JPH0677331B2 - Light head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] Between an optical disc medium and a light guide plate for arranging a prism part for injecting a light beam at a position avoiding an objective lens and an actuator and guiding the beam from the prism part to the objective lens. By arranging the objective lens and the actuator so that they are located at the position, the optical head can be made smaller and thinner.

[Industrial application field]

In order to reduce the size and thickness of the optical disk device, various companies are studying reduction in size and thickness of the optical head, but the present invention relates to the optical head in which such reduction in size and thickness is required.

[Conventional technology]

FIG. 12 is a side view showing an outline of a conventional optical head. D
Is an optical disc medium, the coherent light 2 emitted from the optical system 1 travels in parallel with the optical disc medium surface, is reflected by the prism mirror 3 toward the optical disc medium D side, and is focused on the optical disc medium D via the objective lens 4. To be done. Further, for focusing and tracking, the objective lens 4 is driven vertically and horizontally by the actuator 5 composed of an electromagnet.

[Problems to be solved by the invention]

Conventionally, the optical head has been made thinner by devising the structure of the actuator section 5 of the objective lens 4.
As shown in FIG. 12, the prism mirror 3, the objective lens 4, and the lens actuator 5 are indispensable for guiding the beam 2 parallel to the optical disk medium surface to the optical disk medium D side. The total thickness of these layers limits the thickness, which limits the reduction in thickness.

A technical problem of the present invention is to solve such a problem and to enable further thinning.

[Means for solving problems]

FIG. 1 is a side view for explaining the basic principle of the optical head according to the present invention. 6 is a light guide, and at least a light guide plate 7
And a prism portion 8.

The objective lens 4 is arranged between the light guide plate 7 and the optical disc medium D, and the prism portion 8 is arranged at a position which does not overlap the objective lens 4 in the optical axis direction of the objective lens 4. There is.

Further, a hologram H1 for incident a light beam is provided on a side surface of the prism portion 8 which is perpendicular to the surface of the optical disc medium D, and a surface of the light guide plate 7 on the side of the optical disc medium D faces the objective lens 4. Then, it has a hologram H2 for emitting a light beam.

[Action]

The prism part 8 guides the light beam 10 incident from the direction parallel to the surface of the optical disc medium D to the light guide plate 7, and the light beam guided by the light guide plate 7 is changed by the hologram H2. It is taken out from the light guide plate 7 to the objective lens 4 side. Then, it is irradiated onto the optical disc medium D via the objective lens 4.

As is clear from FIG. 1, only the thin light guide plate 7 exists in the area of the objective lens 4 and the actuator 5 which hinders the thinning of the optical head. The prism portion 8 which requires a space in the vertical direction is arranged at a position avoiding the objective lens 4 and the actuator 5. Therefore, compared to the conventional structure of FIG. 12,
The thickness is greatly reduced as shown by the dimension d.

〔Example〕

Next, practical examples of how the optical head according to the present invention is embodied will be described. FIG. 2 is a perspective view showing a first embodiment of the optical head according to the present invention. The light guide 6
It is made of a transparent polyhedron (for example, optical glass such as BK7), and has a light guide plate 7 having a thickness of 1 to 2 mm and a prism portion 8 of 45 degrees. An incident hologram H1 is provided on a side wall 11 of the prism portion 8 perpendicular to the surface of the optical disc medium D. The surface S ₃ of the light guide plate 7 on the optical disk medium D side has a hologram H 2 for emission. 2 holograms H
The directions of the lattice stripes 1 and H2 are the z direction for the entrance hologram H1 and the y direction for the exit hologram H2. The surface of the optical disk medium D is parallel to the x, y plane. Incident hologram H
The plane wave vertically incident on 1 is diffracted by the hologram H1 and enters the prism unit 8. Then, first, the light is totally reflected by the slope S ₁ of the prism and goes to the bottom S ₂ . Next, the light is totally reflected by the bottom surface S ₂ , enters the outgoing hologram H 2 on the upper surface S _{3 of the} light guide plate 7, diffracts, and then exits in the z-axis direction. The number of total reflections may be changed depending on the length 1 of the light guide plate 7 in the x direction.

If only the above optical path is extracted and shown, it becomes as shown in FIG. When this optical path is expanded, it becomes as shown in FIG. In the unfolded state like this, hologram H1,
H2 is parallel to each other. Normally, when a hologram element is used, when the wavelength of the light source changes, the diffraction angle changes, and the focus when moving the light with the objective lens moves. However, in this embodiment, both holograms H1 and H2 have the same spatial frequency, and both holograms are parallel to each other.
Therefore, the wavelength of the light source fluctuates and the incident hologram H1
Even if the diffraction angle θ at is changed to the direction indicated by the chain line, the exit hologram H2 is also diffracted by the same angle θ in the opposite direction and cancels, so that the incident condition of the parallel light with respect to the objective lens does not change. Therefore, a good beam spot can always be maintained regardless of whether the semiconductor laser has a single mode or multiple modes and whether or not there is a mode hop.

FIG. 5 is a second embodiment and shows a case where the incident and outgoing angles of the plane wave with respect to the holograms H1 and H2 are changed. That is, the inclination of the gratings of both holograms H1 and H2 in the film thickness direction is the second
Since the case of FIG. 5 is closer to vertical than that of the figure, it is easy to create a hologram. Because, in FIG. 2, the light beam 10 is vertically incident on the hologram H1. Therefore, in order to manufacture the hologram H1, the light 13 vertically incident on the hologram H1 is produced as shown in FIG. 6 (a). And the light 15 traveling in the same direction as the beam 14 traveling from the hologram H1 to the surface S1 interfere with each other, so that the incident angles of the two manufacturing lights 13 and 15 are different from each other, which makes it difficult to manufacture a hologram having high diffraction efficiency. On the other hand, when the incident surface 11a is tilted so that the incident beam 10 and the manufacturing light 15 have the same angle as shown in FIG. 5, FIG.
, The incident angles of the two production lights 13 and 15 become equal,
It becomes easy to manufacture a hologram with high diffraction efficiency.

As shown in FIG. 5, since the exit hologram H2 is also inclined by the same angle as the entrance hologram H1, the optical path from the incident light beam 10 to the exit light beam 12 is unfolded as shown in FIG. Therefore, the entrance hologram H1 and the exit hologram H2 are parallel to each other.

FIG. 8 is a side view showing a third embodiment of the optical head according to the present invention, and FIG. 9 is a perspective view of the same embodiment. In this embodiment, the PBS film 16 is arranged between the prism portion 8 and the light guide plate 7 perpendicularly to the surface of the optical disc medium D. Further, a λ / 4 plate 17 is arranged between the exit hologram H2 and the objective lens 4, and a hologram lens 18 is arranged on the end face of the light guide plate 7.

In this embodiment, the collimated light 10 is diffracted by the incident hologram (plane wave grating) H1 and enters the prism-shaped transparent body 8. The light totally reflected by the slope S1 passes through the PBS film 16 arranged perpendicularly to the optical disc surface, and the light guide plate 7
After being totally reflected by the bottom surface S4, it is diffracted by the outgoing hologram (plane wave grating) H2 and becomes a beam perpendicular to the optical disc medium D. The above is represented by the optical path. Then, it further passes through the λ / 4 plate 17 and the objective lens 4 and is focused on the optical disc medium D. Although the reflected signal light from the optical disk medium D returns in the outward path of →→, it is reflected by the PBS film 16 because the polarization plane is rotated by the λ / 4 plate 17, and → the upper surface of the light guide plate 7 as shown in After being totally reflected by S3 and the bottom surface S4, the hologram lens 18 guides the light to a photodetector 19.

Also in this embodiment, when the bending of the optical path due to reflection is developed, the two holograms H1 and H2 are parallel to each other. As a result, even if the wavelength of the light source changes as described above, the incident angle with respect to the objective lens 4 does not change. On the other hand, the hologram lens 18 for focusing the signal light is provided with the focus and track error detection functions. In this case, the focusing point moves due to the wavelength variation of the light source, but the influence can be suppressed by devising the dividing method of the detector. As described above, in this embodiment, since the photodetector 19 is incorporated in the movable part, the moving accuracy of the movable part has a margin.

The hologram lens 18 has a light-collecting function as shown in FIG. 10 (a). Instead of the hologram lens 18, as shown in FIG. 10 (b), a plane wave grating and an optical lens 20 are combined. It is also possible to configure a light collecting system.
A beam splitter having a small polarization dependency can be used instead of the PBS16.

FIG. 11 is a perspective view showing the appearance of an optical head manufactured based on each of the above examples. The light guide 6, the objective lens 4, the actuator 5 thereof, and the like according to the present invention are mounted on a common substrate to form the movable portion 22, and perform tracking (coarse) operation in the direction of arrow a. Further, the prism 21 is provided on the entrance hologram H1 of the prism portion 8 in the embodiment of FIG.
By adding, tracking of the entire movable part 22 (coarse)
The direction and the direction of the collimated light 10 from the light source fixing portion 1 are made to coincide with each other, and the movable portion is prevented from changing the incident angle and the incident position of the light beam 10. Focusing is performed by moving the objective lens 4 up and down, and tracking (fine adjustment) is performed by the rotational force of the actuator 5.

Each hologram in the present invention may be directly formed on the light guide, or a separately prepared hologram may be attached to the light guide.

〔The invention's effect〕

As described above, according to the present invention, the light beam 10 parallel to the surface of the optical disc medium is made incident on the prism portion 8 by the incident hologram H1, and the total reflection from the prism portion 8 to the light guide plate 7 causes the inside of the light guide plate 7. Is guided to the vicinity of the objective lens 4 and taken out by the exit hologram H2. Therefore, the prism portion 8 having a large dimension in the thickness direction avoids the objective lens 4 and the actuator 5, and disposes only the flat light guide plate 7 on the objective lens 4 and the actuator 5 side, thereby making the optical head thin and small. Can be realized.

[Brief description of drawings]

FIG. 1 is a side view for explaining the basic principle of an optical head according to the present invention, FIG. 2 is a perspective view of a first embodiment of the present invention, FIG. 3 is a perspective view showing an optical path in the same embodiment, and FIG. Is a developed view of the same optical path, FIG. 5 is a perspective view showing a second embodiment of the present invention, FIG. 6 is a drawing showing a method of manufacturing an entrance hologram, and FIG. 7 is an optical path in the embodiment of FIG. Figure showing expanded,
FIG. 8 is a side view showing a third embodiment of the present invention, FIG. 9 is a perspective view of the same embodiment, FIG. 10 is a side view illustrating a focusing system for a detector, and FIG. 11 is an optical head. Perspective view showing the completed state of
FIG. 12 is a side view of a conventional optical head. In the figure, D is an optical disk medium, 1 is an optical system, 4 is an objective lens, 5 is an actuator, 6 is a light guide, 7 is a light guide plate, 8 is a prism part, 10 is an incident light beam, H1 is an incident hologram, and H2 is H2. Indicates the hologram for emission.

Claims (5)

[Claims] 1. A light guide (6) having a light guide plate (7) and a prism part (8), wherein an objective lens (4) is provided between the light guide plate (7) and the optical disk medium (D). The prism portion (8) is arranged at a position that does not overlap the objective lens (4) in the optical axis direction of the objective lens (4). A hologram (H1) for incident a light beam is provided on a side surface perpendicular to the surface of D), and the surface of the light guide plate (7) on the optical disk medium (D) side faces the objective lens (4). And an optical head having a hologram (H2) for emitting a light beam. 2. A plane wave whose optical axis is parallel to the surface of the optical disc medium is made incident on the light guide (6) from the incident hologram (H1) and propagated, and the exit hologram (H2).
The optical head according to claim (1), characterized in that the optical head is configured to enter the objective lens (4) such that its optical axis is perpendicular to the optical disk medium surface. 3. The two holograms (H1) and (H2) have the same spatial frequency, the lattice spacing is the same throughout the hologram, and the lattice fringes are straight lines. The optical head according to the item 1). 4. A structure in which the two hologram surfaces are parallel when the light path is equivalently linearized by considering the reflection of the light path for each reflecting surface inside the light guide (6). The optical head according to claim (1), characterized in that 5. A thin film (PBS) (16) having a polarization separation function is disposed in the optical path from the entrance hologram (H1) to the exit hologram (H2), and the exit hologram (H2) is provided. By providing the λ / 4 plate (17) on the front side or the back side and the lens means (18) at one end of the light guide plate (7), the reflected signal light from the optical disk medium (D) is transferred to the PBS.
It is characterized in that it is separated by (16), and the separated light is guided to one end of the light guide plate by total reflection in the light guide plate (7) and focused on the photodetector (19) by the lens means (18). The optical head according to claim (1).