JP2526206B2 - Optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In an optical pickup such as an optical disk device, the present invention arranges each optical system linearly on one optical axis, and at that time, mainly
By using a quarter-wave plate, two surface relief gratings orthogonal to each other in the groove direction, and a transparent rectangular parallelepiped, the light flux from the semiconductor laser light source is reflected at the focal point and returns to the vicinity of the original position for detection. Thus, the optical pickup can be reduced in weight and size by integrating a part of each of the above optical systems, thereby providing an optical pickup capable of shortening access time.

[Industrial applications]

The present invention relates to an optical pickup in an optical disc device and the like that can realize weight reduction and size reduction.

[Conventional technology]

In order to shorten the access time of an optical disc device, which is a large-capacity storage device, research into weight reduction and miniaturization of optical pickups (optical heads) has been actively conducted.

FIG. 11 shows the configuration of a conventional optical pickup. The light flux from the semiconductor laser is collimated lens, prism, PB
After passing through S, it is converted by the 1/4 wave plate and focused by the objective lens. Next, the reflected light from the focal point passes through the objective lens again, is converted by the 1/4 wavelength plate, and after the optical path is changed by PBS, it is converged on the photodetector by the converging lens.

Next, FIG. 12 shows an example of application to an optical disk device using the optical pickup having the configuration as shown in FIG. The optical pickup is diametrically accessed on a rotating optical disc by a linear motor.

[Problems to be solved by the invention]

In the above-mentioned conventional example, since the optical pickup having the configuration shown in FIG. 11 uses a lot of glass products as an optical system, a certain size is required to obtain accuracy. In addition, since the optical path is changed on the way, the size in the direction of each optical path is also required, and there is a limit to miniaturization and weight reduction.

On the other hand, the access time of the optical disk device as shown in FIG. 12 depends on how fast the optical pickup can be moved by the linear motor, and the lighter the weight of the optical pickup, the better the performance. The conventional optical pickup having the configuration as shown in FIG. 11 has a problem that the weight is several tens of grams and the access time (10 to 20 msec) equivalent to that of a magnetic disk device cannot be obtained. .

In order to eliminate the above-mentioned problems, the present invention makes it possible to arrange each optical system in a straight line along the optical axis and arrange the light detecting means on the outer periphery of the laser light source, thereby making the device compact and lightweight. It is an object of the present invention to provide an optical pickup that can realize high speed and shorten access time.

[Means for solving problems]

In order to solve the above problems, the present invention provides a focus (9),
The objective hologram lens (1), 1/4 wavelength plate (2), two surface relief type gratings (3, 4), transparent rectangular parallelepiped (5), hologram lens (6), and laser light source (7) Are arranged linearly on one optical axis (10) in order, and on the outer periphery of the laser light source (7) in a plane (7, 8) including the laser light source (7) and orthogonal to the optical axis (10). A structure in which a light detecting means (8) is arranged, and the two surface relief type gratings (3, 4) are arranged so that the grating (3) diffracts S-polarized light and the grating (4) diffracts P-polarized light. Have.

[Action]

In the above means, the light flux from the laser light source (7) is diffracted by the hologram lens (6) so as to intersect in the transparent rectangular parallelepiped (5), and the diffracted light passes through the transparent rectangular parallelepiped (5) and then P-polarized light is diffracted by the surface relief type grating (4) so as to be parallel to the optical axis (10), and the diffracted light is transmitted through the surface relief type grating (3) and then in the 1/4 wavelength plate (2). It is converted and further focused on the focal point (9) by the objective hologram lens (1). On the other hand, the reflected light from the focal point (9) is diffracted by the objective hologram lens (6) so as to be parallel to the optical axis (10), and the diffracted light is the 1 /
After being converted by the four-wave plate (2), the S-polarized light is diffracted by the surface relief type grating (3), and after passing through the surface relief type grating (4) and the transparent rectangular parallelepiped (5), a hologram lens (6) Is diffracted by and converges on the light detecting means (8).

As described above, since each optical system is arranged linearly on one optical axis (10), the optical system other than the objective hologram lens (1) can be integrated, and the component parts are made of glass products. Since the number is small, the size and weight can be reduced, and the access time can be shortened.

〔Example〕

 Hereinafter, examples of the present invention will be described in detail.

{Structure of Optical Pickup (FIG. 1)} FIG. 1 is a diagram showing the structure of the optical pickup according to the present invention. The figure (a) is a side view and the figure (b) is a perspective view. A hologram lens 6 for converting semiconductor laser light from a semiconductor laser 7 polarized in the front-back direction of the paper surface into a plane wave (to be described later) traveling toward the optical axis 10 is formed on one surface bcgf of the transparent rectangular parallelepiped 5, and the transparent rectangular parallelepiped is A disk-shaped surface-relief type grating 4 which receives a light wave propagating in the optical waveguide 5 and converts it into a plane wave parallel to the optical axis 10 is formed on the other surface adhe. Further, the surface relief type grating 3 formed on the disc-shaped quarter wave plate is superposed. This time,
The grooves 3 and 4 are formed so that the grooves are stacked in the directions orthogonal to each other. That is, the grating 3 is parallel to the side ad so that the S polarized light is diffracted, and the grating 4 is parallel to the side ae so that the P polarized light is diffracted. The pitch of each groove is set so that each polarized light is diffracted with maximum efficiency. Next, the in-line type objective hologram lens 1 attached to the actuator 11 is arranged above the quarter wavelength plate. The transparent rectangular parallelepiped 5 portion and the semiconductor laser 7 portion have an integral structure as described later.

{Operation of Optical Pickup (FIGS. 2, 3, and 4)} Next, the operation of the optical pickup having the above configuration will be described. First, the shaded areas A to D in FIG. 1 indicate the optical paths of one half of the light flux from the semiconductor laser 7. The other half is similar, and both are symmetrical. The P-polarized laser light A from the semiconductor laser 7 is diffracted by the objective hologram lens 6 and converted into a plane wave B that obliquely advances toward the optical axis 10 and travels straight within the transparent rectangular parallelepiped 5. That is, the light beams from the hologram lens 6 cross each other in the transparent rectangular parallelepiped 5 as shown in FIG. Next, the P-polarized plane wave B is diffracted by the grating 4 and converted into a plane wave parallel to the optical axis 10. Next, since this plane wave is P-polarized light, it passes through the grating 3 as it is and is converted by the quarter-wave plate 2 to become a plane wave C. The plane wave C is further focused by the objective hologram lens 1 on the focal point 9 on the optical disk surface. Here, the crossing of the light flux in the transparent rectangular parallelepiped 5 is
This is for increasing the spatial frequency of the hologram lens 6 (shortening the pitch interval) and improving the diffraction efficiency.

Next, the behavior of the reflected light from the focal point 9 on the optical disk surface will be described with reference to FIGS. First, the reflected light becomes a plane wave parallel to the optical axis 10 by the objective hologram lens 1, and then converted by the 1/4 wavelength plate 2 to become S-polarized light. This plane wave is converged on the photodetector 8 by the grating 3, the transparent rectangular parallelepiped 5 and the hologram lens 6 as shown below. The grating 4 is S
Since it is polarized light, it is transmitted as it is, contrary to the time of incidence. FIG. 2 shows the position on the photodetector 8 after the plane wave is diffracted by the grating 3, travels inside the transparent rectangular parallelepiped 5, and is further diffracted by the hologram lens 6. The beam incident position immediately before entering the grating 3 was divided into four, and the numbers I to IV were assigned. The reflected light that has passed through each of the segments I to IV is focused on the segment of the same number on the photodetector 8. Next, the specific optical path will be described using the example of FIG. For example, the reflected light incident on the segment IV (Fig. 2) of the grating 3 is reflected by the grating 3 in Figs. 3 (a) and 3 (b).
As shown in (1), it becomes the first-order diffracted light and the -1st-order diffracted light and travels in the transparent rectangular parallelepiped 5. Note that each segment is divided into squares for convenience. The first-order diffracted light is as shown in FIG.
After the total reflection occurs on the abcd surface, it reaches the hologram 6 and is focused on the segment IV on the photodetector 8. On the other hand, the −1st order diffracted light reaches the hologram lens 6 as shown in FIG. 2B and is similarly converged on the segment IV on the photodetector 8.
As a result, both the 1st-order and -1st-order diffracted light are detected by the photodetector 8.
Converged to the same segment above. Figure 3 (c),
(D) is segment I of grating 3 (Fig. 2)
When incident on.

As described above, the photodetector 8 is determined by the segment position of the reflected light from the optical disk surface which is incident on the grating 3.
The position to converge on is determined. Therefore, by using the photodetector 8 as shown in FIG. 4, the focus 9 (FIG. 1)
It is possible to detect the defocus and the track shift on the optical disk surface. That is, a normal detection position is determined by the detection output relations p + q = r + s, p + s = q + r, and when p + q ≠ r + s is detected, it is determined that a track deviation on the optical disk surface has occurred, and p + s ≠.
When q + r is detected, it can be determined that defocus has occurred.

In addition, instead of the transparent rectangular parallelepiped 5, a mirror surface may be used to totally reflect the light, or even if the transparent rectangular parallelepiped 5 is omitted, the same effect as that of the above-described embodiment is obtained.

{Structure of Objective Hologram Lens (FIG. 5)} Next, FIG. 5 shows a practical structure of the objective hologram lens 1 of FIG. As the in-line type objective hologram lens, one having a single element as shown in FIG. 3A or having each diffracted optical path as shown in FIGS.
It is possible to think of a sheet structure.

{Example of optical pickup (Figs. 6 and 7)} Next, Fig. 6 shows an example of the optical pickup of Fig. 1. In this way, it is possible to actuate only the objective hologram lens 1 and to incorporate the integrated optical systems 2 to 8 inside the actuator 11, and it is possible to make it lightweight, compact and thin. Further, since the optical pickup according to the present invention is lightweight and compact, in addition to the reciprocating linear movement as in the conventional embodiment as shown in FIG. 12, it is attached to the rotating arm as shown in FIG. It is also possible to let

[Other Embodiments of the Present Invention (FIGS. 8 to 10)] Next, another example of the two surface relief holograms will be described with reference to FIG.

The divergent light from the semiconductor laser 7 is incident on the grating 4.
By setting the polarization of the divergent light from the laser light to be orthogonal to each other, the elliptical divergent light from the semiconductor laser 7 is rounded. Then, the light (wavelength λ) incident on the grating 4 as P-polarized light from the semiconductor laser 7 is diffracted.
If the center pitch of the grating 4 is d, then λ / d≈0.8
It is about time. That is, if the wavelength of the laser light of the semiconductor laser 7 is 0.8 μm, d≈1 μm (spatial frequency≈1
000 lines / mm) should be set. The light diffracted by the grating 4 is incident on the grating 3. However, in order to prevent the P-polarized light from being almost diffracted by the grating 3, the grating 3 has λ / d≈1.6, that is, d≈0.5 μm (spatial frequency) = 2000 lines / mm mm). Thus, the light transmitted through the grating 3 is incident on the grating 3 as S-polarized light via the quarter-wave plate 2, the objective hologram lens 1, and the focal point 9. The light diffracted by the grating 3 is S
Since it is polarized light, it goes to the photodetector 8 in order to almost pass through the grating 4.

In the embodiment shown in FIG. 8, the transparent rectangular parallelepiped 5 is unnecessary, but the semiconductor laser 7 and the photodetector 8 are arranged at different positions.

Figure 9 shows the relationship between λ / d and diffraction efficiency η.
= 0.8, the diffraction efficiency η of P-polarized light becomes large, and that of λ / d = 1.6, the diffraction efficiency η becomes large.

Further, FIG. 10 shows a hologram lens 1 for focusing light, which is integrated in a grating 3, and this configuration enables further miniaturization.

〔The invention's effect〕

According to the present invention, since each optical system of the optical pickup can be arranged linearly and can be integrated, it is possible to configure a lightweight and small-sized optical pickup. It is possible to shorten the access time.

[Brief description of drawings]

FIGS. 1 (a) and 1 (b) are configuration diagrams of an optical pickup according to the present invention, FIG. 2 is an illustration of a positional relationship of reflected light, and FIGS. 3 (a), 3 (b) and 3 (c). , (D) are explanatory views of the optical path of the reflected light, FIG. 4 is a configuration diagram of the photodetector, and FIGS. 5 (a), (b), and (c) are actual configurations of the objective hologram lens. FIG. 6 is a configuration diagram of an embodiment of an optical pickup according to the present invention, FIG. 7 is an explanatory view of an embodiment of the optical pickup according to the present invention to an optical disc device, and FIG. 8 is a surface relief type of two sheets. FIG. 9 is a sectional view showing another example of the hologram, FIG. 9 is a characteristic diagram showing diffraction efficiency in the configuration of FIG. 8, FIG. 10 is a sectional view showing another example of the configuration of FIG. 8, and FIG. FIG. 12 is a configuration diagram of a conventional optical pickup, and FIG. 12 is a configuration diagram of an embodiment of the conventional optical pickup in an optical disc device. 1 ... Objective hologram lens, 2 ... 1/4 wavelength plate, 3, 4 ... Grating, 5 ... Transparent cuboid, 6 ... Hologram lens, 7 ... Semiconductor laser, 8 ... Photodetector, 9 ... … Focus, 10 …… Optical axis, 11 …… Actuator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinya Hasegawa, 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Fujitsu Limited (72) Inventor, Yushi Inagaki 1015, Uedotachu, Nakahara-ku, Kawasaki City, Fujitsu Limited (56) References JP-A 61-17232 (JP, A) JP-A 59-33636 (JP, A) JP-A 56-161582 (JP, A) JP-A 55-147655 (JP, A)

Claims (13)

(57) [Claims] 1. A hologram lens (6) for diffracting a light beam from a laser light source (7) and polarized light in the opposite direction, and a diffracted light from the hologram lens (6) which travels straight or is reflected in the opposite direction. Reflecting means (5) for directing or reflecting the polarized light from the laser beam to enter the hologram lens (6).
A surface relief type grating (4) which diffracts the polarized light from the reflection means (5) and causes the polarized light from the opposite direction to go straight and enter the reflection means (5), and the surface relief type grating ( 4) The polarized light from the surface relief type grating (4) is made to go straight, and the polarized light whose polarization direction is different from that of the surface relief type grating (4) from the opposite direction is diffracted and is incident on the surface relief type grating (4). 3) and the phase of polarized light from the surface relief type grating (3) is converted, and the phase of polarized light from the opposite direction is converted and is incident on the surface relief type grating (3).
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An objective hologram lens (1) which is incident, and a light detection means (8) which is arranged on the outer circumference of the laser light source (7) and detects a light flux from the hologram lens (6). Optical pickup. 2. The optical pickup according to claim 1, wherein the two surface relief type gratings (3, 4) are formed such that their groove directions are orthogonal to each other. 3. An optical pickup according to claim 1, wherein the grating (3) diffracts S polarized light and the grating (4) diffracts P polarized light. 4. The optical pickup according to claim 1, wherein said reflecting means (5) is a transparent rectangular parallelepiped. 5. A light beam from the laser light source (7) is diffracted by the hologram lens (6) so as to intersect within the transparent rectangular parallelepiped (5), and the diffracted light passes through the transparent rectangular parallelepiped (5). , Is diffracted by the surface relief type grating (4) so as to be parallel to the optical axis (10), and the diffracted light is converted in the 1/4 wavelength plate (2) after passing through the surface relief type grating (3). Then, the objective hologram lens (1) causes the focus (9).
On the other hand, the reflected light from the focal point (9) is diffracted by the objective hologram lens (6) so as to be parallel to the optical axis (10), and the diffracted light is reflected by the quarter wavelength plate (2). ), The light is diffracted by the surface relief type grating (3), further transmitted through the surface relief type grating (4) and the transparent rectangular parallelepiped (5), and then diffracted by the hologram lens (6), and then the light detecting means is obtained. (8)
The optical pickup according to claim 1, wherein the optical pickup converges upward. 6. A quarter-wave plate (2), two surface relief type gratings (3, 4), a transparent rectangular parallelepiped (5), a hologram lens (6), a laser light source (7) and a light detecting means ( The optical pickup according to claim 1, characterized in that 8) is integrally formed, and only the objective hologram lens (1) is actuated. 7. The optical pickup according to claim 1, wherein the laser light source (7) is a semiconductor laser. 8. The light detecting means (8) has a plurality of detection areas, and the reflected light from the focus (9) is converged to a specific detection area among the plurality of detection areas in a normal state. The optical system (1 to 6) is adjusted so that defocus or track deviation is detected when light detection is performed from another detection area. The optical pickup according to any one of item 2. 9. A surface relief type grating (4) for diffracting a light beam from a laser light source (7) and allowing polarized light from the opposite direction to go straight, and a polarized light from the surface relief type grating (4) to go straight. A surface relief type grating (3) which diffracts polarized light having a polarization direction different from that of the surface relief type grating (4) from the opposite direction and enters the surface relief type grating (4), and the surface relief type grating The phase of the polarized light from (3) is converted, the phase of the polarized light from the opposite direction is converted, and the light is incident on the surface relief type grating (3).
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An optical pickup comprising: an objective hologram lens (1) which is incident; and a light detecting means (8) which detects a light beam from the hologram lens (6). 10. A hologram lens (6) for diffracting a light beam from a laser light source (7) and polarized light from the opposite direction, and polarized light from the hologram lens (6) to diffract the polarized light from the opposite direction. Surface relief type grating (4) in which light goes straight and enters the hologram lens (6)
And, the polarized light from the surface relief type grating (4) is made to go straight, and the polarized light having a polarization direction different from that of the surface relief type grating (4) from the opposite direction is diffracted to obtain the surface relief type grating (4). To the surface relief type grating (3) which is incident on the surface relief type grating (3) and the phase of polarized light from the surface relief type grating (3) is converted, and the phase of polarized light from the opposite direction is converted to the surface relief type grating (3). Incident on 1 /
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An objective hologram lens (1) which is incident, and a light detection means (8) which is arranged on the outer circumference of the laser light source (7) and detects a light flux from the hologram lens (6). Optical pickup. 11. A hologram lens (6) for diffracting a light beam from a laser light source (7) and a polarized light in the opposite direction, and the diffracted light from the hologram lens (6) goes straight or is reflected in the opposite direction. Reflecting means (5) for directing or reflecting the polarized light from the laser beam to enter the hologram lens (6).
A surface relief type grating (4) which causes the polarized light from the reflecting means (5) to go straight, and diffracts the polarized light from the opposite direction to enter the reflecting means (5), and the surface relief type grating ( 4) diffracts the polarized light from the surface relief type grating (4) which is diffracted and makes a polarized light having a polarization direction different from that of the surface relief type grating (4) from the opposite direction go straight to enter the surface relief type grating (4). 3) and the phase of polarized light from the surface relief type grating (3) is converted, and the phase of polarized light from the opposite direction is converted and is incident on the surface relief type grating (3).
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An objective hologram lens (1) which is incident, and a light detection means (8) which is arranged on the outer circumference of the laser light source (7) and detects a light flux from the hologram lens (6). Optical pickup. 12. A surface relief type grating (4) for advancing a light beam from a laser light source (7) straight and diffracting polarized light from the opposite direction, and diffracting polarized light from the surface relief type grating (4). A surface relief type grating (3) which makes a polarized light having a polarization direction different from that of the surface relief type grating (4) from the opposite direction go straight to enter the surface relief type grating (4), and the surface relief type grating The phase of the polarized light from (3) is converted, the phase of the polarized light from the opposite direction is converted, and the light is incident on the surface relief type grating (3).
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An optical pickup comprising: an objective hologram lens (1) which is incident; and a light detecting means (8) which detects a light beam from the hologram lens (6). 13. A hologram lens (6) for diffracting a light beam from a laser light source (7) and polarized light in the opposite direction, and a polarized light from the hologram lens (6) is made to go straight.
The surface relief type grating (4) which diffracts polarized light from the opposite direction and enters the hologram lens (6)
And diffracts the polarized light from the surface relief type grating (4), and advances the polarized light having a polarization direction different from that of the surface relief type grating (4) from the opposite direction to go straight to the surface relief type grating (4). To the surface relief type grating (3) which is incident on the surface relief type grating (3) and the phase of polarized light from the surface relief type grating (3) is converted, and the phase of polarized light from the opposite direction is converted to the surface relief type grating (3). Incident on 1 /
A four-wave plate (2) and polarized light from the quarter-wave plate (2) are converged on a storage medium, and reflected light from the storage medium is diffracted to the quarter-wave plate (2). An objective hologram lens (1) which is incident, and a light detection means (8) which is arranged on the outer circumference of the laser light source (7) and detects a light flux from the hologram lens (6). Optical pickup.