JP2002082045A - Photometric system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably take measurements with spatially high resolution in a short time by means of a simple arrangement using one frequency COM generator. SOLUTION: This system comprises a source 11 of laser beams serving as a light source which emits a coherent light beam L0; a light frequency COM generator 12 on which the laser beam L0 impinges from the source 11; a modulation signal generator 13 for generating a modulation signal SMOD imparted to the light frequency COM generator 12; a light separator and synthesizer 14 for separating and synthesizing a reference light beam LREF from and with an object light beam LOB; a light delay path 15 providing a delay of a predetermined time τ to the reference light beam LREF separated from the object light beam by the light separator and synthesizer 14; and a photodetector 16 for detecting changes in intensity of light caused by interference between the reference light beam LREF and the object light beam LOB synthesized with each other by the light separator and synthesizer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measurement system which requires a wide spectrum width at an arbitrary wavelength, and more particularly to an optical measurement system for realizing high-speed and high-resolution measurement.

[0002]

2. Description of the Related Art Conventionally, as an optical measurement system for realizing a spatially high-resolution measurement, a wide spectral width in an arbitrary wavelength range represented by an optical coherence tomography (OCT) device is required. Optical measurement systems are known.

[0003] As the OCT apparatus, for example, there is one as shown in FIG. The OCT apparatus uses a beam splitter 1102 to convert a light L1101 emitted from a light source 1101 having a short coherence distance into an object light L1102 and a reference light L11.
03. The object light L1102 is transmitted to the scanner 11
Object light L1104 reflected by the measurement sample S
The light is then incident on the beam splitter 1102 again. The reference light L1103 is supplied to the reference light mirror 11 positioned by the motor 1106 via the frequency shifter 1104.
The light is reflected at 05 and is again incident on the beam splitter 1102.

[0004] The object light L1104 and the reference light L1103 are combined by being incident on a beam splitter 1102, and are incident on a photodetector 1107 as interference light L1105. The photodetector 1107 detects interference light whose light intensity is modulated by interference between the object light L1104 and the reference light L1103, and generates a detection signal. The detection signal is subjected to, for example, filtering and A / D conversion in the signal processing circuit 1108 and input to the control unit 1109. In the control unit 1109,
Based on the input signal, for example, an image indicating the internal structure of the measurement sample S is generated as a measurement result. The control unit 1109 also controls the motor drive circuit 1110 based on the input signal and the feedback signal from the motor 1106.
Is controlled to drive the motor 1106. Control unit 1
In 109, the scanner 1103 is controlled to scan the object light L1102 on the surface of the measurement sample S.

In the OCT apparatus 1000 having such a configuration, the measurement sample S is moved in the Z direction or the reference mirror 1105 is moved in the X direction.
To the measurement sample S or the reference mirror 110
The reflectance distribution in the depth direction of the measurement sample S is obtained by obtaining the distance moved by 5. Thereby, OCT
The apparatus 1000 can measure the internal shape and the external shape of the measurement sample S by performing the tomographic measurement of the measurement sample S by obtaining the reflectance distribution in the depth direction. This OCT
The device 1000 can be used for observing the inside of a living body by using, for example, light in a wavelength range from red to near infrared.

Further, in the conventional OCT apparatus 1000, when a pulse laser is emitted as the light source 1101 having a short coherence distance, measurement is performed using a component in which interference occurs due to the timing of pulses reflected by the reference mirror 1105 being matched. The internal structure of the sample S can be observed.

As described above, the OCT apparatus 1000 can realize spatially high-resolution measurement of the internal structure, refractive index, thickness, and the like of an object.

[0008]

However, in the OCT apparatus, it is necessary to modulate the mechanical delay distance of the reference light in order to obtain information on the surface shape and depth direction of the object to be measured. There was a problem that it took a lot of time.

That is, in the conventional OCT measuring apparatus 1000, since the light source 1101 is usually single, it is necessary to mechanically control the position of the reference mirror 1105 in the X direction to control the interference. . Here, the operating speed of the reference mirror 1105 is limited, and the conventional OCT
In the fixing device 1000, it often takes a long time to measure the measurement sample S.

Further, conventionally, an optical frequency domain interferometry (OFD) has been conventionally used.
Although a tomography apparatus to which a technique referred to as R) is applied has been proposed, it is actually necessary to sweep the frequency of a laser to be used over a wide range, and at this time, mechanical driving is used.

Accordingly, the present invention has been proposed in view of the above-described circumstances, and has a simple configuration using a single frequency comb generator, which is capable of measuring spatially high resolution in a short time and stably. It is an object of the present invention to provide an optical measurement system capable of performing the measurement.

[0012]

Optical measurement system according to the present invention SUMMARY OF THE INVENTION includes a light source for emitting light having a coherence, the first period tau ₁ second period at a first frequency f _m tau the ₂ modulates a modulation signal generating means for generating a repeating cycle modulated signal of a predetermined second frequency f _m + Delta] f, by a modulation signal from the modulation signal generation means incident light from the light source, the incident light frequency and a center frequency, having said the first period tau ₁ sideband every first frequency f _m intervals, second
The period tau ₂ is the optical frequency comb generator means for generating a measuring light having a sideband every second frequency f _m + Delta] f intervals, separate measurement light from the optical frequency comb generator in the reference beam and the object beam Light separating means, a light delay means for delaying one of the reference light and the object light separated by the light separating means for a predetermined time, reflected light or transmitted light of the object light by the object to be measured, and the reference light And light detecting means for detecting a change in light intensity due to interference between the reference light and the object light synthesized by the light synthesizing means.

Further, the optical measuring system according to the present invention includes a light source for emitting light having a coherence, the first period tau ₁ in the second period tau ₂ at a first frequency f _m the a modulation signal generating means for generating a modulation signal of the second frequency f _m + Delta] f at a predetermined repetition period, modulates the incident light from the light source by the modulated signal from the modulation signal generation means, the center frequency of the incident light and frequency, first the aforementioned first time period tau ₁
It has a sideband for each frequency f _m spacing, in the second period tau ₂ and an optical frequency comb generator means for generating a measuring light having a sideband every second frequency f _m + Delta] f intervals, the optical frequency A light separating means for separating the measurement light from the comb generating means into a reference light and an object light, an optical delay means for giving a predetermined time delay to one of the reference light or the object light separated by the light separating means, A scanning unit that scans the irradiation position of the object light separated by the light separation unit on the measurement object, a light combining unit that combines the object light reflected by the measurement object and the reference light, and the light combining unit Detection means for detecting a change in light intensity due to interference between the synthesized reference light and object light, and shape detection means for detecting shape information of the measurement target based on the interference detection result from the detection means, Scanned by the above scanning means And in using a plurality of shape information generated by the shape detection means, characterized in that it comprises an image generating means for generating an image showing a shape of the measuring object.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

In the optical measuring system according to the present invention, for example, as shown in FIG. 1, one optical frequency comb generator (Optical Frequency Comb Generator) is used in principle, and optical coherent tomography (OCT: Optical Coherence) is used. Tom
ography) device 10.

As shown in FIG. 1, the OCT apparatus 10 has a laser light source 11 for emitting coherent light L ₀ , and a laser light L ₀ from the laser light source 11. Optical frequency comb generator 12 into which light is incident
And a modulation signal S given to the optical frequency comb generator 12.
A modulation signal generator 13 for generating a _MOD , an optical separator / combiner 14 for separating / combining the reference light L _REF and the object light L _OB ,
The reference light L _REF separated by the light separation / combiner 14
And a photodetector 1 for detecting a change in light intensity due to interference between the reference light L _REF and the object light L _OB synthesized by the light splitter / synthesizer 14.
6 In the OCT apparatus 10, the laser light source 11 has a coherent laser beam L ₀ having a predetermined frequency.
Occurs. The laser light L ₀ generated by the laser light source 11 is incident on the optical frequency comb generator 12.

The optical frequency comb generator 12 converts the laser light L generated by the laser light source 11 into a modulated signal
By modulating with the modulation signal S _MOD given by 3, the measurement light L _MES having a sideband (side band) at each frequency interval of the modulation signal S _{MOD with} the frequency of the laser light L ₀ as a center frequency is generated. I do. The optical frequency comb generator 12 includes, for example, an EOM (Electro-Optic Modulator) and a reflecting mirror disposed so as to face the EOM, and the EOM and the reflecting mirror constitute an optical oscillator.

The modulation signal generator 13 has a first period τ₁ To
Is the first frequency f_m In the second period τ _Two Has a second frequency
f_m + Δf modulated signal S_MOD Is issued at a predetermined repetition cycle
Live. Where τ₁ = Τ_Two = Τ and 2τ repetition
The first frequency f_m And the second frequency f_m + Δf change
Tone signal S_MOD Is generated by the modulation signal generator 13
And

The optical frequency comb generator 1 to which the modulation signal S _MOD generated by the modulation signal generator 13 is given.
In 2, the first period tau ₁ of the modulated signal S _MOD of the first frequency f _m is given as the center frequency ν the frequency of the laser beam L _0, side strips at equal frequency intervals of the first frequency f _m to generate waves, kf _m (k = -m from the center frequency [nu, -
m + 1, -m + 2, ..., 0, 1, 2, ..., n)
The measurement light L _MES having the sideband of the frequency component of
Also, the modulated signal S _MO second _{period D} is given tau ₂ of the second frequency f _m + Delta] f, the center frequency ν the frequency of the laser beam L _0, equal frequency spacing of the second frequency f _m + Delta] f in sideband is generated, from the center frequency ν k (f _m +
Δf) (k = −m, −m + 1, −m + 2,..., 0,
1, 2, and generates a measurement light L _MES having sideband frequency components of n). The measurement light L _MES generated by the optical frequency comb generator 12 is incident on the optical splitter / combiner 14.

The light separator / combiner 14 is, for example, a half mirror.
And the optical frequency comb generator 12
Generated measurement light L_MES With reference light L_REF And object light L_OBTo
To separate. The reference light separated by the light separation / combiner 14
Illumination L_REF Gives a predetermined time delay by the optical delay path 15.
After that, the light is again incident on the light separating / combining device 14.
Also, the object light separated by the light separation / combiner 14
L_OBIs irradiated on the object OB to be measured, and the reflected light is
The light is again incident on the optical separation / combiner 14. And this light
The demultiplexer / synthesizer 14 is controlled by the optical delay path 15 for a predetermined time.
Reference light L given a delay of_REF And the object to be measured OB
The emitted object light L_OBInterference light L obtained by combining _DET The photo detector
Emitted to 16.

Here, the optical delay path 15 is provided with a delay τ time equal to half the repetition period 2τ of the modulation signal S _MOD generated by the modulation signal generator 13 by the optical separation / combiner 14. This is given to the separated reference light L _REF .
The optical delay path 15 has, for example, a total reflection mirror 15B at the end.
The optical fiber 15A has a length that gives a delay amount of τ / 2 time in one way.

In the optical measurement system having such a configuration, the optical separation / combination unit 14 delays a time τ equal to half the repetition period 2τ of the modulation signal S _MOD generated by the modulation signal generator 13. By giving the separated reference light L _REF , the light separating / combining unit 14
The first period tau ₁ which object beam L _OB is modulated at a first frequency f _m, the object beam L _OB that is modulated at a first frequency f _m is modulated at a second frequency f _m + Delta] f Reference light L
_REF and the object light L _OB has the second frequency f _m
+ Δf in the second period τ ₂ ,
It becomes the object beam L _OB modulated at a frequency f _m + Delta] f of is combined with the reference light L _REF which is modulated at a first frequency f _m that.

[0023] Here, the τ ₁ = τ ₂ = τ, the first frequency f _m and the second frequency f _m + Delta] f at a repetition period of 2τ
Of the modulation signal S _MOD the modulation signal generator 13 is assumed to be generated, the modulation signal generator 13 in the emitted modulated signal S repetition period the light splitting a delay equal τ time half the time 2τ the _MOD By giving the reference light L _REF separated by the combiner 14, as shown in FIG. 2, in the light separator / combiner 14, the entire period of the first period τ ₁ and the second period τ ₂ And the interference light L _DET obtained by combining the object light L _OB and the reference light L _REF whose modulation frequencies differ by Δf
Can be obtained. Note that the detection output of the interference light L _DET of the detection output and the second period tau ₂ of the interference light L _DET in the first period tau ₁ by the optical detector 16, respectively the time-reversal signal of each other. Further, even if the delay given to the reference light L _REF is not τ time, the object light L _OB and the reference light L
_The light L _DET can be obtained during a period when the modulation frequency of the _REF satisfies the condition different by Δf.

Note that, using two optical frequency comb generators, the object light L _OB and the reference light L whose modulation frequencies differ by Δf are used.
_Although it is possible to separately generate _REF and _REF , it is necessary to strictly manage the temperature characteristics and the like of each optical frequency comb generator. By using the measurement light L _MES generated by the generator separately for the reference light L _REF and the object light L _OB , 1
An optical measurement system capable of performing stable measurement in a short time and with a simple configuration using two frequency comb generators can be realized.

Here, according to the principle of OCT, the resolution is determined by the spectrum width of the light source used. This is the same for the optical frequency comb, and the resolution is improved by broadening the spectrum of the optical frequency comb. Therefore, in the present invention, the measurement light L generated by the optical frequency comb generator 12 is used.
_As shown in FIG. 3, the _MES is amplified by the optical amplifier 17 to the extent that nonlinearity is generated, and is incident on the optical demultiplexer / combiner 14 via the SC fiber 18. The SC fiber 18 is an abbreviation of a supercontinuum fiber, and is a fiber that easily causes self-phase modulation with small dispersion, for example. With this, the comb, which is a pulse in the function of the time axis, expands its spectrum by self-phase modulation,
Resolution increases.

However, in this case, it is necessary that the reference light L _REF does not pass through the dispersive medium while being delayed and enters the photodetector 16, and if the reference light L _REF is delayed by an optical fiber or the like, it is necessary to compensate for it. . There are two approaches to this solution.
One method performs compensation using a device capable of dispersion compensation, for example, a dispersion compensating fiber. Another method compensates during the signal processing, for example by digital signal processing or analog signal processing. In the embodiment of the OCT apparatus described below, both of these methods are included, but only one of them may be used.

FIG. 4 shows an OCT apparatus 10 to which the present invention is applied.
0 shows an example.

The OCT apparatus 100 includes a measurement light generation unit 1
10, a measurement light injection unit 120, a measurement unit 130, a signal processing unit 140, and a control unit 150.

The measurement light generator 110 includes a laser light source 111 which emits light having coherence, an optical frequency comb generator 112 into which laser light L ₀ is incident from the laser light source 111, Optical frequency comb generator 112
And a modulation signal generating unit 113 for providing a modulation signal to the control signal.

The laser light source 111 is a single mode CW laser, and is stabilized by temperature control or the like. The optical frequency comb generator 112 has fiber input and fiber output, and is configured by putting a phase modulator in an optical resonator composed of two mirrors. The optical frequency comb generator 112, the modulated signal S _MOD having a frequency f _m is an integral multiple of the free spectral range of the optical resonator is provided by the modulation signal generator 113.

The optical frequency comb generator 112 generates an optical frequency comb as the measurement light L _MES by modulating the laser light L ₀ from the laser light source 111 with the modulation signal S _MOD , but the modulation frequency slightly fluctuates. However, the output of the optical frequency comb, ie, the measurement light L _MES is possible. Note that the measurement light generation unit 110 does not need to be an optical frequency comb generator.
As a result, any light source having the same output characteristics that can control the carrier frequency and the repetition frequency equivalent to those of the optical frequency comb may be used.

The modulation signal generator 113 has a frequency f
A microwave oscillator 113 that oscillates a microwave signal of _m
A; a phase shifter 113B for phase modulating the oscillation output of the microwave oscillator 113A;
A phase control signal generator 113C for providing a phase control signal to B
Consists of

The phase control signal generator 113C is connected to the control unit 1
For example, as shown in FIG. 5A, the difference between the maximum value and the minimum value of the phase is a sawtooth wave having a width of △ φ _pp around φ ₀ as shown in FIG. Is given to the phase shifter 113B. Phase shifter 113
Modulation signal inputted to the optical frequency comb generator 112 through the B is, ± around the frequency f _m, as shown in (B) of FIG. 5 △ φ _pp / 2πτ frequency-modulated signal S _MOD
Becomes

The system controller 151 of the control unit 150 uses the timing when the slope of the sawtooth-shaped phase control signal changes from positive to negative or from negative to positive to capture the interference signal as data. Trigger.

Thus, assuming that the object light L _OB and the reference light L _REF arrive at the photodetector 135 with a time difference of τ, as described later, at that time, the relative position as shown in FIG. frequency difference is proportional to △ phi _pp to, △ φ _pp / (π
τ) [Hz]. Compared Here, FIG. 1 △ phi _pp
/ (Πτ) corresponds to △ f and f _m- △ φ _pp / (2πτ)
Corresponds to f _m .

The depth at which the interference signal S _DET can be measured continuously is proportional to the magnitude of the phase fluctuated by the sawtooth wave,
Can be continuously observed up to a depth of up to _{c △ φ pp / (2n sample} πf m) in this device. This is an observable range when the measurement is performed from time A to time B shown in FIG. 5, for example. Here, c is the speed of light, and n _sample is the refractive index of the object. For example, △ φ _pp = π, f _m = 6 GHz, n
_{When sample} = 1.5, the interference signal S _DET can be measured to a depth of 1.7 cm. As in the signal example shown in FIG. 5C, a time-reversed signal of the signal measured from time A to time B is obtained in the period from time B to time C.

The speed quantity v corresponding to the mirror speed in the method of moving the mirror with the conventional Michelson interferometer is given by:
c △ phi becomes _pp / _{(2πf m τ).} Here, for example, f _m
= 6 GHz, △ φ _pp = π, τ = 5 μs, v =
5000 m / s, which can realize an ultra-high speed of 15 times or more the speed of sound.

Next, the measurement light is generated by the measurement light generation unit 110.
Measurement light L_MES Measurement light that makes the light incident on the measurement unit 130
The injection unit 120 is provided with the measurement light L_MES Generate nonlinearities
The optical amplifier 121 amplifies the light to a certain extent. And
The measurement light L amplified by the optical amplifier 121_MES But
Enter into Percontinuum (SC) fiber 122
Fired. This SC fiber 122 has a self-position inside.
Measurement light L by phase modulation _MES That is, the optical frequency comb
Enlarge the cuttle. This increases the resolution. Obedience
In the past, spectral expansion was performed using a similar method.
The tor width has reached 30 THz, and the resolution is equal to the speed of light / (2
n_sampleSpectrum width), the resolution is 3 μm or less.
It can be seen that high resolution can be obtained. The above SC file
The spectrum is expanded by Iver 122, and the resolution is improved.
Measurement light L_MES Self-phase modulation occurs in the subsequent process.
In order not to come in
To reduce the peak intensity,
Incident on the vessel 131.

The light separating / combining unit 131 of the measuring unit 130
Then, the measurement light L _MES generated by the measurement light generation unit 110 is branched, and one is _input to the optical delay line 132 as the reference light L _REF , and the other is input from the dispersion compensation fiber 133 to the scanner 134 as the object light L _OB. The object to be measured OB is irradiated therethrough.

The optical delay line 132 includes a dispersion compensating fiber 132A, a delay fiber 132B, a frequency shifter 1
32C and a mirror 132D. This optical delay path 13
Reference light L _REF incident on the dispersion compensating fiber 1
32A, delay fiber 132B and frequency shifter 13
2C, is reflected by the mirror 132D, and is again passed through the frequency shifter 132C, the delay fiber 132B, and the dispersion compensation fiber 132A.
31. The frequency shifter 132C outputs the reference light L
The frequency of the _REF is shifted by f _S round-trip. As a result, the frequency shift equivalent to the Doppler shift is changed to the reference light L
Generate on _REF . Thus, the frequency shifter 132C
By modulating the reference light L _REF with f _S ,
As described later, phase information can be obtained by detecting the interference signal S _DET as an AC signal, and a frequency component of f _S ± m △ f can be identified.

Further, has been the object beam L _OB separated by the light separating and synthesizing unit 131, the object beam L _OB irradiated to the measurement object OB via the scanner 134 from the dispersion compensating fiber 133, the scanner 134 and distributed Compensating fiber 1
The light is incident on the light separating / combining device 131 via 33.

Here, the delay time given to the reference light L _REF by the optical delay line 132 is _equal to the delay time of the optical splitter / combiner 1.
The length of each fiber is set so as to be larger by τ than the delay time required for the object light L _OB separated by 31 to be reflected by the object to be measured OB and return to the light splitter / combiner 131. Have been. Note that the dispersion compensating fibers 132A and 133 are the characteristics of the delay fiber 132B,
Alternatively, depending on the configuration of the signal processing system, 1: not necessary, 2: either is required, 3: both may be required, but the dispersion and length are set so as to compensate for the dispersion of the delay fiber 132B, Try to minimize the effect on interfering signals.

Here, the dispersion compensating fibers 132A, 1
Reference _numeral 33 serves to equalize the dispersion on the path experienced by the reference light L _REF and the dispersion on the path experienced by the object light L _OB when they differ. For example, when the delay fiber 132B has a positive dispersion, for example, the dispersion compensating fiber 132A
For example, a high-order dispersion is compensated using a dispersion compensating fiber 133 using an optical fiber having a negative dispersion. As a result, it is possible to reduce the influence of the dispersion by the delay fiber 132B on the interference signal and reduce the deterioration of the resolution.

For example, the length of the delay fiber 132B,
Refractive index, first-order and second-order group velocity dispersions are represented by L _C and n, respectively.
_C , k _2C and k _3C, and the dispersion compensating fiber 132
The length, refractive index, first-order and second-order group velocity dispersions of A are denoted by L _D , n _D , k _2D, and k _3D , respectively. Let L _E , n _E , k _2E, and k _3E be the group velocity variances of, respectively, a condition for obtaining a delay time τ τ = 2 (L _C n _C + L _D n _D −L _E n _E ) / C First order group to compensate for the velocity dispersion condition _{0 = L C k 2C + L} D k 2D -L E k 2E secondary condition for compensating for group velocity dispersion _{0 = L C k 3C + L} D k 3D -L E k 3E triplicate The simultaneous equations L _C , L _D and L _E may be determined. It is also possible to compensate for higher order dispersions. Although an example using an optical fiber is shown here, dispersion may be compensated for using a black reflector or the like, or spatially compensated for using a prism pair or the like.

In the scanner 134, the object light L _OB is incident from the light separating / combining unit 131 of the measuring unit 130 via the dispersion compensating fiber 133. This scanner 134
The object light L _OB is scanned on the surface of the measurement object OB according to the scanner control signal given by the scanner control signal generator 152 of the control unit 150. Also, the scanner 134
The object light L _OB reflected inside the object to be measured _OB is incident, and the object light L _OB is returned to the light separating / combining unit 131 of the measuring unit 130 via the dispersion compensation fiber 133.

As shown in FIG. 6, for example, as shown in FIG. 6, the scanner 134 outputs the object light L _OB which enters from the dispersion compensating fiber 133 via the fiber collimator 134A and irradiates the object to be measured OB via the lens 134D. The first polygon mirror 134B performs scanning in the direction perpendicular to the paper of the drawing, and further, the second polygon mirror 134B.
By C, scanning is performed in the direction parallel to the plane of the drawing. Also,
For example, as shown in FIG. 7, the scanner 134 may perform scanning in a direction perpendicular and parallel to the paper surface by using an acousto-optic element 134F instead of the first and second polygon mirrors 134B and 134C. . Acousto-optic device 1
When scanning using 34F, the acousto-optic device may cause a frequency shift of light. In that case, it is necessary to remove the effect of the frequency shift by the scanner 134 from the interference signal. For example, the signal processing unit 140 uses the scanner 13
4 is estimated from the signal of the control unit 150 and is removed from the interference signal. Further, as shown in FIG. 7, another frequency shift correction acousto-optic device 134E
The frequency shift may be eliminated by using an AOM for frequency shift correction on hardware.

In the above description, the scanning in the depth direction is performed electrically, but the scanning in the left and right direction of the object is performed mechanically and acousto-optically. Therefore, the final OC
The operating speed of the T device is determined by this scan speed. The OCT apparatus can be configured without using such a scanner 134.

That is, as shown in FIG. 8, the measuring unit 130 is transmitted from the measuring light injection unit 120 through the optical fiber 123.
The measurement light L _MES incident on the light separating / combining device 131 is spatially propagated from the optical fiber 123 and converted into parallel light by the collimator lens 136A.
1 Here, the collimator lens 136A that converts the measurement light L _MES into parallel light selects an appropriate focal length, and irradiates the object light L _OB to the entire object OB. On the other hand, the reference light L _REF is converted into a parallel beam that has been similarly expanded, and is transmitted through the optical delay path 1
32. In light separating and synthesizing unit 131, among the object light L _OB reflected from the measurement object OB, by installing the half mirror so as to interfere with the reference light L _REF to light returned by the same path object light L _OB The interference light L _DET is generated by combining with the reference light L _REF . Then, the interference light L _DET is detected by the photodetector array 135A.

At this time, for example, the object light L _OB illuminated on the object to be measured OB along the path between the points P and P ′ and reflected therefrom interferes with the reference light L _REF at different points on the photodetector array 135A, respectively. Generates light L _DET . The photodetector array 1
There are different photodetectors at two different points on 35A,
An interference signal S _DET can be obtained independently of each other. The respective time waveforms of the photodetector array 135A are recorded simultaneously, for example, signals from time A to time B in FIG. Each photodetector of the photodetector array 135A detects the interference light L _DET of the object light L _OB and the reference light L _REF reflected at each point of the measurement object _OB, and independently detects interference signals. S _DET can be obtained, from which internal information of the measurement object OB can be obtained.

Therefore, if this method is used, the beam of the object to be measured OB can be simultaneously measured without performing beam scanning on the object.
Dimensional information can be obtained. Also, the reference light L _REF
By using an optical frequency comb for the object light LOB and the object light _LOB , information in the depth direction can be obtained at high speed. Therefore, the three-dimensional information of the object can be obtained at a higher speed without using any mechanical or acousto-optical method.

For example, when the present optical frequency comb is used, the time required for one measurement in the present method is τ. Therefore, for example, ultrahigh-speed measurement can be realized with τ = 5 μs.

Note that, as shown in FIG.
C, 136D, 136E, and 136F are used to irradiate the entire object OB with the object light L _OB to form an optical image of the object OB on the photodetector array 135A, and the reference light L _REF is Photodetector array 135A as parallel beam
With the configuration of irradiating upward, the object OB to be measured can be used even when the object OB is large and light needs to be irradiated from a distance.

In the OCT apparatus 100 shown in FIG. 4, the signal processing unit 140 includes the reference light L _REF and the object light L modulated by f _S detected by the photodetector 135.
Interference signal S obtained as detection output of interference light L _DET of _OB
DET is entered.

In the signal processing section 140, unnecessary noise is removed by a band-pass filter or the like, amplified, and the interference signal S _DET modulated at f _S is frequency-converted, for example, to _facilitate subsequent signal processing. , A / D converted and digitized. Thereafter, for example, the following some signal processing is performed.

1. For example, the interference signal S _DET may pass through a long delay fiber 132B, and the signal may be disturbed due to the dispersion of the optical fiber, for example, the resolution may be reduced. In that case, a process for correcting it is performed. The digitized signal is stored in the delay fiber 132 in advance, for example.
The effect of dispersion, such as B, is calculated from the structure of the optical fiber, and a calculation is performed to convert the signal into a signal with reduced influence of dispersion. Alternatively, a calculation is performed to convert a signal into a signal in which the influence of dispersion is reduced from a result of measurement using a sample having a simple reflection measurement such as a metal mirror in advance.

Here, the latter example will be described. Complex amplitude of the output by the optical frequency comb generator 112 measurement light m following sideband _{E m (t) = E m} exp (i2πνt + i2πmf m t + imφ
(t)). i is a prime number. Dispersion compensating fiber 13
2A, 133 0 the length of the delay fiber length When L of ^{_{132B, E m 'exp (i2πνt}} + i2πf S is after the preceding light propagating through the optical fiber and ignoring secondary and subsequent components of the group velocity dispersion t + i2πmf _m t-i
_{k 0C L C -ik 1C L C} (2πmf m) -ik 2C L C (2πm
f _m) are expressed as ^{2/2 + imφ (t-} τ)). Thus the interference signal between the m-th order sideband when the measurement object OB is mirror ^{_{Re [E m 'E m *}} exp (i2πf S t-ik 0C L C -ik 1C L C
_{(2πmf m) -ik 2C L C} (2πmf m) 2/2 + im (φ (t
−τ) −φ (t)))]. Here, for the time t is from 0 to τ, φ (t−τ)
-Φ (t) = - a _{2 △ φ pp / τt, 2} △ φ pp / τ = 2π △ f To signal far ^{_{E m 'E m * cos (}} 2π (f S -m △ f) t- k _{0CL C} -k _1CL
An interference signal proportional to _{C (2πmf m) -k 2C L} C (2πmf m) 2/2))). By Fourier transforming the interference signal, among the signal components, have a phase component of a frequency of f _S frequency components -m △ f is the light [nu + mf _m, the comparison measure this and other frequency components The value of the first order group velocity variance k _2C can be determined. Thus _{exp (ik 2C L C (2πmf} m) 2/2))) As a result of correcting the dispersion if Jozure Fourier transformed value of the interference signal is obtained from the actual measurement.

2. For example, a process of emphasizing a high-frequency component (a component far from f _{S; a} component having a large absolute value of m) included in the signal is performed, and a calculation for converting the signal into a signal with improved resolution is performed.

3. For example the variation of the frequency of the signal f _S in modulated interference signal calculated from the signal, by determining the Doppler shift amount, to obtain the velocity of the target object.

4. For example, the amount of light absorption for each wavelength is measured from the spectrum shape of the interference signal, and the refractive index and the like of the target object are obtained.

5. Calculate the envelope of the interference signal.

From the above information, the shape, velocity distribution, refractive index distribution and the like of the object to be measured can be comprehensively obtained.

Here, a method using digital calculation has been described as a method of compensating for the dispersion contained in the interference signal. However, an analog element such as a SAW device which is a dispersive element may be used.

6. When scanning is performed by the scanner 134 using the acousto-optic device 134F as shown in FIG. 7, the acousto-optic device 134F may cause a frequency shift of light. In that case, it is necessary to remove the effect of the frequency shift by the scanner 134 from the interference signal. The effect of the frequency shift by the scanner 134 is estimated from the signal of the system controller 151 and is removed from the interference signal.

Further, in the OCT apparatus 100 shown in FIG.
1, the signal processed by the signal processing unit 140 and the phase control signal generator 11 of the measurement light generation unit 110.
3C, a scanner control signal generator 1 for generating a scanner control signal to be given to the scanner 134 of the measuring unit 130
The control signal to the control unit 52 is integrated, converted into a data format recognized by a person as an image or the like in accordance with an input performed by the user, and transmitted to the image output device 153. For example, a three-dimensional image or a cross-sectional image is output as a moving image.

Here, the OCT apparatus 100 shown in FIG. 4 uses the optical delay line 132 which gives a delay time of τ time in both directions, but as shown in FIG. 10, gives a delay amount of τ time in one way. A configuration using the optical delay line 132 may be employed.

[0066] In the OCT apparatus 200 shown in FIG. 10, provided a light separator 231A and synthesizer 231B in place of the optical separating and combiner 131 described above, the reference light L _REF measurement light L _{ME S} by the optical splitter 231A Separate into the object light L _OB . The reference light L _REF separated from the measurement light L _MES by the light splitter 231A is applied to an optical delay line 2 that gives a one-way delay amount of τ time.
A delay amount of τ time is given by 32, and the light enters the optical combiner 231B via the isolator 232D. The optical delay line 232 includes a dispersion compensating fiber 232A, a delay fiber 232B, a frequency shifter 232C, and an isolator 232D. The object light L _OB separated from the measurement light L _MES by the light separator 231A is transmitted from the dispersion compensating fiber 233 to the isolator 2.
The light enters the light combiner 231B through the light combiner 34, passes through the light combiner 231B, and enters the scanner 134. In the OCT apparatus 200, the other components are the above-described OCT apparatus.
Since it is the same as the CT apparatus 100, it is denoted by the same reference numeral in FIG. 10 and detailed description thereof will be omitted.

As described above, the present invention has been described with respect to an optical measurement system for realizing a spatially high-resolution measurement represented by an OCT apparatus, among optical measurement systems requiring a wide spectral width in an arbitrary wavelength range. However, the present invention is also applied to a measuring device that requires a high optical frequency resolution.

The OCT device is a device for measuring spatial resolution, but at the same time can measure response characteristics and phase characteristics due to differences in wavelength of target light.

For example, the present invention can also be used to measure the wavelength dependence of reflection of an optical device or the like that is connected to an object to be measured by an optical fiber without using a scanner.

In this case, high-resolution measurement equal to the modulation frequency of the optical frequency comb can be realized in a short time.

For example, an m-order sideband is reflected from an object, and the complex amplitude is the transfer function of the sample A _m = A (ν + m
f _m) is changed to A _m E _m ^'from E _m by. A portion corresponding to the m-th order frequency components obtained therefrom signals ^{_{Re [A m E m 'E}} m * exp (i2πf S t-ik 0C L-ik 1C
_{L (2πmf m) -ik 2C L} (2πmf m) 2/2 + im (φ
(t−τ) −φ (t)))]. This component is, for example, φ (t−τ) −φ (t) = − 2 △
When φ _pp / τ t = 2π △ ft, the frequency component of f _s −n △ f of the electrical signal is obtained by Fourier transform,
Only A _m can be determined by previously measuring the variance or the like of E _m and delay fibers.

Further, for example, the configuration shown in FIG. 11 can be used for measurement of a transmission type device such as a filter.

FIG. 11 shows an optical device having a basic configuration.
The transmission measurement device 20 of the₀ Out
A laser light source 21 that emits light, and a laser light source 1
1 to laser light L₀ Frequency comb generator 2 into which light is incident
2 and the modulation signal S given to the optical frequency comb generator 22.
_MOD And a modulation signal generator 23 for generating
Measurement light L generated by creature 23_MES With reference light L_REF 
And object light L_OBLight separator 24 for separating light into light
Reference light L separated by 24_REF A predetermined time τ
From the optical delay path 25 for providing
Measurement light L _MES Is incident through the object to be measured OB
And a delay of a predetermined time τ by the optical delay path 25.
Given reference light L_REF Is incident on the photosynthesizer 26
And the reference light L synthesized by the light synthesizer 24_REF When
Object light L_OBInterference light L with_DET Changes in light intensity
And a photodetector 27.

In the optical device transmission measuring apparatus 20 having such a configuration, a transmission device such as a filter can be measured as the object to be measured OB, and the transmission and reflection characteristics of the optical device and the like can be measured with high resolution and high speed. Can be done.

Further, the optical device measuring apparatus 300 shown in FIG. 12 is a modification of the OCT apparatus 200 shown in FIG. 10 described above, which performs reflection measurement and transmission measurement of an optical device. The control signal generator 152 is omitted, and a second light splitter 331A, a second light combiner 331B, and a second light detector 335 are provided.

In this optical device measuring apparatus 300,
The second light splitter 331A is connected to the isolator 232D.
The reference light L incident on the light combiner 231B via the_REF To
The light is further branched and the second reference light L_REF2To generate this second
Reference light L_REF2To the second light combiner 331B
You. The second light combiner 331B converts the object OB to be measured
Object light L that has passed_OBIs incident, and the second reference light L
_REF2And object light L_OBAnd the second interference light L_DET Generate a
Then, the second interference light L_DET To the second photodetector 335
Make it incident. This second photodetector 335 is connected to the second
Interference light L_DET2Changes in the light intensity of the
Interference signal S for transmission measurement obtained by _DET2The signal
This is supplied to the processing unit 140.

In this optical device measuring apparatus 300,
The other components are the same as those of the above-described OCT apparatus 200, and therefore are denoted by the same reference numerals in FIG. 12 and detailed description thereof will be omitted.

The optical device measuring apparatus 30 having such a configuration is described.
At 0, transmission and reflection characteristics can be measured simultaneously with high resolution and high speed. In addition, if the measurement is performed in a configuration in which the input and output of the specific object OB are inverted, the S parameter of the optical device can be measured.

[0079]

As described above in detail, according to the present invention, in the optical frequency comb generating means, the first period τ ₁
The modulation signal from the modulation signal generating means in the second period tau ₂ at a first frequency f _m which generates at a predetermined repetition cycle modulated signal of the second frequency f _m + Delta] f is the coherence of the light source by modulating the incident light with and a center frequency of the incident light, the the first time period tau ₁ has a sideband every first frequency f _m spacing, in the second period tau ₂ Is the second
, Measuring light having sidebands is generated at intervals of the frequency f _m + Δf, and the generated measuring light is separated into reference light and object light by a light separating means, and given to the reference light by a predetermined time delay by an optical delay means. By combining the reflected light or transmitted light of the object light by the object to be measured with the reference light delayed by a predetermined time by the optical delay means by a light combining means, interference light between the reference light and the object light is obtained. Is generated, and the change in the light intensity of the interference light is detected by the detecting means, so that the spatially high-resolution measurement can be performed in a short time and stably with a simple configuration using one frequency comb generator. it can.

Further, the irradiation position of the object light separated by the light separating means is scanned on the object to be measured, and shape information for detecting the shape information of the object to be measured is detected based on the interference detection result from the detecting means. Using a plurality of pieces of shape information generated by the means, an image showing the shape of the measurement object is generated by the image generating means, so that the configuration is simple and stable in a short time using a single frequency comb generator. An optical measurement system that functions as an OCT device that performs spatially high-resolution measurement can be realized.

[0081]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an OCT apparatus to which the present invention is applied.

FIG. 2 is a diagram showing a temporal change of an object beam and a reference beam in the OCT apparatus.

FIG. 3 is a block diagram showing a basic configuration of an OCT apparatus configured to increase resolution.

FIG. 4 is a block diagram showing a configuration of an embodiment of an OCT apparatus to which the present invention is applied.

FIG. 5 is a diagram schematically showing an operation of a modulation signal generator in a measurement light generator of the OCT apparatus.

FIG. 6 is a diagram schematically illustrating a configuration example of a scanner in a measurement unit of the OCT apparatus.

FIG. 7 is a diagram schematically illustrating another configuration example of the scanner.

FIG. 8 is a diagram schematically illustrating a configuration example of a main part when an OCT apparatus is configured without using a scanner.

FIG. 9 is a diagram schematically illustrating another configuration example of the main part when the OCT apparatus is configured without using the scanner.

FIG. 10 is a block diagram illustrating another configuration example of the OCT apparatus to which the present invention is applied.

FIG. 11 is a block diagram showing a basic configuration of a transmission measurement apparatus for an optical device to which the present invention is applied.

FIG. 12 is a block diagram illustrating a configuration example of an optical device measurement apparatus to which the present invention has been applied.

FIG. 13 is a block diagram showing a configuration of a conventional OCT apparatus.

[Explanation of symbols]

10 OCT device, 11 laser light source, 12 optical frequency comb generator, 13 modulation signal generator, 14 optical separator / combiner, 15 optical delay line, 16 optical detector, 17 optical amplifier, 18 SC fiber, OB measurement object , 20
Transmission measuring device, 21 laser light source, 22 optical frequency comb generator, 23 modulation signal generator, 24 optical separator, 25
Optical delay paths 25, 26 Optical synthesizer, 27 Optical detector, 10
0 OCT device, 110 measurement light generator, 111 laser light source, 112 optical frequency comb generator, 113 modulation signal generator, 113A microwave oscillator, 113B phase shifter, 113C phase control signal generator, 120 measurement light injector, 121 Optical amplifier, 122 SC fiber, 130 Measurement unit, 131 Optical separator / combiner, 132
Optical delay path, 133 dispersion compensating fiber, 134 scanner 134, 130 measuring unit, 132A dispersion compensating fiber, 132B delay fiber, 132C frequency shifter, 132D mirror 132D, 140 signal processing unit, 150 control unit, 151 system controller, 152 scanner control Signal generator, 153 image output device, 200 OCT device, 231A light separator, 2
31B optical synthesizer, 232 optical delay line, 232D isolator, 232C frequency shifter, 300 optical device measuring apparatus, 331A second optical separator, 331B second
335, the second photodetector

Continuation of the front page F term (reference) 2F064 AA15 CC04 FF01 GG02 GG12 GG22 GG51 GG55 GG70 JJ03 JJ15 2F065 AA52 BB05 CC16 DD03 FF51 GG04 JJ01 LL02 LL12 LL53 LL57 MM16 MM26 NN08 GG01 GG01 GG08 MM01 MM09

Claims (6)

[Claims] 1. A coherent light source for emitting light having a, the first period tau ₁ second period at a first frequency f _m tau ₂
The modulates a modulation signal generating means for generating a repeating cycle modulated signal of a predetermined second frequency f _m + Delta] f, by a modulation signal from the modulation signal generation means incident light from the light source, the incident light the frequency and the center frequency, the the first time period tau ₁ has a sideband every first frequency f _m spacing, in the second period tau ₂ second frequency f _m +
Optical frequency comb generating means for generating measurement light having sidebands at every Δf interval; light separating means for separating the measuring light from the optical frequency comb generating means into reference light and object light; separation by the light separating means An optical delay unit that delays one of the reference light and the object light for a predetermined time; a light combining unit that combines the reference light with the reflected light or transmitted light of the object light by the measurement target; and the light combining unit. An optical measurement system comprising: a detection unit configured to detect a change in light intensity due to interference between the synthesized reference light and the object light. 2. The optical measurement system according to claim 1, wherein said optical delay means comprises an optical fiber. 3. An optical amplifying means for amplifying measurement light generated by the optical frequency comb generator to such an extent that non-linearity is generated by an optical amplifying means, and making the measuring light incident on the light separating means via a supercontinuum fiber. The optical measurement system according to claim 1, wherein: 4. A coherent light source for emitting light having a, the first period tau ₁ second period at a first frequency f _m tau ₂
The modulates a modulation signal generating means for generating a repeating cycle modulated signal of a predetermined second frequency f _m + Delta] f, by a modulation signal from the modulation signal generation means incident light from the light source, the incident light the frequency and the center frequency, the the first time period tau ₁ has a sideband every first frequency f _m spacing, in the second period tau ₂ second frequency f _m +
Optical frequency comb generating means for generating measurement light having sidebands at every Δf interval; light separating means for separating the measuring light from the optical frequency comb generating means into reference light and object light; separation by the light separating means An optical delay unit that delays one of the reference light and the object light by a predetermined time, a scanning unit that scans an irradiation position of the object light separated by the light separation unit on a measurement target, and the measurement target Light combining means for combining the object light reflected by an object with the reference light; detecting means for detecting a change in light intensity due to interference between the reference light and the object light combined by the light combining means; and the detecting means Based on the interference detection result from, based on the shape detection means for detecting the shape information of the object to be measured, by scanning with the scanning means, using a plurality of shape information generated by the shape detection means, measurement Optical measurement system, characterized in that it comprises an image generating means for generating an image showing the shape of an elephant thereof. 5. The optical measurement system according to claim 4, wherein said optical delay means comprises an optical fiber. 6. The measuring light generated by the optical frequency comb generator is amplified by an optical amplifying means to such an extent that nonlinearity is generated, and the amplified light is incident on the light separating means via a supercontinuum fiber. The optical measurement system according to claim 5, wherein: