JPH09223328A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head recording/reproducing information on two kinds of optical disks with different thickness of transparent substrates. SOLUTION: Light A in a divergent state radiated from a semiconductor laser 1 provided on a specified position is divided into two luminous fluxes B, C by a beam splitter 2, and the optical path lengths of two luminous fluxes B, C divided by the beam splitter 2 are adjusted by using an optical path length adjusting optical path and an optical path length adjusting lens 10. Further, by varying the optical path length of the optical path length adjusting optical path and by automatically focusing, the outgoing light from an objective lens 6, on which two luminous fluxes B, C are made incident, are respectively image- formed on prescribed two different positions on an optical axis. Further, recording information is recorded on an optical disk D and reproduced from the optical disk D by the light modulated by optical modulators provided in individual path parts of two luminous fluxes B, C. Further, a spherical aberration is prevented from occurring by the spherical aberration correcting member 9 of the objective lens 6 provided in the optical path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head, in particular, two types of optical discs configured such that the distance from the surface of the transparent substrate to the signal surface is different, or from the surface of the transparent substrate to the signal surface. , An optical pickup used for reading recorded information from an optical disc having a two-layer structure provided with two signal surfaces having different distances, and a recording / reproducing device capable of optically recording and reproducing information on the optical disc. The present invention relates to an optical head such as an optical recording / reproducing element.

[0002]

2. Description of the Related Art With the increasing demand for recording various information signals at a high recording density, in recent years, high density recording and reproduction of information signals has been performed by information recording media made on the basis of various constitutional principles and operating principles. Was started. For example, magnetic recording according to an information signal is performed on a ferromagnetic recording layer of the information recording medium, or recording / reproducing is performed using a magneto-optical recording medium, or an information signal is recorded on the signal surface of the information recording medium. It has already been practically practiced to form an unevenness according to the above to record an information signal and reproduce the recorded information signal by an optical means.

Since it has become possible to easily obtain a semiconductor laser that operates stably, various optical recording media (hereinafter referred to as an optical disk It may be listed)
However, since it is possible to perform recording and reproduction in a non-contact state, it is resistant to scratches and dust, and has the advantage that a large storage capacity can be obtained by high-density recording.
Alternatively, it is well known that research and development for practical use are currently underway, and a large amount of information signals are recorded from the master in which information signals are recorded by pits formed as geometric recesses or protrusions. As a duplicated recorded optical disc (playback-only optical disc), for example, a compact disc is widely used, and as a rewritable optical disc, for example, a magneto-optical disc and other optical discs such as an office file memory and other uses. Has been put into practical use in.

By the way, an optical head (optical pickup) used for optically reading an information signal from the above-mentioned optical disk, as is well known, includes a component for handling an optical signal of recorded information, an automatic focus control system, The automatic tracking control system, the automatic tilt control system, and other components for automatic control are included. That is, the optical head makes reproduction light emitted from, for example, a semiconductor laser incident on an objective lens through an afocal optical system or without an afocal optical system, and determines a predetermined amount from a surface of a transparent substrate of an optical disc. A minute light spot of the reproduction light focused by the objective lens is imaged on the signal surface provided at a predetermined distance, and a minute light spot of the reproduction light formed on the signal surface. The reflected light from is given to, for example, a so-called 4-division photodetector via an optical system including at least an objective lens, and an adder and subtraction connected to the 4-division photodetector. A recording information signal, a focus error signal, a tracking error signal, and the like can be output from an arithmetic circuit including a container and the like.

The above-mentioned optical head is required to have a different optical system configuration corresponding to the difference in the structure of the optical disk to be reproduced.
That is, since the CD (compact disc) which has been widely spread as one of the optical discs has a signal surface at a position 1.2 mm from the surface of a transparent substrate, the above-mentioned optical head for CD reproduction is transparent. It is possible to excellently perform the reading operation of the information signal from the optical disc having the signal surface at a position 1.2 mm from the surface of the substrate. However, recently, as an optical disc capable of higher density recording than a CD, an optical disc in which a signal surface is installed at a position of 0.6 mm from the surface of a transparent substrate, or from the surface of a transparent substrate, for example, In addition to the signal surface being installed at a position of 0.6 mm, an optical disc having a laminated structure in which the signal surface is installed at a position 1.2 mm from the surface of the transparent substrate has also appeared.

As described above, the optical head is required to have a different optical system configuration corresponding to the difference in the structure of the optical disk to be reproduced by the optical head. , An optical head for reproducing a CD (compact disc) having a structure in which a signal surface is set at a position 1.2 mm from the surface of the transparent substrate is used. It is not possible to accurately read an information signal from an optical disc having a structure in which the signal surface is installed at a position of 0.6 mm.
In order to solve the above-mentioned problem, conventionally, as disclosed in, for example, JP-A-6-259804, two semiconductor lasers are used, and one of the two semiconductor lasers is used. Using the radiated laser beam, an information signal can be read from a CD (compact disc) having a structure in which the signal surface is installed at a position 1.2 mm from the surface of the transparent substrate. In addition, using a laser beam emitted from the other one of the two semiconductor lasers described above, a signal surface is installed at a position of 0.6 mm from the surface of the transparent substrate. There has been proposed an optical head configured to read an information signal from an existing optical disc.

Another proposal that can solve the above-mentioned problem is, for example, in 19p-S-4 "Bifocal optical head (I)" of the autumn 1994 academic conference of Applied Physics, one semiconductor. The laser light emitted from the laser is collimated by the lens for adjusting the optical path length and then incident on the objective lens through the hologram element.
An optical head configured to generate a minute light spot by reproduction light on both the signal surface installed at the position m and the signal surface installed at a position 0.6 mm from the surface of the transparent substrate. It is disclosed.

[0008]

However, in the former solution of the above-mentioned two proposals, in the signal surface provided individually at two positions having different distances from the surface of the transparent substrate of the optical disk. There is a problem that a dedicated semiconductor laser is required as a light source of reproduction light used for reading an information signal from one specific one, and the latter solution among the above-mentioned two already proposed. There is only one reproduction light source used for reading an information signal from a signal surface provided separately at two positions with different distances from the surface of the transparent substrate of the optical disk, but the objective Since the hologram element is provided in the afocal optical system up to the lens, the predetermined reproduction operation cannot be performed unless the stability of the laser light source is maintained at a high level. In a problem, the appearance of their problem-free optical head has been determined.

The optical head described so far has been an optical pickup used for reading recorded information from a recorded optical recording medium (optical disk). For example, from the surface of a transparent substrate. Using an optical disk having an optical recording layer formed on the signal surface installed at one position or both of the position of 0.6 mm and the position of 1.2 mm from the surface of the transparent substrate, the above is described. Equipped with a recording / reproducing function capable of optically recording an information signal to be recorded on an optical recording layer of an optical disc and reading the information signal from the optical disc having the information signal recorded on the optical recording layer. The advent of optical heads was also highly anticipated.

Further, as described above, an optical disc having a signal surface at both the position of 0.6 mm from the surface of the transparent substrate and the position of 1.2 mm from the surface of the transparent substrate,
Since it is not possible to fabricate the distance between the two signal surfaces to be exactly constant over the entire signal surface thereof, even if the distance between the two signal surfaces in the optical disk to be recorded / reproduced varies, The optical recording layer of the optical disc is capable of properly recording the information signal to be recorded and reading the information signal from the signal surface on which the information signal is recorded. Was needed and a good solution to do so was sought.

[0011]

The optical head of the present invention comprises:
The divergent light emitted from one light source (for example, one semiconductor laser) provided at a specific position is split into two light beams by a beam splitter, and one of the two light beams is The light flux passes through the first optical path and the second optical path to enter the objective lens, and a minute light spot due to the light emitted from the objective lens is at a first distance from the surface of the transparent substrate of the optical disc. An image is formed at the position of the signal surface to be installed, and the other light beam of the two light beams split by the beam splitter is passed through the optical path for adjusting the optical path length and then the second light beam. The position of the signal surface, which is made to enter the objective lens through the optical path and emitted from the objective lens at a second distance smaller than the first distance from the surface of the transparent substrate of the optical disc. Second
And a reflected light beam from the first minute light point and a reflected light beam from the second minute light point. The reflected light flux which is being focused on and is being focused and is emitted from the objective lens by a beam splitter.
One of the two split reflected light fluxes described above is
The reflected light flux from the first minute light spot is made incident on the first photodetector provided near the position where an image is formed, and the other of the two divided light fluxes described above is described above. The reflected light beam from the second minute light spot is made incident on the second photodetector provided near the position where the image is formed, so that the signals can be individually reproduced from the two signal surfaces of the optical disk. During the reproducing operation, the objective lens is displaced on the optical axis by the actuator of the automatic focus control system of the objective lens to which the focus error signal obtained based on the detected force from the first photodetector is given. , The first minute light spot is always imaged at the position of the signal surface installed at the first distance from the surface of the transparent substrate of the optical disc, and the first light spot from the second photodetector The optical path length of the optical path length adjusting optical path is changed by an actuator of the optical path length adjusting optical path of the optical path length adjusting optical path to which a focus error signal obtained based on the detected force is applied, so that the second minute optical point is recorded on the optical disk. The image is always formed at the position of the signal surface installed at the second distance from the surface of the transparent substrate. In addition, as described above, the same objective lens is used to actually form an image on each of the above-mentioned signal surfaces based on the image formation at the two signal surface positions at different distances from the surface of the transparent substrate of the optical disk. If spherical aberration that cannot be ignored occurs with,
A member for correcting spherical aberration of an objective lens in a predetermined one optical path of two optical paths for individually passing two light fluxes obtained by splitting a divergent light emitted from a laser light source by a beam splitter. Is provided to enable good correction. The light in a divergent state emitted from one light source (for example, one semiconductor laser) provided at the specific position is split into two light beams by a beam splitter,
One of the two light beams is caused by the light emitted from the objective lens after passing through the first optical path including the optical modulator and the second optical path to enter the objective lens. The minute light spot is the first from the surface of the transparent substrate of the optical disc.
The image is formed on the optical recording layer installed at a distance of 2 mm, and the other light beam of the two light beams split by the beam splitter passes through the optical path length adjusting optical path provided with the optical modulator. After that, the light emitted from the objective lens by being incident on the objective lens via the second optical path is coupled to the optical recording layer provided at the second distance from the surface of the transparent substrate of the optical disc. By forming an image, an information signal can be recorded in the optical recording layer provided on the optical disc. Further, as described above, one of the two light fluxes obtained by dividing the light in a divergent state emitted from one semiconductor laser provided at a specific position into two light fluxes by a beam splitter, It is also possible to configure the optical head so that the optical path length adjusting optical path using an optical path length adjusting lens (for example, a collimating lens) is passed. As described above, in the optical head of the present invention, the optical path lengths of the two light beams obtained by dividing the reproduction light in a divergent state emitted from one semiconductor laser provided at a specific position of the optical pickup into two are obtained. By adjusting using the optical path length adjusting optical path and the optical path length adjusting lens, the outgoing light from the one objective lens on which the two light fluxes are incident is determined in advance on the optical axis. Can be imaged at two different positions, and
The optical system including the objective lens has a predetermined optical axis 2
Since one of the two different positions does not cause spherical aberration, the other of the predetermined two different positions on the optical axis described above has a spherical surface. Although aberration will occur, spherical aberration can also be prevented from occurring at the other position by the action of the spherical aberration correcting member of the objective lens provided in the optical path. When two different predetermined positions on the optical axis are close to each other, no problematic spherical aberration occurs even if the above-mentioned spherical aberration correcting member of the objective lens is not used. Of course, you can do so.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific contents of the optical head of the present invention will be described in detail below with reference to the accompanying drawings. 1 to 8 are block diagrams showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element,
9 to 12 are block diagrams showing a schematic configuration when the optical head of the present invention is implemented as an optical pickup, FIG. 13 is a cross-sectional view showing a configuration example of an optical disc, and FIG. 14 is an optical modulator. It is a figure for explanation. In FIGS. 1 to 12, reference numeral 1 denotes one semiconductor laser used as a light source. The light source 1 in the optical head shown in FIGS. 1 to 8 is one semiconductor laser used by switching between the recording light source and the reproducing light source, and FIGS. The light source 1 in the optical head shown in (1) is one semiconductor laser used for reproduction.

In each figure, 2 to 5 are beam splitters (half prisms, half mirrors), 6 is an objective lens, 7 and 8 are total reflection mirrors, 9 is a spherical aberration correction member of the objective lens, and 10 is an optical path. A length adjusting lens, 11 and 12 are photodetectors, 13 is a focusing lens, D is an optical disk,
Reference numerals 17 and 18 in FIGS. 1 to 8 denote optical modulators. In addition,
The optical head of the present invention illustrated in FIGS. 1 to 12 shows a configuration example in which the spherical aberration correcting member 9 of the objective lens is provided in the optical path for adjusting the optical path or in the first optical path. As will be described later, when the difference between the distances L1 and L2 from the surface of the transparent substrate 14 to the signal surface at different positions on the optical disk D to be reproduced by the optical head is small, the above-mentioned objective is used. Of course, it is not necessary to use the spherical aberration correction member 9 of the lens.

First, the optical disc D illustrated in FIG.
In the figure, 14 is a transparent substrate, and 15 and 16 are signal surfaces. On the signal surfaces 15 and 16 of the optical disc D (recorded optical recording medium), sequential channel words formed by channel bits obtained by converting a data word to be recorded and reproduced according to a predetermined modulation method. The mark recording method is applied to record information in the form of marks (pits) and non-marks (lands), and a reflective surface for reproducing light is formed on the signal surface. In FIG. 13, 14a is the surface of the transparent substrate 14, and the reproduction light emitted from the objective lens 6 is incident on the optical disc D from the surface 14a of the transparent substrate 14. FIG. 13A shows the signal surface 1 at a position L1 (first distance) from the surface 14a of the transparent substrate 14.
5 shows an example of the structure of an optical disc D in which the optical disc 5 is provided.

Further, FIG. 13B shows an optical disc D in which the signal surface 16 is provided at a position (second distance) of L2 (where L2 <L1) from the surface 14a of the transparent substrate 14.
13C shows an example of the configuration of FIG. 13, and FIG. 13C shows the signal surface 15 at a position L1 from the surface 14a of the transparent substrate 14.
From the surface 14a of the transparent substrate 14 (where L2 <
An example of the configuration of an optical disc D provided with a signal surface 16 at a position L1), that is, an optical disc having a configuration in which two signal surfaces 15 and 16 are laminated is shown.
For example, in a compact disc (CD), the signal surface is arranged at a distance of 1.2 mm from the surface 14a of the transparent substrate 14, and high density recording is performed as compared with the above-mentioned CD, for example, a digital video disc. (DVD)
Then, the signal surface is 0.6 m from the surface 14a of the transparent substrate 14.
The position of a distance of m, or the signal surface is formed at a position of a distance of 0.6 mm and 1.2 mm from the surface 14a of the transparent substrate 14. An optical recording layer is provided at the above-mentioned position of the signal surface in an optical disc which is not only for reproduction but also for recording.

By the way, the objective lens 6 used as a constituent member of the optical head (optical recording / reproducing element, optical pickup) is originally designed as an optical disk D to be reproduced by the optical head, and thus the optical disk D has a configuration. Since the spherical aberration is satisfactorily corrected when the reproducing operation is performed, the optical disk D in the configuration mode planned as the optical disk D to be reproduced is, for example, the transparent substrate 14 Assuming that the configuration is such that the signal surface 15 is provided at the position from the surface 14a to L1 of the transparent substrate 14, the signal surface 16 is provided at the position from the surface 14a to L2 of the transparent substrate 14 by the optical head. When the reproduction operation is performed by using the optical disk D having the above configuration as the reproduction target optical disk, the difference in the thickness of the transparent substrate 14 is used. Small light spot on have the signal surface becomes what has spherical aberration.

Therefore, the divergent reproduction light A emitted from one light source 1 (semiconductor laser 1) provided at a specific position of the optical head is divided into two by the beam splitter 2, and two reproduction light beams are obtained. 2 set individually for B and C
The optical path lengths of the two optical paths are adjusted by using the optical path length adjusting optical path and the optical path length adjusting lens 10 so as to have predetermined different optical path lengths. When the light emitted from the single objective lens 6 on which the light flux of C is incident is made to form images at image formation points at two different predetermined positions on the optical axis, the above-mentioned two reproductions are performed. With one reproduction light beam B (or C), which is one of the predetermined ones of the light beams B and C, spherical aberration occurs at an image forming point at one of the two predetermined positions on the optical axis. Of the two reproduction light beams B and C described above, one of the predetermined reproduction light beams B (or C) of the two reproduction light beams B and C described above is used when the objective lens 6 is designed to exhibit a characteristic that does not cause Other reproduction light flux C (or B By, so that the spherical aberration occurs at the imaging point of the other positions of the predetermined two different positions on the optical axis described above.

Therefore, in the optical head of the present invention, the spherical aberration correcting member 9 of the objective lens is provided in a predetermined optical path so that spherical aberration does not occur at the image forming point at the other position. The spherical aberration correction member 9 of the objective lens is provided so that spherical aberration does not occur. As the spherical aberration correcting member 9 of the objective lens described above, for example, a transparent plate having a predetermined thickness and having a suitable refractive index can be used, and as the spherical aberration correcting member 9 of the objective lens, the optical path length adjustment is performed. The optical element may be configured so that it can also be used as an optical element. When the image forming points at two different predetermined positions set on the optical axis are close to each other, the objective lens is used at a position intermediate between the distances between the two adjacent image forming points. If an objective lens designed to satisfactorily correct spherical aberration when the image forming point is generated is used, the spherical aberration correcting member 9 of the objective lens described above is not particularly used. Needless to say, it is possible to prevent spherical aberration that becomes a problem.

As described above, the divergent reproduction light A emitted from one light source 1 provided at a specific position of the optical head.
Is split into two by the beam splitter 2
The two reproduction light beams B and C emitted from the laser beam are made incident on the common objective lens 6 after passing through the individually set optical paths, and the position of the image forming point of the reproduction light beam B formed by the objective lens 6 and In order to set the position of the image forming point of the reproduction light beam C imaged by the objective lens 6 to two specific positions separated by a predetermined distance on the optical axis, the reproduction light beam described above is used. It is necessary that the optical path length of the B optical path and the optical path length of the reproduction light flux C described above are set to specific optical path lengths different from each other.

Therefore, in the optical head of the present invention, the optical path length of the reproduction light beam B and the optical path length of the reproduction light beam C are set to predetermined optical path lengths, respectively.
The optical path length is adjusted, and as the above-mentioned optical path length adjusting means, an optical path length adjusting optical path, an optical path length adjusting means such as the optical path length adjusting lens 10 or the like is used, and The optical path length of the optical path and the optical path length of the reproduction light flux C are set to predetermined optical path lengths.

First, the optical head of the present invention shown in FIGS. 1 to 8, that is, the optical head used as an optical recording / reproducing element for both recording and reproduction will be described.
The optical head of the present invention shown in FIG. 1 to FIG. 8 is an optical path of a side path (detour) type with respect to the first optical path formed between the beam splitter 2 and the beam splitter 3, that is, The beam splitter 2 → total reflection mirror 7 → total reflection mirror 8 → beam splitter 3 is provided with an optical path for adjusting the optical path length, and an optical modulator 18 is provided in the first optical path. Further, the optical modulators 17 are provided in the optical paths for adjusting the optical path length.

As the above-mentioned optical modulator 17 (18), an optical modulator formed by using an acousto-optical light modulating element, an optical modulator formed by using an electro-optical light modulating element,
Among various optical modulators such as an optical modulator configured using a magneto-optical light modulator, one having a desired characteristic can be selected and used. FIG. 14 is a diagram showing a schematic configuration of an example of an optical modulator configured by using an acousto-optic optical modulator as the optical modulators 17 and 18, and in FIG.
Is an acousto-optic member made of a material having an acousto-optic effect, 19 is an electro-acoustic conversion element (for example, a piezoelectric vibrating element), 21 is a sound absorbing material layer, and 17a (18a) is an input of a high frequency electric signal for modulation. It is a terminal. Examples of the material having the acousto-optic effect described above include TeO2, PbMoO4,
Tellurium glass, heavy flint glass, etc. are used.

The optical modulator 17 (18) described above is supplied from a modulation signal generator (not shown) to the optical modulator 17 (18).
A high frequency electric signal for modulation is supplied to the input terminal 17a (18a) of the. Input terminal 1 of optical modulator 17 (18)
The modulation signal generator for supplying a high frequency electric signal for modulation to 7a (18a) uses, for example, a carrier wave of a predetermined high frequency by a modulation signal having a frequency value which is a fraction of the frequency of the carrier wave or less. It is configured so that a frequency-modulated wave signal obtained by frequency modulation can be output. Then, the input terminal 17a of the optical modulator 17 (18) described above.
The ultrasonic vibration generated by the piezoelectric vibrator 19 driven by the high-frequency electric signal for modulation supplied via (18a) travels in the acousto-optic member 20 as a traveling wave, whereby The refractive index of the optical member is periodically changed, and the acousto-optical member 20 functions as a diffraction grating with respect to the light Li incident on it.

Therefore, the light incident on the wavefront of the traveling wave of the ultrasonic wave traveling in the acousto-optic member 20 at a specific angle (Bragg angle) is incident at the specific angle by the diffraction grating. The light is diffracted in the direction opposite to the direction and emitted from the acousto-optic member 20. (L in FIG. 14
1). As described above, the ultrasonic wave generated in the piezoelectric vibrator 19 and propagating in the acousto-optic member 20 as a traveling wave is not reflected on the end surface of the acousto-optic member 20 facing the end surface where the piezoelectric vibrator 19 is provided. The sound absorbing material layer 21 provided so as to function as the terminal end prevents the reflected wave from being converted into heat energy.

In the optical modulator 17 (18) illustrated in FIG. 14, the incident light Li is the light source 1 (semiconductor laser).
The recording laser beam or the reproducing laser beam emitted from the laser beam is a laser beam having a light intensity in a state of being divided into ½ by the beam splitter 2. The laser light to be emitted from the laser light source 1 is generated by an optical head including the optical recording / reproducing element illustrated in FIGS. 1 to 8 as an information signal on the optical recording layer of the optical disc. When the operation mode is set to perform the recording operation, the optical intensity is set so that the information signal can be satisfactorily recorded on the optical recording layer of the optical disc D, and FIGS. The optical head performs the recording operation so that the optical head has a sufficiently small light intensity necessary for performing the reading operation of the information signal recorded on the signal surface of the optical disk. The light intensity of the laser light emitted from the light source 1 is switched between the case and the case where the optical head performs the reproducing operation.

In an optical disc D having an optical recording layer for recording / reproducing information signals by an optical head having an optical recording / reproducing element, the optical recording layer is so-called. It is possible to use the optical disc D which is a phase change type optical recording material, a magneto-optical recording material, a bubble type optical recording material, or other various optical recording materials. The optical intensity of the laser light to be emitted from the light source 1 of the optical head is appropriate in accordance with the type of the optical recording layer of the optical disc D to be recorded / reproduced. Is set to.

In the first optical path formed between the beam splitter 2 and the beam splitter 3 in the optical head used as the optical recording / reproducing element for recording / reproducing shown in FIGS. The optical modulator 18, the optical modulator 17, etc., which are separately provided in the optical path for adjusting the optical path length of a side path (a detour) type with respect to the first optical path, have optical heads from the optical disk D. In the case of being used for the information signal read operation, the optical head outputs a constant read light having a small light intensity necessary for reading the information signal from the optical disk, and the optical head writes the information signal to the optical disk D. When it is used for, the writing light whose light intensity changes according to the information signal for the optical disc is output.

As the optical modulators 17 (18) provided individually in the first optical path and the optical path for adjusting the optical path in the optical head shown in FIGS.
For example, in the case where the optical modulator configured by using the acousto-optical light modulating element described above with reference to FIG. 14 is used, the 0th-order diffracted light Lo indicated by reference numeral Lo in FIG. , Write light, and read light. Therefore, the first-order diffracted light L1 indicated by reference numeral L1 in FIG. 14 is prevented from entering the second optical path. In order to prevent the above-mentioned first-order diffracted light L1 from proceeding to the second optical path, for example, a light absorbing film may be provided at the exit portion of the first-order diffracted light L1 in the optical modulator 17 (18). Good.

First, in the optical head having the recording / reproducing function shown in FIG. 1, two light beams B and C obtained by dividing the beam into two by the beam splitter 2 (two recording operations when the optical head performs a recording operation). The light beams B and C and one light beam B of the two light beams B and C) when the optical head performs the reproducing operation are provided with the optical modulator 18 formed between the beam splitter 2 and the beam splitter 3. The light beam B that has passed through the first optical path and is incident on the beam splitter 3 and has passed through the beam splitter 3 is a second beam that is formed between the beam splitter 3 and the objective lens 6.
Is reflected by the beam splitter 4 in the optical path of the objective lens 6
Incident on. The light flux B incident on the objective lens 6 is
A light spot having a minute diameter is generated on the signal surface 15 provided at a position at a distance L1 from the surface 14a of the transparent substrate 14 on the optical disc D.

Further, two light beams B and C obtained by being divided into two by the beam splitter 2 described above.
The other luminous flux C of the beam enters the beam splitter 3 after passing through the optical path length adjusting optical path including the optical modulator 17, the spherical aberration correcting member 9 and the total reflection mirrors 7 and 8. To do. The spherical aberration correction member 9 is used for the beam splitter 2
And the beam splitter 3 may be installed at any part of the optical path length adjusting optical path. A light beam C ′ that has entered the beam splitter 3 after passing through the optical path length adjusting optical path and is reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. . Then, the light flux C ′ incident on the objective lens 6 causes a light spot having a minute diameter to be generated on the signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D.

When the optical head is performing a recording operation for recording an information signal on the optical recording layer of the optical disc D, the minute light spots imaged on the signal surfaces 15 and 16 respectively are In the optical path of No. 1 and the optical path for adjusting the optical path length, the intensity is modulated by the modulated light by the optical modulators 18 and 17, respectively,
Information signals are recorded on the optical recording layer of the optical disc D. Further, when the optical head is performing a reproducing operation for reading an information signal from the optical disc D, a reflected light beam B ′ from a minute light spot due to the light beam B imaged on the signal surface 15 of the optical disc D is obtained. The reflected light beam C ′ from the minute light spot formed by the light beam C imaged on the signal surface 16 of the optical disc D is focused by the single objective lens 6 in common to the objective lens 6
Inject from Of the two reflected light beams B ′ and C ′ emitted from the objective lens 6 while being focused, the reflected light beams B ′ and C ′ transmitted through the beam splitter 4 are transmitted.
Is split into two by the beam splitter 5.

The reflected light beams B'and C'transmitted through the beam splitter 5 and the reflected light beams B'and C'reflected by the beam splitter 5 are both imaged on the signal surface 15 of the optical disc D. The reflected light beam B'from the minute light spot by the formed light beam B and the reflected light beam C'from the minute light spot by the light beam C imaged on the signal surface 16 of the optical disc D. One of the reflected light beams B'and C'transmitted through the beam splitter 5 is electrically reflected by the photodetector 12 provided near the image forming position of the reflected light beam B '. The other reflected light flux C ′ of the reflected light fluxes B ′ and C ′ that has been converted into a signal and reflected by the beam splitter 5 is provided near the image forming position of the reflected light flux C ′. It is converted into an electric signal by the photodetector 11 present. The reflected light to be subjected to photoelectric conversion by the photodetectors 11 and 12 may be reversed from that in the above description.

As described above, the objective lens 6 used as a constituent member of the optical head can be reproduced by the optical head from the optical disk D in the configuration mode originally intended as the optical disk D to be recorded and reproduced. When it is performed, the spherical aberration can be satisfactorily corrected. Then, in the optical head having the recording / reproducing function shown in FIG. 1, the optical disc D having the configuration mode planned as the optical disc D to be reproduced has the surface 14 of the transparent substrate 14.
In the case where the signal surface 15 is provided at a position at a distance (first distance) from a to L1, the objective lens 6 which is made so as not to cause spherical aberration is used. It was an example of the case. However, the optical head having the recording / reproducing function shown in FIG. 2 is the optical disc D having the configuration mode planned as the optical disc D to be recorded / reproduced.
However, in the case where the signal surface 16 is provided at the distance L2 (second distance) from the surface 14a of the transparent substrate 14, spherical aberration is not generated. 2 shows an example in which the objective lens 6 is used.

The optical head having the recording / reproducing function shown in FIG. 2 differs from the optical head having the recording / reproducing function shown in FIG.
The optical disc D, which is originally designed to correct the spherical aberration, is designed as the optical disc D to be reproduced. The optical disc D has a distance L2 from the surface 14a of the transparent substrate 14 (second
The objective lens 6 that is adapted to the case where the signal surface 16 is provided at the position (distance) is used, and accordingly, the above-mentioned objective lens 6 is used. Surface 14 of transparent substrate 14 of finished optical disc D
The spherical aberration correction member 9 of the objective lens is provided in the optical path (first optical path) of only the light beam B imaged on the signal surface 15 provided at a position L1 (a first distance) from a. With respect to other configurations, there is no difference from the optical head having the recording / reproducing function described with reference to FIG. 1, and the recording / reproducing operation corresponds to the above-mentioned difference in the configuration. However, the specific detailed description thereof will be omitted.

Next, in the optical head having the recording / reproducing function shown in FIG. 3, the luminous flux A emitted from the light source 1 in a divergent state is divided into two by the beam splitter 2 and two luminous fluxes B, C One of the two light beams B and C obtained by splitting the light beam by the beam splitter 2 is formed between the beam splitter 2 and the beam splitter 3 and is used as an optical path length adjusting lens 10. The light passes through the first optical path including the optical modulator 18 and enters the beam splitter 3. In the following description, the optical path length adjusting lens 10 provided in the first optical path is
The light beam B is said to be a collimator lens, and the light beam B incident on the beam splitter 3 from the above-mentioned first optical path is a parallel light beam. In implementing the present invention, the optical path length adjusting lens 10 described above is not limited to a collimating lens, and a positive (or negative) lens having a characteristic capable of performing necessary optical path length adjustment may be used. May be used.

The light beam B that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. The light beam B incident on the objective lens 6 produces a light spot having a minute diameter on the signal surface 16 provided at a position of a distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. The signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the above-mentioned optical disc D is
This is the position of the rear focal point of the objective lens 6.

Further, the two light beams B and C obtained by being divided into two by the beam splitter 2 described above.
The other light flux C in the beam enters the beam splitter 3 after passing through the optical path length adjusting optical path including the optical modulator 17, the spherical aberration correcting member 9 and the total reflection mirrors 7 and 8. . The spherical aberration correcting member 9 may be installed in any part of the optical path length adjusting optical path formed between the beam splitter 2 and the beam splitter 3. After passing through the optical path for adjusting the optical path, the light enters the beam splitter 3 and
The light beam C ′ reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. The light beam C ′ incident on the objective lens 6 has a signal surface 15 provided at a position at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disc D.
To produce a light spot with a small diameter.

When the optical head is performing a recording operation for recording an information signal on the optical recording layer of the optical disc D, the minute light spots imaged on the signal surfaces 15 and 16 respectively are In the optical path of No. 1 and the optical path for adjusting the optical path length, the intensity is modulated by the modulated light by the optical modulators 18 and 17, respectively,
Information signals are recorded on the optical recording layer of the optical disc D. Further, when the optical head is performing a reproducing operation such as reading an information signal from the optical disc D, a reflected light beam B ′ from a minute light spot due to the light beam B imaged on the signal surface 16 of the optical disc D is obtained. The reflected light beam C ′ from the minute light spot formed by the light beam C formed on the signal surface 15 of the optical disc D is incident on the common single objective lens 6. Then, a reflected light beam B ′ from a minute light spot formed by the light beam B imaged on the signal surface 16 of the optical disc D is emitted from the objective lens 6 as a parallel light beam B ′, and the signal on the optical disc D is also described. A reflected light beam C ′ from a minute light spot formed by the light beam C imaged on the surface 15 is emitted from the objective lens 6 as a reflected light beam C ′ that is being focused.

Of the two reflected light beams B'and C ', which are the reflected light beam B'in the state of parallel light beam emitted from the objective lens 6 and the reflected light beam C'in the state of being converged as described above,
The reflected light beams B ′ and C ′ that have passed through the beam splitter 4 are split into two by the beam splitter 5. The reflected light beams B ′ and C ′ that have passed through the beam splitter 5 and the reflected light beams B ′ and C ′ that have been reflected by the beam splitter 5 are both light beams imaged on the signal surface 16 of the optical disc D. It is composed of a reflected light beam B ′ from a minute light spot by B and a reflected light beam C ′ from a minute light spot by a light beam C imaged on the signal surface 15 of the optical disc D. One of the reflected light beams B ′ and C ′ reflected by the beam splitter 5 is focused by the focusing lens 13 and provided near the rear focal position of the focusing lens 13. The other reflected light beam C'of the reflected light beams B'and C'converted into an electric signal by the photodetector 12 which has passed through the beam splitter 5 is the reflected light beam C'of the reflected light beam C '. It is converted into an electric signal by the photodetector 11 provided near the image forming position. It is needless to say that the reflected light to be subjected to photoelectric conversion by the photodetectors 11 and 12 may be reversed from the case described above, but the photoelectric conversion of the reflected light beam B ′ is performed. It is natural that the photodetector used in this case should be preceded by a focusing lens.

As mentioned above, each photodetector 11,
Even if the mixed light of the reflected light beams B ′ and C ′ is given to 12, the positions where the photodetectors 11 and 12 are installed are the two reflected light beams B ′ and C that constitute the mixed light. This is because one of the two reflected light beams B'or C'is located at the image forming position, and the photodetectors 11, 12 out of the two reflected light beams incident on the photodetectors 11, 12 described above. The reflected light beam that does not form an image at the position is blurred so that the information contained in the reflected light beam cannot be read by the photodetectors 11 and 12. ，
In 12, the information contained in the reflected light that is the target of detection can be satisfactorily detected. In the optical head having the recording / reproducing function shown in FIG. 3, the optical disk D having a configuration originally intended as the reproduction target optical disk D has a distance L2 (second distance) from the surface 14a of the transparent substrate 14. This is an example of the case where the objective lens 6 which is made so as not to cause spherical aberration is used in the case where the signal surface 16 is provided at the position (4).

Further, originally, the optical disk D to be recorded / reproduced.
When the optical disk D of the configuration mode planned as is the configuration mode in which the signal surface 15 is provided at the position of the distance L1 (first distance) from the surface 14a of the transparent substrate 14. In addition, by using the objective lens 6 made so as not to cause spherical aberration, the optical path length adjusting lens 10 and the optical modulator 1 are provided in the first optical path as shown in FIG.
When configuring the optical head having the recording / reproducing function of the configuration mode in which 8 is provided, the spherical aberration correction member 9 provided in the optical path for optical path adjustment in FIG. 3 is replaced by the beam splitter 2 and the beam splitter 3. First configured between and
The configuration may be changed so as to be provided in the optical path on the incident light side of the optical path adjusting lens 10 provided in the optical path.

Next, FIG. 4 shows an optical disc D to be recorded and reproduced.
When the optical disk D of the configuration mode planned as is the configuration mode in which the signal surface 15 is provided at the position of the distance L1 (first distance) from the surface 14a of the transparent substrate 14. In addition, the objective lens 6 that is made so as not to cause spherical aberration is used, and the optical modulator 17 and the objective lens are provided between the total reflection mirror 7 and the total reflection mirror 8 in the optical path for adjusting the optical path length. Spherical aberration correcting member 9 and optical path adjusting lens 1
0, and an example of an optical head having a recording / reproducing function configured by providing separate optical modulators in the first optical path and the optical path length adjusting optical path. In the optical head having the recording / reproducing function shown in FIG. 4,
The divergent light beam A emitted from the light source 1 is divided into two by the beam splitter 2 into two light beams B and C. One light beam B of the two light beams B and C obtained by dividing the light beam by the beam splitter 2 is
The light enters the beam splitter 3 after passing through a first optical path including an optical modulator 18 which is formed between the beam splitter 2 and the beam splitter 3.

The light beam B which has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. The light beam B incident on the objective lens 6 has a signal surface 1 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disc D.
5, a light spot having a minute diameter is generated. Further, the other luminous flux C of the two luminous fluxes B and C obtained by being split into two by the above-mentioned beam splitter 2 is the total reflection mirrors 7 and 8, the optical modulator 17, and the spherical aberration correcting member. 9 and an optical path adjusting lens 10 and passes through an optical path length adjusting optical path, and then enters the beam splitter 3. In the following description, it is assumed that the optical path length adjusting lens 10 provided in the optical path length adjusting optical path is a collimating lens, and the light flux C incident on the beam splitter 3 from the optical path length adjusting optical path. Is a parallel light flux.

The above-mentioned optical path length adjusting lens 10 used in the practice of the present invention is not limited to a collimating lens, but has a characteristic that the necessary optical path length adjustment can be performed (or positive (or). Negative) lenses may be used. The light beam C that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. The light beam C incident on the objective lens 6 causes a light spot having a minute diameter to be generated on the signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. The signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the above-mentioned optical disc D is
This is the position of the rear focal point of the objective lens 6.

The optical disc D shown in FIG. 4 has a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 and a distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. Although the signal surface 16 provided at the position is laminated (see (c) of FIG. 13), the optical head having a recording / reproducing function is used as a reproduction target. The optical disc D as the optical disc D having the configuration as illustrated in FIG. 13A in which the signal surface 15 is provided only at the position of the distance L1 from the surface 14a of the transparent substrate 14 in the optical disc D, or the optical disc D. 13B, in which the signal surface 16 is provided only at a position at a distance L2 from the surface 14a of the transparent substrate 14 in FIG. Of course, even if it is used.

When the optical head is performing a recording operation for recording an information signal on the optical recording layer of the optical disk D, the minute light spots imaged on the signal surfaces 15 and 16 respectively are In the optical path of No. 1 and the optical path for adjusting the optical path length, the intensity is modulated by the modulated light by the optical modulators 18 and 17, respectively,
Information signals are recorded on the optical recording layer of the optical disc D. Further, when the optical head is performing a reproducing operation for reading an information signal from the optical disc D, a reflected light beam C ′ from a minute light spot due to the light beam C imaged on the signal surface 16 of the optical disc D is obtained. The reflected light beam B ′ from the minute light spot formed by the light beam B formed on the signal surface 15 of the optical disc D is incident on the common single objective lens 6. Then, a reflected light beam C ′ from a minute light spot formed by the light beam C formed on the signal surface 16 of the optical disc D is emitted from the objective lens 6 as a parallel light beam C ′, and the signal on the optical disc D is also described. A reflected light beam B ′ from a small light spot formed by the light beam B imaged on the surface 15 is emitted from the objective lens 6 as a reflected light beam B ′ that is being focused.

Of the two reflected light beams C'and B ', which are the reflected light beam C'in the state of parallel light beam emitted from the objective lens 6 and the reflected light beam B'in the state of being converged as described above,
The reflected light beams C ′ and B ′ that have passed through the beam splitter 4 are split into two by the beam splitter 5. The reflected light beams C ′ and B ′ transmitted through the beam splitter 5 and the reflected light beams C ′ and B ′ reflected by the beam splitter 5 are both light beams imaged on the signal surface 15 of the optical disc D. It is composed of a reflected light beam C ′ from a minute light spot by C and a reflected light beam B ′ from a minute light spot by a light beam B imaged on the signal surface 16 of the optical disc D.

One of the reflected light beams C'and B'reflected by the beam splitter 5 is reflected by the focusing lens 13 and focused on the rear focal point of the focusing lens 13. The reflected light beam C ′, which has been converted into an electric signal by the photodetector 11 provided in the vicinity and has passed through the beam splitter 5,
The other reflected light beam B'of B'is the reflected light beam B '.
It is converted into an electric signal by the photodetector 12 provided near the image forming position. In addition, the photodetector 11 described above,
It is needless to say that the reflected light to be subjected to the photoelectric conversion by 12 may be reversed to the case described above, but the optical path to the photodetector used for the photoelectric conversion of the reflected light flux C ′. Naturally, a focusing lens should be placed in front.

As described above, each photodetector 11,
Even if the mixed light of the reflected light beams C ′ and B ′ is given to 12, the positions where the photodetectors 11 and 12 are installed are the two reflected light beams C ′ and B that form the mixed light. This is because one of the two reflected light beams C'or B'is formed at the image forming position, and among the two reflected light beams incident on the photodetector 11, 12, the photodetector 11, 12 is detected. The reflected light beam that does not form an image at the position is in a blurred state in which the information contained in the reflected light beam cannot be read by the photodetectors 11 and 12. ，
In 12, the information contained in the reflected light that is the target of detection can be satisfactorily detected.

In addition, the optical disc D having the configuration originally intended as the optical disc D to be reproduced is provided with the signal surface 16 at a position L2 (second distance) from the surface 14a of the transparent substrate 14. In the case of such a configuration mode as described above, by using the objective lens 6 made so as not to cause spherical aberration, the optical path length is adjusted in the optical path adjusting optical path as shown in FIG. When configuring the optical head having the recording / reproducing function in the configuration mode in which the adjusting lens 10 is provided, the spherical aberration correcting member 9 provided in the optical path adjusting optical path in FIG. The configuration may be changed so that it is provided in the first optical path formed between the beam splitter 3.

Next, the optical head having the recording / reproducing function shown in FIGS. 5 to 8 is an optical path forming a part of the optical system of the optical head described with reference to FIGS. By displacing a part of the adjusting optical path by the operation of the automatic control system to change the optical path length of the optical path adjusting optical path,
In the optical disc D having the configuration as illustrated in FIG. 3C, that is, in the optical disc having two signal surfaces, the above-mentioned two signal surfaces 15 and 16 may have different intervals. Even so, the recording / reproducing operation on the above-mentioned two signal surfaces is preferably performed.

In the optical head having the recording / reproducing function shown in FIGS.
Is fixedly connected to the drive shaft 23 of the
By the operation of 2, the drive is displaced in the direction of arrow Y in the figure. Among the optical members forming the optical system of the optical path for adjusting the optical path, the total reflection mirrors 7 and 8, the lens 10 for adjusting the optical path, etc. are used as the constituent members of the optical path for adjusting the optical path to be mounted on the mounting member 24. As described above, it is advantageous to use only optical members in which it is essential to always match the optical axes of each other, it is advantageous in that the mass of the movable portion by the above-mentioned actuator can be reduced. In this case, it goes without saying that the optical modulator 17 and the spherical aberration correcting member 9 may be attached to the attaching member 24.

In the optical head having the recording / reproducing function shown in FIGS. 5 to 8 (the same applies to the reproduction-only optical head described later with reference to FIGS. 9 to 12), 11
Reference numerals A and 12A receive reflected light from the optical disc D to be subjected to photoelectric conversion, output a reproduction signal corresponding to the recorded information on the optical disc D, generate a focus error signal, and a tracking error signal. It is a photodetection unit having a configuration having a function capable of generating Then, the above-described photodetection units 11A and 12
As A, a condenser lens, a cylindrical lens,
A four-division photodetector, a subtractor and an adder,
A well-known structure to which a so-called astigmatism detection unit is applied can be used to detect the focus error signal.

In the optical head having the recording / reproducing function shown in FIGS. 5 to 8 (the same applies to the reproduction-only optical head described later with reference to FIGS. 9 to 12), 19 is the objective lens 6 Is an actuator configured to be capable of displacing the optical axis direction and a direction orthogonal to the optical axis direction. The actuator 19
Is an objective lens 6 driven and controlled by the focus control signal and the tracking control signal generated by the control circuit 20 to which the focus error signal and the tracking error signal generated by the photodetector 12A are supplied. The optical disc D is generated by the above-described light flux B incident on the lens 6.
A good light spot with a minute diameter is always generated at a predetermined position on the signal surface of the. As the actuator 19, an electrodynamic type actuator having a well-known structure can be used.

Next, the actuator 2 to which the focus control signal generated by the control circuit 21 is supplied based on the focus error signal generated by the photodetection section 11A.
Reference numeral 2 designates a driving member 23 fixedly connected to the drive shaft 23 of the actuator 22 in the direction of an arrow Y in the drawing for driving displacement so as to pass through the optical system of the optical path for adjusting the optical path and enter the objective lens 6. The above described light flux C always produces a good light spot having a minute diameter on the signal surface of the optical disc D. As the actuator 22, it is possible to favorably use an electrodynamic type actuator.

As described above, in the optical head having the recording / reproducing function shown in FIGS. 5 to 8, the light beam C passing through the optical system of the optical path for optical path adjustment and incident on the objective lens 6 causes
The focus control signal generated by the control circuit 21 is supplied to the actuator 22 based on the focus error signal generated by the photodetector 11A to which the reflected light from the light spot having a small diameter generated on the signal surface of the optical disc D is applied. By supplying and displacing the mounting member 24 connected and fixed to the drive shaft 23 of the actuator 22 in the direction of the arrow Y in the drawing, the mounting member 24 passes through the optical system of the optical path for adjusting the optical path to the objective lens 6. The light spot generated on the signal surface of the optical disc D by the incident light flux described above is always made to be a light spot having a good minute diameter by the operation of the automatic control system described above. Even if the distance between the two signal surfaces varies during manufacturing, the recording / reproducing operation will not be inconvenient.

The configuration of the optical path length adjusting optical path described above is not limited to the configuration illustrated in FIGS. 1 to 8, but may be the beam splitter 2 → total reflection described above. A transparent parallel plate having an appropriate refractive index in the optical path of the mirror 7 → total reflection mirror 8 → beam splitter 3,
A positive lens (or a negative lens) having an appropriate curvature made of a medium having an appropriate refractive index may be inserted so that the required optical path length can be obtained. This point also applies to the optical heads illustrated in FIGS. 9 to 12 described later.

Further, in the optical head shown in FIGS. 1 to 8 used as an optical recording / reproducing element for recording / reproducing, the first head formed between the beam splitter 2 and the beam splitter 3 is used. Side path (detour) with respect to the optical path
The optical path of the type, that is, the beam splitter 2 → the total reflection mirror 7 → the total reflection mirror 8 → the beam splitter 3 is configured to function as an optical path for adjusting the optical path length. At the same time, the optical modulator 18 is provided in the above-mentioned first optical path, and the optical modulator 17 is also provided in the above-mentioned optical path for adjusting the optical path length. Therefore, in the optical head as the recording / reproducing element illustrated in FIGS. 1 to 8, each optical path includes the optical characteristics of the optical modulator inserted and used in each optical path described above. Will be set.

Next, the optical head (optical pickup) shown in FIGS. 9 to 12 which is used as a read-only optical pickup will be described. In the configuration examples of the optical head of the present invention respectively illustrated in FIGS. 9 to 12, the optical disc D is driven and rotated at a predetermined rotation speed by a rotation drive mechanism (not shown). First, in the optical head (optical pickup) shown in FIG.
One reproduction light beam B of the two reproduction light beams B and C obtained by dividing the beam by the beam splitter 2 is
The reproduction light beam B that has passed through the first optical path formed between the beam splitter 2 and the beam splitter 3 and is incident on the beam splitter 3 and has passed through the beam splitter 3 is the beam splitter 3 and the objective lens 6. The beam is reflected by the beam splitter 4 in the second optical path formed between and and enters the objective lens 6. The reproduction light beam B incident on the objective lens 6 is transmitted through the transparent substrate 14 of the optical disc D.
A light spot having a minute diameter is generated on the signal surface 15 provided at a position at a distance L1 from the surface 14a.

The other reproduction light beam C of the two reproduction light beams B and C obtained by dividing the beam into two by the above-mentioned beam splitter 2 is an optical path constituted by total reflection mirrors 7 and 8. After passing through the optical path for length adjustment, it enters the beam splitter 3. Spherical aberration correction member 9
May be installed in any part of the optical path length adjusting optical path formed between the beam splitter 2 and the beam splitter 3. The reproduction light beam C ′ that has entered the beam splitter 3 after passing through the optical path length adjusting optical path and is reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. To do. Then, the reproduction light beam C ′ incident on the objective lens 6 causes a light spot having a minute diameter to be generated on the signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D.

The optical disk D shown in FIG. 9 has a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 and a distance L2 from the surface 14a of the transparent substrate 14 in the optical disk D. The optical disk D to be reproduced by the optical head has a configuration such that the signal surface 16 provided at the position is laminated (see (c) of FIG. 13). Distance L from the surface 14a of the transparent substrate 14 in the optical disc D
The structure as illustrated in FIG. 13 (a) in which the signal surface 15 is provided only at the position 1 or the surface 14 of the transparent substrate 14 in the optical disc D.
It goes without saying that the configuration as illustrated in FIG. 13B in which the signal surface 16 is provided only at the position of the distance L2 from a may be used.

As described above, the reflected light beam B'from the minute light spot formed by the reproduction light beam B imaged on the signal surface 15 of the optical disk D and the reproduction light beam C imaged on the signal surface 16 of the optical disk D are described above. The reflected light beam C ′ from the minute light spot due to is emitted from the objective lens 6 in a state where it is focused by one common objective lens 6. Of the two reflected light beams B ′ and C ′ emitted from the objective lens 6 while being focused, the reflected light beams B ′ and C ′ transmitted through the beam splitter 4 are converted by the beam splitter 5 into two beams. Will be divided.

Both the reflected light beams B'and C'transmitted through the beam splitter 5 and the reflected light beams B'and C'reflected by the beam splitter 5 are imaged on the signal surface 15 of the optical disc D. The reflected light beam B ′ from the minute light spot by the reproduced light beam B and the optical disc D
The reflected light flux C ′ from the minute light spot by the reproduced light flux C imaged on the signal surface 16 in FIG. One of the reflected light beams B ′ and C ′ transmitted through the beam splitter 5 is reflected by the photodetection unit 12A provided near the image forming position of the reflected light beam B ′. The reflected light beams B ′, C ′ are converted into signals and reflected by the beam splitter 5.
The other reflected light beam C ′ of the above is converted into an electric signal by the photodetection section 11A provided near the image forming position of the reflected light beam C ′.

As the above-mentioned photodetection sections 11A and 12A, those having a well-known structure including, for example, a condenser lens, a cylindrical lens, a four-division photodetector, a subtractor and an adder are used as described above. By receiving the reflected light from the optical disc D to be subjected to photoelectric conversion, a reproduction signal corresponding to the recorded information on the optical disc D is output, a focus error signal is generated, and a tracking error signal is generated. To generate. Therefore, the actuator 19 configured to be able to displace the objective lens 6 in the optical axis direction and the direction orthogonal to the optical axis direction has the focus error signal and the tracking error signal generated by the photodetection unit 12A. The objective lens 6 is driven and controlled by the focus control signal and the tracking control signal generated by the control circuit 20 to which the signal is supplied, and the above-described light beam B incident on the objective lens 6 causes the predetermined signal on the signal surface of the optical disc D. A light spot with a good minute diameter is always generated at the position.

Further, the photodetection section 11A outputs a reproduction signal, and the control circuit 21 to which the focus error signal generated by the photodetection section 11A is supplied receives the focus error generated based on the focus error signal. The control signal is supplied to the actuator 22. Thereby,
The actuator 22 drives and displaces the mounting member 24, which is fixedly connected to the drive shaft 23 thereof, in the direction of the arrow Y in the drawing, passes through the optical system of the optical path for optical path adjustment, and enters the objective lens 6. The light beam C always produces a good light spot with a fine diameter on the signal surface of the optical disc D.

As described above, in the optical head (optical pickup) shown in FIG. 9, the light beam C passing through the optical system of the optical path for adjusting the optical path and incident on the objective lens 6 causes it to be generated on the signal surface of the optical disk D. The focus control signal generated by the control circuit 21 is supplied to the actuator 22 on the basis of the focus error signal generated by the photo-detecting section 11A to which the reflected light from the light spot with a minute diameter is given, and the actuator 22 is driven. By drivingly displacing the mounting member 24 fixedly connected to the shaft 23 in the direction of the arrow Y in the figure, the optical flux is passed through the optical system of the optical path for optical path adjustment and enters the objective lens 6. Since the light spot generated on the signal surface of D is always a good light spot with a fine diameter due to the operation of the automatic control system described above, the Even when manufacturing the disk D to a variation has occurred in the interval between the two signals surfaces, it does not occur that as trouble physician playback operation occurs for that. This also applies to the optical head (optical pickup) described later with reference to FIGS. 10 to 12.

As described above, the objective lens 6 used as a constituent member of the optical head performs the reproducing operation of the optical disk D having the configuration originally intended as the optical disk D to be reproduced by the optical head. When
The optical head (optical pickup) shown in FIG. 9 has a configuration such that spherical aberration can be corrected well.
The optical disc D of the configuration mode planned as the optical disc D to be reproduced has a configuration mode in which the signal surface 15 is provided at a position L1 (first distance) from the surface 14a of the transparent substrate 14. In the case where the objective lens 6 made to prevent spherical aberration is used, the optical head (optical pickup) shown in FIG. The optical disc D having the configuration mode that is planned as the signal surface 1 is located at a position L2 (second distance) from the surface 14a of the transparent substrate 14.
This is an example of the case where the objective lens 6 that is made so as not to cause spherical aberration is used in the case of the configuration mode in which 6 is provided.

The optical head (optical pickup) shown in FIG. 10 is different from the optical head (optical pickup) shown in FIG. 9 in terms of the structure because of the spherical aberration originally applied to the objective lens 6. Of the optical disc D in the configuration mode which is planned as the optical disc D to be reproduced.
Is suitable for the case where the signal surface 16 is provided at a position L2 (second distance) from the surface 14a of the transparent substrate 14. The use of the lens 6 and, along with it, the surface 14a of the transparent substrate 14 of the optical disc D described above.
The spherical aberration correction member 9 of the objective lens is provided in the optical path (first optical path) of only the reproduced light beam B imaged on the signal surface 15 provided at a position from L1 to L1 (first distance). The other configurations are the same as those of the optical head (optical pickup) described with reference to FIG. 9, and the operations are different only in the operations corresponding to the above-mentioned configuration differences. Therefore, a detailed description thereof will be omitted.

Next, in the optical head (optical pickup) shown in FIG. 11, the reproducing light beam A in the divergent light state emitted from the reproducing light source 1 is split into two by the beam splitter 2. Two reproduction light beams B and C are formed.
One reproduction light beam B of the two reproduction light beams B and C obtained by dividing the beam by the beam splitter 2 is formed between the beam splitter 2 and the beam splitter 3.
The light enters the beam splitter 3 through the first optical path provided with the optical path length adjusting lens 10. In the following description, it is assumed that the optical path length adjusting lens 10 provided in the first optical path is a collimating lens,
The reproduction light beam B incident on the beam splitter 3 from the above-mentioned first optical path is a parallel light beam. In implementing the present invention, the optical path length adjusting lens 10 described above is not limited to a collimating lens, and a positive (or negative) lens having a characteristic capable of performing necessary optical path length adjustment may be used. May be used.

The reproduction light beam B that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. . The reproduction light beam B incident on the objective lens 6 produces a light spot having a minute diameter on the signal surface 16 provided at a position of a distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. The signal surface 16 provided at the distance L2 from the surface 14a of the transparent substrate 14 in the above-mentioned optical disc D is the position of the rear focal point of the objective lens 6.

Further, the other reproduction light beam C of the two reproduction light beams B and C obtained by dividing the beam into two by the above-mentioned beam splitter 2 is an optical path including total reflection mirrors 7 and 8. The light enters the beam splitter 3 after passing through the optical path for length adjustment. Spherical aberration correction member 9
May be installed in any part of the optical path length adjusting optical path formed between the beam splitter 2 and the beam splitter 3. The reproduction light beam C ′ that has entered the beam splitter 3 after passing through the optical path length adjusting optical path and is reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. To do. Then, the reproduction light beam C ′ incident on the objective lens 6 causes a light spot having a minute diameter to be generated on the signal surface 15 provided at the position of the distance L1 from the surface 14a of the transparent substrate 14 in the optical disc D.

The optical disc D shown in FIG.
In the optical disc D, the signal surface 15 provided at the position of distance L1 from the surface 14a of the transparent substrate 14 and the signal surface 16 provided at the position of distance L2 from the surface 14a of the transparent substrate 14 are laminated. The optical disc D to be reproduced by the optical head (optical pickup) has a distance from the surface 14a of the transparent substrate 14 in the optical disc D. 13A in which the signal surface 15 is provided only at the position L1 or only at a position at a distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. It goes without saying that the configuration as illustrated in FIG. 13B in which the signal surface 16 is provided may be used.

As described above, the reflected light beam B'from the minute light spot by the reproduction light beam B imaged on the signal surface 16 of the optical disk D and the reproduction light beam C imaged on the signal surface 15 of the optical disk D are described. The reflected light beam C ′ from the minute light spot due to is incident on one common objective lens 6. Then, a reflected light beam B ′ from a minute light spot formed by the reproduction light beam B imaged on the signal surface 16 of the optical disk D is emitted from the objective lens 6 as a parallel reproduction light beam B ′, and the optical disk D is also described. A reflected light beam C ′ from a minute light spot by the reproduced light beam C imaged on the signal surface 15 at is emitted as a reflected light beam C ′ that is being converged from the objective lens 6.

Of the two reflected light beams B'and C ', which are the reflected light beam B'in the state of parallel light beam emitted from the objective lens 6 and the reflected light beam C'in the state of being converged as described above,
The reflected light beams B ′ and C ′ that have passed through the beam splitter 4 are split into two by the beam splitter 5. Both of the reflected light beams B ′ and C ′ transmitted through the beam splitter 5 and the reflected light beams B ′ and C ′ reflected by the beam splitter 5 are imaged on the signal surface 16 of the optical disc D. It is composed of a reflected light beam B ′ from a minute light spot due to the light beam B and a reflected light beam C ′ from a minute light spot due to the reproduction light beam C imaged on the signal surface 15 of the optical disc D. One of the reflected light beams B ′ and C ′ reflected by the beam splitter 5 is focused by the focusing lens 13 and provided near the rear focal point of the focusing lens 13. The other reflected light flux C ′ of the reflected light fluxes B ′ and C ′ that have been converted into an electrical signal by the photodetection unit 11A that has passed through the beam splitter 5 is the reflected light flux C ′. It is converted into an electric signal by the photodetector 12A provided near the image forming position. FIG.
In the optical head (optical pickup) 1 shown in FIG. 1, an optical disk D having a configuration originally intended as an optical disk D to be reproduced is located at a position L2 (second distance) from the surface 14a of the transparent substrate 14. This is an example of the case where the objective lens 6 which is made so as not to cause spherical aberration is used in the case of the configuration mode in which the signal surface 16 is provided.

Further, the optical disc D having the configuration originally intended as the optical disc D to be reproduced is provided with the signal surface 15 at the position L1 (first distance) from the surface 14a of the transparent substrate 14. If the objective lens 6 is constructed so that spherical aberration does not occur, the optical path length in the first optical path is changed as shown in FIG. When the optical head (optical pickup) having the configuration mode in which the adjustment lens 10 is provided is configured, the spherical aberration correction member 9 provided in the optical path adjustment optical path in FIG. The configuration may be changed so that it is provided in the optical path on the incident light side of the optical path adjusting lens 10 that is provided in the first optical path that is provided between the splitter 3.

Next, FIG. 12 shows an optical disk D having a configuration planned as an optical disk D to be reproduced, with a signal surface 15 at a position L1 (first distance) from the surface 14a of the transparent substrate 14. In the case of the configuration as provided, the objective lens 6 which is made so as not to cause spherical aberration is used, and the total reflection mirror 7 and the total reflection in the optical path for adjusting the optical path length are used. An embodiment of an optical head (optical pickup) configured by providing a spherical aberration correcting member 9 of an objective lens and an optical path adjusting lens 10 between the mirror 8 and the mirror 8 is shown. In the optical head (optical pickup) shown in FIG. 12, the reproducing light beam A in the divergent light state emitted from the reproducing light source 1 is split into two by the beam splitter 2 and two reproducing light beams B and C are obtained. It is said that One reproduction light beam B of the two reproduction light beams B and C obtained by being divided into two by the beam splitter 2 is formed between the beam splitter 2 and the beam splitter 3.
Of light and enters the beam splitter 3.

The reproduced light beam B which has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. . The reproduction light beam B incident on the objective lens 6 produces a light spot having a minute diameter on the signal surface 15 provided at a position at a distance L1 from the surface 14a of the transparent substrate 14 in the optical disc D. Further, the other reproduction light beam C of the two reproduction light beams B and C obtained by being divided into two by the beam splitter 2 is the total reflection mirrors 7 and 8, the spherical aberration correction member 9 and the optical path adjusting member. After passing through the optical path length adjusting optical path configured with the lens 10, the light enters the beam splitter 3. In the following description, it is assumed that the optical path length adjusting lens 10 provided in the optical path length adjusting optical path is a collimating lens, and the reproduction light flux that enters the beam splitter 3 from the optical path length adjusting optical path. C is a parallel light flux. The optical path length adjusting lens 10 may be a positive lens or a negative lens.

Now, the reproduction light beam C that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and is reflected by the objective lens 6. Incident. The reproduction light flux C incident on the objective lens 6 causes a light spot having a minute diameter to be generated on the signal surface 16 provided at the position of the distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. The signal surface 16 provided at the distance L2 from the surface 14a of the transparent substrate 14 in the above-mentioned optical disc D is the position of the rear focal point of the objective lens 6.

The optical disc D shown in FIG. 12 is
In the optical disc D, the signal surface 15 provided at the position of distance L1 from the surface 14a of the transparent substrate 14 and the signal surface 16 provided at the position of distance L2 from the surface 14a of the transparent substrate 14 are laminated. The optical disc D to be reproduced by the optical head (optical pickup) has a distance from the surface 14a of the transparent substrate 14 in the optical disc D. 13A in which the signal surface 15 is provided only at the position L1 or only at a position at a distance L2 from the surface 14a of the transparent substrate 14 in the optical disc D. It goes without saying that the configuration as illustrated in FIG. 13B in which the signal surface 16 is provided may be used.

As described above, the reflected light beam C'from the minute light spot by the reproduction light beam C imaged on the signal surface 16 of the optical disk D and the reproduction light beam B imaged on the signal surface 15 of the optical disk D are described above. The reflected light flux B ′ from the minute light spot due to is incident on one common objective lens 6. Then, a reflected light beam C ′ from a minute light spot formed by the reproduction light beam C formed on the signal surface 16 of the optical disk D is emitted from the objective lens 6 as a reproduction light beam C ′ of a parallel light beam, and the optical disk D described above is also used. A reflected light beam B ′ from a minute light spot formed by the reproduced light beam B formed on the signal surface 15 at is emitted as a reflected light beam B ′ that is being focused from the objective lens 6.

Of the two reflected light beams C ′ and B ′, which are the reflected light beam C ′ in the state of the parallel light beam emitted from the objective lens 6 and the reflected light beam B ′ in the state of being converged as described above,
The reflected light beams C ′ and B ′ that have passed through the beam splitter 4 are split into two by the beam splitter 5. Both the reflected light beams C ′ and B ′ transmitted through the beam splitter 5 and the reflected light beams C ′ and B ′ reflected by the beam splitter 5 are imaged on the signal surface 15 of the optical disc D. It is composed of a reflected light beam C ′ from a minute light spot by the light beam C and a reflected light beam B ′ from a minute light spot by the reproduction light beam B imaged on the signal surface 16 of the optical disc D.

One of the reflected light beams C'and B'reflected by the beam splitter 5 is focused by the focusing lens 13 and the rear focal position of the focusing lens 13 is focused. The reflected light beam C ′, which has been converted into an electric signal by the photodetection section 11A provided in the vicinity and has passed through the beam splitter 5,
The other reflected light beam B'of B'is the reflected light beam B '.
It is converted into an electric signal by the photodetector 12A provided near the image forming position.

Then, when the focus control signal generated by the control circuit 21 is supplied to the actuator 22 based on the focus error signal generated by the photodetection section 11A, the actuator 22 is fixedly coupled to the drive shaft 23 of the actuator 22. By drivingly displacing the attached member 24 in the direction of the arrow Y in the drawing, the above-mentioned light flux which has passed through the optical system of the optical path for adjusting the optical path and is incident on the objective lens 6 is generated on the signal surface of the optical disc D. Since the light spot is always made to be a light spot having a good small diameter by the operation of the automatic control system described above, it is assumed that the distance between the two signal surfaces is varied when the optical disc D is manufactured as described above. However, this does not cause any trouble in the reproduction operation.

The optical disc D having the configuration originally intended as the optical disc D to be reproduced is provided with the signal surface 16 at a position L2 (second distance) from the surface 14a of the transparent substrate 14. In the case of such a configuration mode as described above, by using the objective lens 6 made so as not to cause spherical aberration, the optical path length is adjusted in the optical path adjusting optical path as shown in FIG. When configuring an optical head (optical pickup) having a configuration mode in which the adjustment lens 10 is provided, the spherical aberration correction member 9 provided in the optical path adjustment optical path in FIG. The configuration may be changed so that it is provided in the first optical path formed between the splitter 3 and the splitter 3.

[0085]

As is apparent from the above detailed description, the optical head of the present invention uses, as a light source, a divergent light emitted from one semiconductor laser provided at a specific position of the optical head. The beam splitter splits the two light fluxes, and the optical path lengths of the two light fluxes split by the beam splitter are adjusted using an optical path length adjusting optical path and an optical path length adjusting lens. Light emitted from one objective lens on which a light beam is incident can be imaged at two different predetermined positions on the optical axis, and two predetermined light beams on the optical axis can be formed. Since one of the different positions does not cause spherical aberration, the other one of the two different predetermined positions on the optical axis is as follows. Although surface aberration will occur, spherical aberration can be prevented from occurring at the other position as well due to the action of the spherical aberration correcting member of the objective lens provided in the optical path. Recording of information signals on two types of optical discs having transparent substrates having different thicknesses, or optical discs having a two-layered signal surface, which can satisfactorily solve the problem of the conventional optical head, The information signal from the optical disc can be read well, and the light spot having a minute diameter generated on the signal surface of the optical disc D by the light flux passing through the optical system for the optical path adjustment and entering the objective lens. The focus control signal generated by the control circuit is supplied to the actuator based on the focus error signal generated by the photodetector that receives the reflected light from By drivingly displacing the mounting member connected and fixed to the drive shaft of the actuator, a light spot that is generated on the signal surface of the optical disc by the light flux that has passed through the optical system for the optical path adjusting and enters the objective lens, The operation of the automatic control system always produces a good light spot having a small diameter. Therefore, even if the distance between the two signal surfaces varies during the manufacture of the optical disc D as described above, the recording / reproducing operation will be performed. However, the present invention can provide an optical head having a simple structure and good characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration when an optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 2 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 3 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 4 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 5 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 6 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 7 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 8 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical recording / reproducing element.

FIG. 9 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical pickup.

FIG. 10 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical pickup.

FIG. 11 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical pickup.

FIG. 12 is a block diagram showing a schematic configuration when the optical head of the present invention is implemented as an optical pickup.

FIG. 13 is a cross-sectional view showing a configuration example of an optical disc.

FIG. 14 is a sectional view for explaining an optical modulator.

[Explanation of symbols]

1 ... Reproduction light source (semiconductor laser), 2-5 ... Beam splitter (half prism, half mirror), 6 ... Objective lens, 7, 8 ... Total reflection mirror, 9 ... Objective lens spherical aberration correction member, 10 ... Optical path length adjusting lens, 11, 12 ... Photodetector, 11A, 12A ... Photodetector, 13 ... Focusing lens, 14 ... Transparent substrate, 14a ... Surface of transparent substrate 14, 1
5, 16 ... Signal plane, 17, 18 ... Optical modulator, 19, 22
... actuator, 20, 21 ... control circuit, 23 ... actuator drive shaft, 24 ... mounting member, D ... optical disk,

Claims (10)

[Claims] 1. An information signal is recorded by forming a minute light spot of light incident from the transparent substrate side of an optical disc on a signal surface of the optical disc, or a light detector reflected from the signal surface is used as a photodetector. And a means for splitting a light beam in a divergent light state emitted from the one light source, which is fixedly installed at a predetermined position, in an optical head adapted to obtain a reproduction signal. Then, one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path that is configured to include the optical modulator, and then the second optical path is applied to the objective lens. The first light of the above-mentioned light source is made incident on the position of the signal surface installed at a first distance from the surface of the transparent substrate of the optical disk by the above-mentioned objective lens.
And a second light flux of the two light fluxes generated by the above-mentioned two-division is passed through the optical path length adjusting optical path including the optical modulator. , Is incident on an objective lens via a second optical path, and the objective lens is placed at a position of a signal surface that is installed at a second distance smaller than the first distance from the surface of the transparent substrate of the optical disc. Means for forming an image of a second minute light spot of the light from the light source, and a first photodetector provided near the image forming position of the reflected light from the first minute light spot, An optical head comprising: a second photodetector provided near an image forming position of reflected light from a second minute light spot. 2. An information signal is recorded by forming a minute light spot by the light incident from the transparent substrate side of the optical disk on the signal surface of the optical disk, or the light reflected from the signal surface is detected by a photodetector. And a means for splitting a light beam in a divergent light state emitted from the one light source, which is fixedly installed at a predetermined position, in an optical head adapted to obtain a reproduction signal. And one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path including the optical path length adjusting lens and the optical modulator, and then the second optical path. The first minute light spot of the light from the light source at the position of the signal surface installed at the second distance from the surface of the transparent substrate of the optical disc by the objective lens. And the means of After passing the other light beam of the two light beams through the optical path length adjusting optical path including the optical modulator,
The light beam passes through the second optical path and is incident on the objective lens, and the objective lens is installed at a position of a signal surface which is installed at a first distance different from the second distance from the surface of the transparent substrate of the optical disc. Means for forming an image of a second minute light spot of the light from the light source, and a first photodetector provided near the image forming position of the reflected light from the first minute light spot, An optical head comprising: a second photodetector provided near an image forming position of reflected light from a second minute light spot. 3. An information signal is recorded by forming a minute light spot of light incident from the transparent substrate side of the optical disc on the signal surface of the optical disc, or a light detector that reflects light reflected from the signal surface. And a means for dividing a light beam in a divergent light state emitted from the light source, the light source being fixedly installed at a predetermined position in the optical head for giving a reproduction signal. And one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path provided with the optical modulator, and then passed through the second optical path to enter the objective lens, A means for focusing the first minute light spot of the light from the light source on the position of the signal surface installed at the first distance from the surface of the transparent substrate of the optical disk by the objective lens; 2 caused by division
The other light of the one light flux is passed through an optical path length adjusting optical path including an optical modulator and an optical path length adjusting lens, and then passed through a second optical path to enter an objective lens, The second minute light spot of the light from the light source is connected to the position of the signal surface installed at the second distance different from the first distance from the surface of the transparent substrate of the optical disc by the objective lens of. Image forming means, and a first photodetector provided near the image forming position of the reflected light from the first minute light spot,
An optical head comprising: a second photodetector, which is provided with the reflected light flux from the second minute light spot near the image forming position via a focusing lens. 4. An optical signal is recorded on a signal surface of an optical disk by recording a minute light spot formed by light incident from the transparent substrate side of the optical disk, or light reflected from the signal surface is detected by a light detecting section. And a means for dividing a light beam in a divergent light state emitted from the light source, the light source being fixedly installed at a predetermined position in the optical head for giving a reproduction signal. And one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path including the optical modulator, and then is passed through the second optical path to the objective lens. The first light of the above-mentioned light source is made incident on the position of the signal surface installed at a first distance from the surface of the transparent substrate of the optical disk by the above-mentioned objective lens.
And a second light flux of the two light fluxes generated by the above-mentioned two-division is passed through an optical path length adjusting optical path including an optical modulator. , Is incident on an objective lens through a second optical path, and the objective lens is placed at a position of a signal surface which is installed at a second distance smaller than the first distance from the surface of the transparent substrate of the optical disc. Means for forming an image of the second minute light spot of the light from the light source, and a first light detection section provided near the image forming position of the reflected light from the first minute light spot, A second photodetector provided near the image forming position of the reflected light from the second minute light spot and a focus error signal obtained based on the detected force from the first photodetector are given. An actuator for the automatic focus control system of the objective lens,
An optical head comprising: an actuator of an optical path length control system of an optical path for adjusting an optical path, to which a focus error signal obtained based on the detected force from the second photodetector is given. 5. An information signal is recorded by forming a minute light spot by the light incident from the transparent substrate side of the optical disk on the signal surface of the optical disk, or the light reflected from the signal surface is detected by a light detecting section. And a means for dividing a light beam in a divergent light state emitted from the light source, the light source being fixedly installed at a predetermined position in the optical head for giving a reproduction signal. And one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path including the optical path length adjusting lens and the optical modulator, and then through the second optical path. The first minute light spot of the light from the light source at the position of the signal surface installed at the second distance from the surface of the transparent substrate of the optical disk by the objective lens. And the means of After passing the other light beam of the two light beams through the optical path length adjusting optical path including the optical modulator,
The light passes through the second optical path and is incident on the objective lens, and the objective lens is provided at the position of the signal surface which is installed at a first distance different from the second distance from the surface of the transparent substrate of the optical disc. Means for forming an image of the second minute light spot of the light from the light source, and a first light detection section provided near the image forming position of the reflected light from the first minute light spot, A second photodetector provided near the image forming position of the reflected light from the second minute light spot and a focus error signal obtained based on the detected force from the first photodetector are given. An actuator of an automatic focus control system of the objective lens and an actuator of an optical path length control system of an optical path for adjusting an optical path to which a focus error signal obtained based on the detected forces from the second photodetector are provided. Optical head. 6. An information signal is recorded by forming a minute light spot of light incident from the transparent substrate side of the optical disk on the signal surface of the optical disk, or light reflected from the signal surface is detected by a light detecting section. And a means for dividing a light beam in a divergent light state emitted from the light source, the light source being fixedly installed at a predetermined position in the optical head for giving a reproduction signal. And one of the two light beams generated by the above-mentioned two divisions is passed through the first optical path provided with the optical modulator, and then passed through the second optical path to enter the objective lens, A means for focusing the first minute light spot of the light from the light source on the position of the signal surface installed at the first distance from the surface of the transparent substrate of the optical disk by the objective lens; 2 caused by division
The other light of the one light flux is passed through an optical path length adjusting optical path including an optical modulator and an optical path length adjusting lens, and then passed through a second optical path to enter an objective lens, The second minute light spot of the light from the light source is connected to the position of the signal surface installed at the second distance different from the first distance from the surface of the transparent substrate of the optical disc by the objective lens of. An image forming means, and a first photodetector provided near the image forming position of the reflected light from the first minute light spot,
The reflected light flux from the second minute light spot is obtained based on the second light detection unit provided near the image forming position via the focusing lens and the detected force from the first light detection unit. And an actuator of an automatic focus control system of an objective lens to which a focus error signal is applied, and an optical path length of an optical path for adjusting an optical path to which a focus error signal obtained based on the detected force from the second photodetector is applied. An optical head comprising a control system actuator. 7. The optical head according to claim 1, further comprising means for changing the light output of the light source between the recording operation mode and the reproducing operation mode. 8. A reproduction light signal is obtained by forming a minute light spot on the signal surface of the optical disk by the reproduction light incident from the transparent substrate side of the optical disk and applying the reflected light from the signal surface to the photodetection section. In such an optical head, one light source fixedly installed at a predetermined position, a means for dividing the reproducing light flux in a divergent light state emitted from the light source into two, and the two divisions One of the two light fluxes generated by the laser beam passes through the first optical path and the second optical path and is incident on the objective lens, and the objective lens causes a first distance from the surface of the transparent substrate of the optical disc. Means for forming the first minute light spot of the reproduction light at the position of the signal surface installed on the optical disk, and the other of the two light beams generated by the above-mentioned two divisions for adjusting the optical path length. After passing the optical path, the second optical path Then, the second small amount of reproduction light is placed at a position of the signal surface, which is installed at a second distance smaller than the first distance from the surface of the transparent substrate of the optical disk by the objective lens. Means for forming an image of a different light point, a first photodetector provided near the image forming position of the reflected light from the first minute light point, and a reflection from the second minute light point A second photodetector provided near the image forming position of the light, and an actuator of an automatic focus control system of the objective lens to which a focus error signal obtained based on the detected force from the first photodetector is given. An optical head comprising: an actuator of an optical path length control system of an optical path for adjusting an optical path, to which a focus error signal obtained on the basis of the detected forces from the second photodetector is given. 9. A reproduction light signal is obtained by forming a minute light spot on the signal surface of the optical disk by the reproduction light incident from the transparent substrate side of the optical disk, and applying the reflected light from the signal surface to the photodetection section. In such an optical head, one light source fixedly installed at a predetermined position, a means for dividing the reproducing light flux in a divergent light state emitted from the light source into two, and the two divisions One of the two light beams generated by the above-mentioned objective lens is made to pass through the first optical path provided with the optical path length adjusting lens and then through the second optical path to enter the objective lens. By means of means for forming an image of the first minute light spot of the reproduction light at the position of the signal surface provided at the second distance from the surface of the transparent substrate of the optical disc, and the two means generated by the two divisions. The optical path length adjustment of the other of the light beams After passing through the adjusting optical path, passing through the second optical path and entering the objective lens, the objective lens is installed at a first distance different from the second distance from the surface of the transparent substrate of the optical disc. Means for forming an image of a second minute light spot of the reproduction light at the position of the signal surface to be formed,
A first photodetector provided near the image forming position of the reflected light from the first minute light spot, and a second light detecting unit provided near the image forming position of the reflected light from the second minute light spot. From the first photodetector, the actuator of the automatic focus control system of the objective lens to which the focus error signal obtained based on the detected forces from the first photodetector is given, and the second photodetector. And an actuator of an optical path length control system of an optical path for adjusting an optical path to which a focus error signal obtained based on the detected force of the optical path is detected. 10. A reproduction light signal is obtained by forming a minute light spot of the reproduction light incident from the transparent substrate side of the optical disk on the signal surface of the optical disk and applying the reflected light from the signal surface to the photodetection section. In such an optical head, one light source fixedly installed at a predetermined position, a means for dividing the reproducing light flux in a divergent light state emitted from the light source into two, and the two divisions One of the two light beams generated by the second light beam after passing through the first optical path
Of the reproduction light at the position of the signal surface installed at the first distance from the surface of the transparent substrate of the optical disk by the objective lens.
Means for forming an image of a minute light spot and the other light flux of the two light fluxes generated by the above-mentioned two divisions, after passing through the optical path length adjustment optical path provided with the optical path length adjustment lens, The light passes through the second optical path and is incident on the objective lens, and is reproduced by the objective lens at the position of the signal surface which is installed at the second distance different from the first distance from the surface of the transparent substrate of the optical disc. Means for forming an image of a second minute light spot of light, a first photodetector provided in the vicinity of an image forming position of the reflected light from the first minute light spot, and the second minute light A second photodetector provided with a reflected light beam from a different light spot near the imaging position via a focusing lens, and a focus error signal obtained based on the detected forces from the first photodetector described above are given. An objective lens automatic focus control system actuator, Optical head of comprising an actuator of the optical path length control system in the optical path length adjusting optical path focusing error signal is given, obtained on the basis of the detection Todoroki from the light detection unit.