JPH075550Y2 - Optical device for optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an optical pickup used in a magneto-optical recording / reproducing apparatus and the like, and in particular, an error occurs in a scanning error detection operation due to reflected light from a boundary surface of a prism. The present invention relates to an optical device of an optical pickup that is prevented from occurring.

[Conventional technology]

FIG. 5 is a plan view showing an optical device of an optical pickup used in a conventional magneto-optical recording / reproducing device.

Reference numeral 1 is a semiconductor laser. The laser beam emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and is incident on the incident surface 3 a of the beam shaping prism 3. As shown in FIG. 4, the far-field pattern of the laser beam emitted from the chip 1a in the semiconductor laser 1 is not a perfect circle, and the horizontal radiation angle θ〃 is smaller than the vertical radiation angle θ⊥. It has a circular shape. In the beam shaping prism 3, when the laser beam θ ′ direction is incident in the inclination direction of the incident surface 3a, this radiation angle θ ′ is expanded by an appropriate shaping ratio, and a laser having a substantially circular cross section is formed. A beam is formed.

The laser beam that passes through the beam shaping prism 3 passes through the first light splitting surface A that is a boundary surface between the beam shaping prism 3 and the second prism 4, and further the second prism 4
Through the light emitting surface E of the. Then, the light is reflected in the right angle direction by the total reflection prism 5, condensed by the objective lens 6 and condensed on the recording surface Da of the optical disc D (see FIG. 6). Further, the reflected beam reflected from the recording surface Da is reflected by the total reflection prism 5, and is reflected from the light emitting surface E to the second prism 4.
It returns to the inside and is reflected by the first light splitting surface A toward the second prism 4. A third prism 7 is joined to the second prism 4, and a second light splitting surface B is formed at the boundary thereof. The beam reflected by the first light dividing surface A passes through the second light dividing surface B and is detected by the light receiving element 8 for detecting a tracking error. The beam reflected by the second light splitting surface B in the perpendicular direction passes through the condenser lens 9 and the toric lens 10 and is detected by the light receiving element 11 for focus error detection.

A monitor light receiving element 12 is arranged in the optical path direction (upward direction in FIG. 5) in which the laser beam emitted from the semiconductor laser 1 is reflected by the first light splitting surface A. The light receiving element 12 is provided for automatic power control. The reason why the monitor light receiving element 12 of this type is provided is as follows. As shown in FIG. 4, in the semiconductor laser 1, a light receiving element 1b for monitoring is provided behind the chip 1a in the case, and the laser beam emitted backward from the chip 1a is generated by the light receiving element 1b. It is detected, and the drive voltage of the semiconductor laser can be controlled based on the detected amount.
However, if the light receiving element 1b in the semiconductor laser 1 is used as a monitor, the beam reflected from the recording surface Da of the optical disc D returns to the semiconductor laser after passing through the first light splitting surface A, and this light is used for monitoring. Will be detected by the light receiving element 1b. In order to effectively use the laser emitted from the semiconductor laser 1 to record and erase information on the disc, the transmittance of the first light dividing surface A is set to, for example,
It is necessary to form as high as 80 to 90%. Therefore, the amount of return light transmitted through the light splitting surface A increases, and this is detected by the light receiving element 1b in the semiconductor laser 1. If most of the returned light is detected by the light receiving element 1b, the monitor function for controlling the semiconductor laser cannot be accurately exhibited. Therefore, as shown in FIG. 5, the monitor light-receiving element 12 is arranged at a position where the return beam from the optical disc D is not irradiated,
The return light from the optical disk D is made so that it cannot be detected by the monitor light receiving element 12.

[Problems to be solved by the device]

As mentioned above, in the optical pickup for magneto-optical recording and reproduction,
In order to secure a sufficient optical power for recording and erasing information, the transmittance of the first light splitting surface A is as high as 80 to 90%. Therefore, of the return light from the optical disc, the ratio of the light reflected by the first light splitting surface A toward the second prism 4 is reduced to about 10 to 20%. Further, if the transmittance of the second light splitting surface B is 50%, the amount of light input to the light receiving element 8 for tracking error detection and the light receiving element 11 for focus error detection will be further reduced. Thus, the amount of light incident on the light receiving element 8 or 11 for error detection is extremely small,
When the light reflected by the surface in each optical element shown in FIG. 5 is incident on the light receiving element 8 or 11, it causes an offset in the error detecting operation. It is the light output surface E of the second prism 4 that is particularly problematic as the reflection on the surface inside the optical element. The laser beam emitted from the semiconductor laser 1 is the first
The light is transmitted through the light splitting surface A and is emitted to the outside from the light exiting surface E. However, a part of this light is reflected by the light exiting surface E and is reflected by the first light splitting surface A, and then is received by the light receiving element 8 or 11. It will be incident. As described above, since the amount of light emitted from the semiconductor laser and transmitted through the first light splitting surface A is large, the reflected light from the light emitting surface E becomes a non-negligible amount, and this reflected light causes tracking error and The focus error detection operation tends to be offset.

The present invention is to solve the above conventional problems,
To provide an optical device of an optical pickup capable of maintaining high detection accuracy of an error signal by preventing reflected light from a light emitting surface of a prism from entering a light receiving element for detecting a tracking error and a focus error. I am trying.

[Means for Solving the Problems]

In the optical device of the optical pickup according to the present invention, a beam shaping prism is arranged on a light emitting optical path of a light emitting element, and light is transmitted and reflected at an interface between the beam shaping prism and a second prism joined to the beam shaping prism. The light splitting surface is formed to be inclined, and an objective lens facing the optical disk is disposed in the optical path direction that passes through the light splitting surface and exits from the second prism, and the objective lens is reflected from the recording surface of the optical disk. An error detection unit for detecting a scanning error due to a spot of light formed on the recording surface of the optical disc is provided in the optical path direction in which the return light passing through is reflected by the light splitting surface, and The light output surface of the second prism in the direction of the objective lens is formed so as to be inclined with respect to a surface perpendicular to the optical axis of light emitted from the light emitting element and transmitted through the light splitting surface. Is shall.

[Action]

In the above means, the beam emitted from the light emitting element is shaped by the beam shaping prism to be a beam having a substantially circular cross section. Then, through the light splitting surface, the second
It is sent to the objective lens from the light output surface of the prism. At this time, part of the light emitted from the light emitting element is reflected by the light exit surface of the second prism, but this light exit surface is not perpendicular to the optical axis of the light passing through the first split surface, but at a constant angle. Therefore, the reflected light from the light exit surface is sent by the first light splitting surface in a direction inclined with respect to the direction of the error detection unit. Therefore, the reflected light from the light emitting surface does not enter the light receiving element for detecting the tracking error and the focus error, and the detection error of the error signal does not occur.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings of FIGS.

FIG. 1 is a plan view showing an optical device of an optical pickup according to the present invention.

Reference numeral 1 is a semiconductor laser, 2 is a collimating lens, 3 is a beam shaping prism, 14 is a second prism, 17 is a third prism, 5 is a total reflection prism, 6 is an objective lens, 9 is a condenser lens, and 10 is A toric lens, 11 is a light receiving element for focus error detection, and 8 is a light receiving element for tracking error detection.

The boundary between the beam shaping prism 3 and the second prism 14 is the first light splitting surface A, and the boundary between the second prism 14 and the third prism 7 is the second light splitting surface. The first light splitting surface A formed between the beam shaping prism 3 and the second prism 14 has a thickness of 80 to 80 mm so that recording or erasing can be performed on the disk by effectively utilizing the beam light quantity. The transmittance is about 90%.

Reference numeral 12 is a monitor light receiving element. The monitor light-receiving element 12 detects and monitors the amount of light emitted from the semiconductor laser 1, and the drive voltage of the semiconductor laser 1 is controlled based on the detection output of the monitor light-receiving element 12. You can control it.

Further, in this embodiment, the light output surface E ₁ of the second prism 14 is formed to be inclined. This tilt amount passes through the collimator lens 2 and the beam shaping prism 3 and
Plane E ₀ perpendicular to the optical axis O ₁ of the light transmitted through the light splitting surface A of
In contrast, the angle is θ _{0 in} the clockwise direction. Since the light exit surface E ₁ is inclined in this way, the light exit surface E ₁ is
The optical axis O ₁ of the light emitted from will be broken. The total reflection prism 5 and the objective lens 6 are arranged in the direction of the optical axis O ₁ .

Next, the operation will be described.

The laser beam emitted from the semiconductor laser 1 is collimated by the collimator lens 2 and shaped by the beam shaping prism 3 so that the beam has a substantially circular cross section. The laser beam transmitted through the shaping prism 3 is
The light is transmitted through the first light splitting surface A between the shaping prism 3 and the second prism 14, and is sent from the light output surface E ₁ to the total reflection prism 5. Then, the light is reflected by the total reflection prism 5 in the right angle direction, and is condensed by the objective lens 6 to be condensed on the recording surface Da of the optical disc D. The reflected beam reflected from the recording surface Da is reflected by the total reflection prism 5 and returns to the original state, and is reflected by the first light splitting surface A toward the second prism 14. Further, the light passes through the second light dividing surface B and is detected by the light receiving element 8 for detecting a tracking error. The beam reflected by the second light splitting surface B in the perpendicular direction passes through the condenser lens 9 and the toric lens 10 and is detected by the light receiving element 11 for focus error detection.

Further, the laser beam emitted from the semiconductor laser 1 is reflected by the first light splitting surface A in a right angle direction, which is detected by the monitor light receiving element 12, and the drive voltage of the semiconductor laser 1 is controlled based on this detection output. To be done.

In the above operation, 80 to 90% of the light transmitted through the collimator lens 2 and the beam shaping prism 3 is the first light.
The light is transmitted through the light splitting surface A and exits from the light exit surface E ₁ , but a part of this light is reflected by the light exit surface E ₁ . The light emitting surface E ₁ is
Since it inclined by theta ₀ with respect to the optical axis O perpendicular plane E ₀ to _1, the optical axis O _A of the reflected light from the exit surface E _1, without passing through the O _1, inclined proceeds first Is reflected by the light splitting surface A. Therefore, the optical axis O _A of the reflected light is the light receiving element 8 for detecting the tracking error and the light receiving element 11 for detecting the focus error.
Will be out of the center of. By appropriately setting the θ ₀ , the reflected light from the light emitting surface E ₀ does not enter the light receiving elements 8 and 11, and an offset does not occur in the tracking error and focus error detection operations.

Next, an appropriate value of the inclination angle θ ₀ of the light output surface E ₁ of the second prism 14 is obtained.

FIG. 2 shows an enlarged path of light that passes through or is reflected by the light exit surface E ₁ of the second prism 14. Light emitted from the semiconductor laser 1 passes through the first beam splitting surface A by the optical axis of the O _1, so the optical axis of the O ₂ at the light exit surface E ₁ in the direction of the total reflection prism 5 proceeds. In FIG. 2, O ₀ -O ₀ is the light emitting surface E
It is a virtual line that is orthogonal to ₁ . The angle between the virtual line O ₀ -O ₀ and the optical axis O ₁ is θ ₀ . Also, this virtual line O ₀ -O ₀ and the outgoing optical axis O ₂
The angle between and is θ ₁ . At this time, the angle formed by the reflected optical axis O _A emitted from the semiconductor laser 1 and reflected by the light exit surface E ₁ and the optical axis O ₁ is 2θ ₀ . Further, the incident angle and the reflection angle of the reflected optical axis O _A with respect to the light dividing surface A are α. When the sum of the interior angles of a right-angled triangle whose sides are O ₁ and O _A is calculated, it is 2θ ₀ + α + 45 ° + 90 ° = 180 °, so 2θ ₀ + α = 45 °. Therefore, the angle formed by the optical axis O _A1 reflected by the first light splitting surface A and the vertical line O _{A0 in the} figure is 2θ ₀ .

Here, for convenience of calculation, the perpendicular line O _A0 passing through the reflection point by the light splitting surface A and the center 8 of the light receiving element 8 in FIG.
The lateral displacement δ from a is ignored. In this case, the third
As shown in the figure, the path between the reflected optical axes O _A and O _A1 can be approximately represented by a straight line without the light splitting surface A. In FIG. 3, 8a is the center position of the light receiving element 8, and the position separated from this by X is the arrival position of the reflected optical axes O _A and O _A1 . It suffices that the reflected light does not enter the light receiving element 8 due to the shift of X. If the total distance between the reflected optical axes O _A and O _A1 is l, then tan2θ ₀ ≉X / l. Here, the effective diameter of the collimating lens 2 is d ₁ , and the effective light receiving diameter of the light receiving element 8 for detecting the tracking error is d ₂
Then, when X becomes larger than (d ₁ + d ₂ ) / 2, the reflected light cannot be detected by the light receiving element 8. Substituting this condition into the above equation, tan2θ ₀ ≧ (d ₁ + d ₂ ) / 2l. This formula shows that the reflected light from the light emitting surface E ₁ is received by the light receiving element 8
Is a condition of θ ₀ for not detecting.

If the effective diameter of the collimator lens 2 is d ₁ = 5 mm, the effective light receiving diameter of the light receiving element 8 is d ₂ = 5 mm, and l is 10 mm, then θ ₀ ≧ 14 °. In reality, the amount of deviation of δ is taken into consideration in FIG. 2, so the angle of θ ₀ may be smaller.

Next, when the light exit surface E ₁ of the second prism 14 is tilted by θ ₀ , the beam shaped by the beam shaping prism 3 is reshaped by the light exit surface E ₁ , and the beam of the elliptical cross section is again generated. Becomes Therefore, we calculate this effect.

The beam shaping ratio M at the light exit surface E ₁ is Is. Here, as described above, when θ ₀ = 14 °, the refractive index n =
When it is set to 1.51, the shaping ratio M is 0.96, and it can be seen that the influence on the beam shaping is small. Also, as described above, the second
If the deviation amount δ in the figure is taken into consideration, θ ₀ can be further reduced, so that the shaping rate M is actually 1
It is a value close to.

It is possible to prevent the reflected light from entering the light receiving element 11 for detecting the focus error in the same manner.

〔effect〕

As described above, according to the present invention, since the light output surface of the second prism is inclined, the reflected light from this light output surface is detected by the light receiving element for tracking error detection and the light receiving element for focus error detection. Is gone
The offset for detecting the focus and tracking error signals does not occur.

[Brief description of drawings]

FIG. 1 is a plan view showing an optical device of an optical pickup according to the present invention, and FIG. 2 is an enlarged plan view showing a light emitting surface portion thereof.
FIG. 3 is an explanatory view for calculating an optical path, FIG. 4 is a perspective view showing an internal structure of a semiconductor laser, FIG. 5 is a plan view showing an optical device of a conventional optical pickup, and FIG. It is a side view. 1 ... Semiconductor laser (light emitting element), 3 ... Beam shaping prism, 14 ... Second prism, 6 ... Objective lens, 8
…… Light receiving element for tracking error detection, 11 …… Light receiving element for focus error detection, 12 …… Monitor light receiving element, A …… Light splitting surface, E ₁ …… Light emitting surface.

Claims (1)

[Scope of utility model registration request] 1. A beam shaping prism is disposed on a light emitting optical path of a light emitting element, and a light splitting surface for transmitting and reflecting light is provided on a boundary surface between the beam shaping prism and a second prism joined to the beam shaping prism. An objective lens that is formed so as to be inclined and is opposed to the optical disc in the optical path direction that passes through this light splitting surface and exits from the second prism, is returned from the recording surface of the optical disc and passes through the objective lens. Is provided with an error detection unit for detecting a scanning error due to a light spot formed on the recording surface of the optical disc in the optical path direction reflected by the light splitting surface, and
The optical surface of the optical pickup of the second prism is formed such that the light output surface toward the objective lens is inclined with respect to the surface perpendicular to the optical axis of the light emitted from the light emitting element and transmitted through the light splitting surface. apparatus