Optical pickup and optical disk apparatus

An optical pickup includes a light emitting device, a prism, and an objective lens. The light emitting device emits a laser beam. The prism has an entrance face and an exit face. In the prism, the laser beam emitted from the light emitting device is perpendicularly incident on the entrance face, is parallel-shifted, is perpendicularly reflected, and is emerged from the exit face. The objective lens focuses the laser beam emerged from the prism on a recording surface of an optical disk.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application JP 2006-172988 filed in the Japanese Patent Office on Jun. 22, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical pickups for use in optical disk apparatuses.

2. Description of the Related Art

Laser diodes have been widely used as laser sources of optical pickups for used in optical disk apparatuses. The laser diodes have many advantages. For example, since the size of each laser diode is small and the power consumption thereof is low, the size of an optical pickup including the laser diode can be minimized.

A laser beam emitted from a laser diode has an elliptical cross-sectional shape (far-field pattern). Consequently, a spot formed by focusing the laser beam through an objective lens is also elliptical. In an optical pickup including such a laser diode, in order to optimize the shape of a laser beam spot to be formed on a track, the laser diode is mounted on the optical pickup such that the optical axis of the laser diode is rotated by a predetermined angle. Consequently, the track is irradiated with a laser beam rotated by the predetermined angle such that a beam spot with an optimum shape is formed on the track.

An integrated optical pickup is proposed as one of optical pickups for use in optical disk apparatuses. The integrated optical pickup includes, for example, a laser diode, a top emission prism, a package which is a molded part, made of ceramic, for sealing the laser diode and the prism, and an integrated optical assembly including a beam splitter, a diffraction grating, and a photodetector such that the integrated optical assembly is mounted on the package. Japanese Unexamined Patent Application Publication No. 2003-248960 discloses such an integrated optical pickup.

SUMMARY OF THE INVENTION

In recent years, miniaturization of laser diodes has been progressing. Further, various shaped laser diodes are widely diffused. In other words, in addition to a conventional cylindrical laser diode in a metal package, there are non-cylindrical laser diodes, such as a laser diode sealed in an elliptical columnar metal package and a chip type laser diode directly mounted on a chip.

However, those non-cylindrical laser diodes are difficult to mount such that the optical axis of the laser diode is rotated in order to optimize the shape of a beam spot formed on a track. Further, since the rotated non-cylindrical laser diode is mounted, the height of the laser diode is increased, thus preventing miniaturization of an optical pickup including the laser diode.

According to an approach to the optimization of a spot shape and the miniaturization of an optical pickup, the following arrangement as shown inFIG. 9is proposed: An optical system composed of a laser diode1and a top emission prism2is mounted on a mounting surface3A of a package3such that the optical system is deviated from the longitudinal axis of the package3. Consequently, a laser beam, which is reflected by the top emission prism2and is emerged from the package3, is rotated to optimize the shape of a beam spot formed on a track of an optical disk. In this arrangement, however, although it is unnecessary to rotate the optical axis of the laser diode1, the width w of the package3is increased. Disadvantageously, the entire size of an optical pickup is increased.

According to an approach to preventing the increase in the width of the package3, a relay mirror4can be used. The relay mirror4reflects a laser beam emitted from the laser diode1to the top emission prism2as shown inFIG. 10. Disadvantageously, the number of components constituting an optical pickup is increased. Unfortunately, an error in assembly of the optical pickup may be easily caused.

According to another approach, a roof prism is used as the top emission prism2as shown inFIG. 11. Since the top emission prism2has a reflecting function which is realized by the relay mirror4inFIG. 10, the number of components is not increased. Unfortunately, the roof prism has a complex structure, i.e., the arrangement of reflecting faces of the roof prism is complicated. Therefore, the roof prism is difficult to mass produce efficiently.

It is desirable to provide a small and simplified optical pickup capable of optimizing the shape of a beam spot formed on a track and an optical disk apparatus including the optical pickup.

According to an embodiment of the present invention, an optical pickup includes the following elements. A light emitting device emits a laser beam. A prism has an entrance face and an exit face. In the prism, the laser beam emitted from the light emitting device is perpendicularly incident on the entrance face, is parallel-shifted, is perpendicularly reflected, and is emerged from the exit face. An objective lens focuses the laser beam emerged from the prism on a recording surface of an optical disk.

In accordance with this embodiment, the single prism allows for parallel shift of a laser beam and upward deflection thereof. Advantageously, when the light emitting device is rotated in order to optimize the shape of a laser beam spot on a track, the width of the optical pickup can be minimized.

According to another embodiment of the present invention, an optical disk apparatus has an optical pickup including the following element. A light emitting device emits a laser beam. A prism has an entrance face and an exit face. In the prism, the laser beam emitted from the light emitting device is perpendicularly incident on the entrance face, is parallel-shifted, is perpendicularly reflected, and is emerged from the exit face. An objective lens focuses the laser beam emerged from the prism on a recording surface of an optical disk.

In accordance with this embodiment, the single prism allows for parallel shift of a laser beam and upward deflection thereof. Advantageously, when the light emitting device is rotated in order to optimize the shape of a laser beam spot on a track, the width of the optical pickup can be minimized.

According to each of the embodiments of the present invention, when the light emitting device is rotated in order to optimize the shape of a laser beam spot oh a track, the width of the optical pickup can be minimized, since the single prism allows for parallel shift of a laser beam and upward deflection thereof. Advantageously, a small and simplified optical pickup capable of optimizing the shape of a laser beam spot on a track and an optical disk apparatus including the optical pickup can be realized.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(1) Structure of Optical Disk Apparatus

FIG. 1shows an optical disk apparatus10according to an embodiment of the present invention. A controller11controls the entire optical disk apparatus10. The controller11controls a motor12to rotate an optical disk13and also controls an optical pickup15to irradiate the optical disk13with a laser beam. The optical pickup15detects a laser beam reflected by the optical disk13, generates a reproduction signal, and supplies the signal to a signal processor14. The signal processor14performs predetermined signal processing on the reproduction signal and outputs the resultant signal to the outside.

(2) Structure of Optical Pickup

FIG. 2shows the structure of the optical pickup15according to an embodiment of the present invention. The optical pickup15includes an optical assembly20, a collimating lens21, a quarter wave plate22, and an objective lens23. Those components are mounted on an optical pickup base (not shown), which will be referred to as an OP base hereinafter. The OP base is, for example, an aluminum die casting.

The optical assembly20includes a box-like open bottom package27, serving as a holder, and various optical elements arranged on the package27. A laser diode25and a top emission prism26are attached to a mounting face27A, serving as the upper inner surface of the package27. A lid27B is attached to the open bottom of the package27such that the laser diode25and the top emission prism26are enclosed in the package27.

A photodetector28, a spacer30, a mold compound element29, and a prism assembly31are mounted in sequence on the upper outer surface of the package27. The photodetector28receives a laser beam reflected by the optical disk13to obtain a reproduction signal and various servo error signals. The mold compound element29has a diffraction grating29A and a hologram29B. The prism assembly31includes a plurality of prisms.

In the optical assembly20, a laser beam emitted from the laser diode25is deflected upward using the top emission prism26and is incident on a polarization beam splitter (PBS)31A of the prism assembly31through an aperture27C and the mold compound element29.

The PBS31A transmits the laser beam coming from the top emission prism26on the basis of the direction of polarization of the laser beam and allows the laser beam, serving as an output laser beam, to enter the collimating lens21.

The collimating lens21transforms the output laser beam passing through the PBS31A from diverging light into parallel light. Further, the quarter wave plate22transforms the leaser beam from linearly polarized light into circularly polarized light and allows the resultant beam to enter the objective lens23. The objective lens23focuses the output laser beam on the optical disk13to irradiate a recording layer of the optical disk13with the laser beam.

In addition, the objective lens23collects a laser beam reflected from the optical disk13irradiated with the output laser beam. Further, the quarter wave plate22transforms the laser beam passing through the objective lens23into linearly polarized light whose polarization direction is different from that of the output laser beam by 90° and allows the resultant beam to enter the collimating lens21. The collimating lens21transforms the laser beam from the parallel light into converging light and allows the resultant beam to enter the prism assembly31.

The PBS31A of the prism assembly31reflects the reflected laser beam by 90° to a total reflection mirror31B. The total reflection mirror31B reflects the laser beam, which is reflected by the PBS31A, by 90° and allows the reflected laser beam to enter the photodetector28through the hologram29B of the mold compound element29. The photodetector28generates various detection signals on the basis of the amount of the received laser beam and supplies the signals to the signal processor14(seeFIG. 1) in the optical disk apparatus10.

(3) Arrangement of Top Emission Prism and Laser Diode

The arrangement of the components, including the top emission prism26, in the package27according to this embodiment of the present invention will now be described in detail.

FIG. 3shows the package27viewed from below. The top emission prism26is mounted on the mounting face27A so as to cover the aperture27C at the center of the mounting face27A. The laser diode25is mounted close to one face of the top emission prism26(along the longitudinal axis of the package27) on the mounting face27A.

FIG. 4shows the top emission prism26in accordance with the embodiment of the present invention. The top emission prism26is formed by cutting a long right-angle prism100, whose cross section is an isosceles right triangle, such that two parallel cut lines each form a predetermined angle α (in this case, α=40°) with one edge of a first surface (upper surface inFIG. 4) of the prism100.

The top emission prism26, serving as a modified triangular prism, has an entrance face26A, a first reflecting face26B, a second reflecting face26C, an upward reflecting face26D which serves as a third reflecting face26D, and an exit face26E. The entrance face26A is a rectangle. The first reflecting face26B is a right triangle and is adjacent to the entrance face26A with an edge26abtherebetween. The second reflecting face26C is a right triangle that is congruent to and parallel to the first reflecting face26B and is adjacent to the entrance face26A with an edge26actherebetween. The upward reflecting face26D is a parallelogram and is adjacent to the entrance face26A with an edge26adtherebetween. Similarly, the upward reflecting face26D is adjacent to the first reflecting face26B with an edge26bdand is also adjacent to the second reflecting face26C with an edge26cdtherebetween. The exit face26E is a parallelogram whose one pair of opposite angles each have an angle α=40° and is adjacent to the entrance face26A with an edge26aetherebetween. Similarly, the exit face26E is adjacent to the first reflecting face26B with an edge26betherebetween, is adjacent to the second reflecting face26C with an edge26cetherebetween, and is adjacent to the upward reflecting face26D with an edge26detherebetween.

In the top emission prism26, the angle (corresponding to the edge26ab) formed by the entrance face26A with the first reflecting face26B is the angle α=40°. The first reflecting face26B is parallel to the second reflecting face26C as described above.

Each of the angle formed by the entrance face26A with the exit face26E, that formed by the first reflecting face26B with the exit face26E, and that formed by the second reflecting face26C with the exit face26E is a right angle (90°).

Further, each of the angle formed by the entrance face26A with the upward reflecting face26D and that formed by the upward reflecting face26D with the exit face26E is 45°.

The top emission prism26is mounted on the mounting face27A of the package27such that the exit face26E covers the aperture27C. The laser diode25is mounted on the mounting face27A of the package27such that the laser beam emitting face of the laser diode25is opposite the entrance face26A of the top emission prism26.

Accordingly, the laser diode25is mounted on the package27such that a laser beam emitted from the laser diode25is rotated relative to the longitudinal axis of the package27by a set angle β (β=90°−α=50°), i.e., the emitted laser beam forms the set angle β with the longitudinal axis of the package27. This arrangement allows for the optimization of the shape of a laser beam spot on a track of an optical disk when the optical disk is irradiated with the laser beam focused through the objective lens23(seeFIG. 2), the laser beam being rotated by the set angle β.

Referring toFIGS. 5A to 6, a laser beam L emitted from the laser diode25is perpendicularly incident on the entrance face26A of the top emission prism26. The entrance face26A transmits the laser beam L in accordance with the angle of incidence of the laser beam such that the laser beam is obliquely incident on the first reflecting face26B, as shown by an optical path segment L1.

The first reflecting face26B of the top emission prism26reflects the incident laser beam L to the second reflecting face26C such that the reflected laser beam is obliquely incident on the second reflecting face26C, as shown by an optical path segment L2. The second reflecting face26C reflects the incident laser beam L to the upward reflecting face26D, as shown by an optical path segment L3.

As described above, the entrance face26A, the first reflecting face26B, and the second reflecting face26C are perpendicular to the exit face26E and the laser beam L is perpendicularly incident on the exit face26E. Accordingly, the optical path segments L1to L3in the top emission prism26are located in a plane parallel to the exit face26E. Since the first reflecting face26B is parallel to the second reflecting face26C, the optical path segments L1and L3are parallel to each other. When let the spacing between the first and second reflecting faces26B and26C be the interplanar spacing t, the distance D between the optical path segments L1and L3is expressed by the following expression.
D=t/sin α(0°<α<90°)  (1)

Therefore, the top emission prism26shifts the laser beam L perpendicularly incident on the entrance face26A to the second reflecting face26C in the plane parallel to the exit face26E by the distance D and allows the shifted laser beam to impinge on the upward reflecting face26D.

Since the upward reflecting face26D forms an angle of 45° with the exit face26E as described above, the laser beam L is incident on the upward reflecting face26D at an angle of incidence of 45°. Consequently, the upward reflecting face26D upwardly reflects the laser beam L at a right angle such that the laser beam is perpendicularly incident on the exit face26E, as shown by an optical path segment L4. The exit face26E of the top emission prism26transmits the laser beam L according to the angle of incidence thereof without processing, so that the laser beam L emerging from the exit face26E passes through the aperture27C of the mounting face27A and travels upward.

Again referring toFIG. 3, the laser diode25is mounted in a substantially central portion in the widthwise direction of the package27such that a laser beam emitted from the laser diode25forms the set angle β with the longitudinal axis of the package27. Accordingly, the laser diode25emits a laser beam such that the laser beam travels from the substantially central portion in the widthwise direction of the package27to the outside. Since the top emission prism26is arranged so as to face the laser beam emitting face of the laser diode25, the first reflecting face26B and the second reflecting face26C, each of which forms the angle α with the entrance face26A, are parallel to each other in the lengthwise direction of the package27.

Referring toFIG. 5B, in the top emission prism26, the incident laser beam L is parallel-shifted by the distance D, is incident on the upward reflecting face26D, and is reflected upward by the upward reflecting face26D, so that the laser beam L emerges from the exit face26E. In other words, the top emission prism26shifts the laser beam L, emitted from the laser diode25toward the outside of the package27, to the center in the widthwise direction of the package27and then reflects the laser beam L upward using the upward reflecting face26D below the aperture27C arranged at the center of the package27.

The optical pickup15uses the top emission prism26, which shifts the laser beam L in parallel and deflects the laser beam upward as described above, according to the present embodiment of the present invention. Although the laser diode25is rotated in order to optimize the spot shape on the track, the laser diode25can be arranged in substantially the center in the widthwise direction of the package27. Advantageously, the width of the package27can be remarkably reduced as compared to conventional packages.

In addition, the optical pickup15includes a submount25A for holding the laser diode25for attachment of the laser diode25to the package27, as shown inFIG. 3. The submount25A is arranged at the center in the widthwise direction of the package27and the laser diode25is attached to the submount25A such that the laser diode25is shifted in accordance with the position of the optical path of the laser beam in the top emission prism26. Since the submount25A whose outer dimensions are larger than those of the laser diode25is arranged at the center in the widthwise direction of the package27, the width of the package27can be reduced to an absolute minimum.

Furthermore, since the first reflecting face26B and the second reflecting face26C of the top emission prism26are parallel to the lengthwise direction of the package27, the width of the package27can be prevented from increasing, although both of the laser diode25and the top emission prism26are rotated.

(4) Operation and Advantages

In the optical pickup15with the above-described structure, in order to optimize the spot shape on the track, the laser diode25is arranged such that the laser beam emitted from the laser diode25is rotated relative to the longitudinal axis of the package27by the set angle β and the laser beam L emitted from the laser diode25toward the outside of the package27is deflected using the top emission prism26such that the laser beam is parallel-shifted and is then reflected upward. Although the laser diode25is rotated for optimization of the spot shape, the laser diode25can be arranged in substantially the center of the widthwise direction of the package27. Advantageously, the width of the package27can be remarkably reduced as compared to the conventional packages, resulting in a reduction in width of the optical pickup15.

In addition, since the laser beam can be shifted and be deflected upward by the top emission prism26alone, it is unnecessary to arrange the relay mirror4shown inFIG. 10. Therefore, the width of the optical pickup15can be reduced without increasing the number of components of the optical pickup15.

The top emission prism26can be manufactured by cutting a long right-angle prism such that two parallel cut lines for formation of the first and second reflecting faces26B and26C each form the angle α with one edge, serving as the edge26ae, of the right-angle prism. Accordingly, the top emission prism26can be more simply manufactured with higher accuracy than various prisms, such as a roof prism, for this kind of applications. Advantageously, the structure of the entire optical pickup15can be simplified.

Further, the exit face26E of the top emission prism26can be used as a reference surface for mounting on the package27and the entrance face26A thereof can be used as a reference surface for arrangement of the laser diode25. Consequently, an error in assembly of the optical pickup15can be suppressed.

The above-described arrangements allow for realization of a small and simple optical pickup capable of optimizing the shape of a laser beam spot on a track.

(5) Other Embodiments

In the above-described embodiment, the top emission prism26is formed such that the first reflecting face26B, the second reflecting face26C, and the upward reflecting face26D each totally reflect a laser beam inward. The present invention is not limited to this structure. A glass member or an optical material, such as optical plastic, may be laminated on any one of the first reflecting face26B, the second reflecting face26C, and the upward reflecting face26D, alternatively, glass members or optical materials, such as optical plastic, having different indices of refraction may be laminated on a plurality of reflecting faces so that each laminated face reflects a laser beam.

FIG. 7Ashows another embodiment of the top emission prism26in which a first reflective glass member26B1is laminated on the first reflecting face26B and a second reflective glass member26C1is laminated on the second reflecting face26C.FIG. 7Bshows another embodiment of the top emission prism26in which an upward reflective glass member26D1is laminated on the upward reflecting face26D.FIG. 7Cshows another embodiment of the top emission prism26in which the first reflective glass member26B1, the second reflective glass member26C1, and the upward reflective glass member26D1are laminated on the first reflecting face26B, the second reflecting face26C, and the upward reflecting face26D, respectively.

In those cases, designing of layers on the reflecting faces can be easily made and fluctuation of laser beam reflection can be suppressed. The effect of suppressing the fluctuation of laser beam reflection is brought to the fore as the top emission prism26is arranged in a divergent optical path.

In the foregoing embodiment, the right-angle prism is cut along two lines, each of which forms the angle α (=40°) with one edge, serving as the edge26ae, of the prism, to form the first reflecting face26B and the second reflecting face26C which are parallel to each other, thus forming the top emission prism26including rhomboidal surfaces. The present invention is not limited to this example. The top emission prism26may be chamfered to such extent that the chamfered part does not hinder the progress of a laser beam passing through the top emission prism26. For example, when the edge26adof the top emission prism26is cut in parallel to the exit face26E, a face26X is formed as shown inFIG. 8. In this case, the height of the top emission prism26measured from the exit face26E, serving as a base, is reduced, resulting in a reduction in size of the entire optical pickup15. The top emission prism26may be positioned using the face26X as an attachment surface.

In the foregoing embodiment, the right-angle prism is cut along two lines, each of which forms the angle α (=40°) with one edge, serving as the edge26ae, of the prism such that the first reflecting face26B forms an angle of 40° with the entrance face26A and the second reflecting face26C forms an angle of 40° with an extension of the entrance face26A. The present invention is not limited to this example. The angle α may be determined in accordance with the set angle of rotation of the laser diode25, the set angle being determined on the basis of the angle of rotation of a laser beam spot on a track.