JP2013224845A - Distance measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance measurement system that exhibits an excellent resolving power of an in-plane, and what's more, an excellent resolving power to a height or a refractive index distribution in an out-of-plane and exhibits an excellent resolving power of a distance.SOLUTION: Transmission antennas 11 and 12 mounted onto an aircraft 10 transmit transmission waves of Asin(2π(fc+fm)t) and Asin(2π(fc-fm)t) based on a carrier signal frequency fc and a modulation frequency fm to a measurement target G on the ground. The transmission waves are irradiated to the measurement object G with irradiation areas A and B almost overlapped with each other but slightly shifted by a center distance Δx. Reception antennas 13 and 14 are disposed on an extension of a part letting an almost center of overlapped irradiation areas A and B of the transmission waves be a boundary. When a sum signal or a difference signal of signals received by the reception antennas 13 and 14 is used to detect a phase shift, height information about irradiation areas A and B. When the difference signal is used, in contrast to the sum signal, only a part at which a phase difference occurs contributes to the phase difference and thus, the resolving power becomes high and sensitivity becomes extremely high.

Description

The present invention relates to a distance measurement system that accurately measures the distance to a measurement object using electromagnetic waves.

  With a conventional optical microscope, it was impossible to observe or measure a measurement object below the diffraction limit. As an alternative, probe microscopes (STM, AFM, NFOS, etc.) and scanning electron microscopes have been developed and used in many fields. Since this scanning electron microscope uses a very thin beam as a scanning electron probe, the resolution is high and the depth of focus is significantly larger than that of an optical microscope. However, observation of a measurement object with low conductivity such as a cell requires that the sample that is the measurement object is coated with platinum palladium or gold having good conductivity, and often involves damage to the cell itself. Obviously, it was impossible to observe and measure living cells.

  A probe microscope measures the distance from the measurement object by using an atomic force, tunnel current, optical near field, etc. It is. However, it is difficult to move the probe at high speed, and it is difficult to handle because the distance to the object to be measured is very close, and it takes a lot of time to acquire two-dimensional information. .

  On the other hand, it is also possible to apply a system that radiates electromagnetic waves like a radar, detects reflected electromagnetic waves from the measurement object, and basically measures the distance to the measurement object by the time difference between transmission and reception. Though conceivable, such a system requires various signal processing algorithms and is complicated, and the size of the measurement object that can be detected is limited.

  On the other hand, heterodyne interferometry is well known for measuring distances with high accuracy. Here, the optical heterodyne method using light is described, but the same concept is applied to other electromagnetic waves. In this optical heterodyne method, two laser beams with different frequencies are made to interfere, a beat signal of the difference frequency is created, and the phase change of this beat signal is detected with a resolution of about 1/500 of the wavelength, The distance to the measurement object is measured while measuring the change in the height direction of the surface.

  In Japanese Patent Application Laid-Open No. 59-214706 of Patent Document 1 below, two beams having different wavelengths are generated adjacent to each other using an acousto-optic device, and a phase change between these two beams is detected. A method for accumulating phase changes to obtain a surface profile is disclosed. However, in this patent document 1, unevenness information is obtained by making two beams close to each other slightly larger than the beam profile, detecting an average phase difference in the two beam profiles by heterodyne detection, and integrating sequentially. It was what you get.

Therefore, according to this Patent Document 1, the unevenness information can be measured for the measurement object that is assumed to be flat such as a semiconductor wafer, but the information in the beam profile is It could not be extracted, and the resolution in the in-plane beam profile could not be increased.
Note that the resolution of ordinary electromagnetic waves is limited by the limits of so-called Abbe's theory. This limit was a result of the diffraction phenomenon of waves, and was regarded as a theoretical limit that could not be exceeded.

JP 59-214706 A

  As described above, in the distance measuring device using the conventional heterodyne detection, the distance cannot be measured with a resolution equal to or lower than the wavelength of the applied electromagnetic wave. Therefore, even if the electromagnetic wave irradiation region is made smaller than the wavelength, it was only possible to calculate the average distance of the region that is equal to or greater than the wavelength.

Similarly, in a conventional optical measuring device using heterodyne detection, a main object to be measured is a flat surface such as a semiconductor wafer. For this reason, in order to increase the in-plane resolution, a near field such as an electron microscope or an AFM (atomic force microscope) must be used.
However, with respect to the electron microscope, it is necessary to process living organisms, cells, and the like in particular, so it has been impossible to observe living and measure the refractive index distribution. On the other hand, AFM is not suitable for observation of living organisms and cells because the processing speed is not sufficient, so it is not possible to see changes in state in real time. It was not easy to use.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a distance measurement system that has high in-plane resolution, high resolution with respect to height and refractive index distribution, and high distance resolution.

In order to achieve the above-mentioned object, the distance measuring system according to claim 1 irradiates two coherent electromagnetic waves having different frequencies from each other while having the same region on the object to be measured. Irradiating means to perform,
Electromagnetic wave detecting means for detecting electromagnetic waves from at least two regions in the measurement object across a boundary line extending in a direction substantially perpendicular to the shifted direction;
A signal creation means for creating a difference signal or a sum signal of the outputs of the electromagnetic waves detected by the electromagnetic wave detection means at symmetrical positions across the boundary line;
A measuring means for obtaining a measured value by calculating a phase difference or an intensity difference of the difference signal or the sum signal; and
It consists of a distance measurement system including

The operation of this claim will be described below.
Two coherent electromagnetic waves having slightly different frequencies are separated so that most of the irradiation areas are overlapped and partially offset, and the measurement object is irradiated by the irradiation means. An electromagnetic wave reflected from the measurement object or transmitted through the measurement object is detected by an electromagnetic wave detection means that is a detector adapted to the irradiated electromagnetic wave. At this time, two or more detectors are to be measured so that the electromagnetic waves in at least two regions sandwiching a boundary line extending in a direction substantially perpendicular to the direction in which the irradiated electromagnetic waves are shifted can be detected. If the detectors are arranged at a distance that can be regarded as a far field, the detectors detect electromagnetic waves, respectively, as follows.

The signal creation means creates all the sum signals of the above-mentioned detectors divided into two or more and the difference signal between the detectors across the boundary, and detects a slightly different frequency difference (beat signal) based on these signals Thus, the phase shift from the input signal can be measured. In the measuring means, based on the sum signal of the outputs of all detectors, an integrated value of the region corresponding to the irradiation area of the phase difference according to the separation degree of the region irradiated with the two electromagnetic waves is effectively given, and the differential interference microscope According to the same principle as described above, a resolution of about a fraction of the wavelength can be obtained, and the distance between the detector and the measurement object can be obtained with this resolution.
Further, in order to increase the resolution, the measurement means uses the difference signal between the detectors with the boundary line between them, and effectively, the differential of the phase difference according to the degree of separation between the areas irradiated with the two electromagnetic waves is obtained. The integral value of the region corresponding to the irradiation area is given. In this case, compared with the sum signal, only the portion where the phase difference occurs contributes to the phase difference, so the sensitivity is remarkably increased.

  From the above, it is possible to improve the lateral resolution comparable to the resolution according to the degree of beam separation. This is an outstanding feature that is not seen in distance measurement by normal heterodyne detection. As a result, a lateral resolution much higher than the lateral resolution dominated by the wavelength can be obtained. The same effect as described above can be obtained depending on the intensity of the beat signal.

  From the above, it is possible to obtain a distance measuring system that has a high resolution with respect to height and refractive index distribution, a distance resolution of about 1/500 of a wavelength, and a remarkably high in-plane resolution. Further, since the places where two electromagnetic waves having different frequencies are generated can be brought close to each other, the path can be almost shared. For this reason, it becomes a distance measurement system remarkably resistant to external environmental changes, vibrations, and the like.

  For example, if two transmitting antennas that generate two microwaves and radio waves having slightly different frequencies are prepared, and a plurality of receiving antennas are prepared so as to be arranged as described above, and these are mounted on an aircraft, The transmitting antenna is almost a point source when viewed from the object to be measured, and radio waves in the atmosphere travel on the same optical path, so that correct distance measurement is possible even if there is an aircraft shake or the like.

Moreover, in order to achieve the said objective, invention of the distance measuring system which concerns on Claim 2 has a light source which radiate | emits coherent light,
A first means that converts the light emitted from the light source into two light beams that are separated and irradiated in a state of being close to each other while being modulated to different frequencies;
A second means for one-dimensionally scanning or two-dimensionally scanning the two lights;
A third means for irradiating the measurement object with the two light beams scanned two-dimensionally;
A direction substantially perpendicular to the direction in which the two lights are separated is defined as a boundary line, and the reflected light or transmitted light from the measurement object is received in at least two parts across the boundary line. Means,
A fifth means for creating a difference signal or a sum signal of outputs of light received by the fourth means in a region sandwiching the boundary line;
A sixth means for obtaining a measured value by obtaining a phase difference or an intensity difference of the difference signal or the sum signal;
A distance measurement system including

The first means according to the present invention is an acousto-optic element or a spatial modulator, and the acousto-optic element or the spatial modulator is preferably obtained by adding two modulation signals.
The two-dimensional scanning of the second means according to the present invention is preferably a combination of two one-dimensional scanning elements or one using a two-dimensional scanning element.
The light that the third means according to the present invention irradiates the measurement object is preferably parallel light, convergent light, or divergent light.
Further, the sixth means according to the present invention is preferably one using heterodyne detection based on a difference between two modulated frequencies.

Next, the operation of these claims will be described below.
In the distance measuring system according to these claims, the electromagnetic wave according to claim 1 is applied to light.
In these claims, the light from the light source is DSB-modulated by a first means such as an acousto-optic element or a spatial light modulator to produce a beam that is two lights having slightly different frequencies and emission directions. By scanning these two beams toward the objective lens which is the third means by the second means which is a one-dimensional or two-dimensional scanning optical element independent of the modulation frequency, Two adjacent beams will scan over the measurement object.

  When the object to be measured is a reflective object, the light receiving element which is the fourth means arranged at a position almost conjugate with the acousto-optic element detects a slightly different frequency difference (beat signal) of the beam, Two beat signals can be acquired. Further, when the measurement object is a transmission object, these two beat signals can be detected by the same light receiving element arranged at a position not far from the measurement object, although it is a far field.

  When a light receiving element that is divided into two or more with a dividing line extending in a direction perpendicular to the beam separating direction is used as the light receiving element, all the sum signals and boundary lines of the light receiving element are The fifth means creates a difference signal between the sandwiched light receiving elements, detects a slightly different frequency difference (beat signal) based on these signals, and measures a phase shift from the input signal. In the sixth means, for example, based on the sum signal of the outputs of all the light receiving elements, the integral value of the region corresponding to the beam diameter of the phase difference according to the separation degree of the two beams condensed by the objective lens is effectively obtained. Therefore, as the resolution substantially equivalent to that of the differential interference microscope is obtained, the distance between the light receiving element and the measurement object can be obtained with this resolution.

  In order to further increase the resolution, if the difference signal between the light receiving elements adjacent to each other among the light receiving elements divided into two or more is acquired, the two beams condensed by the objective lens are effectively obtained. An integral value of a region corresponding to the differential beam diameter of the phase difference according to the degree of separation is given. In this case, as compared with the sum signal, only the portion where the phase difference occurs contributes to the phase difference, and thus the sensitivity is remarkably increased. Accordingly, it is possible to improve the lateral resolution comparable to the resolution according to the beam separation degree. This is a distinguishing feature that is not found in ordinary differential interference microscopes. As a result, a lateral resolution much higher than the lateral resolution dominated by the wavelength can be obtained.

In summary, according to the present invention, it is possible to provide a distance measurement system with high resolution for height and refractive index distribution, high distance measurement accuracy, and high in-plane resolution.
In addition, when the present invention is applied to a microscope, it has a very high in-plane resolution, and further, by performing two-dimensional scanning once, the height and refractive index distribution can be measured. Three-dimensional measurement such as a change in the state of a micromachine or the like can be performed in real time. For this reason, it has the big characteristic which cannot be compared with the laser scanning confocal microscope etc. which acquire the conventional 2-dimensional information and integrate | accumulate in a 3-dimensional direction.
Furthermore, when the present invention is applied to a transmission microscope, living organisms and cells can be observed and measured with high resolution. For this reason, it has the big characteristic which the electron microscope which inactivates a cell etc. and measures does not have.

  As described above, in the distance measurement system according to the present invention, two electromagnetic waves having slightly different frequencies are projected close to each other and projected onto the measurement object using the reflected wave or the transmitted wave. Two or more detectors are arranged across the boundary line at the center of the overlapping portion of the electromagnetic wave region, and the phase difference or intensity difference is detected from the heterodyne signal obtained from the sum signal or difference signal from these two or more detectors. .

  In this way, it is possible to accurately observe and measure the surface profile of the measurement object, the thickness of the transmission object, the refractive index distribution, and the like with an in-plane resolution that is greater than the diffraction limit. In particular, when a difference signal is used, this effect is increased. For this reason, it is possible to observe and measure changes in the state of cells and microorganisms, transient changes in the surface state, and the like.

On the other hand, if you use a commercially available autostereoscopic display or a 3D display using polarized glasses, you can also display 3D 3D images at video rates, which is useful in education, research, and medicine. can do. In addition, since two beams passing through almost the same path that are very close to each other are used, observation and measurement that are not easily affected by disturbance or the like can be performed.

It is the schematic which shows Example 1 which concerns on the distance measurement system of this invention. It is explanatory drawing showing the irradiation area | region on the ground by Example 1 which concerns on the distance measurement system of this invention. It is a block diagram which shows Example 1 which concerns on the distance measurement system of this invention. It is a block diagram of the optical system which shows Example 2 which concerns on the distance measurement system of this invention. It is a figure which expands and shows the objective lens of FIG. 4, and a measurement object peripheral part. It is a block diagram of the optical system which shows Example 3 which concerns on the distance measurement system of this invention. It is a figure which shows the spatial modulator applied to Example 4 which concerns on the distance measurement system of this invention, Comprising: (A) is a schematic diagram of a spatial modulator, (B) is the voltage applied to a spatial modulator. FIG. 3 is a diagram showing a current pattern.

  Embodiments 1 to 4 of the distance measurement system according to the present invention will be described below in detail with reference to the drawings.

Embodiment 1 of a distance measurement system according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram showing the configuration of the distance measurement system of the present embodiment. A transmitting antenna 11 and a transmitting antenna 12 which are microwave parabolic antennas are mounted on both ends of the airplane 10 shown in FIG.

  The microwave transmission antenna 11 and the transmission antenna 12 mounted on the airplane 10 in this way are Asin (2π (fc + fm) t) and Asin (2π (fc−) based on the carrier signal frequency fc and the modulation frequency fm. The transmission wave of fm) t) is transmitted to the measurement object G such as the landform which is a three-dimensional shape on the ground so as to spread in a cone shape having the same size. As shown in FIGS. 1 and 2, each transmitted wave is slightly shifted by the center distance Δx although the irradiation areas A and B substantially overlap the measurement object G on the ground, for example, by tilting the parabolic antenna. It comes to be irradiated.

  On the other hand, on the extension of the portion of the airplane 10 between the transmission antenna 11 and the transmission antenna 12 and having the boundary at the approximate center of the irradiation areas A and B where the respective transmission waves overlap, At least two receiving antennas 13 and 14 are arranged.

  That is, the two receiving antennas 13 and 14 can receive the microwaves having spatial frequencies in two directions shifted from the spatial frequency zero of the microwave reflected from the measurement object G to the irradiation areas A and B, respectively. It has become. For this reason, the signals received by the respective receiving antennas 13 and 14 become beat signals having a frequency of 2 fm as a result of interference of microwaves having two frequencies reflected from the measurement object G.

  Furthermore, the airplane 10 shown in FIG. 3 has not only a transmitter (not shown) for transmitting the microwaves from the transmission antennas 11 and 12 but also a sum signal based on the signals received by the reception antennas 13 and 14. A signal generating device 16 that is a signal generating means for generating a difference signal, a measuring device 17 that is a measuring means for measuring the height of the airplane 10 from the phase shift of these signals, and a hard disk that stores height data and the like A memory 18 such as a drive is mounted.

  Here, when the phase shift is detected using the sum signal or difference signal of the signals received by the receiving antenna 13 and the receiving antenna 14, height information of the two irradiation areas A and B is obtained. Specifically, the signal generating device 16 generates a sum signal of the receiving antennas 13 and 14 and a difference signal between the receiving antennas 13 and 14, and based on these signals, a slightly different frequency difference (beat signal) is generated. Thus, the phase shift from the input signal is measured by the measuring device 17.

  As the measuring instrument 17 obtains a resolution of about a fraction of the wavelength from the sum signal, the distance between the airplane 10 having the receiving antennas 13 and 14 and the measurement object G is obtained with this resolution. Some height information is obtained. Further, if the difference signal is used in the measuring instrument 17, only the portion where the phase difference is generated contributes to the phase difference as compared with the sum signal, so that the resolution is increased and the sensitivity is remarkably increased.

  In the present embodiment, two reception antennas are used. However, three or more reception antennas may be installed. Further, if a transmitter is mounted instead of the signal creation device 16, the measurement device 17 and the memory 18, the signal creation device 16, the measurement device 17 and the memory 18 may be installed on the ground.

Hereinafter, the operation principle of this distance measurement system will be described in detail.
Assume that the center distance Δx between the two microwave irradiation areas A and B shown in FIG. 2 is set to be equal to or less than the diffraction limit of these microwaves. In this case, the microwave irradiation areas A and B do not fall below the diffraction limit of Abbe's theory, but are microwaves of different frequencies that are slightly shifted, so that heterodyne detection is performed. , Differential information can be obtained. At this time, if the sum signal of the receiving antenna 13 and the receiving antenna 14 is used, it is substantially equivalent to a kind of differential interference microscope of an optical microscope, and if these difference signals are used, the lateral resolution is much higher than that of the differential interference microscope. Is obtained.

Think in one dimension for simplicity. First, let Ae ^{jθ (x)} be the phase distribution of the profile d (x) of the measurement object G on the ground or the sea. Here, θ (x) = 2πd (x) / λ. In the case of reflection as in the present embodiment, the path difference is doubled, so half of the observed θ (x) may be used as height information.
Now, as described above, the center distance between the two microwave irradiation areas A and B on the measurement object G is Δx, and the microwave complex amplitude distribution on the ground or the sea is u (x). In this case, in a place sufficiently away from the measuring object G, the Fourier transform of the product of the profile of the measuring object G and the beam profile is performed.

In this distance measurement system, the microwave received by one receiving antenna is modulated by ej ^{(ωc-ωm) t} and is received by the other receiving antenna separated by the center distance Δx. The microwave is modulated by ej ^{(ωc + ωm) t} .
Therefore, the complex amplitude distribution E on the receiving antennas 13 and 14 is as follows.
E = ∫ (Ae ^{jθ (x)} u (x) e ^jkx dx · e ^{j (ωc-ωm) t} + Ae ^{jθ (x + Δx)} u (x) e ^jkx dx · e ^{j (ωc + ωm) t} )

When the intensity I is detected by these receiving antennas 13 and 14, since I = EE ^* and further heterodyne detection of 2ωm, the following equation (1) is obtained.
I (k) = A ² ∫e ^{j (θ (x) −θ (x ′ + Δx ′)} u (x) u (x ′) e ^{jk (x−x ′)} dxdx′e ^−j2ωmt
+ A ² ∫e ^{−j (θ (x) −θ (x ′ + Δx ′)} u (x) u (x ′) e ^{jk (x−x ′)} dxdx′e ^j2ωmt (1)

2 and the boundary line C in FIGS. 1 and 2, and a position sandwiching the boundary line C between the irradiation areas A and B. The two receiving antennas 13 and 14 are arranged away from the measurement object corresponding to the position along the separation direction. First, let us consider how the sum signal of the signals received by the two receiving antennas 13 and 14 will be. Since it is considered to be a Fourier transform plane at a position away from the object to be measured, if the maximum spatial frequency that can be received by the receiving antenna is Kmax, the intensity I can be obtained from the following equation for the sum signal.
I = ∫I (k) dk (integration range is -Kmax to Kmax)
= A ² ∫cos (θ (x) −θ (x ′ + Δx ′) − 2ωmt) u (x) u (x ′) sin (Kmax (x−x ′)) / (x−x ′) dxdx ′

If the receiving antenna is enlarged and arranged to receive up to a wide spatial frequency,
Since sin (Kmax (x−x ′)) / (x−x ′) = Kδ (x−x ′), the following equation (2) is obtained.
I = A ² ∫cos (θ (x) −θ (x + Δx) −2ωmt) u (x) ² dx (2)

That is, the phase difference between the separation positions of the two microwaves is integrated by the weight of the microwave profile.
When the equation (2) is modified, the following equation is obtained.
Iq = A ² ∫cos (θ (x) −θ (x + Δx) u (x) ² dx · cos (2ωmt)
Ii = A ² ∫sin (θ (x) −θ (x + Δx) u (x) ² dx · sin (2ωmt)

Accordingly, the observed phase difference Θ is represented by the following equation (3) by orthogonal transformation.
Θ = tan ⁻¹ (∫sin (θ (x) −θ (x + Δx)) u (x) ² dx / ∫cos (θ (x) −θ (x + Δx)) u (x) ² dx) ... (3)

On the other hand, when the difference signal between the two receiving antennas 13 and 14 is considered, the following equation is obtained in the same manner as the sum signal.
I = ∫I (k) dk (integration range is 0 to Kmax) −∫I (k) dk (integration range is −Kmax to 0)
= A ² ∫sin (θ (x) −θ (x ′ + Δx ′) − 2ωmt) u (x) u (x ′) (cos (Kmax (x−x ′) − 1) / (x−x ′ dxdx '

If the receiving antenna is enlarged and arranged to receive up to a wide spatial frequency,
Since (cos (Kmax (x−x ′) − 1) / (x−x ′) = δ ′ (x−x ′) + 1 / x (δ (x) −1), the following equation (4) become that way.
I = A ² ∫d / dx (sin (θ (x) −θ (x + Δx) −2ωmt)) u (x) ² dx (4) Equation (4) Then, it becomes as follows.
Iq = A ² d / dx (sin (θ (x) −θ (x + Δx)) u (x) ² dx · cos (2ωmt)
Ii = −A ² ∫d / dx (cos (θ (x) −θ (x + Δx)) u (x) ² dx · sin (2ωmt)

Therefore, the phase difference Θ observed by the orthogonal transformation is expressed by the following equation (5).
Θ = tan ⁻¹ (−∫d / dx (cos (θ (x) −θ (x + Δx)) u (x) ² dx / ∫d / dx (sin (θ (x) −θ (x + Δx )) u (x) ² dx) (5)

Here, the expressions (3) and (5) are compared. The following points are qualitatively understood.
First, the equation (3) shows the phase difference obtained as a result of smoothing the phase difference between two points separated by the center distance Δx between the irradiation areas A and B with the weight function of u (x). The average phase difference in the irradiation areas A and B is shown. This is a process equivalent to a differential interference microscope.
On the other hand, in the expression (5), the differential of the phase difference between the two points separated by the center distance Δx between the irradiation areas A and B is smoothed by the weight function of u (x). It will be restored.
Therefore, when the airplane 10 flies, it is possible to acquire phase difference and position information with a lateral resolution corresponding to the degree of separation between the irradiation areas A and B.

Although the case where two receiving antennas are arranged is described here, a plurality of array antennas are arranged from the measuring object G along the separation direction of two microwaves in the vicinity of the center of the region where the irradiation regions A and B overlap. The same applies when they are arranged apart. In particular, when a difference output is obtained, a difference calculation is performed between a plurality of corresponding array antennas among a plurality of array antennas arranged corresponding to the vicinity of the center of the overlapping portion of the irradiation areas A and B. You can do it.
Further, if only the sum output of a plurality of array antennas is used, the same can be realized by using one receiving antenna substantially.

  In order to simplify the explanation, the formula is simplified assuming that the spatial frequency to be acquired is wide. However, when the spatial frequency that can be acquired is not large, the δ function portion in the formula becomes a convolution. However, the resolution is essentially improved. In this case, a slight blur occurs in the profile or the like of the measurement object G.

In the above description, the phase has been described in detail, but the same can be said for the intensity. In particular, for a profile change smaller than that of the irradiation regions A and B, a pattern in the far field of interference fringes formed by interference between the zeroth-order diffracted wave and the first-order diffracted wave of the Fourier transform of the irradiated region. Is different between the two receiving antennas 13 and 14, the difference signal between the receiving antennas 13 and 14 appears as an intensity difference reflected in the slope of the profile.
As described above, by using heterodyne detection and processing spatial frequency information on the Fourier transform plane, it is possible to bring about a very high improvement in lateral resolution, particularly in the difference calculation.

The concept of Example 2 of the distance measurement system according to the present invention will be described below.
Light emitted from a coherent light source such as a laser is modulated into light of substantially two different frequencies by an acousto-optic device or a spatial modulator as the first means. At this time, for example, when an acoustooptic element is used, the diffraction fringes are modulated by the interaction between the surface acoustic wave of the acoustooptic element and light. The light that has undergone Doppler shift undergoes frequency modulation and is emitted as first-order diffracted light. On the other hand, when a spatial light modulator is used, the same effect can be obtained by modulating the diffraction fringes written in the spatial light modulator.

  In this way, the light subjected to frequency modulation is emitted from the first means while being separated into two lights close to each other. These two lights are scanned two-dimensionally by a pupil transmission optical system or the like as the second means, and irradiated onto the measurement object with an objective lens or the like as the third means. A light receiving element as a fourth means, which is a distance away from the measurement object and is divided into two or more along the separation direction of the two lights, reflects from the measurement object or is measured The light transmitted through the object is received as light sandwiching a boundary line extending in a direction substantially perpendicular to the separation direction of the two lights.

  In this way, the light received by the light receiving element is photoelectrically converted, and in the fifth means, the difference signal between the outputs at the symmetrical positions with the direction substantially perpendicular to the separation direction of the two lights as the boundary line or Create a sum signal. The difference signal or sum signal is subjected to heterodyne detection in the sixth means to detect a phase difference or an intensity difference.

  The detected phase difference or intensity difference indicates height information of the profile of the surface of the measurement object in the case of reflection, and indicates information such as thickness and refractive index distribution in the case of transmission. At this time, the microwave irradiation areas A and B described in the first embodiment may be considered as a diffraction limited spot diameter narrowed by the objective lens. That is, in the heterodyne detection based on the sum signal of each photoelectrically converted signal, as a result of smoothing the phase difference between two points separated by the center distance of the two light beams with a weight function of u (x) The obtained phase difference is shown. For this reason, the heterodyne detection based on this sum signal indicates an average phase difference in the beam, which is a process equivalent to a differential interference microscope.

On the other hand, in the heterodyne detection based on the difference signal between the photoelectrically converted signals, the differential of the phase difference at two points separated by the center distance of the beam is smoothed by the weight function of u (x). , Roughly restoring the original function.
As described above, when the beam is scanned by the pupil transmission optical system, the phase difference and the position information can be acquired with the lateral resolution corresponding to the beam separation degree.

  In the above description, the case where the light receiving element divided into two with the optical axis as the boundary line is applied is described, but the same applies to the case where a plurality of light receiving elements are arranged away from the measurement object along the beam separation direction. . In particular, when a difference output is obtained, it may be performed between adjacent light receiving elements across a boundary line. If only the sum output of a plurality of light receiving elements is used, the same can be realized by using one light receiving element.

  With respect to the measurement object, if there is an inclination of the profile in the beam, the direction in which light is reflected or transmitted qualitatively differs, so that a difference output as intensity is given to the two light receiving elements. More specifically, if there is a profile change smaller than the beam diameter, the far field of interference fringes formed by the interference between the zeroth-order diffracted wave and the first-order diffracted wave of the Fourier transform in the region irradiated with light. Since the pattern at 2 differs between the two light receiving elements, the difference signal between the two light receiving elements appears as an intensity difference reflecting the inclination of the profile.

A second embodiment of the distance measuring system according to the present invention will be specifically described below with reference to the drawings.
FIG. 4 is a block diagram illustrating the configuration of the distance measurement system according to the present embodiment. As shown in FIG. 4, a collimator lens 22 is provided between a laser 21 that is a light source from which laser light is emitted and an acousto-optic device (AOD) 23 to which an operation is controlled by connecting an AOD driver 24. Has been placed. The acoustooptic device 23 also includes a pupil transmission magnifying lens system 25 comprising two lenses, a two-dimensional scanning device 26 for two-dimensionally scanning the input laser light, and separating and emitting the input laser light. The polarizing beam splitters 27 are arranged in order.

  Further, a pupil transmission lens system 30 composed of two lenses is located adjacent to the polarization beam splitter 27, and an objective lens 31 is arranged next to the object G1 for measurement. That is, these members are arranged along the optical axis L. On the other hand, a light receiving element 28 and a light receiving element 29, which are sensors, are disposed at positions adjacent to the polarization beam splitter 27 in a direction orthogonal to the direction in which the optical axis L passes. The light receiving elements 28 and 29 are connected to a signal comparator 33 that compares signals from the light receiving elements 28 and 29, respectively. The signal comparator 33 finally processes the data and the profile of the measurement object G1. Etc. are connected to a data processing unit 34 for obtaining the above.

  The laser 21 is a gas laser such as He—Ne, a semiconductor laser, or a solid laser, and generates coherent laser light. The laser light is converted into a parallel light beam by the collimator lens 22 and is incident on the acoustooptic device 23. At this time, the incident beam diameter of the laser light is optimized using a diaphragm mechanism (not shown) or the like in consideration of the pupil transmission magnifying lens system 25 in the subsequent stage. Further, a DSB modulation signal such as sin (2πfct) sin (2πfmt) is applied as a modulation signal to the acoustooptic device 23 from the AOD driver 24.

When such modulation is performed, the acoustooptic device 23 to which two frequency modulations of fc + fm and fc-fm have been applied generates an acoustic dense wave corresponding to the pitch d of the Bragg diffraction grating. That is, if the velocity of the ultrasonic wave is Va and the applied frequency is f, d = Va / f. Specifically, the beam, which is laser light incident on the acoustooptic device 23, is separated into ± first-order diffracted light by the dense waves, and each diffracted light is modulated at a frequency of frequency fc ± fm. For example, TeO ₂ is used as the material of the acoustooptic device 23, and the sound velocity of this material is 660 m / s.

  When 40 MHz is selected as the frequency fc of the carrier frequency, d = 16.5 μm, and when the He—Ne laser is used for the laser 21, the diffraction angle θ is about 2.19791 degrees. In FIG. 4, the optical axis L is illustrated as not changing, but in practice, the optical system after the acousto-optic element 23 is tilted by the diffraction angle θ or a bias is applied to the two-dimensional scanning device 26. In this case, the inclination of the diffraction angle θ is effectively given.

  When a frequency fm of about 10 kHz is added to this carrier frequency, the ± first-order diffracted light becomes θ = 2.19847 degrees and θ = 2.19737 degrees, and is modulated at 40.01 MHz and 39.99 MHz, respectively. When laser light is incident on the objective lens 31 while maintaining this angle, if the focal length of the objective lens 31 is 2 mm and NA 0.9, the center distance of the beam is about 0.6 μm, and the diffraction at this time The limit is w = 0.857 μm. That is, the beam separation degree is made smaller than that of the diffraction limited system.

  If the beam separation, which is the center distance of the beam, is further reduced, the resolution can be improved. However, if the frequency of the heterodyne detection is lowered, the processing speed becomes slow. In this case, if an acoustooptic device having a higher sound speed is used, the Bragg diffraction grating pitch d can be increased, and the processing speed can be improved. In fact, one with a sound velocity Va of about 4.2E + 3 m / s is also known and commercially available.

  Here, the pupil transmission magnifying lens system 25 disposed between the acoustooptic element 23 and the polarization beam splitter 27 transmits the position of the exit surface of the acoustooptic element 23 to the next two-dimensional scanning device 26 in a conjugate manner. The light that has passed through the pupil transmission magnifying lens system 25 is sent to the two-dimensional scanning device 26, and this two-dimensional scanning device is provided by the pupil transmission lens system 30 that is conjugated to the pupil position of the objective lens 31. 26 enters the objective lens 31 as ± first-order diffracted light having an angular difference. In this way, two beams that are very close to each other and have the same diameter can be obtained, such as a beam LA indicated by a solid line and a beam LB indicated by a dotted line in FIG.

  The frequency of the two beams LA and LB is “light frequency + carrier frequency fc ± modulation frequency fm”. When the center distance between two close beams is set below the diffraction limit as described above, each beam does not fall below the diffraction limit of Abbe's theory, but with slightly shifted light at different frequencies. Therefore, differential information can be acquired by performing heterodyne detection. Further, the light receiving element 29 shown in FIG. 4 is divided into two or more light receiving elements, the optical axis L is a boundary line C, and a dark line is formed in a direction perpendicular to the beam separation direction across the boundary line C. These light receiving elements are arranged, and a beat signal is obtained from the sum signal or difference signal thereof. At this time, if a sum signal is used, it is substantially equivalent to a differential interference microscope, and if a difference signal is used, a much higher lateral resolution can be obtained.

Here, the property of the light transmitted to the measuring object G1 will be specifically described. The light narrowed down by the objective lens 31 becomes two adjacent beams LA and LB as shown in FIG. 5, and is sent to the measurement object G1. Note that the complex amplitude Ea of the beam LA and the complex amplitude Eb of the beam LB are expressed by the following equations.
Ea = Aexpj (2π (fo + fc + fm) t)
Eb = Bexpj (2π (fo + fc-fm) t + δ)
Δ in the expression of the complex amplitude Eb represents the phase difference in the height direction of the beam LB with respect to the beam LA, and fo represents the frequency of light. Note that, as described above, the interval between the two beams is determined by the modulation frequency fm applied to the acoustooptic device 23, and is thus independent of the scanning speed.

  The two beams LA and LB reflected by the measurement object G1 shown in FIGS. 4 and 5 are guided to the light receiving element 29 via the objective lens 31, the pupil transfer lens system 30, and the polarization beam splitter 27. If the light receiving element 29 is arranged at a position conjugate with the position of the two-dimensional scanning device 26, the two beams LA and LB return to the same position, so that the phase difference δ between the two beams LA and LB becomes a beat signal. Detected.

That is, since the light receiving element 29 has a structure having a photoelectric conversion unit (not shown), the intensity I of the two beams LA and LB on the light receiving element 29 is a value based on the following formula and the photoelectric conversion of the light receiving element 29 is performed. Is sent to the signal comparator 33.
I = (Ea + Eb) (Ea + Eb) ^* = A ² + B ² + 2ABcos (2π * 2fmt + δ)
Accordingly, the phase difference δ can be measured by performing phase comparison of heterodyne detection at a frequency of 2 fm using the signal comparator 33 shown in FIG. In this way, phase information is acquired.

  By the way, the light receiving element 28 disposed opposite to the light receiving element 29 with the polarization beam splitter 27 is also configured to have a photoelectric conversion unit (not shown), but an incident beam of diffracted light generated by the acoustooptic element 23 is used. The beat signal enters the light receiving element 28 and is detected by the photoelectric conversion unit of the light receiving element 28. That is, since the phase difference generated in the optical system or the like up to the acoustooptic device 23 is detected by the photoelectric conversion unit of the light receiving device 28, the light receiving device 28 serves to provide a phase reference.

  On the other hand, in the light receiving element 29 as described above, a beat signal obtained by adding phase difference information between the two beams LA and LB is detected by the photoelectric conversion unit in the light receiving element 29 and sent to the signal comparator 33. It is done. Therefore, the true phase difference δ is detected by performing the two phase comparisons in the signal comparator 33. The true phase difference δ is δh = λδ / 4π, which is the average phase difference between the beam LA and the beam LB, that is, difference information of the average height h. Here, λ represents the wavelength of the laser 21.

  If these pieces of information are sent to a data processing unit 34 composed of a CPU, a memory, etc. connected to the signal comparator 33, the data processing unit 34 records this information together with the plane scanning information, and the measurement object G1 is recorded. Surface profile information can be easily derived. Further, it is possible to obtain even higher speed data by using the acoustooptic device 23 having a speed Va as high as possible.

  As described above, by using the optical system of the distance measurement system of this embodiment, it is possible to acquire three-dimensional measurement data every time two-dimensional scanning is performed. For this reason, according to the distance measurement system of the present embodiment, it is possible to observe and measure a change in the state of cells and microorganisms, a transient change in the surface state, and the like at high speed.

  In addition, since a 3D stereoscopic image can be displayed by using a commercially available autostereoscopic display or a 3D display using polarized glasses, the apparatus should be useful in education, research, and medicine. Can do. At this time, since the degree of overlap of the two beams is made smaller than the beam diameter, the path difference between the two beams hardly occurs. For this reason, the influences of disturbances and vibrations are generated simultaneously by the two beams, and these influences are offset.

  On the other hand, in the present embodiment, an example in which the beam separation degree is much smaller than the individual beam diameters has been shown. However, by increasing the modulation frequency, the beam separation degree is increased and the beam diameter is approximately equal to the beam diameter. The optical system of the present invention is also useful when a degree of separation is required.

  In this embodiment, an example using a two-dimensional scanning device has been described. However, if the application requires simple data in only one direction, the two-dimensional scanning device is replaced with a one-dimensional scanning device. The same effect can be obtained. As these one-dimensional scanning devices, galvanometer mirrors, resonant mirrors, rotating polygon mirrors, and the like can be employed. In addition, the two-dimensional scanning device can be realized by preparing two one-dimensional scanning devices for the X direction and the Y direction and passing through the pupil transfer lens system. Further, a micromirror device using a micromachine technique may be used. As this micromirror device, both one-dimensional and two-dimensional devices are known and commercialized.

  As described above, by processing the spatial frequency information on the Fourier transform plane, it is possible to bring about a very high lateral resolution improvement, particularly in the difference calculation. Similarly, as described above, the intensity difference signal is data reflecting the height of the profile data.

In this embodiment, an embodiment in which the reflection optical system described in Embodiment 2 is replaced with a transmission optical system will be described.
FIG. 6 is a block diagram showing a distance measuring system using a transmission type optical system according to the present embodiment. Since the main optical system is the same as that of the second embodiment, a description thereof will be omitted. However, in this embodiment, as shown in FIG. 6, the light collected by the objective lens 31 is transmitted through the measurement object G2. The light receiving element 49 is characterized in that it is disposed on the opposite side of the objective lens 31 with the measurement object G2 interposed therebetween. That is, in the case of the present embodiment, the light receiving element 49 divided in such a manner that the dark line extends in the direction perpendicular to the separation direction of the two beams is arranged on the extended line of the optical axis L of the objective lens 31 as the light receiving element. Yes.

  As described above, according to the present embodiment, the light receiving element 49 can be arranged close to the measuring object G2 as compared with the reflection type optical system, so that the obtainable spatial frequency can be set very high. . As a result, since the reproducibility of the spatial frequency of the measurement object G2 is improved, the lateral resolution can be further improved. In particular, observation and measurement of living organisms and cells can be performed with very high resolution in the state of being alive. This is a feature that is greatly different from a measuring instrument such as an electron microscope that cannot be observed unless the living body is killed even at a high magnification.

This embodiment is characterized in that a spatial modulator is used instead of the acousto-optic element 23 as a member for applying modulation.
FIG. 7 is a conceptual diagram showing the spatial modulator of this embodiment. The magnetic garnet film 53A constituting the spatial modulator 53 as shown in FIG. 7A is provided with electrodes (not shown) so that each pixel can be driven by voltage or current, and the spatial modulator 53 is arranged at the position of the acoustooptic device 23 in FIG. By applying voltage and current to each pixel of the magnetic garnet film 53A, the polarization plane of each pixel is rotated by the magneto-optic effect. The degree of rotation of this polarization plane depends on the magnitude of the applied voltage and current. Determined by. As a spatial modulator 53 having such a structure, there is a spatial modulator 53 having 128 × 128 pixels and a response speed of 15 ns.

  Further, in FIG. 7B, the intensity or phase of the light that has passed through the polarization beam splitter 27 in FIG. 4 is perpendicular to the scanning direction of the spatial modulator 53 so that it becomes a strip-like sine grating. A voltage or current is applied to each pixel in the manner shown. At this time, the lattice can be moved at a speed v by causing a single vibration of a frequency fm = ± 2πv / d out of phase with respect to each pixel.

That is, when the pitch of the sine wave lattice is d and the moving speed is v, the following equation is obtained.
Acos {2π / d (x−vt)} = A / 2 (expj {2π / d (x−vt)} + expj {−2π / d (x−vt)})
For this reason, ± 1st-order diffracted light has a modulation frequency of fm = ± 2πv / d. In the case of intensity, a zero-order DC component is generated, but since it is a DC component, there is no influence on the beat signal.

  Here, the ± first-order diffracted light is set to a degree that the beams overlap to a desired extent according to the pitch of the sine grating and the magnification of the pupil transmission magnifying lens system as in the second embodiment. Further, if the speed v is determined so that the modulation frequency fm is about 8 MHz, the same effect as in the second embodiment can be obtained. The response speed of the spatial modulator 53 is 15 ns, but the current spatial modulator is digitally binary.

  However, analog modulation is possible, and the response speed at that time may be deteriorated by about an order of magnitude. By using it in combination with the pupil transfer magnifying lens system, a modulation frequency of 8 MHz or more can be sufficiently obtained. It is possible to get. In this case, the pupil transmission magnifying lens system is simplified as compared with the second embodiment. This is because the modulation frequency is determined by the response speed of the device, but the beam separation can be reduced by increasing the grating pitch as much as possible.

  Therefore, since the minimum degree of separation is determined by the size of the device, high-speed scanning can be performed if selected appropriately. Note that the drive circuit and the like can be simplified by making the pixels of the spatial modulator 53 described above into strips as shown in FIG.

In the acoustooptic device 23, if an element that causes Ramanus diffraction is used, the modulation frequency is fm, so that ± 1st-order diffracted light can have a modulation frequency of fm according to the following equation.
Acos (2πfmt) = A / 2 ((expj {2πfmt)} + expj {−2π / fmt})
In this case, the same effect can be obtained with a simple modulation signal rather than modulation such as DSB modulation.

  The light receiving element 28 is used in the second to fourth embodiments. However, the light receiving element 28 is omitted, and there is no measurement object G1, G2, or the objective lens 31 is largely defocused and two-dimensional. It is conceivable to perform scanning and store the phase information in the memory of the data processing unit 34 together with the two-dimensional scanning information. Since this phase information is a phase shift of the optical system and the electrical system, true phase information can be acquired by correcting the phase information in the case where the measuring object G1 exists, using this as a reference value. In this way, the light receiving element 28 is not necessary, and a correction value can be obtained before observing the measurement object G1, thereby enabling highly accurate measurement.

  Thus, by obtaining the correction value before observing the measuring objects G1 and G2, in particular in Example 3, after performing the monitor or the cell shape determination when flowing cells or the like through the microchannel. It will have a tremendous effect on applications such as seeding cells.

  That is, since the microchannel is an element that allows cells or the like to flow in one direction, a one-dimensional scanning device that scans in a direction perpendicular to the direction of the channel is prepared instead of the two-dimensional scanning device 26 of the second and third embodiments. That's fine. In this way, it is only necessary to store the phase relating to very few points only in the one-dimensional scanning direction, and the optical system is simplified. Since obtaining the same effect even if the intensity information is obtained is the same as described above, the description thereof will be omitted.

  The embodiments according to the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

  The present invention can be applied not only to the distance to the measurement object and the shape of the measurement object, but also to various types of measurement equipment such as a microscope.

DESCRIPTION OF SYMBOLS 10 Airplane 11,12 Transmission antenna 13,14 Reception antenna 16 Signal preparation apparatus 17 Measurement equipment 21 Laser 22 Collimator lens 23 Acoustooptic element 24 AOD driver 25 Pupil transmission magnification lens system 26 Two-dimensional scanning device 27 Polarizing beam splitter 28, 29 Light receiving element 30 Pupil transmission lens system 31 Objective lens 33 Signal comparator 34 Data processing unit 49 Light receiving element 53 Spatial modulator G Measurement object G1 Measurement object G2 Measurement object

Claims (6)

Irradiation means for irradiating two coherent electromagnetic waves having different frequencies with each other while having the same region on the object to be measured;
Electromagnetic wave detecting means for detecting electromagnetic waves from at least two regions in the measurement object across a boundary line extending in a direction substantially perpendicular to the shifted direction;
A signal creation means for creating a difference signal or a sum signal of the outputs of the electromagnetic waves detected by the electromagnetic wave detection means at symmetrical positions across the boundary line;
A measuring means for obtaining a measured value by calculating a phase difference or an intensity difference of the difference signal or the sum signal; and
Distance measuring system including. A light source that emits coherent light;
A first means that converts the light emitted from the light source into two light beams that are separated and irradiated in a state of being close to each other while being modulated to different frequencies;
A second means for one-dimensionally scanning or two-dimensionally scanning the two lights;
A third means for irradiating the measurement object with the two light beams scanned two-dimensionally;
A direction substantially perpendicular to the direction in which the two lights are separated is defined as a boundary line, and the reflected light or transmitted light from the measurement object is received in at least two parts across the boundary line. Means,
A fifth means for creating a difference signal or a sum signal of outputs of light received by the fourth means in a region sandwiching the boundary line;
A sixth means for obtaining a measured value by obtaining a phase difference or an intensity difference of the difference signal or the sum signal;
Distance measuring system including.   The distance measuring system according to claim 2, wherein the first means is an acousto-optic element or a spatial modulator, and two modulation signals are added to the acousto-optic element or the spatial modulator.   The distance measuring system according to claim 2 or 3, wherein the two-dimensional scanning of the second means uses a combination of two one-dimensional scanning elements or a two-dimensional scanning element.   The distance measurement system according to any one of claims 2 to 4, wherein the light that the third means irradiates the measurement object is parallel light, convergent light, or divergent light.   6. The distance measuring system according to claim 2, wherein the sixth means uses heterodyne detection based on a difference between two modulated frequencies.

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