JPH08247714A - Displacement measuring instrument - Google Patents

Abstract

PURPOSE: To provide an inexpensive displacement measuring instrument the optical system of which can be reduced in size and weight and does not require any optical axis adjustment, the substrate of which does not require any special machine work, and then, the bulk optical element of which does not required any lens for condensing light and which has a large tolerance against manufacturing errors. CONSTITUTION: Optical waveguides 22 and 25, waveguide type beam splitters 23 and 26, and light condensing grating couplers 24 and 27 are respectively formed on the front and rear surfaces of a substrate 21. Light rays emitted from light sources 28 and 29 are respectively condensed to points C and D in a free space on the front surface side of the substrate 21 through the couplers 24 and 27 after the light rays are guided through the waveguides 22 and 25. Reflected light rays from a surface to be detected respectively return to the couplers 24 and 27 and are led to photodetectors 30 and 31 through the beam splitters 23 and 26. The difference between the detecting signals of the photodetectors 30 and 31 is obtained from a differential amplifier 32.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device using an optical waveguide device, and can be used as, for example, a focus error detecting device for an optical disk or the like.

[0002]

2. Description of the Related Art In recent years, optical waveguide devices have attracted attention in the fields of optical communication and optical measurement. The reason is that the use of the optical waveguide device has the advantages that the size and weight of the optical system can be reduced and the adjustment of the optical axis becomes unnecessary.

As one of the applications of the optical waveguide device, an optical disk pickup shown in FIG. 5 has been proposed (Ura et al., IEICE Transactions, (C), J69-C, 5, p.
p. 609, 1986).

In this optical disc pickup, as shown in FIG. 5, the SiO ₂ buffer layer 2 is formed on the surface of the Si substrate 1.
The waveguide layer 3 is formed via the above, and the waveguide layer 3 constitutes a slab waveguide. In a part of this slab waveguide,
The condensing grating coupler 4, the twining condensing beam splitter 5, and the photodiodes 6 to 9 are formed. A semiconductor laser 10 that supplies two-dimensional divergent guided light into the waveguide layer 3 is provided at the end of the substrate 1.

The divergent guided light from the semiconductor laser 10 is guided through the waveguiding layer 3 and is supplied to the condensing grating coupler 4 via the towing grating condensing beam splitter 5. The condensing grating coupler 4 condenses this light on the surface of the optical disk 11 (that is, at one point in the free space on the surface side of the substrate 1), and reflects the reflected light from the optical disk 11 in the waveguide again by inverse coupling. Lead to. The twining condensing beam splitter 5 adjacent to the condensing grating coupler 4 is a transmission Bragg grating, which divides the wavefront of the returning light into two parts, separates the optical axis by deflection, and uses the weak lens action to detect two detection points A. , B is focused.
As described above, the twing grating focusing beam splitter 5 has the functions of wavefront division, deflection and light focusing.
The photodiodes 6 and 7 are provided on both sides of the detection point A,
The photodiodes 8 and 9 are provided on both sides of the other detection point B.

The focus error detection of the optical disc pickup shown in FIG. 5 is based on the principle of the Foucault method. When the optical disk 11 shifts far away, the return light is focused in front of the detection point, so a large photocurrent flows through the inside photodiodes 7 and 8. When the optical disk 11 shifts near, the return light is focused behind the detection point. Since a large photocurrent flows through the outer photodiodes 6 and 9, the difference between the photocurrent of the inner photodiodes 7 and 8 and the photocurrent of the outer photodiodes 6 and 9 causes a focus error. A detection signal is obtained. It should be noted that the focus error detection means that the displacement of the optical disc 11 is detected, and if this function is focused, this optical disc pickup can be regarded as a displacement measuring device.

The read signal of the optical disk pickup shown in FIG. 5 is obtained by taking the sum of the photocurrents of the four photodiodes 6-9. Further, the tracking error detection is based on the principle of the push-pull method, and if there is no error, an equal amount of photocurrent flows through the photodiode that is symmetrical with respect to the line connecting the semiconductor laser 10 and the focusing grating coupler 4. However, since the symmetry of the light wave is broken due to the error occurrence, the error signal can be obtained by taking the difference of the photocurrents of the symmetric photodiodes.

[0008]

The above-mentioned conventional optical disk pickup can reduce the size and weight of the optical system, does not require the adjustment of the optical axis, and specially processes the substrate. It was excellent because it was not necessary and a lens by a bulk optical element for condensing light was unnecessary.

However, in the conventional optical disc pickup, as described above, the focus error detection is based on the principle of the Foucault method.
The photodiodes 6 to 9 with respect to B must be arranged strictly. For this reason, the precision during manufacturing is strict,
It becomes expensive.

The present invention has been made in view of the above circumstances, and it is possible to reduce the size and weight of an optical system, eliminate the need for adjusting the optical axis, and use a special machine for a substrate. It is an object of the present invention to provide an inexpensive displacement measurement device that does not require processing, does not require a lens by a bulk optical element for condensing light, has a large allowable range of errors during manufacturing, and is inexpensive.

[0011]

In order to solve the above-mentioned problems, a displacement measuring apparatus according to a first aspect of the present invention is directed to a substrate, a first optical waveguide formed on the surface of the substrate, and a first conductor. A wave-type beam splitter and a first condensing grating coupler, a second optical waveguide formed on the back surface of the substrate, a second waveguide type beam splitter and a second condensing grating coupler, and the first First light supply means for supplying a first light flux into the optical waveguide, second light supply means for supplying a second light flux into the second optical waveguide, and first and second light detection And differential operation means for obtaining the difference between the detection signal of the first photodetector and the detection signal of the second photodetector. The first optical waveguide is
The first light flux supplied by the first light supply means is guided to the first waveguide beam splitter. The first
Of the waveguide type beam splitter supplies the first light flux guided by the first optical waveguide to the first focusing grating coupler. The first condensing grating coupler emits the supplied first light flux so as to condense it at a first point in a free space on the side of the surface of the substrate and is based on the first light flux. The reflected light from the surface to be inspected by the emitted light is supplied to the first waveguide type beam splitter. The first waveguide beam splitter guides a part of the reflected light supplied from the first condensing grating coupler to the first photodetector via the first optical waveguide. The second optical waveguide guides the second light flux supplied by the second light supply means to the second waveguide beam splitter. The second waveguide beam splitter supplies the second light flux guided by the second optical waveguide to the second focusing grating coupler. The second condensing grating coupler transmits the supplied second light flux to a free space on the surface side of the substrate,
The light is emitted so as to be condensed at a second point different from the first point, and the reflected light from the surface to be inspected by the emitted light based on the second light flux is directed to the second waveguide beam splitter. Supply. The second guided beam splitter splits a part of the reflected light supplied from the second focusing grating coupler into the second waveguide through the second optical waveguide.
Lead to the photo detector. The light collecting optical axis of the first light collecting grating coupler and the light collecting optical axis of the second light collecting grating coupler are substantially coincident with or substantially parallel to each other. The substrate is transparent to the emitted light and the reflected light of the second light flux.

A displacement measuring apparatus according to a second aspect of the present invention is the displacement measuring apparatus according to the first aspect, wherein the first focusing grating coupler is substantially coupled with the light based on the second light flux. The second condensing grating coupler does not substantially combine with the light based on the first light flux.

A displacement measuring apparatus according to a third aspect of the present invention is the displacement measuring apparatus according to the second aspect, wherein the first light flux and the second light supply supplied by the first light supply means are provided. The second light flux supplied by the means is linearly polarized light having different polarization directions.

A displacement measuring apparatus according to a fourth aspect of the present invention is the displacement measuring apparatus according to the second aspect, wherein the wavelength of the first luminous flux supplied by the first light supply means and the second The second supplied by the light supply means of
Is different from the wavelength of the luminous flux.

A displacement measuring apparatus according to a fifth aspect of the present invention is the displacement measuring apparatus according to any one of the first to fourth aspects, wherein the first waveguide type beam splitter and the first condensing grating are used. A coupler is arranged adjacent to each other, and the second waveguide type beam splitter and the second condensing grating coupler are arranged adjacent to each other.

A displacement measuring apparatus according to a sixth aspect of the present invention is the displacement measuring apparatus according to any one of the first to fifth aspects, wherein the first waveguide type beam splitter is the first condensing grating. The part of the reflected light supplied from the coupler is focused on the first photodetector, and the second waveguide type beam splitter is supplied from the second focusing grating coupler. The part of the reflected light is focused on the second photodetector.

A displacement measuring apparatus according to a seventh aspect of the present invention is the displacement measuring apparatus according to any one of the first to sixth aspects, wherein the first light supply means is provided on one end side of the substrate. The second light supply means is provided on the other end side of the substrate.

[0018]

According to the displacement measuring apparatus according to the first to seventh aspects of the present invention, the surface to be inspected is arranged in the vicinity of the first and second points.

The first light beam supplied by the first light supply means is guided to the first condensing grating coupler through the first optical waveguide and the first waveguide type beam splitter, and the first light collecting grating coupler is connected. It is emitted so as to be condensed at the first point in the free space on the surface side of the substrate by the condensing grating coupler. The reflected light from the surface to be inspected, which is the emitted light based on the first light flux, is again supplied to the first waveguide type beam splitter by the first focusing grating coupler, and the first waveguide type beam splitter. Is guided to the first photodetector via the first optical waveguide and detected by the first photodetector. Therefore, if the surface to be inspected is at the first point, the amount of reflected light returning to the first condensing grating coupler becomes the largest and the detection signal of the first photodetector becomes the largest, Is shifted from the first point in the direction of the converging optical axis by the first condensing grating coupler, the amount of reflected light returning to the first condensing grating coupler becomes smaller, and the detection by the first photodetector becomes smaller. The signal becomes smaller.

Similarly, the second light flux supplied by the second light supply means is guided to the second focusing grating coupler via the second optical waveguide and the second waveguide type beam splitter, The second condensing grating coupler emits the light so as to condense it at a second point in the free space on the surface side of the substrate. The reflected light from the surface to be inspected by the emitted light based on the second light flux is supplied again to the second waveguide type beam splitter by the second condensing grating coupler, and the second waveguide type beam splitter is provided. Is guided to the second photodetector via the second optical waveguide and detected by the second photodetector. Therefore, when the surface to be inspected is at the second point, the amount of reflected light returning to the second condensing grating coupler becomes the largest and the detection signal of the second photodetector becomes the largest, From the second point to the direction of the light collecting optical axis of the second light collecting grating coupler (in this direction, the light collecting optical axes of the first and second light collecting grating couplers substantially coincide with each other, or Since the light beams are substantially parallel to each other, the light amount of the reflected light returning to the second condensing grating coupler becomes smaller as the deviation from the direction of the condensing optical axis by the first condensing grating coupler occurs. Then, the detection signal of the second photodetector becomes small.

Therefore, since the first point and the second point are different from each other, the detection signal of the first photodetector and the second signal are detected.
The difference from the detection signal of the photodetector, that is, the output of the differential calculation means indicates the displacement amount (or position) of the surface to be inspected in the direction of the converging optical axis.

The displacement measuring apparatus according to the first to seventh aspects of the present invention is based on such a principle and is not based on the principle of the Foucault method unlike the conventional optical disk pickup described above. The photodetector can obtain the amount of displacement of the surface to be inspected by simply receiving the return light (or part of it) from the first and second waveguide beam splitters. Therefore, unlike the above-mentioned conventional optical disk pickup, it is not necessary to strictly arrange the first and second photodetectors, accuracy in manufacturing is not required so much, and the cost is low.

In the displacement measuring device according to the first to seventh aspects of the present invention, the first and second optical waveguides, the first and second waveguide type beam splitters, and the first and second optical waveguides are provided with respect to the substrate.
Since the second condensing grating coupler is formed, the size and weight of the optical system can be reduced, the optical axis need not be adjusted, and special machining is required for the substrate. In addition, there is no need for a lens with a bulk optical element for collecting light.

By the way, the first condensing grating coupler produces light based on the second light flux (especially, the light emitted from the second condensing grating coupler and the reflected light from the surface to be inspected by the emitted light). The second condensing grating coupler couples with the light based on the first luminous flux (especially, the emitted light from the first condensing grating coupler and the reflected light from the surface to be inspected by the emitted light). If so, the combined light becomes a noise component.

Therefore, in order to prevent such noise, as in the second aspect of the present invention, the first focusing grating coupler does not substantially combine with the light based on the second luminous flux, and the second It is preferable that the condensing grating coupler of is not substantially coupled with the light based on the first luminous flux. Specifically, as in the third aspect of the present invention, the first light flux and the second light flux are made into linearly polarized light having different polarization directions, or as in the fourth aspect of the present invention. The light flux and the second light flux may be lights having different wavelengths.

Further, as in the fifth aspect of the present invention, the first
If the waveguide type beam splitter and the first condensing grating coupler are arranged adjacent to each other, and the second waveguide type beam splitter and the second condensing grating coupler are arranged adjacent to each other, further miniaturization is achieved. This is preferable because it can be achieved. However, in the present invention, these do not necessarily have to be arranged adjacent to each other.

In the present invention, each return light may not be focused on each photodetector and each photodetector may receive only a part of each return light, but in that case, each photodetection is performed. The amount of light received by the device decreases and the SN ratio decreases. Therefore, as in the sixth aspect of the present invention, it is preferable that each waveguide beam splitter has a function of condensing each return light to each photodetector.

Further, in the present invention, the first and second light supply means can be formed on the substrate by appropriately selecting the type of the substrate, but the first and second light supply means are provided outside the substrate. In the case of providing the second light supply means, as in the seventh aspect of the present invention, the first light supply means is provided on the one end side of the substrate and the second light supply means is provided on the other end side of the substrate. It is preferable to provide it on the side, because the first and second light supply means can be made compact without hitting each other.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A displacement measuring apparatus according to an embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic perspective view of a displacement measuring device according to this embodiment. FIG. 2 is a schematic sectional view taken along the line II-II in FIG. FIG. 3 is a schematic sectional view showing a usage state of the displacement measuring apparatus according to the present embodiment, and is a schematic sectional view corresponding to FIG.

As shown in these drawings, the displacement measuring apparatus according to this embodiment includes a substrate 21, a first optical waveguide 22 formed on the surface of the substrate 21, a first waveguide type beam splitter 23, and First condensing grating coupler 24
And a second optical waveguide 25 formed on the back surface of the substrate 21,
The second waveguide type beam splitter 26, the second condensing grating coupler 27, and the first optical waveguide 22 have the first optical waveguide 22.
A first light source 28 such as a semiconductor laser as a first light supply means for supplying a light flux of
Of the second light source 29 such as a semiconductor laser as the second light supply means for supplying the light flux of the second light source, the first and second photodetectors 30 and 31 such as photodiodes, and the first photodetector 30. And a differential amplifier 32 as a differential calculation means for obtaining the difference between the detection signal and the detection signal of the second photodetector 31.

The first optical waveguide 22 is the first light flux (divergent guided light in this embodiment) supplied from the first light source 28.
Is guided to the first waveguide type beam splitter 23,
Return light described later from the first waveguide type beam splitter 23 is guided to the first photodetector 30. Similarly, the second optical waveguide 25 guides the second light flux (divergent guided light in this embodiment) supplied from the second light source 29 to the second waveguide type beam splitter 26, and The return light described later from the waveguide beam splitter 26 is guided to the second photodetector 31. The first and second optical waveguides 22 and 25 are slab waveguides, which are composed of waveguide layers formed on the entire front and back surfaces of the substrate 21.

The substrate 21 emits light to the second point D, which will be described later, from the second condensing grating coupler 27 by the second light flux and reflected light (return light) from the surface 33 to be detected by the emitted light. ), A material having a light-transmitting property is used. For example, the material of the substrate 21 is a polymer, glass, a dielectric crystal such as LiNbO ₃ (lithium niobate) single crystal, a semiconductor such as Si, or Ga.
A compound semiconductor such as As may be used. When Si is used, the photodetectors 30 and 31 can be integrated on the substrate 21. When a compound semiconductor such as GaAs is used,
The light sources 28 and 29 and the photodetectors 30 and 31 can be integrated on the substrate 21. For example, the transmission wavelength range of LiNbO ₃ is 0.4 to
5 μm, the transmission wavelength range of LiTaO ₃ (lithium tantalate) is 0.45 to 5 μm, and the transmission wavelength range of Si is 1.2 to
10 μm, the transmission wavelength range of GaAs is 0.9 to 16 μm,
The transmission wavelength range of InP is 1 to 14 μm, the transmission wavelength range of SiO ₂ is 0.12 to 4.5 μm, the transmission wavelength range of Pyrex glass (trade name) is 0.28 to 4.5 μm, the transmission wavelength range of soda glass Is 0.44 to 3.4 μm,
When these materials are used as the material of the substrate 21, the second light source 29 may be one that generates light having a wavelength within the corresponding transmission wavelength range as the second light flux.

In this embodiment, the first light source 28 and the first photodetector 30 are provided at one end of the substrate 21, and the second light source 29 and the second photodetector 31 are Board 2
1 is provided at the other end. With such an arrangement, the first and second light sources 28 and 29 can be made compact without colliding with each other.

Although not provided in this embodiment,
If necessary, the substrate 21 and the first and second optical waveguides 2
A buffer layer may be formed between 2 and 25. This buffer layer also emits light from the second condensing grating coupler 27 to the later-described second point D by the second light flux and reflected light (return light) from the surface 33 to be detected by the emitted light.
For, a light-transmitting material is used.

The first waveguide type beam splitter 23 converts the first light flux guided by the first optical waveguide 22 into a first light beam.
And to supply it to the condensing grating coupler 24 of
A part of the reflected light (return light) supplied from the first condensing grating coupler 24 is guided to the first photodetector 30 via the first optical waveguide 22. Similarly, the second waveguide type beam splitter 26 uses the second condensing grating coupler 27 for the second light flux guided by the second optical waveguide 25.
And a part of the reflected light (return light) supplied from the second condensing grating coupler 27 is guided to the second photodetector 31 via the second optical waveguide 25. In this way, the first and second guided beam splitters 23, 2
It suffices that 6 has a function of splitting the forward light and the backward light (return light), but in the present embodiment, the first waveguide type beam splitter 23 is the first condensing grating. A part of the reflected light supplied from the coupler 24 is condensed on the first photodetector 30, and the second waveguide type beam splitter 26 is supplied from the second condensing grating coupler 27. It also has a function of condensing a part of the reflected light on the second photodetector 31. As a result, the amount of light received by the first and second photodetectors 30, 31 increases and S
The advantage that the N ratio becomes large is obtained.

First and second guided beam splitters 2
The above-mentioned functions of the third and the third waveguides 26 are, for example, configured by configuring the first and second waveguide type beam splitters as a transmission type Bragg grating formed in a part of the first and second optical waveguides 22 and 25. This can be achieved by setting the spacing of the grating pattern, chirping, etc. according to the wavelength or polarization state of the corresponding first or second light flux.

The first focusing grating coupler 24 is
The supplied first light flux is emitted so as to be condensed at the first point C in the free space on the surface side of the substrate 21, and is reflected from the surface 33 to be detected by the emitted light based on the first light flux. The light (return light) is supplied to the first waveguide beam splitter 23. Similarly, the second focusing grating coupler 2
Reference numeral 7 causes the supplied second light flux to be emitted so as to be condensed at a second point D in the free space on the surface side of the substrate 21 (this second point D is different from the first point C). Together with the second
The reflected light (return light) from the surface 33 to be inspected, which is the emitted light based on the light flux of, is supplied to the second waveguide type beam splitter 26. In the present embodiment, the light collecting optical axis of the first light collecting grating coupler 24 and the light collecting optical axis of the second light collecting grating coupler 27 are made to coincide with each other, and the substrate 21
Extends in the normal direction. However, if the surface 33 to be inspected is a flat surface, both converging optical axes may be substantially parallel,
It does not have to match. The condensing optical axis is the substrate 2
It may be inclined with respect to the normal direction of 1.

The first and second condensing grating couplers 24 and 27 are waveguide elements for coupling the guided light and a spherical wave having a focal point at one point in space and are composed of a grating pattern having bending and chirping. To be done. The above-described functions of the first and second condensing grating couplers 24 and 27 are to set the bending and chirping of the grating pattern according to the wavelength and polarization state of the corresponding first or second light flux. Can be realized by

The first and second waveguide type beam splitters 23 and 26 and the first and second condensing grating couplers 24 and 27 are relief type and refractive index modulation type including etching type and cladding type. It can be configured using any type of grating, such as.

In this embodiment, the first waveguide type beam splitter 23 and the first focusing grating coupler 2 are used.
4 are arranged adjacent to each other, and the second waveguide type beam splitter 26 and the second condensing grating coupler 27 are arranged adjacent to each other. In the present invention, these do not necessarily have to be arranged adjacently, but if they are arranged adjacently,
It is preferable because the size can be reduced.

Next, the operation of the displacement measuring apparatus according to this embodiment will be described.

First, when the present apparatus is used, as shown in FIG. 3, the optical disk or other surface 33 to be inspected is the first one.
Between the point C and the second point D.

The first light flux supplied from the first light source 28 is passed through the first optical waveguide 22 and the first waveguide type beam splitter 23, and the first condensing grating coupler 2
4 and is emitted by the first condensing grating coupler 24 so as to be condensed at a first point C in the free space on the surface side of the substrate 21. The reflected light from the surface 33 to be inspected, which is the emitted light based on the first light flux, is again supplied to the first waveguide type beam splitter 23 by the first focusing grating coupler 24, and the first waveguide type beam splitter 23 is supplied. The light is guided by the splitter 23 to the first photodetector 30 via the first optical waveguide 22, and is detected by the first photodetector 30.
Therefore, when the surface 33 to be inspected is at the first point C, the amount of reflected light returning to the first condensing grating coupler 24 becomes the largest and the detection signal of the first photodetector 30 becomes the largest, Reflected light returning to the first condensing grating coupler 24 as the surface 33 to be inspected deviates from the first point C in the direction of the converging optical axis of the first condensing grating coupler 24 (vertical direction in FIG. 3). And the detection signal of the first photodetector 30 becomes small. The relationship between the position of the surface 33 to be inspected in the direction of the converging optical axis and the detection signal of the first photodetector 30 is shown as a curve X in FIG. Note that “0” on the horizontal axis in FIG. 4A indicates the first point C and the second point D.
The reference position between and is shown.

Similarly, the second light flux supplied by the second light source 29 is guided to the second condensing grating coupler 27 via the second optical waveguide 25 and the second waveguide type beam splitter 26. Then, the second condensing grating coupler 27 causes the second point D in the free space on the side of the surface of the substrate 21.
It is emitted so that it may be condensed to. The reflected light from the surface 33 to be inspected, which is the emitted light based on the second light flux, is again supplied to the second waveguide type beam splitter 26 by the second focusing grating coupler 27, and the second waveguide type beam splitter 26 is supplied. The light is guided by the splitter 26 to the second photodetector 31 via the second optical waveguide 25, and is detected by the second photodetector 31. Therefore, if the surface 33 to be inspected is at the second point D, the amount of reflected light returning to the second converging grating coupler 27 becomes the largest and the detection signal of the second photodetector 31 becomes the largest. , The surface 33 to be inspected is from the second point D to the direction of the converging optical axis by the second condensing grating coupler 27 (this direction is the first condensing grating coupler 24.
Is the same as the direction of the converging optical axis. )
The amount of the reflected light returning to the second condensing grating coupler 27 becomes small and the detection signal of the second photodetector 31 becomes small. The relationship between the position of the surface 33 to be inspected in the direction of the converging optical axis and the detection signal of the second photodetector 31 is shown in FIG.
Shown as curve Y.

Therefore, since the first point C and the second point D are different, the detection signal of the first photodetector 30 and the second point D
Difference from the detection signal of the photodetector 31, that is, the output signal of the differential amplifier 32 has an S-shaped characteristic as shown in FIG. It indicates the amount of displacement (or position) in the axial direction. Note that FIG. 4 (b)
FIG. 6 is a diagram showing the relationship between the position of the surface 33 to be inspected in the direction of the light collection optical axis and the output signal of the differential amplifier 32. When the displacement measuring device according to this embodiment is used as a focus error signal detecting device for an optical disk or the like, the differential amplifier 3
The output signal of 2 corresponds to the focus error signal.

The displacement measuring apparatus according to the present embodiment is based on such a principle and is not based on the principle of the Foucault method unlike the conventional optical disk pickup described above. Therefore, the first and second photodetectors 30, 31 are used. The surface 33 to be inspected can be obtained by simply receiving the returned light (partially a part thereof) from the first and second waveguide type beam splitters 23 and 26, respectively.
Can be obtained. Therefore, unlike the above-mentioned conventional optical disk pickup, it is not necessary to strictly arrange the first and second photodetectors 30 and 31, precision in manufacturing is not required so much, and the cost is low.

Then, in the displacement measuring apparatus according to the present embodiment, the first and second optical waveguides 22,
25, first and second guided beam splitters 23, 2
6, first and second focusing grating couplers 24, 2
Since 7 is formed, it is possible to reduce the size and weight of the optical system and eliminate the need for adjusting the optical axis.
The substrate 21 does not need to be specially machined, and the lens by the bulk optical element for condensing the light is unnecessary.

By the way, the first condensing grating coupler 24 emits light based on the second luminous flux (in particular, the emitted light from the second condensing grating coupler 27 and the reflected light from the surface 33 to be inspected by the emitted light. ) Or the second
When the condensing grating coupler 27 is combined with the light based on the first light flux (particularly, the emitted light from the first condensing grating coupler 24 and the reflected light from the surface 33 to be inspected by the emitted light), The combined light becomes a noise component. In particular, the first light flux and the second light flux
If the light flux of is the same in wavelength and polarization state, such coupling may occur.

Therefore, in order to prevent such noise, the first condensing grating coupler 24 does not substantially combine with the light based on the second luminous flux, and the second condensing grating coupler 27 makes the first condensing grating coupler 27. It is preferable that the light is not substantially combined with the light based on the luminous flux of. Specifically, the first light flux and the second light flux may be linearly polarized light having different polarization directions, or the first light flux and the second light flux may have different wavelengths. That is, in the present embodiment, the first light source 28 uses the linearly polarized light in the first polarization direction (for example, the light that becomes TE polarized light in the first optical waveguide 22) as the first light beam and the first light beam. The second light source 29 supplies the linearly polarized light having a second polarization direction different from the first polarization direction (for example, T in the second optical waveguide 25).
The light that becomes M-polarized light) may be supplied into the second optical waveguide 25 as the second light flux. Alternatively, in the present embodiment, the first light source 28 supplies the light of the first wavelength as the first light flux into the first optical waveguide 22, and the second light source 29 is the second light different from the first wavelength. It is sufficient to supply the light of the wavelength as the second light flux into the second optical waveguide 25. Of course, in these cases, the first luminous flux and the second luminous flux
The grating patterns of the first and second condensing grating couplers 24 and 27 are determined according to the luminous flux of.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.

Further, the displacement measuring device according to the present invention can be used not only as a focus error detecting device for an optical disk or the like but also for measuring the displacement of various other test objects. Is.

[0053]

As described above, according to the present invention,
The size and weight of the optical system can be reduced, the adjustment of the optical axis is not required, no special machining is required for the substrate, and the bulk optical element for converging light is used. No lens is required, and the tolerance of the manufacturing error is large, and the cost is low.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an optical waveguide device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view taken along the line II-II in FIG.

FIG. 3 is a schematic sectional view showing a usage state of the optical waveguide device according to the embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the position of the test surface in the direction of the light-gathering optical axis and the detection signal of the photodetector and the output signal of the differential amplifier. FIG. It is a figure which shows the relationship between the position of an optical axis direction, and the detection signal of a photodetector, FIG.4 (b) shows the position of the condensing optical axis direction of a to-be-tested surface, the detection signal of a photodetector, and a differential amplifier. It is a figure which shows the relationship with an output signal.

FIG. 5 is a schematic perspective view showing a conventional optical disc pickup.

[Explanation of symbols]

 21 substrate 22 first optical waveguide 23 first waveguide type beam splitter 24 first condensing grating coupler 25 second optical waveguide 26 second waveguide type beam splitter 27 second condensing grating coupler 28 1 light source 29 2nd light source 30 1st photodetector 31 2nd photodetector 32 differential amplifier 33 test surface

Claims (7)

[Claims] 1. A substrate and a first formed on the surface of the substrate.
Optical waveguide, a first waveguide type beam splitter and a first condensing grating coupler, and a second optical waveguide formed on the back surface of the substrate, a second waveguide type beam splitter and a second condensing grating. A grating coupler, a first light supply means for supplying a first light flux into the first optical waveguide, and a second light supply means for supplying a second light flux into the second optical waveguide, The first photodetector and the second photodetector; and differential operation means for obtaining the difference between the detection signal of the first photodetector and the detection signal of the second photodetector. The optical waveguide guides the first light flux supplied by the first light supply means to the first waveguide type beam splitter, and the first waveguide type beam splitter is the first optical waveguide. The first light flux guided by the first condensing grating coupler The first condensing grating coupler supplies the first condensing grating coupler with the first condensing grating coupler so as to condense the first luminous flux so as to condense at a first point in a free space on the side of the surface of the substrate, The reflected light from the surface to be inspected by the emitted light based on the light flux is
Of the reflected light supplied from the first condensing grating coupler, and the first guided beam splitter splits a part of the reflected light supplied from the first condensing grating coupler through the first optical waveguide. The second optical waveguide is guided to the second waveguide type beam splitter, and the second optical waveguide is guided to the second waveguide type beam splitter. The wave-shaped beam splitter supplies the second light flux guided by the second optical waveguide to the second condensing grating coupler, and the second condensing grating coupler supplies the supplied second light flux. From the surface to be inspected by the emitted light based on the second luminous flux, the luminous flux is emitted so as to be condensed at a second point different from the first point in a free space on the surface side of the substrate. Reflected light of the second waveguide type beam The second light guide type beam splitter supplies a part of the reflected light supplied from the second condensing grating coupler to the second photodetector through the second optical waveguide. And a light collecting optical axis of the first light collecting grating coupler and a light collecting optical axis of the second light collecting grating coupler are substantially coincident with or substantially parallel to each other, and the substrate is The displacement measuring device is characterized in that it has translucency with respect to the emitted light and the reflected light by the second light flux. 2. The first focusing grating coupler is substantially not coupled with the light based on the second light flux, and the second focusing grating coupler is substantially uncoupled with the light based on the first light flux. The displacement measuring device according to claim 1, wherein the displacement measuring device is not coupled to. 3. The first light flux supplied by the first light supply means and the second light flux supplied by the second light supply means are linearly polarized lights having different polarization directions from each other. The displacement measuring device according to claim 2. 4. The wavelength of the first light flux supplied by the first light supply means and the wavelength of the second light flux supplied by the second light supply means are different. The displacement measuring device according to claim 2. 5. The first waveguide type beam splitter and the first condensing grating coupler are arranged adjacent to each other, and the second waveguide type beam splitter and the second condensing grating coupler are adjacent to each other. The displacement measuring device according to any one of claims 1 to 4, wherein the displacement measuring device is arranged in a plurality. 6. The first waveguide beam splitter comprises:
The part of the reflected light supplied from the first converging grating coupler is condensed on the first photodetector, and the second waveguide type beam splitter includes the second waveguide beam splitter.
The displacement measuring device according to any one of claims 1 to 5, wherein the part of the reflected light supplied from the condensing grating coupler is condensed on the second photodetector. 7. The first light supply means is provided on one end side of the substrate, and the second light supply means is provided on the other end side of the substrate. 7. The displacement measuring device according to any one of 1 to 6.