JP3018538B2 - Optical waveguide device, confocal laser scanning differential interference microscope using the same, and information detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. 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 is composed of a laser light source, an illumination optical system for converging a light beam from the laser light source on a test object to form a light spot, and a detecting surface for detecting the light beam from the test object. A focusing optical system that focuses light on the top, a detection unit that detects a light beam focused on the detection surface, and a scanning unit that relatively moves the light spot with respect to the test object, Laser light is condensed on the test object, and light is detected on the detection surface through the pinhole opening. For this reason, it has an advantage that the depth of focus is very shallow, and is going to be used for various applications.

[0003]

To obtain a differential interference image using such a confocal laser scanning microscope can be realized by using a configuration of a differential interference device in a conventional general optical microscope. . However, since a complicated configuration is required, and a special objective lens, a Nomarski prism, a wave plate, and the like with a small distortion are required, it is difficult to manufacture each optical element with a desired accuracy, resulting in an expensive device. there were.

[0004] It is an object of the present invention to provide a confocal laser scanning differential interference microscope which is small in size, easy to manufacture, and capable of independently obtaining phase information and amplitude information of an object.

[0005]

In order to achieve the above object, the present invention uses a waveguide device and obtains a differential interference image by a principle completely different from that of the conventional structure. That is, in a confocal laser scanning microscope, a substrate having an electro-optical effect in which a channel waveguide is formed is provided in a light detection unit, and the channel waveguide has an incident end surface on the detection surface and an electrode is provided on the substrate surface. Having a divided double mode waveguide region and a waveguide branch region for branching the double mode waveguide into two single mode waveguides, and further transmitting light propagating through the two branched single mode waveguides. And a detection element for detection.

In a so-called epi-illumination type confocal laser scanning microscope in which the same objective lens is shared between the illumination optical system and the condensing optical system, the detecting means has an electro-optical effect in which a channel waveguide is formed. A substrate, wherein the channel waveguide has a double-mode waveguide region having an end surface on the detection surface and an electrode provided on the substrate surface, and a waveguide for branching the double-mode waveguide into three single-mode waveguides A light spot formed on a test object through an objective lens by guiding an illumination light beam from a laser light source to a central one of the three single mode waveguides. It is also possible to adopt a configuration in which detection elements for detecting light propagating through two outer single-mode waveguides among the single-mode waveguides are provided.

[0007]

According to the present invention, the laser spot reflected by the object to be detected again becomes a spot image on the detection surface by a condensing optical system including an objective lens, an imaging lens, and the like. When the double mode channel waveguide is arranged at the position where the spot image is formed such that the center of the spot image coincides with the center of the double mode channel waveguide, the spot image amplitude distribution in the width direction of the waveguide is aligned with the spot center. If the origin is an even function, only the even mode is excited in the double mode waveguide. Otherwise, both the even and odd modes are excited. Here, if a waveguide branch region that branches into a single mode channel waveguide is provided after the double mode region, an equal amount of light is distributed to two branches when only the even mode is excited, and in other cases Since the interference between the even mode and the odd mode occurs, the amount of light distributed to the two branches is generally not equal. In general, if the test object has a slope, that is, a physical slope, as well as any slope that changes the optical path length such as a refractive index slope, and a slope 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, if the two modes are distributed, the light amounts become unequal. Therefore, by detecting the difference between the amounts of light propagating through the two branches, the microscopic inclination of the test object can be detected.

Now, let the inclination angle of the test object be θ, sin θ = α
And Let u (x) denote the spot amplitude distribution when the inclination is 0,
Assuming that the eigenfield distribution of the double mode waveguide is fe (x) and fo (x) for both the even and odd modes, u (x) and fe
(X) is an even function, and fo (x) is an odd function. The spot amplitude distribution uα (x) when there is a slope is k = 2π / λ
As (λ: wavelength), uα (x) ≒ u (x) exp (ikαx) = u (x) [cos (kαx) + isin (kαx)] (1)

Here, the excitation efficiency η _e of the even mode is

[0010]

(Equation 1)

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

[0012]

(Equation 2)

## EQU1 ## An integration range is appropriately selected, and if | kαx | ≪2π in this range, then cos (kαx) ≒ 1, sin (kαx) ≒ kαx, so that u (x), fo (x), and fe (x) Since it is a constant function, it can be seen that η _e ∝constant η _o ∝iα (4). The light intensity change due to the interference between the even mode and the odd mode is represented by I∝ | η _e ± iη _o exp ｛where C ₁ and C ₂ are real constants and φ is the phase difference between the even and odd modes at the branch point. _{^{iφ} | 2 = | C 1}} ± iαC 2 exp {iφ} | 2 (5) Therefore, taking into exp {iφ} = ± i ( 5) is approximately ^{_{I = C 1 2 ± 2αC 1}} C 2 (6) As a result, a change in intensity proportional to α is obtained, and a so-called differential image can be obtained.

Therefore, in order to obtain such a differential image, at the branch point between the double mode and the single mode,
It is necessary to provide an odd multiple of 90 ° of phase difference between both modes. For this reason, the length L of the double mode region is defined as 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 becomes 180 °). 2m + 1) / 2 (m = 0, 1, 2,...) (7)

Since equation (1) considers the inclination of an object, it assumes a phase object. The present invention can be applied not only to a phase object but also to an intensity-modulated 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. At this time, η _e ≒ constant and η _o ∝α (9), so that the ratio of the amount of light distributed to the two branches due to the interference of the even and odd modes becomes the maximum between the two modes at the branch point. When a phase difference of an integral multiple of 180 ° is provided,
That is, this is the case where exp {iφ} = ± 1 in the equation (5).

Therefore, in order to view the differential image of the intensity-modulated object, it is preferable that the length L of the double mode region is an integral multiple of the coupling length Lc. L = mLc (m = 1, 2,...) (10) That is, a differential image of only the phase modulation portion or the intensity modulation portion of the object can be viewed depending on how the length L of the double mode region is set.

When the substrate has an electro-optic effect as in the present invention, the complete coupling length Lc is changed by applying a voltage to this region via an electrode arranged on the double mode region. Can be. Therefore, even if the length of the double mode region is a constant value L, it is possible to satisfy both the above expressions (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 coupling length Lc in the double mode region is changed to Lc ₁ and Lc _2, for a given length L of the double mode _{region, L ≒ mLc 1 (m =} 1,2, ...) L ≒ Lc _{2 (2m + 1) / 2} (m = 0,1,2, ...) by is configured to hold, it is possible to obtain the amplitude information of the object as described above (10) in the case of Lc _1, Lc
_In the case of ₂ , the phase information of the object can be obtained as in the above equation (7).

[0019]

FIG. 1 is a schematic structural view 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 used.
, And is incident on the objective lens 4 and is focused on the object plane 5.
Light reflected by the object plane 5 and transmitted through the half mirror 2 again through the objective lens 4 and the XY two-dimensional scanning means 3 is incident on the incident end face of the channel waveguide 7 formed on the substrate 6 having the electro-optical effect. The light is focused on the arranged detection surface. The channel waveguide 7 is a double mode waveguide in which an electrode 17 is provided on a substrate, and the light propagated in the double mode waveguide 7 reaches the branch region 8 and the power is applied to the two single mode waveguides 9 and 10. The light is distributed and reaches two photodetectors 11 and 12 bonded to the substrate 6. Since the incident end of the channel waveguide 7 has the same function as a pinhole, this configuration constitutes a confocal laser scanning microscope. Here, the half mirror 2 and the objective lens 4 form an illumination optical system, and the objective lens 4 forms a condenser optical system.

As described above, when a point on the object 5 illuminated by the laser spot has a slope or a reflectance gradient, the phase distribution or the intensity distribution of the laser spot formed on the incident end of the channel waveguide 7. Is inclined. Due to this inclination, even and odd modes are excited in the double mode waveguide 7, and the ratio of the optical power reaching the two photodetectors 11 and 12 changes due to interference of both modes. Therefore, the operation detecting means
By taking the differential signal 14 of the output of the two detectors 11 and 12 by the 13, a minute step or a change in reflectance on the object surface can be detected. At this time, when observing the phase distribution of the object with the complete coupling length as Lc, the length L of the double mode region is as follows: L = Lc (2m + 1) / 2 (m = 0, 1, 2,...) When observing the intensity distribution of the object, L = mLc (m = 1, 2,...) May be used, and this configuration is a differential interference system, as described above.

Here, since the substrate 6 has an electro-optic effect, the complete coupling length Lc can be changed by changing the voltage applied to the electrode 17. Therefore, the above 2
One condition is to adjust the voltage applied to the electrode 17,
The same holds for the length L of the same double mode area. That is, the phase distribution and the intensity distribution of the object can be independently detected by one waveguide device.

Specifically, the control means 15 for storing and imaging the differential signal 14 from the XY two-dimensional scanning means 3 in correspondence with the position of the light beam on the object to be inspected, is transmitted to the monitor 16. Can be displayed. In the above embodiment, the electrode 17 for applying a voltage to the double mode waveguide 7 has two electrodes symmetrical with respect to the waveguide 7. Depending on the direction of the crystal axis, etc.), the electrode arrangement as shown in FIG. 1 is not always optimal.

FIG. 2 is a schematic diagram showing a second embodiment of the present invention. In this configuration, the illumination optical system and the condensing optical system share the objective lens 28, and one of the detection waveguides is used. The unit also has a function of an illumination system for guiding a laser beam.
The laser light source 21 is a semiconductor laser, and is a single mode channel waveguide formed on a substrate 22 having an electro-optical effect.
In order to maximize the optical coupling efficiency with respect to 23,
It is fixed to. Laser light incident on waveguide 23 branches
After passing through 24, the light propagates through the double mode waveguide 25 in which the electrode 35 is provided on the substrate surface. In the branch 24 of the waveguide,
Three single mode waveguides are coupled to the double mode waveguide 25, and the single mode waveguide in the middle
23 is used for illumination, and the two outer single-mode waveguides are used for detection described later. At this time, the center line of the middle single mode channel waveguide 23 and the double mode waveguide
By making the positional relationship such that the center line of 25 coincides with the center line, light incident on the double mode waveguide 25 from the middle single mode channel waveguide 23 excites only the even mode in the double mode waveguide 25. Therefore, the laser light is actually emitted from the end face 26 in a single mode state.

The illumination light beam emitted from the end face of the double mode waveguide 25 enters the objective lens 28 via the XY two-dimensional scanning means 27 and is focused on the object plane 29. Object surface 29
After being reflected by the objective lens 28 and the XY two-dimensional scanning means 27 again, the light flux is condensed on the detection surface 26 on which the end face of the channel waveguide 25 formed on the substrate 22 is arranged. A laser spot is formed. Thereafter, as in the first embodiment, the power ratio distributed to the two single mode channel waveguides 30 and 31 changes with the inclination of the object plane, and the photodetectors 32 and 33 fixed to the substrate 22 change the power ratio. Waveguide 3
If the light from 0 and 31 is detected and a differential signal 34 is obtained, a differential interference signal can be obtained. In FIG. 2, actuation signal 34 and XY
A control unit and a monitor for forming an image based on a signal from the two-dimensional scanning unit 27 are omitted because they are equivalent to the configuration of the first embodiment shown in FIG.

In each of the embodiments described above, the objective lens is used in common for the illumination optical system and the condensing optical system, and constitutes a so-called epi-illumination type microscope. Except for the configuration of the second embodiment shown in FIG. 2, the illumination optical system can be configured as a so-called transmission microscope in which an illumination optical system is arranged on one side of the test object and a condensing optical system is arranged on the other side. Needless to say.

In each of the above embodiments, the laser light source and the photodetector are external to the waveguide device. However, if a silicon substrate is used, the photodetector can be mounted on the same substrate as the waveguide device. 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, thus reducing the size, weight, and adjustment of the device. Can go further. In addition, the double mode waveguide can be replaced by two single mode waveguides arranged close to each other. Further, it is needless to say that an image having various contrasts can be obtained by applying an appropriate processing to the operation signal from the light detecting element for detecting the light intensity passing through the two single mode waveguides. .

[0027]

As described above, according to the present invention, there is no need for a special objective lens or a special optical element such as a Nomarski prism or a wave plate, and a small and simple structure based on a new principle using a waveguide. And a confocal laser scanning differential interference microscope comprising: Further, in particular, the configuration of the second embodiment shown in FIG. 2 has an advantage that alignment of the laser light source and the light receiving side pinhole, which has been difficult in the related art, becomes unnecessary. Then, by changing the complete coupling length Lc of the double mode region using the electro-optic effect of the substrate, the phase modulation portion and the intensity modulation portion of the object can be independently taken out, and their differential images can be seen. This separation of phase information and intensity information shows the essential features and usefulness of the microscope according to the present invention.

[Brief description of the 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]

 1,21,41 Laser light source 7,25,51,61 Double mode waveguide 9,10,31,32,33,52,53,62,63 Single mode waveguide 11,12,21,32,33,54 , 55,64,65 Photodetector 17,35 electrodes

Continuation of the front page (56) References JP-A-4-208913 (JP, A) JP-A-2-44554 (JP, A) JP-A-2-91831 (JP, A) JP-A-61-288102 (JP, A) JP-A-2-68738 (JP, A) JP-A-2-267513 (JP, A) JP-A-3-78720 (JP, A) JP-A-3-278009 (JP, A) 4-209339 (JP, A) JP-A-4-252444 (JP, A) OPTICS COMMUNICAT IONS, VOL. 85 (1991), P. 177-182, Proceedings of the Conference on Laser Microscopy, 7th (May 10, 1991), p. 18-23 Optics, Vol. 24 (12) (1995), p. 729-730 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 21/00 G02B 21/06-21/36 G01B 11/00-11/30 G11B ⁷ /12-7/22

Claims (14)

(57) [Claims] A double mode channel waveguide region having an incident end face for receiving light and exciting one or both of an even mode and an odd mode in accordance with the light incident on the incident end face; A waveguide branch region for branching the channel waveguide region into two channel waveguides; a detection element for detecting light propagating through the two channel waveguides; and an even-odd in the double mode channel waveguide region Means for changing a complete coupling length of a mode, wherein the optical information is detected by a detection signal from each of the detection elements. 2. A laser light source; an illumination optical system for condensing a light beam from the laser light source to form a light spot on a test object; and condensing a light beam from the test object on a detection surface. A condensing optical system, a double mode channel waveguide region having an incident end face on the detection surface, and exciting one or both of the even mode and the odd mode according to light incident on the incident end face; A waveguide branch region for branching the double mode channel waveguide region into three channel waveguides; a detection element for detecting light propagating through two outer channel waveguides among the three channel waveguides; Even- in the double mode channel waveguide region
Means for changing a complete coupling length of an odd mode, wherein a light beam from the laser light source is guided to a central channel waveguide among the three channel waveguides, Emitted from the incident end face,
An optical waveguide device, wherein the optical waveguide device is configured to be guided onto the test object via the objective lens, and detects information on the test object by a detection signal from each of the detection elements. 3. The optical waveguide device according to claim 2, wherein said central channel waveguide is a single mode channel waveguide. 4. The optical waveguide device according to claim 2, wherein a center line of the central channel waveguide coincides with a center line of the double mode channel waveguide. 5. When the length of the double mode channel waveguide region is L and the full coupling length of the even-odd mode in the double mode channel waveguide region is Lc, the perfect coupling length is changed. the even by means of - the complete coupling length Lc of the odd mode is changed to Lc ₁ and _{Lc 2, L ≒ mLc 1 (} m = 1,2, ...) to the length L of the double mode channel waveguide region _{3. The} structure according to claim 1, wherein L ≒ Lc ₂ (2m + 1) / 2 (m = 0, 1, 2,...).
5. The optical waveguide device according to 3 or 4. 6. The optical waveguide device according to claim 1, wherein the means for changing the complete coupling length is an electrode provided on the substrate surface. 7. A laser light source, an illumination optical system for converging a light beam from the laser light source to form a light spot on a test object, and condensing a light beam from the test object on a detection surface. A light-collecting optical system, light-detecting means for detecting a light beam condensed on the detection surface, and scanning means for relatively moving the light spot with respect to the test object; A light detection unit having an incident end face on the detection surface, a double mode channel waveguide region for exciting one or both of an even mode and an odd mode in accordance with light incident on the incident end face; 2 channel waveguide regions
A waveguide branch region for branching into two channel waveguides; a detection element for detecting light propagating through the two branched channel waveguides; and an even-odd mode in the double mode channel waveguide region. A confocal laser scanning differential interference microscope having means for changing a complete coupling length, wherein information on a test object is obtained by a detection signal from each of the detection elements. 8. A laser light source; an illumination optical system for converging a light beam from the laser light source to form a light spot on a test object; and condensing a light beam from the test object on a detection surface. A light-collecting optical system, light-detecting means for detecting a light beam condensed on the detection surface, and scanning means for relatively moving the light spot with respect to the test object; The illumination optical system and the condensing optical system share the same objective lens, and the light detection means has an incident end surface on the detection surface, and performs even mode and odd mode according to light incident on the incident end surface. A double mode channel waveguide region that excites one or both of them; a waveguide branch region that branches the double mode channel waveguide region into three channel waveguides; Change the perfect coupling length of the odd mode Has a means for the light beam from the laser light source after being guided to the center of the channel waveguide of the three channel waveguides, and exits from the incident end face of the double-mode channel waveguide region,
The light guide is configured to be guided onto the object to be inspected via the objective lens, and the light detecting means detects light propagating through two outer channel waveguides among the three channel waveguides. A confocal laser scanning differential interference microscope having a configuration having an element, wherein information on an object to be inspected is obtained by a detection signal of the detection element. 9. The confocal laser scanning differential interference microscope according to claim 8, wherein a center channel waveguide among the three channel waveguides is a single mode channel waveguide. 10. The confocal laser scanning differential interference microscope according to claim 8, wherein a center line of the central channel waveguide coincides with a center line of the double mode channel waveguide. . 11. When the length of the double mode channel waveguide region is L and the full coupling length of the even-odd mode in the double mode channel waveguide region is Lc, the perfect coupling length is changed. the even by means of - the complete coupling length Lc of the odd mode is changed to Lc ₁ and _{Lc 2, L ≒ mLc 1 (} m = 1,2, ...) to the length L of the double mode channel waveguide region 9. The structure according to claim 7, wherein L ≒ Lc ₂ (2m + 1) / 2 (m = 0, 1, 2,...).
The confocal laser scanning differential interference microscope according to 9 or 10. 12. A confocal laser scanning device according to claim 7, wherein said means for changing the complete coupling length is an electrode provided on said substrate surface. Differential interference microscope. 13. A double mode channel waveguide region having an incident end face for receiving light and exciting one or both of an even mode and an odd mode in accordance with the light incident on the incident end face. Changing the complete coupling length of the double mode channel waveguide region to a desired value, and obtaining the light information according to the desired value of the complete coupling length from the intensity distribution in the width direction of the double mode channel waveguide region. How to detect. 14. A light intensity propagating in a width direction of the double mode channel waveguide region is detected by splitting light propagating in the double mode channel waveguide into two channel waveguides and detecting the light. The method according to claim 13, wherein: