JPH09259459A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head for changing a position for reading optical information according to the kind of an optical information recording medium, which is realized at a low cost and capable of employing a low output light source and reading optical information at a high speed. SOLUTION: An intermediate lens 5 and an objective lens 4 are disposed on the optical axis of a laser beam from a semiconductor laser 1 reflected by a beam splitter 2. The intermediate lens 5 is moved toward the objective lens 4 by a specified distance by conducting power to a driving coil 8 and laser beams are collected in the moved condition thereof. Thus, the light collecting position of the objective lens 4 is located in the focal position (optical information recording surface of CD) of the objective lens 4 when the intermediate lens 5 is in a normal position while the light collecting position thereof is located before the focal position (optical information recording surface of DVD) when the intermediate lens 5 is moved. Thus, the optical information of the CD and the DVD can be read by a photodetector 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for reading optical information from an optical information recording medium.

[0002]

2. Description of the Related Art At present, compact discs (CDs) are in widespread use, and the market is expanding. On the other hand, a digital video disk (DVD) has been standardized as a next-generation CD, and its widespread use is expected from home and abroad as a central medium in the video field or information field. To use these media conveniently,
Although it is desired that the drive devices have compatibility so that two types of discs can be used, CDs and DVDs
Since the focus position and the numerical aperture (NA) of the objective lens are different between and, the conventional objective lens is used as it is for CD and DVD.
It cannot be used for and.

Therefore, as a technique in which a CD and a DVD can be used, a hologram is formed in the center of the objective lens, and
Optical heads with different focus positions and NA have been considered. (Nikkei Mechanical 1995.7.10 No.4
58). However, the process for forming the hologram on the objective lens is difficult, and the manufacturing with resin is difficult, so that the cost rises and the laser with sufficient output must be concentrated at both focal points. The required output of the semiconductor laser also increases.

On the other hand, as a countermeasure against the above technique, an optical head having two types of objective lenses has been proposed (Nikkei Mechanical 1995.8.7 No. 460). In this system, two lenses are attached to a shaft-sliding type actuator, and the lenses are switched according to CD and DVD by the rotation of the shaft.

[0005]

However, in the above-mentioned prior art, since the actuator portion for rotating the shaft is complicated and the inertia weight becomes large, a high-speed reading operation requiring high-speed followability is required. Then, there is a possibility that the reading of the optical information becomes uncertain.

The present invention has been made in view of the above circumstances, and an object thereof is a light source that can be implemented at a low cost and has a low output in a configuration in which the reading position of optical information is changed according to the type of optical information recording medium. It is an object of the present invention to provide an optical head capable of reading the optical information at high speed.

[0007]

According to the invention of claim 1, the light from the light source is condensed on the optical information recording surface of the optical information recording medium by the intermediate lens and the objective lens via the beam splitter. Is irradiated. And the photodetector
The light reflected by the optical information recording surface and received through the objective lens, the intermediate lens and the beam splitter is detected.

At this time, the distance from the objective lens to the optical information recording surface of the optical information recording medium and the size of the beam spot required to read the optical information differ depending on the type of the optical information recording medium. Therefore, if the incident angle of the light to the objective lens is adjusted by moving the position of the intermediate lens along the optical axis, the condensing position of the objective lens and the size of the beam spot light are changed. It is possible to handle changes in type.

According to the second aspect of the present invention, the light from the light source is converted into parallel light when passing through the beam splitter and the collimator lens, and is condensed by the intermediate lens and the objective lens of the optical information recording medium. It is irradiated onto the optical information recording surface. Then, the photodetector detects the light reflected by the optical information recording surface and received through the objective lens, the intermediate lens, the collimator lens and the beam splitter. When the incident angle of light to the objective lens is adjusted by moving the position of the intermediate lens along the optical axis, the focusing position of the objective lens and the size of the beam spot are changed. Can be changed.

According to the third aspect of the present invention, the intermediate lens can be moved by controlling the energization of the drive coil, so that the intermediate lens can be moved easily and at high speed.

According to the invention of claim 4, since the holding means holds the intermediate lens at the moving position, it is not necessary to move the intermediate lens.

According to the fifth aspect of the present invention, when the first attracting means is energized, the first attracting means attracts the magnetized body provided on the intermediate lens, so that the intermediate lens is positioned at the first position. be able to. In this case, since the magnetized body generates the residual magnetic field, the first magnetized means maintains the magnetized state with respect to the magnetized body even if the energization state of the first magnetizing means is stopped.

Similarly, when the second attracting means is energized, the second attracting means attracts the magnetized body, so that the intermediate lens can be positioned at the second position. In this case, since the magnetized body generates a residual magnetic field, the second magnetized means maintains the magnetized state with respect to the magnetized body even if the energization state of the second magnetizing means is stopped.

According to the sixth aspect of the present invention, the mechanical component for moving the intermediate lens and the mechanical component for moving the objective lens can be used in common, so that the overall structure can be simplified. At the same time, the positional accuracy of the intermediate lens with respect to the objective lens can be improved.

[0015]

FIG. 1 shows a first embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 schematically shows the configuration of the optical head. In FIG. 1, a semiconductor laser 1 as a light source emits a laser beam having a specific wavelength. The beam splitter 2 is arranged on the optical axis of the semiconductor laser 1, and reflects the laser beam emitted from the semiconductor laser 1 in the orthogonal direction.

An objective lens unit 3 is arranged on the optical axis of the laser beam reflected by the beam splitter 2. The objective lens unit 3 is configured by uniting the objective lens 4 and the intermediate lens 5. That is,
In the objective lens unit 3, the magnet 6a is fixed inside the body 6, and the first drive coil 7 and the second drive coil 8 are provided inside the magnet 6a by the spring members 7a and 8a.
They are elastically supported by a. The objective lens 4 is fixed to the first driving coil 7, and the intermediate lens 5 is fixed to the second driving coil 8.

In this case, the objective lens 4 moves up and down by controlling the energization of the first driving coil 7, and the focus control by the objective lens 4 can be performed according to the up and down movement. Further, the intermediate lens 5 includes the second drive coil 8
Is in the normal position in the non-energized state, the laser beam incident from the beam splitter 2 is converted into parallel light at the normal position, and the second driving coil 8 is energized in a predetermined distance in the direction of the objective lens 4. By moving, the laser beam incident from the beam splitter 2 is condensed. Therefore, the focus position of the laser beam by the objective lens 4 is the focus position of the objective lens 4 when the second drive coil 8 is energized, and is the front side of the focus position when the second drive coil 8 is not energized.

That is, a CD as an optical information recording medium has an optical information recording surface formed on the bottom surface of a disk-shaped substrate having a thickness of 1.2 mm, whereas a DVD has a thickness of 0 mm. It is formed by laminating two discs each having an optical information recording surface on the bottom surface of a disc-shaped substrate of 6 mm. Due to such a difference in standards, both the CD and the DVD have a thickness of 1.2 mm, but the optical information recording surface of the CD is located 1.2 mm deep from the substrate surface, whereas the DV
The optical information recording surface of D is located 0.6 mm behind the substrate surface. Further, since the size of the pit formed on the optical information recording surface of the DVD is smaller than that of the DVD, it is necessary to narrow down the beam spot, and as a means therefor, it is necessary to increase the numerical aperture (NA).

Therefore, since it is impossible to read the optical information from the optical information recording surface of the CD and the DVD with the single objective lens 4, the objective lens 4 can be moved by moving the intermediate lens 5 as described above. Focusing position and numerical aperture (N
I am trying to change A).

On the other hand, on the optical axis of the objective lens 4, a cylindrical lens 9 and a photodetector 10 are arranged at a position behind the beam splitter 2. The cylindrical lens 9 changes the luminous flux shape of the laser beam reflected on the optical information recording surface of the CD or DVD according to the focus shift. That is, since the cylindrical lens 9 functions as a lens in a predetermined direction (vertical direction with respect to the drawing) and functions as a lens in a direction orthogonal to the predetermined direction (horizontal direction with respect to the drawing), the cylindrical lens 9 is used. The cross-sectional shape of the light flux of the passed laser beam gradually changes in the direction perpendicular to the drawing along the optical axis from a vertically elongated elliptical shape to a perfect circle to a horizontally elongated elliptical shape.

The photodetector 10 is composed of four-division photodiodes in the shape of "T", and the detection signal output from each photodiode is used for focus control and tracking control for the optical head. It is also used as a reproduction signal indicating optical information.

In this case, the four-division photodiode constituting the photodetector 10 is a laser beam which has passed through the cylindrical lens 9 in a state where the optical information recording surface of the CD or DVD is correctly positioned at the converging position of the objective lens 4. It is positioned so that the light flux becomes a perfect circle. Therefore, when the shape of the beam spot received by the photodetector 10 is a perfect circle, it can be determined that the optical information recording surface of the CD or DVD is located at the focus position of the objective lens 4, and the photodetector 10
When the shape of the beam spot received by is a vertically elongated elliptical shape, it can be determined that the optical information recording surface is farther than the focus position of the objective lens 4, and the shape of the beam spot received by the photodetector 10 is In the case of a horizontally long elliptical shape, it can be determined that the optical information recording surface is closer to the focus position of the objective lens 4, and therefore the focus of the objective lens 4 is determined based on the detection result of the photodetector 10. Control can be performed.

The four-division photodiode of the photodetector 10 is also used for outputting a tracking error signal. In other words, the four-division photodiode is used as a two-division photodiode in which two groups are used. When the tracking is normal, the signal levels of the detection signals from the two photodiodes are the same, but the tracking If the deviation occurs, a difference occurs in the signal levels of the detection signals from the two sets of photodiodes. Therefore, by driving a tracking actuator (not shown) so as to suppress the difference in the signal levels to zero. Tracking control can be performed. Then, by summing the outputs of the 4-division photodiodes of the photodetector 10, it is possible to obtain a reproduction signal indicating optical information.

Now, the case of reading the optical information of a CD with the optical head having the above-mentioned structure will be described. Semiconductor laser 1
The laser beam emitted from is reflected by the beam splitter 2 and passes through the intermediate lens 5 and the objective lens 4 to be condensed. At this time, since the intermediate lens 5 is located at the normal position, the laser beam is converted into a parallel beam by the intermediate lens 5 and then focused by the objective lens 4 at the focal position. As a result, the optical information recording surface of the CD located at the focal position of the objective lens 4 is irradiated with the laser beam in a condensed state (shown by the solid line in FIG. 1).

The laser beam reflected by the optical information recording surface of the CD passes through the objective lens 4, the intermediate lens 5, the beam splitter 2 and the cylindrical lens 9, and then is received by the photodetector 10 in a condensed state. . Therefore, focus control and tracking control can be performed based on the signal from the photodetector 10, and a reproduction signal indicating optical information can be obtained.

Next, a DVD is produced by using the optical head having the above structure.
The second drive coil 8 is energized to read the optical information. Then, the intermediate lens 5 moves in the direction of the objective lens 4 by a predetermined distance. At this time, the laser beam emitted from the semiconductor laser 1 and passing through the intermediate lens 5 passes through the objective lens 4 in a condensed state. Thereby, the objective lens 4
The focus position of is on the front side of the focus position.

In this case, the laser beam passing through the objective lens 4 (shown by the broken line in FIG. 1) is collected at a large incident angle as compared with the laser beam when reading the optical information of the CD (shown by the solid line in FIG. 1). Since the light is emitted, the numerical aperture (NA) is largely changed while changing the converging position as described above.

Here, the numerical aperture (NA) of the lens will be described. The numerical aperture (NA) of the lens shown in FIG. 2 can be expressed by the following formula.

## EQU1 ## NA = n.sin .theta. = Na / R (where n is the refractive index of the lens substrate)

The relationship between the diameter w of the beam spot condensed by the lens shown in FIG. 2 and NA can be expressed by the following equation.

(2) w = 0.41λ / NA

Since the pit area of the DVD is smaller than that of the CD in order to support high density recording, it is necessary to narrow down the beam spot applied to the pit.
In this case, since the diameter of the beam spot can be narrowed down by increasing the numerical aperture (NA) as shown in the equation 2, it is possible to use the optical head of the CD for DVD. Then, as in the case of reading the optical information of the CD described above, focus control and tracking control are performed based on the signal from the photodetector 10, and a reproduction signal indicating the optical information can be obtained.

According to the above structure, the semiconductor laser 1
In the configuration of condensing the laser beam from the objective lens 4 by the objective lens 4, the intermediate lens 5 shortens the focal position of the objective lens 4 and increases the numerical aperture (NA), so that a hologram is formed on the objective lens. It can be implemented at low cost compared to the structure. Further, since it is possible to effectively use all of the light from the semiconductor laser 1 while switching the two converging positions according to the CD and the DVD, it is possible to employ the semiconductor laser 1 having a low output. Furthermore, since the intermediate lens 5 is provided integrally with the objective lens unit 3, compared to a configuration in which the objective lens is exchanged according to CD and DVD, the size is small, the inertial weight is small, and high-speed reading operation is surely performed. You can follow.

FIG. 3 shows a second embodiment of the present invention,
The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. The second embodiment is characterized in that an intermediate lens is provided in a structure including a collimator lens for converting the laser beam from the semiconductor laser 1 into a parallel beam.

That is, in FIG. 3, the beam splitter 2
On the optical axis of the laser beam from the collimator lens 11
Are arranged. Further, the intermediate lens 13 is unitized with the objective lens 4 in the objective lens unit 12, and the intermediate lens 13 is moved by a predetermined distance in the direction of the objective lens 4 by energizing the second driving coil 8. .

In this case, when the intermediate lens 13 moves a predetermined distance in the direction of the objective lens 4 in response to the energization of the second driving coil 8, the laser beam (shown by the solid line in FIG. 3) to the objective lens 4 is emitted. Since the incident angle becomes larger than the incident angle of the laser beam (shown by the broken line in FIG. 3) when the intermediate lens 13 is located at the normal position, the numerical aperture (NA) of the objective lens 4 becomes large. , The beam spot can be narrowed down.

According to the second embodiment, the beam from the semiconductor laser 1 is once converted into parallel light by the collimator lens 11 and the intermediate lens 13 is obtained while exhibiting the same effect as that of the first embodiment. Since the light is focused by the objective lens 4, the influence of the optical aberration of the lens can be reduced as compared with the first embodiment.

4 to 6 show a third embodiment of the present invention. The third embodiment is characterized in that it has a function of holding the intermediate lens 5 in the moving position. That is, in the objective lens unit 14, the magnet 15a is provided inside the rectangular frame-shaped main body 15 and the magnetic pole piece 16 is provided upright. The second drive coils 7 and 8 are provided so as to penetrate therethrough (see FIG. 5).

The first and second drive coils 7 and 8 are the main body 1
5, one end of which is supported by spring members 7b and 8b. In this case, the spring member 8b as a holding means for supporting the second drive coil 8 is elastically deformable from the shape shown by the solid line in FIG. 6 to the shape shown by the broken line, and is elastically deformed to the shape shown by the broken line. When elastically deformed, the elastically deformed state is maintained, and when the elastically deformed state is released, the original shape is restored. Here, the spring member 8
When b is the shape shown by the solid line in FIG. 6, the laser spot emitted from the objective lens 4 is focused on the optical information recording surface of the CD.

When reading the optical information of the DVD, the second drive coil 8 is energized. Then, since the second drive coil 8 is attracted to the magnet 15a, the intermediate lens 5 moves in the direction of the objective lens 4 against the elastic force of the spring member 8b.

At this time, when the spring member 8b changes from the shape indicated by the solid line to the shape indicated by the broken line in FIG. 6 along with the movement of the intermediate lens 5, the spring member 8b maintains the shape indicated by the broken line. As a result, the intermediate lens 5 is held at the moving position even when the power supply to the second drive coil 8 is stopped, so that the focus position of the laser spot by the objective lens 4 is set on the optical information recording surface of the DVD. Can be adjusted.

When reading the optical information of a CD, the second
The drive coil 8 is energized in the opposite direction. Then, since the second drive coil 8 repels the magnet 15a, the intermediate lens 5
Moves in the direction opposite to the objective lens 4 against the elastic force of the spring member 8b. As a result, the shape of the spring member 8b returns to the original shape and the intermediate lens 5 is positioned at the initial position. Therefore, even if the energization of the second drive coil 8 is terminated, the laser spot is collected by the objective lens 4. The light position can be adjusted.

According to the third embodiment, when the position of the intermediate lens 5 is moved in response to the change of the optical information recording medium, it is sufficient to energize the second drive coil 8 for a short time. Therefore, it is possible to significantly reduce the current consumption while achieving the same effects as those of the first embodiment.

FIG. 7 shows a support structure for the intermediate lens 5 in the fourth embodiment of the present invention. The fourth embodiment is characterized in that when the intermediate lens 5 is held at the moving position, the accuracy of the moving position is improved. Objective lens unit 1
In FIG. 7, a first electromagnet 19 and a second electromagnet 20 are opposed to each other inside the main body portion 18 with a predetermined distance therebetween.

Here, while the frame surrounding the first and second electromagnets 19 and 20 is formed of a non-magnetic material, the first and second electromagnets are formed in the portion facing the electromagnet on the other side. Magnetic bodies 19a and 20a are provided respectively. in this case,
The first electromagnet 19 and the first magnetic body 19a constitute a first attracting means, and the second electromagnet 20 and the second magnetic body 20a constitute a second attracting means.

On the other hand, the intermediate lens 5 is pivotally supported on the main body 18 by a spring member 21. An arm portion 22 as a magnetized body is provided on the outer side of the intermediate lens 5, and the arm portion 22 is located in the gap between the first and second electromagnets 19 and 20. The arm portion 22 is made of a ferromagnetic material, and is magnetized in accordance with the interlinking of the magnetic field, and has a characteristic that the residual magnetic field is generated even if the magnetic field is removed. Have. Note that FIG. 7 shows an initial state in which no residual magnetic field is generated in the arm portion 22.

When the first electromagnet 19 is energized, the magnetic field generated from the first electromagnet 19 is linked to the arm portion 22 provided on the intermediate lens 5. Then, the arm portion 22 is magnetized and the first magnetic body 1 provided in the first electromagnet 19 is
Adsorbed to 9a and positioned at the first position. As a result, the intermediate lens 5 moves in the opposite direction to the objective lens 4,
The laser beam emitted from the objective lens 4 is focused on the optical information reading surface of the CD. At this time, even if the power supply to the first electromagnet 19 is stopped, the residual magnetic field is generated in the arm portion 22, so that the arm portion 22 does not move the first electromagnet 19 to the first position.
The magnetic substance 19a is attracted to the magnetic substance 19a to maintain the moving state to the first position.

When reading the optical information of the DVD, the second electromagnet 20 is energized. Then, the arm portion 22 is magnetized and attracted to the second magnetic body 20 provided on the second electromagnet 20 to be positioned at the second position. At this time, even if the power supply to the second electromagnet 20 is stopped, since the residual magnetic field is generated in the arm portion 22, the arm portion 22 is provided with the second magnetic body 20 a provided in the second electromagnet 20. Adsorbed on the second
Keep moving to the position. Therefore, the intermediate lens 5
Moves in the direction of the objective lens 4, so that the laser beam emitted from the objective lens 4 can be focused on the optical information reading surface of the DVD.

According to the fourth embodiment, the intermediate lens 5 can be accurately positioned at the first and second positions, so that the laser spot from the objective lens 4 can be collected as compared with the above embodiments. The accuracy of the light position can be improved.

The present invention is not limited to the above embodiments, but can be modified or expanded as follows. By increasing the output intensity of the semiconductor laser 1, write-once and rewritable optical disks can be supported. In this case, a polarization beam splitter is used as the beam splitter, and a quarter wavelength plate is arranged on the optical axis reaching the polarization beam splitter and the optical disc.

[Brief description of drawings]

FIG. 1 is an overall schematic view showing a first embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a numerical aperture of a lens.

FIG. 3 is a view corresponding to FIG. 1, showing a second embodiment of the present invention.

FIG. 4 is a view corresponding to FIG. 1, showing a third embodiment of the present invention;

FIG. 5 is a plan view of an objective lens unit.

FIG. 6 is a vertical cross-sectional view of a main part showing movement of an intermediate lens.

FIG. 7 is a view corresponding to FIG. 6 showing a fourth embodiment of the present invention.

[Explanation of symbols]

1 is a semiconductor laser (light source), 2 is a beam splitter, 4
Is an objective lens, 5 is an intermediate lens, 9 is a cylindrical lens, 10 is a photodetector, 11 is a collimator lens, 13
Is an intermediate lens, 8b is a spring member (holding means), 19 is a first electromagnet (first attraction means), 19a is a first magnetic body (first attraction means), and 20 is a second electromagnet (first attraction means). No. 2 attraction means) and 20a are second magnetic bodies (second attraction means).

Claims (6)

[Claims] 1. A light source, a beam splitter provided on the optical axis of the light source, an objective lens for condensing light from the beam splitter onto an optical information recording surface of an optical information recording medium, and the optical information recording. In an optical head including a photodetector that receives light reflected by a surface via the objective lens and a beam splitter, the optical head moves along the optical axis between the beam splitter and the objective lens. An optical head comprising an intermediate lens which is provided so as to adjust an incident angle of light to the objective lens according to a moving position. 2. A light source, a beam splitter provided on the optical axis of the light source, a collimator lens for converting the light from the beam splitter into parallel light, and the light from the collimator lens for an optical information recording medium. An optical head comprising: an objective lens that collects light on an optical information recording surface; and a photodetector that receives light reflected by the optical information recording surface via the objective lens, a collimator lens, and a beam splitter. And an objective lens that is movably provided along the optical axis between the objective lens and the objective lens and that adjusts an incident angle of light to the objective lens according to a moving position. Optical head. 3. The optical head according to claim 1, wherein the position of the intermediate lens is adjusted by utilizing attraction and repulsion between the magnet and the driving coil. 4. The optical head according to claim 1, further comprising holding means for holding the intermediate lens in a moving position. 5. A magnetized body provided on the intermediate lens, and first attracting means for attracting the magnetized body to a first position in response to energization and maintaining the magnetized body in a non-energized state. And a second adsorbing means for adsorbing the magnetized body to the second position in accordance with energization and maintaining the adsorbed state of the magnetized body in the non-energized state. The described optical head. 6. The optical head according to claim 1, wherein the intermediate lens is unitized with the objective lens.