JP4031450B2 - Optical pickup device - Google Patents

Description

  The present invention relates to an optical pickup device capable of recording / reproducing information on two different types of optical recording media.

  In recent years, in the field of information recording, there has been remarkable progress in technology related to optical information recording methods. This optical information recording method has many advantages such as non-contact recording / reproduction and compatibility with each memory type such as read-only type, write-once type, and rewritable type. A wide range of applications from industrial to consumer use is considered.

  Examples of the recording medium used in the optical information recording system include optical disks such as compact disks (abbreviated CD) and digital versatile disks (abbreviated DVD), and magneto-optical disks such as minidiscs (abbreviated MD). Here, these recording media used in the optical information recording method are collectively referred to as an optical recording medium.

  Various optical pickup devices for mounting on a recording / reproducing apparatus for recording information on the information recording surface of the optical recording medium or reproducing information on the information recording surface have been proposed. Recently, a single type of optical recording medium has been proposed. In addition to recording / reproduction, CD / DVD compatible optical pickup devices capable of recording / reproducing information on optical recording media having different standards, such as CD and DVD, have been commercialized.

  FIG. 5 is a diagram showing a simplified configuration of a conventional optical pickup device 1 capable of recording / reproducing with respect to two types of optical recording media having different standards. The conventional optical pickup device 1 shown in FIG. 5 includes a first semiconductor laser 2 that outputs laser light in a 650 nm wavelength band used for recording / reproduction for a DVD, and a 790 nm wavelength laser used for recording / reproduction for a CD, for example. And a second semiconductor laser 3 that outputs light.

  In the conventional optical pickup device 1, the light beams emitted from the first semiconductor laser 2 and the second semiconductor laser 3 have their optical axes coaxially transmitted by the color combining / separating dichroic prism 4, transmitted through the beam splitter 5, and collimated by the collimating lens 6. It becomes parallel light and is focused on the information recording surface of the CD or DVD which is the optical recording medium 8 by the objective lens 7. The reflected light reflected by the optical recording medium 8 passes through the objective lens 7 again, is collected by the collimating lens 6, enters the beam splitter 5, the direction of travel is bent by the beam splitter 5, and the photodetector 9. Reaches the first light receiving element 11 or the second light receiving element 12.

  At this time, the position of the photodetector 9 is directed in the direction of the arrows 13a and 13b and the second semiconductor so that the beam spot of the reflected light can be received at a desired position on the first and second light receiving elements 11 and 12. The position of the laser 3 is adjusted in the direction of the arrows 14a and 14b. The first and second light receiving elements 11 and 12 convert the received reflected light into an electric signal and output it. The output signal is amplified by an amplifier, and the gain is corrected by an automatic gain correction circuit. The level is adjusted to a certain range.

  FIG. 6 and FIG. 7 are diagrams schematically showing the configuration of another conventional optical pickup device 15 capable of recording / reproducing with respect to two types of optical recording media having different standards. The other conventional optical pickup device 15 is similar to the above-described conventional optical pickup device 1, and therefore, the corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  In another conventional optical pickup device 15 shown in FIG. 6, a first semiconductor laser 2 having a 650 nm wavelength band used for recording / reproducing with respect to a DVD, and a second semiconductor laser 3 having a 790 nm wavelength band used for recording / reproducing with respect to a CD, Is used, and a two-wavelength semiconductor laser 16 is used which is arranged and fixed at intervals of 100 to 300 μm. As a two-wavelength semiconductor laser, a monolithic two-wavelength semiconductor laser in which laser chips having two different wavelength bands are formed in one chip may be used. By using such a two-wavelength semiconductor laser 16 as a light source, optical components such as a color synthesis / separation dichroic prism can be omitted, so that the optical pickup device can be miniaturized by reducing the number of components, and optical. System design can be simplified.

  However, as shown in FIG. 7, the first semiconductor laser 2 and the second semiconductor laser 3 provided in the two-wavelength semiconductor laser 16 usually have an error δ of about 10 μm in the arrangement interval α that is the relative position between them. Therefore, for example, when the position of the first light receiving element 11 of the photodetector 9 is adjusted to the beam spot of the reflected light emitted from the first semiconductor laser 2 and reflected by the optical recording medium 8, the light is emitted from the second semiconductor laser 3. Therefore, there is a problem that adjustment cannot be performed so that the position of the second light receiving element 12 of the photodetector 9 is adapted to the beam spot of the reflected light reflected by the optical recording medium 8.

  That is, the beam spot of either one of the reflected light and the beam spot should be received by a distance f (δ) corresponding to the error δ of the arrangement interval α between the first semiconductor laser 2 and the second semiconductor laser 3. Since the light receiving element deviates from the desired position and the amount of light received by the light receiving element is reduced, the performance and reliability are lowered, which causes a decrease in yield in manufacturing the apparatus.

  By the way, optical parts that change the optical path of the light emitted from the light source in a desired direction include a reflecting mirror, a prism, a hologram element, a diffraction grating, and the like. These optical parts are used as components of an optical pickup device. Yes. For example, a diffraction grating used as a component part of an optical pickup device is used as an optical path changing member and also as an optical branching part that splits a beam into a plurality of parts (for example, see Patent Document 1).

  In the optical pickup device disclosed in Patent Document 1, the diffraction grating includes a portion where the grating is formed and a portion where the grating is not formed, and the diffraction grating moves relative to the light emitted from the light source. By doing so, the emitted light passes through either the part where the grating of the diffraction grating is formed or the part where the grating is not formed. When the emitted light passes through the grating forming portion, the beam is diffracted and branched into three, and in the portion where the grating is not formed, one beam passes without being diffracted and branched as one beam.

  As described above, in the optical pickup device disclosed in Patent Document 1, it is possible to reversibly change the emitted light to both one spot and three spots by moving the diffraction grating relative to the emitted light. Thus, both the 1-spot method and the 3-spot method, which are widely used as tracking error signal detection methods for following the track of the optical recording medium when recording / reproducing information on / from the optical recording medium. Applicable to detection methods.

  However, although the optical pickup apparatus proposed in Patent Document 1 discloses a technique that can cope with both the detection method of the tracking error signal detection method of the 1-spot method and the 3-spot method, a plurality of wavelengths emitted from the light source are different. No technical idea is disclosed for adjusting each of the light beams so that the beam spot of the light reflected by the optical recording medium is irradiated to a desired position of the light receiving element provided in the photodetector.

JP-A 61-148634

  An object of the present invention is to provide signal detection reliability capable of irradiating a desired position of a light receiving element provided in a photodetector with two light beam spots having different wavelengths emitted from a light source and reflected by an optical recording medium. It is to provide an optical pickup device with high accuracy.

The present invention relates to a light source capable of emitting a first light having a wavelength λ1 and a second light having a wavelength λ2, an objective lens for condensing the light emitted from the light source on an information recording surface of an optical recording medium, and optical recording In an optical pickup device comprising at least a photodetector that detects reflected light reflected by a medium or a magneto-optical recording medium, and a diffraction grating that guides the reflected light to the photodetector,
The diffraction grating is
A plurality of diffraction grating surfaces that transmit the first light of wavelength λ1 and diffract the second light of wavelength λ2,
The first light having the transmitted wavelength λ1 and the second light having the diffracted wavelength λ2 are arranged so as to be guided to the same photodetector, and are orthogonal to the optical axis of the reflected light incident on the photodetector. The optical pickup device is provided so as to be movable in the direction in which it is moved.

In the present invention, the diffraction grating surface provided in the diffraction grating is
The cross-sectional shape at the cut surface has periodic irregularities, the phase difference between the transmitted light of the concave portion and the transmitted light of the convex portion is an integral multiple of 2π with respect to the wavelength λ1, and 2π with respect to the wavelength λ2. It is formed to be a non-integer multiple.

In the present invention, the periodic uneven projections of the diffraction grating surface are
There are a plurality of step portions per pitch of the cycle, and the phase difference between transmitted light in each step portion is an integral multiple of 2π with respect to the wavelength λ1, and a non-integer multiple of 2π with respect to the wavelength λ2. It is formed so that it may become.

  According to the present invention, the optical pickup device includes a diffraction grating that includes a plurality of diffraction grating surfaces that transmit the first light having the wavelength λ1 and diffract the second light having the wavelength λ2, and the diffraction grating has the transmitted wavelength. The first light of λ1 and the second light of diffracted wavelength λ2 are arranged so as to be guided to the same photodetector, and move in a direction perpendicular to the optical axis of the reflected light incident on the photodetector Provided possible.

  In the optical pickup device configured as described above, the diffraction grating is moved in the direction orthogonal to the optical axis of the reflected light and disposed at a suitable position, thereby transmitting the first diffraction grating without being diffracted. The light and the second light diffracted by the diffraction grating can be irradiated to a desired position of the light receiving element provided in the same photodetector. As a result, both the first light and the second light used for recording / reproducing information can be irradiated to a suitable position of the light receiving element provided in the photodetector, so that the light receiving element is sufficient for signal detection. It is possible to receive a sufficient amount of light. Therefore, an optical pickup device having excellent signal quality detected by the photodetector and high reliability in recording / reproducing information is realized.

  According to the present invention, the diffraction grating surface provided in the diffraction grating has irregularities with a periodic cross-sectional shape, and the phase difference between the transmitted light of the concave portion and the transmitted light of the convex portion is 2π with respect to the wavelength λ1. It is formed to be an integral multiple and a non-integer multiple of 2π with respect to the wavelength λ2. As a result, the first light having the wavelength λ1 is linearly transmitted without being diffracted by the diffraction grating, and the second light having the wavelength λ2 is diffracted by the diffraction grating. That is, a wavelength-selective diffraction grating that does not act as a diffraction grating for the first light of wavelength λ1 and acts as a diffraction grating for the second light of wavelength λ2 is realized with a simple configuration.

  Moreover, according to the present invention, the periodic uneven projections of the diffraction grating surface are formed so as to have a plurality of stepped portions per one pitch of the cycle, and the phase difference between transmitted light in each stepped portion is It is formed to be an integral multiple of 2π with respect to the wavelength λ1 and a non-integer multiple of 2π with respect to the wavelength λ2. This realizes a wavelength-selective diffraction grating that does not act as a diffraction grating for the first light having the wavelength λ1 and acts as a diffraction grating for the second light having the wavelength λ2.

  FIG. 1 is a diagram showing a simplified configuration of an optical pickup device 20 according to an embodiment of the present invention. The optical pickup device 20 includes a light source 23 that is a two-wavelength semiconductor laser capable of emitting two lights having two different wavelengths λ1 and λ2, and information emitted from the light source 23 is recorded on the information recording medium 30. An objective lens 26 that condenses on the surface, and a collimator that is provided between the objective lens 26 and the light source 23 to collimate the light emitted from the light source 23 and collect the reflected light reflected by the optical recording medium 30. A lens 25, a beam splitter 24 that transmits light emitted from the light source 23 and reflects reflected light from the optical recording medium 30, and two wavelengths that transmit first light of wavelength λ1 and diffract light of wavelength λ2. The diffraction grating 27 having a plurality of diffraction grating surfaces for use in the direction of the arrow 31 perpendicular to the optical axis of the reflected light that is reflected by the beam splitter 24 and incident on the photodetector 29 Drive means 28 for moving the diffraction grating 27, and includes a said light detector 29 for receiving and detecting the reflected light from the optical recording medium 30.

  A light source 23 that is a two-wavelength semiconductor laser includes a first semiconductor laser 21 that emits first light having a wavelength λ1, a second semiconductor laser 22 that emits second light having a wavelength λ2, and first and second semiconductor lasers 21. , 22 and a cap 32 attached to the stem 32 so as to cover the first and second semiconductor lasers 21 and 22 attached to the stem 32. Here, the first semiconductor laser 21 emits light having a wavelength λ1 = 650 nm used for recording / reproducing information with respect to a DVD, and the second semiconductor laser 22 has a wavelength λ2 = used for recording / reproducing information with respect to a CD. 790 nm light is emitted. The light source 23 is configured to emit light by switching to one of the first semiconductor laser 21 and the second semiconductor laser 22 in accordance with the type of the optical recording medium 30 that is a target for recording / reproducing information. .

  The beam splitter 24 is formed of, for example, a prism, and transmits light emitted from the light source 23 as described above, reflects reflected light from the optical recording medium 30 and guides it to the diffraction grating 27. The collimator lens 25 converts the incident light that has passed through the beam splitter 24 into parallel light and enters the objective lens 26, and condenses the reflected light from the optical recording medium 30 to enter the beam splitter 24.

  The photodetector 29 that receives the reflected light reflected by the optical recording medium 30 and further reflected by the beam splitter 24 is provided with two first and second light receiving elements 35, provided on the substrate 34. 36. The first and second light receiving elements 35 and 36 are composed of photoelectric conversion elements such as photodiodes, for example, and the first light receiving element 35 is used to receive and detect the first light reflected by the optical recording medium 30. The second light receiving element 36 is used to receive and detect the second light reflected by the optical recording medium 30. The first and second light receiving elements 35 and 36 convert the light received and detected into electrical signals corresponding to the amount of light, and send them to a reproduction signal processing circuit, a servo control unit, etc. via a circuit formed on the substrate 34. . The photodetector 29 is provided so that its position can be adjusted in the directions of the arrows 45a and 45b.

  FIG. 2 is a perspective view showing the configuration of the diffraction grating 27, and FIG. 3 is a cross-sectional view showing the configuration of the diffraction grating 27. The diffraction grating 27 is provided between the beam splitter 24 and the photodetector 29 on the optical path of the reflected light from the optical recording medium 30. The diffraction grating 27 includes a plurality (three in the present embodiment) of diffraction grating surfaces that transmit the first light having the wavelength λ1 and diffract the second light having the wavelength λ2, and transmit the first light and the diffraction having the transmitted wavelength λ1. The second light having the wavelength λ2 is arranged so as to be guided to the same photodetector 29, and is configured to be movable in the direction of the arrow 31 perpendicular to the optical axis of the reflected light.

Hereinafter, the configuration of the diffraction grating 27 will be described with reference to FIGS. 2 and 3. In the diffraction grating 27, a plurality of diffraction grating surfaces G1, G2, and G3 are formed on one diffraction grating substrate 37. Since the diffraction grating surfaces G1, G2, and G3 are formed to have different grating pitches P1, P2, and P3, the diffraction angles β of the + 1st order diffracted light expressed by the following formula (1) are also β1, β2, respectively. , Different from β3. Since the irradiation position on the photodetector 29 of the second light diffracted by the diffraction grating 27 is determined by the diffraction angle β and the distance L from the diffraction grating 27 to the photodetector 29, the second light is reflected. What is necessary is just to set the pitch P of the diffraction grating surface formed in the diffraction grating 27 according to wavelength (lambda) 2, so that light may be received by the 2nd light receiving element 36. FIG.
sin β = λ / P (1)

  Of the diffraction grating surfaces formed on the diffraction grating 27 of the present embodiment, a diffraction grating surface G2 having no grating is selected. In other words, the diffraction grating surface G2 can be compared to a case where the pitch P2 is infinite and only the grating groove portion is formed. This diffraction grating surface G2 is used only for transmitting the first light that is not diffracted by the diffraction grating 27 when information is recorded / reproduced with respect to the DVD using the first light of wavelength λ1. It is done. Therefore, in the diffraction grating 27 of the present embodiment, the diffraction grating surface that transmits the first light of wavelength λ1 without diffracting and diffracts the second light of wavelength λ2 is actually the diffraction grating surface G1 and the diffraction grating surface. It will be two of G3.

  Further, the detailed configuration of the diffraction grating 27 is illustrated with respect to the diffraction grating surface G1. The diffraction grating surface G1 provided in the diffraction grating 27 is formed so that the cross-sectional shape has a periodic repetition of the concave portion 38 and the convex portion 39.

When the repetition pitch of the unevenness in the diffraction grating surface G1 formed in this way is P1, and the so-called grating groove depth for forming the unevenness is d1, the light 40 that passes through the recess 38 with respect to the light with the wavelength λ (hereinafter referred to as “light”). The phase difference φ generated between the concave portion transmitted light and the light 41 transmitted through the convex portion 39 (hereinafter referred to as convex portion transmitted light) is given by the following equation (2).
2π (n−1) × d1 / λ (2)
Where n: refractive index

  In the diffraction grating surface G1, the phase difference between the concave transmitted light 40 and the convex transmitted light 41 based on the formula (2) is an integral multiple of 2π with respect to the wavelength λ1, and a non-integer with 2π with respect to the wavelength λ2. It is formed to be doubled. That is, the grating groove depth d1 of the diffraction grating surface G1 is such that (n−1) × d1 is an integral multiple of the wavelength λ1 with respect to the wavelength λ1 = 650 nm of the first light. For the wavelength λ2 = 790 nm, (n−1) × d1 is formed to be a non-integer multiple of the wavelength λ2.

  By forming the grating groove depth d1 in this way, the light having the wavelength λ1 is transmitted linearly without being diffracted because the phase change by the diffraction grating surface G1 is an integral multiple of 2π, and the light having the wavelength λ2 is transmitted through the diffraction grating. Since the phase change due to the surface G1 is a non-integer multiple of 2π, it is diffracted, so it does not act as a diffraction grating for the first light of wavelength λ1, and acts as a diffraction grating for the second light of wavelength λ2. A wavelength selective diffraction grating 27 is realized. Specific examples of the grating groove depth d1 are as follows. For example, when a member having a refractive index n = 1.5 is used and (n−1) × d1 is set to be equal to λ1, the grating groove depth is set. By setting the length d1 to 1.3 μm, it is possible to obtain the diffraction grating 27 that linearly transmits the first light with the wavelength λ1 = 650 nm and has a diffraction action only with respect to the second light with the wavelength λ2 = 790 nm.

  Driving means 28 for moving the diffraction grating 27 in the direction of the arrow 31 perpendicular to the optical axis of the reflected light is connected to the diffraction grating 27. For the driving means 28, for example, a stepping motor or the like that can set the driving amount with high accuracy is used.

  In the present embodiment, the wavelength λ2 = 790 nm is selected as the second light. However, the present invention is not limited to this, and a diffraction grating surface to be used according to an arbitrary wavelength λ2 used as the second light is determined in advance. The driving means 28 moves the diffraction grating 27 in the direction of the arrow 31 so that the predetermined diffraction grating surface is positioned on the optical path of the reflected light of the second light.

  In the optical pickup device 20 of the present embodiment, when information is recorded / reproduced with the first light that is linearly transmitted without being diffracted by the diffraction grating 27, the diffraction grating surface G2 on which the above-described grating is not formed is the first. The diffraction grating 27 is moved to a predetermined position by the drive means 28 so as to be positioned on the optical axis of the reflected light of the light. When recording / reproducing information with the second light diffracted by the diffraction grating 27, for example, the diffraction grating 27 is driven by the driving means 28 so that the diffraction grating surface G1 is positioned on the optical axis of the reflected light of the second light. Is moved to a predetermined position.

  As described above, in the optical pickup device 20, whether the light is emitted from the first or second semiconductor laser 21, 22 is detected by a detector (not shown), and the detection output is output to the driving unit 28. As a result, the drive means 28 can be operated to move the diffraction grating 27 to a predetermined position in the direction of the arrow 31.

  Hereinafter, an information reproduction operation in the optical pickup device 20 of the present embodiment will be briefly described. The first light of wavelength λ1 emitted from the first semiconductor laser 21 of the light source 23 passes through the beam splitter 24, becomes parallel light by the collimator lens 25, and is condensed on the information recording surface of the optical recording medium 30 by the objective lens 26. The The light reflected by the information recording surface of the optical recording medium 30 passes through the objective lens 26 again, is collected by the collimating lens 25, is bent in the traveling direction by the beam splitter 24, and enters the diffraction grating 27. At this time, the diffraction grating 27 is moved by the driving means 28 so that the diffraction grating surface G2 is positioned on the optical axis of the reflected light of the first light. Since the diffraction grating 27 does not act as a diffraction grating for the first light with the wavelength λ1, the first light with the wavelength λ1 passes through without being diffracted by the diffraction grating 27, and the first light receiving element of the photodetector 29 Reach 35.

  On the other hand, the second light of wavelength λ 2 emitted from the second semiconductor laser 22 of the light source 23 passes through the beam splitter 24, becomes parallel light by the collimator lens 25, and is collected on the information recording surface of the optical recording medium 30 by the objective lens 26. Lighted. The light reflected by the information recording surface of the optical recording medium 30 passes through the objective lens 26 again, is collected by the collimating lens 25, is bent in the traveling direction by the beam splitter 24, and enters the diffraction grating 27.

  At this time, the diffraction grating 27 has a driving means 28 so that a diffraction grating surface, for example, a diffraction grating surface G1, which is selected in advance to diffract the reflected light of the second light, is positioned on the optical axis of the reflected light of the second light. + 1st order diffracted light 42 by the diffraction grating surface G 1 of the second light reaches the second light receiving element 36 of the photodetector 29.

  Thus, in the case where information is reproduced using either the first light or the second light, to a suitable position of the first or second light receiving element 35, 36 provided in the photodetector 29, Since the reflected light of the first light or the second light can be irradiated, the first or second light receiving elements 35 and 36 can receive a sufficient amount of light for reproducing information (the same applies to recording). . Therefore, the optical pickup device 20 having excellent signal quality detected by the photodetector 29 and high reliability in recording / reproducing information is realized.

  FIG. 4 is a cross-sectional view showing the configuration of the diffraction grating 50 provided in the optical pickup device according to the second embodiment of the present invention. Since the optical pickup device of the present embodiment is configured in the same manner as the optical pickup device 20 of the first embodiment except for the diffraction grating 50, the illustration and description of the overall configuration are omitted.

  The feature of the diffraction grating 50 provided in the optical pickup device of the present embodiment is that the uneven convex portion 51 formed at the pitch P1 of the diffraction grating surface G4 has a plurality of step portions (this embodiment) per one pitch P1 of the period. In this embodiment, there are three steps: first to third step portions 51a, 51b, 51c), the phase difference between transmitted light in each step portion 51a, 51b, 51c, and the first step in each step portion 51a, 51b, 51c. The phase difference between the first to third convex transmitted light 52a, 52b, 52c and the concave transmitted light 53 is an integral multiple of 2π with respect to the wavelength λ1, and is a non-integer multiple of 2π with respect to the wavelength λ2. It is to be formed.

  In the present embodiment, the formation pitch of each stepped portion constituting the convex portion 51 of the diffraction grating 50 is (P1) / 4, and the pitch P1 of the concave and convex portions is the concave portion 54 and the first to third stepped portions 51a and 51b. , 51c. Further, the diffraction grating 50 is configured such that the step between the recess 54 and the first step 51a of the protrusion 51 and the step between the steps are all d1, that is, the step of the first step 51a with respect to the recess 54 is d1. The step of the second step portion 51b with respect to the recess 54 is 2 × d1, and the step of the third step portion 51c with respect to the recess 54 is 3 × d1.

  In the diffraction grating surface G4, the phase difference between the concave portion transmitted light 53 and each convex portion transmitted light 52a, 52b, 52c, and the phase difference between each convex portion transmitted light are an integral multiple of 2π with respect to the wavelength λ1, Further, it is formed to be a non-integer multiple of 2π with respect to the wavelength λ2. That is, the level difference d1 of the diffraction grating surface G4 is such that (n−1) × d1 is an integral multiple of the wavelength λ1 and the wavelength λ2 of the second light is λ1 = 650 nm with respect to the wavelength λ1 = 650 nm of the first light. For 790 nm, (n−1) × d1 is set to be a non-integer multiple of wavelength λ2.

  Specific examples of the dimension of the step d1 are as follows. For example, when a member having a refractive index n = 1.5 is set so that (n−1) × d1 is equal to λ1, the step d1 is 1.3 μm. That is, the step of the first step 51a relative to the recess 54 is 1.3 μm, the step of the second step 51b relative to the recess 54 is 2.6 μm, and the step of the third step 51c relative to the recess 54 is 3.9 μm. By doing so, the diffraction grating 50 that linearly transmits the first light with the wavelength λ1 = 650 nm and exerts the diffraction action only on the second light with the wavelength λ2 = 790 nm is obtained.

  The optical pickup device according to the second embodiment including such a diffraction grating 50 can achieve the same effects as the optical pickup device 20 according to the first embodiment, and improve the diffraction efficiency of a specific diffraction order. Therefore, various designs and manufactures are possible depending on the application.

  As described above, in the present embodiment, the unevenness formed in the diffraction grating is a simple step shape, but is not limited to this, and is, for example, a sawtooth wave-shaped blazed grating shape. Also good. Although the optical pickup device does not include a diffraction grating that forms a sub-beam, when a tracking method such as a three-beam method or a differential push-pull method is employed, a diffraction grating that forms a sub-beam is separately provided. It may be configured as follows.

It is a figure which simplifies and shows the structure of the optical pick-up apparatus 20 which is one Embodiment of this invention. 3 is a perspective view showing a configuration of a diffraction grating 27. FIG. 3 is a cross-sectional view showing a configuration of a diffraction grating 27. It is sectional drawing which shows the structure of the diffraction grating 50 with which the optical pick-up apparatus which is 2nd Embodiment of this invention is equipped. It is a figure which simplifies and shows the structure of the conventional optical pick-up apparatus 1 which can record / reproduce with respect to two types of optical recording media from which a specification differs. It is a figure which simplifies and shows the structure of another conventional optical pick-up apparatus 15 which can record / reproduce with respect to two types of optical recording media from which a specification differs. It is a figure which simplifies and shows the structure of another conventional optical pick-up apparatus 15 which can record / reproduce with respect to two types of optical recording media from which a specification differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Optical pick-up apparatus 21, 22 Semiconductor laser 23 Light source 24 Beam splitter 25 Collimating lens 26 Objective lens 27, 50 Diffraction grating 28 Driving means 29 Photo detector 30 Optical recording medium 35, 36 Light receiving element 37 Diffraction grating substrate 38, 54 Recess 39 , 51 Convex 40, 53 Concave transmitted light 41, 52 Convex transmitted light

Claims (3)

A light source capable of emitting a first light of wavelength λ1 and a second light of wavelength λ2, an objective lens for condensing the light emitted from the light source on the information recording surface of the optical recording medium, and reflected by the optical recording medium In an optical pickup device comprising at least a photodetector that detects reflected light and a diffraction grating that guides the reflected light to the photodetector,
The diffraction grating is
A plurality of diffraction grating surfaces that transmit the first light of wavelength λ1 and diffract the second light of wavelength λ2,
The first light having the transmitted wavelength λ1 and the second light having the diffracted wavelength λ2 are arranged so as to be guided to the same photodetector, and are orthogonal to the optical axis of the reflected light incident on the photodetector. An optical pickup device is provided so as to be movable in a moving direction. The diffraction grating surface of the diffraction grating is
The cross-sectional shape has periodic irregularities, and the phase difference between the light transmitted through the concave portion and the light transmitted through the convex portion is an integral multiple of 2π with respect to the wavelength λ1, and a non-integer multiple of 2π with respect to the wavelength λ2. The optical pickup device according to claim 1, wherein the optical pickup device is formed as follows. The convex part of the periodic unevenness on the diffraction grating surface is
There are a plurality of step portions per pitch of the cycle, and the phase difference between transmitted light in each step portion is an integral multiple of 2π with respect to the wavelength λ1, and a non-integer multiple of 2π with respect to the wavelength λ2. The optical pickup device according to claim 2, wherein the optical pickup device is formed as follows.

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