Optical pickup

An optical pickup includes an optical base mounted with at least one optical element, a light source that supplies light incident on the at least one optical element, and a tilt spacer that is disposed between the light source and the optical base to adjust a characteristic of the light that enters the optical base. With the characteristic of the light that enters the optical base adjusted by the tilt spacer, the optical base and the light source are fixed directly to each other.

BACKGROUND

1. Technical Field

The present disclosure relates to an optical pickup that performs recording, erasing, and reproduction on an optical disk.

2. Description of the Related Art

Mounting a semiconductor laser to an optical base of an optical pickup to have an optical axis as designed is a critical challenge in production of the optical pickup. To solve this challenge, in PTL 1, a semiconductor laser is fixed to a laser diode (LD) holder formed with a spherical or arcuate surface that is centered around an emission point of the semiconductor laser, and the LD holder is fitted to a similarly formed spherical or arcuate surface of an optical base or an optical axis adjustment holder for rotational adjustment and X-Y adjustment of the semiconductor laser. In this way, light power distribution adjustment and optical axis tilt adjustment are carried out.

CITATION LIST

Patent Literature

SUMMARY

With explosively increasing digital data in markets in recent years, storage devices such as a hard disk and a semiconductor memory increasingly have larger capacities and are required to store data for a fixed period of time or more. As such, there is a move toward reconsideration of an optical disk that conventionally has recorded mainly music, video and the like as a device for storing long-term storage data because of the optical disk's long-term storage property, low bit unit price, and maintainability.

Thus, in tandem with higher density of the optical disk than ever, further miniaturization, higher precision, and long-term reliability are prerequisites for an optical pickup that performs recording/reproduction on the optical disk. To achieve recording/reproduction with higher density than ever, a light spot on an optical disk recording surface needs to be smaller, a light power distribution (hereinafter described as a far-field pattern (FFP)) needs to be free of deviation, and an optical axis of light emitted from a semiconductor laser needs to be aligned with a peak point of the FFP and needs to be perpendicularly incident on the optical disk.

FIG. 9illustrates structure of an optical pickup in a conventional example. In optical pickup701that is used in conventional optical disk drive700, semiconductor laser103is fixed to semiconductor laser holder711. As shown inFIG. 10, semiconductor laser holder711is provided with arc-shaped convex surface801. An angle of contact with optical base702into which semiconductor laser holder711is inserted is adjusted at arc-shaped convex surface801. In this way, rotational adjustment or X-Y adjustment of semiconductor laser holder711is carried out. This results in FFP adjustment and optical axis adjustment in optical pickup701. In this method, however, because of being fixed to optical base702by bonding via semiconductor laser holder711, semiconductor laser103easily gets out of position in a long-term reliability test, so that there are problems in miniaturization and securement of long-term reliability.

A measure such as below is taken against the above problems. Semiconductor laser103that has a smaller shift of an optical axis and a smaller shift of the FFP is selectively used and is fixed directly to optical base902(FIG. 11). Optical pickups901thus assembled undergo test selection, and those that are satisfactory are used. However, semiconductor lasers103and optical pickups901that are not selected are problematically wasted in this method.

Based on the above problems, the present disclosure aims to provide a smaller optical pickup with higher precision and long-term reliability.

An optical pickup disclosed in the present application includes an optical base mounted with at least one optical element, a light source that supplies light incident on the at least one optical element, and a tilt spacer that adjusts a characteristic of the light that enters the optical base, the tilt spacer being disposed between the light source and the optical base. With the characteristic of the light that enters the optical base adjusted by the tilt spacer, the optical base and the light source are fixed directly to each other.

In comparison with conventional optical pickups, an optical axis of the light source, for example, can thus be adjusted with respect to the optical base, and because the light source is fixed directly to the optical base by, for example, bonding after the adjustment, improved reliability can be achieved for this fixed part.

The optical pickup of the present disclosure that can be provided has higher precision and long-term reliability.

Arcuate surfaces that allow rotation of a semiconductor laser are respectively formed along two axial directions at respective edges of the tilt spacer of substantially cylindrical shape. The optical base is provided with a stepped hole into which the tilt spacer and the semiconductor laser are inserted, and the stepped hole has such a hole diameter as to form not less than a given clearance with the tilt spacer as well as with the semiconductor laser. The tilt spacer of substantially cylindrical shape has such an inside diameter as to form not less than a given clearance with an outer periphery of a cap of the semiconductor laser. An optical axis tilt and an FFP of the semiconductor laser can thus be adjusted along the two axial directions.

A middle of the arcuate surface of an arc-shaped projection that is formed on the tilt spacer's end face (a light-source-end counterface) and abuts on the semiconductor laser's stem having a mounting reference surface is substantially aligned with an emission point of the semiconductor laser, so that a shift of the emission point that might be caused by rotation of the semiconductor laser can be minimized, and FFP adjustment effected by the rotation and optical axis adjustment effected by the movement can be carried out without interference.

The arcuate surface of an arc-shaped projection that is formed on the tilt spacer's end face (an optical-base-end counterface) opposite from the light-source-end counterface is formed to make contact with the semiconductor laser's emission plane including the emission point. A bottom face of the stepped hole provided in the optical base is aligned with the emission plane. A radius of the arcuate surface is made as large as possible. A shift of the emission point that might be caused by rotation of the semiconductor laser can thus be minimized, and FFP adjustment effected by the rotation and optical axis adjustment effected by the movement adjustment can be carried out without interference.

The respective arcuate surfaces of the arc-shaped projections respectively formed on the counterfaces provided at the respective edges of the tilt spacer of substantially cylindrical shape are such that, for example, a direction of the arcuate surface at the light-source-end counterface is a longitudinal mode direction (θ⊥) of a semiconductor laser beam, while a direction of the arcuate surface at the optical-base-end counterface is a transverse mode direction (θ∥) of the semiconductor laser beam, whereby interference with an FFP that might be caused by rotation along the two axial directions can be minimized. As such, a substantial improvement in ease of work can be achieved. It is to be noted that respective directions of the arcuate surfaces are not limited to the above condition. There is no problem even when, for example, the direction of the arcuate surface making contact with the stem of the semiconductor laser may be a main shaft-countershaft direction of the optical pickup, while the direction of the opposite arcuate surface is an inner periphery-outer periphery direction of the optical pickup.

Since the semiconductor laser can be fixed directly to the optical base, which has other optical components, mechanism components, and others fixed, after the FFP adjustment and the optical axis adjustment of the semiconductor laser, deformation, deterioration and others of the optical base that might be caused by, for example, temperature, humidity, external force, and impact are dispersed. Accordingly, influence on the individual components can be minimized, and consequently, the optical pickup can have excellent reliability.

DETAILED DESCRIPTION

Exemplary embodiments are hereinafter described in detail with reference to the accompanying drawings where appropriate. However, detailed descriptions that are more than necessary may be omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of substantially identical configurations are omitted. This is to avoid unnecessary redundancy in the following descriptions and to facilitate understanding by those skilled in the art.

The inventor(s) of the present disclosure provide the accompanying drawings and the following descriptions to help those skilled in the art to fully understand the present disclosure and thus do not intend to limit the subject matter defined in the appended claims thereby.

First Exemplary Embodiment

FIG. 1is a perspective external view of an optical pickup according to a first exemplary embodiment. InFIG. 1, light emitted from semiconductor laser103has its traveling direction bent by polarization beam splitter104and then is converted to collimated light by collimator lens105. The collimated light is bent perpendicularly toward optical disk120by laser mirror106and passes through quarter-wave plate107. By passing through quarter-wave plate107, the light changes from linearly polarized light to circularly polarized light. The circularly polarized light is concentrated by objective lens108to be incident as a minute light spot on a recording surface of optical disk120. In this way, information can be recorded on, erased from or reproduced by optical disk120.

The light incident on optical disk120is reflected off the recording surface. The light reflected from optical disk120travels in a direction opposite to an optical path of the light incident on optical disk120from semiconductor laser103and repasses through quarter-wave plate107, thereby becoming linearly polarized light in a direction perpendicular to a polarized direction of the incident light. Because of this characteristic, the reflected light is separated from the optical path of the incident light when passing through polarization beam splitter104and is concentrated by detection lens109to be guided to photodetector110. At this photodetector110, for example, focus error signal FE is detected by an astigmatic method, track error signal TE is detected by a push-pull method, and information signal RF is detected as data read from optical disk120.

In order to make the following description of the exemplary embodiment easy to understand, a direction in which semiconductor laser103emits light is described as a Z direction, a direction that is perpendicular to the Z direction and is substantially parallel to the recording surface of optical disk120is described as an X direction, and a direction perpendicular to both the X direction and the Z direction is described as a Y direction. Directions that are opposite are described as a Z-minus direction, an X-minus direction, and a Y-minus direction, respectively.

FIG. 2is a see-through diagram with semiconductor laser103and tilt spacer111assembled to optical base102. Semiconductor laser103is inserted into tilt spacer111at a side having key projection301. Cap203of semiconductor laser103passes through a hollow part of tilt spacer111and projects at an optical-base side of tilt spacer111. A projecting amount of cap203of semiconductor laser103is determined by contact between stem202of semiconductor laser103and a contact surface of tilt spacer111.

Semiconductor laser103assembled to tilt spacer111is inserted into optical base102. Optical base102has stepped hole205into which tilt spacer111assembled with semiconductor laser103is inserted. An optical-base-end contact surface of tilt spacer111makes contact with a receiving face of this stepped hole205. Tilt spacer111having semiconductor laser103is thus assembled to optical base102.

Emission point201indicates a logical emission position when semiconductor laser103emits light. Emission plane204is a logical plane where light emission is uniform when the light is emitted by semiconductor laser103.

FIG. 3illustrates the semiconductor-laser-end contact surface of tilt spacer111. Tilt spacer111includes, on its side where tilt spacer111makes contact with semiconductor laser103, semiconductor-laser-end counterface302, key projection301, and semiconductor-laser-end arc-shaped projections303. Tilt spacer111has a substantially cylindrical shape.

Semiconductor-laser-end counterface302is one of two sides that define a cylindrical part of tilt spacer111having a substantially cylindrical shape. Semiconductor-laser-end counterface302is substantially planar and faces stem202of semiconductor laser103.

Key projection301suppresses relative rotational position shifts of tilt spacer111and semiconductor laser103around a Z-axis. Key projection301is formed at an outer periphery of tilt spacer111so as to fit into a key groove formed in an outer periphery of stem202of semiconductor laser103and also to fit into a key groove formed in optical base102.

Each of semiconductor-laser-end arc-shaped projections303is a bulging part of semiconductor-laser-end counterface302. It is preferable that a middle of an arcuate surface of this semiconductor-laser-end arc-shaped projection303be substantially aligned with emission point201.

FIG. 4is an enlarged view of a contact part between tilt spacer111and stem202of semiconductor laser103. As shown inFIG. 4, tilt spacer111and semiconductor laser103make contact with each other at key projection301and semiconductor-laser-end arc-shaped projections303. Semiconductor-laser-end counterface302faces a Z-side face of stem202of semiconductor laser103but does not make contact in its entirety.

Semiconductor laser103can be angularly adjusted around emission point201, which is located at a middle of semiconductor-laser-end arc-shaped projections303of tilt spacer111, with respect to tilt spacer111within a predetermined range on a Y-Z plane. By abutting on semiconductor-laser-end arc-shaped projections303, semiconductor laser103has its further projection from the optical-base side (in the Z direction) of tilt spacer111controlled.

FIG. 5illustrates the optical-base-end contact surface of tilt spacer111. Tilt spacer111includes, on its side where tilt spacer111makes contact with optical base102, optical-base-end counterface304and optical-base-end arc-shaped projections305.

Optical-base-end counterface304faces the receiving face of stepped hole205provided in optical base102.

Each of optical-base-end arc-shaped projections305is a bulging part of optical-base-end counterface304. Similarly to semiconductor-laser-end arc-shaped projection303, optical-base-end arc-shaped projection305rises from the counterface. However, optical-base-end arc-shaped projection305bulges in a more extensive area as compared with semiconductor-laser-end arc-shaped projection303.

FIG. 6is an enlarged view of a contact part between tilt spacer111and optical base102. Optical-base-end arc-shaped projection305is shaped to rise gently as compared with semiconductor-laser-end arc-shaped projection303. Specifically, an area covered by optical-base-end arc-shaped projection305in entire optical-base-end counterface304is larger than an area covered by semiconductor-laser-end arc-shaped projection303in semiconductor-laser-end counterface302. As such, while optical-base-end arc-shaped projection305and semiconductor-laser-end arc-shaped projection303rise to the same degree (by the same projecting amount in a Z-plus direction and a Z-minus direction, respectively), there is a difference in gentleness or steepness between the respective projecting amounts of optical-base-end arc-shaped projection305and semiconductor-laser-end arc-shaped projection303.

Although magnitudes of gentleness or steepness are not limited to any specific values in the present exemplary embodiment, these values vary depending on, for example, a wavelength characteristic of light that is output by semiconductor laser103used as a light source or where a logical emission point or emission plane is positioned for light that is emitted by semiconductor laser103mounted to tilt spacer111.

Consideration is given to a cut section (hereinafter, a cross section) of tilt spacer111, having a substantially cylindrical shape, that is circular. In the example ofFIG. 2, an X-Y plane is parallel to this cross section. Semiconductor-laser-end counterface302and optical-base-end counterface304are projected on this cross section. Accordingly, semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305that are respectively provided at these two counterfaces are projected on the cross section. The cross section is concentric with the cylindrical part of tilt spacer111. When viewed from a center of this cross section, it can be said that a phase difference between respective projection positions of semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305is indicative of relative phase positions of semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305on tilt spacer111.

In the present exemplary embodiment, the relative phase positions of semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305are not limited to a specific combination. However, it is preferable that semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305be disposed in a substantially orthogonal position relationship.

Thus, tilt spacer111can be angularly adjusted with respect to optical base102along optical-base-end arc-shaped projection305within a predetermined range on an X-Z plane. With optical-base-end arc-shaped projections305abutting on the receiving face of stepped hole205, further entry of tilt spacer111in the Z-plus direction is controlled.

With semiconductor-laser-end arc-shaped projections303and optical-base-end arc-shaped projections305of tilt spacer111, semiconductor laser103can be rotationally adjusted with respect to optical base102along directions θx, θy around an X-axis and a Y-axis, respectively. In other words, rotational adjustments of semiconductor laser103along directions θx, θy with respect to optical base102are achieved by rotation of tilt spacer111with respect to optical base102on the X-Z plane and rotation of semiconductor laser103with respect to tilt spacer111on the Y-Z plane.

Not less than a given clearance is provided between a mounting hole of optical base102and the outer periphery of tilt spacer111, between the mounting hole of optical base102and the outer periphery of stem202of semiconductor laser103, and between an inner periphery of tilt spacer111and an outer periphery of cap203of semiconductor laser103. With these clearances provided, semiconductor laser103is susceptible of movement adjustment along the X- and Y-axes with respect to optical base102or tilt spacer111and is thus susceptible of FFP adjustment and optical axis adjustment.

With suitable setting of the above-described respective projecting amounts of semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305, logical emission point201and logical emission plane204that are shown inFIG. 2can be seized as references in the above-described angular adjustments along directions θx, θy and the above-described movement adjustments along the X- and Y-axes. For this reason, the respective projecting amounts of semiconductor-laser-end arc-shaped projection303and optical-base-end arc-shaped projection305may be determined according to respective logically set positions of emission point201and emission plane204.

When assembled to optical base102, semiconductor laser103is optically adjusted via tilt spacer111. After completion of this adjustment, semiconductor laser103is fixed to optical base102with an adhesive, for example. In this way, semiconductor laser103and optical base102are joined directly to each other.

In a prior art, semiconductor laser holder711is first fixed to optical base702, and semiconductor laser103is fixed to semiconductor laser holder711. As such, optical base702and semiconductor laser103are fixed to each other via, for example, two bonding parts. As compared with cases where there is one joint, reliability, for example is deteriorated.

With the technique disclosed in the present exemplary embodiment, while optical adjustment between semiconductor laser103and optical base102is carried out via tilt spacer111, semiconductor laser103and optical base102are joined directly to each other after the adjustment. As such, in comparison with the prior art, further improvements in qualities such as reliability and durability can be achieved.

In the example explained in the above description, optical-base-end arc-shaped projections305are shaped to rise more gently than semiconductor-laser-end arc-shaped projections303. However, the content disclosed in the present application is not limited to this. Semiconductor-laser-end arc-shaped projections303may be shaped to rise more gently than optical-base-end arc-shaped projections305.

Preferably, the optical-base-end bulging parts are different in shape from the semiconductor-laser-end bulging parts. With the bulging parts rising more gently in shape on one of the sides and rising more steeply in shape on the other side, rotational adjustment of semiconductor laser103and direction adjustment of an optical axis can be major when carried out along the steeply rising bulging parts and can be minor when carried out along the gently rising bulging parts.

In the example explained in the above description, the semiconductor-laser-end contact surface and the optical-base-end contact surface are each provided with the two bulging parts; however, the disclosure of the present application is not limited to this. The semiconductor-laser-end contact surface and the optical-base-end contact surface may each be provided with not less than three bulging parts or one bulging part. As another alternative, the semiconductor-laser-end contact surface and the optical-base-end contact surface may have different numbers of bulging parts.

The description of the present exemplary embodiment is based on the premise that tilt spacer111has a substantially cylindrical shape. However, the content described in the present application is not limited to an entirely cylindrical shape. For example, tilt spacer111may be cylinder-based in shape, but its semiconductor-laser-end opening and optical-base-end opening may not be of equal size. The principle described in the above exemplary embodiment is equally applicable to this case.

In the example explained in the present exemplary embodiment, “the semiconductor-laser-end arc-shaped projection” and “the optical-base-end arc-shaped projection” are both arc-shaped projections; however, the disclosure of the present application is not limited to this. The projections may each have another basic shape such as a triangle-based shape having a rounded apex. In other words, the projections may have any shape so long as their outside shapes are smooth. In this case, “the semiconductor-laser-end arc-shaped projection” and “the optical-base-end arc-shaped projection” that are described in the above exemplary embodiment may be a “semiconductor-laser-end projection” and an “optical-base-end projection”, respectively.

In the example explained in the present exemplary embodiment, semiconductor laser103is used as the light source; however, the content of the present application is not limited to this. The light source may be another device that can be put to practical use as a light source of an optical pickup. As such, “the semiconductor-laser-end counterface” and “the semiconductor-laser-end arc-shaped projection” that are used in the description of the present exemplary embodiment, for example may be referred to as a “light-source-end counterface” and a “light-source-end arc-shaped projection”, respectively.

FIG. 7is a see-through perspective view illustrating an example in which tilt spacer501is assembled according to another exemplary embodiment.FIG. 8is a perspective external view of tilt spacer501according to this exemplary embodiment. Tilt spacer501differs from tilt spacer111in that key projection301is replaced by rotation restricting bosses502that restrict rotation of tilt spacer501around the Z-axis. This exemplary embodiment is otherwise similar to the above exemplary embodiment.

The optical pickup disclosed in the present application includes the light source and the tilt spacer that adjusts a directional characteristic of light that is output by the light source. The optical axis and a position of the light source, for example are adjusted by the tilt spacer. With these adjusted, the light source is fixed directly to the optical base of the optical pickup. The tilt spacer is substantially shaped into a cylinder. The light source is partly inserted into the hollow part of this cylinder. The light-source-end projection provided at the light-source-end counterface that is one of the sides of the cylinder inhibits more insertion of the light source toward the optical base than is necessary and enables rotational adjustment of the optical axis of the light source around the first axis (X-axis) in the predetermined angular range. The optical-base-end projection provided at the optical-base-end counterface that is the other side of the cylinder inhibits more insertion of the tilt spacer mounted with the light source than is necessary and enables rotational adjustment of the optical axis of the light source around the second axis (Y-axis), which is orthogonal to the first axis, in the predetermined angular range. The predetermined clearance is provided between the light source and the tilt spacer as well as between the tilt spacer, which is mounted with the light source, and the optical base, thus enabling adjustment along directions parallel to the plane formed by the first axis and the second axis. After these adjustments are carried out, the semiconductor laser and the optical base are fixed directly to each other.

According to the disclosure of the present application, the light source can have the characteristic of its light, which enters the optical base, adjusted via the tilt spacer with respect to the optical base including at least one optical element. This adjustment enables specified rotational adjustment and specified parallel adjustment with respect to the optical base. Through these adjustments, a desired intensity distribution of the light that enters the optical pickup, for example can be obtained. Because the adjusted light source is fixed directly to the optical base, the optical pickup that can be made has higher reliability than conventional optical pickups.

Other Exemplary Embodiments

The exemplary embodiments are described above as being illustrative of the technique disclosed in the present application. However, the technique of the present disclosure is not limited to these exemplary embodiments and is also applicable to other exemplary embodiments including appropriate changes, replacements, additions, and omissions.

An optical pickup disclosed in the present application can be utilized as, for example, an optical pickup that records information on an optical information recording medium such as an optical disk.