JP2009025245A - Device for observing optical interference - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for observing optical interference capable of detecting frequency axis information. <P>SOLUTION: In an interference optical system 20, an optical frequency comb generated by an optical frequency comb generator 20 from laser light emitted from a laser light source 10 is divided into reference light and measurement light to enter them into a reference optical system 40 and a measurement optical system 50; interference light Pc of reference light Pa and measurement light Pb is generated which are returned respectively from the reference optical system 40 and the measurement optical system 50; light spectrum contained in the interference light Pc generated by the interference optical system 20 is separated by a spectrometer 60 and each the light spectrum is detected by a photodetector array 70; outputs of each the spectrum detected by the photodetector array 70 are supplied to a signal processor 80. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention observes the surface to be measured by detecting interference light between the reflected light of the measurement light irradiated on the surface to be measured and the reflected light of the reference light irradiated on the reference surface by the reference surface. The present invention relates to an optical interference observation apparatus.

  As one of the non-destructive tomographic techniques used in the medical field, etc., optical coherence tomography (OCT: Optical Coherence Tomography) that uses temporally low coherence light as a probe is known. It has been. Since OCT uses light as a measurement probe, OCT has an advantage that it can measure the refractive index distribution, spectral information, polarization information (birefringence distribution), etc. of the object to be measured (see, for example, Patent Document 1).

  The OCT 800 is based on a Michelson interferometer, and its principle is shown in FIG.

  The light emitted from the light source 801 is collimated by a collimator lens 802 and then split into reference light and object light by a beam splitter 803. The object light is condensed on the measurement object 805 by the objective lens 804 in the object arm, scattered and reflected there, and then returns to the objective lens 804 and the beam splitter 803 again.

  On the other hand, the reference light is reflected by the reference mirror 807 after passing through the objective lens 806 in the reference arm, and returns to the beam splitter 803 through the objective lens 806 again. Thus, the object light and the reference light that have returned to the beam splitter 803 are incident on the condenser lens 808 together with the object light, and are collected on the photodetector 809 (a photodiode or the like).

  The light source 801 of the OCT 800 uses a light source of temporally low coherence light (light emitted from the light source at different times is extremely difficult to interfere). In a Michelson interferometer using temporally low coherence light as a light source, an interference signal appears only when the distance between the reference arm and the object arm is approximately equal. As a result, when the intensity of the interference signal is measured by the photodetector 809 while changing the optical path length difference (τ) between the reference arm and the object arm, an interference signal (interferogram) for the optical path length difference is obtained.

  The shape of the interferogram shows the reflectance distribution in the depth direction of the measured object 805, and the structure in the depth direction of the measured object 805 can be obtained by one-dimensional axial scanning. Thus, in the OCT 800, the structure in the depth direction of the measurement object 805 can be measured by optical path length scanning.

  In addition to the scanning in the axial direction, a two-dimensional cross-sectional image of the object to be measured can be obtained by performing a two-dimensional scanning by adding a horizontal mechanical scanning. The scanning device that performs the horizontal scanning includes a configuration in which the object to be measured is directly moved, a configuration in which the objective lens is shifted while the object is fixed, and a pupil of the objective lens while the object to be measured and the objective lens are fixed. The structure etc. which rotate the angle of the galvanometer mirror in the surface vicinity are used.

  The basic OCT has been developed as follows: a wavelength scanning type OCT that obtains a spectral interference signal by scanning the wavelength of a light source, and a spectral domain OCT that obtains a spectral signal using a spectroscope. The latter is a Fourier domain OCT. There is.

  As described in Non-Patent Document 1, the wavelength scanning type OCT irradiates a living body with light, continuously changes the wavelength of the irradiation light, and returns from the reference light and a different depth in the living body. This system obtains a tomographic image by causing light to interfere with an interferometer and analyzing the frequency component of the interference signal. This technology is expected as an advanced system because it can construct a tomographic image with extremely high resolution from frequency analysis of signals from inside the object. The wavelength scanning type OCT is suitable for practical use such as an endoscope in that it has high measurement sensitivity and is resistant to dynamic noise. Here, the wider the wavelength scanning band of the irradiated light, the higher the frequency analysis band, so that the resolution in the depth direction increases.

  In the Fourier domain OCT, the wavelength spectrum of the reflected light from the object to be measured is acquired with a spectrometer (spectrum spectrometer), and Fourier transform is performed on this spectrum intensity distribution, so that the real space (OCT signal space) is obtained. This Fourier domain OCT does not need to scan in the depth direction, and can measure the cross-sectional structure of the object to be measured by scanning in the x-axis direction.

  Like the Fourier domain OCT, the polarization-sensitive OCT acquires the wavelength spectrum of the reflected light from the object to be measured with a spectrum spectrometer. For example, horizontal linearly polarized light, vertical linearly polarized light, 45 ° linearly polarized light, and circularly polarized light passed through a four-wavelength plate, etc. Only the horizontally polarized component is incident on the spectrum spectrometer to cause interference, and only the component having a specific polarization state of the object light is extracted and subjected to Fourier transform. This polarization sensitive OCT also does not need to be scanned in the depth direction.

JP 2007-101365 A Handbook of Optical Coherence Tomography, p41-43, Mercel Dekker, Inc. 2002

  The conventional Fourier domain OCT uses a broadband light source, and the output light is split by a diffraction grating in a spectroscope and a spectral interference signal is obtained by a light receiving element. However, a white broadband light source such as a light emitting diode is used. Therefore, the value of the optical frequency that is split by the diffraction grating and incident on the light receiving element depends on the performance of the spectrometer and the arrangement of the light receiving elements. Since the information on the frequency axis is inaccurate, it is difficult to improve the accuracy of the distance information in the real space obtained by Fourier transform of the spectrum intensity.

  Accordingly, an object of the present invention is to provide an optical interference observation apparatus that can detect information on the frequency axis or absolute distance information in real space with high accuracy in view of the above-described problems.

  Other objects of the present invention and specific advantages obtained by the present invention will become more apparent from the description of embodiments described below.

  An optical interference observation apparatus according to the present invention generates an optical frequency comb and emits it, and divides the optical frequency comb emitted from the optical frequency comb generator into reference light and measurement light for reference. An interference optical system that enters the optical system and the measurement optical system, generates interference light between the reference light and the measurement optical system that returns from the reference optical system and the measurement optical system, and the reference light that is split in the interference optical system is incident A reference optical system that returns the incident reference light to the interference optical system, and the measurement light divided in the interference optical system is incident, the incident measurement light is irradiated onto the measurement surface, and the measurement surface Is separated by the measurement optical system for returning the measurement light reflected at the interference optical system, the optical spectrum separation means for separating the optical spectrum contained in the interference light generated by the interference optical system, and the optical spectrum separation means. Each light A light detection means comprising a plurality of light detectors for detecting the vector, the detection output of the optical spectrum by the light detecting means; and a signal processing means supplied.

  In the optical interference observation apparatus according to the present invention, for example, the reference optical system irradiates the reference surface with the incident reference light, and returns the reference light reflected by the reference surface to the interference optical system.

  Moreover, the optical interference observation apparatus according to the present invention includes, for example, a frequency shifter inserted in either the reference light path of the reference optical system or the measurement light path of the measurement optical system, and the reference light or measurement light Is shifted by the frequency shifter and returned to the interference optical system.

  In the present invention, the information on the frequency axis can be detected with high accuracy by using an optical frequency comb generator which is a light source having a spectral distribution of equal intervals instead of the broadband light source in the conventional Fourier domain OCT. .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Needless to say, the present invention is not limited to the following examples, and can be arbitrarily changed without departing from the gist of the present invention.

  As shown in FIG. 1, the optical interference observation apparatus 100 according to the present invention has a laser light source 10 that emits laser light and an optical frequency comb generator in which laser light is incident from the laser light source 10. 20 and the optical frequency comb emitted from the optical frequency comb generator 20 is divided into reference light and measurement light, and enters the reference optical system 40 and measurement optical system 50. The reference optical system 40 and measurement optical system 50 The interference optical system 30 that generates the interference light Pc of the reference light Pa and the measurement light Pb that is returned from the laser beam, and the reference light divided by the interference optical system 30 are incident. The incident reference light is converted into the interference optical system 30. The reference optical system 40 to be returned to and the measurement light divided in the interference optical system 30 are incident, the incident measurement light is irradiated onto the measurement surface 51, and the measurement light reflected on the measurement surface 51 is reflected on the measurement light 51 Interference light A measurement light system 50 returned to the system 30, a spectroscope 60 for separating the optical spectrum contained in the interference light Pc generated by the interference optical system 30, and a plurality of light spectra separated by the spectroscope 60. And a signal processing unit 80 to which a detection output of the photodetector array 70 is supplied.

  In the optical interference observation apparatus 100, the laser light source 10 emits laser light having a frequency ν.

  The optical frequency comb generator 20 is a light source having a spectral distribution with equal intervals.

  The optical frequency comb generator 20 is composed of, for example, an EOM (electro-optic modulator) and a reflecting mirror disposed so as to face the EOM, and an optical oscillator is configured by the EOM and the reflecting mirror. This is a modulation type optical frequency comb generator, and a modulation signal having a frequency fm is given by an external oscillator 21. As shown in FIG. 2, the optical frequency comb generator 20 emits from the laser light source 10 an optical frequency comb having sidebands (sidebands) generated at equal frequency intervals that match the frequency fm of the modulation signal. Based on the emitted laser light, the light is emitted. Further, the center frequency of the optical frequency comb emitted from the optical frequency comb generator 20 coincides with the incident laser frequency ν.

  In this optical interference observation apparatus 100, the frequency ν of the laser light emitted from the laser light source 10 and the frequency fm of the modulation signal of the optical frequency comb generator 20 can be adjusted independently.

  Here, the optical frequency comb emitted from the optical frequency comb generator 20 has a fixed relative phase relationship, and the accuracy and stability of the frequency interval are the accuracy and stability of the microwave frequency fm. Match. In the microwave frequency band, an oscillator having a narrow spectrum width and high frequency stability can be easily obtained, so that the optical comb output from the optical comb generator is a very accurate optical frequency scale. If the incident laser is replaced with a stabilizing laser, the absolute frequency of all sidebands can be fixed.

  In the optical interference observation apparatus 100 having such a configuration, the optical frequency comb emitted from the optical frequency comb generator 20 is divided into measurement light and reference light by the half mirror 31 of the interference optical system 30 as an optical pulse, and the reference optical system. 40 and the measurement optical system 50.

  The reference optical system 40 irradiates the reference surface 41 with the reference light incident from the interference optical system 30 and returns the reference light Pa reflected by the reference surface 41 to the interference optical system 30. The measurement optical system 50 irradiates the measurement surface 51 with the measurement light incident from the interference optical system 30, and returns the measurement light Pb reflected by the measurement surface 51 to the interference optical system 30.

  Then, the interference optical system 30 superimposes the reference light Pa and the measurement light Pb returned from the reference optical system 40 and the measurement optical system 50 on the semi-transparent mirror 31, thereby causing interference light between the reference light Pa and the measurement light Pb. Generate Pc.

Here, in the interference optical system 30, the measurement light (delayed pulse) Pb reflected by the measurement target surface 51 superimposed by the semi-transparent mirror 31 and the reference light (reference pulse) Pa reflected by the reference surface 31 are shown in FIG. As shown in FIG. 3, there is a time difference t ₀ corresponding to a difference in distance from the half mirror 31 to the measured surface 40 and the reference surface 31, that is, a difference in optical path length. Due to the nature of the Fourier transform, the spectrum of the measurement light (delayed pulse) Pb reflected by the surface to be measured 40 is the spectrum of the reference light (reference pulse) Pa reflected by the reference surface 31, as shown in FIG. Has a phase characteristic proportional to the frequency.

  Then, interference light generated by superimposing the measurement light (delayed pulse) Pb reflected by the surface to be measured 40 and the reference light (reference pulse) Pa reflected by the reference surface 31 by the half mirror 31 in the interference optical system 30. As shown in FIG. 5, when Pc is decomposed into optical spectrum components by the spectroscope 60, frequency characteristics appear in the intensity of each optical spectrum component detected by the photodetector array 70.

  Here, each side of the optical spectrum component decomposed by the spectroscope 60 is incident on each element of the photodetector array 70 via the collimator lens 61.

  The spectroscope 60 uses an optical element such as a diffraction grating or a prism having a function of separating an optical path according to a frequency. A plurality of single photodetectors can be used in place of the photodetector array 70.

In the signal processing unit 80, the time difference t ₀ corresponding to the distance difference from the semi-transparent mirror 31 to the reference surface 41 and the measured surface 51 is calculated from the frequency characteristics of the intensity of each optical spectral component detected by the photodetector array 70. calculated from the time difference t ₀ obtained can be determined the distance difference.

That is, as described above, the spectrum of the measurement light (delayed pulse) Pb reflected by the surface to be measured 51 corresponds to the spectrum of the reference light (reference pulse) Pa reflected by the reference surface 41 as shown in FIG. Therefore, the time difference t ₀ is obtained from the relative phase gradient 2πft ₀ of the delayed pulse Pb with respect to the reference pulse Pa based on the detection output by the photodetector array 70, and the obtained time difference t ₀ is obtained. The distance difference can be obtained from _zero .

Note that if there is group delay dispersion in the middle path, the relationship between frequency and phase deviates from a straight line. In this case, the time difference t ₀ is obtained by inserting a compensation element for group delay dispersion or estimating only a linear component by signal processing.

  Here, in the reference optical system 40 in which the reference light is incident from the interference optical system 30 as in the optical interference observation apparatus 110 illustrated in FIG. 6, the frequency of the incident reference light is shifted by the frequency shifter 42, and the frequency The reference light Pa that has been shifted may be returned to the interference optical system 30. In this optical interference observation apparatus 110, the same components as those in the optical interference observation apparatus 100 are denoted by the same reference numerals in FIG. 6, and detailed description thereof is omitted.

  In this optical interference observation apparatus 110, the interference optical system 30 includes a first semi-transparent mirror 31A that separates the optical frequency comb incident from the optical frequency comb generator 20 into reference light and measurement light, the reference optical system 40, and measurement. There is provided a second semi-transparent mirror 31B that returns from the optical system 50 and superimposes the reference light Pa and the measurement light Pb to generate an interference light Pc between the reference light Pa and the measurement light Pb. The reference light separated by the first half mirror 31A is incident on the reference optical system 40, and the measurement light is incident on the measurement optical system 50 via the second half mirror 31B. Yes.

  Further, the reference optical 40 receives the reference light separated by the first semi-transparent mirror 31A of the interference optical system 30, operates by the output of the oscillator 43, and shifts the frequency of the incident reference light by fa. A frequency shifter 42 is provided, and the reference light Pa whose frequency is shifted by the frequency shifter 42 is returned to the second semi-transparent mirror 31B of the interference optical system 30 via the first reflecting mirror 41A and the second reflecting mirror 41B. It is like that.

  The frequency shifter 42 includes, for example, an acoustooptic modulator (AOM) that changes the phase of the reference light by an acoustooptic interaction using ultrasonic waves generated inside.

  The interference optical system 30 is returned from the reference optical system 40 and the measurement optical system 50, and the reference light Pa and the measurement light Pb are superimposed on the reference beam Pa and the measurement light Pb in the second half mirror 31B. Interference light Pc is generated. The interference light Pc generated by the interference optical system 30 is decomposed into optical spectrum components by the spectroscope 60 and detected by the photodetector array 70.

  In the optical interference observation apparatus 110 having such a configuration, assuming that the frequency of the laser element emitted from the laser light source 10 is ν and the frequency of the modulation signal supplied from the external oscillator 21 to the optical frequency comb generator 20 is fm, FIG. 7A, the measurement light Pb having the center (0th order) frequency of ν and the nth order comb mode frequency of ν + nfm is returned to the interference optical system 30 via the measurement optical system 50, and FIG. (B), a reference Pa having a center (0th order) frequency of ν + fa and an nth-order comb mode frequency of ν + fa + nfm is returned to the interference optical system 30 via the reference system 40.

  Therefore, the beat frequency of the interference light Pc generated in the interference optical system 30 is that the zero-order frequency is (ν + fa) −ν = fa, and the n-order frequency is {ν + fa + nfm} − (ν + nfm) = fa (where, n = 0, ± 1, ± 2,...), that is, all are fa.

  That is, each element of the photodetector array 70 detects each optical spectrum component having a beat frequency fa.

Here, the electric field e _n (t) of the interference wave of the n-th mode is expressed by the following equation (1).

  In this equation (1), ν is a laser frequency, fa is a shift frequency, n is a comb mode order, fm is a modulation frequency, ETn is an electric field of measurement light, and ERn is an electric field of reference light. Furthermore, θn is the relative phase of the measurement light pulse with respect to the phase of the nth mode of the reference light pulse.

The detection output current i _n (t) by the photodetector array 70 is expressed by the following equation (2).

  In the formula (2), a is a proportionality constant.

Therefore, the signal processing unit 80 can know the relative phase / amplitude between the sidebands in real time by comparing the phase and amplitude of the AC signals i _n (t) simultaneously detected by the photodetector array 70.

  When measuring the DC component of the interference signal, it is not easy to obtain the amplitude of the measurement light and the phase difference between adjacent sidebands from the measured voltage value, but the frequency in the reference light path as in the optical interference observation device 110 is not easy. By inserting the shifter 42, the signal observed by the photodetector array 70 becomes the shift frequency fa, so that phase comparison by signal processing in the signal processing unit 80 can be easily performed, and an AC component is observed. Therefore, the phase and amplitude of the interference signal can be known with one detector per mode.

  The optical interference observation apparatus 110 measures the time delay of the measurement light path of the measurement optical system 50 with respect to the time delay of the reference light path of the reference optical system 40.

  Here, instead of inserting the frequency shifter 42 into the reference light path of the reference optical system 40, the frequency shifter 42 may be inserted into the measurement light path of the measurement optical system 50.

  Further, like the optical interference observation apparatus 120 shown in FIG. 8, a reference surface 41 using a semi-transparent mirror is provided in the measurement light path of the measurement optical system 50, and the measurement optical for the time delay of the reference light path of the reference optical system 40 The distance between the reference surface 41 and the measured surface 51 is determined by measuring the time delay of the measurement light path of the system 50 with respect to the two reflecting surfaces of the reference surface 41 and the measured surface 51 and calculating the difference in distance. Can be measured.

  Since this optical interference observation apparatus 120 has the same configuration as the optical interference observation apparatus 110 except for the measurement optical system 50, the same components are denoted by the same reference numerals in FIG. Description is omitted.

  In the optical interference observation apparatus 110 and the optical interference observation apparatus 120, a frequency shifter 42 that can be used in a reciprocating manner can be used. For example, in the optical interference observation apparatus 130 shown in FIG. The frequency shifter 42 may be used in a reciprocating manner so that a frequency shift of fa / 2 is given for each of the forward path and the return path.

  Since this optical interference observation apparatus 130 has the same configuration as the optical interference observation apparatus 110 except for the reference optical system 50, the same components are shown with the same reference numerals in FIG. Description is omitted.

  In the above description, the case where the path difference or distance between the reference surface and the surface to be measured is measured has been described. However, the measurement optical system 50 scans the surface to be measured with the measuring light and is obtained by the photodetector array 70. The optical interference observation apparatus according to the present invention can be applied to an optical coherence tomography apparatus, such as generating a tomographic image of the measurement target surface 51 in the signal processing unit 80 based on the detected output.

  In the case of a configuration that performs DC phase comparison, for example, two spectrometers 60A and 60B, photodetector arrays 70A and 760B, and a signal processing unit 80A, as in the optical interference observation apparatus 140 shown in FIG. The phase and amplitude can be measured by measuring the voltages of the sin component and the cos component of the interference signal with the configuration including 80B.

  This optical interference observation apparatus 140 includes a ８ wavelength plate 44 in the reference light path of the reference optical system 40, and the optical frequency comb generator 20 converts the polarization of the optical frequency comb output of the ８ wavelength plate 44. Adjustment is made so as to have a component orthogonal to the component coincident with the crystal axis.

  The 1/8 wavelength plate 44 provided in the reference light path of the reference optical system 40 reciprocally applies a phase shift of 1/4 wavelength to one polarization component of the reference light incident from the interference optical system 30.

  The interference optical system 30 includes a polarization beam splitter 32 that separates a 1/4 wavelength phase-shifted interference light by the ８ wavelength plate 44, and the interference lights Pca and Pcb separated by the polarization beam splitter 32. Are incident on the first spectroscope 60A and the second spectroscope 60B. One interference light Pcb separated by the polarization beam splitter 32 is reflected by the reflecting mirror 33 and is incident on the second spectroscope 60B.

Then, the light spectrum included in the interference light Pca is separated by the first spectroscope 60A and detected by the first photodetector array 70A, and the light included in the interference light Pcb by the second spectroscope 60B. The spectrum is separated and detected by the second photodetector array 70B. The signal processing unit 80, together with the first signal processing unit 80A based on the detection output of the first photodetector array 70A, to calculate the voltage of _a n cos [theta] _n component of the interference light Pca, the second signal Based on the detection output from the second photodetector array 70B by the processing unit 80B, the voltage of the an _n sin θ _n component of the interference light Pcb is calculated, and the phase and the phase are determined from the calculated sin component and cos component voltages of the interference signal. The amplitude can be determined.

  Here, in the optical interference observation apparatuses 100, 110, 120, 130, and 140 having the above-described configuration, a mode-locked laser may be used instead of the optical frequency comb generator 20 using the laser light source 10 and the EOM. In this case, the characteristics of the spectrometer 60 and the arrangement of the photodetector array 70 are adjusted so that one frequency component is input to one element in accordance with the center frequency of the mode-locked laser to be used and the optical comb frequency interval.

  Further, as shown in FIG. 5, each of the optical spectrum components decomposed by the spectroscope 60 is incident on one sideband for each element of the photodetector array 70 via the collimator lens 61. It is assumed that the optical spectral components are detected by the photodetector array 70. However, as in the optical interference observation device 150 shown in FIG. In place of the photodetector array 70, the number of photodetectors 70A, 70B, and 70C corresponding to the optical spectrum to be detected is provided, and the detection outputs by the photodetectors 70A, 70B, and 70C are detected. The signal processing unit may obtain the phase / amplitude information. Also in this case, one side band is incident on each of the photodetectors 70A, 70B, and 70C.

  In this optical interference observation apparatus 150, the same constituent elements as those of the optical interference observation apparatus 100 are denoted by the same reference numerals in FIG. 11, and detailed description thereof is omitted.

It is a block diagram which shows the basic composition of the optical interference observation apparatus which concerns on this invention. It is the figure which showed typically the optical frequency comb output from the optical frequency comb generator of the said optical interference observation apparatus on a frequency axis. It is the figure which showed typically the measurement light (delay pulse) and the reference light (reference pulse) which were superimposed in the interference optical system of the said optical interference observation apparatus on a time axis. It is the figure which showed typically the phase characteristic with respect to the spectrum of the reference light (reference pulse) of the spectrum of the said measurement light (delayed pulse) on the frequency axis. It is the figure which showed typically a mode that the interference light generate | occur | produced in the interference optical system of the said optical interference observation apparatus was decomposed | disassembled into each optical spectrum component with a spectrometer, and it detected with a photodetector array. It is a block diagram which shows the other structural example of the optical interference observation apparatus which concerns on this invention. It is the figure which showed typically the measurement light and reference light which are returned to the interference optical system in the said optical interference observation apparatus on a frequency axis. It is a block diagram which shows the further another structural example of the optical interference observation apparatus which concerns on this invention. It is a block diagram which shows the further another structural example of the optical interference observation apparatus which concerns on this invention. It is a block diagram which shows the further another structural example of the optical interference observation apparatus which concerns on this invention. It is a block diagram which shows the further another structural example of the optical interference observation apparatus which concerns on this invention. It is a figure which shows the principle of an optical coherence tomography apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Laser light source, 20 Optical frequency comb generator, 21 External oscillator, 30 Interference optical system, 31, 31A, 31B Semi-transparent mirror, 32 Polarization beam splitter, 33 Reflective mirror 40 Reference optical system, 41 Reference surface, 41A, 41B Reflective mirror , 42 Frequency shifter, 43 Oscillator, 44 1/8 wavelength plate, 50 measurement optical system, 51 surface to be measured, 60, 60A, 60B spectrometer, 61 collimator lens, 70, 70A, 70B photodetector array, 80, 80A , 80B Signal processor, 100-150 Optical interference observation device

Claims (3)

An optical frequency comb generator for generating and emitting an optical frequency comb;
The optical frequency comb emitted from the optical frequency comb generator is divided into reference light and measurement light, incident on the reference optical system and measurement optical system, and the reference light returned from the reference optical system and measurement optical system and measurement. An interference optical system that generates interference light, and
A reference optical system that receives the reference light split in the interference optical system and returns the incident reference light to the interference optical system;
A measurement optical system that receives the measurement light split in the interference optical system, irradiates the measurement light incident on the surface to be measured, and returns the measurement light reflected by the surface to be measured to the interference optical system;
An optical spectrum separating means for separating an optical spectrum included in the interference light generated by the interference optical system;
A light detection means comprising a plurality of light detectors for detecting each light spectrum separated by the light spectrum separation means;
An optical interference observation apparatus comprising: signal processing means to which detection output of each optical spectrum by the light detection means is supplied.   2. The optical interference observation apparatus according to claim 1, wherein the reference optical system irradiates the reference surface with the incident reference light and returns the reference light reflected by the reference surface to the interference optical system. A frequency shifter inserted into either the reference light path of the reference optical system or the measurement light path of the measurement optical system;
3. The optical interference observation according to claim 1, wherein the frequency of one of the reference light and the measurement light is shifted by the frequency shifter and returned to the interference optical system. 4. apparatus.

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