US 8,014,257 B2 · Extraction optical system and optical head device including the same

Abstract

An object of the present invention is to provide an extraction optical system capable of separating and extracting a signal light and a stray light with a simple configuration, and an optical head device including the same. A phase plate and a phase plate are +λ/4 phase plates, while a phase plate and a phase plate are −λ/4 phase plates. A focal line, a focal line and a focal line represent a focal line of a stray light, a focal line of a reproduction light and a focal line of a stray light, respectively. All beams of the reproduction light enter the state in which a polarization direction is rotated by 90 degrees after passing through the phase element. In contrast to the all light bundles of the reproduction light, polarization directions of all light bundles of the stray lights and are not rotated even after passing through the phase element.

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Drawings

Claims10

Dependent claims

An extraction optical system extracting, from a light bundle in which a signal light component and stray light components are mixed, said signal light component,

said light bundle being supplied through a light focus optical device focusing said light bundle and astigmatism adding means adding astigmatism to said light bundle,
the extraction optical system comprising:
a first phase element including:
a first phase change area generating a phase difference of (+¼) times of a wavelength to polarization components of said light bundle which are in an orthogonal relationship;
and
a second phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
a second phase element including:
a third phase change area generating a phase difference of (+¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
and
a fourth phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
and
a separation element allowing only said signal light component among said signal light component and said stray light components which have passed through said first phase element to pass therethrough, or absorbing or reflecting only said stray light component thereamong in accordance with polarization directions thereof, wherein:
said first phase element is divided into said first phase change area and said second phase change area by a first boundary, the first boundary being parallel to a first focal line in which said signal light component forms an image into a line shape on a side closer to said light focus optical device than a first focal point position on an optical axis of said light focus optical device at which said signal light component focused by said light focus optical device is formed into a smallest circle of confusion by said astigmatism adding unit, and being orthogonal to the optical axis of said light focus optical device;
said second phase element is divided into said third phase change area and said fourth phase change area by a second boundary parallel to said first boundary;
said first phase change area and said third phase change area are disposed to be symmetrical with respect to said first focal line;
said second phase change area and said fourth phase change area are disposed to be symmetrical with respect to said first focal line;
said first phase element is disposed between said first focal point position and said first focal line;
and
said second phase element is disposed between said first focal line and a second focal line in which said stray light components form an image into a line shape on a side closer to said light focus optical device than a second focal point position at which said stray light components form a smallest circle of confusion on the side closer to said light focus optical device than said first focal point position.

16 more elements

An optical head device, comprising:

an extraction optical system extracting, from a light bundle in which a signal light component and stray light components are mixed, said signal light component;
a light source emitting said light bundle to an optical disk including a plurality of recording layers;
and
an objective lens focusing said light bundle emitted from said light source on the recording layer to be accessed among said plurality of recording layers,
wherein:
said extraction optical system is supplied with said light bundle through a light focus optical device focusing said light bundle and an astigmatism adding unit adding astigmatism to said light bundle;
said extraction optical system includes:
a first phase element including:
a first phase change area generating a phase difference of (+¼) times of a wavelength to polarization components of said light bundle which are in an orthogonal relationship;
and
a second phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
a second phase element including:
a third phase change area generating a phase difference of (+¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
and
a fourth phase change area generating a phase difference of (−¼) times of a wavelength to the polarization components of said light bundle which are in an orthogonal relationship;
and
a separation element allowing only said signal light component among said signal light component and said stray light components which have passed through said first phase element to pass therethrough, or absorbing or reflecting only said stray light component among said signal light component and said stray light components in accordance with polarization directions thereof;
and
a light receiving device disposed at a first focal point position on an optical axis of said light focus optical device at which said signal light component focused by said light focus optical device is formed into a smallest circle of confusion by said astigmatism adding unit and converting one of said signal light component and said stray light components which have passed through said separation element into an electrical signal;
said first phase element is divided into said first phase change area and said second phase change area by a first boundary, the first boundary being parallel to a first focal line in which said signal light component forms an image into a line shape on a side closer to said light focus optical device than said first focal point position, and being orthogonal to the optical axis of said light focus optical device;
said second phase element is divided into said third phase change area and said fourth phase change area by a second boundary parallel to said first boundary;
said first phase change area and said third phase change area are disposed to be symmetrical with respect to said first focal line;
said second phase change area and said fourth phase change area are disposed to be symmetrical with respect to said first focal line;
said first phase element is disposed between said first focal point position and said first focal line;
said second phase element is disposed between said first focal line and a second focal line in which said stray light components form an image into a line shape on a side closer to said light focus optical device than a second focal point position at which said stray light components form a smallest circle of confusion on the side closer to said light focus optical device than said first focal point position;
and
said extraction optical system is disposed, together with said light focus optical device and said astigmatism adding means, in an optical path of return lights reflected by said optical disk through said objective lens, and extracts said signal light component from said return lights with said return light reflected by said recording layer to be accessed among said plurality of recording layers being said signal light component and said return lights reflected by recording layers other than said recording layer to be accessed among said plurality of recording layers being said stray light components.

24 more elements

Dependencies are inferred from the claim text.

Description8,219 words

Summary1,943 words

#The present invention relates to an extraction optical system which separates and extracts a return light from a specific object and a return light from other object, which becomes a stray light, among return lights from a plurality of objects, and to an optical head device which separates and extracts a signal light component from a light beam which is reflected from a multilayer recording medium and includes both a signal light component and a stray light component.

#Conventionally, capacities of various types of optical disks have been increased by reducing a volume of information written on tracks of the disk and also reducing a size of a focusing spot on a focal plane through reduction of a wavelength of a laser light used in recording and reproducing and employment of an objective lens having a large numerical aperture.

#For example, in a compact disc (CD), a thickness of a disk substrate serving as a light transmission layer (transparent protective layer and space layer provided on an information recording layer, which is also referred to as a transparent substrate) is approximately 1.2 mm, a laser light wavelength is approximately 780 nm, a numerical aperture (NA) of an objective lens is 0.45, and a capacity is 650 MB. Further, in a digital versatile disc (DVD), a thickness of a disk substrate serving as a light transmission layer is approximately 0.6 mm, a laser light wavelength is approximately 650 nm, an NA is 0.6, and a capacity is 4.7 GB. For example, a DVD is used as a disk having a thickness of 1.2 mm by bonding two disk substrates having a thickness of approximately 0.6 mm to each other.

Brief description of the drawings10 figures

#FIG. 1 is a schematic configuration diagram of an optical head device using an extraction optical system according to a first embodiment of the present invention.

#FIG. 2 is a diagram showing an example of a light receiving surface pattern of a light receiving device.

#FIG. 3 are diagrams briefly showing a state of a stray light from a layer other than a reproducing layer of a multilayer disk in the light receiving device.

Detailed description6,056 words

#FIG. 1 is a schematic configuration diagram of an optical head device including an extraction optical system according to a first embodiment of the present invention.

#In FIG. 1, a light beam 2 radiated from a semiconductor laser 1 which is a light source is converted into a parallel light bundle by a collimator lens 3. A beam splitter 4 includes a reflective film 5, and in this case, deflects the light beam 2 by 90 degrees in a −z direction. An objective lens 6 focuses the light beam 2 deflected by the beam splitter 4 on an information recording surface of an optical disk 7. A return light 8 obtained by the light beam 2 being reflected by the optical disk 7 passes through the objective lens 6 and the beam splitter 4 again. A light focus lens 9 is a lens for focusing the return light 8 on a light receiving device 11, and a cylindrical lens 10 is a lens as means of adding astigmatism to the return light 8. Note that the means of adding astigmatism is not limited to a cylindrical lens, and may be, for example, a hologram element having a curved diffraction pattern or the like.

#An extraction optical system 30 indicated by a dotted line frame is composed of a phase plate 20a, a phase plate 20b, a phase plate 21a, a phase plate 21b and an analyzer 22. The return light 8 which has passed through the cylindrical lens 10 passes through the extraction optical system 30 to be received by the light receiving device 11.

Facts

Application

12/738,549Filed 22 Aug 2008

Priority

JP 2007-27092318 Oct 2007

Published

US 2010/0214903 A126 Aug 2010

Granted

6 Sep 2011

Term ends

22 Aug 2028

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification8 codes

G11B 7/1369
Separate or integrated refractive elements, e.g. wave plates: active plates, e.g. liquid crystal panels or electrostrictive elements
G11B 7/131
Optical detectors therefor: arrangement of detectors in a multiple array
G11B 7/1365
Means for guiding the beam from the source to the record carrier or from the record carrier to the detector: separate or integrated refractive…
G11B 7/1381
Means for guiding the beam from the source to the record carrier or from the record carrier to the detector: non-lens elements for altering the…

Timeline

18 Oct 2007Priority claimedJP 2007-270923
22 Aug 2008Application filedUS 12/738,549
19 Apr 2010Assigned to Mitsubishi Electric Corporationassignment of assignor's interest
26 Aug 2010PublishedUS 2010/0214903 A1
6 Sep 2011GrantedUS 8,014,257 B2
12 Oct 2026TodayWithin its term
22 Aug 2028Term endsEstimated

Extraction optical system and optical head device including the same

Life of this patent

Extraction optical system and optical head device including the same

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims10

Description8,219 words

Drawings

Classification8 codes

Life of this patent

Description8,219 words