JPH06243481A - Objective lens position detecting method - Google Patents

Abstract

PURPOSE:To provide a objective lens position detecting method which can detect the position of an objective leans without attaching any position detecting member to the movable part of the objective lens. CONSTITUTION:An optical pickup which turns the luminux flux received from a laser light source 1 into the parallel lights by a collimator lens 2 and then condenses them on an optical information recording medium 6 as a minute optical spot by an objective lens 5 to record, reproduce or erase the information is provided. The means 7 and 8 which make the luminous flux incident on the lens 5 through the outside of the optical axis of the lens 5, reflect on the medium 6 and then converge on a photodetector 10 are also provided. The position of the lens 5 is detected by the signal of the photodetector 10. Thus it is possible to detect the position of the lens 5 without attaching any position detecting member to the movable part of the lens actuator. Therefore the size and the weight of the lens actuator can be reduced. Furthermore such problems of the lens 5 can be eliminated as optical axis shift and the defective operations that are caused in a tacking state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting an objective lens position of an optical pickup of an optical information recording / reproducing apparatus such as an optical disk drive.

[0002]

2. Description of the Related Art In an optical information recording / reproducing apparatus such as an optical disk drive for recording / reproducing information on / from an optical information recording medium such as an optical disk, generally, as shown in FIG. The groove 6b is provided, and recording / reproducing is performed by using a place called a land 6c between the guide grooves as a track. That is, an optical system called an optical pickup is used to collimate a light beam from a laser light source into parallel light, and then the parallel light is condensed as a minute light spot on a track of an optical information recording medium by an objective lens to record information. It is for reproducing or erasing. In addition, 6a in FIG. 8 is a transparent substrate,
6d is a recording layer. The track pitch of the optical information recording medium 6 is generally 1.6 μm, and when a spot having a diameter of about 1 μm narrowed by the objective lens 5 hits the track center, the reflected light passes through the transparent substrate 6 a and the objective lens 5. , Is guided to the two-division light receiving element 9 for track detection as a symmetrical reflection intensity distribution.

Here, the tracking accuracy required to follow the track is required to be 0.1 μm. For example, if a track shift occurs as shown in FIG. A difference occurs between the outputs of the light receiving section A and the light receiving section B, and the difference signal is fed back to the actuator of the objective lens as a tracking error signal, and the actuator drives the objective lens 5 in the track orthogonal direction so that the difference signal becomes zero. And correct it. However, when the tracking is performed for 20 to 30 μm, even if the spot is located at the center of the track and the intensity distribution of the reflected light amount is symmetrical, the optical axes of the objective lens 5 and the light receiving element 9 are displaced as shown in FIG. 8C. Occurs, the light flux entering the light receiving element 9 becomes asymmetrical, and the detection system determines that the tracking error occurs even though the tracking is normal, which causes a problem that accurate tracking cannot be performed.

In order to solve the above problem, there has been proposed a technique for correcting the optical axis shift by providing a means for detecting the position of the objective lens in the actuator of the objective lens and detecting the position of the objective lens in the tracking direction. (JP-A-62-139143). FIG. 9 shows an example of a conventional technique, and is a diagram schematically showing an objective lens actuator 30 of an optical pickup having an objective lens position detecting means. In FIG. 9, reference numeral 31 is a magnetic yoke,
Reference numeral 32 is a magnet, 33 is a bobbin for supporting the objective lens 5, 34 is a focusing coil wound around the bobbin 33 for driving the objective lens 5 in the optical axis direction, and 35 is for driving the objective lens 5 in the track orthogonal direction. Tracking coil, 36 is a leaf spring that supports the bobbin 33, 37
Is an aperture that is fixed to the bobbin and moves integrally with the objective lens, 38 is a light emitting diode (LED), 39 is a light receiving element for position detection, and 40 is a base of the actuator.
Although not shown, an optical pickup optical system (a movable part optical system in the case of a separation type optical pickup) including the objective lens actuator 30 shown in FIG. 9 is mounted on a carriage, and the carriage is orthogonal to a track by a known moving mechanism. The optical pickup optical system as a whole (the movable portion optical system in the case of a separation type optical pickup) is moved in the track orthogonal method when performing large tracking.

Now, in the actuator 30 shown in FIG. 9, when the objective lens 5 is tracked, the objective lens 5
An aperture 37 that moves integrally with the bobbin 33 that supports the LED is provided, and one end of the aperture 37 having the opening is provided with an LED.
38 is arranged in the optical path between the light receiving element 39 and the light receiving element 39, and the light receiving element 39 detects the irradiation position of the light passing through the opening on the light receiving surface to detect the position of the objective lens 5. That is, when the objective lens 5 deviates from the specified position range in which normal tracking can be performed, the irradiation position on the light receiving surface of the light receiving element 39 changes, so that the output of the light receiving element 39 changes,
The position of the objective lens 5 can be detected from the amount of change. Therefore, if this detection signal is fed back to the carriage moving mechanism and the carriage (entire optical pickup or movable part optical system) is moved, the optical axis deviation between the objective lens 5 and other optical systems such as the light receiving element will occur. It is corrected and can return to normal tracking operation.

[0006]

By the way, in the actuator 30 shown in FIG. 9, in order to detect the position of the objective lens 5, the position detecting aperture 37 is provided.
The position detection LED 38 and the light receiving element 39 are integrally provided on the bobbin 33 that supports the pedestal 40 of the actuator.
However, in order to provide the position detecting member such as the aperture 37 on the bobbin 33, which is the movable portion of the actuator, a considerable space is required and the actuator becomes large. The problem arises. Further, by mounting the aperture 37 on the movable portion side of the actuator 30, the movable portion becomes heavy and unbalanced, which may cause a malfunction during focusing or tracking. The present invention has been made in view of the above circumstances, and an objective lens position that enables position detection of an objective lens without attaching a position detecting member such as an aperture to a movable portion of an actuator for focusing and tracking of the objective lens. It is intended to provide a detection method.

[0007]

In order to achieve the above object, in the objective lens position detecting method according to the first aspect, after the light flux from the laser light source is made into parallel light, optical information is recorded as a minute light spot by the objective lens. In an optical pickup for recording / reproducing or erasing information by condensing on a medium, a light beam incident on the objective lens from outside the optical axis is reflected by the optical information recording medium and the reflected light is converged on a light receiving element. The position of the objective lens is detected from the signal of the light receiving element.

According to the objective lens position detecting method of claim 2,
In the objective lens position detecting method according to the first aspect, the light flux incident on the objective lens from outside the optical axis is a part of the parallel laser light flux. Further, in the objective lens position detecting method according to claim 3, in the objective lens position detecting method according to claim 1, the light beam incident on the objective lens from outside the optical axis is emitted from a light emitting element arranged outside the effective light beam of the parallel laser light beam. The luminous flux is

According to the objective lens position detecting method of claim 4,
After the light flux from the laser light source is collimated, it is reflected by the optical information recording medium in the optical pickup that records, reproduces, or erases information by focusing it on the optical information recording medium as a minute light spot by the objective lens. The light emitting element is arranged so as to enter the objective lens from outside the optical axis, and the light flux from the light emitting element is converged on the light receiving element arranged outside the effective light flux of the parallel laser light flux by the objective lens,
The position of the objective lens is detected from the signal of the light receiving element.

According to the objective lens position detecting method of claim 5,
In an optical pickup for recording / reproducing or erasing information by collimating a light beam from a laser light source into a small light spot by an objective lens on an optical information recording medium, the objective lens is off-axis. The incident light beam from the lens is reflected at the interface with the air of the objective lens, the reflected light is converged on the light receiving element arranged outside the effective light beam of the parallel laser light beam, and the position of the objective lens is detected from the signal of the light receiving element. It is characterized by

According to the objective lens position detecting method of claim 6,
In the objective lens position detecting method according to the fifth aspect, the light flux entering the objective lens from outside the optical axis is a part of the parallel laser light flux. Further, in the objective lens position detecting method according to claim 7, in the objective lens position detecting method according to claim 5, the light flux incident on the objective lens from outside the optical axis is emitted from a light emitting element disposed outside the effective light flux of the parallel laser light flux. It is a light flux.

According to the objective lens position detecting method of claim 8,
In the objective lens position detecting method according to any one of claims 1 to 7, the light receiving element is a two-divided light receiving element. Also,
According to the objective lens position detecting method of claim 9, the method of claim 1
In the objective lens position detecting method described in (1), the light receiving element is a non-divided irradiation position detecting element.

[0013]

In the objective lens position detecting method of the present invention,
A light beam incident on the objective lens from outside the optical axis is reflected by the optical information recording medium, the reflected light is converged on the light receiving element, and the position of the objective lens is detected from the signal of the light receiving element. In principle, the converging action of the objective lens is utilized, and as shown in FIG. 10, the condensing point of the light beam incident from the outside of the optical axis of the objective lens 5 moves on the optical axis C (the objective lens is large. The position of the objective lens is detected by utilizing the shift due to the tracking operation) and detecting the shift of the condensing point by the light receiving element. Therefore, according to the present invention, the detection member integrated with the movable portion of the objective lens actuator is unnecessary, and the position of the objective lens 5 can be detected without affecting the movable portion of the actuator at all.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the illustrated embodiments. FIG. 1 is a schematic diagram of an optical pickup optical system showing a first embodiment of the present invention. In the figure, reference numeral 1 is a semiconductor laser, 2 is a collimator lens, 3 is a beam splitter, 4 is a deflection prism, and 5 is an objective. A lens, 6 is an optical information recording medium such as an optical disk, 7 and 8 are mirrors, 9 is a two-divided light receiving element for track detection, and 10 is a light receiving element for objective lens position detection. In FIG. 1, a laser light flux emitted from a semiconductor laser 1 is collimated by a collimator lens 2 and most of the light flux is reflected by a deflecting prism 4 via a beam splitter 3 and is reflected by an objective lens 5 on an optical information recording medium 6. It is focused as a minute spot on the. Then, the reflected light from the optical information recording medium 6 becomes parallel light through the objective lens 5, enters the beam splitter 3 through the deflection prism 4, is reflected by the beam splitter 3, and is split into two for track detection. The light is incident on the light receiving portions A and B of the light receiving element 9,
Track detection and information detection are performed. Incidentally, FIG.
The focus signal detector and the objective lens actuator are not shown.

In the present embodiment, the beam splitter 3
The first mirror 7 is arranged in the optical path between the deflecting prism 4 and the deflecting prism 4, and the ineffective light flux which is not incident on the objective lens 5 as a part of the parallel light flux is reflected by the first mirror 7 and is extracted out of the optical path. The reflected light beam is reflected by the second mirror 8 toward the deflecting prism 4, is incident on the objective lens 5 as off-axis light from outside the optical axis of the objective lens 5 via the deflecting prism 4, and the converged light is recorded as optical information. The light is reflected by the medium 6 and enters the light receiving element 10 for detecting the position of the objective lens. The objective lens position detecting light receiving element 10 is, for example, a two-divided light receiving element as shown in FIG. 2, and as shown in FIG. 10, the condensing point of the light beam incident from the outside of the optical axis of the objective lens 5 is the objective lens. Since the optical axis C of 5 deviates due to the movement (a large tracking operation of the objective lens), the condensing point on the two-division light receiving element 10 moves in accordance with the movement of the objective lens 5, and both light receiving portions 10 of the two-division light receiving element 10 move.
A difference occurs between the outputs of a and 10b, and this difference signal becomes the objective lens position signal. That is, when the optical axis C of the objective lens 5 and the optical axes of other optical systems coincide with each other, the light-converging point of off-axis light is the light-receiving portions 10a of the two-divided light-receiving element 10 for detecting the objective lens position. If it is adjusted so as to be located at the center of 10b and the difference signal of the outputs of both the light receiving sections 10a and 10b at this time by the differential amplifier 20 is adjusted to 0,
When the objective lens 5 moves, the position of the objective lens can be easily detected from the signal of the differential amplifier 20. Then, if this signal is fed back to the carriage movement mechanism of the optical pickup, the optical axis shift of the objective lens 5 can be corrected,
Normal tracking operation can always be performed.

Next, FIG. 3 is a schematic view of an optical pickup optical system showing a second embodiment of the present invention. The optical pickup of the embodiment shown in FIG. 3 is a so-called separation type optical system, and the semiconductor laser 1, the collimator lens 2, the beam splitter 3, and the track detection light receiving element 9 are fixed to the fixed portion 1.
The movable part optical system 13 including the deflecting prism 4, the objective lens 5, and an actuator (not shown) is installed on the side of the optical disk 5 to seek the optical information recording medium 6 as a carriage. In this embodiment, a light emitting element 11 such as an LED is arranged outside the effective light flux of the parallel laser light flux as means for allowing the light flux to enter the objective lens 5 from outside the optical axis.
The light flux from is incident on the objective lens 5 as off-axis light, and the converged light is reflected by the optical information recording medium 6 and is incident on the light receiving element 12 for detecting the position of the objective lens. Here, the light receiving element 12 for detecting the objective lens position is an undivided irradiation position detecting element as shown in FIG. 4, and a difference occurs in the output signals from the left and right electrodes depending on the position of the condensing point on the light receiving surface. , Differential amplifier 2
If the difference signal is taken by 1, it becomes a position detection signal. In the case of a non-divided irradiation position detection element, since there is no division line, it is difficult to understand the center position and it is difficult to adjust the position of the focusing point at the time of assembly, but as shown in FIG. The differential amplifier 22 and the initial offset setting circuit 23 of
An initial offset setting circuit 23 sets an initial value as an offset so that the output of the second differential amplifier 22 becomes 0 when the optical axis of the objective lens 5 and the optical axes of other optical systems coincide with each other. If so, the position of the objective lens 5 can be easily detected from the signal of the second differential amplifier 22, and the strict position adjustment of the non-divided irradiation position detection element 12 becomes unnecessary.

In FIG. 3, the arrangement of the light emitting element 11 and the light receiving element 12 is reversed, and the light flux from the light emitting element (11) is reflected on the optical information recording medium 6 and then enters the objective lens 5 from outside the optical axis. Even if the objective lens 5 converges the light flux from the light emitting element (11) on the light receiving element (12) arranged outside the effective light flux of the parallel laser light flux, the position of the objective lens is similarly detected. be able to.
Further, in the present embodiment, the example in which the non-divided irradiation position detection element 12 is used as the light receiving element for detecting the objective lens position is shown, but a two-divided light receiving element may be used. Further, similarly, the non-divided irradiation position detecting element 12 can be used as the light receiving element for detecting the objective lens position in the embodiment of FIG.

Next, FIG. 5 is a schematic view showing only a main part of an optical pickup optical system showing a third embodiment of the present invention.
In the present embodiment, as in FIG. 1, a part of the incident light flux (parallel laser light flux) is used as the off-axis light incident on the objective lens 5, and (a) reflects the light flux on the two surfaces of the prism 16. Objective lens 5 through the deflection prism 4
Is received as off-axis light, is reflected by the upper surface (interface of the objective lens with air) 5a of the objective lens 5, and the reflected light is again arranged outside the effective light flux of the parallel laser light flux via the deflection prism 4. It converges on the element 12 and detects the position of the objective lens 5 from the signal of the light receiving element 12. The surface of the objective lens 5 (the interface with air when it is composed of a plurality of lenses) generally has about 2% of reflected light, and this embodiment uses the reflection and condensing property of the interface 5a with the air of the objective lens 5. Then, it is possible to detect the objective lens position equivalent to that in FIG. The prism for extracting the light flux may be a refraction type prism 16 'as shown in FIG. 5 (b). Further, in the illustrated example, the non-divided irradiation position detecting element is used as the light receiving element 12 for detecting the objective lens position, but a two-divided light receiving element can also be used.

Next, FIG. 6 is a schematic view showing only a main part of an optical pickup optical system showing a fourth embodiment of the present invention.
In the present embodiment, similar to the embodiment of FIG. 5, the reflection and converging property of the surface (interface with air) 5a of the objective lens 5 is utilized, but the light flux entering the objective lens 5 from outside the optical axis. Is a light flux from a light emitting element 11 such as an LED arranged outside the effective light flux of the parallel laser light flux, and the light flux from the light emitting element 11 is incident on the objective lens 5 via the deflection prism 4 and then on the surface 5a of the objective lens 5. The light flux is reflected and converged again on the light receiving element 10 via the deflecting prism 4, and the position of the objective lens 5 is detected. In the illustrated example, a two-divided light receiving element is used as the light receiving element 10 for detecting the objective lens position, but a non-divided irradiation position detecting element can also be used.

Now, as shown in the above four embodiments, in the present invention, the position of the objective lens 5 is detected by utilizing the condensing action of the objective lens 5 itself, and the light flux incident from outside the optical axis of the objective lens 5 is used. The position of the objective lens is detected by utilizing the fact that the light-condensing point of (1) shifts due to the movement of the optical axis (tracking of the objective lens), and the light-receiving element detects the shift of the light-condensing point. Since it is not necessary to attach a position detecting member such as the aperture shown in FIG. 2 to the movable portion of the lens actuator, the actuator can be made smaller and lighter, and the movable portion of the actuator is not adversely affected. Therefore, according to the present invention, it is possible to solve the problem of the optical axis shift of the objective lens during tracking without increasing the size of the lens actuator. In each embodiment, the members 7, 8, 16, 16 'for extracting the light beam or the light emitting element 11 and the light receiving elements 10, 12 are arranged in the carriage, but like the separation type optical system shown in FIG. When the movable part optical system and the fixed part optical system are separated from each other, the light beam extracting members 7, 8, 16, 16 ′ or the light emitting element 1
1, and the light receiving elements 10 and 12 are arranged on the movable section optical system side.

[0021]

As described above, in the objective lens position detecting method according to the first aspect, the condensing point of the light beam incident from outside the optical axis of the objective lens is caused by the movement of the optical axis (tracking of the objective lens). The position of the objective lens is detected by detecting the shift of the condensing point by the light receiving element by utilizing the shift, so that the detection member is integrated with the movable portion of the focusing and tracking actuator of the objective lens. Therefore, the position of the objective lens can be detected without affecting the movable part of the actuator.
Therefore, according to the present invention, it is possible to reduce the size and weight of the objective lens actuator, and it is possible to solve the problem of the optical axis shift of the objective lens during tracking and the problem of malfunction.

According to the objective lens position detecting method of claim 2,
In the objective lens position detecting method according to the first aspect, since a part of the parallel laser light flux (ineffective light flux) is used as the light flux incident on the objective lens from outside the optical axis, no special light emitting element is required. Further, in the objective lens position detecting method according to claim 3, in the objective lens position detecting method according to claim 1, a light beam emitted from a light emitting element arranged outside the effective light beam of the parallel laser light beam as a light beam entering the objective lens from outside the optical axis. Since the luminous flux is used, an optical member for taking out the parallel laser luminous flux is unnecessary and an off-axis luminous flux can be easily produced. Claim 4
According to the objective lens position detecting method of (1), the same operational effects as those of the first and third aspects can be obtained.

In the objective lens position detecting method of the fifth aspect, a light beam entering the objective lens from outside the optical axis is reflected at the interface of the objective lens with the air, and the reflected light is outside the effective light beam of the parallel laser light beam. It converges on the placed light receiving element,
Since the position of the objective lens is detected from the signal of the light receiving element, the detection system can be arranged between the objective lens and the fixed optical system,
It is not necessary to dispose a light receiving element, a light emitting element, or the like outside, and it is possible to prevent deterioration due to adhesion of dust or the like.

According to the objective lens position detecting method of claim 6,
In the objective lens position detecting method according to the fifth aspect, since a part of the parallel laser light flux (ineffective light flux) is used as the light flux incident on the objective lens from outside the optical axis, no special light emitting element is required. Further, in the objective lens position detecting method according to claim 7, in the objective lens position detecting method according to claim 5, a light beam emitted from a light emitting element arranged outside the effective light beam of the parallel laser beam as the light beam entering the objective lens from outside the optical axis. Since the luminous flux is used, an optical member for taking out the parallel laser luminous flux is unnecessary and an off-axis luminous flux can be easily produced.

According to the objective lens position detecting method of claim 8,
In the objective lens position detecting method according to any one of claims 1 to 7, since a two-divided light receiving element is used as a light receiving element, it is set to 2 in the initial state where the optical axis of the objective lens and the optical axis of another optical system are coincident with each other.
The position can be adjusted easily by arranging so that the condensing point of the off-axis light is located at substantially the center position of both light receiving surfaces of the split light receiving element, that is, the dividing line position. The position signal of the objective lens can be obtained from In the objective lens position detecting method according to claim 9, since the undivided irradiation position detecting element is used as the light receiving element in the objective lens position detecting method according to any one of claims 1 to 7, the optical axis of the objective lens and the optical axis of another optical system are used. When the initial state is coincident with each other, it is arranged so that the condensing point of the off-axis light is located in the approximate center of the light receiving surface, and if the initial value of the output signal at this time is set as an offset, the position signal of the objective lens is directly The position can be adjusted more roughly than in the case of using the two-divided light receiving element. Further, since there is no dividing line on the light receiving surface, the linearity of the position signal is good.

[Brief description of drawings]

FIG. 1 is a schematic view of an optical pickup optical system showing a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a light receiving element for detecting an objective lens position.

FIG. 3 is a schematic view of an optical pickup optical system showing a second embodiment of the present invention.

FIG. 4 is a diagram showing another example of the light receiving element for detecting the position of the objective lens.

5A is a schematic view showing only a main part of an optical pickup optical system showing a third embodiment of the present invention, and FIG. 5B is a view showing another example of a light beam extraction prism. .

FIG. 6 is a schematic view showing only a main part of an optical pickup optical system showing a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing an example of an objective lens position signal detection system when a non-divided irradiation position detection element is used as a light receiving element for detecting an objective lens position.

8A and 8B are principle explanatory views showing an example of a track detection method of an optical pickup, FIG. 8A is a view showing a state and a reflection intensity distribution when a spot is on a track, and FIG. FIG. 9C is a diagram showing a state and a reflection intensity distribution when the spot is on the track, and FIG. 7C is a diagram showing a state and a reflection intensity distribution when the optical axis of the objective lens is deviated from the optical axis of the light receiving element. .

FIG. 9 is a diagram showing an example of a conventional technique, and is a perspective view schematically showing an actuator for an objective lens of an optical pickup.

FIG. 10 is a diagram illustrating the principle of the objective lens position detecting method according to the present invention.

[Explanation of symbols]

1 ... Semiconductor laser 2 ... Collimator lens 3 ... Beam splitter 4 ... Deflection prism 5 ... Objective lens 6 ... Optical information recording medium 7, 8 ... For extracting parallel laser beam Mirror 9 ... 2-division light receiving element for track detection 10 ... Light receiving element for objective lens position detection (2-division light receiving element) 11 ... Light emitting element 12 ... Light receiving element for objective lens position detection (non-divided irradiation Position detection element) 13 ... Movable part optical system 15 ... Fixed part optical system 16, 16 '... Prism for parallel laser beam extraction C ... Optical axis of objective lens

Claims (9)

[Claims] 1. An optical pickup for recording / reproducing or erasing information by collimating a light beam from a laser light source into a parallel light beam and forming a minute light spot on the optical information recording medium by the objective lens. On the other hand, the objective lens position is characterized in that a light beam entering from outside the optical axis is reflected by the optical information recording medium, the reflected light is converged on the light receiving element, and the position of the objective lens is detected from the signal of the light receiving element. Detection method. 2. The objective lens position detecting method according to claim 1, wherein the light beam entering the objective lens from outside the optical axis is a part of the parallel laser light beam. 3. A method of detecting the position of an objective lens according to claim 1, wherein the light beam incident on the objective lens from outside the optical axis is a light beam from a light emitting element arranged outside the effective light beam of the parallel laser light beam. Objective lens position detection method. 4. An optical information recording in an optical pickup for recording / reproducing or erasing information by collimating a light beam from a laser light source into a parallel light and then focusing it on an optical information recording medium as a minute light spot by an objective lens. The light emitting element is arranged so that it is incident on the objective lens from outside the optical axis after being reflected on the medium, and the light beam from the light emitting element is converged by the objective lens on the light receiving element placed outside the effective light beam of the parallel laser light beam. And detecting the position of the objective lens from the signal of the light receiving element. 5. An optical pickup for recording / reproducing or erasing information by condensing a light beam from a laser light source into a parallel light and then focusing it on an optical information recording medium as a minute light spot by the objective lens. On the other hand, a light beam incident from outside the optical axis is reflected at the interface with the air of the objective lens, and the reflected light is converged on a light receiving element arranged outside the effective light beam of the parallel laser light beam, and the objective lens is obtained from the signal of the light receiving element. A method for detecting the position of an objective lens, characterized in that the position of the lens is detected. 6. The objective lens position detecting method according to claim 5, wherein the light beam entering the objective lens from outside the optical axis is a part of the parallel laser light beam. 7. The objective lens position detecting method according to claim 5, wherein the light flux incident on the objective lens from outside the optical axis is a light flux from a light emitting element arranged outside the effective light flux of the parallel laser light flux. Objective lens position detection method. 8. An objective lens position detecting method according to claim 1, wherein the light receiving element is a two-divided light receiving element. 9. The objective lens position detecting method according to claim 1, wherein the light receiving element is a non-divided irradiation position detecting element.