Optical unit and optical pickup

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an optical unit that can be used in an optical disk device that optically records and reproduces information on a recording medium such as an optical disk, and an optical pickup that includes an optical unit as a light source, and in particular, a CD or a CD-R. It relates to an optical unit and an optical pickup capable of playing a recording medium having a different protective layer thickness such as a DVD.

【0002】

[Previous technology]

Various proposals have been made conventionally as an optical pickup device that can be used for recording media having different protective layer thicknesses. For example, a proposal has been made in Japanese Patent Application Laid-Open No. 10-308031 (Reference 1). This is an optical pickup device consisting of first and second semiconductor lasers with different wavelengths and two beam splitters with polarization characteristics, such as digital video disc (DVD), compact disc (CD), and CD-R ( An unpolarized optical system is disclosed using an unpolarized film that can reproduce (additional type), has a small amount of light loss, and has low angle dependence.

【0003】

More specifically, the structure is described in paragraphs [0016] and [0017] on page 4 of the same document. The optical system is equipped with a first semiconductor laser (for CD) and a second semiconductor laser (for DVD), and guides the light beam emitted from each laser to a common optical path, such as CD, CD-R, DVD, etc. It is designed to record and reproduce the recording medium of the above. The common optical path is composed of components arranged on the base, that is, first and second beam splitters, mirrors, objective lenses, sensor lenses, light receiving elements, and the like.

【0004】

[Problems to be Solved by the Invention]

[1] According to the above configuration, the thickness of the protective layer for CDs, CD-Rs, DVDs, etc. (for example, the depth from the bottom surface of the disc to the information recording layer is 1.2 mm for CDs and 0.6 mm for DVDs). Although different recording media can be reproduced, for that purpose, a prism consisting of a beam splitter with two polarization characteristics, a semiconductor laser, an optical detector, etc. are arranged, so that the number of parts is large as an optical pickup device and the assembly time is large. It is a configuration that is extremely difficult to reduce in cost. Therefore, it is desirable to reduce the number of components of this type of device configuration, for example, as an optical pickup, which can reproduce recording media with different protective layer thicknesses, and thus also reduce assembly man-hours. This can be achieved while easily achieving cost reduction.

【0005】

[2] On the other hand, as an optical pickup for recording / reproducing DVDs, CDs, etc., there is a proposal made in Japanese Patent Application Laid-Open No. 10-233033 (Reference 2). Here, two hologram packages (units) are used.

【0006】

In the optical system, the optical unit for DVD and the optical unit for CD are arranged so as to form approximately 90 degrees from the beam splitter as a starting point, and reach the objective lens from the beam splitter (or through the collimator lens). The optical unit for the DVD is arranged in a direction substantially parallel to the optical axis of light (leading to), and the optical unit for the CD is arranged in a direction substantially perpendicular to the optical axis (same as above). References, page 8 paragraph [0038], page 10 paragraph [0064], etc.). Here, each optical unit is arranged as being separately packaged so as to include a light emitting source having a different wavelength, a photodetector, a diffraction grating, etc., and pages 8 to 9 of the same document, respectively. By the playback operation described in (paragraphs [0046] to [0051]) and the like, playback is performed when the recording medium is a DVD and when the recording medium is a CD, but as described above, two hologram packages (units) are used. Since it is used, there is a certain limit to miniaturization.

【0007】

Here, for example, if the sharing of the hologram unit can be appropriately realized, it will be more advantageous in terms of providing a small pickup and reducing the size of the optical system. More desirablely, such a unit can be shared, and miniaturization and the like can be appropriately realized.

【0008】

The present invention can solve problems in the prior art based on the above-mentioned considerations and further, based on the considerations described later, can reduce the number of component parts, and can realize advantageous miniaturization and the like. It is an attempt to do so.

【0009】

[Means for solving problems]

According to the present invention, the first semiconductor laser and the second semiconductor laser that emits a light beam having a wavelength different from that of the first semiconductor laser are provided, and the first semiconductor laser, the second semiconductor laser, and light are provided. There is a beam splitter that guides the light beam emitted from the laser in the same direction by arranging the detector on the substrate, irradiates the recording medium with the light beam transmitted through this beam splitter, and detects the reflected light from the recording medium. An optical unit that detects an information signal by receiving light with a device. A diffraction grating is formed in a beam splitter on a surface parallel to a substrate on which a light detector is arranged, and the diffraction grating spreads the light beam. An optical unit is provided that is arranged on the lens for adjusting the. Therefore, in the present invention, it is possible to avoid an increase in the numerical aperture, which requires assembling man-hours and makes it difficult to reduce the cost, the occupied area of the optical system can be reduced, and the lens is used on the objective lens. The numerical aperture (NA) can be adjusted, which makes it possible to achieve miniaturization in an advantageous manner. According to a preferred example, the disadvantages of the prior art can be solved by using a plurality of semiconductor lasers and photodetectors, for example, directly on a semiconductor substrate (Si substrate), or a semiconductor laser with a photodetector via a submount. It is placed on a metal plate, etc., and integrated with a beam splitter provided with a diffraction grating on the light input / output surface. For example, the number of components as an optical pickup can be reduced, and the optical unit can be sealed to improve reliability. It is possible to improve the durability. Further, for example, it becomes possible to provide a small optical pickup. According to the present invention, an optical pickup using the optical unit as described above is obtained, a lens is arranged between the first semiconductor laser and the beam splitter, and the first semiconductor laser and the second semiconductor laser are An optical pickup is provided that includes the above-mentioned optical unit, which is characterized by being arranged at a position conjugate with each other with respect to a collimator lens.

【0010】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 5 show an embodiment of the present invention. Of these, FIG. 1 shows an example of an optical unit according to the present invention and an optical pickup configuration using the optical unit, and FIGS. 2 to 5 show a configuration example of an applicable diffraction grating and photodetector.

【0011】

[Optical unit] In the figure, LD1 and LD2 are semiconductor lasers that emit light beams having different wavelengths. For example, a semiconductor laser having a wavelength of 780 nm (first semiconductor laser LD1) and a semiconductor laser having a wavelength of 630 to 650 nm (No. 1). 2 semiconductor laser LD2). In the optical unit according to this embodiment, these semiconductor lasers, the five-segment photodetector 1 arranged in the vicinity of the first semiconductor laser, and the second semiconductor laser arranged in the vicinity of the second semiconductor laser are used. -Two photodetectors (two photodetectors divided into three and four) 2 and 3 sandwiching the Za are arranged on the semiconductor substrate (Si (silicon) substrate) 10.

【0012】

As the 5-split photodetector, for example, one having 5-split photodetectors 1PD1 to 1PD5 as shown in FIG. 2 can be used, and each of the other two photodetectors is virtual as shown in FIG. 3, for example. Those having each divided light receiving element 2PD1 to 2PD3 and 3PD1 to 3PD4 located on both sides of the LD light beam point can be used. Here, the T direction is a direction parallel to the track direction of the recording medium 80. As described above, a plurality of (two) semiconductor lasers and photodetectors can be arranged on the semiconductor substrate (Si substrate).

【0013】

The semiconductor substrate is integrated within, for example, a cylindrical or rectangular parallelepiped package 20 made of metal or resin and sealed by a trapezoidal beam splitter 30. The beam splitter guides the light beam emitted from the laser in the same direction so as to irradiate the recording medium with the light beam transmitted through the beam splitter. Here, the prism portions 30a and 30b having a triangular shape and a parallel quadrilateral shape. When reflected from a recording medium, the light path is formed so that the reflected light is received by a light detector and an information signal is detected. In addition to the function of the beam splitter itself, here, As shown in the figure, the unit can also have the function of an integrated / sealed structure.

【0014】

In this case, in the case of the optical unit of this embodiment, the package unit is composed of the semiconductor lasers LD1, LD2, the photodetectors 1,2,3, the semiconductor substrate 10, and the beam splitter 30 (as described later). , Multiple diffraction gratings are formed on a plane parallel to the semiconductor substrate on which the photodetector is placed in the beam splitter, and one diffraction grating is placed on the lens for adjusting the spread angle of the light beam. It is possible to effectively share the above (including the configuration), etc., and one package is sufficient, which also has an advantageous effect on reducing the number of parts. Moreover, as a result of using and utilizing the beam splitter 30 as an element as described above, the adoption of such an integrated and sealed structure is advantageous for miniaturization and reduction, and at the same time, reliability and durability. It will also be advantageous for improving the above.

【0015】

Further, the beam splitter and its upper surface, lower surface (injection / exit surface) and the like will be described as follows. The beam splitter surface (BS surface) 31 at the junction of the prism portions 30a and 30b is, for example, an unpolarized beam splitter with a multilayer film having a P-polarized light transmittance (Tp) of 50% and an S-polarized light reflectance (Rs) of 50%. It can be a mode in which it is formed, or instead, a mode in which a wavelength selection filter is formed (see, for example, the fourth embodiment below). In the case of a wavelength selection filter, the filter can be, for example, a filter that transmits a light beam having a wavelength of 780 nm and reflects a light beam having a wavelength of 630 nm to 650 nm.

【0016】

A 1/4 wave plate 40 can be joined to the trapezoidal upper surface, but this is not necessary when the beam splitter is unpolarized. Further, on the lower surface parallel to the semiconductor substrate 10, for example, a four-divided hologram element (first diffraction element) 41 composed of a dividing line parallel to the track (T) of the recording medium 80 and a dividing line orthogonal to the dividing line 41. (Fig. 4) and a grating (second diffracting element) 42 that separates the light beam emitted from the second semiconductor laser into three diffracted lights and irradiates the recording medium 80 with the light beam are formed. As described above, in this example, the beam splitter 30 can be the original in which a plurality of (two) diffraction gratings are formed on a surface parallel to the semiconductor substrate on which the photodetector is arranged, and the plurality of diffraction gratings can be formed. The grating consists of a grating element (Gr) for 3 beams and a hologram element (HOE). Thus, the semiconductor lasers LD1, LD2 and the photodetectors 1,2,3 are arranged on the semiconductor substrate 10, and the beam splitter 30 is provided with a diffraction grating on the light input / output surface via the package 20 portion. It can be integrated with the above and have a structure to be sealed. Further, for example, a spherical lens 50 is formed between the four-divided hologram element and the beam splitter surface. The lens changes the divergence angle of the light beam as shown in the drawing, and is a lens formed on the prism portion 30a here (further mentioned later, a silica-drial lens may be used). On the other hand, on the 45-degree slope (inclined end face of the prism portion 30b), for example, a hologram element having a different grating pitch (third) as shown in FIG. 5 consisting of a dividing line parallel to the track (T) of the recording medium. (Diffraction element) 43 can be formed (this does not have to be used).

【0017】

As the recording medium 80, a DVD, a CD-R, or a CD can be used as described later. However, regarding the photodetector for DVD and the focus and tracking detection during playback when the recording medium 80 is a DVD, the recording medium 80 may be used. When this is performed by the light receiving elements 2PD1 to 2PD3 and 3PD1 to 3PD4 as illustrated in FIG. 3, for example, the detection method described in JP-A-8-22624 (Reference 3) and the like (for example, the same document). (See Figure 15) can be used, which are incorporated and referenced herein. For example, specifically, partial PD1 to 2PD3 are used as photodetectors for focusing error signal detection, and partials 3PD1 to 3PD4 are used as photodetectors for tracking error signal detection, and the detection output by the diffracted light incident on them is used. By calculating, a servo signal and an information signal can be obtained. Further, when the recording medium 80 is a CD-R or a CD and the light receiving elements 1PD1 to 1PD5 as shown in FIG. 2 illustrated above are used, for example, Sharp Technical Report No. 72, 1998/12 The technique of the detection method of FIG. 3 (b) on page 39 of the month (Reference 4) can be used, which is also incorporated herein by reference. In this case, for example, for focus error signal detection, Focus error signal: PD2-PD3 (PD2: detection output of part 1 PD2, PD3: detection output of part 1 PD2) However, when obtaining such an optical detection output, the overall arrangement configuration of each part 1PD1 to 1PD5 can be as shown in Fig. 2 because the dimensions in the left-right direction of the figure can be small. Adopting a photodetector is more advantageous because it fits in the package 20.

【0018】

In the optical pickup configuration using the optical unit as described above, in the embodiment shown in FIG. 1, there are an objective lens 75 provided above the beam splitter 30 and a recording medium 80 for recording or reproducing information. The reflection mirror 71 indicated by the chain line can adopt a configuration in which it is inserted when it is thin.

【0019】

The operation of the optical unit or the optical pickup of this embodiment having the above configuration will be further described below. As for the recording medium 80 to be applied, as mentioned above, for example, CD-Rs, CDs, and DVDs having different protective layer thicknesses can be used. In this case, the recording medium 80 used is the CD-R. The corresponding semiconductor laser side of the two semiconductor lasers LD1 and LD2 is made to emit light (at this time, the other semiconductor laser side is not made to emit light) according to whether it is a CD or a DVD. The objective lens 75 (commonly used and the same) focuses the light beam on the recording track at the convergence position as shown.

【0020】

Now, as shown in the figure, for example, assuming that the recording medium 80 is playing a DVD with a substrate thickness of 0.6 mm, the semiconductor laser side having a wavelength of 630 nm is made to emit light, and the position where the optical spot for CD (1.2 mm side) is formed. A light spot with a light beam having a wavelength of 630 nm is formed closer to the position (on the recording medium surface formed at a shallow depth from the lower surface of the disk), and conversely, a CD-R, CD with a substrate thickness of 1.2 mm. At the time of reproduction, the semiconductor laser side with a wavelength of 780 nm is made to emit light, and the position is farther than the position where the optical spot for DVD (0.6 mm side) is formed (on the recording medium surface formed at a deep depth position from the lower surface of the disc). ), A light spot with a light beam having a wavelength of 780 nm is formed. Regarding the principle and basic operation of a so-called bifocal light pickup that uses two semiconductor lasers with different wavelengths, for example, reference 1 above, pp. 5 to 6 (paragraph [0029], [paragraph [0029], [] 0030] etc.), and the relevant part is incorporated and referred to here.

【0021】

Then, at the time of reproduction of each recording medium, the light beam incident on the beam splitter 30 and guided in the same direction by the beam splitter surface 31 and transmitted through the beam splitter is transferred by the objective lens 75 to the corresponding recording medium 80 (DVD, DVD, Alternatively, the reflected light obtained from the corresponding recording medium by irradiating the CD-R, CD) returns as return light in this order of the objective lens 75 and the beam splitter 30, and is emitted from the beam splitter 30. Then, as described above, the information signal is detected, focused, and tracked by being guided to the corresponding optical detector side of the optical detectors 1, 2, and 3 arranged around the semiconductor laser on the semiconductor substrate 10. Although detection is performed, the spherical lens 50 provided in the triangular prism portion 30a of the beam splitter 30 has the following regarding the irradiation of the recording medium with a light beam when the recording medium 80 is a DVD. It can be made to function as having such an action.

【0022】

[Spherical lens] When enabling both CD-R and CD playback and DVD playback, looking at the numerical aperture (NA) on the objective lens, CD-R, CD and DVD The numerical aperture is different from and. In the case of CD-R and CD, the numerical aperture NAl on the objective lens 75 is, for example, 0.45. On the other hand, in the case of a DVD that uses a short wavelength, has a substrate thickness of 0.6 mm, and should form a light spot at a closer position, the numerical aperture NA2 is 0.6. Therefore, in order to realize this, by arranging the spherical lens 50 in the optical path as shown in the figure, the numerical aperture on the objective lens can be adjusted. That is, the numerical aperture NAl is determined by the position of the light emitting point of the second semiconductor laser and the objective lens 75. Therefore, since it can be determined in this way, the spread angle of the light beam is changed so that the numerical aperture NA2 becomes 0.6 accordingly.

【0023】

The spherical lens 50 of the triangular prism portion 30a can function as a lens for adjusting the spreading angle of the light beam based on such an aim. This means that the NA (numerical aperture) on the objective lens 75 can be adjusted, and the configuration is such that two semiconductor lasers and a photodetector are arranged on one semiconductor substrate 10, and this is further packaged. The above-mentioned advantageous configuration in which 20 is interposed and integrated with the beam splitter 30 to form a sealed structure is maintained (thus, the position, arrangement configuration, etc. of the semiconductor laser in such a configuration are not changed), and the above. It means that it can be realized. Also in the present embodiment, there is no lateral light path by the beam splitter 30, the occupied area of the optical system is reduced, the number of parts is small, and it can be stored in one package 20. As you can see, these advantages are not lost, and it also means that the required numerical apertures NA1 and NA2 can be achieved, because there is no lateral optical path for the optical unit or semiconductor laser by the beam splitter. The occupied area of the optical system can be reduced, and the NA (numerical aperture) on the objective lens 75 by the lens (here, the spherical lens 50) can be adjusted, resulting in miniaturization. As already mentioned, the spherical lens 50 may be a silica dramatic lens.

【0024】

A plurality of semiconductor lasers and photodetectors are arranged on a semiconductor substrate and integrated with a beam splitter provided with a diffraction grating on the light input / output surface, for example, the number of components as an optical pickup is reduced, and the optical unit is sealed. By adopting the structure, reliability and durability can be improved, and the miniaturization can be achieved. The one according to the above embodiment is further based on this, and the following technologies are added. There is also the advantage of being able to do so, which makes it even more effective.

【0025】

In the above configuration, the spherical lens 50 can realize the numerical aperture NA2 = 0.6 on the objective lens 75 in the case of DVD when the numerical aperture NA1 = 0.45 on the objective lens 75 in the case of CD-R and CD. Therefore, in design, a lens having a predetermined numerical aperture (specifically, a concave lens) is selected and provided in advance so as to obtain such a numerical aperture of the light beam. This means that the focal length has been extended in a pseudo manner.

【0026】

Here, another measure to do so is that of the method relating to the refractive index of the glass material (glass material) used, and therefore, from this point, it is reflected by the BS surface to the objective lens. There is a correspondence from the viewpoint of whether the glass materials are the same or different in the optical path of the system to reach and the optical path of the system to go straight to the objective lens. Further, from the viewpoint of improving the utilization efficiency by preventing the amount of light from fluctuating depending on the incident angle and lowering the utilization efficiency, it is preferable to reduce the incident angle dependence. It is desirable to be able to.

【0027】

[1] BS is made into a highly refracting glass material. As shown in the following equation, the optical path length that passes through the glass material becomes long. d = d (1- (1 / n)) (n: Refractive index of material, d: Change in optical path length) Compared to the case where a general BK7 glass material (refractive index 1.52) is used, for example, when SFS1 (manufactured by HOYA Corporation) is used, the refractive index n of SFS1 is, for example, n = approximately 1.9 at a wavelength of 630 to 650 nm. Since (n = 1.89 at a wavelength of 780 nm), the term (1 / n) in the above equation becomes smaller than in the case of BK7, and as a result, if d'is constant, d becomes larger. In this way, it becomes longer by the above formula, so it is advisable to increase n.

【0028】

[2] A high refractive index glass material is preferable for the incident angle dependence (incident light beam having P or S polarization characteristics). For example, the above SFS1 (n = 1.9).

【0029】

[3] A glass material with a concave lens surface is a combination of high refractive index glass materials such as SFS1 (n = 1.9), and other glass materials are a combination of BK7 (n = 1.52) (effect; the optical path length can be shortened), or vice versa. is there. Here, in the former aspect, the triangular prism portion 30a is the glass material of SFS1, and the glass material of the parallelogram prism portion 30b is BK7.

【0030】

On the other hand, in the latter reverse combination mode, the parallelogram prism portion 30b may be the glass material of SFS1 and the triangular prism portion 30a may be the glass material of BK7. If the refractive index of the glass material of the triangular prism portion 30a is increased, the optical path length can be increased, but conversely, if the refractive index is decreased, there is an advantage that the spreading angle can be increased. By adopting the opposite aspect and selecting the glass material of the glass of the concave lens, the spreading angle can be increased.

【0031】

In the above embodiment, a concave lens is used as the spherical lens 50, but it can also be used when the spherical lens 50 is a convex lens.

【0032】

Further, in the embodiment, the applicable dividing line of the diffraction grating or the dividing line direction of the photodetector for focusing is shown as illustrated in FIGS. 2 to 5 with respect to the track (T), but the present invention is not limited to this. .. Therefore, the dividing line of the diffraction grating or the dividing line direction of the photodetector for focusing may be in the range of 0 to 45 ° with respect to the track.

【0033】

6 to 8 show another embodiment (second embodiment) of the present invention. This embodiment is an improvement of the above-described embodiment (first embodiment), and is an optical unit compatible with a CD-R and a DVD-ROM. Regarding the first embodiment, the principle configuration such as sharing, integration, and hermetically sealed structure of the unit, and the action and effect, which have already been described, can be basically the same as those of the first embodiment (this point). Is the same in other examples). The main parts of this embodiment will be described below.

【0034】

According to this embodiment, as shown in FIG. 6, roughly, the semiconductor lasers LD1 and LD2, the photodetectors 4 and 5, and the semiconductor substrate 10 on which these semiconductor lasers LD1 and LD2 and the photodetectors 4 and 5 are arranged. It has a grating element 44 and a hologram element 45 (FIG. 7) as a diffraction grating provided on the lower surface of the beam splitter parallel to the beam splitter, and a collimator lens 72 is arranged between the trapezoidal beam splitter 30 and the objective lens 75. At the same time, the spherical lens 50 is formed between the grating element 44 and the beam splitter surface 31, and the optical unit also has a photodetector 101 for front monitoring. The first semiconductor laser LD1 is a laser having a wavelength of 780 nm (S-polarized light), and the second semiconductor laser LD2 is a laser having a wavelength of 630 to 650 nm (P-polarized light).

【0035】

For the wavelength of 780 nm of the first semiconductor laser, the unpolarized beam splitter surface 31 (BS) has Ts (S polarization transmittance); 50%, Rs (S polarization reflectance); 50%, and the second For wavelengths of semiconductor lasers of 630 to 650 nm, Tp (P polarization transmittance): 0 to 50%, Rp (P polarization reflectance); 50 to 100%. At the bottom of the beam splitter 30, there is a grating (second diffraction grating) between the beam splitter 30 and the first semiconductor laser (LD1), and a spherical lens 50 is formed between the grating 44 and the beam splitter surface 31. .. In the illustrated example, a thin plate having a diffraction grating formed as a grating for 3 beams is joined to the lower surface of the beam splitter 30 to form a grating element 44, but the configuration is not limited to this, and this point will be described later. .. Furthermore, a photodetector 101 for front monitoring that monitors the output light amount of the two semiconductor lasers LD1 and LD2 is joined to the vertical surface of the trapezoidal prism surface of the beam splitter 30 (the side surface of the triangular prism portion 30a). ..

【0036】

[Hologram (HOE)] The hologram element 45 and the like are as follows. When each recording medium (CD-R or DVD-ROM) is used, it is diffracted depending on the state of P-polarized light or S-polarized light from the silver recording medium 80. Specifically, the hologram (HOE) divided into four at the center of the optical axis is guided to the photodetectors 4 and 5, respectively, but as shown in Fig. 7, each of the diagonal planes a1, a2; b1 and b2. The diffraction is different. Regions a1 and a2 are P-polarized diffraction, and regions b1 and b2 are S-polarized diffraction. In this embodiment, when the corresponding recording medium 80 (CD-R) is irradiated with the light beam having a wavelength of 780 nm and the corresponding recording medium 80 (DVD-ROM) is irradiated with the light beam having a wavelength of 630 to 650 nm. However, the reflected light obtained in each case is incident on the quadrant hologram element 45, and therefore, the information signal can be detected by receiving the reflected light from the corresponding recording medium 80 with the photodetectors 4 and 5. However, in this case, the information signal is 2/3, the 1/3 component is the 0th-order diffracted light, and the remaining 2/3 component is the ± 1st-order diffracted light. More specifically, for the photodetector, focus, and tracking detection, for example, the detection method described in the above-mentioned document 3 (see, for example, FIG. 4 of the same document) can be used.

【0037】

[About the spherical lens] Further, in the present embodiment, the spherical lens 50 positions the first semiconductor laser LD1 and the second semiconductor laser LD2 at positions conjugate with each other with respect to the collimator lens 72 whose light beam is parallel light. Have been placed. Thus, here, the spherical lens 50 is arranged between the first semiconductor laser LD1 and the beam splitter surface 31, and the first semiconductor laser LD1 and the second semiconductor laser LD2 are conjugated to each other with respect to the collimator lens 72. It is placed in a suitable position. As a result, the condition of the distance relationship from each light emitting point of each semiconductor laser arranged on the same semiconductor substrate 10 to the collimator lens 72 can be set by the lens 50 in which the numerical aperture is selected in advance, and as a result, the first Similar to the embodiment, the NA (numerical aperture) on the objective lens 75 can be adjusted, and as shown in FIG. 6, the required numerical aperture NA1 (for example, 0.45) and the numerical aperture NA2 (0.6) described above are set in the first embodiment. It can be realized with the same effect as in the case of.

【0038】

FIG. 8 shows the shapes and the like of the light receiving elements of the photodetectors 4 and 5 that can be applied. This is an example of the position and shape of the ± 1st-order diffracted light and the light receiving element that have passed through the 4-segment hologram element 45 illustrated in FIG. 7, and each of the two photodetectors 4 and 5 has an LD emission point as shown in the figure, for example. Those having each divided light receiving element 4PD1 to 4PD3 (3-divided PD) and 5PD11 to 5PD42 (8-divided PD) located on both sides of (0th-order diffracted light) can be used. Basically, the area parts 4PD1 to 4PD3 are used as photodetectors for focusing error signal detection, and the area parts 5PD11 to 5PD42 are used as photodetectors for tracking error signal detection, and the detection output by the diffracted light incident on them is used. Servo signals and information signals can be obtained by calculation.

【0039】

Here, in the figure, the diffracted light of each of the diffracted light when the light beam having a white color pattern of 630 to 650 nm is applied to the recording medium 80 and when the light beam having a black color pattern of 780 nm is applied to the recording medium 80. The states represented by the symbols a11, b11, a21, b21 and a12, b12, a22, b22 are the photodetector front focus (the state in which the focus is on the front side of the photodetector surface) and the photodetector, respectively. This is an example of the position and shape of the diffracted light in the rear focus of the photodetector (the state where the focus is on the back side of the photodetector surface). Furthermore, the detection output in the area part 5PD11, 5PD21, 5PD31, 5PD41, 5PD12, 5PD22, 5PD32, 5PD42 is set to PD respectively.₁₁, PD₂₁, PD₃₁, PD₄₁, PD₁₂, PD₂₂, PD₃₂, PD₄₂In the detection method by the 3-beam method, the phase difference method, and the push-pull method, each detection can be performed by the following calculation and method.

【0040】

[3 beam method] (PD₁₂+ PD₄₂)-(PD₁₁+ PD₄₁) [Phase difference method] (PD₂₁+ PD₃₂)-(PD₂₂+ PD₃₁) [Push-pull method] (PD₂₂+ PD₃₂)-(PD₂₁+ PD₃₁) 【0041】

Data information is obtained by the total output of PD11 to PD42 and PD1 to PD3 in all areas.

【0042】

Therefore, for tracking error signal detection, for example, when a light beam having a wavelength of 780 nm is applied to the recording medium 80 (CD-R), three light beams (dl to d3 (spots)) are applied to the 4-divided hologram element 45 by a 3-beam method. )), The diffracted light becomes six light beams on the two-divided light receiving element divided in parallel with the track (T) direction of the recording medium 80. When the recording medium 80 (DVD-ROM) is irradiated with a light beam having a wavelength of 630 to 650 nm, it is incident on the 4-split hologram element 45 by a phase difference method with one light beam (dl only), and the diffracted light is 2. There are two light beams on the split light receiving element. In this embodiment, the photodetectors 4 and 5 can be implemented in such a configuration.

【0043】

[Relationship between a spherical lens in a trapezoidal prism and a diffraction grating] In this embodiment, after forming a spherical lens 50 composed of a space portion in a state where a glass material (SFS1 or BK7) is etched with respect to the triangular prism portion 30. , A thin plate (grating element 41) on which a diffraction grating is formed is joined. Even if such a configuration is followed, the same effect as that of the first embodiment can be obtained, but if a diffraction grating is formed on the surface of the spherical lens in order to reduce the number of parts, such a thin plate is unnecessary. .. Therefore, in this respect, it becomes more advantageous and more effective. Therefore, the present invention may be carried out in this way.

【0044】

Further, using an unpolarized beam splitter, the polarization characteristics of the short wavelength (630 to 650 nm) semiconductor laser are met (in the example, the P polarization characteristic of the beam splitter is 0 to 10% in Tp of the P polarized semiconductor laser). When Rs is selected from 90 to 100%), the light utilization efficiency is improved and the durability of the short wavelength semiconductor laser can be improved. The present invention may be carried out in this way.

【0045】

Next, still another embodiment of the present invention (third embodiment), for example, an optical unit compatible with recording or reproduction of a magneto-optical disk for optical modulation recording and a CD-R. Will be described with reference to FIG. In this embodiment, two lasers with different wavelengths, LD1 (wavelength 780 nm) and LD2 (wavelength 630 to 650 nm), are arranged on the semiconductor substrate 10 and packaged with a beam splitter 30 with prism portions 30a, 30b, and 30c. It is an optical unit with a structure sealed with 20 interposed therebetween.

【0046】

The prism portion is composed of a triangular prism portion 30a and two parallelogram prism portions 30b and 30c, and the triangular prism portion 30a is a prism portion made of a material of BK7 and a material of, for example, SFS1. The interface between the triangular prism portion 30a and the parallelogram prism portion 30b is a wavelength selection filter (dichroic mirror surface) 32, and the interface between the parallelogram prism portions 30b and 30c is a beam splitter made of a multilayer film. A surface 34 is formed. That is, in this embodiment, regarding the spherical lens for adjusting the spreading angle of the light beam, here, for example, BK7 (low) formed by ion etching on a prism made of a material of SFS1 (high refractive index n = 1.9). A lens portion made of a material having a refractive index n = 1.52) is formed as a hemispherical lens 51. A diffraction grating 46 for three beams is provided at the position of such a lens. Therefore, as shown in the figure, between the semiconductor laser LD1 and the triangular prism portion 30a, there is a lens portion 51 capable of adjusting the spread angle of the light beam emitted from the semiconductor laser LD1, and the diffraction grating 46 is arranged on such a lens. This has the effect of preventing optical distortion of the thin plate due to the adhesive force between the triangular prism portion 30a and the diffraction grating 46 (grating surface) for 3 beams.

【0047】

Further, as shown in the figure, between the prism portion and the semiconductor substrate 10, an analyzer 111 (Wollaston prism) for detecting a photomagnetic signal and three photodetectors 6a and 6b arranged on the semiconductor substrate 10 are provided. , 7 are formed. When the semiconductor laser LD2 emits light, the light beam from the semiconductor laser is reflected by the inclined end face of the parallel quadrilateral prism portion 30c and directed toward the junction surface between the triangular prism portion 30a and the parallel quadrilateral prism portion 30b. It can be led to the collimator lens 72. Regarding the return light when reflected from the recording medium, the light beam guided from the triangular prism portion 30a into the parallel quadrilateral prism portion 30b is reflected at the junction surface between the prism portion 30b and the parallel quadrilateral prism portion 30c. It can be guided to the analyzer to cause the light detector to receive light.

【0048】

In this embodiment, further, when the thickness of the prism portion is h as shown in the figure, the distance between the two semiconductor lasers LD1 and LD2, that is, the semiconductor laser LD1 having a wavelength of 780 nm and the semiconductor laser LD2 having a wavelength of 630 to 650 nm The arrangement interval on the semiconductor substrate 10 is 1.5 h, which is 1.5 times the thickness h of the prism portion (the detector 111 is arranged in the space of 1.5 h). ). In the above configuration, the numerical aperture of the collimator lens 72 has an image point side distance difference of 1.5 h. Therefore, in order to change the image point side distance difference of 1.5h from 0.7 to 1.0, for example, the hemispherical lens 51 (or, as mentioned in the first embodiment, a cylindrical lens may be used) is used. In this way, the hemispherical lens 51 brings the light emitting point of the semiconductor laser LD2 having a wavelength of 630 to 650 nm closer (pseudo), and thus can be a flat optical unit, that is, the prism portions 30a, 30b, 30c and the collimator lens 72. The distance between the lens and the lens is narrowed, and the size is reduced. Even with such a configuration, the unit can be shared, integrated, sealed, and other effects can be achieved as in the first embodiment, and the NA (numerical aperture) on the objective lens (not shown) is adjusted and set by the lens 51. It is possible, for example, NA = 0.38 to 0.45 and NA = 0.6 can be realized, and it is advantageous for flatness and miniaturization. [Action in the case of FIG. 9] The action in the case of FIG. 9 will be explained. In the figure, the divergent light beam of linearly polarized light having a wavelength of 630 to 650 nm (LD2) is reflected by the reflecting surface and is a beam. It passes through the splitter surface 34, is reflected by the die clock mirror surface 32, and becomes a parallel light beam by the collimator lens 72. Then, it passes through an objective lens (not shown) and converges on the recording surface of the optical magnetic recording medium. The light beam (return light) reflected on the recording surface of the photomagnetic recording medium passes through the objective lens and the collimator lens 72 again, is reflected by the die clock mirror surface 32, and is reflected by the beam splitter surface 34. The linear polarization having the component of the car rotation signal passes through the Wollaston prism 111, is separated into three light beams, and is received by the three light detectors 6a, 6b, 7 on the semiconductor substrate 10 and is photomagnetic. Information on the recording surface of the recording medium can be recorded or reproduced. For recording or reproduction of a linearly polarized divergent light beam with a wavelength of 780 nm (LD1), it is parallel to the unpolarized beam splitter surface 31 in the beam splitter 30 of the trapezoidal prism of FIG. 6 and borders in the air. The reflecting surface has the same function as the beam splitter surface 34. Then, the information on the recording surface of the phase change recording medium can be recorded or reproduced by passing through the Wollaston prism 111 and receiving light by the photodetector 7.

【0049】

Yet another embodiment of the present invention (fourth embodiment) will be described with reference to FIG. As will be described later, this embodiment is compatible with a magneto-optical MO (for optical modulation recording) transparent substrate thickness of 1.2 mm and an ASMO (magnetic field modulation recording) transparent substrate thickness of 0.6 mm. It is suitable for an optical unit having a property. As shown in FIG. 10, in the illustrated example, the semiconductor lasers LD1 (wavelength 780 nm) and LD2 (wavelength 630 to 650 nm) having different wavelengths, these semiconductor lasers LD1, LD2 and the two optical detectors 8,9 Diffraction gratings (here, 3) are arranged to face the respective semiconductor lasers LD1 and LD2 on the lower surface side of the beam splitter 30 by the semiconductor substrate 10 on which the above is arranged, the two detectors 115, 116, and the prism portions 30a, 30b', 30d, respectively. It has a beam diffraction grating 46 and a transmissive polarizing hologram element47), and an optical detector 101 for front monitoring of a semiconductor laser having a wavelength of 780 nm and a wavelength of 630 to 650 nm.

【0050】

Here, regarding the diffraction grating 46 for the above three beams, when used for MD, as shown in the figure, a transparent spacer 121 having a concave lens 120 formed on one surface is used as an arrangement position of the diffraction grating 46. It may be used to form on the spacer. In this example, such a structure is adopted, and thus even in this case, a lens portion (concave lens 120) capable of adjusting the spreading angle of the light beam from the semiconductor laser LD1 between the semiconductor laser LD1 and the triangular prism portion 30a. Exists, and the diffraction grating 46 can be configured to be arranged on the lens. Then, by forming the concave lens 120 on the exit surface and providing the diffraction grating 46 for 3 beams on the incident surface in this way, the following advantages are brought about. That is, by selecting the thickness of the spacer 121 used, the position of the diffraction grating 46 for 3 beams can be selected. This leads to easy matching with the track spacing on the recording medium surface, and therefore, in the above configuration, such a point can be mentioned as a further advantage.

【0051】

Hereinafter, the prism portion, the two diffraction gratings, the components on the semiconductor substrate, the relationship with the package, and the like will be further described in this order.

【0052】

[Prism] A wavelength selection filter 32 is formed at the junction between the triangular prism portion 30 and the parallelogram prism portion 30b'joined with the triangular prism surface. The wavelength selection filter has 100% S-polarized light reflection, 70% P-polarized light transmission, and 30% reflection for the wavelength of the semiconductor laser LD2 having a wavelength of 630 to 650 nm, and the wavelength of the semiconductor laser LD1 having a wavelength of 780 nm. It can be formed by a multilayer film that transmits 50% P-polarized light and reflects 100% S-polarized light.

【0053】

Further, the joint portion between the parallelogram prism portion 30b'and the trapezoidal prism portion 30d joined to the parallelogram prism surface is a reflective polarizing hologram 33 (for example, a reflective polarized hologram having no dividing line). This shall be P-polarized ± 1st-order diffracted light 15% and 0th-order diffracted light 70% for the wavelength of the semiconductor laser LD2 with a wavelength of 630 to 650 nm, and for the wavelength of the semiconductor laser LD1 with a wavelength of 780 nm. Let the first-order diffracted light of P-polarized light be, for example, 20%.

【0054】

The relationship with the diffraction grating is as follows. That is, there are two diffraction gratings (46,47) on the incident surface from the semiconductor lasers LD1 and LD2 having two different wavelengths, corresponding to each semiconductor laser as shown in the figure. Opposing the semiconductor laser LD2 with wavelengths of 630 to 650 nm is a transmissive polarized hologram 47 (for example, divided into three) (+1st-order diffracted light is a convex lens, -1st-order diffracted light is a hologram with a concave lens action). Yes, this is formed on the underside of the parallel quadrilateral prism portion 30b'. The other is the diffraction grating 46 for 3 beams, which faces the semiconductor laser LD1 having a wavelength of 780 nm. As already mentioned, this is formed on a spacer 121 having a concave lens 120 and having a predetermined thickness provided on the lower surface of the triangular prism portion 30a. Further, on the side surface (vertical surface) of the triangular prism portion 30a, a photodetector 101 for front monitoring for LD that monitors the amount of light emitted from the semiconductor lasers LD1 and LD2 is directly bonded with an ultraviolet curable adhesive.

【0055】

[Relationship with components and packages on the semiconductor substrate] On the semiconductor substrate (Si substrate) 10, two semiconductor lasers LD1 and LD2 and two photodetectors 8,9 (for example, two divided into six) Photodetectors), and on these photodetectors are detectors 115,119 (here, polarizing beam splitters (polarizing prisms)) tilted 45 degrees with respect to the active surface of the semiconductor laser. Two optical waveguide elements such as those described in 10-241199 (Reference 5) are arranged. When the prisms are joined at each portion 30a, 30b', 30d as shown in the figure, the dimensions are set to be 2δ larger than that of the semiconductor substrate 10. In order to prevent oxidation of the semiconductor lasers LD1 and LD2 and the photodetectors 8 and 9, the semiconductor substrate 10 on which the semiconductor laser is mounted is surrounded by the package 20, and the openings are joined by the prism and sealed. At that time, both δ portions are formed to be joint portions to be joined by an adhesive between the upper end edge of the package 20 and the prism. In this way, as in the case of, for example, the one described in JP-A-10-334498 (Reference 5), the concave lens is not inserted or removed from the divergent light, and therefore the drive device is not required. As a result, the optical pickup is made smaller.

【0056】

[Action] Hereinafter, the operation of the optical unit or the optical pickup having the configuration according to this embodiment will be described by taking the case of using recording media having different substrate thicknesses as an example. Here, a case where an ASMO (magnetic field modulation recording) disk having a substrate thickness of 0.6 mm and a 1.2 mm disk for optical modulation recording are inserted as described above will be described.

【0057】

When a disk with a substrate thickness of 0.6 mm is inserted into the device, based on this, the semiconductor laser LD2 with a wavelength of 630 to 650 nm emits light under the control of a control unit (not shown), and the transmissive polarized hologram 47 divided into three parts. (80% transmission) is transmitted, reflected by the reflective polarized hologram 33 (80% reflection) without dividing lines, and reflected by the wavelength conversion filter 32 (70% reflection), which are not shown in FIG. 10, respectively. , It passes through the collimator lens, passes through the objective lens, and converges on the recording surface with a substrate thickness of 0.6 mm.

【0058】

The light beam reflected on the recording medium surface returns to the optical unit shown in the figure in the order of the objective lens and the collimator lens, is reflected by the wavelength conversion filter 32, and the ± 1st-order diffracted light is emitted by the reflective polarized hologram 33. It is incident on one of the polarizing prisms, the detector (one of the detectors 115 and 116), and thus the polarization is separated, and the light is received by the two light detectors 8 and 9 divided into six. Here, in the case of simultaneous emission with the semiconductor laser LD1 having a wavelength of 780 nm, it is possible to adopt a configuration in which the incident surface of the analyzer is coated with a wavelength selection filter for cutting the wavelength of 780 nm. In this case, focus detection is performed by the beam size method, and tracking detection is performed by the push-pull method (in this case, the transmission type polarized hologram element is unnecessary). Information on the recording medium surface can be obtained from the difference signals of the two photodetectors 8 and 9.

【0059】

When a disk with a substrate thickness of 1.2 mm (optical modulation recording) for optical modulation recording is inserted, the semiconductor laser LD1 with a wavelength of 780 nm emits light. The light beam from the semiconductor laser LD1 passes through a concave lens 120 as shown in the figure, where the divergence angle is changed, and the light beam is incident on the wavelength conversion filter 32 and transmitted (50% transmitted). It is guided in the same direction as described, and as a result, it converges on a recording surface having a substrate thickness of 1.2 mm via a collimator lens and an objective lens.

【0060】

Similarly, the light beam reflected on the recording medium surface returns in the order of the objective lens and the collimator lens, is reflected by the wavelength conversion filter 32, and the ± 1st-order diffracted light is transmitted from the other polarizing prism by the reflective polarizing hologram 33. It is incident on the detector (the other of the detectors 115 and 116), polarized and separated, and received by two light detectors 8 and 9 divided into six. The information on the recording medium surface and the detection of the servo system are the same as those for the 0.6 mm substrate thickness disk by the semiconductor laser LD2 emission of the wavelength 630 to 650 nm described above. In this case as well, as in the other examples described above, the diffraction grating 46 for 3 beams arranged on the lens for adjusting the spreading angle of the light beam (concave lens 120 in this example) is 3 beams. It is a combination of the transmission type polarizing hologram 47 and the case of using the tracking for the purpose. For example, it has a guide surface with a substrate thickness of 1.2 mm and is 0. When recording information on the recording surface of an optical recording medium (disk) having at least two recording surfaces (multilayer structure via spacers) with a substrate thickness of 6 mm, two 6 divisions for 780 nm in this case Information on the recording surface can be obtained from the total sum of all of the photodetectors, and the recording surface and the guide surface can be servo-controlled independently. At this time, when tracking detection is performed by the 3-beam method, the transmission hologram divided into three and the + 1st-order diffracted light diffracted by the transmission hologram can be received by the photodetector divided into five. In the focus and tracking control operation by irradiating the guide track with a light beam with a wavelength of 780 nm, the normal initial operation (for example, after rotating the disk, causing the semiconductor laser to emit light, and then performing the focus search, the control track is controlled by tracking control. Can be irradiated with a light beam and read the desired information after on-track), in which case it is irradiated with light beams of two different wavelengths, but first irradiated with a light beam of a semiconductor laser with a wavelength of 780 nm. However, by detecting on-track on the guide track and then emitting a semiconductor laser with a wavelength of 630 to 650 nm for information recording and reproduction, there is no control instability and the initial operation at the time of initialization can be shortened.

【0061】

The present invention is not limited to the above embodiments. For example, the additional technique derived in consideration of the selection of the refractive index of the glass material described in relation to the first embodiment can be added in other examples, and therefore, the applicable description is given. The parts can be interchanged and applied to each configuration in other embodiments as well.

【0062】

[Effect of the invention]

According to the present invention, the occupied area of the optical system can be reduced, the numerical aperture of the lens on the objective lens can be adjusted, and it is possible to advantageously realize miniaturization and the like. Further, a plurality of semiconductor lasers and photodetectors are arranged directly on a metal plate together with the photodetector, for example, directly on a semiconductor substrate or via a submawite, and a diffraction grating is provided on the light input / output surface. By integrating with the provided beam splitter, for example, the number of components as an optical pickup can be reduced and the optical unit can be sealed, so that reliability and durability can be improved.

[Simple explanation of drawings]

[Figure 1]

It is a figure which shows the structure of one Example of this invention.

[Figure 2]

It is a figure which shows the example of the applicable diffraction grating.

[Fig. 3]

It is also a figure which shows an example of a diffraction grating.

[Fig. 4]

It is a figure which shows the example of the structure of the photodetector which can be applied.

[Fig. 5]

Similarly, it is a figure which shows the example of the structure of the photodetector.

[Fig. 6]

It is a figure which shows the structure of another Example of this invention.

[Fig. 7]

It is a figure which provides the explanation of the hologram (hologram pattern) in the same example.

[Fig. 8]

Similarly, it is a figure which provides the explanation of the shape of the light receiving element of a photodetector.

[Fig. 9]

It is a figure which shows the structure of still another Example of this invention.

[Fig. 10]

It is a figure which shows the structure of still another Example of this invention.

[Explanation of symbols]

1 Photodetector 1PD1 ~ 1PD5 Light receiving element (light receiving area) 2,3 photodetector 2PD1 ~ 2PD3, 3PD1 ~ 3PD4 Light receiving element (light receiving area) 4,5 Photodetector 4PD1 ~ 4PD3,5PD11 ~ 5PD42 Light receiving element (light receiving area) 6a, 6b, 7 photodetector 8,9 Photodetector 10 Semiconductor substrate (Si substrate) 20 packages 30 beam splitter 30a, 30b, 30b', 30c, 30d Prism part 31,34 Beam splitter surface 32 wavelength selection filter 33 Reflective Polarized Hologram 40 1/4 wave plate 41 Hologram element (diffraction grating) 42 Grating 43 Hologram element (diffraction grating) 44 Grating 45 Hologram element (diffraction grating) 46 3 Diffraction grating for beam 47 Transmission type polarizing hologram element (diffraction grating) 50 spherical lens 51 hemispherical lens 71 Reflective mirror 72 Collimator lens 75 Objective lens 80 Recording medium 101 Photodetector for front monitor 111 Photon 115,116 Photon 120 concave lens 121 spacer LD1, LD2 semiconductor laser