurement apparatus in which a mode interval frequency, which is a frequency interval between adjacent mode lights in the comb light, is larger than an optical frequency resolution of the spectroscopic optical system.
16. A measuring device for measuring an emission spectrum of a light source to be measured by heterodyne detection,
    A comb light source that outputs comb light including a plurality of mode lights having different frequencies;
    A photodetector that detects the intensity of the combined light of the comb light and the measured light of the measured light source;
    An electrical spectrum analyzer to which an output of the photodetector is input.
17. Between the comb light source and the spectroscopic optical system,
    A first wavelength converter that converts comb light in the near-infrared wavelength band into comb light in the mid-infrared wavelength band that is longer than the near-infrared wavelength band;
    The comb light converted into the mid-infrared wavelength band in the first wavelength conversion unit is converted again to the comb light in the near-infrared wavelength band after being transmitted or reflected by the sample to be measured. The measurement apparatus according to claim 1, further comprising a wavelength conversion unit.
18. Between the comb light source and the dual comb receiver,
    A first wavelength converter that converts comb light in the near-infrared wavelength band into comb light in the mid-infrared wavelength band that is longer than the near-infrared wavelength band;
    The comb light converted into the mid-infrared wavelength band in the first wavelength conversion unit is converted again to the comb light in the near-infrared wavelength band after being transmitted or reflected by the sample to be measured. The measurement apparatus according to claim 11, further comprising a wavelength conversion unit.

Images