JP3245135B2 - Optical measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating an object to be measured, in particular, a light scattering medium with a light beam, and utilizing the light transmitted (transmitted or reflected) through the object to be measured to obtain the light of the object to be measured. The present invention relates to an optical measurement device that performs measurement.

[0002]

2. Description of the Related Art Imaging techniques for using X-rays to see through, for example, biological tissue or the internal morphology of a sample naturally or covered with an artificial coating are known in the medical, scientific and industrial fields. Widely used in

[0003] In recent years, optical image measurement technology using a laser light source or the like is safe, that is, de-radiation and de-isotope. Have been. Above all, optical image measurement of living tissue is one of promising application fields.

[0004] By the way, a sample having a non-uniform component such as a human body or a living tissue (analyte to be measured) is generally invisible because its light is remarkably multiple-scattered inside. It is. The biggest difficulty in optically measuring such a scattering medium is how to extract the signal light that follows the optical path that can be tracked, out of the transmitted light or reflected light emitted from the test sample in all directions. It is in.

[0005] One of the methods for making this possible is an optical coherent detection method which focuses on the loss of coherence of signal light due to light scattering [see, for example, K. et al. P. Ch
an, B .; Devaraj, M .; Yamada, H .; I
nabas, "Physicsin Medicine"
and Biology ", Vol. 42, 855 (1
997)].

The optical coherent detection method is an optical measurement method based on an optical heterodyne detection method.

FIG. 15 is a basic configuration diagram of such a conventional optical heterodyne detection system.

In FIG. 1, a coherent light beam emitted from a laser light source 1 is split into a signal light and a reference light by a first beam splitter 2. The signal light is
For example, the signal light is incident on the specimen 6 made of a scattering medium, and the signal light transmitted through the specimen 6 is transmitted through the second beam splitter 8 and is incident on the photodetector 9.

On the other hand, the reference light undergoes a frequency shift of Δf by a frequency shifter 3 such as an AOM (acoustic optical element), and is superimposed on the signal light by a second beam splitter 8 and is incident on a photodetector 9. I do. In FIG. 15,
4 and 5 are reflection mirrors, and 7 is an X- drive for driving the specimen 6 to be measured.
The Y stage 10 is a signal processing system that processes a signal obtained from the photodetector 9.

On the light receiving surface of the photodetector 9, interference light composed of signal light and reference light having different frequencies is generated, and the light detector 9 corresponds to a frequency difference Δf between the signal light and the reference light. A frequency heterodyne signal is output.

The optical measurement based on such an optical heterodyne detection method is not only a straight light component that travels straight without being essentially scattered, but also a time coherence of incident light that propagates forward while being scattered. It is characterized in that the scattered light component emitted from the scatterer can be detected while holding the portion.

FIG. 16 is a diagram showing a state of light scattering that is received by a conventional signal light on the entrance and exit surfaces of a scattering medium and inside.

In this figure, 11 is a scattering medium, 12 is an incident light wave, 13 is an outgoing light wave, and arrows in the scattering medium 11 indicate the spatial spread of the incident light beam accompanying scattering.

As shown in FIG. 16, in addition to surface scattering, multiple scattering received inside the scattering medium 11 causes
A noticeable distortion occurs in the wavefront of the light emitted from. The same applies to the signal light emitted while maintaining a part of the time coherence of the incident light.

Here, the detection of the signal light by the optical heterodyne detection method has been described with reference to the experimental example of measuring the transmitted light shown in FIGS. 15 and 16, but the reflected light from the test object 6 is detected by the optical heterodyne detection. Measurement [for example, Naohiro Tanno, “Optics”, Vol. 28, No. 3, 116
(1999)], the wavefront disturbance of the signal light is a common problem.

It has already been pointed out that such a spatially disturbed signal light cannot be effectively detected by the conventional optical heterodyne method [for example, K. et al. P. Chan, D .;
K. Ki11inger, “Optics Lette
rs ", Vo1.17.1237 (1992)].

Since such spatially disturbed signal light has a spatially random phase and intensity distribution, a strong fluctuation is observed in the detected optical heterodyne signal. This is known as one of laser speckle developments [see, for example, J.-K. C. Dainty, "Las
er Speck1e and Re1ated Ph
enomena ", published by Springer-Ver1ag (New York, 1975)].

As a method for effectively heterodyne-detecting a spatially disturbed optical signal, an optical heterodyne method using a two-dimensional detector array has been proposed [for example, K.K. P.
Chan, K .; Satori, H .; Inaba, "E1
electronics Letters ", Vo1.3
4.11101 (1998)].

FIG. 17 is a diagram showing the basic principle of an optical heterodyne system using a conventional two-dimensional detector array.

In this figure, 21 is a laser light source, 2
2 is a first beam splitter, 23 is a sample to be measured, 24
Is an XY stage, 25, 26, 27, 32, and 33 are lenses, 28 is a second beam splitter, 29 is a two-dimensional photodetector array, 30 and 34 are reflection mirrors, 31 is a phase modulator, and 35 is An array parallel data processing system 36 is a computer.

As shown in FIG. 17, the signal light emitted from the point of interest on the emission surface of the sample 23 to be measured is
The light is condensed at 26, and the signal light is further transmitted to the observation surface by the lens 27. A two-dimensional photodetector array 29 having a plurality of photodetectors is arranged on the observation surface, and the signal light on the surface is
For example, the light is superimposed on the reference light as a plane wave and causes optical interference.

In this case, if the signal light has a spatially irregular phase and intensity distribution, a plurality of interference signals obtained by each light receiving element also have different phases and intensities. Therefore, a plurality of light receiving signals obtained by the plurality of light receiving elements are integrated to form a signal of one point of interest.

Whereas conventionally, speckle noise was reduced by averaging signals "temporally", according to this method, speckle noise is averaged "spatially". The optical measurement can be performed at high speed and with a good signal-to-noise ratio (S / N).

[0024]

However, the light is detected by the conventional optical heterodyne detection method using a single photodetector or the photodetection method using a two-dimensional photodetector array shown in FIG. reception light intensity, the intensity of the reference light and signal light respectively I _r and I _s, also when the frequency difference and phase difference between both the light wave and Δf and [Delta] [theta], are represented as follows [e.g., Yoshizawa, Seta, "Optical heterodyne technology",
New Technology Communications Publishing (1994)].

[0025]

(Equation 1)

In the optical heterodyne measurement for detecting a minute signal light, the intensity of the reference light is much higher than the intensity of the signal light. Therefore, the photocurrent detected by the optical heterodyne method has a large DC component and an amplitude of √. A weak AC component proportional to (I _r I _s ) is superimposed. In conventional optical heterodyne measurement, such an alternating current (AC) component is extracted by, for example, an AC coupling (coupling) method, then amplified by an AC amplifier, and the amplitude is detected using, for example, a rectification detection circuit.

However, when a conventional AC signal detection method is applied to optical heterodyne measurement using a two-dimensional photodetector array, as shown in FIG. 18, a signal processing system having a number of channels corresponding to the number of elements in the array is used. However, there is a problem in practically increasing the number of elements of the array. FIG.
In 8, 41 is a rectifier detector and 42 is an integrating circuit.

The present invention has been made in view of the above circumstances, and has as its object to provide an optical measurement device capable of effectively performing optical heterodyne measurement using a two-dimensional photodetector array.

[0029]

In order to achieve the above object, the present invention provides: [1] In an optical measuring device, a light source for emitting a light beam and a light beam emitted from the light source are connected to an object to be measured. Signal light passing through the arrangement position of the analyte to be arranged,
The optical path passing through the arrangement position of the measured sample and the reference light passing through a different optical path are divided into two, and the signal light after passing through the arrangement position of the measured object, and the reference light passing through the different optical path. Are superimposed on each other, an interference optical system that generates interference light in which the signal light and the reference light interfere with each other, and the interference optical system relatively sets the frequency of the signal light and the frequency of the reference light relatively. A frequency shifter for shifting, and the interference optical system includes an optical device that periodically blocks light on at least one of the optical path of the signal light and the reference light, and sets a cutoff frequency of the optical device to the signal light. And a frequency difference between the reference light and the reference light.

[2] In the optical measuring device according to [1], the light blocking operation of the optical device is synchronized with a reference signal having a frequency equal to a frequency difference between the signal light and the reference light, and The start and end of the cutoff operation are performed by using a specific phase value of the reference signal as a reference, and the interference light is changed to a different measurement start time and a different measurement time by changing the reference phase value to a different value. It is characterized by being cut out by width.

[3] In the optical measuring device according to the above [1], the interference optical system includes a photodetector for obtaining a light detection signal by receiving the interference light, and the interference optical system further comprises: The signal light at the point of interest on the propagation path of the signal light is transmitted to the photodetector on the surface or inside of the test specimen arranged at the arrangement position of the specimen, and Superimposing the reference light, the photodetector has a plurality of light receiving elements arranged spatially, each of which independently obtains a light receiving signal, furthermore, a plurality of light receiving signals obtained by the light detector And a signal processing unit for generating a signal corresponding to the point of interest.

[0032]

Embodiments of the present invention will be described below in detail.

According to the present invention, an AC component is extracted by temporally extracting an optical interference signal obtained by optical heterodyne measurement.

FIG. 1 is a configuration diagram of an optical heterodyne detection system showing a first embodiment of the present invention.

In this figure, 101 is a coherent light source, 102 is a first beam splitter, 103 is a first frequency shifter (AOM1, f ₁ ), 104 and 108 are reflection mirrors, 105, 106 and 113 are lenses, 107 Is a second beam splitter, 109 is a second frequency shifter (AOM2, f ₂ ), 110 is a pulse generator, 111 is a measured object, 112 is an XY stage, 114 is a photodetector, 115 is signal processing. System.

As shown in FIG. 1, a light beam emitted from a coherent light source 101 (for example, a laser light source) that outputs continuous output light is split into a signal light and a reference light by a first beam splitter 102.

The signal light is transmitted, for example, to the second frequency shifter 1
At 09, the frequency shift of f _{2 is applied to} the sample 111 made of, for example, a scattering medium.
1 is condensed by an optical lens 113, passes through a second beam splitter 107, and is
Incident on.

On the other hand, the reference light receives a frequency of f _{1 by} a _first frequency shifter 103 such as an AOM, and is superimposed on the signal light by a second beam splitter 107, so that a photodetector arranged on an observation surface is provided. It is incident on 114.

On the light receiving surface of the photodetector 114, an interference light composed of a signal light having a frequency difference | f ₂ −f ₁ | and a reference light is generated.

Although FIG. 1 is configured based on the principle of a Mach-Zehnder interferometer, the present invention provides a different feature from the conventional optical heterodyne interferometer by providing the following mechanism in the interferometer. Provide an optical measurement device having
Here, at least one of the reference light and the signal light is periodically on-off (blocked). Its on-o
The ff frequency is always the frequency difference between the two light waves (| f ₂ −f ₁
| = Δf).

Such a light blocking operation is described in, for example, FIG.
In this case, at least one of the first frequency shifter and the second frequency shifter may be turned on and off at the frequency Δf. When the frequency shifter is in the “off” state, the light beam incident on the frequency shifter does not receive a frequency shift,
As shown by the dotted line in FIG. 1, the light is emitted from the frequency shifter at the same angle as the incident angle.

Further, according to the present invention, as the photodetector 114 disposed on the observation surface, an image sensor in which light receiving elements are arranged one-dimensionally or two-dimensionally, for example, a CCD (charge)
-Coupled device) Use a camera.

Hereinafter, the measurement principle according to the present invention will be described.

FIG. 2 is an explanatory diagram of the principle of measurement by optical heterodyne detection according to the present invention, wherein the vertical axis indicates the intensity of the interference light and the horizontal axis indicates the time.

A waveform a in FIG. 2A shows a time waveform of the interference light generated on the surface of the photodetector 114 when the signal light and the reference light are both continuous lights in the optical heterodyne measurement. . As shown in the above equation (1), the optical interference signal has a DC component proportional to the intensity of the reference light and the signal light,
| F ₁ −f ₂ | = AC component having a frequency of Δf.

Further, a waveform b in FIG. 2B shows a time waveform of the interference light generated by the present invention.
By “on-off” both light beams of the signal light and the reference light at a frequency of Δf = | f ₁ −f ₂ |, the interference light becomes
It is temporally “cut out” at the frequency Δf. The “cutout” operation of the interference light will be described below using mathematical expressions.

The coherent light emitted from the continuous light source is considered as a sinusoidal wave of an electric field having an amplitude A, each frequency ω (ω = 2πf), and a phase θ. That is,

[0048]

(Equation 2)

The light intensity is expressed as follows.

[0050]

(Equation 3)

In FIG. 1, if the first frequency shifter 103 and the second frequency shifter 109 are always in the “on” state, each of the first frequency shifter 10 and the first frequency shifter 10 is converted into a first-order diffracted light.
The reference light and the signal light emitted from the third and second frequency shifters 109 are both continuous lights, and the respective electric fields E _r and E _s
Can be expressed as follows.

[0052]

(Equation 4)

[0053]

(Equation 5)

Where ω ₁ = 2π (f + f ₁ ) and ω _1
2 = 2π (f + f ₂ ).

Next, the signal light and the reference light are both Δf = | f
Consider that the signal is periodically turned on and off at a frequency of ₁₋ f ₂ |.

For example, "on-off" of the frequency shifter
Assuming that the light intensity of the first-order diffracted light emitted from the frequency shifter by the operation also becomes “on-off”, the “on-off” operation of the frequency shifter modulates the intensity of the continuous light beam incident on the frequency shifter by the modulation rate M The intensity modulation of (t) and the intensity modulation of the modulation rate M (t) are performed on the electric field.

The interference light formed on the surface of the photodetector 114 in FIG. 1 can be expressed as follows.

[0058]

(Equation 6)

Here, Δθ = | θ ₁ −θ ₂ |. Next, the “on-off” operation of the frequency shifter, for example, the rectangular operation shown in FIG.
Expand as follows.

[0060]

(Equation 7)

According to the present invention, T = 1 / Δf = 1 / | f ₁ -f
₂ | A photodetector that accumulates interference light that is temporally cut out at a period of |, for example, a CCD in which light receiving elements are spatially arranged.
(Charge-coupled device) Detection is performed by a camera. Since the electric output of such a storage type photodetector integrates the interference light over a fixed integration time, it is given as follows from equation (6).

[0062]

(Equation 8)

Substituting equation (7) into equation (8) and rearranging, the first term of the integration is:

[0064]

(Equation 9)

And similarly, the second term is

[0066]

(Equation 10)

Is obtained. The third term is

[0068]

[Equation 11]

Is obtained. In Equation (11), if the period T = 2π / Δω of the optical interference signal is sufficiently shorter than the integration time, the interference signal represented by the first term is averaged and regarded as zero. On the other hand, the second term is

[0070]

(Equation 12)

Is obtained. Equations (9), (10) and (1)
From the result of 2), the output of the accumulation type photodetector represented by the equation (8) is given as follows.

[0072]

(Equation 13)

[0073] Formula As can perceive from (13), the output of the photodetector, in addition to the intensity of the signal light and reference light, the optical interference signal amplitude [√ (I _s I _r)] and the phase ([Delta] [theta] ) Is included.

As described above, according to the present invention, the interference light is temporally cut out at the same frequency as the interference frequency, and further, the light interference signal is output as a DC value by using the means for receiving the light with the accumulation type photodetector. This is fundamentally different from the conventional optical heterodyne measurement that outputs an optical interference signal as an AC component.

Further, the present invention is characterized by the following measuring means.

The "cut-out" operation of the interference light according to the present invention will be described. That is, following the measurement of i ₁ expressed by the equation (13), the timing of “cutting out” of the interference light
_A total of two measurements are performed with a time lag of T / 2 and T / 4, respectively, compared to the time of the first measurement. This means that the phase φ in Equation (7) is set to π
And π / 2. Therefore, the following two outputs are obtained from the photodetector 114 in accordance with the respective phase shifts.

[0077]

[Equation 14]

[0078]

(Equation 15)

FIGS. 4 (b), 4 (c) and 4 (d) show the time waveforms of the interference light corresponding to the equations (13), (14) and (15), respectively. . For comparison, a waveform a in FIG. 4A shows a time waveform of a sine wave having a frequency Δf.

The present invention is characterized in that the following signal operation processing is performed.

From equations (13), (14) and (15),

[0082]

(Equation 16)

[0083]

[Equation 17]

[0084]

(Equation 18)

Is calculated. Based on the information, information on the intensity and phase of the signal light is obtained from the following calculation method.

[0086]

[Equation 19]

[0087]

(Equation 20)

It is clear that the timing of cutting out the interference light differs in the measurement of i ₁ , i ₂ and i ₃ . One example of the execution means is shown in FIG. FIG.
5A shows a reference signal, and FIG. 5B shows an on-off signal of a frequency shifter (photoacoustic modulator). Here, a sine wave having the same frequency as the frequency Δf of the optical interference signal is used as a reference signal.

In FIG. 5, _assuming that the measurement times of i ₁ , i ₂ and i ₃ are T _meas , the measurement time T _meas (T _meas
During (≫Δf ⁻¹ ), N (N = T _meas Δf) times of “cutout” of the interference light is performed.

Therefore, in the measurement of i ₁ , for example, in the case of FIG. 1, the start time of the “on” operation of AOM1 and AOM2 is set to the maximum value of the reference signal (cos φ = 1) as the reference point, and Assuming that the end time of the operation is the minimum value of the reference signal (cos φ = −1) as a reference point, in the next measurement of i ₂ , the start time of the “on” operation of AOM1 and AOM2 is the minimum value of the reference signal (cosφ = -1). cosφ = −1) and the end time of the “on” operation may be a point at which the reference signal reaches the maximum value (cosφ = 1).

Further, in the measurement of i ₃ performed after i ₂ , the start time of the “on” operation of AOM1 and AOM2 is the point at which the reference signal reaches a zero value (cos φ = 0), and the “off” operation May be set to a point at which the reference signal reaches the next zero value (cos φ = 0).

As shown in FIG. 5, it is desirable that the measured values of i ₁ , i ₂ and i ₃ be transferred to the signal processing system immediately after detection. During the data transfer, the interference light is always “off”.

Hereinafter, further embodiments will be described.

FIG. 6 is a configuration diagram of an optical heterodyne detection system showing a second embodiment of the present invention. Here, an embodiment using a low-coherent light source of continuous output as a light source of the optical measurement device of FIG. 1 will be described.

In this figure, 201 is a low coherent light source, 202 is a first beam splitter whose position is fixed, 203 is a first frequency shifter (AOM1, f ₁ ),
204 is a second prism to be Z-scanned, 205 and 2
09 is a reflection mirror, 206, 207 and 214 are lenses,
208 is a first prism, 210 is a second frequency shifter (AOM2, f ₂ ), 211 is a pulse generator, 212 is a measured object, 213 is an XY stage, 215 is a second beam splitter, 216 is a second beam splitter. The photodetector 217 is a signal processing system.

In FIG. 6, the low coherent light source 20
1. For example, super luminescent diode (SLD)
And light emitting diodes (LEDs) have a broad spectrum, so their time coherence is a coherent light source,
For example, it is extremely short as compared with a laser light source.

When the time coherence is converted into the coherence length Lc, it can be expressed as Lc ≒ λ ² / Δλ (where λ is the central wavelength of low coherent light and Δλ is its wavelength spread).
In the case of a commercially available near infrared SLD, LcＬＤ50 μm,
In the case of an LED, Lc is about 10 μm.

Therefore, when low coherent light is used,
The difference in the optical path length between the signal light and the reference light in FIG. 6 causes optical interference only when the difference is within the extremely short coherent length. By utilizing this property, it is possible to detect the transmitted light that has propagated through a specific optical path length. [For example, K. P. Chan, M .; Yamada, H .; Ina
da, “Applied Physics B”, Vo
1.63, 249 (1996)].

In the second embodiment (FIG. 6), the first prism 208 whose position is fixed moves in the Z-direction (scan).
By using the possible second prism 204, the optical path length difference between the signal light and the reference light can be adjusted, and the light emitted from the measured object 212 can be detected with a distance resolution of about Lc.

Next, a third embodiment of the present invention will be described.

FIG. 7 is a block diagram of an optical heterodyne detection system showing a third embodiment of the present invention. This embodiment is applied to a Mach-Zehnder interferometer for detecting reflected light from a sample to be measured.

In FIG. 7, reference numeral 301 denotes a low coherent light source, 302 denotes a first beam splitter, 303 denotes a first frequency shifter (AOM1, f ₁ ), 304 denotes a second prism capable of Z-scan, and 305 and 309. Is a reflection mirror, 306, 307, 312, 313, and 315 are lenses, 308 is a fixed first prism, and 310 is a second prism.
Frequency shifter (AOM2, f _2), 311 is a pulse generator, the second beam splitter 314, 316 sample to be measured, 317 photodetector, 318 is a signal processing system.

As the light source, as in the second embodiment (FIG. 6), a low coherent light source 301, for example, an SLD and an LED
Use a light source. By utilizing the extremely short coherence length property of these light sources, optical coherence tomography measurement (for example, see Japanese Patent Publication No. 6-35946 proposed by the present inventor) can be performed by the optical measurement device shown in FIG. Is possible.

As described above, according to the present invention, interference light that is temporally "cut out" is detected by an accumulation type photodetector, for example, a CCD camera in which a light receiving element is spatially arranged. Since commercially available CCD cameras have hundreds of thousands to millions of light receiving elements, if these extremely large numbers of light receiving elements are effectively used, real-time optical image measurement can be performed without sweeping.

FIG. 8 is a diagram showing a first modification of the third embodiment of the present invention.

In the third embodiment, both the first incidence on the sample to be measured and the condensing of the reflected light from the sample to be measured are performed by a single lens, whereas in this embodiment, the single lens is used. Instead, a microlens array 321 is used.

The microlens array 321 has a function of converting an incident signal light beam into a number of light beams to be incident on the sample 316 and a function of condensing the reflected light from the sample 316 at the same time. Fulfill. The collected multiple reflected light beams are superimposed on the reference beam on the second beam splitter 314, and interference light is generated on the surface of the CCD array.

On the other hand, the number of elements of the microlens array used in this embodiment does not necessarily need to be set equal to the number of light receiving elements of the CCD camera. Detecting signal light from one element of the lens array with a plurality of CCD elements is considered to be useful for speckle averaging and enhancement detection of an optical heterodyne signal as described in FIG.

Next, a second modification of the third embodiment of the present invention will be described.

FIG. 9 is a diagram showing a second modification of the third embodiment of the present invention.

Here, the optical measuring device shown in FIG. 7 uses an optical fiber bundle instead of a lens as a signal light transmission means.

As shown in FIG. 9, light incident on the sample 316 to be measured is coupled to the optical fiber bundle 332 by the first micro lens array 331, and passes through the optical fiber bundle 332 to the second micro lens array 333. Transmitted to The second microlens array 333 simultaneously performs the first incidence on the sample 316 and the collection of the reflected light from the sample 316 as in FIG.

According to this embodiment, the use of the optical fiber bundle 332 for the transmission of the signal light allows the sample 316 to be measured to be separated from the optical measurement device, thereby greatly improving the degree of freedom in measurement. There is.

Next, a fourth embodiment of the present invention will be described.

FIG. 10 is a configuration diagram of an optical heterodyne detection system showing a fourth embodiment of the present invention. Here, it is applied to a Fizeau interferometer.

In this figure, 401 is a low coherent light source, 402 is a first beam splitter, and 403 is a first beam splitter.
Frequency shifter (AOM1, f ₁ ), 404 is a prism capable of Z-scanning, 405 and 406 are reflection mirrors,
07 is a second frequency shifter (AOM2, f ₂ );
Is a pulse generator, 409 is a second beam splitter, 4
10, 411, 414 are lenses, 412 is a third beam splitter, 413 is a translucent mirror, 415 is a measured object, 416 is a photodetector, and 417 is a signal processing system.

As shown in FIG. 10, for example, an SLD and an LED light source are used as the low coherent light source 401 as the light source. The signal light and the reference light superimposed by the second beam splitter 409 are expanded in beam diameter by a beam expander including two lenses 410 and 411, transmitted through the third beam splitter 412, and transmitted through the semitransparent mirror 4.
13 is transmitted. A part of the light beam is reflected by the translucent mirror 413, and is again returned to the third beam splitter 41.
Sent back to 2. This is called light beam 1 for convenience.

On the other hand, the light beam transmitted through the translucent mirror 413 is condensed by the lens 414 and is incident on the sample 415 to be measured. The reflected light from the sample under test 415 is
The light is condensed at 14 and transmitted to the translucent mirror 413. Part of the reflected light passes through the translucent mirror 413,
To the beam splitter 412. This is called a light beam 2 for convenience.

The light beam 1 and the light beam 2 are overlapped by a third beam splitter 412, and a part thereof is reflected by the third beam splitter 412 and a photodetector, for example, a light receiving element is spatially arranged. Transmitted to a photodetector (CCD camera) 416.

As in the other embodiments using a low coherent light source as the light source, in the fourth embodiment (FIG. 10), the difference in the optical path length between the signal light and the reference light is within the extremely short coherent length of the light source. Only when is light interference generated. However, the fourth embodiment is different from the other embodiments in that the signal light and the reference light are both included in the light beams 1 and 2.

Assuming that the optical path lengths of the signal light and the reference light superimposed on the light beam 1 are Ls and Lr, respectively, unless the difference between the two is within the extremely short coherent length of the light source, the two light waves are superimposed. However, no optical interference is generated.

On the other hand, the light beam 2 reflected from the test subject 415 has a longer optical path length than the light beam 1 reflected from the translucent mirror 413. Assuming that the difference is ΔL, it can be estimated that the optical path lengths of the signal light and the reference light superimposed on the light beam 2 are Ls + ΔL and Lr + ΔL, respectively.

Then, by scanning the prism 404 in FIG. 10 in the Z direction to adjust the optical path length between the signal light and the reference light so that Ls = Lr + ΔL, the light beam 1 on the surface of the photodetector 416 is adjusted. A reference light included in the
The signal light included in the light beam 2 causes optical interference.

Next, a fifth embodiment of the present invention will be described.

FIG. 11 is a configuration diagram of an optical heterodyne detection system showing a fifth embodiment of the present invention.

In this embodiment, an optical fiber bundle is used as a signal light transmission means in the optical measurement device.

In this figure, 501 is a low coherent light source, 502 is a first beam splitter, and 503 is a first beam splitter.
Frequency shifter (AOM1, f ₁ ), 504 is a Z-scan prism, 505 and 506 are reflection mirrors, 507
Is a second frequency shifter (AOM2, f ₂ ), 508 is a pulse generator, 509 is a second beam splitter, 51
0, 511 is a lens, 512 is a third beam splitter, 513 is a first two-dimensional (micro) lens array,
514 is an optical fiber bundle, 515 is a second two-dimensional (micro) lens array, 516 is a sample to be measured, 51
7, a photodetector; and 518, a signal processing system.

As shown in FIG. 11, light incident on the sample 516 to be measured is coupled to the optical fiber bundle 514 by the first microlens array 513, and is transmitted to the second microlens array 515 via the optical fiber bundle 514. Transmitted. The second microlens array 515 simultaneously performs light incidence on the measured object 516 and collection of reflected light from the measured object 516.

This embodiment is different from the embodiment shown in FIG. 9 in that both the signal light and the reference light reciprocate in the same optical fiber. This is effective in compensating for the disturbance that the optical transmission by the optical fiber receives.

Next, a sixth embodiment of the present invention will be described.

FIG. 12 is a partial configuration diagram of an optical heterodyne detection system according to a sixth embodiment of the present invention.

In this figure, 601 is an optical fiber,
Reference numeral 602 denotes a lens, 603 denotes a beam splitter, 604 denotes reflection coding, 605 denotes a CCD camera, 606 denotes an objective lens, and 607 denotes an object to be measured.

This embodiment is used as a means for transmitting the incident light to the object to be measured in the optical measuring apparatus of the fourth embodiment. That is, the optical fiber 601, the lens 602, the beam splitter 603, the reflection coding 604, and the CCD camera 605 are integrated.

As described above, in this embodiment, the optical fiber 601 is used as a means for transmitting incident light to the sample 607 to be measured, but the optical fiber 601 is not used as a means for transmitting reflected light from the sample 607 to be measured. Different from the fifth embodiment. Therefore, there is no need to use an optical fiber bundle for image transmission, and there is an advantage that the cost is low.

On the other hand, the fifth embodiment has the advantage that the use of an optical fiber allows the sample to be measured to be separated from the optical measurement device, and the degree of freedom in measurement is greatly improved.

Next, a seventh embodiment of the present invention will be described.

FIG. 13 is a partial configuration diagram of an optical heterodyne detection system showing a seventh embodiment of the present invention.

In this figure, 701 is a low coherent light source, 702 is a lens, 703, 705, 707, 70
9, 711, 713, 715 are optical fibers, 704 is a first 2 × 2 optical fiber coupler, 706 is a first frequency shifter (AOM1), 708 is an optical fiber type distance expansion / contraction device, and 710 is a second 2 × 2 optical fiber coupler , 712 are second frequency shifters (AOM2), 714
Is a pulse generator.

In FIG. 13, the low coherent light source 70
Output light from the optical fiber 7
03 and the first 2 × 2 optical fiber coupler 7
04. Here, the first 2 × 2 optical fiber coupler 704 converts the input light into a signal light and a reference light by two.
To divide. The signal light and the reference light are each transmitted through an optical fiber 7
05 and 711, the optical fiber coupling type frequency shifters AOM1 and AOM2 are guided to the input side.

The light having undergone the frequency shift in the AOM is coupled to optical fibers 707 and 713 and output. Then, the signal light from the AOM 2 is transmitted to the second 2 × 2 optical fiber coupler 710 by the optical fiber 713, but the reference light from the AOM 1 passes through the optical fiber type distance expansion / contraction device 708 and then returns to the optical fiber 7.
09 is transmitted to the second optical fiber coupler 710. In the second optical fiber coupler 710,
The signal light and the reference light are superimposed again, and are guided to the sample to be measured by the optical fiber 715 on the output side.

This embodiment is constructed as a means for dividing and superimposing signal light and reference light in the optical measuring devices of the fourth, fifth and sixth embodiments.
If the superposition mechanism of the signal light and the reference light due to 0 is eliminated, the present invention can be applied to other embodiments.

As described above, this embodiment has an advantage that a compact optical measuring device can be realized by using an all-fiber dividing and superposing mechanism for the signal light and the reference light of the optical measuring device.

On the other hand, the optical fiber distance expansion / contraction device 708 used here plays a role of adjusting the optical path length difference between the reference light and the signal light similarly to the above-described Z-scannable prism. An example of the basic configuration is, for example, a structure in which a long optical fiber is wound on a stretchable piezo element.

FIG. 14 is a diagram showing wavefront detection of signal light according to an embodiment of the present invention.

In this figure, reference numeral 801 denotes a sample to be measured;
02 is an objective lens, 803 is an incident wavefront, 804 is a reflected wavefront, and 805 is an impurity.

As shown in this figure, when a plane wave or a spherical wave incident on the sample 801 to be measured is scattered by a minute scattered substance inside the sample 801 to be measured, for example, an impurity 805 in the sample 801 to be measured, The scattered light wave is disturbed. In other words, the phase of a plane wave or spherical wave originally changes from a regular spatial distribution to an irregular one.

According to the present invention, the intensity and the phase of the signal light can be detected at the same time as expressed by the equations (19) and (20). By instantaneously detecting the wavefront in two dimensions, it is also possible to inspect an internal defect of the sample 801 to be measured.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications are possible based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0149]

As described above, according to the present invention, optical heterodyne measurement using a two-dimensional detector array can be effectively performed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical heterodyne detection system showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a measurement principle by optical heterodyne detection of the present invention.

FIG. 3 is an explanatory diagram of a cutoff frequency of an optical device based on optical heterodyne detection of the present invention.

FIG. 4 is a diagram showing a time waveform of interference light obtained by optical heterodyne detection according to the present invention.

FIG. 5 is an explanatory diagram of execution of timing of cutting out interference light by optical heterodyne detection of the present invention.

FIG. 6 is a configuration diagram of an optical heterodyne detection system showing a second embodiment of the present invention.

FIG. 7 is a configuration diagram of an optical heterodyne detection system showing a third embodiment of the present invention.

FIG. 8 is a diagram showing a first modification of the third embodiment of the present invention.

FIG. 9 is a view showing a second modification of the third embodiment of the present invention.

FIG. 10 is a configuration diagram of an optical heterodyne detection system showing a fourth embodiment of the present invention.

FIG. 11 is a configuration diagram of an optical heterodyne detection system showing a fifth embodiment of the present invention.

FIG. 12 is a partial configuration diagram of an optical heterodyne detection system according to a sixth embodiment of the present invention.

FIG. 13 is a partial configuration diagram of an optical heterodyne detection system according to a seventh embodiment of the present invention.

FIG. 14 is a diagram showing wavefront detection of signal light according to an embodiment of the present invention.

FIG. 15 is a basic configuration diagram of a conventional optical heterodyne detection system.

FIG. 16 is a diagram showing a state of light scattering received by a conventional signal light inside and outside of a scattering medium and inside.

FIG. 17 is a basic principle diagram of a conventional optical heterodyne detection system using a two-dimensional detector array.

FIG. 18 is an explanatory diagram in a case where a signal processing system having the number of channels corresponding to the number of elements of a conventional array is required.

[Description of Code] 101 Coherent light source 102, 202, 302, 402, 502 First beam splitter 103, 203, 303, 403, 503, 706
The first frequency shifter (AOM1, f ₁₎ 104,108,205,209,305,309,4
05, 406, 505, 506 Reflecting mirrors 105, 106, 113, 206, 207, 214, 3
06,307,312,313,315,410,41
1,414,510,511,602,606,70
2,802 lens 107,215,314,409,509 Second beam splitter 109,210,310,407,507,712
Second frequency shifter (AOM2, f ₂₎ 110,211,311,408,508,714
Pulse generators 111, 212, 316, 415, 516, 607, 8
01 Specimen to be measured 112, 213 XY stage 114, 216, 317, 416, 517 Photodetector 115, 217, 417, 518, 318 Signal processing system 201, 301, 401, 501, 701 Low coherent light source 204, 304 Second prism 208, 308 First prism 321 Micro lens array 331 First micro lens array 332, 514 Optical fiber bundle 333 Second micro lens array 404, 504 Prism 412 Third beam splitter 413 Translucent mirror 512 Three beam splitters 513 First two-dimensional (micro) lens array 515 Second two-dimensional (micro) lens array 601, 703, 705, 707, 709, 711, 7
13,715 Optical fiber 603 Beam splitter 604 Reflection coding 605 CCD camera 704 First 2 × 2 optical fiber coupler 708 Optical fiber distance stretching device 710 Second 2 × 2 optical fiber coupler 803 Incident wavefront 804 Reflected wavefront 805 Impurity

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification symbol FI G01J 9/04 G01B 11/24 D (58) Investigated field (Int.Cl. ⁷ , DB name) G01N 21/17 610-630 JICST file (JOIS) Practical file (PATOLIS) Patent file (PATOLIS)

Claims (3)

(57) [Claims] 1. A light source for emitting a light beam, and
The light beam emitted from the light source is converted into a signal light passing through a position where the sample to be measured is arranged, and a reference light passing through an optical path different from an optical path passing through the position where the sample to be measured is arranged. And the signal light after passing through the arrangement position of the subject to be measured and the reference light passing through the different optical paths are overlapped with each other, so that the interference light in which the signal light and the reference light interfere with each other (C) a frequency shifter that relatively shifts the frequency of the signal light and the frequency of the reference light, and (d) the interference optical system generates the signal light. And an optical device for periodically blocking light on at least one optical path of the reference light, and (e) making a cutoff frequency of the optical device equal to a frequency difference between the signal light and the reference light. It is characterized by doing Light measuring device for. 2. The optical measurement device according to claim 1, wherein the light blocking operation of the optical device is synchronized with a reference signal having a frequency equal to a frequency difference between the signal light and the reference light,
The start and end of the cutoff operation are performed by using a specific phase value of the reference signal as a reference, and the interference light is changed to a different measurement start time and a different measurement start time by changing the reference phase value to a different value. An optical measurement device characterized by cutting out by time width. 3. The optical measurement apparatus according to claim 1, wherein the interference optical system includes a light detector that obtains a light detection signal by receiving the interference light, and the interference optical system includes the light receiving device. The surface of the sample to be measured placed at the arrangement position of the measurement sample, or inside, while transmitting the signal light of the point of interest on the propagation path of the signal light onto the photodetector, and on the photodetector The photodetectors are superimposed with reference light, and the photodetectors are spatially arranged, each having a plurality of light receiving elements for independently obtaining light receiving signals, and further integrating a plurality of light receiving signals obtained by the photodetectors. And a signal processing unit for generating a signal corresponding to the point of interest.