JPH05127093A - Confocal laser scanning differential interference microscope - Google Patents

Abstract

PURPOSE:To separately provide the differential interference image of the phase distribution and the intensity distribution of an object with compact and easy-to- produce construction without using any special optical elements such as Nomarski prism and wavelength board. CONSTITUTION:On the location of the spot image due to the light collecting optical system of the laser spot reflected by an object to be tested, double mode channel waveguide paths 7 and 17 are arranged. Further, waveguide path branches 8 and 18 dividing a plurarity of channel waveguide paths are provided to detect a microscopic inclination of the object to be tested by detecting the difference of the light quantity passing through each branched channel waveguide path. A pair of such detection means 11 and 12 and 21 and 22 are provided to combine the width direction of the double mode waveguide paths to be crossed. By synthesizing differential signals from each detection means, the differential image of the object can be seen in the arbitrary direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a confocal laser scanning microscope.

[0002]

2. Description of the Related Art A confocal laser scanning microscope comprises a laser light source, an illumination optical system that collects a light beam from the laser light source on a test object to form a light spot, and a light beam from the test object on a detection surface. It has a condensing optical system for converging on the top, a detecting means for detecting the luminous flux condensed on the detection surface, and a scanning means for relatively moving the light spot with respect to the object to be inspected, Laser light is focused on the object to be inspected, and light is detected on the detection surface through the pinhole opening. Therefore, it has an advantage that the depth of focus is very shallow, and is about to be used for various purposes.

[0003]

In order to obtain a differential interference contrast image by using such a confocal laser scanning microscope, it can be realized by using the constitution of the differential interference device in the conventional general optical microscope. .. However, it is difficult to manufacture each optical element with a desired precision because it has a complicated structure and requires a special objective lens, a Nomarski prism, a wave plate, and the like, which is an expensive device. there were.

For this reason, the present inventors have previously proposed Japanese Patent Application No. 2-40.
No. 0212 and Japanese Patent Application No. 3-63107 have proposed a confocal laser scanning differential interference microscope capable of independently obtaining phase information and amplitude information of an object in a small and simple structure using a waveguide. That is, a laser beam is focused on an object to be inspected, a double mode channel waveguide is arranged at the spot image position of the laser spot focusing optical system, and a waveguide branching region is subsequently branched into a plurality of channel waveguides. Is provided. Then, the microscopic tilt of the object to be inspected is detected by detecting the difference in the amount of light passing through the branched channel waveguide. By changing the perfect coupling length of even and odd modes in the double mode region by the electro-optic effect, we proposed a structure that can independently extract the phase-modulated portion and the intensity-modulated portion of the object and view their differential images. Is the latter application.

However, in the above-proposed configuration, although it is possible to obtain the differential signal of the phase information or the amplitude information in the width direction of the double mode waveguide region, There is a problem that the differential signal is not detected in the direction perpendicular to the width direction. This can be achieved by rotating the previously proposed microscope apparatus with respect to the object to be inspected,
There is a problem that a mechanism for rotating the sample and the microscope relative to each other is separately required, and simultaneous observation cannot be performed.

Therefore, an object of the present invention is to provide a confocal laser scanning microscope which can obtain a differential image with contrast in a desired direction without requiring relative rotation between the object to be inspected and the microscope. Especially.

[0007]

The confocal laser scanning microscope according to the present invention is based on the previously proposed configuration and is provided with two detecting means, and the width directions of the double mode waveguide regions in each detecting means are orthogonal to each other. It is a combination to do. Specifically, each of the first and second light detecting means is provided with a substrate having a channel waveguide formed therein, and the channel waveguide has a double mode waveguide region having an incident end face on the detection surface and the double mode waveguide region. Two mode waveguides
A waveguide branch region for branching into two channel waveguides, and a detection element for detecting each light propagating through the two branched channel waveguides.

Further, in a so-called epi-illumination type confocal laser scanning microscope in which the same objective lens is shared by the illumination optical system and the condensing optical system, at least one of the first and second detecting means is used as the detecting means. A branching means for branching the double mode waveguide into three channel waveguides is provided, and 1
It is also possible to adopt a configuration in which the illumination light is supplied from the channel waveguide of the book. Specifically, the central one of the three channel waveguides guides the illumination light beam from the laser light source to form a light spot on the object to be inspected through the objective lens.
It is desirable to adopt a configuration in which a detection element for detecting the light propagating through the two channel waveguides on the outer side of the channel waveguides is provided.

And, first, Japanese Patent Application No. Hei 3-63107.
And at least one of the first and second detection means has an electro-optical effect at least in the double mode waveguide region,
It is also possible to have a structure in which an electrode is provided on the double mode waveguide region.

[0010]

The principle of the present invention has been described in detail in the above-mentioned application, but its outline will be described below. The laser spot reflected by the object to be inspected is condensed by the condensing optical system including an objective lens and an imaging lens.
It becomes a spot image again on the detection surface. If the double-mode channel waveguide is placed at the position where this spot image is formed so that the center of the spot image and the center of the double-mode channel waveguide are aligned, the spot image amplitude distribution in the width direction of the waveguide If the origin is an even function, only the even mode is excited in the double-mode waveguide. In other cases, even and odd modes are excited. Here, if a waveguide branch that branches into two channel waveguides is provided following the double mode region, an equal amount of light is distributed to the two branches when only the even mode is excited, and in the other cases. Since even-mode and odd-mode interference occurs, the amounts of light distributed to the two branches are generally not equal. Generally, when the object to be inspected has an inclination, that is, a physical inclination, as well as all the inclinations that change the optical path length such as the refractive index inclination and the inclinations of the light transmittance distribution or the light reflectance distribution, the amplitude distribution of the spot image becomes It has an odd function component. At this time, even and odd modes are excited in the double mode waveguide, and as a result, the light quantities are not equal when distributed to two branches. Therefore, the microscopic tilt of the object to be inspected can be detected by detecting the difference in the amount of light propagating through the two branches.

Let θ be the tilt angle of the object to be inspected, and sin θ = α
And When the gradient is 0, the spot amplitude distribution is u (x),
If the eigenfield distribution of the double mode waveguide is fe (x), fo (x) for both even and odd modes, u (x), fe
(X) is an even function and fo (x) is an odd function. The spot amplitude distribution uα (x) when there is an inclination is k = 2π / λ
As (λ: wavelength), uα (x) ≈u (x) exp (ikαx) = u (x) [cos (kαx) + isin (kαx)] (1).

Here, the even mode excitation efficiency η _e is

[0013]

[Equation 1]

On the other hand, the excitation efficiency η _o of the odd mode is

[0015]

[Equation 2]

[0016] If the integration range is properly selected and | kαx | << 2π in this range, cos (kαx) ≈ 1, sin (kαx) ≈ kαx, so u (x), fo (x), fe (x) are Since it is a constant function, it can be seen that η _e ≈constant η _o ∝iα (4). The change in light intensity due to the interference between the even mode and the odd mode is C ₁ and C ₂ are real constants, and φ is the phase difference between the even mode and the odd mode at the branch point. I ∝│η _e ± iη _o exp { iφ} | ² = | C ₁ ± iαC ₂ exp {iφ} | ² (5) Therefore, if exp {iφ} = ± i, then (5) is roughly I = C ₁ ² ± 2αC ₁ C ₂ (6) Then, the intensity change proportional to α can be obtained, and a so-called differential image can be obtained.

Therefore, in order to obtain such a differential image, at the branch point of the double mode and the single mode,
It is necessary to provide an odd multiple of 90 ° between the modes. For this reason, the length L of the double mode region is L = Lc (where Lc is the well-known complete coupling length of both modes (the length at which the phase difference between the even and odd modes is 180 °). 2m + 1) / 2 (m = 0, 1, 2, ...) (7) is preferable.

Since equation (1) considers the inclination of the object, it means that a phase object is assumed. The present invention can be applied not only to a phase object but also to an intensity modulation object (an object whose light transmittance or reflectance changes). Such an object can be expressed as, for example, uα (x) = u (x) (1 + αx) (8), where α is a real number. Since η _e ≈ constant and η _o ∝ α (9) at this time, the ratio of the light quantity distributed to the two branches due to the interference between the even and odd modes is the maximum between the two modes at the branch point. When a phase difference of an integer multiple of 180 ° is introduced,
That is, this is the case where exp {iφ} = ± 1 is set in the equation (5).

Therefore, in order to see the differential image of the intensity-modulated object, the length L of the double mode region is preferably an integral multiple of the coupling length Lc L = mLc (m = 1, 2, ...) (10). That is, the differential image of only the phase-modulated portion or the intensity-modulated portion of the object can be seen depending on how the length L of the double mode region is taken.

When the substrate has the electro-optical effect, the complete coupling length Lc can be changed by applying a voltage to this region through the electrode arranged on the double mode region. Therefore, even if the length of the double mode region is a constant value L, it is possible to satisfy both the above formulas (7) and (10) by adjusting the voltage, and the mechanical length of the double mode region is It is possible to obtain the phase information and the amplitude information of the object independently by the electro-optic effect while keeping the constant.

That is, by applying a voltage to the electrodes arranged on the double mode region of the channel waveguide,
The complete bond length Lc in the double mode region is changed to Lc ₁ and Lc ₂ , and for a constant length L of the double mode region, L≈mLc ₁ (m = 1, 2, ...) L≈Lc By setting ₂ (2m + 1) / 2 (m = 0,1,2, ...), the amplitude information of the object can be obtained as in the above equation (10) in the case of Lc _1.
In the case of ₂ , the phase information of the object can be obtained as in the above equation (7).

According to the principle of the differential interference microscope using the channel waveguide as described above, in the present invention, two detecting means are combined so that the width directions of the double mode waveguides are orthogonal to each other. .. Then, the differential information in the directions orthogonal to each other can be obtained from each detecting means, and by combining the signals from both detecting means, it is possible to obtain the differential image as the contrast difference in any direction. ..

Specifically, when the signals obtained by the first and second detecting means are I ₁ and I ₂ , respectively, and the composite signal of the two is I, then I = I ₁ sin θ + I ₂ cos θ Signal processing is performed so that (12). Here, by changing θ in the range of 0 to π, the contrasting direction of the differential image can be changed, and the differential image having the contrast in a desired direction can be obtained without relatively rotating the sample and the microscope. Can be obtained. Practically, it is preferable to appropriately change the value of θ while observing a monitor image as a confocal laser scanning microscope to select a value of θ that allows the differential image of the object to be inspected to be most accurately expressed.

In the present invention, the double mode waveguide region is branched into a plurality of channel waveguides. However, the channel waveguide after branching is not limited to a single mode channel waveguide, and it is possible to guide light. Any channel waveguide can be used as long as it is possible.

[0025]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the present invention. Light emitted from a semiconductor laser light source 1 is reflected by a half mirror 2 and a well-known XY two-dimensional scanning means 3 is shown.
Then, the light enters the objective lens 4 and is condensed on the object plane 5.
The light reflected by the object plane 5 and then transmitted through the half mirror 2 through the objective lens 4 and the XY two-dimensional scanning means 3 again is branched into two optical paths by the second semi-transmissive mirror 28. The light transmitted through the second semi-transmissive mirror 28 is condensed on the incident end face of the channel waveguide 7 formed on the first substrate 6 which constitutes the first detecting means. The light reflected by the second semi-transmissive mirror 28 is
The light is focused on the incident end face of the channel waveguide 17 formed on the second substrate 16 which constitutes the detecting means. First substrate 6 and second
The substrates 16 are both equivalent substrates having an electro-optical effect. The channel waveguide 7 formed on the first substrate 6 is a double mode waveguide in which an electrode 15 is arranged on the substrate, and the light propagating in the double mode waveguide 7 eventually reaches the branching region 8 and two The power is distributed to the single mode waveguides 9 and 10 and reaches the two photodetectors 11 and 12 bonded to the substrate 6.

Similarly, the channel waveguide 17 formed on the second substrate 16 is a double mode waveguide in which an electrode 25 is arranged on the substrate, and the light propagated in the double mode waveguide 17 has a branch region 18 Power is distributed to the two single-mode waveguides 19 and 20, and the two photodetectors 2 bonded to the substrate 16
Reach 1, 22. This configuration constitutes a confocal laser scanning microscope because the incident ends of the channel waveguides 7 and 17 function like pinholes. Here, the half mirror 2 and the objective lens 4 form an illumination optical system, and the objective lens 4 forms a focusing optical system.

As described above, when there is an inclination or a reflectance gradient at one point on the object 5 illuminated by the laser spot, the phase distribution of the laser spot imaged at the incident end of the channel waveguides 7 and 17 or The intensity distribution is inclined, and the direction thereof corresponds to the width direction of each double mode region. Due to the inclination of each double mode region in the width direction, even and odd modes are excited in the double mode waveguides 7 and 17, respectively.
Due to the interference of both modes, two pairs of photodetectors 11,12 and 21,22
The ratio of the optical power reaching to changes. Therefore, the detectors 11, 12 and 21, 22 forming a pair by the operation detecting means 13 and 23, respectively.
By taking the differential signals 14 and 24 of the output of, it is possible to detect a minute step on the object surface or a change in reflectance in each direction.

At this time, the length L of the double mode region is L = Lc (2m + 1) / 2 (m = 0,1,2, ...) When the phase distribution of the object is observed with the complete coupling length as Lc. Similarly, when observing the intensity distribution of the object, it is sufficient to set L = mLc (m = 1, 2, ...) As described above, this configuration is a differential interference system.

Here, since each of the substrates 6 and 16 has an electro-optical effect, if the voltage applied to each of the electrodes 15 and 25 is changed by the voltage adjusting means 60, the complete coupling length Lc can be changed. You can Therefore, the above two conditions are satisfied for the same length L of the double mode region by adjusting the voltage applied to the electrode 15 in the first substrate 6. That is, the phase distribution and the intensity distribution of the object can be detected independently with one waveguide device. The same action can be achieved by adjusting the voltage applied to the electrode 25 on the second substrate 16, but the width direction of the double mode region 17 is set to the first substrate 6
Since it is perpendicular to that of (1), the direction in which the signals of the obtained phase distribution and intensity distribution generate contrast is orthogonal to the direction in which the signals obtained on the substrate 6 generate contrast. As described above, the differential interference images with contrast in the desired direction can be obtained by signal processing the differential signals 14 and 24 obtained by the two substrates 6 and 16.

Specifically, the differential signals 14 and 24 are transferred to the I ₁ ,
When I ₂ is set, the signal processing means 29 causes the combined signal I of the two.
Is processed as given by the above equation (12). The control means 26 stores the output from the signal processing means 29 in correspondence with the position of the light beam on the object to be inspected from the XY two-dimensional scanning means 3, converts it into image information, and monitors it.
The desired differential interference contrast image can be displayed at 27.
Here, θ can be arbitrarily changed in the range of 0 to π with respect to the signal processing means 29, and the direction in which the contrast of the differential image is generated can be arbitrarily changed by appropriately changing this θ. ..

In the above embodiment, the electrodes 15 and 25 for applying a voltage to the double mode waveguides 7 and 17 are two electrodes which are symmetrical with respect to the waveguides 7 and 17, but are used. The electrode arrangement as shown in FIG. 1 is not always optimal depending on the state of the substrate to be formed (the crystal axis direction in the case of a crystal substrate). FIG. 2 is a schematic configuration diagram showing a second embodiment of the present invention. This configuration is also a coaxial incident type configuration in which the objective lens 38 is shared by the illumination optical system and the condensing optical system similarly to that shown in FIG. 1, but a part of the waveguide in the two detecting means is laser light. It also has the function of the lighting system to guide the. As for the first substrate 22 that constitutes the first detection means, the laser light source 31 is a semiconductor laser and has the highest optical coupling efficiency with respect to the single mode channel waveguide 33 formed on the substrate 32 having an electro-optical effect. It is fixed to the substrate 32 so as to be large. The laser light incident on the waveguide 33 propagates through a branch 34 and a double mode waveguide 35 in which an electrode 45 is arranged on the substrate surface. In the waveguide branch 34, three single-mode waveguides are coupled to the double-mode waveguide 35, and the single-mode waveguide 33 in the middle is used for illumination and the two single-mode waveguides on the outside. Is used for detection described later.

At this time, the center line of the center single-mode channel waveguide 33 and the center line of the double-mode waveguide 35 are aligned so that the center line of the center-mode single-mode channel 33 is double-mode guided. Light incident on the waveguide 35 excites only even modes in the double mode waveguide 35. Therefore, in effect, the laser light is emitted from the end face 36 in the single mode state. The second substrate 48 constituting the second detecting means is also configured in the same manner as the substrate 32, and the laser light from the semiconductor laser 47 propagates from the single mode waveguide 49 through the branch 50 to the double mode waveguide 51. , Exits in a single mode state from the end face 52.

The illumination light flux emitted from the end faces of the double mode waveguides 35 to 51 enters the objective lens 38 through the XY two-dimensional scanning means 37 through the semi-transmissive mirror 46, and the object plane 39.
Focused on top. After reflecting off the object plane 39, the objective lens is again
The light flux that has passed through 38 and the XY two-dimensional scanning means 37 is
A part of the first substrate 32 of the first detecting means passes through the semitransparent mirror 46.
And the rest reach the second substrate 48 of the second detection means. The double mode waveguides 35 and 51 formed on the respective substrates are
The light is focused on the end faces (detection faces) 36, 52 of the laser light and a laser spot is formed there. After this, as in the first embodiment, the two outer single-mode channel waveguides 40, 41 and 53, 5 out of the three single-mode waveguides are provided on each substrate.
The power ratio distributed to each of 4 changes with the inclination of the object plane, and the photodetectors 4 fixed to the substrates 32 and 48, respectively.
If the light from the waveguides 40, 41 and 53, 54 is detected at 2, 43 and 55, 56 and the differential signals 44 and 57 are taken, the differential interference signal by each detecting means can be obtained.

Also in this structure, since the substrates 32 and 48 have the electro-optical effect, the complete coupling length Lc can be changed by changing the voltage applied to the electrodes 45 and 58. The phase distribution and intensity distribution of an object can be detected independently with one waveguide device. And likewise the first
Since the width direction of the double mode waveguide 35 on the substrate 32 is perpendicular to the width direction of the double mode waveguide 51 on the second substrate 48, the directions in which the signals of the obtained phase distribution and intensity distribution are contrasted with each other. They are orthogonal,
By performing signal processing on each of the differential signals 44 and 57, a differential interference contrast image having a contrast in a desired direction can be obtained.

In FIG. 2, the voltage adjusting means 60, the signal processing means for the differential signals 44 and 57, the control means and the monitor for imaging with the signals from the XY two-dimensional scanning means are shown in FIG. Since it is the same as the configuration of the first embodiment, it is omitted. In addition, in the configuration shown in FIG.
The illumination light is supplied from the laser light sources 31 and 47 to both 32 and 48, but the illumination light may be supplied from only one of them, and thus the other laser light source is not always necessary. In this case, it is possible by replacing one of the substrates 32 and 48 of the two detection means shown in FIG. 2 with the substrate 6 or 16 shown in FIG. Then, when the laser light source is provided on both substrates, the laser light is supplied from only one of them, and if one of the laser light sources fails, the other is switched to, and the laser light source is not replaced. It is possible to continue operating the microscope.

Materials suitable for forming the channel waveguide in the structure of each of the above embodiments will be described. As a waveguide substrate, soda glass, Pyrex,
Fused silica is known, but these have no electro-optical effect, and it is difficult to integrally configure a laser diode as a light source or a light receiving element into a monolithic structure. When LiNbO ₃ , LiTaO ₃ , GaAs, or InP is used as the substrate, it is possible to change the complete coupling length Lc of the double-mode waveguide region by forming an electrode based on these electro-optical effects. , InP
Then, it is also possible to monolithically integrate the laser diode LD and the detection element. When Si is used for the substrate, the light receiving element can be integrated.
Including these, the materials of the substrate and the waveguide layer for forming the channel waveguide that can be used in the present invention can be arranged as follows, and an appropriate material is used based on the characteristics of each material. Preferably.

[0037]

[Table 1]

By the way, in each of the above-mentioned embodiments, the objective lens is commonly used for the illumination optical system and the condensing optical system, and a so-called epi-illumination type microscope is constructed. Except for the configuration of the second embodiment shown in FIG. 2, a so-called transmission microscope in which the illumination optical system is arranged on one side of the object to be inspected and the condensing optical system is arranged on the other side is not possible. Needless to say.

In each of the above embodiments, the laser light source and the photodetector are external to the waveguide device, but if a silicon substrate is used, the photodetector and the waveguide device will be on the same substrate. If a compound semiconductor substrate such as gallium arsenide is used, both the laser light source and the photodetector can be monolithically integrated on the same substrate as the waveguide, reducing the size and weight of the device and saving the adjustment labor. You can go further. However, when it is difficult to integrally configure the laser light source and the photodetector with the waveguide device, these may be arranged separately and the light may be guided by an optical fiber or a lens system.

The double mode waveguide can be replaced by two single mode waveguides arranged close to each other. Further, it goes without saying that images having various contrasts can be obtained by applying appropriate processing to the actuation signal from the photodetection element that detects the intensity of light passing through the two single mode waveguides. .. Further, in each of the embodiments, the differential signals from the two detecting means are combined and the image processing is performed. However, by displaying the differential signals from the two detecting means on different monitors, there is an object. It is also possible to configure so that the differential image in the direction and the differential image in the direction orthogonal thereto can be observed independently.

In each of the embodiments, the light spot is scanned on the test object by an xy two-dimensional scanner such as a vibrating mirror or a rotating mirror as a means for moving the test object and the light spot relative to each other. However, conversely, it is also possible to fix the light spot and scan the stage on which the object to be inspected is placed. When the light beam in the optical system is oscillated by a vibrating mirror or rotating mirror to scan the light spot, the residual aberration of the optical system affects the light spot on the object to be measured and the light receiving surface of the detecting means (double mode). There is a possibility that the conjugate relationship with the light spot condensed on the end face of the waveguide region) cannot be strictly maintained. In such a case, it is preferable to scan the stage.

[0042]

As described above, according to the present invention, in a confocal laser scanning differential interference microscope using a waveguide and having a small and simple structure, the object to be inspected and the microscope are relatively rotated. The differential image can be observed without causing the contrast in the desired direction. In the configuration of the present invention, it is possible to detect the differential information of the object to be inspected by the difference signal of the amount of light passing through the two branched channel waveguides, but the sum signal is taken instead of the difference. It goes without saying that the case functions as a normal confocal laser scanning microscope.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment.

FIG. 2 is a schematic configuration diagram of a second embodiment.

[Explanation of symbols]

5,39 Object to be inspected 4,38 Objective lens 1,31,47 Laser light source 7,17,35,51 Double mode waveguide 9,10,19,20,33,40,41,49,53,54 Single mode Waveguide 11,12,21,22,42,43,55,56, Photodetector 15,25,45,58 Electrode

Claims (7)

[Claims] 1. A laser light source, an illumination optical system for converging a light beam from the laser light source to form a light spot on an object to be inspected, and a light beam from the object to be inspected to a detection surface. Confocal laser scanning including a condensing optical system, a detecting unit that detects a light beam condensed on the detection surface, and a scanning unit that relatively moves the light spot with respect to the object to be inspected. In the microscope, the light detecting means has first and second detecting means, and each of the first and second detecting means has a substrate on which a channel waveguide is formed, and the channel waveguide is The detector has a double-mode waveguide region having an incident end face on the detection surface, and a waveguide branch region for branching the double-mode waveguide into two channel waveguides, and the first and second detecting means are respectively the above-mentioned. Propagate through two branched channel waveguides And a detection element for detecting each of the light beams, so that the width direction of the double mode waveguide region of the first detection means is perpendicular to the width direction of the double mode waveguide region of the second detection means. A confocal laser scanning differential interference microscope, which is configured to obtain information on an object to be inspected by a detection signal from each detection element of the first and second detection means. 2. A substrate of at least one of the first detecting means and the second detecting means has a third channel waveguide provided in the center of the two channel waveguides.
2. The confocal laser according to claim 1, wherein light from the laser light source is guided through the third channel waveguide and the branch from the double mode channel waveguide onto the object to be inspected by the illumination optical system. Scanning differential interference microscope. 3. The confocal laser scanning differential according to claim 1, wherein the substrate is a semiconductor substrate, and the photodetector element is monolithically formed on the semiconductor substrate together with the waveguide. Interference microscope. 4. The substrate according to claim 1, wherein the substrate is a semiconductor substrate, and the photodetection element and the laser light source are monolithically formed on the semiconductor substrate together with the waveguide. Focal laser scanning differential interference microscope. 5. When the length of the double mode region of the channel waveguide is L and the complete coupling length of the even-odd mode in the double mode region is Lc, L≈mLc (m = 1,2) , ...) L≈Lc (2m + 1) / 2 (m = 0, 1, 2, ...) The confocal laser scanning differential interference microscope according to any one of claims 1 to 4, wherein the relation is satisfied. 6. The at least one of the first and second detecting means, wherein the substrate has an electro-optical effect and also has an electrode on the double mode waveguide region. 5. A confocal laser scanning differential interference microscope according to any one of items 1 to 5. 7. A perfect coupling length Lc of even-odd modes in the double mode region is obtained by applying a voltage to an electrode arranged on the double mode region of the channel waveguide, by the electro-optic effect of the substrate. Lc ₁ and Lc ₂ are changed, and L≈mLc ₁ (m = 1, 2, ...) L≈Lc ₂ (2m + 1) / 2 (m = 0, 1,) for the length L of the double mode region. 2. The confocal laser scanning differential interference microscope according to claim 6, characterized in that