JP2761180B2 - Micro displacement measuring device and optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a small displacement measuring device, a focus error signal detecting device, and an optical pickup device.

[0002]

2. Description of the Related Art Conventionally, as a focus servo method using a focus error signal used in an optical head for a magneto-optical disk, an astigmatism method, a critical angle method, a knife edge method and the like are known. Among them, the astigmatism method is used not only for magneto-optical disks but also for all optical disks including compact disks and laser disks. Known techniques related to the astigmatism method include:
Japanese Patent Publication No. 53-39123 discloses an "automatic focus adjusting device", Japanese Patent Publication No. 57-12188 discloses a "device for focusing a reading light beam on a moving data carrier", and Japanese Patent Publication No. 60-48949 discloses a light source. Apparatus for Reading Information with Beam "and JP-B-61-61178, each of which is disclosed as an" automatic focus adjustment method ".

FIG. 16 shows the principle of operation of the astigmatism method in an optical pickup device. Light emitted from a semiconductor laser (not shown) is collimated by a collimator lens (not shown), passes through a beam splitter 1, is condensed by an objective lens 2, and is irradiated on a surface of an optical disc 3, thereby obtaining information. Is recorded. The reflected light from the optical disk 3 is reflected by the beam splitter 1 via the objective lens 2 this time, and sequentially passes through the condenser lens 4 and the cylindrical lens 5 to form a beam 6 having astigmatism. Beam 6 is divided into four divided light receiving surfaces a,
The focus error signal Fo is detected by being guided to the light receiving element 7 having b, c, and d and sent to the amplifier 8.

In this case, when the optical disk 3 is in focus, the shape of the beam 6 of the reflected light from the optical disk 3 is circular on the four-divided light receiving surfaces a, b, c, d of the light receiving element 7. In this circular shape, the differential output ｛(a + c) − (b +
d) The value of｝ becomes zero, and the value of the focus error signal Fo is not detected. When the optical disk 3 moves farther or closer to the objective lens 2, the shape of the beam 6 changes from a perfect circle to an ellipse, and the differential output does not become zero, so that the value of the focus error signal is positive (far). ) Or negative (close), and the position of the objective lens is adjusted.

[0005]

In recent years, this type of optical disk device has been required to have a shorter access time, and in order to achieve such an object, the size and weight of the optical pickup section have been reduced. Is indispensable. However, in the focus servo method using the astigmatism method as described above, the distance (detection length) to the light receiving element 7 is increased to some extent (several c) in order to detect a change in beam shape.
m), sufficient detection sensitivity cannot be obtained.
Therefore, there is a limit in miniaturization of the conventional optical disk device. In addition, since the spot diameter on the light receiving element 7 is as small as several microns to several tens of microns, adjustment is difficult, and an offset occurs depending on the environment, so that the detected signal becomes unstable.

[0006]

According to the first aspect of the present invention, light from a light source is condensed by an objective lens and irradiated on a measurement object, and light reflected by the measurement object and passed through the objective lens again is incident. The first diffraction grating that generates the first diffracted light of the ± n-order light by performing the second diffraction light of the ± m-order light is different in grating pitch from the first diffraction grating on which the first diffraction light is incident. A second diffraction grating to be generated, and interference fringe generating means for generating interference fringes by interference between the second diffracted lights is provided, and a change in phase and pitch of the generated interference fringes is detected by a light receiving element. An object moving amount calculating means for calculating the moving amount of the object in the optical axis direction is provided.

According to the second aspect of the present invention, light from a light source is condensed by an objective lens and radiated on an object to be measured, and light reflected by the object and passed through the objective lens again enters the ± n-th order. The first equal-pitch diffraction grating that generates the first diffracted light of the light, and the first equal-pitch diffraction grating to which the first diffracted light is incident have the same grating pitch as the first equal-pitch diffraction grating and are relatively And a second equal-pitch diffraction grating that generates second diffracted light of ± m-order light having different phases, and an interference fringe generating unit that generates interference fringes by interference between the second diffracted lights is provided. An object movement amount calculating means for detecting a change in the phase and pitch of the generated interference fringes by a light receiving element and calculating the amount of movement of the object in the optical axis direction is provided.

According to the third aspect of the present invention, the first or second aspect is provided.
In the invention described in the above, the light receiving element that receives the change of the phase and the pitch of the interference fringe generated between the second diffracted lights of the ± m-order light of the interference fringe generating means has a light receiving surface divided into two, and The movement amount is calculated from the difference between the output values of the light receiving surfaces.

According to a fourth aspect of the present invention, recording and reproduction of information is performed by condensing light from a light source by an objective lens and irradiating the recording medium with light, and detecting light reflected from the recording medium by a light receiving element. In the optical pickup device to perform, the first diffraction grating to generate the first diffracted light of ± n order light by the incident light reflected from the recording medium, and the first diffraction grating to which the first diffracted light is incident Has a different lattice pitch ±
a second diffraction grating that generates a second diffracted light of the m-th order light; and an interference fringe generating unit that generates interference fringes by interference between the second diffracted lights is provided at a stage preceding the light receiving element. The change in the phase and pitch of the interference fringes is detected by the four divided light receiving surfaces of the light receiving element, and the distribution of the interference fringes on each of the light receiving surfaces is read to obtain a focus error signal, and the focus error signal is obtained. A recording medium moving amount calculating means for obtaining a track error signal by reading the interference fringe corresponding to the track pattern and obtaining a reproduction recording signal from a total output value of the four divided light receiving surfaces is provided.

According to the fifth aspect of the present invention, light from a light source is condensed by an objective lens and irradiated on a recording medium, and reflected light from the recording medium is detected by a light receiving element to record or reproduce information. A first equal-pitch diffraction grating that generates first diffracted light of ± n-order light by incidence of reflected light from the recording medium, and a first equal pitch grating that receives the first diffracted light. A pitch diffraction grating having a same grating pitch and a second equal-pitch diffraction grating that generates second diffracted light of ± m-order light having a relative phase different from that of the first equal-pitch diffraction grating. An interference fringe generating means for generating interference fringes by interference between diffracted lights is provided in front of the light receiving element, and a change in the phase and pitch of the generated interference fringes is detected by the four divided light receiving surfaces of the light receiving element. And
The focus error signal is obtained by reading the distribution of the interference fringes on each of the light receiving surfaces, and the track error signal is obtained by reading the interference fringes corresponding to the track pattern on the recording medium. A recording medium movement amount calculating means for obtaining a reproduction recording signal from the total output value of the surface is provided.

[0011]

According to the first aspect of the present invention, by providing the interference fringe generating means having the first and second diffraction gratings,
In the cross section of the light emitted from the interference fringe generating means, light beams having different angular displacements interfere with each other by defocusing, and the pitch and phase of the generated interference fringes can be changed by defocusing. Also,
By using diffraction gratings having different pitches, it is possible to generate interference fringes without defocus.

According to the second aspect of the present invention, it is possible to easily form a diffraction grating by setting the first equal pitch diffraction grating and the second equal pitch diffraction grating to have the same pitch.

According to the third aspect of the invention, by dividing the light receiving surface of the light receiving element into two, the process of manufacturing the light receiving element can be simplified.

According to the fourth and fifth aspects of the present invention, the interference fringes obtained by the interference fringe generating means are guided to a light receiving element having four light receiving surfaces. The detection sensitivity can be significantly improved compared to the methods that detect changes in the beam shape, such as the knife-edge method and the astigmatism method. In addition, the large beam shape enables extremely rough adjustment of the optical position. In addition, it is possible to improve the environmental resistance performance, and further, since it is possible to use a plastic housing, the configuration of the optical pickup unit can be reduced in size and thickness.

[0015]

1 to 9 show one embodiment of the invention described in claim 1.
It will be described based on. Before describing the interference fringe generating means, which is the configuration of the main part of the present embodiment, first, the overall configuration of a minute displacement measuring apparatus provided with the interference fringe generating means will be described with reference to FIG. Light emitted from a semiconductor laser 9 (LD) serving as a light source is collimated by a collimator lens 10, reflected by a beam splitter 11, and becomes a beam condensed by an objective lens 12, and is a surface of a measurement object 13. Irradiated on top. Then, the reflected light from the measurement object 13 passes through the objective lens 12 again, and then passes through the beam splitter 11 and enters a double diffraction grating 14 as interference fringe generating means. In this case, the double diffraction grating 14
Is a first diffraction grating 14 for generating first diffracted light of ± n order light.
a and a second diffraction grating 14b having a different grating pitch from the first diffraction grating 14a and generating second diffracted light of ± m order light. Then, the interference fringes generated by the double diffraction grating 14 are guided to a light receiving element 15 (for example, a CCD), so that the phase and the pitch of the interference fringes are measured. A method of calculating the period of the periodic light quantity distribution on the CCD surface and calculating the moving amount of the object 13 can be performed by using the object moving amount calculating means (described later).

Next, a mechanism for generating interference fringes using the double diffraction grating 14 will be described with reference to FIGS. In FIG. 2, a first diffraction grating 14a is arranged on the light source side and a second diffraction grating 1 is arranged on the opposite side on the optical path where the light emitted from the semiconductor laser 9 is collimated by the collimating lens 10.
There is provided a double diffraction grating 14 in which 4b is arranged. Here, as shown in FIG. 3, the grating pitch of the first diffraction grating 14a and lambda _1, a grating pitch of the second diffraction grating 14b and lambda _2, also the diffraction angle of the first diffraction grating 14a theta ₁ And the diffraction angle at the second diffraction grating 14b is θ ₂ . Furthermore, the angle of incidence on the first diffraction grating 14a is assumed to be perpendicular incidence for simplification of the description.

Now, at the first diffraction grating 14a, ± n-order light (n
Is positive), and the second diffraction grating 14b generates + m-th light (m is positive) of the + n-th light and + m-th light (m is positive) of the -n-th light. Generate. And
An interference fringe is generated by causing interference between ± m-order light beams. + Indicates that the incident light is diffracted to the left in the traveling direction, and-indicates that the incident light is diffracted to the right in the traveling direction.

At this time, the diffraction condition expression of the + n-order light at the first diffraction grating 14a is as follows: sin θ ₁ = nλ / Λ ₁ (1) In the case of -nth-order light, n may be replaced with -n, and a description thereof will be omitted. Further, the diffraction condition expression for the second diffraction grating 14b is as follows: -sin θ ₂ + sin θ ₁ = mλ / Λ ₂ (2) From Equations (1) and (2), for θ ₂ , sin θ ₂ = λ (n / Λ ₁ -m / Λ ₂ ) (3) As shown in FIG. 3B, the pitch Λ ₀ of the light intensity distribution 26 of the interference fringes 25a and 25b due to the two plane waves 23a and 23b having the incident angle of θ ₂ passing through the slit 24.
Is as shown in equation (4). Further, the phase β ₀ of the interference fringe 26 due to the relative phase is expressed as in equation (5). Λ ₀ = λ / ( ₂ sin θ ₂ ) (4) β ₀ = β ₁ (5) β ₀ : phase of interference fringes β ₁ : phase between plane waves. relationship with pitch (3), using the equation (4) is expressed as _{1 / (2Λ 0) = n} / Λ 1 -m / Λ 2 ... (6). As for the phase relationship in the case of the double diffraction grating 14, as shown in FIG. 3C, if only the interference of the positive and negative orders of diffracted light is considered, the phase relationship immediately after the diffraction grating is reversed. The phase β _{0 of the} interference fringes
Is expressed as β ₀ = 2β ₂ (7). Thus, it can be seen that the pitch of the interference fringes depends only on the pitch of the double diffraction grating 14, and is completely independent of the wavelength of the incident light. Then, the W ₀ the diameter of the light as shown in FIG. 4, when multiplied respectively the value (6) to the left and right sides of the _{equation, (W 0 / Λ 0)} / 2 = nW 0 / Λ 1 -mW 0 / Λ ₂ ... (8) Here, W ₀ / Λ ₀ is the number of interference fringes generated within the light diameter, and nW ₀ / Λ ₁ and nW ₀ / Λ ₂ are the first diffraction grating 14.
a and the number of diffraction gratings within the light diameter of the second diffraction grating 14b are multiplied by the respective orders. That is, (number of interference fringes) / 2 = order × (number of first diffraction gratings) −order × (number of second diffraction gratings) (9) Thereby, the number of interference fringes and the first diffraction grating 14
a and the number of the second diffraction gratings 14b, and the relationship between the respective orders. In this case, interference fringes naturally occur regardless of which order is used, but using ± 1st-order light is superior to high-order diffracted light in terms of high diffraction efficiency. Specifically, the + 1st-order light generated by the first diffraction grating 14a as shown by P in FIG. 5 and the -1st-order light by the second diffraction grating 14b, and the first-order light as shown by Q in FIG. The efficiency of the + 1st-order light generated by the diffraction grating 14a and the + 1st-order light of the second diffraction grating 14b is the best.

Here, an example of the number of interference fringes will be described. ± using only first-order light, aiming at high resolution, lambda ₁ =
When a very high-density diffraction grating of 0.948 μm is used, Λ ₂ = 0.9 in order to obtain ₀ = 1 mm.
4768 μm. Λ ₁ and Λ ₂ of the difference is about 0.03%
Is very small, but it can be created. If the diameter of the collimated light is about 2 mm, one or two interference fringes will be observed.

Next, a method of measuring a minute displacement by the object movement amount calculating means using the double diffraction grating 14 as described above will be described with reference to FIGS. Now, an objective lens 10 approximately focused on the surface of the object 9 to be measured,
The double diffraction grating 14 is arranged on the optical axis. The focal length of the objective lens 10 is f, the distance between the objective lens 10 and the surface of the object 9 is b ₁ , and the focusing position on the double diffraction grating 14 side is b.
_2, the lens aperture A, the surface of the lens focal length and the measurement subject distance (referred to as defocus) d, in the corner theta (FIG. 6 to be incident on the double diffraction grating 14, an upper optical axis theta ₁ , The lower side of the optical axis is θ ₂ ), the distance between the double diffraction gratings 14 is T, d <
If <f, 1 / f = 1 / b ₁ + 1 / b ₂ (10) θ = A / b ₂ (11) b ₁ = f + d (12) Then, (10) from the equation, b ₂ is represented as _{b 2 = fb 1 / (b} 1 -f) ... (13).

Θ = A (b ₁ −f) / fb ₁ = Ad / f (f + d) ≒ Ad / f ² (14) Here, by setting d << f, light from the objective lens 10 When the objective lens 10 and the double diffraction grating 14 are close to each other in the collimated state and the X axis (X = 0 on the optical axis) is taken as shown in FIG. 7, A = x can be obtained. Is: θ = xd / f ² (15) As described above, the incident angle of the light beam differs depending on the position (x). The light that has entered the double diffraction grating 14 from both sides with respect to the light and that has been diffracted twice by the double diffraction grating 14 has an emission surface (an interference fringe generation surface) as shown in FIG.
Intersect at R. Since these two lights have different emission angles, interference fringes are generated.

Next, the pitch of interference fringes at each position is determined. When light above the optical axis is incident on the position x at y = 0, the angle θ ₃ emitted from the light exit surface R is sin θ ₁ -sin θ ₃ = λ (1 / Λ ₂ − 1 / Λ ₁ ) (16) Since θ ₁ ≒ 0 and θ ₃ ≒ 0, θ ₃ is expressed as follows: θ ₃ = θ ₁ + λ (1 / Λ ₁ −1 / Λ ₂ ) (17) Then, obtain a (1 5) Substituting expression (the 1 ^{_{7), θ 3 = xd / f 2}} + λ (1 / Λ 1 -1 / Λ 2) ... (18). For simplicity, the position X of the light on the exit surface at y = T is given by X = x−T (19) where the diffraction angle of the first diffracted light is 45 °. By substituting equation (19) into equation (18), θ ₃ = d (X + T) / f ² + λ (1 / Λ ₁ -1 / Λ ₂ ) (20) Similarly, when light at a position lower than the optical axis is incident on x at y = 0, the angle θ ₄ emitted from the exit surface R is θ ₄ = d (X−T) / f ² + Λ (1 / Λ ₁ −1 / Λ ₂ ) (21) The incident angles of the two light beams are θ ₃ and θ ₄ respectively, and θ
_{When the} values are _{3 to} 0 and θ _{4 to} 0, the pitch Λ _{0 of the} interference fringes is as follows: Λ ₀ = λ / (| sin θ ₃ + sin θ ₄ |) = λ / (| θ ₃ + θ ₄ |) (22) Then, when the equations (20) and (21) are substituted into the equation (22), 、 ₀ (d) = λ / ｛| 2dT / f ² + 2λ (1 / Λ ₁ −1 / Λ ₂ ) |｝ (23) ). Thus, it can be seen that the interference fringes have the same pitch depending on the defocus d regardless of the position X. Here, when d = 0, Λ ₀ (0) = Λ ₀ and Λ ₀ = １ ／.
Assuming that (1 / Λ ₁ −1 / Λ ₂ ), Λ ₀ (d, X) = λ / (| ² dT / f ² + λ / Λ ₀ |) = 1 / (| 1 / Λ ₀ +2 (d / λ) ) T / f ² |) (24) Equation (24) is a basic equation that describes the pitch of interference fringes. As an example, T = 1 mm, f = 4 mm, Λ ₀ = 1 m
As shown in FIG. 9, Λ ₀ (d) at the time of m is a small displacement d of the object 9 by measuring the pitch 、 _{0 of the} interference fringes.
Is found. Further, the phase of the interference fringes is the same as that of the equation (7). Therefore, the pitch of the interference fringes is measured by applying the double diffraction grating 14 to a minute displacement measuring device as shown in FIG.
Can be calculated.

As described above, the provision of the double diffraction grating 14 causes light beams having different angular displacements to interfere with each other due to defocus in the cross section of the light emitted from the grating, and the pitch of the generated interference fringes. And the phase can be changed by defocusing, whereby a minute displacement can be measured. In addition, 2 having different lattice pitches
Since two diffraction gratings 14a and 14b are used, interference fringes are generated without defocus, and the direction of defocus (positive or negative of d) can be detected.

Next, an embodiment of the present invention will be described with reference to FIGS. The description of the same parts as those of the first aspect of the invention will be omitted.
The same reference numerals are used for the same parts. In the above-described embodiment of the first aspect, the case where the first diffraction grating 14a and the second diffraction grating 14b are the double diffraction gratings 14 having different grating pitches has been described. First and second diffraction gratings 14 as pitch diffraction gratings
The case where the grating pitches in a and 14b are the same and the relative phases of these two diffraction gratings are different is described.

In this case, the fact that the grating pitch is the same means that no interference fringe occurs when the object 9 is not defocused (Λ ₀ → ∞), but an interference fringe occurs when defocus occurs. This means that the minute displacement of the object 9 can be measured by reading the pitch of the interference fringes. In mathematical terms, if す る と₀ → ∞ in equation (24), then Λ ₀ (d) = f ² / ｛| (d / λ) 2T |｝ (25) Also here, two diffraction gratings (ie,
The phases of the first and second diffraction gratings 14a, 14b) are intentionally made different. The phase state at this time is shown in FIG.
This will be described with reference to FIG. Now, it is assumed that ± first-order light (P, Q light) is used. Since the first and second diffraction gratings 14a and 14b have the same pitch and are out of phase by 90 ° (1/4 wavelength), in a state where no defocus occurs (d = 0), FIG. As shown in ()), the P light and the Q light have the same phase plane 27 in parallel, and are in a state of entering each other like a comb. To shift the phase by 90 ° (1/4 wavelength)
When using a combination of ± primary light, two diffraction gratings
Are shifted relative to each other by 1/8 pitch. When defocus occurs (d <0, d> 0),
As shown in FIGS. 10B and 10C, the equiphase surfaces 27 are each microscopically curved. This curvature causes the equiphase surface 27
Intersect with each other, and an interference fringe having a pitch represented by Expression (25) is generated. This interference fringe is formed by the intersection of wavefronts, and the intersection moves as shown by L in FIGS. 10B and 10C, depending on the sign of defocus. This indicates that the left and right phases are inverted. Further, as shown in FIG. 11, the light quantity distribution of the interference fringes qualitatively changes due to defocusing, whereby the left and right A and B regions respectively corresponding to the positions of the P and Q lights are shifted with respect to d = 0. In this case, the state of such a change is reflected in the light receiving element 15.
The value of d can be known by reading with. Therefore, by using the diffraction gratings 14a and 14b having the same grating pitch and different phases, the diffraction grating can be easily formed, and the production cost can be reduced.

Next, an embodiment of the present invention will be described with reference to FIG. It should be noted that claims 1 and 2 described above.
A description of the same parts as those of the described invention is omitted, and the same reference numerals are used for the same parts. In this embodiment, in the minute displacement measuring device according to claim 1 or 2, a change in the phase and pitch of the interference fringe generated between the second diffracted lights of the ± m-order light of the double diffraction grating 14 is received. The light receiving element 15 is divided into two to form light receiving surfaces A and B, and a movement amount is calculated from a difference between output values of the light receiving surfaces A and B. The light receiving surfaces A and B thus divided into two parts are arranged in the left and right optical paths in FIG. 11 as described above, and the change in the light amount distribution of the interference fringes, that is, the light amount difference (AB) is detected. A signal as shown in FIG. 12 can be obtained, whereby a minute displacement can be measured.

In the above-described embodiments of the first and second aspects,
The first diffraction grating 14a generates diffracted light of ± n order light, and the second diffraction grating 14b generates diffracted light of ± m order light. However, there is no particular need to be particular about the order of the diffracted light. Even if the order is used, the interference fringes naturally occur. In particular, by using the ± 1st-order light, the diffraction efficiency is high and the high-order diffraction light is excellent. In addition, the high-order diffracted light has a large diffraction angle, and when incident on the second diffraction grating 14b, is separated from the optical axis, so that a portion that does not contribute to interference remains, whereby ± 1st-order light is most effective, Measurement accuracy can be improved.

Next, an embodiment of the present invention will be described with reference to FIGS. The description of the same parts as those of the first to third aspects of the invention will be omitted, and the same reference numerals will be used for the same parts. In this embodiment, an example in which the measurement principle of the minute displacement measuring device as described in the first to third aspects of the present invention is applied to an optical pickup device will be described. That is, FIG.
In the optical pickup device of No. 3, the double diffraction grating 14 is disposed on the optical path where the light reflected by the optical disk 17 is reflected by the beam splitter 11, and the interference fringes generated by this are shown in FIG. 4 of light receiving element 28
The detection is performed by the divided light receiving surfaces A, B, C, and D. Further, here, a recording medium moving amount calculating means for obtaining respective signals of the focus error signal Fe, the track error signal Te, and the reproduction recording signal Wo (this corresponds to the above-described object moving amount calculating means, and both are shown in the drawing) Z) was provided.

In such a configuration, the semiconductor laser 9
Is transmitted through the collimator lens 10 and the beam splitter 11, changes the optical path by the rising mirror 16, is condensed by the objective lens 12, and is irradiated on the surface of the optical disk 17. The reflected light from the optical disc 17 follows the reverse path, is reflected by the beam splitter 11, and enters the double diffraction grating 14. This allows
The interference fringes generated by the same principle as in the above-described embodiment are received by the light receiving element 28, and the phase and pitch changes of the interference fringes are obtained. Then, the moving amount of the optical disk 17 in the optical axis direction can be detected by the recording medium moving amount calculating means (not shown). The amount of movement in the optical axis direction can be determined by obtaining a focus error signal Fe and a track error signal Te. Focus error signal Fe
Can be obtained by reading the distribution of interference fringes on each of the light receiving surfaces A to D. The track error signal Te can be obtained by reading the interference fringes corresponding to the track pattern (see FIG. 14) on the optical disk 17. Can be. The formula for calculating the focus error signal Fe and the track error signal Te is as follows: Fe = (A + B)-(C + D) (26) Te = (A + D)-(B + C) (27) In this case, the reproduction / recording signal can also be obtained from the total output value of the four divided light receiving surfaces A to D. As the light receiving element 28, the above-described CCD can be used, but it is expensive, so that the use of a photodiode (PD) enables a low-cost configuration.

Next, advantages (first to third) produced by the configuration as in the present embodiment will be described. FIG.
Reference numeral 5 denotes the smallest structural example among the conventional optical pickup devices. Here, a semiconductor laser (LD) 9 and a light receiving element 21 as light receiving means are provided inside a cap 20.
And a hologram 2 having a diffraction function between the LD 9 outside the cap 20 and the collimating lens 10.
2 is provided. In recent years, in the field of optical disks, it has been desired to reduce the thickness of an optical pickup, and it is important to shorten the focal length of the collimator lens 10 to reduce the diameter of the collimated light. However, in the conventional type, the hologram disturbs the collimator with a short focal length.
Since Torrens cannot be used, it cannot be said that sufficient miniaturization and weight reduction have been achieved. However, there is a first advantage that a very small optical pickup can be formed by using the double diffraction grating 14 as in this embodiment.

The light receiving element 2 of the conventional optical pickup
Although the beam diameter on the light receiving element 1 is several tens of microns, in this embodiment, the beam diameter on the light receiving elements 18 and 19 is almost the same as the collimated light diameter and is on the order of millimeters. The adjustment can be made rough. That is, as a specific adjustment method, adjustment between the semiconductor laser 9 and the collimating lens 10 is performed. Next, the collimated light is reflected by using the reference plane, is incident on the double diffraction grating 14, and the grating directions of the diffraction gratings 14a and 14b are fixed perpendicular to the track direction. It is rough and rough. Then, it is only necessary to bring the light receiving elements 18 and 19 close to the double diffraction grating 14 and fix them with an accuracy of several tens of microns while checking the outputs of the light receiving elements 18 and 19. As described above, there is a second advantage that the adjustment can be made rougher than before. Furthermore, since the beam shape on the light receiving surface is large, there is a third advantage that the environment resistance is extremely good. In addition, since plastic can be used for the housing, weight reduction can be achieved, thereby realizing high-speed access and low cost.

[0032]

According to the first aspect of the present invention, light from a light source is condensed by an objective lens and irradiated on a measurement object, and light reflected by the measurement object and passed through the objective lens again enters the object. The first diffraction grating that generates the first diffracted light of the n-th light and the first diffraction grating on which the first diffracted light is incident have a different grating pitch and generate the second diffracted light of the ± m-th light. A diffraction grating having interference fringe generating means for generating interference fringes by interference between the second diffracted lights, detecting a change in the phase and pitch of the generated interference fringes by a light receiving element, Since the measuring object moving amount calculating means for calculating the moving amount in the optical axis direction is provided, light beams having different angular displacements interfere with each other due to defocusing in the cross section of the light emitted from the interference fringe generating means, thereby being generated. The pitch and phase of the interference fringes are By changing the focus, the detection length can be shortened, and the minute displacement can be measured in a stable state. Further, by using diffraction gratings having different pitches from each other, interference fringes can be generated without defocus, and the defocus direction (positive or negative) can be detected.

According to a second aspect of the present invention, the light from the light source is condensed by the objective lens and radiated on the object to be measured. The first equal-pitch diffraction grating that generates the first diffracted light of the light, and the first equal-pitch diffraction grating to which the first diffracted light is incident have the same grating pitch as the first equal-pitch diffraction grating and are relatively And a second equal-pitch diffraction grating that generates second diffracted light of ± m-order light having different phases, and an interference fringe generating unit that generates interference fringes by interference between the second diffracted lights is provided. Since the object movement amount calculation means for detecting the change in the phase and the pitch of the generated interference fringes by the light receiving element and calculating the amount of movement of the object in the optical axis direction is provided, the diffraction grating having the same pitch is thus provided. Use to simplify the creation of diffraction gratings The production cost can be reduced.

According to a third aspect of the present invention, in the first or second aspect of the invention, a change in the phase and pitch of the interference fringe generated between the second diffracted lights of the ± m-order light of the interference fringe generating means is received. The light receiving element has two divided light receiving surfaces, and the amount of movement is calculated from the difference between the output values of these light receiving surfaces, so that the process of manufacturing the light receiving element can be simplified and the production efficiency can be increased. be able to.

According to a fourth aspect of the present invention, light from a light source is condensed by an objective lens and irradiated onto a recording medium, and reflected light from the recording medium is detected by a light receiving element to record or reproduce information. In the optical pickup device to perform, the first diffraction grating to generate the first diffracted light of ± n order light by the incident light reflected from the recording medium, and the first diffraction grating to which the first diffracted light is incident Is different in lattice pitch ± m
A second diffraction grating that generates a second diffracted light of the next light, and an interference fringe generating unit that generates an interference fringe by interference between the second diffracted lights is provided at a front stage of the light receiving element, and the interference fringe is generated. Changes in the phase and pitch of the interference fringes are detected by the four divided light receiving surfaces of the light receiving element, and the distribution of the interference fringes on each of the light receiving surfaces is read to obtain a focus error signal, and a track on the recording medium is obtained. Since a recording medium moving amount calculating means for obtaining a track error signal by reading the interference fringe corresponding to the pattern and obtaining a reproduction recording signal from the total output value of the four divided light receiving surfaces is provided, a conventional knife edge method is used. Signal detection is performed using an interference measurement method that uses interference fringes instead of a method that uses changes in the beam shape, such as the laser beam and the astigmatism method, to significantly improve detection sensitivity. Bets can be, moreover, since the detection length may take shorter than conventional, it is possible to reduce the size of the optical pickup unit. Further, in the detection using such interference fringes, since the beam shape is relatively large, the adjustment of the optical position can be made extremely rough, and the environmental resistance performance can be improved and the signal detection can be stabilized. Further, since a plastic housing can be used in such a configuration, the thickness of the optical pickup section can be reduced, high-speed access can be performed, and the production cost can be reduced.

According to a fifth aspect of the present invention, recording and reproduction of information is performed by condensing light from a light source by an objective lens and irradiating the light on a recording medium, and detecting light reflected from the recording medium by a light receiving element. A first equal-pitch diffraction grating that generates first diffracted light of ± n-order light by incidence of reflected light from the recording medium, and a first equal pitch grating that receives the first diffracted light. A pitch diffraction grating having a same grating pitch and a second equal-pitch diffraction grating that generates second diffracted light of ± m-order light having a relative phase different from that of the first equal-pitch diffraction grating. An interference fringe generating means for generating interference fringes by interference between diffracted lights is provided in front of the light receiving element, and a change in the phase and pitch of the generated interference fringes is detected by the four divided light receiving surfaces of the light receiving element. And on each light receiving surface A focus error signal is obtained by reading the distribution of interference fringes, and a track error signal is obtained by reading the interference fringes corresponding to the track pattern on the recording medium, and reproduction is performed from the total output value of the four divided light receiving surfaces. Since a recording medium movement amount calculation means for obtaining a recording signal is provided, an interference measurement method using an interference fringe is used instead of a conventional method using a change in beam shape such as a knife edge method or an astigmatism method. , The detection sensitivity can be significantly improved, and the detection length can be made shorter than before, so that the optical pickup unit can be downsized.
Further, in the detection using such interference fringes, since the beam shape is relatively large, the adjustment of the optical position can be made extremely rough, and the environmental resistance performance can be improved and the signal detection can be stabilized. Further, since a plastic housing can be used in such a configuration, the thickness of the optical pickup section can be reduced, high-speed access can be performed, and the production cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing an entire configuration of a minute displacement measuring apparatus according to an embodiment of the present invention.

FIG. 2 is an optical path diagram showing an interference fringe generation mechanism using a double diffraction grating.

FIG. 3A is an explanatory diagram showing the principle of generating interference fringes in a double diffraction grating, FIG. 3B is a schematic diagram showing the intensity distribution of interference fringes when two plane waves pass through a slit, c)
FIG. 4 is a schematic diagram showing an intensity distribution of interference fringes immediately after one plane wave is passed through a double diffraction grating.

FIG. 4 is a schematic diagram showing the beam diameter of a beam that has passed through a double diffraction grating.

FIG. 5 is a schematic diagram showing a state of ± first-order light generated by a second diffraction grating.

FIG. 6 is an explanatory diagram showing a method for measuring a small displacement using a double diffraction grating.

FIG. 7 is a schematic diagram showing how a diffraction angle of diffracted light in a double diffraction grating changes.

FIG. 8 is a schematic diagram showing a diffraction diaphragm.

FIG. 9 is a characteristic diagram showing how the pitch of interference fringes changes.

FIG. 10 is a diagram showing a phase state when the phases of two diffraction gratings according to an embodiment of the present invention are different from each other, and (a) is a schematic diagram showing a state without defocus; (B), (c) is a schematic diagram showing a state when defocus has occurred.

FIG. 11 is a schematic diagram showing a light amount distribution of interference fringes.

FIG. 12 is a waveform diagram showing a signal obtained from a light quantity difference on a two-divided light receiving surface according to an embodiment of the invention described in claim 3;

FIG. 13 is an optical path diagram showing an entire configuration of an optical pickup device having a function of a minute displacement measuring device according to an embodiment of the present invention.

FIG. 14 is a front view showing a shape of a light receiving element having a light receiving surface divided into four parts.

FIG. 15 is a partially cutaway perspective view showing a minimal configuration of a conventional optical pickup.

FIG. 16 is an optical path diagram showing a configuration of an optical pickup using a conventional astigmatism method.

[Explanation of symbols]

 Reference Signs List 9 light source 12 objective lens 13 measured object 14a first diffraction grating 14b second diffraction grating 14 interference fringe generating means 15 light receiving element 17 recording medium 28 light receiving means

Claims (5)

(57) [Claims] 1. A light beam from a light source is condensed by an objective lens, illuminated on an object to be measured, reflected by the object to be measured, and re-transmitted through the objective lens. And the first diffraction grating on which the first diffraction light is incident has a different grating pitch ±
a second diffraction grating that generates a second diffracted light of the m-order light, and an interference fringe generating unit that generates an interference fringe by interference between the second diffracted lights is provided. A minute displacement measuring apparatus comprising: a measuring object moving amount calculating means for detecting a change in pitch by a light receiving element and calculating a moving amount of the measuring object in an optical axis direction. 2. A first diffracted light of ± n order light by condensing light from a light source by an objective lens, irradiating the object with an object, irradiating the object with light reflected by the object and passing through the objective lens again. And the first equal-pitch diffraction grating on which the first diffracted light is incident has the same grating pitch and a relative phase different from that of the first equal-pitch diffraction grating by ± m. A second equal-pitch diffraction grating for generating a second diffracted light of the next light, and an interference fringe generating means for generating an interference fringe by interference between the second diffracted lights is provided, and a phase of the generated interference fringe is provided. And a change in pitch by a light receiving element and calculating a moving amount of the object in the optical axis direction by calculating a moving amount of the object in the optical axis direction. 3. A light receiving element for receiving a change in phase and pitch of interference fringes generated between the second diffracted lights of ± m order light of the interference fringe generating means has a light receiving surface divided into two, and each of these light receiving elements has a light receiving surface. 3. The minute displacement measuring device according to claim 1, wherein the movement amount is calculated from a difference between output values of the light receiving surfaces. 4. An optical pickup device for recording and reproducing information by condensing light from a light source by an objective lens and irradiating the recording medium with light, and detecting light reflected from the recording medium by a light receiving element. A first diffraction grating that generates first diffracted light of ± nth order light by incidence of reflected light from the recording medium, and a first diffraction grating on which the first diffracted light is incident have different grating pitches. a second diffraction grating that generates a second diffracted light of the m-th order light; and an interference fringe generating unit that generates interference fringes by interference between the second diffracted lights is provided at a stage preceding the light receiving element. The change in the phase and pitch of the interference fringes is detected by the four divided light receiving surfaces of the light receiving element, and the distribution of the interference fringes on each of the light receiving surfaces is read to obtain a focus error signal, and the focus error signal is obtained. For track patterns Optical pickup device characterized in that a recording medium movement amount calculating means for obtaining a reproduced recording signal from the total output value of the sought track error signal and the four divided light receiving surface by reading the interference fringes response. 5. An optical pickup device for recording and reproducing information by condensing light from a light source by an objective lens and irradiating the light to a recording medium, and detecting reflected light from the recording medium by a light receiving element. A first equal-pitch diffraction grating that generates first diffracted light of ± n-order light by incidence of reflected light from the recording medium, and a first pitch and a grating pitch at which the first diffracted light is incident Having the same and the first equal-pitch diffraction grating and a second equal-pitch diffraction grating that generates a second diffracted light of ± m-order light having a relative phase different from that of the second diffracted light. An interference fringe generating means for generating interference fringes by interference is provided in front of the light receiving element, and a change in the phase and pitch of the generated interference fringes is detected by the four divided light receiving surfaces of the light receiving element. The distribution of interference fringes on the screen And a recording medium for obtaining a focus error signal by reading the interference pattern corresponding to the track pattern on the recording medium, obtaining a track error signal, and obtaining a reproduction recording signal from a total output value of the four divided light receiving surfaces. An optical pickup device comprising a moving amount calculating means.