JP3371305B2 - Optical pickup - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for reproducing information recorded on an optical record carrier such as an optical disk by utilizing its reflected light.

[0002]

2. Description of the Related Art Conventionally, there is known an optical pickup which reproduces information recorded on an optical record carrier such as an optical disk by utilizing its reflected light.

A focus servo system is used in this kind of optical pickup, and as the focus servo system, there are an astigmatism method, a critical angle method, an if edge method and the like. Among them, the astigmatism method (optical disc technology supervised by Morio Onoue
Radio Technology Co., Ltd. (p99) is widely used for optical discs including compact discs and laser discs as well as optical heads for magnetic discs.

The principle is that if the light receiving means (photodetector) is a four-division light receiving surface (each output is A, B, C, D), the incident light is focused on the disk. At that time, the image of the reflected light becomes circular on the 4-division light receiving surface of the photodetector,
At this time, the differential output (A + C)-(B + D) between the diagonal light receiving surfaces, which is the focus error output, becomes zero. On the other hand, if the disc becomes far or near from the objective lens,
The image of the four-division light receiving surface of the photodetector changes from a circular shape to an elliptical shape. Therefore, the focus error output becomes positive (far) or negative (close), so the position of the objective lens is adjusted so that this output becomes zero.

[0005]

By the way, generally, in such an optical pickup, in order to shorten the access time, it is important to reduce the size and weight of the optical pickup. However, in the focus detection method such as the conventional astigmatism method, a change in the shape of the beam is detected, so it is sufficient if the distance (detection length) to the light receiving means (light receiving element) is increased to some extent (several cm). Sensitivity cannot be obtained, and therefore there is a limit to miniaturization. In addition, the spot on the light receiving element is quite small, from several microns to several tens of microns, adjustment is difficult, and an offset occurs depending on the environment, which is unstable.

An object of the present invention is to provide an optical pickup suitable for miniaturization and the like.

[0007]

In order to achieve the above object, the applicant of the present invention has devised a displacement measuring device (optical pickup) as shown in FIG. 1, for example. Referring to FIG. 1, this displacement measuring apparatus is configured such that light from a light source 1 passes through a collimating lens 2 and a beam splitter 3 and an objective lens 4
Concentrate and irradiate the object to be measured (for example, an optical disc) 5 with
The reflected light from the DUT 5 is made incident on the double diffraction grating 6 including the two diffraction gratings 6a and 6b as parallel light through the objective lens 4 and the beam splitter 3, and the double diffraction grating 6
By making parallel light incident on the light receiving means (light receiving element) 7 such as a photodiode, the phase and pitch of the interference fringes generated by the interference between the diffracted light are received. Displacement, eg optical axis direction of DUT 5
(Optical axis direction of incident light to DUT; optical axis direction of objective lens 4) Detects displacement in x (focus error) and displacement in z-axis direction (track error), and DUT 5 The recording signal from is detected.

The principle of interference fringe generation using the double diffraction grating 6 consisting of the first diffraction grating 6a and the second diffraction grating 6b will be described with reference to FIGS. Now
It is assumed that the first diffraction grating 6a and the second diffraction grating 6b of the double diffraction grating 6 have pitches Λ ₁ and Λ ₂ , respectively, and light of the wavelength λ is vertically incident on the first diffraction grating 6a. . Note that the generality of the present invention is not lost even if the incidence is not normal.

In the double diffraction grating 6, the first diffraction grating 6a generates ± n-order light (n is positive), and
In the diffraction grating 6b, the + m-order light of the + n-order light (m is positive) and the + m-order light of the -n-order light (m is positive) are generated. Then, the ± generated by the second diffraction grating 6a
The m-th order lights are caused to interfere with each other to generate interference fringes. In addition, +
Indicates that the incident light is diffracted to the left in the traveling direction, and-represents the opposite case.

Here, the diffraction condition of the + nth order light in the first diffraction grating 6a is expressed by the following equation. In the case of -nth order, n may be replaced with -n, and therefore the description thereof is omitted below.

[0011]

## EQU1 ## sin θ ₁ = nλ / Λ ₁

The diffraction condition of the second diffraction grating 6b is expressed by the following equation.

[0013]

2 −sin θ ₂ + sin θ ₁ = mλ / Λ ₂

From the equations 1 and ₂ , the following equation is derived for θ ₂ .

[0015]

(3) sin θ ₂ = λ (n / Λ ₁ −m / Λ ₂ )

As shown in FIG. 4 (a), when the incident angle of θ ₂ is 2
Pitch Λ _{0 of} interference fringes by two lights (plane waves) BM ₁ and BM ₂
Is expressed by Expression 4, and the phase of the interference fringes due to the relative phase is expressed by Expression 5.

[0017]

[Formula 4] Λ ₀ = λ / (2sin θ ₂ )

[0018]

[Formula 5] β ₀ = β ₁

Here, β ₀ is the phase of the interference fringe, and β ₁ is the phase between the plane waves BM ₁ and BM ₂ . Therefore, the relationship between the pitch of the interference fringes and the pitch of the double diffraction grating is expressed by Equation 6 using Equations 3 and 4.

[0020]

## EQU6 ## 1 / (2Λ ₀ ) = n / Λ ₁ −m / Λ ₂

Regarding the phase relationship in the case of the double diffraction grating 6 (see FIG. 4B), if the problem is only interference of diffracted light of positive and negative orders, the phase relationship immediately after the diffraction grating is reversed. Therefore, the phase of the interference fringe is expressed by the equation 7.

[0022]

(7) β ₀ = 2β ₂

From this, the pitch of the interference fringes is the pitch of the double diffraction grating 6 (that is, the pitch Λ _{1 of} the first diffraction grating 6a).
And the pitch Λ ₂ ) of the second diffraction grating 6b, it is completely independent of the wavelength λ of the incident light. When the light diameter is W ₀ and the right side and the left side of Expression 6 are multiplied, Equation 8 is obtained.

[0024]

[Equation 8] _{(W 0 / Λ 0) /} 2 = nW 0 / Λ 1 -mW 0 / Λ 2

Here, W ₀ / Λ ₀ is the number of interference fringes generated within the light diameter, and nW ₀ / Λ ₁ and mW ₀ / Λ ₂ are in the first diffraction grating 6a and the second diffraction grating 6b. It is obtained by multiplying the number of diffraction gratings within the light diameter by each order. That is,
It becomes the following formula.

[0026]

## EQU9 ## << Number of interference fringes >> / 2 = Order * << Number of first diffraction grating >>-Order * << Number of second diffraction grating >>

As described above, the relationship between the number of interference fringes, the number of the first and second diffraction gratings 6a and 6b, and the order of each was clarified. Although interference fringes are generated regardless of which order is used, ± 1st order light is superior to high order diffracted light because it has high diffraction efficiency. That is, the + 1st-order light generated by the first diffraction grating 6a and the -1st-order light of the second diffraction grating 6b.
(E in FIG. 3) and the −1st order light generated by the first diffraction grating 6a and the + 1st order light (F in FIG. 3) of the second diffraction grating 6b are most effective.

As an example of the number of interference fringes, when only ± 1st-order light is used, when a diffraction grating having a very high density of Λ ₁ = 0.948 μm is used in order to achieve high resolution, Λ ₀ = 1 mm is set large. Therefore, Λ ₂ = 0.94768 μm.

The difference between Λ ₁ and Λ ₂ is about 0.03%, which is very small, but can be created. If the diameter of the collimated light is set to about 2 mm, one or two interference fringes will be observed.

The above is the principle of interference fringe generation using the double diffraction grating 6.

A method of measuring the displacement of the DUT (record carrier) 5 using this double diffraction grating will be described below with reference to FIG.

Referring to FIG. 5, a lens 101 is set on the surface of the object to be measured 5 so as to be substantially in focus, and a double diffraction grating 6 is set on the optical axis of the lens 101.

In FIG. 5, the focal length of the lens 101 is f, the distance between the lens and the surface of the object to be measured is b ₁ , the focusing position on the double diffraction grating side is b ₂ , and the lens aperture is A. There is. Further, the distance (defocus amount) between the lens focus position and the surface of the object to be measured is set to d, and the double diffraction grating 6 (6a, 6a,
The angle of incidence on 6b) is θ (the upper angle of the optical axis is θ ₁ and the lower angle is θ ₂ ). In this case, when the distance between the first and second diffraction gratings 6a and 6b of the double diffraction grating 6 is T and d << f, the following formula is established.

[0034]

## EQU10 ## 1 / f = 1 / b ₁ + 1 / b ₂ θ = A / b ₂ b ₁ = f + d

From Equation 10, b ₂ is expressed by the following equation.

[0036]

B ₂ = fb ₁ / (b ₁ −f)

From equations 10 and 11 θ is expressed by

[0038]

[Equation 12] θ = A (b ₁ −f) / fb ₁ = Ad / f (f + d)
≒ Ad / f ²

Here, it is assumed that the defocus amount d is minute, that is, d << f. In this case, the lens 10
The light emitted from the lens 1 is close to the collimated state,
And the double diffraction grating 6 are close to each other, the x-axis (x = 0 on the optical axis) along the first diffraction grating 6a as shown in FIG.
, And when taking the X axis (X = 0 on the optical axis) along the second diffraction grating 6b, A = x can be obtained, so
Is given by

[0040]

[Equation 13] θ = xd / f ²

As described above, the incident angle of the light beam differs depending on the position (x). The light which has entered the double diffraction grating 6 from both sides with respect to the optical axis and which has been diffracted twice by the double diffraction grating 6 is, as shown in FIG. 5, an emission surface (interference fringe generation surface). Meet at. Since these two lights BM ₃ and BM ₄ have different emission angles,
Interference occurs between these and interference fringes occur.

Next, the pitch of the interference fringes at each position is obtained.
The angle θ ₃ at which light above the optical axis is incident on x at y = 0 and exits at the exit surface is represented by the following equation (see FIG. 7).

[0043]

(14) sin θ ₁ −sin θ ₃ = λ (1 / Λ ₂ −1 / Λ ₁ )

Since θ _{1 to} 0 and θ _{3 to} 0, θ ₃ is given by the following equation.

[0045]

[Equation 15] θ ₃ = θ ₁ + λ (1 / Λ ₁ −1 / Λ ₂ )

Substituting equation 13 into equation 15, the following equation is obtained.

[0047]

[Equation 16] θ ₃ = xd / f ² + λ (1 / Λ ₁ −1 / Λ ₂ )

It is desired to define the position X of the light on the emission surface (y = T) of the second diffraction grating 6b of the double diffraction grating 6, but for the sake of simplicity, the diffraction angle of the first diffraction light is 45 °. Then, the following equation is obtained.

[0049]

X = x−T

Substituting equation 17 into equation 16, the following equation is obtained.

[0051]

[Equation 18] θ ₃ = d (X + T) / f ² + λ (1 / Λ ₁ −1 / Λ ₂ )

Similarly, the angle θ ₄ at which light below the optical axis is incident on x at y = 0 and exits at the exit surface is expressed by the following equation.

[0053]

Θ ₄ = d (X−T) / f ² + λ (1 / Λ ₁ −1 / Λ ₂ )

The pitch Λ ₀ of the interference fringes when the incident angles of the two light beams are θ ₃ and θ ₄ and θ ₃ ˜0 and θ _{4 = 0} are expressed by the following equation.

[0055]

[Formula 20] Λ ₀ = λ / (| sin θ ₃ + sin θ ₄ |) = λ /
(| Θ ₃ + θ ₄ |)

By substituting the equations 18 and 19 into the equation 20, the following equation is obtained.

[0057]

Λ ₀ (d) = λ / [| 2dT / f ² + 2λ (1 /
Λ ₁ -1 / Λ ₂₎ |]

Here, as described above, λ is the wavelength and T is 2
The distance between the two diffraction gratings 6a and 6b, f is the focal length of the objective lens 4, Λ ₁ is the pitch of the first diffraction grating 6a, and Λ ₂ is the pitch of the second diffraction grating 6b. From this equation, it can be seen that the interference fringes generated by the double diffraction grating 6 are fringes of equal pitch Λ ₀ (d) that depend on the defocus amount d regardless of the position X. When the diffraction grating 6a and the diffraction grating 6b have the same pitch (Λ ₁ = Λ ₂ ), the pitch Λ ₀ (d) of the interference fringes is expressed by the following equation.

[0059]

[Formula 22] Λ ₀ (d) = f ² / [| (d / λ) | 2T]

When there is no defocus (when d = 0)
From Equation 22, Λ ₀ → ∞, but interference fringes occur when defocus occurs. Therefore, it is possible to obtain the displacement (more accurately, a minute displacement) d of the object to be measured or the focus error signal Fo by reading the change due to the defocus of the pitch or phase of the interference fringes.

For example, two diffraction gratings 6 having the same pitch
Parallel light is incident on the double diffraction grating 6 composed of a and 6b, and the + 1st order light at the first diffraction grating 6a and the −1st order light at the second diffraction grating 6b (referred to as E light) ) And the −1st-order light at the first diffraction grating 6a and the + 1st-order light (referred to as F light) at the second diffraction grating 6 are caused to interfere with each other, and the pitch Λ
An interference fringe of ₀ (d) can be generated.

Here, the phases of the two diffraction gratings 6a and 6b are
Intentionally shift (the distance between the peaks of the diffraction grating). 8 to 10 show a state where the phases of the two diffraction gratings 6a and 6b are shifted. That is, in FIG. 8 to FIG.
The pitch of the first diffraction grating 6a and the second diffraction grating 6b is Λ
When (= Λ ₁ = Λ ₂ ), the phase difference between the peaks of the first diffraction grating 6a and the valleys of the second diffraction grating 6b is set to Λ / 8, and the ± 1st order light is diffracted light. The case where (the above-mentioned E light and F light) is used is shown, and in this case, the phases of the two diffracted lights (E light and F light) from the second diffraction grating 6b are 90 °.
(1/4 pitch = λ / 4) More specifically, when not in defocus, the E light and the F light have wavefronts parallel to each other, and their equiphase surfaces enter into each other like a comb. At this time, since the E-phase and F-light equiphase surfaces do not intersect, no interference fringes occur.

As described above, FIG. 8 shows the case where there is no defocus as described above. However, when defocus d occurs, the wavefronts of E light and F light are microscopically as shown in FIGS. Each is curved as shown in FIG. Due to this curvature, the equal phase planes intersect, and interference fringes of the pitch Λ ₀ (d) expressed by Formula 22 are generated. The interference fringe is formed by the intersection of the E and F light wavefronts, and the intersection moves depending on whether the defocus is positive or negative, as indicated by CLS in the figure. This means that the left and right phases are reversed. The light amount distribution of the interference fringes qualitatively changes due to defocusing as shown in FIG. 11, and the left side LT and the right side RT in the interference plane are inverted at the boundary of d = 0. Therefore, the defocus d can be known by reading this with the light receiving means.

Specifically, the left side LT and the right side R in the interference plane
A light receiving element (eg, photodiode) is installed at each T, and the amount of light detected by the light receiving element on the left side (output)
The difference DI between A'and the detected light amount (output) B'of the light receiving element on the right side
When F (= A'-B ') is detected, a so-called S-shaped curve as shown in FIG. 12 is obtained.

FIG. 13 is a diagram showing a configuration example of an optical pickup to which the above principle is applied. Here, a semiconductor laser (LD) is generally used as the light source 1. This optical pickup is used in an optical recording / reproducing apparatus that records and reproduces information by condensing and irradiating light from a light source onto a record carrier. In the configuration of FIG. 13, the light from the light source 1 is collimated by a collimating lens. The light is collimated by 2 and is incident on the objective lens 4 through the beam splitter 3, and is condensed by the objective lens 4 to irradiate the record carrier as the DUT 5. The reflected light from the record carrier 5 again enters the double diffraction grating 6 via the objective lens 4 and the beam splitter 3. In the double diffraction grating 6, the reflected light incident on the double diffraction grating 6 causes interference fringes according to the above-described principle, and the generated interference fringes are received by the light receiving means (for example, FIG. 14).
Light is received by the two-divided light receiving element (7) as shown in (a), and the defocus amount d of the record carrier 5 is detected based on the output difference DIF (= A'-B ') of the two-divided light receiving element. The focus error signal Fo is obtained based on the defocus amount d and the focus servo is performed.

In order to detect not only the focus error signal Fo but also the track error signal Tr, the focus detection method is used and the light receiving means 7 is divided into four light receiving elements (each output is as shown in FIG. 14B). A, B, C, D) may be used. Then, the focus error signal Fo is given by
3 and the track error signal Tr is calculated by using the push-pull method.

[0067]

(23) Fo = (A + B)-(C + D)

[0068]

[Equation 24] Tr = (A + D)-(B + C)

Further, the recording signal can be detected by taking the total sum (A + B + C + D) of the outputs A, B, C and D of the four-division light receiving element.

As described above, by using the interference fringes of the double diffraction grating 6, it is possible to provide an optical pickup suitable for miniaturization and the like.

By the way, in order to receive all the light from the double diffraction grating 6 by the light receiving means 7, the area of the light receiving means 7 is set.
An area which is slightly larger than the beam diameter is required (that is, the area of the entire 2-division light receiving element or the area of the 4-division light receiving element, ...). In the case of detecting the focus error signal or the track error signal, there is no particular problem even if the response speed is a little slow, but when reading the record signal from the record carrier 5, high speed is required. Therefore, in order to cope with this, a material for a high-speed compatible light receiving element is required, and the cost is increased by about 20% as compared with a normal light receiving element material.

The present invention is intended to alleviate such problems. That is, when the recording signal from the record carrier 5 is detected, the light receiving means having a small area can be used. Therefore, even when the ordinary light receiving element material is used for the light receiving means, the recording is performed without sacrificing the high speed. It is intended to provide an optical pickup capable of accurately detecting a signal or the like.

Therefore, according to the first aspect of the present invention, the light from the light source is condensed and irradiated to the record carrier, and the recording signal and the focus error signal and / or the track error signal are generated based on the reflected light from the record carrier. In an optical pickup for detection, a transmission / condensing means for transmitting a part of the reflected light from the record carrier and condensing the other part, and a transmitted light from the transmission / collecting means and a focused light are incident. It has a double diffraction grating and a light receiving means for receiving light from the double diffraction grating, and receives the light that is the converged light of the transmitting / focusing means and that has undergone the double diffraction grating by the light receiving means. Then, the recording signal is detected, and the interference fringes which are the transmitted light of the transmitting / focusing means and are generated by the double diffraction grating are received by the light receiving means to detect the focus error signal and / or the track error signal. With this, the focus error signal and / or the track error signal can be detected by making the parallel light from the transmitting / focusing means incident on the double diffraction grating, while the recording signal is generated by the focused light from the transmitting / focusing means. Since it can be detected, a light receiving element with a small light receiving area can be used at the focusing position,
The recording signal can be detected at high speed and with high accuracy by the light receiving element formed of a normal light receiving element material. Also,
In the invention according to claim 1, the focused light from the transmitting / focusing means is
Double diffraction grating, so as not to diffract in the double diffraction grating
Of at least one of the two diffraction gratings forming the
An area where no grid is provided is formed in a part of. this
Allows the focused light from the transmitting / focusing means to form a double diffraction grating.
The focused light is double diffracted so that it is not diffracted.
There is no splitting into multiple beams in the child, therefore
The spot diameter of the focused light can be made smaller. By this
Therefore, it is possible to use a light receiving element with a smaller light receiving area.
It can support lower cost and higher speed.

According to the second aspect of the present invention, the transmitting / focusing means is formed of a grating lens or a lens member of which one part has a lens function and the other part does not have a lens function.

[0075]

The invention according to claim 3 is a light source
Light is focused on the record carrier, and the reflected light from the record carrier is used as the basis.
Therefore, the recording signal and the focus error signal and / or
Optical pickups that detect track error signals
Part of the reflected light from the record carrier and the other part.
Transmission / collection means for collecting light and transmission from transmission / collection means
Double diffraction grating on which light and focused light are incident, and double diffraction grating
And light receiving means for receiving light from the
Receiving means for the focused light of the light which has undergone the double diffraction grating
To detect the recording signal by receiving light by the
Interference fringes that are transmitted light and are generated by the double diffraction grating
Focusing error signal and
/ Or detect a track error signal. This allows
The parallel light from the transmitting / collecting means is incident on the double diffraction grating.
Focus error signal and / or track
Error signal can be detected, while collecting from transmission / collection means
Since the recording signal can be detected by the bundled light,
Can use a light receiving element with a small light receiving area,
The recording signal is generated by the light receiving element formed of the light receiving element material of
Can be detected at high speed and with high accuracy. Also bill
According to the invention of Item 3 , the transmission / focusing means is arranged in a partial region of the double diffraction grating. With this, the transmission / focusing means is arranged in a part of the region of the double diffraction grating, so that the optical pickup can be further downsized. Also bill
In the invention of item 4, the transmitting / collecting means is a grating.
Glens, or some have lens effects and some others
Is formed by a lens member having no lens action.

According to the invention of claim 5, the transmitting / collecting means is provided on the side of the double diffraction grating on which the reflected light from the record carrier is incident, and on the side of the light receiving means of the double diffraction grating. A region where no grating is provided is formed in a part of the diffraction grating. As a result, the transmission / focusing means is provided on the side of the double diffraction grating on which the reflected light from the record carrier is incident, and the diffraction grating on the side of the light receiving means of the double diffraction grating has a partial diffraction grating. Since the region not provided is formed, the device can be downsized and the light receiving element can be downsized.

[0078]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 15 is a block diagram of an embodiment of the optical pickup according to the present invention. Referring to FIG. 15, this optical pickup includes a light source (for example, a semiconductor laser) 1, a collimating lens 2 for collimating the light from the light source 1, a beam splitter 3, and a collimating lens 2. The objective lens 4 for converging and irradiating the light on the record carrier (for example, an optical disk) 5, the reflected light from the record carrier 5 enters through the objective lens 4 and the beam splitter 3, and part of the incident light is transmitted as it is. , Diffraction in which the transmissive / condensing unit 10 that condenses the other part into focused light and the reflected light that is partially transmitted by the transmissive / condensing unit 10 and is partly condensed The interference fringes generated by the interference between the means 6 and the diffracted light from the diffracting means 6 are projected, the interference fringes are received, and information on the displacement of the record carrier 5 (on the objective lens 4 Displacement of the measured object in the optical axis direction (Defocus amount) and / or displacement of the DUT in the track direction (radiation direction of the record carrier) orthogonal to the optical axis direction of the objective lens)
And a light receiving means (for example, a light receiving element such as a photodiode) 7 for detecting a recording signal of the record carrier 5.

Here, for the transmitting / collecting means 10, for example, a grating lens is used. 16 (a),
(b) is a plan view and a side view of a grating lens used in the transmitting / focusing means 10. As shown in FIGS. 16 (a) and 16 (b), this grating lens is a diffraction grating having a concentric circle pattern or a concentric ellipse pattern, and the grating pitch becomes denser as it goes away from the center. There is. When light enters this grating lens,
Part of the incident light is diffracted and focused by the grating lens, which is a diffraction grating in which the grating pitch becomes denser away from the center, but almost all of the incident light is hardly diffracted, and part of the incident light Is transmitted as transmitted light. Therefore, the transmission / focusing means 10 can be realized by this grating lens. In addition, the diffracting means 6 has two diffraction gratings 6a and 6b, as in the device shown in FIGS.
A double diffraction grating consisting of

In the optical pickup having such a structure, the light from the light source 1 is condensed and irradiated onto the record carrier (optical disk) 5 by the objective lens 4, and the reflected light from the record carrier 5 is doubled via the grating lens 10. It is incident on the diffraction grating 6.

At this time, as shown in FIG. 17A, since the transmitted light from the grating lens 10 is incident on the double diffraction grating 6 as parallel light as if the grating lens 10 was not experienced, the above-mentioned is described. The focus error signal Fo and the track error signal Tr can be detected by the same method as the equations (23) and (24).

When the focused light from the grating lens 10 enters the double diffraction grating 6, part of it becomes diffracted light and the rest becomes transmitted light, which goes to the light receiving means 7. Even if a large number of beams are diffracted or transmitted by, each spot becomes small near the focal position. Therefore, if the light receiving means 7 is disposed near the focusing position, this small spot can be received by one small light receiving element and detected as a recording signal.

FIG. 17B shows a structural example of the light receiving means 7. In the example of FIG. 17 (b), the light receiving means 7 has five light receiving elements (four light receiving elements 7a, 7b, 7c,
7d and a light receiving element 7e) having a small light receiving area located in the center thereof are used.

When the five-divided light receiving elements 7a, 7b, 7c, 7d and 7e as shown in FIG. 17 (b) are used as the light receiving means 7, parallel light from the grating lens 10 passes through the double diffraction grating 6. After experiencing, mainly the light receiving elements 7a, 7
It is incident on b, 7c and 7d.

Therefore, the output sum (A + B) of the two light receiving elements 7a and 7b and the output sum (C +) of the two light receiving elements 7c and 7d.
By obtaining the difference [(A + B) − (C + D)] from D), it is possible to detect the defocus amount in the optical axis direction x of the record carrier (optical disc) 5, that is, the focus error.

Further, the sum of outputs of the two light receiving elements 7a and 7d
(A + D) and output sum of two light receiving elements 7b and 7c (B + C)
By obtaining the difference [(A + D)-(B + C)] from the difference, the track error of the record carrier (optical disk) 5 can be detected.

In the present invention, the projected image on the light receiving means 7 is such that the changing direction of the interference fringes of the two diffracted lights from the double diffraction grating 6 and the changing direction of the track pattern image are orthogonal to each other. Therefore, the situation in which they interfere with each other is eliminated, and they can be independently and reliably detected. That is, the focus error and the track error can be accurately detected independently of each other.

The focused light from the grating lens 10 is mainly incident on one light receiving element 7e located at the central portion after experiencing the double diffraction grating 6. Therefore, by the output of the light receiving element 7e, the record carrier (optical disk) 5
It is possible to detect the recording signal of.

As described above, in this embodiment, before the reflected light (parallel light) from the record carrier 5 is made incident on the double diffraction grating 6, the transmitting / focusing means 10 is made to experience a part of the light. The transmitted light is incident on the double diffraction grating 6 as parallel light, and a part of the other focused light is incident on the double diffraction grating 6, so that the light receiving means 7 (light receiving elements 7a to 7e) can operate at high speed. The recording signal can be detected at high speed and with high accuracy by the light receiving element 7e having a small light receiving area without using a material.

In the above-mentioned example, the grating lens is used as the transmitting / collecting means 10 having the function of transmitting a part of the light as it is as the incident light and condensing the other part into a small spot. As shown in FIG. 18, instead of the grating lens, the lens 2 is provided on a part of the flat substrate 20 (at the center).
It is also possible to use the lens member 22 formed with 1.
The portion of the flat substrate 20 where the lens 21 is not formed does not have a lens function.

19A and 19B, the lens member 22 is shown.
An example of is shown. 19 (a) and 19 (b), the parallel light that is incident on the portion of the lens member 22 where the lens 21 is not provided, that is, the portion that does not have the lens action, remains parallel light. Lens member 2
The parallel light that passes through 2 and is incident on the portion where the lens 21 is formed is condensed by the lens 21. Therefore, even when such a lens member 22 is used, as in the case of using the grating lens, a part of the incident light can be condensed and incident on the light receiving element 7e having a small light receiving area, and the small light receiving area can be obtained. The recording signal can be detected at high speed and with high accuracy by the light receiving element 7e.

Any lens having a lens function may be used as the lens 21. Therefore, as shown in FIG.
The present invention is not limited to the normal convex lens processed into a curved surface as shown in (b), but a distributed index lens such as a SELFOC lens can be used.

In the above example, the diffracting means 6 is shown in FIG.
A double diffraction grating similar to that shown in FIG. 13 was used, but the transmitting / focusing means (grating lens or lens member)
When the focused light from 10 is diffracted by such a double diffraction grating, it becomes a plurality of diffracted lights as shown in FIG. 17A, and the diameter of the focused spot becomes slightly large. That is, as the focused light is diffracted and its diameter increases, the light receiving area of the light receiving element 7e needs to be made slightly larger than in the case where the focused light is not diffracted.
In order to make the focused spot diameter smaller and the light receiving element 7e to have a smaller light receiving area, as shown in FIG.
A part of the two diffraction gratings 6a and 6b (that is, transmission /
A double diffraction grating in which a region NL where no grating is provided is formed can be used as the diffracting means 6 in the optical path portion of the focused light from the condensing means 10). In this case, the focused light from the transmitting / collecting means 10 enters the light receiving means 7 as it is without being diffracted by the double diffraction grating 6, so that the light receiving means 7 receives the transmitting / collecting means 10. When it is arranged near the focal length of the focused light from, the diameter of the focused light entering the light receiving means 7 becomes extremely small, and the focused light can be received by the light receiving element 7e having a smaller light receiving area.

In the example of FIG. 20, both diffraction gratings 6 are
Although the regions NL in which the grating is not provided are formed in a and 6b, such regions NL may not be provided in the diffraction grating 7b on the light receiving means 7 side. For example, the diffraction grating 6b on the light receiving means 7 side
If the light receiving means 7 is placed in the vicinity of, the diffraction grating 6b need not be provided with a grating. That is, in this case, the diffraction grating 6b
Therefore, even if a plurality of diffractions occur, the plurality of diffracted lights that are generated do not diffuse so much, so that a small spot diameter can be maintained.

Further, in the above-mentioned embodiment, the transmitting / collecting means 10 is arranged between the beam splitter 3 and the diffracting means (double diffraction grating) 6, but as shown in FIG. The light means 10, that is, the grating lens or the lens member is provided in a partial region of the double diffraction grating 6 (for example, the diffraction grating 6a).
(On the surface of). Further, when the transmission / focusing means 10 is provided on the surface of the diffraction grating 6a, if the other diffraction grating 6b is provided with the area NL where the diffraction grating is not provided, as described above, the spot diameter of the focused light becomes smaller. Can be

In the above example, the transmission / condensing means 10 is provided on the diffraction grating 6a, but it may be provided on the diffraction grating 6b.

In the above example, the light receiving means 7 is
As shown in FIG. 17B, five-divided light receiving elements 7a, 7b,
7c, 7d, and 7e are used to detect the focus error signal, the track error signal, and the recording signal. However, for example, when it is not necessary to detect the track error signal, the light receiving means 7 has 3 as shown in
It is also possible to use the divided light receiving elements 7a ', 7b', 7e. In this case, the focus error signal is the difference (A'- between the outputs A'and B'of the two light receiving means 7a 'and 7b'.
B ′), and the recording signal can be detected by the light receiving element 7e having a small light receiving area arranged in the central portion.

In the above embodiment, the beam splitter 3 transmits the light from the light source 1 and the collimator lens 2 and reflects the reflected light from the record carrier 5, but the opposite is true. In addition, the light from the light source 1 and the collimator lens 2 may be reflected to enter the record carrier 5, and the light reflected from the record carrier 5 may be transmitted.

[0099]

As described above, according to the first and second aspects of the present invention, the focus error signal and the focus error signal are generated by making the parallel light from the transmitting / collecting means incident on the double diffraction grating. Since the recording signal can be detected by the focused light from the transmitting / focusing means while the track error signal can be detected, it is possible to use a light receiving element having a small light receiving area at the focusing position. The formed light receiving element can detect a recording signal at high speed and with high accuracy.

According to the first aspect of the present invention, the focused light from the transmitting / focusing means is prevented from diffracting in the double diffraction grating, so that the focused light has a plurality of luminous fluxes in the double diffraction grating. Therefore, the spot diameter of the focused light can be made smaller. As a result, it is possible to use a light receiving element having a smaller light receiving area, and it is possible to cope with lower cost and higher speed.

According to the third and fourth aspects of the invention, the parallel light from the transmitting / collecting means is input to the double diffraction grating.
Focus error signal and / or
A rack error signal can be detected, but a transmission / collection means
Since the recording signal can be detected by the focused light from the
A light receiving element with a small light receiving area can be used for the position.
The light receiving element made of normal light receiving element material,
The recording signal can be detected at high speed and with high accuracy. Well
In addition, since the transmission / condensing means is arranged in a part of the area of the double diffraction grating, the optical pickup can be further downsized.

[0102] According to the invention described in claim 5, wherein
3. The optical pickup according to claim 1 or 2 , wherein the transmitting / collecting means is provided on a side of the double diffraction grating on which reflected light from the record carrier is incident, and the double diffraction grating receives light. The diffraction grating on the side of the means has a region in which the diffraction grating is not provided, so that the device can be downsized and the light receiving element can be downsized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a displacement measuring device.

FIG. 2 is a diagram for explaining generation of interference fringes.

FIG. 3 is a diagram for explaining generation of interference fringes.

FIG. 4 is a diagram for explaining generation of interference fringes.

FIG. 5 is a diagram for explaining a method of measuring a minute displacement.

FIG. 6 is a diagram for explaining a method of measuring a minute displacement.

FIG. 7 is a diagram for explaining a method of measuring a minute displacement.

8A and 8B are views for explaining detection of a defocus amount of an object to be measured by the displacement measuring device of FIG.

9A and 9B are views for explaining detection of a defocus amount of an object to be measured by the displacement measuring device of FIG.

10 is a diagram for explaining detection of a defocus amount of the object to be measured by the displacement measuring device of FIG.

FIG. 11 is a diagram showing a light amount distribution of interference light depending on a defocus amount.

FIG. 12 is a diagram showing a change in output difference between two light receiving elements according to a change in defocus amount.

FIG. 13 is a diagram showing a configuration example of an optical pickup.

FIG. 14 is a diagram showing a configuration example of a light receiving unit.

FIG. 15 is a configuration diagram of an embodiment of an optical pickup according to the present invention.

16 is a diagram showing a configuration example of a grating lens used in the optical pickup of FIG.

FIG. 17 is a diagram for explaining the operation principle of the optical pickup according to the present invention.

FIG. 18 is a diagram showing a modified example of the optical pickup according to the present invention.

19 is a diagram showing a configuration example of a lens member used in the optical pickup of FIG.

FIG. 20 is a diagram showing a modified example of the optical pickup according to the present invention.

FIG. 21 is a diagram showing a modification of the optical pickup according to the present invention.

FIG. 22 is a diagram showing a configuration example of a light receiving unit.

[Explanation of symbols]

1 light source 2 Collimating lens 3 beam splitter 4 Objective lens 5 record carrier 6 Diffraction means 7 Light receiving means 10 Transmission / condensing means

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 09-7/22

Claims (5)

(57) [Claims] 1. A record carrier is focused and irradiated with light from a light source,
In an optical pickup that detects a recording signal and a focus error signal and / or a track error signal based on the reflected light from the record carrier, a part of the reflected light from the record carrier is transmitted and the other part is collected. And a light-transmitting / collecting means, a double diffraction grating on which the transmitted light from the transmitting / collecting means and the focused light are incident, and a light receiving means for receiving light from the double diffraction grating. The converged light of the transmitting / focusing means, which has undergone the double diffraction grating, is received by the light receiving means to detect a recording signal, and the transmitted light of the transmitting / focusing means is the dual light. The interference fringes generated by the diffraction grating are received by the light receiving means and the focus error signal and / or
Or it is designed to detect track error signals .
The focused light from the transmitting / focusing means is
Form the double diffraction grating to prevent diffraction at the child
Part of at least one of the two diffraction gratings
The optical pickup is characterized in that a region where no grating is provided is formed in . 2. The optical pickup according to claim 1, wherein the transmitting / collecting means is formed of a grating lens or a lens member having a part having a lens function and another part having no lens function. An optical pickup characterized in that 3. A record carrier is focused and irradiated with light from a light source,
Based on the reflected light from the record carrier, a recording signal and a focus signal are generated.
The dust error signal and / or the track error signal
In the optical pickup for detecting,
Transmission / condensation of transmitting part of the reflected light and condensing the other part
Means, and the transmitted light and the focused light from the transmitting / collecting means are incident.
To receive light from the double diffraction grating and
A light receiving means, which is the focused light of the transmitting / focusing means.
The light received by the double diffraction grating is received by the light receiving means.
The transmitted light of the transmitting / focusing means is detected by illuminating the recording signal.
And receive the interference fringes generated by the double diffraction grating.
Focus error signal and / or light received by the optical means
Or it is designed to detect track error signals.
Ri, in a partial region of the double diffraction grating, the optical pickup, wherein the transmission / converging means is disposed. 4. The optical pickup according to claim 3.
The transmitting / collecting means is a grating lens,
Rui partly has a lens effect and the other part has a lens effect
It is formed by a lens member having no
Optical pickup. 5. The optical pickup according to claim 1 or 2 , wherein the transmitting / focusing means is provided on a side of the double diffraction grating on which reflected light from the record carrier enters. An optical pickup characterized in that a region where no grating is provided is formed in a part of the diffraction grating on the light receiving means side of the multiple diffraction grating.