Optical apparatus

Abstract: In an optomagnetic recording polarization optical apparatus according to the present invention, a polarizing film (65) is formed on the photodetectors (63,64) for transmitting light which is linearly polarized along a first polarization direction, to be received by the first photodetector (63), and for reflecting light which is linearly polarized along a second polarization direction which is perpendicular to the first polarization direction. In addition, a λ/4 plate (67) having a total reflection film (68) formed on it is arranged above the photodetectors, such that the light reflected by the polarizing film is rotated and directed to the second photodetector (64).

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a pickup structure for optically reading recorded data from a recording medium. Description of the Prior Art In an optical disk player or the like, as shown in Fig. 1A, a light-emitting-receiving composite element called a laser coupler 11 is used in an optical pickup. In the laser coupler 11, photodiodes 13 and 14 are formed on an Si substrate 12, and a prism 15 is fixed on the photodiodes 13 and 14 by an adhesive. A submount 16 serving as another Si substrate is fixed on the Si substrate 12 by soldering or the like. A photodiode 17 is formed on the submount 16, and a laser diode 21 is fixed on the submount 16 by soldering or the like. In order to reproduce data recorded on a optical disk 22 using the laser coupler 11, part of light 23 emitted from the laser diode 21 is reflected on a surface 15a of the prism 15, transmitted through an objective lens 24, and incident on the optical disk 22. The part of the light 23 which is reflected by the optical disk 22, transmitted through the objective lens 24, and incident on the surface 15a of the prism 15 is refracted and enters into the prism 15. The first half of the light 23 which enters into the prism 15 is incident on the photodiode 13, the second half reflected by the photodiode 13 is totally reflected by a surface 15b of the prism 15, and is incident on the photodiode 14. The photodiode 13, as shown in Fig. 1B, is divided into three parts A, B and C, and the photodiode 14, as shown in Fig. 1C, is divided into three parts D, E and F. An output obtained from these photodiodes 13 and 14 and expressed by: (A + C + E) - (B + D + F) is used as a focus error signal. Therefore, as described above, 50% of the light 23 which enters into the prism 15 through the surface 15a must be incident on the photodiode 13, and the remaining 50% must be reflected by the photodiode 13. For this reason, in the conventional pickup used in an unpolarization optical system recording scheme such as an optical disk, as shown in Fig. 3, an optical semitransparent film 25 (half mirror) having a reflectance of 50% is deposited on a portion of the prism 15 opposite to the photodiode 13. Note that an SiO 2 film 26 serving as a protection film is formed on the surface of the Si substrate 12, and an adhesive layer 27 is interposed between the SiO 2 film 26 and the optical semitransparent film 25 on the photodiode 13. Furthermore, the photodiode 17 receives the light 23 emitted from the rear surface of the laser diode 21 to perform automatic power control. An unpolarization optical system recording scheme can be used for only reading data. As a recording medium capable of repetitively recording and erasing data, an optomagnetic disk serving as a polarization optical system recording scheme is known. A basic optical system of the above optomagnetic disk is shown in Fig. 2. Multi-mode laser light emitted from a semiconductor laser 46 passes through a collimating lens 45 and a beam shaping prism 44 and is incident on a special beam splitter 43. In the special beam splitter 43, 1 ○ the linearly polarized component of the laser light is highly purified, and 2 ○ weak signal light is separated from the laser light. A light-receiving optical system splits light reflected by the special beam splitter 43 into light components to a data signal detecting system and a focus tracking control signal detecting system, and the light component incident on the data signal detecting system is guided to a differential optical system. In addition, the light component incident on the focus tracking control signal detecting system is guided to a focus error signal detecting optical system and to a tracking error signal detecting optical system. As a conventional pickup for recording and reading data on/from the above optomagnetic disk, a pickup obtained by assembling parts such as a polarization beam splitter and fixing them with an adhesive or the like is known. The conventional pickup obtained by assembling these parts does not easily have a small size and a small thickness. A pickup used in a polarization optical system recording scheme must have a structure in which a laser coupler obtained by integrating a laser diode, a microprism and the like is formed to equally split light which enters into the prism into light components to two or more photodiodes. OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide a laser coupler obtained by integrating a laser diode, a microprism and the like to form a pickup using a polarization optical system recording scheme to solve difficulty in realizing a compact, small pickup caused by assembling and adhering conventional parts. The invention is defined in claim 1. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, however, the drawings are not intended to imply limitation of the invention to the specific embodiment, but are for explanation and understanding only. Fig. 1A is a side view showing a conventional structure, and Figs. 1B and 1C are plan views showing a photodiode of the conventional structure in Fig. 1A; Fig. 2 is a view showing the structure of a conventional pickup of an optomagnetic disk which is not integrated with a laser coupler; Fig. 3 is a side view showing another prior art; Fig. 4A is a side view showing an optomagnetic recording pickup to which the embodiment of the present invention is applied, and Fig. 4B is a plan view showing a photodiode in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment of the present invention applied to an optomagnetic recording laser coupler will be described below with reference to Figs. 4A and 4B. As shown in Fig. 4A, in the optomagnetic recording laser coupler 61 to which the embodiment is applied, two photodiodes 63 and 64 are formed on an Si substrate 62. As shown in Fig. 4B, the photodiode 63 is constituted by three parts A to C divided in a direction perpendicular to the alignment direction of the photodiodes 63 and 64, and the photodiode 64 is constituted by three parts D to F divided in the direction of the parts A to C. A polarizing film 65 is formed on the entire upper surface of the Si substrate 62. This polarizing film 65 transmits only a P-polarized light component and reflects an S-polarized light component. A microprism 66 having a trapezoidal section, a height of about 1 mm, and a surface inclined at an angle of 45° is adhered on the polarizing film 65 above the photodiodes 63 and 64. Although the polarizing film 65 is formed on the entire upper surface of the Si substrate 62, the polarizing film 65 may be formed on the entire lower surface of the microprism 66. Furthermore, the polarizing film 65 may be formed on only the upper surface portions of the Si substrate 62 which correspond to the upper portions of the photodiodes 63 and 64, or the polarizing film 65 may be formed on the lower surface portions of the microprism 66 which correspond to the photodiodes 63 and 64. A λ/4 plate 67 is adhered on the upper surface of the microprism 66, and a total reflection film 68 is formed on the λ/4 plate 67. In addition, an unpolarizing film 71 having a reflectance of 50% is formed on the inclined surface of the microprism 66. Note that a phase film using a polymer film having uniform orientation may be used in place of the λ/4 plate 67. As described above, an optomagnetic recording polarization optical system 72 according to the embodiment is formed. In order to constitute the optomagnetic recording laser coupler 61, an Si substrate 73 other than the Si substrate 62 is fixed by a silver paste or the like on the polarizing film 65 at a position opposite to the inclined surface of the microprism 66. A photodiode 74 is formed on the upper surface of the Si substrate 73, and a laser diode 75 is fixed on the upper surface of the Si substrate 73 by soldering or the like. In addition, an optomagnetic recording pickup 77 is constituted by the above optomagnetic recording laser coupler 61 and an objective lens 76. In the optomagnetic recording pickup 77 with the above arrangement, light 78 emitted from the laser diode 75 is polarized light having an electric field component inclined at 45° with respect to the incident surface of the polarizing film 65. The light 78 is incident on the unpolarizing film 71, and only 50% of the light 78 is reflected upward. The photodiode 74 is used to directly monitor light emitted backward from the laser diode 75 and to control the amount of a current injected into the laser diode 75. The light 78 reflected by the unpolarizing film 71 is focused by the objective lens 76 on an optomagnetic disk 79, and the polarization plane of the light is rotated in accordance with a magnetic signal recorded on the optomagnetic disk 79. The light 78 reflected by the optomagnetic disk 79 is incident on the unpolarizing film 71 again, and 50% of the reflected light 78 is transmitted through the unpolarizing film 71. The light 78 transmitted through the unpolarizing film 71 propagates through the microprism 66 and is incident on the polarizing film 65. Only the P-polarized light component of the light 78 incident on the polarizing film 65 is transmitted through the polarizing film 65 and is incident on the photodiode 63, and the S-polarized light component of the light 78 is reflected by the polarizing film 65. The light 78 reflected by the polarizing film 65 propagates through the microprism 66, is transmitted through the λ/4 plate 67, and is incident on the total reflection film 68. The light 78 is reflected by the total reflection film 68 and transmitted through the λ/4 plate 67 again. That is, the light 78 is reciprocated in the λ/4 plate 67 to be converted into a P-polarized light component. The light 78 reflected by the total reflection film 68 propagates through the microprism 66 and is incident on the polarizing film 65. However, since the light 78 is converted into the P-polarized light component as described above, the P-polarized light component is transmitted through the polarizing film 65 and is incident on the photodiode 64. Therefore, an optomagnetic signal is obtained by differential detection expressed by: RF = (A + B + C) - (D + E + F) In addition, when the optomagnetic recording pickup 77 and the optomagnetic disk 79 are set in an in-focus state, as shown in Fig. 4A, the light 78 is focused on the total reflection film 68. For this reason, a focus error signal can be obtained by differential detection expressed by: FE = (A + C + E) - (B + D + F) Therefore, the rotation of the polarization plane of light reflected by the optomagnetic recording medium can be detected by a differential output from the first and second light-receiving elements, and an optomagnetic recording pickup can be formed. In addition, since assembling at the same level as that of a semiconductor chip can be performed, a compact, thin optomagnetic recording pickup can be formed.

Claims: An optical apparatus for reading data from an optomagnetic recording medium (79), said apparatus, comprising a substrate (62); first and second photodetectors (63,64) formed on said substrate (62); a light source (75) for emitting light to be directed toward said recording medium, characterized by a polarizing film (65) formed on said photodetectors for transmitting to said photodetectors light which is linearly polarized along a first polarization direction and for reflecting light which is linearly polarized along a second polarization direction perpendicular to said first polarization direction; a λ/4 plate (67) confronting said polarizing film for receiving light reflected therefrom; a total reflection film (68) formed on the side of said λ/4 plate which is opposite to said polarizing film, for reflecting back to said λ/4 plate light which has been reflected by said polarizing film and is passed through said λ/4 plate; the arrangement being such that said light reflected back from said recording medium is split by said polarizing film (65) into a first component, which is transmitted to said first photodetector (63), and a second component, which is reflected toward said λ/4 plate (67) and is received by said second photodetector (64) after having being reflected by said reflection film (68). The apparatus according to claim 1, further characterized by a prism (66) arranged on said polarizing film (65), said λ/4 plate being arranged on a surface of said prism opposite to the surface on which said polarizing film is formed. The apparatus according to claim 2, further comprising a semitransparent film (71) formed on an inclined surface of said prism, for reflecting light (78) emitted by said light source to said recording medium and for transmitting light reflected back from said recording medium toward said first photodetector.

Inventors: KOJIMA CHIAKI, TANIGUCHI TADASHI, KOJIMA, CHIAKI, TANIGUCHI, TADASHI
Applicants: SONY CORP, SONY CORPORATION
Application year: 1992
Main classification: G11B7
IPC codes: G11B7, G11B11