Multi-level and gray-level diffraction gratings
AssigneeMatsushita Electric Industrial Co., Ltd.
InventorYosuke Mizuyama
Life of this patent
Estimating the term…
Abstract
Multi-level and gray-level diffraction gratings are provided for use in beam splitters and optical pickups. The multi-level and gray-level diffraction gratings are designed for utilization with diffracted light having higher orders than ±1st order of diffracted light. By utilizing such higher orders of diffracted light, the multi-level and gray-level diffraction gratings can be designed to have a plurality of grooves with particular periods and grating depths which can be increased effectively so as to meet minimum manufacturing thresholds and provide high diffraction efficiencies without changing predetermined conditions of the gratings such as a diffraction angle or incident light angle.
Claims37
A diffraction grating for use in an optical pick-up device, said diffraction grating comprising:
- at least two partitions each including a plurality of grooves forming a periodic predetermined shape;
- wherein said plurality of grooves contained in at least one of said at least two partitions have a period to provide a predetermined angle of at least one of +m and −m orders of diffracted light θdif for a predetermined angle of incident light θin (m is an integer greater than 1, and θin and θdif are measured from a grating normal) as follows:
- period=m×p;
- wherein:
- p=±λA /(sin θin−sin θdif);
- ± corresponds to the sign of the at least one of +m and −m orders of diffracted light;
- and
- λ=wavelength of the incident light.
A diffraction grating for use in an optical pick-up device, said diffraction grating comprising:
- at least two partitions each including a plurality of grooves forming a periodic predetermined shape;
- wherein said plurality of grooves contained in a first one of said at least two partitions are designed for use with one of +1st and −1st orders of diffracted light having a first predetermined angle of diffraction for a first predetermined angle of incident light;
- and
- wherein said plurality of grooves contained in a second one of said at least two partitions are designed for use with one of +m and −m orders of diffracted light having a second predetermined angle of diffraction for a second predetermined angle of incident light, wherein m is an integer greater than 1.
A beam splitter for splitting a beam of light reflected from an optical recording medium, said beam splitter being disposed along a travel path of light between a light emitting element and the optical recording medium, said beam splitter comprising:
- a polarization beam splitter surface operable to direct light emitted from the light emitting element towards the optical recording medium and to direct light reflected from the optical recording medium towards a diffraction grating;
- and
- said diffraction grating being disposed to receive the light directed by said polarization beam splitter, said diffraction grating comprising at least two partitions each including a plurality of grooves forming a periodic predetermined shape;
- wherein said plurality of grooves contained in at least one of said at least two partitions have a period to provide a predetermined angle of at least one of +m and −m orders of diffracted light θdif for a predetermined angle of incident light θin (m is an integer greater than 1, and θin and θdif are measured from a grating normal) as follows:
- period=m×p;
- wherein:
- p=±λ/(sin θin−sin θdif);
- ± corresponds to the sign of the at least one of +m and −m orders of diffracted light;
- and
- λ=wavelength of the incident light.
An optical pick-up comprising:
- a light emitting element operable to emit light along a travel path to the optical recording medium;
- a diffraction grating operable to receive light which has been reflected from the optical recording medium, said diffraction grating comprising at least two partitions each including a plurality of grooves forming a periodic predetermined shape;
- wherein said plurality of grooves contained in at least one of said at least two partitions have a period to provide a predetermined angle of at least one of +m and −m orders of diffracted light θdif for a predetermined angle of incident light θin (m is an integer greater than 1, and θin and θdif are measured from a grating normal) as follows:
- period=m×p;
- wherein:
- p=±λ/(sin θin−sin θdif);
- ± corresponds to the sign of the at least one of +m and −m orders of diffracted light;
- and
- λ=wavelength of the incident light;
- and
- a photo-detector operable to receive light diffracted from said diffraction grating and convert the received light into a digital signal.
A method for designing a diffraction grating for use in an optical pick-up device, said method comprising:
- providing at least two partitions on the diffraction grating;
- providing a plurality of grooves forming a periodic predetermined shape on each of the at least two partitions;
- and
- setting a period of the plurality of grooves contained in at least one of the at least two partitions to provide a predetermined angle of at least one of +m and −m orders of diffracted light θdif for a predetermined angle of incident light θin (m is an integer greater than 1, and θin and θdif are measured from a grating normal) as follows:
- period=m×p;
- wherein:
- p=±λ/(sin θin−sin θdif);
- ± corresponds to the sign of the at least one of +m and −m orders of diffracted light;
- and
- λ=wavelength of the incident light.
A method for designing a diffraction grating for use in an optical pick-up device, the diffraction grating including a plurality of partitions each having a plurality of grooves which form a periodic predetermined shape and which have a wavelength of incident light λ, a predetermined angle of incident light θin, a predetermined angle of diffracted light θdif, a predetermined period=p0, and a predetermined depth=d0, said method comprising:
- selecting one of the plurality of partitions;
- setting an m order of diffracted light to be one of +1 (positive order) and −1 (negative order);
- calculating a period p of the plurality of grooves using the following equation:
- p=mλ/(sin θdif−sin θin)
- determining if p is greater than p0 and:
- if p is not greater than p0, then setting m to be one of m+1 (positive order) and m−1 (negative order) and repeating said calculating and determining;
- and
- if p is greater than p0, then obtaining a grating depth d yielding a maximum diffraction efficiency;
- deciding if the obtained grating depth is greater than d0 and:
- if the obtained grating depth is not greater than d0, then setting m to be one of m+1 (positive order) and m−1 (negative order) and repeating said calculating, determining, and deciding;
- and
- if the obtained grating depth is greater than d0, then the obtained grating depth d, period p, and m order are selected as design parameters for the selected partition;
- repeating said selecting, setting, calculating, determining, and deciding for the remaining ones of the plurality of partitions.
A method for designing a diffraction grating for use in an optical pick-up device, said method comprising:
- providing at least two partitions on the diffraction grating;
- forming a plurality of grooves having a periodic predetermined shape on each of the at least two partitions;
- selecting a period of the plurality of grooves contained in a first one of the least two partitions to use one of +1st and −1st orders of diffracted light having a first predetermined angle of diffraction for a first predetermined angle of incident light;
- and
- selecting a period of the plurality of grooves contained in a second one of the at least two partitions to use one of +m and −m orders of diffracted light having a second predetermined angle of diffraction for a second predetermined angle of incident light, wherein m is an integer greater than 1.
An optical pick-up comprising:
- a light emitting element operable to emit light to an optical medium;
- a diffraction grating including a first portion and a second portion operable to diffract light reflected from the optical medium into first diffracted light and second diffracted light, respectively;
- a first photo-detecting section operable to detect the first diffracted light which is diffracted from said first portion of said diffraction grating;
- and
- a second photo-detecting section operable to detect the second diffracted light which is diffracted from said second portion of said diffraction grating;
- wherein an order of the first diffracted light is greater than an order of the second diffracted light.
An optical disc apparatus comprising:
- a light emitting element operable to emit light to an optical disc;
- a diffraction grating including a first portion and a second portion operable to diffract light reflected from the optical disc into first diffracted light and second diffracted light, respectively;
- a first photo-detecting section operable to detect the first diffracted light which is diffracted from said first portion of said diffraction grating;
- and
- a second photo-detecting section operable to detect the second diffracted light which is diffracted from said second portion of said diffraction grating;
- wherein an order of the first diffracted light is greater than an order of the second diffracted light, and the first diffracted light and the second diffracted light are used for a focusing signal and a tracking signal, respectively.
Dependencies are inferred from the claim text.