Polarizer, including thin polarizing film, optical element with polarizer, optical head with polarizer and methods and apparatus for forming same

• US 5,825,022 A
• Filed: 04/30/1996
• Issued: 10/20/1998
• Est. Priority Date: 07/14/1992
• Status: Expired due to Fees

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Takeda, Takashi, Yonekubo, Masatoshi, Arimura, Toshio, Takekoshi, Taro
• Primary Examiner(s): Le, Que
• Assistant Examiner(s): Lee, John R.
• Application Number:
  US08/637,033
• Time in Patent Office: 903 Days
• Field of Search: 250/201.5, 250/201.4, 250/201.2, 250/201.1, 250/216, 250/225, 369/44.14, 369/44.37, 359/720, 359/625, 359/626, 359/629, 359/637, 359/639, 359/640, 359/485, 359/487, 359/488, 359/489, 359/490, 359/494, 359/495, 359/496, 359/497, 359/500, 359/583, 359/586, 359/587
• US Class Current: 250/225
• CPC Class Codes: G02B 5/3025 Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state G02B5/3008, G02B5/3016 take precedence
• CPC Class Codes: G11B 11/10532 Heads
• CPC Class Codes: G11B 11/10536 using thermic beams, e.g. lasers
• CPC Class Codes: G11B 11/10543 using optical beam of radiation
• CPC Class Codes: G11B 2007/13727 Compound lenses, i.e. two or more lenses co-operating to perform a function, e.g. compound objective lens including a solid immersion lens, positive and negative lenses either bonded together or with adjustable spacing
• CPC Class Codes: G11B 7/094 Methods and circuits for servo offset compensation
• CPC Class Codes: G11B 7/131 Arrangement of detectors in a multiple array
• CPC Class Codes: G11B 7/1353 Diffractive elements, e.g. holograms or gratings diffraction gratings per se G02B5/18; holograms per se G02B5/32; grating systems G02B27/44
• CPC Class Codes: G11B 7/1356 Double or multiple prisms, i.e. having two or more prisms in cooperation
• CPC Class Codes: G11B 7/1365 Separate or integrated refractive elements, e.g. wave plates
• CPC Class Codes: G11B 7/1381 Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops G11B7/1353 - G11B7/1369 take precedence

Abstract

A plurality of inclined planes (1419) are formed in the same substrate (1406) and a polarizing optical thin film is provided on these inclined planes. These inclined planes are filled with a transparent material so as to form a small sized and complexed polarizer. This polarizer is excellent in transmission ratio and in extinction ratio. With this polarizer, it is possible to detect a magneto-optical signal with a high signal-to-noise ratio. This polarizer is used as a cover of a package (1408) of an optical head in which a light receiving device (1410, 1411) and a light emitting device (1409) are contained in the form of a single piece. There is also provided an optical element capable of adjusting optical paths so that the optical length of a returning optical beam may be different from the optical length of a forward optical beam. With this optical element, it becomes possible to delete the initial offset in a focusing error signal, and thus adjustment process becomes unnecessary. With these arrangements, it is possible to achieve the size reduction, simplification, and improvement of performance associated with an optical head for use in a magneto-optical recording/reproducing device.

Claims

1. An optical element consisting of a member having a single piece through which converging or diverging forward and returning light beams pass that is configured such that the optical length of said forward light beam is different from that of said returning light beam, said one-piece member including a transparent substrate having at least one inclined plane in a portion of said substrate and a thin polarizing film disposed on said at least one inclined plane;

said forward optical beam and said returning optical beam pass through said member formed in a single piece; and

a refracting power associated with a region through which a forward optical beam passes is different from a refracting power associated with a region through which the returning optical beam passes.

2. An optical element according to claim 1, wherein a convex or concave curved surface is formed locally on the surface thereof.

3. An optical head for use in an optical recording device for recording/reproducing information on/from an magneto-optical recording medium, wherein:

a light source and a light receiving device are contained in one package;

both of light from said light source and returning light from said magneto-optic recording medium pass through the same optical member;

a plurality of inclined planes are formed in said optical member at three or more locations;

said plurality of inclined planes are provided with a polarizing optical thin film;

a first inclined plane is disposed in the optical path from said light source such that the polarization direction of an incident light beam may be P-polarization with respect to the inclined plane;

the returning light from said magneto-optical recording medium is incident on a second and third inclined planes;

said second inclined plane is arranged such that the plane containing the optical axis of the incident light and the normal line to said second inclined plane makes an angle of A°

with respect to the polarization direction of the light beam from said light source; and

said third inclined plane is arranged such that the plane containing the optical axis of the incident light and the normal line to said third inclined plane makes an angle of -A°

with respect to the polarization direction of the light beam from said light source.

4. An optical head according to claim 3, wherein the incident angles of light associated with said second inclined plane and said third inclined plane are equal to or larger than 20°

and said angle A is about 45°

.

5. An optical element consisting of a member having a single piece through which converging or diverging forward and returning light beams pass that is configured such that the optical length of said forward light beam is different from that of said returning light beam, said one-piece member including a transparent substrate having at least one inclined plane in a portion of said substrate and a thin polarizing film disposed on said at least one inclined plane;

at least two different values of refractive indices are partially provided; and

said forward light beam and said returning light beam pass through different areas with different refractive indices.

6. An optical element according to claim 5, wherein said optical element is molded with a transparent resin or glass into a single piece, and a step is provided on the surface thereof.

7. An optical element according to claim 5, wherein said optical element comprises at least two discrete parts that are bonded to each other, and in a situation in which said discrete parts are bonded to each other, a step is formed on the surface thereof.

8. An optical head comprising:

an optical element comprised of a one-piece member through which converging or diverging forward and returning light beams pass that is configured such that the optical length of the forward light beam is different from that of the returning light beam, said one-piece member including a transparent substrate having at least one inclined plane in a portion of said substrate and a thin polarizing film disposed on said at least one inclined plane;

a light receiving device disposed behind said optical element such that said light receiving device is approximately opposed to said optical element, said light receiving device receiving the returning light beam reflected from an optical recording medium;

a semiconductor laser light source that generates the forward light beam and is disposed at a position slightly higher or slightly lower than a position of the light receiving surface of said light receiving device; and

a housing holding said light receiving device and said light source;

wherein said light receiving device and said light source are sealed between said optical element and said housing.

9. An optical head according to claim 8, further comprising means for generating a focusing error signal by detecting a change in a shape of a spot of said returning light beam formed on said light receiving device.

10. An optical head according to claim 8, wherein:

said optical element is made of a transparent resin;

said optical element has a flange at its periphery; and

said flange has a gate for use in injection molding.

11. An optical head according to claim 8, wherein:

said optical element is made of a transparent resin; and

an alignment mark for positioning is formed or printed on the primary surface or the back surface of said optical element and on the surface of said light receiving device.

12. An optical head according to claim 8, wherein a diffraction grating or a hologram is formed on the primary surface or the back surface of said optical element.

13. An optical head according to claim 12, wherein said hologram is a blazed hologram which is blazed into the form of triangular teeth with a pitch of diffraction grooves.

14. An optical head according to claim 8, wherein:

said optical element and said housing are fixed to each other via an adhesive; and

the hardness of said adhesive as cured is lower than the hardness of the materials of said optical element and said housing.

17. An optical head according to claim 11 wherein said light beam splitter is a hologram consisting of a diffraction grating.

18. An optical head according to claim 17, wherein said hologram is a blazed hologram on which blazing processing is performed.

22. An optical head according to claim 8, further comprising an optical element, said optical element being divided into a region coated with an antireflection film and a non-coating region coated with no antireflection film, wherein:

the central portion of a divergence light beam emitted by a light emitting device passes through said region coated with an antireflection film;

a portion of said divergence light beam is reflected from said non-coating region; and

there is provided a second light receiving device for receiving said reflected light so as to detect the emitted light power.

23. An optical head according to claim 22, wherein:

a first light receiving device receives a returning light beam reflected from an optical recording medium; and

said first and second light receiving devices are formed on a substrate in the form of a single piece.

15. An optical head for use in an optical recording device for recording/reproducing information on/from a magneto-optical recording medium, comprising:

a semiconductor laser light source;

a light receiving device;

a polarizer;

a transparent substrate formed on said polarizer having at least one inclined plane and a polarizing optical thin film formed on said at least one inclined plane; and

a light beam splitter that splits light into at least two directions, wherein said polarizer is disposed between said light beam splitter and said light receiving device, said light beam splitter is bonded to one surface of said polarizer via a transparent material, and a package containing said light receiving device and said semiconductor laser light source is bonded to the other surface of said polarizer.

16. An optical head according to claim 15, wherein:

a light beam which has passed through said at least one inclined plane reaches said light receiving device, which includes a pair of sensors, and the resultant outputs of the sensors are added together by an adder, circuit, wherein the plane containing the optical axis of the light beam and the normal line to said at least one inclined plane makes an angle of -A°

with respect to the plane containing the optical axis of the light beam and its polarization direction;

a light beam which has passed through another inclined plane is sensed by another pair of sensors of said light sensing device and the resultant outputs of the sensors are added together by another adder circuit, wherein the plane containing the optical axis of the light beam and the normal line to said inclined plane makes an angle of A°

with respect to the plane containing the optical axis of the light beam and its polarization direction; and

the difference between said addition outputs is detected by a differential amplifier to reproduce a magneto-optical signal.

19. An optical head according to claim 15, wherein said polarizer is bonded to said light beam splitter with a transparent material.

20. An optical head according to claim 15, wherein said polarizer is formed on one surface of one optical member and said light beam splitter is formed on the other surface.

21. An optical head according to claim 15, further comprising an optical element, said optical element being divided into a mirror-finished region and an irregular reflection region with small irregularities, wherein a forward light beam and returning light beam pass through said mirror-finished region.