JP4501583B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device for recording information on or reproducing information from an optical recording medium (hereinafter referred to as an optical disk) having a different thickness or recording density of a disk such as a CD or a DVD.

  2. Description of the Related Art Conventionally, there has been known an optical pickup device capable of recording information or reproducing information (hereinafter, simply referred to as information recording / reproduction) on different types of optical disks such as CD and DVD. Here, it is known that a laser light source having a wavelength near 780 nm is necessary for recording / reproducing information on a CD, and a laser light source having a wavelength near 650 nm is necessary for recording / reproducing information on a DVD. .

  Thus, in order to be able to perform recording / reproduction with respect to optical disks having different wavelengths used for recording / reproducing information in a single unit, so-called two lasers conventionally equipped with two lasers having different oscillation wavelengths. An optical pickup device of the type was put into practical use. In this method, individually manufactured lasers are mounted on one pickup. In recent years, so-called twin lasers, in which a plurality of laser diodes having different oscillation wavelengths are integrated on a single substrate, have been developed and put into practical use in order to reduce the size and price of optical pickup devices.

  In the above-described two-laser optical pickup device or twin-laser-equipped optical pickup device, since optical systems such as a collimator lens and an objective lens are used in common at two different wavelengths, light sources arranged at different positions are used. It is necessary to multiplex so that the optical axes of the two emitted light beams coincide with the optical axis of the optical system of the optical pickup device.

  In the two-laser optical pickup device, an optical prism is used for multiplexing as described above, and light is emitted from light sources arranged at different positions by utilizing the difference in the angle of refraction due to the wavelength dispersion of the optical prism. The optical axes of the two light beams were matched (for example, see Patent Document 1).

In addition, in an optical pickup device equipped with a twin laser, a diffraction element is used to multiplex as described above, a light beam having one wavelength is transmitted (the diffraction order is 0th order), and a light beam having the other wavelength is 1 The optical axes of the two light beams emitted from the light sources arranged at different positions are made to coincide with each other by utilizing the difference in diffraction angle caused by the next diffraction (hereinafter, the diffraction order is the first order) (for example, Patent Document 2). Hereinafter, a light beam that is emitted after being diffracted by the zeroth order by the diffraction element is referred to as zero-order light, and a light beam that is emitted by performing the first-order diffraction by the diffraction element is referred to as primary light.
JP 2001-118279 A JP 2002-163837 A

  Here, it is known that the wavelength of the emitted light from the laser constituting the optical pickup device varies depending on the ambient temperature. Therefore, as disclosed in Patent Document 2, when a diffraction element is used for multiplexing, 0th-order light is not affected by wavelength variation depending on the environmental temperature by being transmitted through the diffraction element. Since the diffraction angle of the next-order diffracted light changes substantially in proportion to the wavelength, the diffraction angle changes depending on the environmental temperature. As a result, the optical axis of the 0th-order light and the optical axis of the 1st-order diffracted light do not coincide with each other, and the 1st-order diffracted light is condensed with the spot position shifted at the position of the light receiving element according to the temperature variation.

  In addition, it is known that focus servo or tracking servo is normally performed based on a sum signal or a difference signal of signals proportional to the amount of light for each region of a light receiving element divided into a plurality of regions. Therefore, in such a conventional optical pickup device, when the position of the focused spot reaching the light receiving element is shifted due to a factor other than the focus error or tracking error, the focus servo or tracking servo cannot be accurately performed. There was a problem.

  The present invention has been made to solve such a problem, and even if it is configured to multiplex using a diffractive element, the fluctuation of the environmental temperature with respect to the positional deviation of the spot of the light beam condensed on the light receiving element. It is an object of the present invention to provide an optical pickup device capable of suppressing the influence of the above.

  In view of the above, the invention according to claim 1 is a first light source that emits a light beam having a first wavelength, and a second light source that emits a light beam having a second wavelength different from the first wavelength. A light source, a forward optical system for guiding the light flux of the first wavelength and the light flux of the second wavelength toward the optical recording medium, and a first light receiving the return light of the first wavelength from the optical recording medium. One light receiving element, a second light receiving element for receiving the return light of the second wavelength from the optical recording medium, and the first light reception of the return light of the first wavelength from the optical recording medium. And a return optical system that guides the return light of the second wavelength from the optical recording medium to the second light receiving element. A first beam that diffracts at least one of a light beam having a first wavelength and a light beam having a second wavelength; The return optical system includes a second diffractive element that diffracts at least one light flux of the return light of the first wavelength and the return light of the second wavelength, and the first diffraction The element and the second diffractive element have diffraction gratings having the same grating pitch, diffract the light beams having the first wavelength at the same diffraction order, and make the light beams having the second wavelength mutually Diffracted at a diffraction order equal to.

  With this configuration, the first diffractive element and the second diffractive element have diffraction gratings having the same grating pitch, diffract the light beams having the first wavelength at the same diffraction order, and the second diffraction element. The effect of environmental temperature fluctuations on the misalignment of the spot of the light beam collected on the light receiving element is used to diffract the light beam of the wavelength with the same diffraction order. An optical pickup device capable of suppressing the above can be realized.

  The invention according to claim 2 is the invention according to claim 1, wherein the first diffractive element and the second diffractive element both diffract the luminous flux of the first wavelength at the first order diffraction order. Both of the light beams having the second wavelength are diffracted at the first order diffraction order.

  With this configuration, in addition to the effect of the first aspect, since the diffraction orders of the diffraction elements are all in the first order, it is possible to realize an optical pickup device with high light utilization efficiency utilizing diffraction with high diffraction efficiency.

  The invention according to claim 3 is the wavelength according to claim 1, wherein the first diffractive element and the second diffractive element can select a wavelength of light to be diffracted by a first order or higher order of diffraction. It has a configuration with selectivity.

  With this configuration, in addition to the effect of the first or second aspect, each diffraction element has wavelength selectivity that allows the wavelength of light to be diffracted at the first or higher order of diffraction to be selected. A high optical pickup device can be realized.

  According to a fourth aspect of the present invention, in the first or third aspect, the first diffractive element and the second diffractive element both diffract the light beam having the first wavelength at the zeroth order of diffraction. And having both the second wavelength light beams diffracted at the first order of diffraction.

  According to this configuration, in addition to the effect of the first or third aspect, each diffraction element diffracts both the first wavelength light fluxes in the order of the zeroth diffraction and the second wavelength light fluxes both in the first order diffraction. Since the diffraction is performed at the order, an optical pickup device with higher light utilization efficiency can be realized.

  The invention according to claim 5 is the periodic structure according to any one of claims 1 to 4, wherein the first diffractive element and the second diffractive element repeat a sawtooth shape in cross section. The structure has a diffraction grating.

  With this configuration, in addition to the effect of any one of claims 1 to 4, each diffraction element has a diffraction grating with a periodic structure in which the cross-sectional shape repeats a sawtooth shape, so that the diffraction element can be easily manufactured. An optical pickup device can be realized.

  According to a sixth aspect of the present invention, in any one of the first to fourth aspects, the first diffractive element and the second diffractive element have a step-like shape in which the cross-sectional shape is a sawtooth shape. It has the structure which has the diffraction grating of the periodic structure which repeats the shape approximated by.

  With this configuration, in addition to the effect of any one of claims 1 to 4, each diffraction element has a diffraction grating having a periodic structure in which the cross-sectional shape repeats a shape approximating a sawtooth shape with a stepped shape. Therefore, it is possible to realize an optical pickup device that can manufacture the diffraction element more easily.

  In the present invention, the first diffractive element and the second diffractive element have diffractive gratings having a grating pitch equal to each other, diffract the light beams having the first wavelength at mutually equal diffraction orders, The effect of environmental temperature fluctuations on the misalignment of the spot of the light beam collected on the light receiving element is used to diffract the light beam of the wavelength with the same diffraction order. It is possible to provide an optical pickup device capable of suppressing the above.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a diagram showing a conceptual configuration of an optical pickup device according to an embodiment of the present invention. 1, the optical pickup apparatus 100 includes a first light source 1a that emits a light flux with wavelength lambda _a, a second light source 1b that emits a light flux with wavelength lambda _b, each light source 1a, a light beam 1b is emitted The combined first diffraction element 2 and the combined light flux are transmitted, and return light from the information recording surface 7a of the first optical disc 7 and the information recording surface 8a of the second optical disc 8 is reflected to be described later. The optical element 3 that leads to the second diffraction element 9, the collimator lens 4 that converts the incident light beam into substantially parallel light, the diaphragm 5, the objective lens 6, and the return light from each of the information recording surfaces 7 a and 8 a a second diffraction element 9 for demultiplexing, the second light receiving element for receiving a first light receiving element 10a for receiving the light flux of wavelength lambda _a after demultiplexing, the light flux of the wavelength lambda _b after demultiplexing 10b.

Here, above the "return light" is an optical flux of the light beam or the wavelength lambda _b of the wavelength lambda _a, is reflected on the information recording surface 7a or the information recording surface 8a refers to the light beam back in the direction of the optical element 3. Further, in the following, the wavelength lambda _a is referred to as a first wavelength, the wavelength lambda _b of the second wavelength.

  The light beam emitted from the first light source 1 a is diffracted by the first diffraction element 2, passes through the optical element 3, the collimator lens 4, the diaphragm 5, and the objective lens 6 in this order, and the information recording surface 7 a of the first optical disk 7. Condensed to Similarly, the light beam emitted from the second light source 1 b is diffracted by the first diffraction element 2 and transmitted through the optical element 3, the collimator lens 4, the diaphragm 5, and the objective lens 6 in this order, and information on the second optical disk 8. Condensed on the recording surface 8a. Hereinafter, an optical system that guides the light beam from the first light source 1a or the second light source 1b toward the information recording surface 7a of the first optical disc 7 or the information recording surface 8a of the second optical disc 8, respectively. It is called a system.

  The light beams condensed on the information recording surface 7a of the first optical disc 7 or the information recording surface 8a of the second optical disc 8 are reflected by the information recording surfaces 7a and 8a, respectively, and the objective lens 6, the diaphragm 5, and the collimator lens. 4, reflected by the optical element 3, demultiplexed by the second diffraction element 9, and enters the first light receiving element 10 a or the second light receiving element 10 b. Hereinafter, an optical system that guides the return light of the first wavelength from the information recording surface 7a to the first light receiving element 10a and guides the return light of the second wavelength from the information recording surface 8a to the second light receiving element 10b. It is called an optical system.

  Here, the output signal of the first light receiving element 10 a is used to generate a read signal, a focus error signal, and a tracking error signal of information recorded on the optical disk recording surface 7 a of the first optical disk 7. Similarly, the output signal of the second light receiving element 10b is used to generate a read signal, a focus error signal, and a tracking error signal of information recorded on the optical disk recording surface 8a of the second optical disk 8.

  The optical pickup device controls the lens in the optical axis direction based on the focus error signal (focus servo), and controls the lens in a direction substantially perpendicular to the optical axis based on the tracking error signal. 1 is provided, but is omitted from the configuration shown in FIG.

  The first light source 1a is composed of, for example, a semiconductor laser, and emits a divergent light beam having a wavelength near 650 nm and linearly polarized light. Similarly, the second light source 1b is constituted by a semiconductor laser, for example, and emits a divergent light beam having a wavelength near 780 nm and linearly polarized light. Here, the wavelengths near 650 nm and 780 nm mean wavelengths in the range of 630 nm to 670 nm and 760 nm to 800 nm, respectively.

  Although the first light source 1a and the second light source 1b are arranged separately, two semiconductor laser chips are mounted on the same substrate in the same package, so-called hybrid type 2 It may be configured to form a wavelength laser light source. Alternatively, the first light source 1a and the second light source 1b are monolithic two-wavelength laser light sources having two light emitting points that emit different wavelengths (see, for example, JP-A-2004-39898). It may be configured to make.

  The first diffractive element 2 is configured by, for example, a diffraction grating, and diffracts the light beams emitted from the light sources 1a and 1b so that the optical axes of the diffracted light beams substantially coincide with each other at a predetermined temperature. . That is, the first diffractive element 2 is configured to multiplex the light beams emitted from the first light source 1a and the second light source 1b. Here, the same-order diffraction can be used for combining the light beams emitted from the first light source 1a and the second light source 1b. Further, it is also possible to multiplex by diffracting one light beam at the 0th order and diffracting the other light beam at an order other than the 0th order. Hereinafter, the first diffraction element 2 is constituted by a diffraction grating, and the diffraction grating constituting the first diffraction element 2 is simply referred to as “diffraction grating of the first diffraction element 2”.

  The optical element 3 transmits the light beam diffracted and combined by the first diffractive element 2 to the collimator lens 4 side, and information on the information recording surface 7a of the first optical disk 7 or the information on the second optical disk 8. The return light from the recording surface 8a is reflected and guided to the second diffraction element 9 side.

  The collimator lens 4 diffracts by the first diffractive element 2 and converts the combined light beam into substantially parallel light.

The aperture 5 is configured to set the numerical aperture NA by selectively limiting the aperture of the light beam from the first light source 1a or the second light source 1b. As a result, when the numerical aperture for the first optical disc 7 and the numerical aperture for the second optical disc 8 are different during recording and reproduction of the optical disc, the numerical aperture can be adjusted by the diaphragm 5. For the light flux of the first wavelength lambda _a so numerical aperture NA is 0.65, for light flux of the second wavelength lambda _b and as the numerical aperture NA is 0.50. The diaphragm 5 includes a mechanical diaphragm and an optical diaphragm, and is not particularly limited.

The objective lens 6, the wavelength lambda _a, a single lens which is aberration corrected to the extent both available in lambda _b, of each of the collimated light of the first wavelength lambda _a and the second wavelength lambda _b optical disk 7 The light is focused on the information recording surface 7 a and the information recording surface 8 a of the optical disk 8. As the objective lens 6, for example, an objective lens disclosed in JP 2001-344798 A can be used.

Note that the objective lens 6 is not limited to the above-described lens. For example, a lens that corrects an aberration that occurs at one of the two wavelengths λ _a and λ _b and an aberration that occurs at the other wavelength are used. A configuration combining an optical member having a function of correcting aberrations may be used.

The first optical disk 7 is a recording medium for writing or reading information using _a light beam having _a first wavelength λa, and has a protective layer thickness of 0.6 mm, for example. Similarly, the second optical disc 8 has a recording medium for writing or reading information by using a light flux with wavelength lambda _b, for example, a protective layer thickness of 1.2 mm.

  The second diffractive element 9 is composed of, for example, a diffraction grating, diffracts the return light from the information recording surfaces 7a and 8a of the optical discs 7 and 8, and the direction of the optical axis of each diffracted light beam is separated. It is configured as follows. That is, the second diffractive element 9 is configured to demultiplex the return light. The same order diffraction can be used for demultiplexing the return light. Further, it is possible to divide one light beam by diffracting it with the 0th order and diffracting the other light beam with an order other than the 0th order. Hereinafter, the second diffraction element 9 is constituted by a diffraction grating, and the diffraction grating constituting the second diffraction element 9 is simply referred to as “diffraction grating of the second diffraction element 9”.

Here, the grating pitch of the diffraction grating of the second diffractive element 9 and the grating pitch of the diffraction grating of the first diffractive element 2 are made substantially equal, and each wavelength λ _a , λ _{b in} the second diffractive element 9 is made. It is preferable to make the order of diffraction of the return light equal to the order of diffraction in the first diffraction element 2 from the following points. That is, by doing in this way, the oscillation wavelength of the light source changes due to a change in the environmental temperature, and the direction of the light beam diffracted and emitted by the first diffraction element 2 and the second diffraction element 9 (hereinafter simply referred to as the emission direction). Is changed so that the first diffraction element 2 and the second diffraction element 9 are substantially the same amount and cancel each other out. The direction of the optical axis of each light beam emitted from the light beam is not affected by fluctuations in environmental temperature. Hereinafter, the surface of the diffraction element from which the incident light exits is referred to as an “exiting surface”.

  The first light receiving element 10a receives the return light from the information recording surface 7a of the first optical disc 7, and reads a read signal, a focus error signal, and a tracking error signal according to the information recorded on the information recording surface 7a. These signals are generated and output to the outside. Similarly, the second light receiving element 10b receives the return light from the information recording surface 8a of the second optical disk 8, and reads a read signal, a focus error signal, and a focus error signal according to the information recorded on the information recording surface 8a. Each signal of the tracking error signal is generated and output to the outside.

  Here, it is preferable that the distance between the first light receiving element 10 a and the second diffractive element 9 is substantially equal to the distance between the first light source 1 a and the first diffractive element 2. Further, it is preferable that the distance between the second light receiving element 10b and the second diffractive element 9 is substantially equal to the distance between the second light source 1b and the first diffractive element 2.

  The first light receiving element 10a and the second light receiving element 10b are configured as a single light receiving element even if they are separately disposed, and light receiving surfaces that differ depending on the position where each light beam is condensed. May be provided.

  Specific examples based on the above-described embodiments of the present invention will be described below. In the optical pickup device according to the present embodiment, the forward optical system and the backward optical system each have diffraction elements having the same grating pitch, and each diffraction element diffracts a light beam having the first wavelength with the same order. At the same time, the light beam having the second wavelength is diffracted with the same order.

  Examples of configurations in which each diffraction element has a first-order diffraction order for diffracting a light beam with a first wavelength and a first-order diffraction order for diffracting a light beam with a second wavelength [example] 1], each diffraction element has an order of diffraction for diffracting a light beam of the first wavelength is 0th order, and an example of a configuration in which the order of diffraction for diffracting the light beam of the second wavelength is 1st order This will be described as [Example 2].

[Example 1]
As shown in FIG. 1, an optical pickup device 100 according to Example 1 includes a first light source 1a that emits a light beam having a first wavelength of 650 nm, and a second light source 1b that emits a light beam having a second wavelength of 780 nm. The first diffraction element 2 for combining the light beams emitted from the light sources 1a and 1b and the information recording surface 7a of the first optical disk 7 and the information recording of the second optical disk 8 while transmitting the combined light beams. The optical element 3 for reflecting the return light from the surface 8a and guiding it to the second diffraction element 9, the collimator lens 4, the diaphragm 5, the objective lens 6, and the return light from the information recording surfaces 7a and 8a. A second diffraction element 9 for demultiplexing, a first light receiving element 10a for receiving a light beam having a first wavelength of 650 nm after demultiplexing, and a light beam having a second wavelength of 780 nm after demultiplexing. And a second light receiving element 10b.

  In the optical pickup device 100 according to Example 1, each diffraction element 2 and 9 has the first order of diffraction for diffracting a light beam with a first wavelength of 650 nm, and the order of diffraction for diffracting a light beam with a second wavelength of 780 nm. Is configured to be primary. Each diffraction element 2 and 9 is made of a diffraction grating having the same grating pitch. First, multiplexing will be described.

  FIG. 2 is an explanatory diagram of multiplexing performed by the optical pickup device 100 according to the first example. In FIG. 2, the light beams emitted from the first light source 1a and the second light source 1b are incident on the first diffraction element 2 with the line indicated by reference numeral 21 and the line indicated by reference numeral 22 as optical axes, respectively. Hereinafter, the surface of the diffraction element on which the light beam enters is simply referred to as “incident surface”.

Here, each light beam is incident on the first diffractive element 2 from a direction perpendicular to the incident surface of the first diffractive element 2 (direction of a line indicated by reference numeral 23) and angles θ _a and θ _b . Hereinafter, an angle formed by a light beam and a direction perpendicular to the incident surface of the first diffraction element 2 is referred to as an incident angle. Each light beam incident on the first diffraction element 2 is emitted from the first diffraction element 2 in a substantially vertical direction. The direction of the light beam emitted from the first diffractive element 2 is parallel to the optical axis of an optical system composed of the collimator lens 4 and the objective lens 6 (hereinafter referred to as the optical axis of the optical pickup device 100). It has become.

Wavelength 650nm of the first light beam source 1a is emitting a lambda _a, when the first grating pitch of the diffraction grating of the diffraction element 2 and p, the first light source 1a is emitted from the first light source 1a light flux with wavelength lambda _a is disposed at a position at an angle of incidence theta _a represented by the following formula (1) in the first diffraction element 2.
θ _a = λ _a / p (1)
Similarly, the wavelength 780nm of the light beam a second light source 1b is emitting a lambda _b, when the first grating pitch of the diffraction grating of the diffraction element 2 and p, the second light source 1b from the second light source 1b light beam emitted wavelength lambda _b is disposed at a position at an angle of incidence theta _b represented by the following formula in the first diffraction element 2 (1).
θ _b = λ _b / p (2)
By arranging the first light source 1a and the second light source 1b in this way, the emission directions when the light beams emitted from the respective light sources 1a and 1b are diffracted and emitted by the first diffraction element 2 match. Will do.

  Next, demultiplexing will be described. FIG. 3 is an explanatory diagram of the demultiplexing performed by the optical pickup device according to the first example. Hereinafter, the grating pitch of the diffraction grating of the second diffraction element 9 is assumed to be q. Return light from the information recording surface 7a of the optical disc 7 or the information recording surface 8a of the optical disc 8 is incident substantially perpendicularly to the incident surface of the second diffraction element 9 with the line indicated by reference numeral 31 in FIG. Each is diffracted at the following diffraction angles.

That is, the light flux of wavelength lambda _a first light source 1a is emitted is diffracted at diffraction angles represented by the following formula (3), the light flux of the wavelength lambda _b of the second light source 1b is emitted, the following The light is diffracted at the diffraction angle represented by Expression (4), and is emitted from the second diffraction element 9 with the line indicated by reference numeral 32 or the line indicated by reference numeral 33 as the optical axis.
λ _a / q (3)
λ _b / q (4)
Since the light beam emitted from the first light source 1a and the light beam emitted from the second light source 1b have different wavelengths, these light beams are demultiplexed by the second diffraction element 9 as described above. Become. Here, the first light receiving element 10a is arranged such that the light receiving surface is positioned on a line indicated by reference numeral 32. Similarly, the second light receiving element 10b is arranged such that the light receiving surface is positioned on a line indicated by reference numeral 33.

  Hereinafter, the behavior of the optical pickup device according to Example 1 when the oscillation wavelength of the light source varies with a change in the operating temperature will be described. FIG. 4 is a diagram showing the optical axis direction of the light beam incident on the first diffraction element 2 and the optical axis direction of the light beam after diffraction when the oscillation wavelengths of the light sources 1a and 1b are changed. The same components as those shown in FIG.

First, the oscillation wavelength lambda _a of the first light source 1a is changed to the oscillation wavelength λ _{a +} Δλ _a by changes in operating temperature. At this time, the diffraction angle when the light beam emitted from the first light source 1a is diffracted by the first diffraction element 2 is expressed by the following equation (5).
(Λ _a + Δλ _a ) / p (5)
The change in the oscillation wavelength lambda _a of the first light source 1a, a diffraction angle by [Delta] [lambda] _{a /} p changes compared to the absence of wavelength variation. When this amount (Δλ _a / p) is Δθ _a , the light flux after the wavelength change is in a direction (direction of a line indicated by reference numeral 23) perpendicular to the exit surface of the first diffractive element 2 and an angle Δθ _a ( (The direction of the line indicated by reference numeral 41).

Similarly, it is assumed that the oscillation wavelength λ _b of the second light source 1b is changed to the oscillation wavelength λ _b + Δλ _b due to a change in the operating temperature. At this time, the diffraction angle when the light beam emitted from the second light source 1b is diffracted by the first diffraction element 2 is expressed by the following equation (6).
(Λ _b + Δλ _b ) / p (6)
The change in the oscillation wavelength lambda _b of the second light source 1b, the diffraction angle by [Delta] [lambda] _{b /} p is changed compared to the absence of wavelength variation. When this amount (Δλ _b / p) is Δθ _b , the light flux after the wavelength change is formed in a direction (direction of a line indicated by reference numeral 23) perpendicular to the exit surface of the first diffraction element 2 and an angle Δθ _b ( (The direction of the line indicated by reference numeral 42).

Thus, the light beam first outgoing direction from the diffraction element 2 is displaced [Delta] [theta] _a and [Delta] [theta] _b by the wavelength variation of the light source, respectively, the first optical disk 7 of the information recording surface 7a, the information of the second optical disk 8 When reflected by the recording surface 8a, made incident on the second diffraction element 9 forms a vertical direction and angle [Delta] [theta] _a or angle [Delta] [theta] _b to the second diffraction element 9.

  Hereinafter, the operation of the optical pickup device 100 when entering the second diffractive element 9 at an angle with the direction perpendicular to the incident surface of the second diffractive element 9 as described above will be described with reference to FIG. . FIG. 5 is a diagram showing the incident direction of the light beam incident on the second diffractive element 9 and the outgoing direction of the light beam emitted from the second diffractive element 9 when the oscillation wavelengths of the light sources 1a and 1b change. The same components as those shown in FIG. 3 are denoted by the same reference numerals.

First, a light beam having _a wavelength (λ _a + Δλ _a ) forms an angle Δθ _a (= Δλ _a / p) with a direction perpendicular to the incident surface of the second diffractive element 9 (direction of a line indicated by reference numeral 31). The diffraction angle when entering the second diffractive element 9 and diffracting by the second diffractive element 9 is expressed by the following equation (7).
(Λ _a + Δλ _a ) / q (7)
The light beam incident on the second diffractive element 9 is diffracted in a direction with the line indicated by reference numeral 53 as the optical axis. The direction of diffraction at this time is a direction perpendicular to the second diffractive element 9 (reference numeral 31). And the angle represented by the following equation (8).
(Λ _a + Δλ _a ) / q−Δλ _a / p (8)
Similarly, a light beam having a wavelength (λ _b + Δλ _b ) forms an angle Δθ _b (= Δλ _b / p) with a direction perpendicular to the incident surface of the second diffractive element 9 (direction of a line indicated by reference numeral 31). The diffraction angle when entering the second diffractive element 9 and diffracting by the second diffractive element 9 is expressed by the following equation (9).
(Λ _b + Δλ _b ) / q (9)
The light beam incident on the second diffractive element 9 is diffracted in a direction with the line indicated by reference numeral 54 as the optical axis. The direction of diffraction at this time is a direction perpendicular to the second diffractive element 9 (reference numeral 31). And the angle represented by the following expression (10).
(Λ _b + Δλ _b ) / q−Δλ _b / p (10)
Here, if the grating pitch q of the diffraction grating of the second diffractive element 9 is made equal to the grating pitch p of the diffraction grating of the first diffractive element 2, Δλ _a / q and Δλ _a / The direction of the light beam after being diffracted by the second diffraction element 9 indicated by reference numeral 53 is the same as the direction of the light beam indicated by reference numeral 32 in FIG. Similarly, the direction of the light beam after diffraction indicated by reference numeral 54 is the same as the direction of the light beam indicated by reference numeral 33 in FIG.

  This is because the diffraction angle change that occurs when the first diffraction element 2 and the second diffraction element 9 are combined due to the influence of wavelength change by making the grating pitch of the diffraction grating of the second diffraction element 9 equal. This shows that the change in the diffraction angle that occurs when demultiplexing is canceled out, and even if the wavelength changes, the emission direction after being diffracted by the second diffraction element 9 does not change. Therefore, even if the temperature fluctuates, the position on the light receiving element where the light flux is collected does not fluctuate.

  Below, the concrete structure of the 1st diffraction element 2 and the 2nd diffraction element 9 is shown. FIG. 6 is a cross-sectional view conceptually showing a part of a cross section of the first diffraction element 2 according to the present embodiment. Here, the surface denoted by reference numeral 61 is an incident surface on which light beams emitted from the light sources 1a and 1b are incident, and the surface denoted by reference numeral 62 is an emission surface from which each light beam is emitted.

  The light beam emitted from the first light source 1a and the light beam emitted from the second light source 1b are incident on the first diffraction element 2 from the direction indicated by the arrow 63 and the direction indicated by the arrow 64, respectively. Each light beam diffracted by the first diffraction element 2 is emitted in the direction of the arrow indicated by the reference numeral 65. When a wavelength change occurs, the light is emitted in a direction deviating from the direction indicated by the arrow 65, as described above.

  The material of the first diffraction element 2 is quartz glass, and the diffraction grating of the first diffraction element 2 is formed using an etching technique. As shown in FIG. 6, the first diffractive element 2 is configured by a diffraction grating having a cross-sectional shape having a periodic structure in which a stepped shape repeats periodically. In this embodiment, the diffraction grating has a periodic structure in which a staircase composed of 6 steps is one cycle, and the step d of each step (step) is 0.254 μm.

  Further, the width of the portion (hereinafter referred to as a flat portion) substantially parallel to the emission surface of each floor was set to 1.67 μm so that the pitch was 10 μm. Such a diffraction grating is called a binary blazed diffraction grating. As described above, by setting the number of steps (in other words, the total number of flat portions in one cycle) to 6 and setting each step d to 0.254 μm, the wavelength emitted by the first light source The diffraction efficiency of the first-order diffraction of the 650 nm light beam and the 780 nm light beam emitted from the second light source can both be 80%.

  FIG. 7 is a sectional view conceptually showing a part of a section of the second diffraction element 9 according to this embodiment. Here, a surface denoted by reference numeral 71 is an incident surface for each return light, and a surface denoted by reference numeral 72 is an exit surface of the second diffraction element 9.

  The light beam emitted from the first light source 1 a and the light beam emitted from the second light source 1 b are reflected by the information recording surfaces 7 a and 8 a of the optical disks 7 and 8, respectively, and are substantially perpendicular to the second diffraction element 9. From one direction (line direction indicated by reference numeral 73). When a wavelength change occurs, the light enters from a direction deviating from the line indicated by reference numeral 73 as described above.

The light flux with wavelength lambda _a diffracted by the second diffraction element 9 (the light flux from the first light source 1a) is emitted in the direction of the arrow shown by reference numeral 74, of a wavelength lambda _b diffracted by the second diffraction element 9 The light beam (the light beam from the second light source 1b) is emitted in the direction of the arrow indicated by reference numeral 75. The material of the second diffractive element 9 and the structure of the diffraction grating of the second diffractive element 9 are the same as those of the first diffractive element 2.

[Example 2]
As shown in FIG. 8, the optical pickup device 800 according to Example 2 includes the same optical elements as the optical pickup device 100 according to Example 1. However, the optical pickup device 100 according to Example 1 includes some optical members. The relative arrangement of is different. In FIG. 8, the same reference numerals are assigned to the same optical members as those of the optical pickup device 100 according to Example 1.

  In the optical pickup device 800 according to Example 2, each of the diffraction elements 2 and 9 does not diffract the light beam having the first wavelength of 650 nm (the diffraction order is 0th order) and diffracts the light beam having the second wavelength of 780 nm (diffraction). The order of (1) is configured as follows. First, multiplexing will be described.

  FIG. 9 is an explanatory diagram of multiplexing performed by the optical pickup device 800 according to the second example. In FIG. 9, the light beam emitted from the first light source 1 a is incident substantially perpendicular to the incident surface of the first diffractive element 2 (in the direction of the line indicated by reference numeral 91), and is diffracted by the first diffractive element 2. Without being performed (the order of diffraction is 0th order), the light is emitted in a direction substantially perpendicular to the emission surface of the first diffraction element 2 (the direction of the line indicated by reference numeral 91).

Wavelength 780nm of the light beam a second light source 1b is emitting a lambda _a, when the first grating pitch of the diffraction grating of the diffraction element 2 and p, the second light source 1b, the light beam a second light source 1b is emitted the optical axis is disposed at an angle theta _b represented by the following formula as the line indicated by reference numeral 91 (11).
θ _b = λ _b / p (11)
The incident direction of the light beam emitted from the second light source 1 b to the first diffraction element 2 is indicated by a line denoted by reference numeral 92. The first diffractive element 2 causes the first diffractive element 2 to perform first-order diffraction by causing the light beam emitted from the second light source 1 b to enter from this direction, and a direction perpendicular to the first diffractive element 2. It is comprised so that it may radiate | emit along (the direction of the line shown with the code | symbol 91).

  In this way, the first diffractive element 2 causes the light beam emitted from the first light source 1 a to be diffracted by the 0th order, and the light beam emitted from the second light source 1 b is first-order diffracted by the first diffractive element 2. By diffracting, the light beams emitted from the light sources 1a and 1b can be combined.

  Next, demultiplexing will be described. FIG. 10 is an explanatory diagram of demultiplexing performed by the optical pickup device 800 according to the second example. Here, q is the grating pitch of the diffraction grating of the second diffraction element 9.

In FIG. 10, the return light from the information recording surfaces 7 a and 8 a of the optical disks 7 and 8 is incident substantially perpendicular to the incident surface of the second diffractive element 9 (the direction of the line indicated by reference numeral 101). Here, the light flux of the first wavelength lambda _a (light flux emitted from the first light source) is (order diffraction order is 0) without being diffracted by the second diffraction element 9, the second diffraction element 9 The light exits substantially perpendicular to the exit surface.

On the other hand, the light flux of the second wavelength lambda _b (light flux emitted from the second light source), relative to the direction perpendicular to the exit surface of the second diffraction element 9 is expressed by the following equation (12) The light is emitted in a direction forming an emission angle (a direction indicated by a reference numeral 102).
λ _b / q (12)
Here, the first light receiving element 10 a is disposed on a line denoted by reference numeral 101, and the second light receiving element 10 b is disposed on a line denoted by reference numeral 102.

  Hereinafter, the behavior of the optical pickup device according to Example 2 when the oscillation wavelength of the light source varies with the change of the operating temperature will be described. In the optical pickup device according to Example 2, the light beam emitted from the first light source 1a is not diffracted by the first diffractive element 2 and the second diffractive element 9 (the diffraction orders are both 0th order), and thus oscillates. Even if the wavelength fluctuates, the light beam emitted from the first light source 1a reaches the first light receiving element 10a without being affected by the emission direction from the diffraction elements 2 and 9.

  Next, the light beam emitted from the second light source 1b may be considered to be subjected to the same action as described in [Example 1] above. That is, by making the grating pitch of the diffraction grating of the first diffractive element 2 equal to the grating pitch of the diffraction grating of the second diffractive element 9, the change of the diffraction angle in the first diffractive element 2 due to wavelength variation The change in the diffraction angle at the second diffractive element 9 can be canceled out by substantially the same amount, and the optical axis direction of each light beam emitted from the second diffractive element 9 varies with the environmental temperature. Is no longer affected. Therefore, the light beam emitted from the second diffractive element 9 reaches the second light receiving element 10b regardless of the wavelength variation.

Specific configurations of the first diffraction element 2 and the second diffraction element 9 according to the present embodiment are shown below. FIG. 11 is a sectional view conceptually showing a section of the first diffraction element 2 according to the present embodiment. The first diffraction element 2 has a configuration in which a first wave plate 111, a polarization diffraction grating 112, and a second wave plate 113 are stacked and fixed. Here, the light beams having the wavelengths λ _a and λ _b are linearly polarized light. The first diffractive element 2 needs to select whether to perform zero-order diffraction (not diffracting) or first-order diffraction depending on the wavelength.

Therefore, the first diffractive element 2 uses the first wave plate 111 to change the polarization direction of a light beam having a predetermined wavelength (hereinafter, referred to as _a light beam having _a wavelength λa) to a specific polarization direction, and to another wavelength (hereinafter, referred to as a light beam). the light flux with wavelength lambda _b. is orthogonal to the polarization direction of the light beam), a polarizing diffraction grating 112 is diffracted only the light beam of a particular polarization direction, and is configured to undo the polarization direction at the second wavelength plate 113 Yes.

The polarization direction of the light beam (wavelength λ _a ) emitted from the first light source 1a and the polarization direction of the light beam (wavelength λ _b ) emitted from the second light source 1b are the same in the first direction. A light source is disposed so as to be incident on the diffraction element 2. The first wave plate 111, a polycarbonate subjected to uniaxial stretching and fixed to the glass substrate, and functions as a (5/2) wavelength plate to the light flux of the wavelength lambda _a emitted from the first light source 1a, the was created that as a phase difference plate which functions as a half-wave plate for the light flux of the emitted wavelength lambda _b of the second light source 1b.

By first wave plate 111 has the function of the retardation plate, to act as a real (1/2) wavelength plate with respect to light flux of wavelength lambda _a, the polarization direction of incident light having a wavelength lambda _a Is rotated 90 °. On the other hand, with respect to incident light of wavelength lambda _b, is substantially equivalent to the absence of waveplate, there is no rotation of the polarization direction. In this way, by rotating the polarization direction of only a linearly polarized light beam having _a predetermined wavelength (wavelength λ _a ), light emitted from the linearly polarized first light source 1 a that has been polarized in the same direction (wavelength λ _a ). And the polarization direction of the light emitted from the second light source 1b (wavelength λ _b ) are orthogonalized.

  FIG. 12 is a cross-sectional view conceptually showing a part of the cross section of the polarization diffraction grating 112 constituting the first diffraction element 2. The polarization diffraction grating 112 is formed by bonding a birefringent material layer 121 and an isotropic material layer 122, and the birefringent material layer 121 has a cross-sectional shape having a periodic structure in which a stepped shape is periodically repeated. The isotropic material layer 122 is configured to form a diffraction grating and fill the stepped portion.

Here, as a material of the birefringent material layer 121 and the isotropic material layer 122, a birefringent material and an isotropic material satisfying two conditions described below were used. First, the first condition is a first optical system which polarization direction of the light flux of wavelength lambda _a after passing through the wavelength plate 111 is to be perpendicular to the longitudinal direction of the diffraction plaid configuration, transmitted through the wavelength plate 111 When the refractive index of the birefringent material layer 121 with respect to the light beam having the wavelength λ _a after the above is n ₁₁ (λ _a ) and the refractive index of the isotropic material layer 122 is n ₂ (λ _a ), the following formula ( The relationship expressed by 13) is almost satisfied.
n ₁₁ (λ _a ) = n ₂ (λ _a ) (13)
The second condition is the configuration of the optical system in which the polarization direction of the light beam having the wavelength λ _b after passing through the wave plate 111 is parallel to the longitudinal direction of the diffraction grating stripe, and the wavelength λ _b after passing through the wave plate 111 When the refractive index of the birefringent material layer 121 with respect to the light beam is n ₁₂ (λ _b ) and the refractive index of the isotropic material layer 122 is n ₂ (λ _b ), the relationship represented by the following formula (14): Is almost satisfied.
n ₁₂ (λ _b ) ≠ n ₂ (λ _b ) (14)
By configuring the optical system and the polarization diffraction grating 112 so as to satisfy the above conditions, without diffracting the light flux with wavelength lambda _a (diffraction order is zero order), the polarization direction orthogonal to the light flux of wavelength lambda _a it is possible to diffract the light flux with wavelength lambda _b that, have a function of selective diffraction to the first diffraction element 2. Here, a polymer liquid crystal was used as the birefringent material, and an epoxy ultraviolet curable resin was used as the isotropic material.

  Table 1 shows the refractive indexes of the birefringent material and the isotropic material used for the polarization diffraction grating 112.

  The polarization diffraction grating 112 is overlapped and fixed so as to cover a 0.5 mm thick cover glass (glass material BK7) 123 on the side of the isotropic material layer 122, and a 0.5 mm thick cover on the birefringent material layer 121 side. The glass (glass material BK7) 124 is overlapped and fixed so as to cover it. In this example, the grating of one cycle is composed of 8 steps, each step has a height of 0.449 μm, and the width of the flat portion of each stage is 1.25 μm so that the grating pitch is 10 μm. A diffraction grating having a shape was produced.

By configuring the first diffractive element 2 as described above, the transmittance of a light beam having a wavelength of 650 nm that performs zero-order diffraction is 95%, and the diffraction efficiency of the first-order diffraction of a light beam having a wavelength of 780 nm is 83%. be able to. Here, as with the first wave plate 111, the second wave plate 113 also fixes a uniaxially stretched polycarbonate to a glass substrate and emits _a light beam having a wavelength λa emitted from the first light source 1a. relative to (5/2) acts as a wavelength plate to create what was set to be a phase difference plate which functions as a half-wave plate for the light flux of the emitted wavelength lambda _b from the second light source 1b.

By the second wave plate 113 has the function of the retardation plate, to act as a real (1/2) wavelength plate with respect to light flux of wavelength lambda _a, the polarization direction of incident light having a wavelength lambda _a Is rotated 90 °. On the other hand, with respect to incident light of wavelength lambda _b, is substantially equivalent to the absence of waveplate, there is no rotation of the polarization direction. In this way, by rotating the polarization direction only for a linearly polarized light beam having _a predetermined wavelength (wavelength λ _a ), the light emitted from the linearly polarized first light source 1 _a (wavelength λ _a ) and the second light beam are orthogonal to each other. The polarization direction of the outgoing light (wavelength λ _b ) from the light source 1 b can be returned to the polarization direction when entering the first diffraction element 2.

  FIG. 13 is a cross-sectional view conceptually showing a cross section of the second diffraction element 9 according to this embodiment. Similar to the first diffraction element 2, the second diffraction element 9 includes a first wave plate 131, a polarization diffraction grating 132, and a second wave plate 133. The material used for manufacturing the second diffraction element 9 and the structure of the diffraction grating of the second diffraction element 9 are the same as the material used for manufacturing the first diffraction element 2 and the structure of the diffraction grating. did.

  In the above embodiment, the description has been made on the assumption that the CD and the DVD are compatible. However, the BLURAY (registered trademark) disk or the HD-DVD (High Definition DVD) which is about to be put into practical use and the conventional DVD are used. It can be effectively applied to combinations. Similarly, the present invention can be effectively applied to a combination of a BLURAY (registered trademark) disk or an HD-DVD and a CD.

  In this embodiment, the optical system is configured as a so-called infinite optical system using a collimator lens, but the range to which the present invention is applied is not limited to an infinite optical system, It may be a finite optical system that does not use a collimator lens.

  In this embodiment, the diffraction element having a diffraction grating having a periodic structure in which the cross-sectional shape repeats a sawtooth shape is taken up. However, the present invention uses a diffraction element in which a wave plate and a polarization diffraction grating are combined. The configuration is not limited. Specifically, a diffraction element having a diffraction grating having a periodic structure in which a cross-sectional shape repeats a shape approximating a sawtooth shape by a stepped shape is used, but a diffraction element having a diffraction grating having another cross-sectional shape is used. It's okay.

  Furthermore, in the present embodiment, the description has been made by taking up an element that combines a wavelength plate and a polarization diffraction grating as a diffraction element having wavelength selectivity, but the present invention provides a diffraction element that combines a wavelength plate and a polarization diffraction grating. It is not limited to the structure to be used. Specifically, organic pigments and fillers are combined so that the refractive index is equal to one wavelength even in a diffraction grating in which the grating depth is converted to an optical path length and is an integral multiple of one wavelength. A configuration using a diffraction grating or a configuration using other diffraction elements may be used.

  As described above, in the optical pickup device according to the embodiment of the present invention, the first diffractive element and the second diffractive element have diffraction gratings having a grating pitch equal to each other, and have the first wavelength. In order to diffract the light beams with the same diffraction order and diffract the light beams of the second wavelength with the same diffraction order, the light beams are collected on the light receiving element even if they are combined using a diffraction element. It is possible to suppress the influence of the fluctuation of the environmental temperature on the positional deviation of the spot of the luminous flux.

  In addition, since the diffraction orders of the diffraction elements are all first-order, it is possible to realize an optical pickup device with high light utilization efficiency using diffraction with high diffraction efficiency.

  In addition, since each diffraction element has wavelength selectivity capable of selecting the wavelength of light to be diffracted by the first or higher order of diffraction, an optical pickup device with high light utilization efficiency can be realized.

  In addition, since each diffraction element diffracts both the light flux of the first wavelength at the 0th-order diffraction order and diffracts both the light flux of the second wavelength at the 1st-order diffraction order, the use efficiency of light is further improved. A high optical pickup device can be realized.

  In addition, since each diffraction element has a diffraction grating having a periodic structure in which the cross-sectional shape repeats a sawtooth shape, the diffraction element can be easily manufactured.

  Further, since each diffraction element has a diffraction grating having a periodic structure in which a cross-sectional shape repeats a shape obtained by approximating a sawtooth shape with a stepped shape, the diffraction element can be manufactured more easily.

  Even if the optical pickup device according to the present invention is configured to multiplex using a diffractive element, there is an effect that it is possible to suppress the influence of environmental temperature fluctuations on the positional deviation of the spot of the light beam condensed on the light receiving element. The present invention can also be applied to uses such as an optical pickup device that performs recording and reproduction of useful different optical recording media.

The figure which showed notionally one structural example of the optical pick-up apparatus which concerns on embodiment of this invention. Explanatory drawing about the multiplexing which the optical pick-up apparatus 100 which concerns on Example 1 of the Example of this invention performs. FIG. 3 is an explanatory diagram of demultiplexing performed by the optical pickup device 100 according to Example 1 of the embodiment of the present invention. Explanatory drawing which shows the optical axis direction of the incident light beam to the 1st diffraction element 2, and the optical axis direction of the light beam after diffraction when the oscillation wavelength of each light source 1a, 1b changes. Explanatory drawing which shows the incident direction of the light beam which injects into the 2nd diffraction element 9 when the oscillation wavelength of each light source 1a, 1b changes, and the outgoing direction of the light beam emitted from the 2nd diffraction element 9. FIG. Sectional drawing which shows notionally a part of cross section of the 1st diffraction element 2 which concerns on the Example of this invention. Sectional drawing which shows notionally a part of cross section of the 2nd diffraction element 9 which concerns on the Example of this invention. The figure which showed notionally one structural example of the optical pick-up apparatus based on Example 2 of the Example of this invention. Explanatory drawing about the multiplexing which the optical pick-up apparatus 800 which concerns on Example 2 of the Example of this invention performs. Explanatory drawing about the demultiplexing which the optical pick-up apparatus 800 which concerns on Example 2 of the Example of this invention performs. Sectional drawing which shows notionally the cross section of the 1st diffraction element 2 which concerns on the Example of this invention. FIG. 3 is a cross-sectional view conceptually showing a part of a cross section of a polarization diffraction grating 112 constituting the first diffraction element 2. Sectional drawing which shows notionally the cross section of the 2nd diffraction element 9 which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b Light source 2, 9 Diffraction element 3 Optical element 4 Collimator lens 5 Diaphragm 6 Objective lens 7, 8 Optical disk 7a, 8a Information recording surface 10a, 10b Light receiving element 21, 63, 91 The light beam which the 1st light source 1a emitted Optical axes 22, 64, 92 Optical axes 23, 65 of the luminous flux emitted from the second light source 1 b Optical axes 31, 73, 101 of the luminous flux after the combination Optical axes 32, 73, 101 of the luminous flux incident on the second diffraction element 9 53, 74, 101 Optical axis of the first wavelength light beam after demultiplexing 33, 54, 75, 102 Optical axis of the second wavelength light beam after demultiplexing 41 The light beam emitted from the first light source 1a The direction in which the first diffractive element 2 exits 42 The direction in which the light beam emitted from the second light source 1b exits the first diffractive element 2 51 The return light of the light beam emitted from the first light source 1a is the second diffractive element 9 Optical axis of the light beam incident on the second light source 52 The optical axis of the luminous flux on which the return light of the luminous flux emitted from 1b enters the second diffractive element 9 61 The incident surface of the first diffractive element 2 62 The outgoing surface of the first diffractive element 2 71 of the second diffractive element 9 Incident surface 72 Output surface of second diffraction element 9 100 Optical pickup device 111 First wave plate 112 Polarization grating 113 Second wave plate 121 Birefringent material layer 122 Isotropic material layer 123, 124 Cover glass 131 First wave plate 133 Second wave plate 132 Polarization diffraction grating

Claims (6)

A first light source that emits a light beam having a first wavelength, a second light source that emits a light beam having a second wavelength different from the first wavelength, the light beam having the first wavelength, and the second light source. A forward optical system that guides a light beam having a wavelength toward the optical recording medium, a first light receiving element that receives the return light having the first wavelength from the optical recording medium, and the second optical system from the optical recording medium. A second light receiving element for receiving return light having a wavelength; and guiding the return light having the first wavelength from the optical recording medium to the first light receiving element, and the second wavelength from the optical recording medium. An optical pickup device including a return optical system that guides the return light of the return light to the second light receiving element,
The outward optical system includes a first diffractive element that diffracts at least one of the light beam having the first wavelength and the light beam having the second wavelength,
The return optical system has a second diffractive element that diffracts at least one light flux of the return light of the first wavelength and the return light of the second wavelength,
The first diffractive element and the second diffractive element have diffraction gratings having a grating pitch equal to each other, diffract the light beams of the first wavelength at mutually equal diffraction orders, and An optical pickup device that diffracts light beams of wavelengths with the same diffraction order.   The first diffractive element and the second diffractive element both diffract the light beam having the first wavelength at the first-order diffraction order, and both the light beam having the second wavelength are the first-order diffraction order. The optical pickup device according to claim 1, wherein the optical pickup device is diffracted by a laser beam.   2. The optical pickup device according to claim 1, wherein the first diffraction element and the second diffraction element have wavelength selectivity capable of selecting a wavelength of light to be diffracted by a first or higher order of diffraction.   The first diffractive element and the second diffractive element both diffract the light beam having the first wavelength at the order of the 0th order diffraction, and both the light beam of the second wavelength are the order of the first order diffraction. The optical pickup device according to claim 1, wherein the optical pickup device is diffracted by a light beam.   5. The optical pickup device according to claim 1, wherein each of the first diffraction element and the second diffraction element includes a diffraction grating having a periodic structure in which a cross-sectional shape repeats a sawtooth shape.   The first diffraction element and the second diffraction element each include a diffraction grating having a periodic structure in which a cross-sectional shape repeats a shape obtained by approximating a sawtooth shape with a stepped shape. The optical pickup device according to the item.

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