JPS62283428A - Optical pickup - Google Patents

Abstract

PURPOSE:To prevent an offset due to deviation of a beam being a tracking error from being caused by tilting a light member whose incident face and emitting face receiving/giving a beam are formed in parallel to the beam and providing a drive mechanism moving the beam in parallel in tracking with the displacement of the objective lens to an optical system main body of an optical pickup. CONSTITUTION:A beam of a linearly polarized light radiated from a laser element 11 provided to the optical system main body 10 is subjected to circular parallel luminous flux in the luminous quantity distribution by a collimator lens 12 and a shaped prism 13, a circularly polarized light by a 1/4 wavelength plate 15 via a polarized beam splitter 14 and the result is made incident in the light refractive member 31. The member 31 is titled by the drive mechanism 32 in response to the displacement of the objective lens 20, the beam is moved in parallel and a spot is formed on a disk D. In this case, the objective lens 20 is moved by Xmm in the radial direction C and displaced on a position shown in broken lines, a current is injected to the drive mechanism 32 in response to the current injected to an actuator 21, the beam transmitted through the member 31 is moved by Xmm in parallel in the same direction and the optical axis of the objective lens 20 is made coincident with the center axis of the beam.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention Industrial Benefits 1 This invention provides an optical disc that is reciprocated in the radial direction.
The present invention relates to improvements in optical pickups that record information on optical discs or read information recorded on optical discs.

Conventionally, optical pickups have been provided with an optical system A as shown in FIG.

The optical system A is movably provided with respect to the optical system main body 10 and the optical system main body 10, which emits a beam toward the optical disc D side and receives the beam reflected by the optical disc D, and is movable with respect to the optical system main body 10. It consists of an objective lens 20 that follows the track of the optical disk D and forms an image.

A beam emitted from a laser probe 11 provided in the optical system main body 10 is converted into a parallel beam by a collimating lens 12, and the light amount distribution is made circular by a shaping prism 13.

Further, this beam passes through a polarizing beam splitter 14 and a quarter wavelength plate 15, is reflected by a fixed mirror 16, and enters an objective lens 20. The light intensity distribution of the beam incident on the objective lens 20 is concentric with the center axis 0 of the beam, as shown in FIG. 5, and the light intensity decreases as the distance from the center increases.

The beam focused on the optical disc D by the objective lens 20 is reflected by the optical disc D, passes through the objective lens 20 and the quarter-wave plate I5 again, and is reflected by the polarizing beam splitter 14. , condensing lens 1
7. The photodetector 19 passes through the cylindrical lens 18.
image on top.

Tracking error, that is, the deviation between the spot of the beam focused on the optical disc D and the pit carved on the optical disc D, is the deviation of the light intensity distribution of the beam reflected by the optical disc D in the radial direction C. It is detected from the light receiving element 19.

Problems to be Solved by the Invention However, in the optical system A as described above, in order to make the beam follow the track of the optical disk D, only the objective lens 20 is displaced, and the optical axis n of the objective lens 10 and the beam are If a deviation occurs between the central axis 0 of It ends up. Further, as shown in FIG. 6, this shift increases depending on the amount of displacement of the objective lens 20.

Therefore, the light intensity distribution of the beam reflected by the optical disk D includes not only the deviation due to the misalignment between the spot and the pit described above, but also the deviation due to the displacement of the objective lens 20, resulting in an offset caused by the tracking error. Therefore, there is a problem that stable tracking servo cannot be performed for the optical pickup A.

Purpose of the invention This invention has been made in view of the above problems,
To provide an optical pickup capable of always performing stable tracking servo without generating an offset due to beam deviation in a tracking error signal even when an objective lens is displaced with respect to an optical system body.

Problems & Means for Solving In order to achieve the above object, the present invention provides a light refracting member in which an incident surface through which a beam enters and exits and an exit surface are formed in parallel to the optical system body of an optical pickup.

Drive 4 to tilt the light refracting member with respect to the beam and move the beam in parallel to follow the displacement of the objective lens! It is characterized by having a & structure.

Since the present invention has the above-described configuration, the light refracting member moves the beam in parallel according to the amount of displacement of the objective lens,
The beam can always be made incident on the objective lens with a concentric uniform light intensity distribution centered on the optical axis of the objective lens.

EXAMPLES The present invention will be explained below based on the drawings. Figures 1 to 3
The figure shows one embodiment of the invention. In the drawings, the same reference numerals are given to parts or members that are the same as or equivalent to the conventional ones.

The optical pink-up optical system B consists of an optical system main body 30 and an objective lens 20.

The optical system main body 30 includes a laser element ll that emits a beam,
Collimating lens 1 that converts this beam into a circular parallel light beam
2 and shaped prism 13. Polarizing beam splitter-14
, quarter wave plate 15. Condensing lens 17, cylindrical lens 18. It is composed of a light receiving element 19 and a light refracting member 31 in which an entrance surface 31a through which a beam enters and exits and an exit surface 31b are formed in parallel.

The objective lens 20 is driven by an actuator 21 in the radial direction C while keeping the optical axis 0 parallel in accordance with a tracking servo signal, and the light refracting member 31 is driven by a drive provided on the lower surface according to the displacement of the objective lens 20. The aircraft is also tilted by 32.

In this example, the light refracting member 3I is a cubic block made of optical glass, and refracts the beam according to the incident angle to translate the beam. Here, the refractive index of the light refractive member 31 is n, and the distance from the incident surface 3La to the exit surface 31b is Q(m
m), the tilt angle of the incident beam and the light refraction member 31 is R
(rad, ), the distance between the outgoing beam and the incoming beam is approximately n as shown in Figure 2.
It can be expressed as -1 □・Sad・R (fflIll).

Next, the operation of the optical system B mentioned above will be explained.

A linearly polarized beam emitted from a laser element 11 provided in the optical system main body 1O is converted into a parallel light beam with a circular light intensity distribution by a collimating lens 12 and a shaping prism 13, and is transmitted through a polarizing beam splitter 14 to be divided into four parts. The one-wavelength plate 15 converts the light into circularly polarized light, and the light is incident on the light refraction member 31 . The light refracting member 31 is tilted by the above-mentioned drive mechanism 32 according to the displacement of the objective lens 20 to translate the beam. The beam moved by the light refracting member 31 is reflected by the fixed mirror 16 and enters the objective lens 20,
Connect the spots on the optical disc D.

At this time, the objective lens 20 moves in the radial direction C by X (mm)
When the object is moved to the position shown by the broken line in FIG. 1, in order to match the optical axis 0 of the objective lens 20 and the central axis p of the beam, the beam passing through the light refracting member 31 must also move in the same direction. It is necessary to move in parallel by X (mm). here,
The structure is such that current is injected into the drive mechanism 32 in accordance with the current injected into the actuator 21 .

Assuming that the shift sensitivity of the actuator 2I is α (am/A) and the rotation sensitivity of the drive mechanism 32 is β (rad, /A), α
If the constant represented by nl is γ, the actuator 21 has i
When the current (A) is injected, the drive mechanism 32 receives the current 71 (
When the current A) is injected, the light refracting member 3I tilts by R (rad) with respect to the beam, and the beam follows the objective lens 20 to the position indicated by the two points Il'1 line X( m
m) translated.

The beam reflected by the optical disk D is again converted into a parallel beam by the objective lens 20 and reflected by the fixed mirror 16. The returning beam, which is circularly polarized light that rotates in the opposite direction from the previous one, is 4
The half-wave plate 15 converts the light into linearly polarized light that is perpendicular to the previous one, and the light refracting member 31 returns the beam to the same optical path as when it was emitted.The beam enters the polarizing beam splitter 14. reflected by the condenser lens 17
The image is then formed on the light receiving element 19 through the cylindrical lens 18.

The light receiving element 19 detects a tracking error from the state of the focused beam.

By such an operation, the optical axis 0 of the objective lens 20 and the central axis p of the beam can always be aligned, so that the tracking error detected from the light receiving element 19 does not include an offset, and the optical pickup can be stably mounted. You can apply a servo.

As explained above, the optical pickup of the present invention includes a light refracting member in which the incident surface and the exit surface through which the beam enters and exits are formed parallel to each other in the optical system body of the optical pickup, and this light refracting member. Because the structure includes a drive mechanism that tilts the beam relative to the beam and moves the beam in parallel to follow the displacement of the objective lens, when the tracking servo is applied and the objective lens is displaced, the light refracting member adjusts the displacement of the objective lens. Since the beam is moved in parallel according to the amount of light, the beam is always incident on the objective lens with an even light intensity distribution in a concentric circle centered on the optical axis of the objective lens, which prevents tracking errors from occurring due to offset due to beam bias. do not have.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the optical system of the optical pickup amplifier according to the present invention, FIG. 2 is an explanatory diagram showing the action of the light refracting member, and FIG. 3 is a beam beam in the optical system shown in FIG. 1. Figure 4 is a configuration diagram showing the optical system of a conventional optical pickup, and Figure 5 shows the relationship between the light quantity distribution of the beam and the objective lens in the optical system shown in Figure 4. FIG. 6 is a graph showing the relationship between the amount of displacement of the objective lens and the deviation between the objective lens and the beam. B... Optical system of optical pickup D... Optical disk 30... Optical system main body 20... Objective lens 3
I... Light refraction member 31a... Incident surface 31b.
...Output surface 32...Drive mechanism Fig. 2 Fig. 3 Fig. 4

Claims (1)

[Scope of Claims] An optical system body that emits a beam toward an optical disk and receives the beam reflected by the optical disk, and an optical system that is movably provided with respect to the optical system body and that rotates the optical axis. In an optical pickup that is reciprocated in a radial direction of the optical disk, the optical system includes an objective lens that makes the beam follow a track of the optical disk and forms an image while keeping the beam parallel. The main body includes a light refraction member in which an entrance surface and an exit surface through which the beam enters and exits are formed in parallel, and the entrance surface and exit surface of the light refraction member are tilted with respect to the beam, so that the displacement of the objective lens is adjusted. An optical pickup comprising: a drive mechanism that moves the beam in parallel to follow the beam.