JPS60140553A - Optical pickup - Google Patents

Abstract

PURPOSE:To prevent the distribution of the quantity of incident light from changing considerably even if an objective is moved, by making the moving direction of the objective coincident with the direction of an exit angle theta of a semiconductor laser. CONSTITUTION:The p-n junction face of a semiconductor laser 11 as a light source which is arranged in the focus position of a collimation lens 3 approximately is provided orthogonally to an optical information recording carrier (disc) 7, and the exit light from the semiconductor laser 11 passes a non-polarizing beam splitter 12, where a dielectric multilayered film or a metallic thin film is formed on a diagonal face 121, and is converted to parallel light by the collimation lens 3 and passes a mirror 5 and is focused as a minute spot on a track 71 on the recording face of the optical information recording carrier 7. This minute spot is formed as a spot 13 which is narrow and long in the lengthwise direction of the track 71 and is indicated by oblique lines. A part of the reflected light from the track 71 is condenced by an objective 6 and passes the course of exit from the semiconductor laser 11 and is reflected on the non-polarizing beam splitter 12 and passes a detecting optical system 8 and is converted to an electric signal by a photoelectric transducer 9.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to optical pickup, and in particular to optical pickup of information recorded on optical information recording media such as compact discs (hereinafter referred to as CDs) and video discs (VDs). The present invention relates to improvements in optical pickups used to optically read out information obtained by optical pickup.

[Technical background of the invention and its problems]

Next, the structure and function of a conventional optical pickup will be explained using FIG.

That is, the light emitted from the semiconductor laser (1) as a light source disposed approximately at the focal point of the collimation lens (3) passes through the deflection beam splitter (2) and is converted into parallel light by the collimation lens (3). , a quarter-wave plate (4), a mirror (5), and an objective lens (6) to form an image on an optical information recording medium (disc) (force recording track (7,) as a minute spot. be done.

Tracks (7,) on the recording surface of this information recording carrier (7)
Information is recorded by the presence or absence of bits with a depth of approximately 1/4 wavelength, and due to diffraction by these pits, a portion of the reflected light from the recording surface of the information recording carrier (force) is reflected by the objective lens ( 6) Since the light is focused by the semiconductor laser (1) and becomes linearly polarized light with a polarization direction perpendicular to that emitted from the semiconductor laser (1), it is reflected by the polarizing beam splitter (2) and sent to the detection optical element (8). The signal is then converted into an electrical signal by a photoelectric converter (9).

This electrical signal is separated into a focus error signal that indicates the distance error between the objective lens (6) and the recording surface, a tracking error signal that indicates the deviation between the track and the minute spot on the recording surface, and an information signal that includes the recorded content. be done.

Of these, the focus error signal and the tracking error signal are wide packed into the actuator (1) to drive the objective lens (6).
) to accurately adjust the position of the recording surface and the position of the minute light spot on the track. Specifically, the former adjustment moves the objective lens (6) in the optical axis direction, and the latter adjustment moves the objective lens (6) in the normal direction of the track.

In order to allow this objective lens (6) to move in the normal direction of the track, the diameter of the light beam incident on the objective lens (6) must be larger or smaller than the entrance pupil of the objective lens (6). Must be. If this is not done, the light emitted from the objective lens will change significantly when the objective lens moves in the normal direction of the recording track.

However, in order to form a sufficiently small minute light spot on the recording surface, the numerical aperture (N, A) of the objective lens must be used at once, and for this reason the diameter of the light beam incident on the objective lens is The entrance pupil of the lens plus the amount of movement of the objective lens must be greater than or equal to the G diameter. In order to avoid this, at least a structure should be adopted in which the light source, collimation lens, and objective lens are integrated and driven, but this structure naturally increases the mass and puts strain on the actuator. Therefore, it is not very practical.

Up to this point, we have explained why the 1M diameter of the incident light beam must be large when only the objective lens is moved, but the distribution of the light amount within this diameter range affects the quality of the minute light spot on the recording surface. , it is desirable to be as centrally symmetrical as possible.

In other words, if the incident light has a Gaussian distribution in the entrance pupil plane of the objective lens, the minute light spot will also have a glass distribution.
If the distribution is uniform within the entrance pupil plane, it will be an Airy distribution, but it is well known that in reality it takes a value intermediate between the two.

On the other hand, the semiconductor laser that serves as the light source also has a unique emitted light /! depending on its structure. ! The output angle θ in the direction parallel to the pn junction surface is approximately 5° to 10° in half width, and the output angle θ1 in the direction perpendicular to the pn junction surface is approximately 30' in half width. It is common to have

Also, the collimation lens has a numerical aperture (NA) of 0.1.
~0.2 is used, so the emission angle of the light emitted from the semiconductor laser as a light source is 11° to 2.
Light of 2' or less is made to enter the objective lens as parallel light. Under such conditions, the light quantity distribution within the parallel rays is close to a uniform distribution in the θ□ direction, and close to a Gaussian distribution in the θ direction, and neither distribution is symmetrical with respect to the center point.

Therefore, in order to make the distribution as symmetrical as possible with respect to the center point, it is considered that the θ〃 and θU of the semiconductor laser should be brought close together, or the numerical aperture of the collimation lens should be made as small as possible. Since it is related to the structure of the semiconductor laser itself, it cannot be changed, and as for the latter, the smaller the numerical aperture, the more
Since the light emitted from the semiconductor laser cannot be used effectively, it cannot be made too small, and NA=0.12 to 0.
A realistic value is about 15.

Under the light intensity distribution conditions described above, the objective lens is
Deciding in which direction to move is a major problem for optical pickups.

In order to ensure that the distribution of light incident on the objective lens changes greatly even when the objective lens is moved, it is desirable that the direction of movement can be set in the direction of the emission angle θ from the semiconductor laser.

Also, considering the polarization of light, the emitted light from a semiconductor laser is pn
The junction direction is P polarization, and a polarization beam splitter placed immediately after the semiconductor laser transmits the P polarization component and reflects the S polarization component. Therefore, in an optical system in which light from a light source passes through a polarizing beam splitter, the emission angle θl direction of the semiconductor laser becomes the moving direction of the objective lens.
This is the opposite of the conditions stated above. In order to make the emission angle θl direction of the semiconductor laser equal to that of the objective lens, it is sufficient to change the positional relationship between the photoelectric converter and the light source and rotate the semiconductor laser chip by 90''. The light heading toward the polarizing beam splitter is reflected by the reflective surface of the polarizing beam splitter and passes through the polarizing beam splitter.

The difference between reflection and transmission through a beam splitter is that if the reflecting surface of the beam splitter is uneven, the phase of the light will be disrupted in proportion to the product of twice the unevenness and the refractive index. In the case of transmission, the position of the light is disturbed in proportion to the product of the unevenness and the difference in refractive index on both sides of the reflective surface. Therefore, if it is attempted to pass the light from the light source through the polarizing beam sinter by reflection, the surface precision of the reflecting surface must be high and the irregularities must be reduced, which causes an increase in cost. In this case, it is said that the surface accuracy should be about 1/6 of that for transmission.

To avoid this high cost and make the direction of the output angle equal to the direction of movement of the objective lens, the entire optical pickup excluding the actuator must be rotated by 90', or the mirrors must be removed and the light source, deflection beam splitter, collimation lens, /4 The wave plate and the objective lens should be arranged on the same straight line, that is, the entire surface axis should be set perpendicular to the disk, but the former allows most of the optical pickup to occur when reading out the outermost track. It protrudes from the disc, but in the opposite case it hits the disc's rotational axis, and in the latter case there is still the problem that the overall height of the pickup becomes high, which is disadvantageous for incorporating it into the player. .

Another possible structure is to change the mounting position of the detection optical system of the photoelectric converter to the upper or lower surface of the optical pickup as shown in Figure 1, and rotate the light source and deflection beam splitter 90 degrees around the optical axis. However, in this case, the detection optical system and photoelectric converter protrude from the top or bottom of the optical pickup, resulting in the problem that the height of the optical pickup must be increased in order to avoid hitting the disk. There is.

As mentioned above, when trying to satisfy various conditions, the direction of movement of the objective lens is the output angle from the pn junction of the semiconductor laser is θ, and the force direction is the direction of the force, and the movement of the objective lens significantly changes the incident light distribution. This is an unavoidable situation.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned problems.The moving direction of the objective lens is made to match the emission angle θl direction of the semiconductor laser, so that even if the objective lens moves, the incident light amount distribution changes significantly. It is an object of the present invention to provide an optical pickup having an optical system capable of preventing such problems.

[Summary of the invention]

That is, the present invention includes a semiconductor laser as a light source provided so that the pn junction surface is perpendicular to the disk, a non-polarizing beam splitter that notifies the light emitted from the semiconductor laser, and
A collimation lens that converts the light from the non-polarizing beam splitter into parallel rays, an objective lens that focuses the parallel rays from the collimation lens through a mirror onto a track on the recording surface of the disk, and a reflection from the track. It is equipped with at least a detection optical system that reflects the light by a non-polarizing beam splitter via a mirror and a Colin X John lens, and then passes it through, and a photoelectric converter that photoelectrically converts the light from the detection optical system, and a microscopic spot. This optical pickup is characterized in that it can be formed into an elongated shape in the longitudinal direction of the track.

[Embodiments of the invention]

Next, an embodiment of the optical pickup of the present invention will be explained with reference to FIGS. 2 and 3. In the figure, the same reference numerals as in the prior art indicate the same parts.

That is, the pn junction surface of the semiconductor laser (II) as a light source, which is disposed approximately at the focal point of the collimation lens (3), is provided so as to be perpendicular to the optical information recording medium (disc) (7). The emitted light of the semiconductor laser Ql) is emitted from the dielectric multilayer film or metal thin film on the diagonal surface (121
After passing through the non-polarizing beam splitter Q formed in This minute spot is imaged on the track (7I) on the recording surface of the disk (7) as shown in FIG.
The spot (1
3).

Then, a part of the reflected light from the track (7) is focused by the objective lens (6), passes through the path emitted from the semiconductor laser a9, and is reflected by the non-polarizing beam splitter Q, and is reflected by the detection optical system. (8) and is converted into an electrical signal by a photoelectric converter (9).

p, s of the polarization direction of the emitted light from the above-mentioned non-polarizing beam splitter (1 or 1 is the semiconductor laser αl as a light source)
Since it has the function of transmitting half of the incident light and reflecting the other half, it is possible to replace the conventional polarizing beam splitter (2) with this non-polarizing beam splitter and eliminate the 1/4 wavelength plate. By doing so, the conventional semiconductor laser (1) can be rotated by 90 degrees without changing the arrangement of other optical systems. The emission angle θ in the direction perpendicular to the pn junction surface can be made to coincide with the upward direction.

However, in this case, by providing the non-polarizing beam splitter a2, a loss of 1/2 of the light intensity occurs on the outward path, but this is due to the difference between the light intensity of the semiconductor laser α1) and the photoelectric converter (9). This can be compensated for by increasing the gain of the conversion circuit, and since the moving direction of the objective lens (6) and the direction of the emission angle θ of the semiconductor laser 01) match, the numerical aperture (NA) of the collimation lens (3) ) can be set relatively large without having to forcefully reduce it. As a result, the efficiency with which parallel light beams can be used improves, so it is possible to compensate for the decrease in the amount of light reaching the photoelectric converter due to the non-polarizing beam splitter ll'16.

〔Effect of the invention〕

As described above, according to the present invention, the moving direction of the objective lens can be set to the emission angle θ of the 6I junction of the semiconductor laser, so it is possible to obtain a light pickup with extremely little change in the incident light distribution due to the movement of the objective lens. It is possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the structure of a conventional optical pickup, FIGS. 2 and 3 are views showing an embodiment of the optical pickup of the present invention, FIG. vJ2 is a perspective view showing the structure, and FIG. FIG. 2 is an explanatory diagram showing the relationship between tracks and minute spots. 1.11 Semiconductor laser 2 ... Deflection beam splitter 3 ... Collimation lens 4 ... 1/4 wavelength plate 5. Mirror 6 - ...
・Objective lens 7-・Disk 7m...Track 8 Detection optical system 9...Photoelectric converter 10
・・Actuator 11 ・ −・Non-polarizing beam splitter 13 ・・Minute spot smart person Patent attorney + # Top - Male Figure 1

Claims (1)

[Claims] A semiconductor laser as a light source provided so that a pn junction surface is perpendicular to the disk, a non-polarizing beam splitter that passes the light emitted from the semiconductor laser, and converting the light from the non-polarizing beam splitter into parallel light. a collimation lens; an objective lens that images a parallel light beam from the collimation lens as a minute spot on a track on a recording surface of a disk via a mirror; and a collimation lens that focuses reflected light from the track via the mirror and the collimation lens. and a photoelectric converter that photoelectrically converts the light from the detection optical system, and the microspot is elongated in the longitudinal direction of the track. An optical pickup characterized by being shaped so that it can be shaped.