JP2009176391A - Optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup performing recording and reproducing for a plurality of types of optical disks by using three different kinds of wavelengths, wherein constituent components are standardized and high three-wavelength compatibility is achieved by setting an appropriate focus pull-in range corresponding to the format of each optical disk. <P>SOLUTION: The optical pickup includes: emission parts for emitting optical beams of three wavelengths corresponding to a plurality of types of optical disks respectively; a condensing optical device 36 for condensing the optical beam of each wavelength on an optical disk; a divergence angle conversion element 37 which is movable in an optical axis direction and converts the divergence angle of an optical beam to a predetermined divergence angle according to the moved position in the optical axis direction; a common photodetector 41 for receiving a returning optical beam separated by optical path separation means 38 and 39; and a phase conversion part 43 which is disposed between the condensing optical device 36 and the light-receiving part 40, imparts a phase difference to the optical beam of each wavelength to convert the phase state of a wave surface of the optical beam to a state different from those of the other optical beams. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup for recording and / or reproducing information signals on three different types of optical discs and an optical disc apparatus using the same.

  In recent years, as a next-generation optical disc format, an optical disc capable of high-density recording (hereinafter referred to as a “high-density recording optical disc”) in which signals are recorded and reproduced using a light beam having a wavelength of about 405 nm by a blue-violet semiconductor laser has been proposed. ing. As this high-density recording optical disk, a structure in which the thickness of the protective layer (cover layer) for protecting the signal recording layer is thin, for example, 0.1 mm has been proposed.

  In providing optical pickups corresponding to these high-density recording optical disks, conventional optical disks having different formats such as a CD (Compact Disc) having a used wavelength of about 785 nm and a DVD (Digital Versatile Disc) having a used wavelength of about 655 nm. Those that are compatible with are desired. Thus, there is a need for an optical pickup and an optical disk apparatus that have compatibility between optical disks of different formats that have different disk structures and accompanying laser specifications.

  By the way, the above-described high-density recording optical discs and optical discs such as DVDs and CDs each have standards (formats) for preserving the uniformity and compatibility of popular media and devices for recording and reproducing them. These standards (format books) describe various requirements regarding the product technology, but the so-called 3 for recording or reproducing information signals on the three different types of optical disks as described above. In order to realize wavelength compatibility, it is particularly important to satisfy the requirements for servo signals for focus servo, which is one of the description items.

  In the case of performing the three-wavelength compatibility as described above, it is necessary to make it possible to realize a system for a high-density recording optical disk in addition to the conventional system for optical disks such as DVD and CD. It is necessary to satisfy the required specification of the focus error signal suitable for the focus servo corresponding to the. The required specification of the focus error signal suitable for the focus servo corresponding to the format of each optical disc varies depending on the difference in the specifications of the optical disc determined by such a plurality of types of formats.

  In particular, the waveform of the focus error signal is deeply related to the optical system and the electrical system of the optical pickup, and the S-shaped waveform pull-in range (hereinafter referred to as “return magnification”) is referred to as the optical path return magnification (hereinafter also referred to as “return magnification”). , Also referred to as “focus pull-in range”).

  For example, considering a conventional system, the focus pull-in range suitable for BD (Blu-ray Disc (registered trademark)), which is a high-density recording optical disc, is about 1.5 μm to 3.5 μm, which is suitable for DVD and CD. The focus pull-in range was about 4.0 μm to 12.0 μm.

  If this focus pull-in range does not match the format of each optical disc, the sensitivity of the focus servo is reduced, or defocus occurs and appropriate focus servo cannot be performed. There was a risk that problems such as failure to perform well could occur. In order to provide an appropriate focus pull-in range for each of the three wavelengths used, it is necessary to set an optimum return magnification. The return magnification is mainly determined by the focal length of the objective lens, the incident magnification to the objective lens, and the focal length of other optical components arranged in the return optical system. In view of the above, conventionally, for example, as shown in FIG. 17, two or more light receiving elements are used, and multiple lenses as coupling lenses having different curvatures are separately provided in optical paths other than the common optical path of the return path system. A method of placing the device on the surface has been used or studied. Here, the configuration of the optical pickup that has been conventionally studied shown in FIG. 17 will be described.

  The optical pickup 160 shown in FIG. 17 has a common objective lens corresponding to three-wavelength light beams, and solves the problems of the conventional optical pickup having two objective lenses. In other words, since the optical pickup 160 needs to be mounted on two actuators for driving the objective lens, it solves problems such as an increase in the weight of the actuator and a decrease in sensitivity.

  Specifically, the optical pickup 160 includes a light source unit 163 such as a laser diode having an emission unit that emits a light beam having a wavelength of about 785 nm with respect to an optical disk such as a CD, and a wavelength of about 655 nm with respect to an optical disk such as a DVD. A light source 162 such as a laser diode having an emission part that emits a light beam, a light source 161 such as a laser diode having an emission part that emits a light beam having a wavelength of about 405 nm with respect to a high-density recording optical disk, and a high-density recording A common objective lens 164 for optical disc, DVD, and CD, and a diffractive optical element 165 for correcting aberrations are provided.

  The optical pickup 160 includes a movable collimator lens 167, a quarter wavelength plate 175, a rising mirror 176, beam splitters 168A, 168B, 169A, gratings 173A, 173B, 173C, and the like.

  Further, the optical pickup 160 includes a multi-lens 172B and a photodetector 171B as a return light detection system for an optical disk such as a DVD and a CD, and a multi-lens as a return light detection system for a high-density recording optical disk. 172A and a photodetector 171A, and a beam splitter 169B for guiding a predetermined light beam to each return light detection system.

  The light beam having a wavelength of about 785 nm emitted from the light source unit 163 is reflected by the beam splitter 168B, passes through the beam splitter 169A, and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of about 1.1 mm.

  The light beam having a wavelength of about 655 nm emitted from the light source unit 162 is reflected by the beam splitter 168A, passes through the beam splitters 168B and 169A, and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of 0.6 mm. The return light having a wavelength of 785 nm and a wavelength of 655 nm reflected by the signal recording surface of the optical disc is reflected by the beam splitter 169B via the beam splitter 169A, and detected by the multi-lens 172B by the photodetector 171B having a photodetector and the like.

  The light beam having a wavelength of about 405 nm emitted from the light source unit 161 is transmitted through the beam splitters 168A, 168B, and 169A and enters the objective lens 164. The objective lens 164 is focused on the signal recording surface of an optical disc having a protective layer having a thickness of about 0.1 mm. The return light having a wavelength of 405 nm reflected by the signal recording surface of the optical disk passes through the beam splitter 169A, passes through the beam splitter 169B, and is detected by the multi-lens 172A by the photodetector 171A having a photodetector or the like.

  In the return optical system of the optical pickup 160, the focal length and the arrangement of the DVD / CD multi-lens 172B and the multi-lens 172A for the high-density recording optical disc are appropriately adjusted, so that the optical pickup 160 can be used for optical discs such as DVD and CD. By setting the return magnification of the light beam with the wavelength of 785 nm and the wavelength of 655 nm and the return magnification of the light beam with the wavelength of 405 nm for the high density recording optical disc, an appropriate focus pull-in range can be given for each wavelength.

  The optical pickup 160 shown in FIG. 17 as described above is provided with an objective lens 164 corresponding to a light beam of three wavelengths and a diffractive optical element 165 for correcting aberrations, thereby recording and / or recording on three different types of optical disks. In addition to realizing reproduction, an appropriate focus pull-in range is set for each optical disk, that is, compatibility among a plurality of types of optical disks is realized.

  However, the optical pickup 160 shown in FIG. 17 has a problem in terms of cost reduction and miniaturization because the number of parts is increased due to the necessity of providing two photodetectors having light receiving elements. That is, the optical pickup 160 is not only costly because, for example, two photodetectors are necessary, but also includes an element such as a beam splitter that separates and enters the light beams corresponding to these photodetectors. In addition, a plurality of parts such as a multi-lens as a magnification conversion lens for condensing on the light receiving element of each photodetector is required, and the wiring is routed from two locations, which makes the configuration complicated. However, there is a problem that the configuration as a whole is complicated and miniaturization of the apparatus is hindered.

  As described above, the optical pickup shown in FIG. 17 has a problem that the number of parts increases and the optical system becomes complicated. In addition, by providing a plurality of multi-lenses and light receiving elements, the number of steps for adjusting them increases, and it takes a lot of time to manufacture an optical pickup, which complicates the configuration of the apparatus and prevents miniaturization. There was a problem of becoming.

  Therefore, in order to realize further miniaturization, simplification of the configuration, simplification of the adjustment process, and the like, it is desired to configure an optical pickup having an optical system including one light receiving unit and one photodetector. When an optical pickup is composed of only one objective lens and a photodetector having one light receiving section, it is not possible to set a difference in the return magnification for the three types of wavelengths used, and the focus servo signal waveform is appropriate. That is, there is a problem that a desired focus pull-in range cannot be obtained as described above.

  Further, when reproducing a multi-layer optical disk having a plurality of signal recording surfaces as the above-described high-density recording optical disk, for example, a double-layer optical disk, stray light from a recording surface different from the recording surface on which the signal is reproduced is generated. It is necessary to consider that the light is incident on the light receiving surface. In an optical system that does not have a sufficiently large return magnification, the problem due to interference increases, and the reproduction characteristics may be adversely affected. It is desirable to have a return magnification (return magnification) of a certain level or more.

  Thus, from the viewpoint of making the focus pull-in range appropriate, the return magnification corresponding to each format is optimized, and the objective lens and the light receiving element for each wavelength used corresponding to each optical disc. It has been very difficult to achieve both compatibility with three wavelengths and the miniaturization of the apparatus and the simplification of the configuration by making the common use.

JP 2007-220215 A

  An object of the present invention is an optical pickup that performs recording and / or reproduction with respect to a plurality of types of optical discs using three different types of wavelengths, and simplifies the configuration and reduces the size of the apparatus by using common components. An optical pickup capable of achieving an appropriate focus pull-in range corresponding to the format of each optical disc, and achieving compatibility between three-wavelength compatibility by obtaining a compact configuration and a good servo signal. And providing an optical disk apparatus using the same.

  An optical pickup according to the present invention records and / or reproduces an information signal by selectively irradiating a plurality of light beams having different wavelengths to an optical disc arbitrarily selected from a plurality of types of optical discs. In the above, the first emission part that emits the light beam of the first wavelength, the second emission part that emits the light beam of the second wavelength longer than the first wavelength, and the second wavelength A third emitting section for emitting a light beam having a longer third wavelength, a condensing optical device for condensing the light beams having the first to third wavelengths on the signal recording surface of the corresponding optical disc, It is arranged on the optical path between the first to third emission parts and the condensing optical device and is movable in the optical axis direction. Predetermined divergence angle of light beam with wavelength 3 A divergence angle conversion element that converts the divergence angle, a photodetector having a common light receiving unit that receives the first to third return light beams reflected by the optical disc, and the condensing optics A refraction provided between the device and the light receiving unit, imparts a phase difference to each of the light beams having the first to third wavelengths, and differs from the other light beams for at least one light beam. A phase conversion unit that converts the phase state of the wavefront into a state substantially equivalent to the application of force.

  An optical disc apparatus according to the present invention includes a driving unit that holds and rotates an optical disc arbitrarily selected from a plurality of types of optical discs, and a plurality of optical discs that have different wavelengths with respect to the optical disc that is rotationally driven by the driving unit. An optical disc apparatus having an optical pickup that records and / or reproduces an information signal by selectively irradiating a light beam. The optical pickup used in the optical disc apparatus uses the above-described optical pickup. .

  The present invention uses a common optical system having a common objective lens corresponding to three types of wavelengths used and a common light receiving element to collect a light beam having a wavelength corresponding to each optical disk, and from the optical disk. In an optical system of an optical pickup that detects and reflects information signals and records and / or reproduces information signals on a plurality of types of optical discs, at least one of light beams having first to third wavelengths that are different from each other. By converting the phase state of each light beam by a phase conversion unit that converts the phase state of the wavefront into a state almost equivalent to giving a different refractive power to the other light beam to the light beam of Depending on the situation, the return path magnification can be optimized, so that it is possible to set an appropriate focus pull-in range corresponding to each optical disc format. And then, to realize good recording and / or reproducing for each optical disc while realizing miniaturization of simplification and device configurations.

  Hereinafter, an optical disk apparatus using an optical pickup to which the present invention is applied will be described with reference to the drawings.

  As shown in FIG. 1, an optical disc apparatus 1 to which the present invention is applied includes an optical pickup 3 for recording / reproducing information from / on an optical disc 2, a spindle motor 4 as a driving means for rotating the optical disc 2, and an optical pickup 3. And a feed motor 5 for moving the optical disk 2 in the radial direction. The optical disc apparatus 1 is an optical disc apparatus that realizes compatibility between three standards capable of recording and / or reproducing information on three types of optical discs having different formats and an optical disc in which recording layers are stacked.

  The optical disk used here is, for example, an optical disk such as CD (Compact Disc), CD-R (Recordable), CD-RW (ReWritable) using a semiconductor laser having an emission wavelength of about 785 nm, or an emission wavelength of about 655 nm. Optical discs such as DVD (Digital Versatile Disc), DVD-R (Recordable), DVD-RW (ReWritable), DVD + RW (ReWritable) using semiconductor lasers, and semiconductor lasers with a shorter emission wavelength of about 405 nm (blue-violet) It is a high-density recording optical disk such as a BD (Blu-ray Disc (registered trademark)) that can be used for high-density recording.

  In particular, the following three types of optical disks 2 for reproducing or recording information by the optical disk apparatus 1 have a protective layer formed with a first thickness of about 0.1 mm and record and reproduce a light beam with a wavelength of about 405 nm. Recording / reproducing a light beam having a wavelength of about 655 nm having the first optical disk 11 such as the above-described BD capable of high-density recording used as light and a protective layer formed with a second thickness of about 0.6 mm. A second optical disk 12 such as a DVD used as light, and a CD such as a CD that has a protective layer formed with a third thickness of about 1.1 mm and uses a light beam with a wavelength of about 785 nm as recording / reproducing light. 3 is used as an example.

  In the optical disc apparatus 1, the spindle motor 4 and the feed motor 5 are driven and controlled in accordance with the disc type by a servo control unit 9 that is controlled based on a command from a system controller 7 that also serves as a disc type discriminating unit. The first optical disk 11, the second optical disk 12, and the third optical disk 13 are driven at a predetermined number of rotations.

  The optical pickup 3 is an optical pickup having a three-wavelength compatible optical system. The optical pickup 3 irradiates a recording layer of an optical disc having a different standard with a light beam having a different wavelength from the protective layer side, and reflects the light beam reflected on the recording layer. Is detected. The optical pickup 3 outputs a signal corresponding to each light beam from the detected reflected light.

  The optical disc apparatus 1 generates a focus error signal, a tracking error signal, an RF signal and the like based on a signal output from the optical pickup 3, and demodulates a signal from the preamplifier 14 or a signal from an external computer 17 or the like. A signal modulator / demodulator and error correction code block (hereinafter referred to as a signal modulator / demodulator & ECC block) 15, an interface 16, a D / A / A / D converter 18, and an audio / visual processing unit 19. And an audio / visual signal input / output unit 20.

  The preamplifier 14 generates a focus error signal by an astigmatism method or the like based on an output from the photodetector, generates a tracking error signal by a three beam method, a DPD method, a DPP method, or the like, and further generates an RF signal. A signal is generated, and the RF signal is output to the signal modulation & ECC block 15. Further, the preamplifier 14 outputs a focus error signal and a tracking error signal to the servo control unit 9.

  The signal modulation & ECC block 15 performs LDC-ECC and BIS on the digital signal input from the interface 16 or the D / A / A / D converter 18 when recording data on the first optical disk. Error correction processing is performed by an error correction method such as 1-7PP, and then modulation processing such as 1-7PP method is performed. The signal modulation & ECC block 15 performs error correction processing according to an error correction method such as PC (Product Code) when recording data on the second optical disc, and then performs modulation processing such as 8-16 modulation. Do. Further, when recording data on the third optical disc, the signal modulation & ECC block 15 performs error correction processing by an error correction method such as CIRC, and then performs modulation processing such as 8-14 modulation processing. Then, the signal modulation & ECC block 15 outputs the modulated data to the laser control unit 21. Further, when reproducing each optical disk, the signal modulation & ECC block 15 performs demodulation processing based on the RF signal input from the preamplifier 14, further performs error correction processing, and converts the interface 16 or data to D / A. , Output to the A / D converter 18.

  When data is compressed and recorded, a compression / decompression unit may be provided between the modulation & ECC block 15 and the interface 16 or the D / A / A / D converter 18. In this case, the data is compressed by a method such as MPEG2 or MPEG4.

  The servo controller 9 receives a focus error signal and a tracking error signal from the preamplifier 14. The servo control unit 9 generates a focus servo signal and a tracking servo signal so that the focus error signal and the tracking error signal become zero, and an objective lens such as a biaxial actuator that drives the objective lens based on these servo signals. Drive control of the drive unit. Further, a synchronization signal or the like is detected from the output from the preamplifier 14, and the spindle motor is servo-controlled by CLV (Constant Linear Velocity), CAV (Constant Angular Velocity), or a combination of these.

  The laser control unit 21 controls the laser light source of the optical pickup 3. In particular, in this specific example, the laser control unit 21 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode. Also, control is performed to vary the output power of the laser light source depending on the type of the optical disc 2. The laser control unit 21 switches the laser light source of the optical pickup 3 in accordance with the type of the optical disc 2 detected by the disc type determination unit 22.

  The disc type discriminating unit 22 detects a change in the amount of reflected light from the surface reflectance, the shape and the external difference between the first to third optical discs 11, 12, and 13 to detect different formats of the optical disc 2. be able to.

  Each block constituting the optical disc apparatus 1 is configured to be able to perform signal processing based on the specification of the optical disc 2 to be mounted, according to the detection result in the disc type discriminating unit 22.

  The system controller 7 controls the entire apparatus according to the type of the optical disk determined by the disk type determination unit 22. Further, the system controller 7 performs recording / reproduction based on address information and table information (TOC) recorded in a premastered pit or groove in the innermost periphery of the optical disc in response to an operation input from the user. The recording position and reproduction position of the optical disc to be performed are specified, and each unit is controlled based on the specified position.

  The optical disc apparatus 1 configured as described above rotates the optical disc 2 by the spindle motor 4, drives and controls the feed motor 5 in accordance with a control signal from the servo control unit 9, and controls the optical pickup 3 on the optical disc 2. Information is recorded on and reproduced from the optical disc 2 by moving to a position corresponding to a desired recording track.

  Specifically, when recording / reproducing is performed by the optical disc apparatus 1, the servo control unit 9 rotates the optical disc 2 by CAV, CLV, or a combination thereof. The optical pickup 3 irradiates a light beam from a light source, detects a returning light beam from the optical disc 2 by a photodetector, generates a focus error signal and a tracking error signal, and based on these focus error signal and tracking error signal Then, the objective lens is driven by the objective lens driving mechanism to perform focus servo and tracking servo.

  When recording is performed by the optical disc apparatus 1, a signal from the external computer 17 is input to the signal modulation / demodulation & ECC block 15 through the interface 16. The signal modulation / demodulation & ECC block 15 adds a predetermined error correction code as described above to the digital data input from the interface 16 or the A / D converter 18, and further performs a predetermined modulation process and outputs a recording signal. Generate. The laser control unit 21 controls the laser light source of the optical pickup 3 based on the recording signal generated by the signal modulation / demodulation & ECC block 15 to record on a predetermined optical disk.

  Further, when the information recorded on the optical disc 2 is reproduced by the optical disc apparatus 1, the signal modulation / demodulation & ECC block 15 performs a demodulation process on the signal detected by the photodetector. If the recording signal demodulated by the signal modulation / demodulation & ECC block 15 is for computer data storage, it is output to the external computer 17 via the interface 16. Accordingly, the external computer 17 can operate based on the signal recorded on the optical disc 2. If the recording signal demodulated by the signal modulation / demodulation & ECC block 15 is for audio visual, it is converted from digital to analog by the D / A converter 18 and supplied to the audio / visual processing unit 19. Audio visual processing is performed by the audio / visual processing unit 19 and output to an external speaker or monitor (not shown) via the audio / visual signal input / output unit 20.

  Here, the recording / reproducing optical pickup 3 described above will be described in detail. As described above, the optical pickup 3 has a wavelength different from that of an optical disc arbitrarily selected from the three types of first to third optical discs 11, 12, and 13 having different formats such as the thickness of the protective layer. This is an optical pickup that records and / or reproduces information signals by selectively irradiating a plurality of light beams.

  As shown in FIG. 2, the optical pickup 3 to which the present invention is applied includes a first light source unit 31 having a first emission unit that emits a light beam having a first wavelength, and a second light source that has a second wavelength longer than the first wavelength. A second light source part 32 having a second emission part for emitting a light beam with a wavelength of 3 and a third emission part for emitting a light beam with a third wavelength longer than the second wavelength; The objective lens 34 and the diffractive optical element 35 constituting the condensing optical device 36 for condensing the light beam emitted from the third to third emission portions on the signal recording surface of the optical disc 2, and the first to third emission portions And a converging optical device 36 and is movable in the direction of the optical axis, and converts the divergence angle of the light beams of the first to third wavelengths into a substantially parallel light state or a predetermined state. As a divergence angle conversion element that adjusts and emits light so that it has a divergence angle of And a collimator lens 37.

  In addition, the optical pickup 3 is focused on the signal recording surface of the optical disc 2 by the objective lens 34 and is reflected by the signal recording surface, and the first to third return light beams (hereinafter referred to as “return light beams”). The first and second beam splitters 38 and 39 functioning as optical path separating means for separating the optical path of each of the outgoing light beams emitted from the first to third emitting sections. A photodetector 41 having a common light receiving unit 40 for receiving light beams of the first to third wavelengths in the return path (returned) separated by the first and second beam splitters 38 and 39; A magnification conversion lens (cup) that is provided between the beam splitter 38 and the light receiving unit 40 and condenses the light beams of the first to third wavelengths in the return path from the first beam splitter 38 on the light receiving surface of the light receiving unit 40. Ring lens A multi-lens 42 that functions as a multi-lens 42, and a multi-lens 42 and a first beam splitter 38, each of which has a desired wavelength by adding a phase difference to the first to third light beams. And a phase conversion element 44 having a phase conversion unit 43 that converts the phase state of the wavefront to a state substantially equivalent to applying a predetermined refractive power to the light beam.

  The optical pickup 3 is provided between the first emission part of the first light source part 31 and the first beam splitter 38, and receives the light beam having the first wavelength emitted from the first emission part. Provided between the first grating 45 diffracted into three beams for detection of a tracking error signal and the like, the second and third emission parts of the second light source part 32, and the second beam splitter 39, A second grating that diffracts the light beams of the second and third wavelengths emitted from the second and third emission sections into three beams for detecting a tracking error signal or the like, respectively.

  Further, the optical pickup 3 is provided between the collimator lens 37 and the objective lens 34, and a quarter-wave plate 47 that gives a quarter-wave phase difference to the incident light beams having the first to third wavelengths. The light beam that is provided between the objective lens 34 and the quarter-wave plate 47 and reflects the light beam that has passed through the above-described optical components in a plane orthogonal to the optical axes of the objective lens 34 and the diffractive optical element 35 stands. A raising mirror 48 that emits a light beam in the direction of the optical axis of the objective lens 34 and the diffractive optical element 35 is provided.

  The first light source unit 31 includes a first emission unit that emits a light beam having a first wavelength of about 405 nm to the first optical disc 11. The second light source unit 32 emits a light beam having a second wavelength of about 655 nm to the second optical disc 12, and a third wavelength for the third optical disc of about 785 nm. And a third emitting part for emitting the light beam. In the second light source unit 32, the second and third emission units are on the same plane orthogonal to the optical axes of the light beams having the second and third wavelengths emitted from the second and third emission units. It arrange | positions so that each light emission point may be located in the inside. Here, the first emission part is arranged in the first light source part 31 and the second and third emission parts are arranged in the second light source part 32. However, the present invention is not limited to this. Instead, the first to third emission units may be arranged in separate light source units, but the second and third emission units are arranged in a common light source unit as described above. It is advantageous to simplify the configuration and reduce the size of the apparatus.

  The first grating 45 is provided between the first light source unit 31 and the first beam splitter 38, and the light beam having the first wavelength emitted from the first emission unit of the first light source unit 31. Is diffracted into three beams for detection of a tracking error signal or the like and emitted to the first beam splitter 38 side.

  The second grating 46 is provided between the second light source part 32 and the second beam splitter 39, and the second and second light emitted from the second and third light emission parts of the second light source part 32. The light beams having the three wavelengths are diffracted into three beams for detection of tracking error signals and the like, and emitted to the second beam splitter 39 side. The second grating 46 is a so-called two-wavelength grating having wavelength dependence, and has a function of diffracting light beams having the second and third wavelengths into predetermined three beams.

  The first beam splitter 38 reflects the light beam of the first wavelength diffracted and incident by the first grating 45 and emits it to the second beam splitter 39 side. A separation surface 38a that transmits a light beam having a wavelength and emits the light beam toward the multi-lens 42 side is provided. The separation surface 38a exhibits the above-described function by being formed with wavelength dependency, polarization dependency, and the like. The first beam splitter 38 has an optical path of the light beam having the first wavelength on the return path and an optical path of the light beam having the first wavelength on the forward path emitted from the first emitting section by the separation surface 38a. It functions as an optical path separating means for separating the two.

  The second beam splitter 39 transmits the light beam having the first wavelength in the forward path from the first beam splitter 38 to be emitted to the collimator lens 37 side, and transmits the second and second forward beams from the second grating 46. 3 is a combined separation surface that reflects and guides the light beam of the third wavelength to the collimator lens 37 side and transmits the light beam of the first to third wavelengths on the return path to the first beam splitter 38 side. 39a. The composite separation surface 39a exhibits the above-described function by being formed having wavelength dependency, polarization dependency, and the like. The second beam splitter 39 synthesizes the optical path of the light beam having the first wavelength of the forward path and the optical paths of the light beams having the second and third wavelengths on the forward path by the combining / separating surface 39a. It functions as an optical path synthesis means for guiding to the lens 37 side. In addition, the second beam splitter 39 has the combined separation surface 39a so that the optical paths of the light beams of the second and third wavelengths in the return path and the second and third paths of the forward paths emitted from the second and third emitting sections are used. It functions as an optical path separating means for separating the optical path of the light beam of the third wavelength.

  The optical pickup 3 is configured such that the first and second beam splitters 38 and 39 have a function as an optical path separating unit, and the second beam splitter 39 has a function as an optical path combining unit. However, the present invention is not limited to this, and the optical path synthesis means for synthesizing the optical paths of the first to third wavelength light beams in the forward path and the optical paths of the first to third wavelength light beams in the return path What is necessary is just to comprise so that the optical path separation means to isolate | separate from the optical path of the outward path | route of the light beam of each 1st thru | or 3rd wavelength and to guide to the light-receiving part 40 side may be provided.

  The collimator lens 37 is provided between the second beam splitter 39 and the quarter-wave plate 47 and is movable in the optical axis direction. The first to the first collimator lens 37 are moved according to the moved position in the optical axis direction. It functions as a divergence angle conversion element that converts the divergence angle of the light beam having the wavelength of 3 to a predetermined divergence angle. Further, the optical pickup 3 is provided with collimator lens driving means 49 for driving the collimator lens 37 in the optical axis direction and moving it.

  As will be described later, the collimator lens 37 in the optical pickup 3 is provided with a light beam of each return wavelength that is given a different refractive power for each wavelength by the phase conversion element 44 and guided to the common light receiving unit 40 by the multi lens 42. Depending on the type of the incident light beam, predetermined positions P1, P2, and P3 in the optical axis direction (see FIG. 7) so as to be appropriately focused on the same plane, that is, on the light receiving surface of the light receiving unit 40. ). In addition, for example, the other optical components such as the first and second light source units 31 and 32 are configured to collect the light beam of each wavelength via the collimator lens 37 moved to a different position for each wavelength. It is comprised so that it may collect light appropriately. That is, the collimator lens 37 is moved to predetermined positions P1, P2, and P3 for each type of emitted light beam, and changes the state of the light beam having the first to third wavelengths according to the moved position. Thus, the light beam of each wavelength can be condensed on the same light receiving surface of the light receiving unit 40 via the phase conversion element 44 that gives different refractive power for each wavelength.

  At this time, the collimator lens driving means 49 is controlled by the system controller 7 in accordance with the type of the optical disc 2 detected by the disc type discriminating unit 22 to drive the collimator lens 37 and the above-described first. To third positions P1, P2, and P3.

  The quarter-wave plate 47 imparts a quarter-wavelength phase to the light beams having the first to third wavelengths in the forward path whose divergence angle has been converted by the collimator lens 37, so that the circularly polarized light is converted from the linearly polarized state. The light is emitted to the rising mirror 48 as a state, and the light beam having the first to third wavelengths in the return path guided from the rising mirror 48 is given a phase of ¼ wavelength, so that the linearly polarized light is changed from the circularly polarized state. As a state, the light is emitted to the collimator lens 37 side.

  The rising mirror 48 reflects the light beam given the phase difference of ¼ wavelength by the ¼ wavelength plate 47, and aligns the optical axis with the optical axis of the objective lens 34, and the diffractive optical element 35. To the side.

  The objective lens 34 condenses the incident light beams having the first to third wavelengths on the signal recording surface of the optical disc 2. The objective lens 34 is movably held by an objective lens driving mechanism such as a biaxial actuator (not shown). The objective lens 34 is moved and operated by a biaxial actuator or the like based on the tracking error signal and the focus error signal generated by the return light from the optical disk 2 detected by the photodetector 41, so that the optical disk 2 is moved in two axial directions, ie, a direction approaching and separating from the optical disc 2 and a radial direction of the optical disc 2. The objective lens 34 focuses the light beam from the first to third emission portions so that the light beam is always focused on the signal recording surface of the optical disc 2 and the focused light beam is focused on the optical disc 2. To follow the recording track formed on the signal recording surface. A diffractive optical element 35 (to be described later) is held in a lens holder of an objective lens driving mechanism that holds the objective lens 34 so as to be integrated with the objective lens 34, and the tracking direction of the objective lens 34 is configured. Even when the field of view is swung, such as moving to the diffracting optical element 35, the following effects of the diffractive portion 50 provided in the diffractive optical element 35 can be appropriately exhibited.

  The diffractive optical element 35 includes, for example, a diffractive portion 50 including a plurality of diffractive regions on the incident-side surface as one surface thereof. Each of the light beams of the third wavelength is diffracted so as to have a predetermined order and is incident on the objective lens 34, that is, is incident on the objective lens 34 as a light beam in a diffusing state or a converging state having a predetermined divergence angle. By using this single objective lens 34, the light beams having the first to third wavelengths are appropriately condensed so as not to generate spherical aberration on the signal recording surfaces of the three types of optical disks corresponding thereto. Is possible.

  Specifically, as shown in FIGS. 3A and 3B, the diffractive portion 50 provided on the incident-side surface of the diffractive optical element 35 is provided on the innermost peripheral portion and has a substantially circular shape. 1 diffraction region (hereinafter also referred to as “inner annular zone”) 51, and a second diffraction region (hereinafter also referred to as “intermediate annular zone”) 52 provided outside the first diffraction region 51. And a ring-shaped third diffraction region (hereinafter also referred to as “outer ring zone”) 53 provided outside the second diffraction region 52.

  The first diffractive region 51 that is the inner annular zone is formed with a first diffractive structure having an annular shape and a predetermined depth, and the first diffractive region 51 passes through the objective lens 34 of the light beam having the first wavelength that passes therethrough. In order to form an appropriate spot on the signal recording surface of the optical disc, the diffracted light of the order that is collected is dominant, that is, generated to have the maximum diffraction efficiency with respect to other orders of diffracted light.

  In addition, the first diffraction region 51 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing therethrough by the first diffraction structure. It is generated so that the diffracted light of the order of light is dominant, that is, has the maximum diffraction efficiency with respect to the diffracted light of other orders.

  In addition, the first diffraction region 51 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing through the first diffraction structure. It is generated so that the diffracted light of the order of light is dominant, that is, has the maximum diffraction efficiency with respect to the diffracted light of other orders.

  Thus, the first diffraction region 51 is formed with a diffractive structure that is suitable for the diffracted light of the predetermined order to be dominant with respect to the light beam of each wavelength described above. 1 corrects and reduces spherical aberration when a light beam of each wavelength, which has passed through one diffraction region 51 and is made a diffracted light of a predetermined order, is condensed on the signal recording surface of each optical disk by the objective lens 34. Make it possible.

  The second diffractive region 52, which is the middle annular zone, is formed with a second diffractive structure that is annular and has a predetermined depth and is different from the first diffractive structure. The diffracted light of the order that is condensed to form an appropriate spot on the signal recording surface of the first optical disk via the objective lens 34 of the light beam of the wavelength is dominant, that is, the diffracted light of other orders With respect to the maximum diffraction efficiency.

  The second diffractive region 52 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength that passes through the second diffractive structure. It is generated so that the diffracted light of the order of light is dominant, that is, has the maximum diffraction efficiency with respect to the diffracted light of other orders.

  The second diffractive region 52 is formed by the second diffractive structure so as to form an appropriate spot on the signal recording surface of the third optical disc via the objective lens 34 of the light beam having the third wavelength passing therethrough. It is generated so that the diffracted light of the order other than the order of light is dominant, that is, the diffracted light of the other order has the maximum diffraction efficiency. The second diffractive region 52 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing through the second diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  Thus, the second diffraction region 52 is formed with a diffraction structure suitable for the diffracted light of the predetermined order to be dominant with respect to the light beams of the respective wavelengths. Spherical aberration when the light beams of the first and second wavelengths that have passed through the two diffraction regions 52 and have been diffracted to a predetermined order are condensed on the signal recording surface of each optical disk by the objective lens 34. It can be corrected and reduced.

  The third diffractive region 53 that is the outer ring zone is formed with a third diffractive structure that is ring-shaped and has a predetermined depth and is different from the first and second diffractive structures. The diffracted light of the order that is condensed to form an appropriate spot on the signal recording surface of the first optical disc through the objective lens 34 of the light beam of one wavelength is dominant, that is, other orders The maximum diffraction efficiency is generated for the diffracted light.

  The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing through the third diffractive structure. It is generated so that the diffracted light of the order other than the order of light is dominant, that is, the diffracted light of the other order has the maximum diffraction efficiency. The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the second optical disc through the objective lens 34 of the light beam having the second wavelength passing therethrough by the third diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  The third diffractive region 53 is formed by the third diffractive structure so as to form an appropriate spot on the signal recording surface of the third optical disc via the objective lens 34 of the light beam having the third wavelength passing therethrough. It is generated so that the diffracted light of the order other than the order of light is dominant, that is, the diffracted light of the other order has the maximum diffraction efficiency. The third diffractive region 53 is gathered so as to form an appropriate spot on the signal recording surface of the third optical disc through the objective lens 34 of the light beam having the third wavelength passing therethrough by the third diffractive structure. The diffraction efficiency of the diffracted light of the order of light can be sufficiently reduced.

  Thus, the third diffraction region 53 is formed with a diffractive structure that is suitable for the diffracted light of the predetermined order to be dominant with respect to the light beam of each wavelength described above. 3 corrects and reduces the spherical aberration when the light beam of the first wavelength which has passed through the diffraction region 53 of the third light and is made the diffracted light of the predetermined order is condensed on the signal recording surface of the optical disk by the objective lens 34. Make it possible.

  Here, in the first to third diffraction regions 51, 52, and 53 described above, for example, an annular shape centered on the optical axis and the sectional shape of the annular zone is a blazed shape or a staircase shape with a predetermined depth. It is formed to become. In each diffractive structure of each diffractive region 51, 52, 53, the groove depth and the groove width of the diffracted light of a predetermined order so that the spot condensed on the signal recording surface of the optical disc is optimum as described above. The diffraction angle and the diffraction efficiency of the diffracted light of this order are formed in a predetermined range.

  The first to third diffraction regions 51, 52, and 53 function to limit the aperture of the light beams having the respective wavelengths that pass therethrough. That is, the first diffraction region 51 is formed in a size corresponding to, for example, NA = 0.45, and the second diffraction region 52 is formed, for example, in a size corresponding to about NA = 0.6. The third diffraction region 53 is formed in a size corresponding to, for example, about NA = 0.85. The first to third diffraction regions 51, 52, and 53 make it possible to limit the aperture of the light beam having the first wavelength that passes through the first diffraction region 51, 52, and 53 so that the NA is, for example, about 0.85. It is possible to limit the aperture so that the NA of the light beam having a wavelength of about 0.60 becomes, for example, and to limit the aperture so that the NA of the light beam of the third wavelength passing through, for example, about 0.45. Make it possible to do. As described above, the diffractive portion 50 including the first to third diffractive regions 51, 52, and 53 can perform aperture limiting with numerical apertures corresponding to three types of optical disks and three types of light beams. This eliminates the need for providing an aperture limiting filter or the like that has been necessary for the conventional optical pickup, and does not require adjustment when the optical filter is disposed, thereby enabling simplification, downsizing, and cost reduction of the configuration of the optical pickup.

  In the above description, as shown in FIG. 4A, the diffractive portion 50 including the three diffractive regions 51, 52, and 53 is provided on the incident side surface of the diffractive optical element 35 provided separately from the objective lens 34. However, the present invention is not limited to this, and may be provided on the exit side surface of the diffractive optical element 35. Furthermore, the diffractive portion 50 having the first to third diffractive regions 51, 52, and 53 may be configured to be integrally provided on the incident side or exit side surface of the objective lens 34. For example, FIG. ), An objective lens 34B having a diffractive portion 50 may be provided on the incident-side surface. For example, in the case where the diffractive portion 50 is provided on the incident side surface of the objective lens 34B, the surface shape of the incident side surface required as a function of the objective lens is used as a reference, and the diffractive structure as described above is used. A surface shape that matches the surface shape is formed. The objective lens 34B configured as described above is different from the diffractive optical element 35 and the objective lens 34 described above as the condensing optical device 36 by two elements, but only one element and three different ones. It functions as a condensing optical device that appropriately collects light beams of wavelengths so that spherical aberration does not occur on the signal recording surface of the corresponding optical disk. By providing the diffractive portion 50 integrally with the objective lens 34B and using it as a condensing optical device constituting an optical pickup to which the present invention is applied, it is possible to further reduce the number of optical components and reduce the size of the configuration. The objective lens 34B in which the diffractive part having the same function as that of the diffractive part 50 is integrally provided on the incident side or outgoing side surface is used for the optical pickup, thereby reducing aberrations and the like so that the optical pickup can be compatible with the three wavelengths. In addition to realizing this, the number of parts will be reduced, the structure can be simplified and miniaturized, and high productivity and low cost will be realized.

  As described above, the condensing optical device 36 composed of the objective lens 34 and the diffractive optical element 35 and the condensing optical device composed of the objective lens 34B have the divergence angle converted by the collimator lens 37 and substantially parallel light as described above. The light beam having the first wavelength is condensed well on the signal recording surface of the first optical disc, and the divergence angle is converted by the collimator lens 37 to obtain the diffused light having the predetermined divergence angle. The light beam is condensed well on the signal recording surface of the second optical disc, and the light beam having the third wavelength converted into the diffused light having a predetermined divergence angle by the collimator lens 37 is converted into the light beam of the third optical disc. It is formed so as to be well focused on the signal recording surface.

  The phase conversion element 44 is disposed on the optical path between the first beam splitter 38 and the multi-lens 42, has a predetermined phase structure on one surface thereof, and has incident first to third wavelengths. A phase converter that converts the phase state of the wavefront to a state that is substantially equivalent to giving a phase difference to each light beam and giving a refractive power different from that of the other light beam to at least one light beam. 43.

  In the following description, the phase difference for converting the phase state of the wavefront to a state substantially equivalent to applying a predetermined refractive power (also referred to as “power”) is also referred to as “power phase difference”. . In other words, the phase conversion unit 43 of the phase conversion element 44 has a function similar to that of applying a predetermined power phase difference to a light beam having a predetermined wavelength to thereby apply a refractive power to the light beam. In the following description, the refractive power that is regarded as substantially equivalent to the phase state of the predetermined wavefront converted by applying a power phase difference to the light beam of the predetermined wavelength by the phase conversion unit 43 This is the refractive power of the phase conversion unit 43 with respect to a light beam having a predetermined wavelength. Similarly, the focal length of the thin lens having the same refractive power as that of the phase conversion unit 43 is referred to as the focal length of the phase conversion unit 43 with respect to the light beam having the predetermined wavelength. Further, here, the refractive power that refracts the incident light beam in the optical axis direction, that is, the refractive power that refracts in the direction converging with respect to the incident direction is defined as a positive refractive power. A refractive power that is refracted in the direction of separating, that is, refracted in a direction of diverging with respect to the incident direction is referred to as negative refractive power.

  Then, the phase conversion element 44 is reflected by the phase conversion unit 43 on the signal recording surface of each optical disc, and the objective lens 34, the diffractive optical element 35, the rising mirror 48, the quarter wavelength plate 47, and the collimator lens 37. Through the second and first beam splitters 39 and 38 and separated from the outgoing light beam, respectively, and the phase difference with respect to the returned first to third wavelength light beams incident thereon. By providing, the phase state of the wavefront of the light beam of each wavelength is converted and emitted to a state substantially equivalent to applying different refractive powers to at least two types of light beams.

  For example, the phase conversion element 44 converts the phase state of the wave front to a state substantially equivalent to that which gives almost no refractive power to the incident light beam of the first wavelength, and For the light beam, the phase state of the wavefront is converted to a state substantially equivalent to the application of a predetermined positive refractive power, and the predetermined positive refraction is applied to the incident light beam of the third wavelength. The phase state of the wavefront is converted to a state that is substantially the same as that for applying force. In this way, the phase conversion element 44 can be brought into a state similar to the case where the refractive power is given by a lens or the like by giving a predetermined phase difference and setting the wavefront to a predetermined phase state, that is, It will have a lens effect.

At this time, the phase conversion unit 43 of the phase conversion element 44 has a refractive power P _{λ2 applied} to the light beam of the second wavelength larger than the refractive power P _{λ1 applied} to the light beam of the first wavelength. The phase state of the wavefronts of the light beams of the first and second wavelengths is converted into a state substantially equivalent to (P _λ1 <P _λ2 ), and the refractive power P imparted to the light beam of the first wavelength _.lambda.1 greater than the refractive power P _{[lambda] 3} to impart to the third wavelength of the light beam _{(P λ1 <P λ3)} phase states of the wavefront of consisting of the first and the light beam of the third wavelength substantially equal state Convert. The refracting powers P _λ2 and P _{λ3 applied} to the light beams of the second and third wavelengths may have a predetermined difference as will be described later. The description will be made assuming that it is refractive power. As a result, the phase conversion element 44 is in substantially the same state as providing different refractive powers to the two types of light beams, the first wavelength light beam and the second and third wavelength light beams. The phase state of the wave front of each light beam is converted and emitted.

By way replace this to the focal length as described above, the phase conversion element 44 having a phase converter 43, the focal length from the focal length f _Piramuda1 to the first wavelength of the light beam with respect to the second wavelength of the light beam f _Piramuda2 is configured to decrease _{(f pλ1> f} pλ2), small focal length _{f Piramuda3} respect than the focal length _{f Piramuda1} to the first wavelength of the light beam 3 of the wavelength of the light beam _{(f pλ1> f pλ3} ). Here, the positive focal length refers to the distance from the element to the condensing point in the light traveling direction, and is infinite when the element does not act.

  Specifically, as shown in FIGS. 5 (a) and 5 (b), the phase conversion unit 43 has an annular phase structure centered on the optical axis, and the radial direction and the optical axis direction of the phase structure. As shown in FIGS. 5B and 5C, a cross-sectional shape including a step-shaped phase structure having a plurality of step portions formed with a predetermined height (depth) and a predetermined width is provided. Is provided. FIG. 5C schematically shows the step shape of the cross section of the phase structure. A straight line parallel to the horizontal line indicating the plane on which the cross sectional shape is a reference and the horizontal line. Although shown as being formed from a straight line indicated by orthogonal vertical lines, in practice, as described later, a phase structure based on a target acquisition target phase (see FIG. 11) (see FIG. 12). Reference) is formed. That is, this phase structure is formed in a shape determined so that a predetermined phase difference can be given to a light beam of a predetermined wavelength, and a horizontal line indicating a plane whose cross-sectional shape is a reference It is not formed only from a straight line parallel to the vertical line and a vertical line, but is formed to have a shape having a straight line (inclined surface) or a curved line (curved surface) inclined with respect to this straight line. Yes.

  In other words, the phase structure of the phase converter 43 includes the second and third wavelength light beams as at least one of the first to third wavelength light beams and the first light beam as the other light beam. It is formed in such a shape as to give a phase difference for making a wavefront in a phase state substantially equivalent to giving different refractive powers to two types of light beams of a wavelength and a light beam of such a wavelength. The phase conversion unit 43 having a structure converts the phase state of the wavefront by giving a predetermined phase difference to each of these two types of light beams.

  The phase converter 43 formed with a predetermined annular zone phase structure gives a predetermined phase difference to the light beam of each wavelength according to the depth of the incident light beam at the position in the radial direction where the light beam is incident. By doing so, the phase state of the wave front of the passing light beam is converted.

  The phase conversion element 44 having the phase conversion unit 43 gives almost no phase difference to the light beam of the first wavelength over the entire surface, that is, the influence of the phase conversion element 44 on the incident light beam. It emits without giving. On the other hand, the phase conversion element 44 having the phase conversion unit 43 gives the second and third wavelengths to the light beams of the second and third wavelengths by giving a predetermined phase difference according to the position in the radial direction. The phase state of the wavefront of the light beam having the third wavelength is converted, that is, the light beam having the second and third wavelengths is emitted with the same effect as that of applying a predetermined refractive power (power). .

  That is, in the phase conversion element 44, since the phase conversion unit 43 hardly converts the phase state of the wavefront of the light beam having the first wavelength, as shown in FIG. Without applying refractive power to Bλ1i, the light beam Bλ1o having the first wavelength in a state of divergence angle (convergence state) substantially the same as the incident light beam Bλ1i is emitted. In contrast, in the phase conversion element 44, as shown in FIG. 6B, the phase conversion unit 43 converts the phase state of the wavefronts of the light beams of the second and third wavelengths into a desired state. A positive refracting power is applied to the incident light beams Bλ2i and Bλ3i of the second wavelength, and the incident light beams Bλ2i and Bλ3i are refracted in the direction of the optical axis (more converged). The light beams Bλ2o and Bλ3o having the second and third wavelengths are emitted. At this time, in FIG. 6A and FIG. 6B, the condensing point Pfλ1 of the light beam of the first wavelength is different from the condensing points Pfλ2 and Pfλ3 of the light beams of the second and third wavelengths. Although it is a figure like this, this shows the condensing point when entering in the same state to show the function of the phase conversion unit 43 to the last, in fact, as described above, 7A and 7B, the condensing points Pfλ1, Pfλ2 ′, and Pfλ3 ′ are positioned on the same plane by moving the collimator lens 37 back and forth in the optical axis direction. In other words, the light can be appropriately condensed on the light receiving surface of the light receiving unit 40 common to the respective wavelengths. Specifically, the collimator lens 37 has positions P2 and P3 when the light beams of the second and third wavelengths are condensed compared to the position P1 when the light beam of the first wavelength is incident. By controlling the drive so as to be on the phase conversion element 44 side, the incident state of the light beam of each wavelength on the phase conversion element 44 is changed, and the refractive power is affected by the phase conversion unit 43 as described above. The problem of receiving can be solved, that is, each light beam can be appropriately condensed on the light receiving surface of the common light receiving unit 40. In FIG. 7B, for convenience, the positions P2 and P3 are illustrated as being located at the same position. However, in actuality, the positions P2 and P3 may be different positions and may be the same positions.

The phase conversion element 44 having the phase conversion unit 43 is disposed on the optical path through which only the return light beam passes, and does not give refractive power to the light beam of the first wavelength λ1, and the second and third light beams are not provided. By applying a predetermined refractive power only to the light beams having the wavelengths λ2 and λ3, the optical magnification of the return path system can be optimized according to the wavelength used, that is, the use of the first optical disk. It is possible to reduce the return magnifications M _λ2 and M _λ3 at the second and third wavelengths, which are used wavelengths of the second and third optical discs, with respect to the return magnification M _λ1 at the first wavelength, which is the wavelength. To.

  In the optical pickup 3 having the phase conversion unit 43 as described above, the phase conversion unit 43 is provided between the light receiving unit 40 and the first beam splitter 38, that is, on the optical path through which only the return light beam passes. By applying a phase difference to each of the light beams having the first to third wavelengths and converting the phase state of the wavefront to a predetermined state, the other light beams are different from at least one light beam. In an optical system of an optical pickup that performs recording / reproduction with respect to a plurality of types of optical disks by using a common objective lens 34 and a common light receiving unit 40 by making the state substantially equivalent to applying different refractive powers. The magnification of the return optical system (return path optical system) for each wavelength (also referred to as “return path magnification”) can be set to a predetermined magnification, and the focus pull-in range can be set to a desired value suitable for each format. To enable Rukoto.

Here, the predetermined magnification refers to a magnification that allows the focus pull-in range to be adapted to each format of the first to third optical disks. The focus pull-in range is a range in which the actuator can be driven according to the control signal to perform the focus operation. Specifically, as shown in FIG. 8, the horizontal axis represents the defocus amount of the objective lens. When the focus error signal FE calculated as will be described later is taken on the vertical axis, peaks between S-shaped waveforms appearing (hereinafter also referred to as “S-shaped pp”), that is, an upper limit peak position and a lower limit The distance in the horizontal axis direction from the peak position. In general, the focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 suitable for the formats of the first to third optical discs are such that Sji _λ1 with respect to the first wavelength is 1.5 μm <Sji _λ1 <3. Sji _λ2 and Sji _λ3 for the second and third wavelengths are 4.0 μm <Sji _λ2 and Sji _λ3 <12.0 μm.

  Here, it will be described that the focus pull-in range can be adapted by setting the magnification of the returning optical system to a predetermined magnification.

The standard of the focus pull-in range of the first to third optical discs as described above is defined by the format. Generally, the focus pull-in ranges of the first optical disc that are actually set are second and third. It is preferable to set it shorter than the focus pull-in range of the optical disc. On the other hand, the S-shaped pp (Sji) indicating the focus pull-in range described above, when the astigmatic difference is Δ and the return magnification of the optical system is M, Sji = Δ / (2 × M ² ) the relationship is satisfied. Here, the astigmatic difference Δ means the distance between the focal lines of the front focal line and the rear focal line formed by astigmatism generated by the multi-lens 42 or the like. The return path magnification M is a value calculated based on the focal length of an optical component arranged in the return path optical system, which will be described later. Here, in order to set Sji to a desired value for each wavelength, it is necessary to change one or both of Δ and M to provide wavelength selectivity. In general, both the astigmatism difference Δ when the light receiving unit and the multi-lens having the astigmatism providing function are common, and the return path magnification M when the optical path from the optical disk to the light receiving unit is common, are both wavelength selective. However, in the optical pickup 3 to which the present invention is applied, the return magnification M is provided with wavelength selectivity by providing the phase conversion unit 43. It is. In order to set the focus pull-in range to a desired value as described above, at least the return magnification M _λ1 of the light beam of the first wavelength for the first optical disc is set to the second value for the second and third optical discs. And it is necessary to make it larger than the return magnifications M _λ2 and M _λ3 of the light beam of the third wavelength.

That is, as described above, the return magnifications M _λ1 , M _λ2 , and M _λ3 of the light beams of the respective wavelengths are set to predetermined values, so that the desired light beams of the respective wavelengths can be obtained for each optical disc. Focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 can be obtained.

For example, the return magnification for the light beam of the first wavelength by the return optical system including the objective lens 34, the collimator lens 37, the phase conversion element 44 and the multi lens 42 that guides each light beam reflected by the optical disk to the light receiving unit 40. When M _λ1 is set, the return magnification for the light beam of the second wavelength by the return optical system is M _λ2, and the return magnification for the light beam of the third wavelength by the return optical system is M _λ3 , From the viewpoint, by satisfying the relationship of 15.75 ≦ M _λ1 ≦ 25.00, the relationship of 12.50 ≦ M _λ2 ≦ 18.00, and the relationship of 11.50 ≦ M _λ3 ≦ 16.25, A desired focus pull-in range can be obtained for each light beam of each wavelength.

  Here, as the phase conversion unit constituting the optical pickup 3, it is provided on one surface of the phase conversion element 44, and does not apply refractive power to the light beam of the first wavelength, and the second and third components. However, the phase conversion unit constituting the optical pickup to which the present invention is applied is not limited to this. What is necessary is just to convert the phase state of the wavefront to a state substantially equivalent to giving a refractive power different from that of the other light beam to at least one light beam. A phase conversion unit that gives almost no refractive power to the light beam and gives negative light power to the light beam of the first wavelength may be provided.

  Here, as another example of the phase conversion element constituting the optical pickup 3, a phase conversion element 44B and a phase conversion unit 43B provided on one surface thereof will be described.

  The phase conversion element 44B is disposed on the optical path between the first beam splitter 38 and the multi-lens 42, has a predetermined phase structure on one surface thereof, and has incident first to third wavelengths. A phase converter that converts the phase state of the wavefront to a state that is substantially equivalent to giving a phase difference to each light beam and giving a refractive power different from that of the other light beam to at least one light beam. 43B.

  The phase conversion element 44B converts the phase state of the wavefront into a state substantially equivalent to applying a predetermined negative refractive power to the incident light beam of the first wavelength, and enters the incident second and second light beams. For the light beam having the wavelength of 3, the phase state of the wavefront is converted into a state substantially equivalent to the case where almost no refractive power is applied. In this manner, the phase conversion element 44B can be brought into a state similar to that in which a refractive power is given by a lens or the like by giving a predetermined phase difference and setting the wavefront to a predetermined phase state, that is, It will have a lens effect.

At this time, similarly to the phase conversion unit 43 described above, the phase conversion unit 43B of the phase conversion element 44B converts the light beam having the second wavelength from the refractive power P _λ1 ′ applied to the light beam having the first wavelength. In addition to converting the phase state of the wavefronts of the light beams of the first and second wavelengths to a state substantially equivalent to the case where the refractive power P _λ2 ′ to be applied is large (P _λ1 ′ <P _λ2 ′), the first The refractive power P _λ3 ′ applied to the light beam of the third wavelength is larger than the refracting power P _λ1 ′ applied to the light beam of the wavelength (P _λ1 ′ <P _λ3 ′). The phase state of the wavefront of the light beams of the first and third wavelengths is converted into a state.

  Specifically, the phase conversion unit 43B is composed of a ring-shaped phase structure centered on the optical axis in the same manner as the phase conversion unit 43 described above, and the cross-sectional shape including the radial direction and the optical axis direction of the phase structure is It is formed so as to have a shape based on the phase difference applied to each wavelength described above.

  The phase conversion element 44B having the phase conversion unit 43B gives a predetermined phase difference to the light beam of the first wavelength according to the position in the radial direction, so that the wavefront of the light beam of the first wavelength is increased. The phase state is converted, that is, the light beam having the same wavelength as the incident light beam having the first wavelength is emitted with the same effect. On the other hand, the phase conversion element 44B having the phase conversion unit 43B gives almost no phase difference to the light beams of the second and third wavelengths over the entire surface, that is, the phase of the phase of the incident light beam. The light is emitted without being affected by the conversion element 44.

The phase conversion element 44B having the phase conversion unit 43B is disposed on the optical path through which only the return light beam passes, and applies a predetermined negative refractive power only to the light beam having the first wavelength λ1, and the second In addition, by not giving refractive power to the light beams of the third wavelengths λ2 and λ3, the optical magnification of the return path system can be optimized according to the wavelength used, that is, the first optical disc The return magnifications M _λ2 and M _λ3 at the second and third wavelengths, which are used wavelengths of the second and third optical disks, _are made smaller than the return magnification M _λ1 at the first wavelength that is the use wavelength. enable.

  In the optical pickup provided with the phase conversion unit 43B as described above in place of the phase conversion unit 43 described above, the phase conversion unit 43B is disposed between the light receiving unit 40 and the first beam splitter 38, that is, the light beam in the return path. At least one light beam by providing a phase difference to each of the first to third wavelength light beams and converting the phase state of the wavefront to a predetermined state. On the other hand, by using a common objective lens 34 and a common light receiving unit 40, it is possible to perform recording / recording on a plurality of types of optical disks by applying a refractive power different from that of other light beams. The return path magnification in the optical system of the optical pickup that performs the reproduction can be set to a predetermined magnification, thereby making it possible to set the focus pull-in range to a desired value suitable for each format.

  By the way, the multi-lens 42 is disposed on the optical path between the first beam splitter 38 and the light receiving unit 40 and has, for example, a refracting surface so that the multi-lens 42 with respect to the light beam emitted from the phase conversion element 44 and incident thereon. Then, a predetermined magnification and refractive power are applied, and the light is appropriately condensed on the light receiving surface of the light receiving unit 40 such as a photodetector of the photodetector 41. Further, the multi-lens 42 has, for example, a cylindrical surface, thereby giving astigmatism for detecting a focus error signal or the like to the returning light beam. As described above, the multi-lens 42 functions as an astigmatism element to exhibit the astigmatism imparting function and condenses the incident light beams of the respective wavelengths on the common light receiving unit 40. Therefore, the divergence angle conversion function is exhibited by functioning as an element for converting the divergence angle. Here, the multi-lens 42 is described as having a divergence angle conversion function by having a refracting surface and also having an astigmatism providing function by having a cylindrical lens surface. It may be configured to have only one of the point aberration imparting functions, and may have the same function by arranging other optical components and optical systems.

  Further, the phase conversion unit 43 of the phase conversion element 44 described above may be configured to be integrally formed on one surface of the multi-lens 42. In this case, the phase structure functioning as the phase conversion unit 43 has a curved surface such as a refracting surface of a multi-lens or a cylindrical surface as a reference surface. It is formed in a shape based on the height (depth) for each position. In this way, by configuring the phase conversion unit 43 so as to be integrated with the multi-lens 42, it is possible to further simplify the configuration of the optical pickup and reduce the size thereof, and to increase practical convenience.

  The photodetector 41 includes a light receiving unit 40 including a light receiving element such as a photodetector. The common light receiving unit 40 receives the returned light beams having the first to third wavelengths collected by the multi-lens 42. Then, various detection signals such as a focus error signal and a tracking error signal are detected together with the information signal.

  The optical pickup 3 configured as described above moves the objective lens 34 on the basis of the focus error signal and tracking error signal obtained by the photodetector 41, thereby moving the optical pickup 2 relative to the signal recording surface of the optical disc 2. The objective lens 34 is moved to the in-focus position, the light beam is focused on the signal recording surface of the optical disc 2, and information is recorded on or reproduced from the optical disc 2.

  The optical pickup 3 includes first to third emission units that emit light beams having first to third wavelengths, and first to third wavelength light beams that are emitted from the first to third emission units. One surface of the objective lens 34 constituting the condensing optical device 36 for condensing the light onto the signal recording surface of the optical disc and the diffractive optical element 35 disposed on the forward optical path of the light beam having the first to third wavelengths The diffractive part 50 has first to third diffractive areas 51, 52, 53, and the first to third diffractive areas 51, 52, 53 are ring-shaped. The first to third diffractive structures having predetermined depths are generated so that the diffracted light of the predetermined diffraction order is dominant with respect to the light beam of each wavelength. Each is configured to have a diffractive structure. For three types of optical discs having different working wavelengths, it is possible to appropriately collect the corresponding light beams on the signal recording surface using a common objective lens 34, and to make the configuration complicated. In addition, the three-wavelength compatibility using the objective lens 34 in common is realized, and good information signal recording and / or reproduction is realized for each optical disc.

  Here, the objective lens 34 is provided at a position on the incident side of the light beam condensed on the optical disk by the objective lens 34, and the aberration of the light beam of each wavelength condensed on the optical disk by the objective lens 34 is reduced. The condensing optical device 36 constituting the optical pickup 3 is configured from the diffractive optical element 35 having the diffractive portion 50 to realize the three-wavelength compatibility with the common objective lens, but the optical pickup 3 is configured. The condensing optical device 36 is not limited to this, and is configured by the objective lens 34B having a diffractive structure that reduces the aberration of the light beam of each wavelength as the diffractive portion 50 on at least one surface as described above. In that case, the configuration can be further simplified and downsized. Here, the aberration reduction is realized by the diffractive portion 50 having the three-wheeled body on the so-called one surface composed of the first to third diffractive regions 51, 52, 53. However, the present invention is not limited to this. The diffractive structure provided on both sides may have the same function as the diffractive portion 50. However, in the case where the diffractive portion 50 described above is provided, the apparatus is downsized and the configuration is simplified. Further, it is advantageous for improving the light utilization efficiency and omitting the adjustment process.

  As described above, the optical pickup 3 is provided on one surface of the diffractive optical element 35 constituting the condensing optical device 36, and the diffractive portion 50 having the first to third diffractive regions 51, 52, 53 Optimum diffraction efficiency and diffraction angle can be given for each region with respect to the light beam of each wavelength, and the three types of first to third optical disks 11, 12, and 13 having different formats such as the thickness of the protective layer are provided. Spherical aberration on the signal recording surface can be sufficiently reduced, and by sharing optical components such as the objective lens 34, the apparatus can be miniaturized and the configuration can be simplified, and light beams with three different wavelengths can be used. In addition, it is possible to read and write signals with respect to a plurality of types of optical disks 11, 12, and 13.

  Further, the optical pickup 3 is provided on an optical path through which only the return light beam passes, and converts the phase state of the wavefront by giving a phase difference to the light beams of the first to third wavelengths. By having a phase conversion unit 43 that converts the phase state of the wavefront into a state substantially equivalent to giving a refractive power different from that of the other light beams to at least one light beam, The optical magnification (return magnification) of the return optical system can be set to a predetermined magnification, and the focus pull-in range can be adapted to each format.

  Here, as described above, by providing the phase conversion element 44 in front of the light receiving unit 40, a lens effect can be given only to a desired wavelength, and thereby a desired return magnification (return magnification) M. The fact that the pull-in range Sji can be obtained will be described in detail.

  First, it is provided only in the optical path of the return optical system that constitutes the optical pickup 3, and gives a phase difference to each of the light beams of the first to third wavelengths, and the other of the at least one light beam. As a phase converter that converts the phase state of the wavefront to a state substantially equivalent to applying a refractive power different from that of the light beam, a positive refractive power is applied to the light beams of the second and third wavelengths described above, When the phase conversion unit 43 that converts the phase state of the wavefront of the light beam of each wavelength is provided in a state that is substantially equivalent to a state in which almost no refractive power is applied to the light beam of the first wavelength, the specific numerical values are implemented. It will be described as Example 1.

<Example 1>
In the optical pickup 3 described above, the objective lens 34, the diffractive optical element 35, the rising mirror 48, the quarter wavelength plate 47, the collimator lens 37, the second beam splitter 39, the first beam splitter 38, and the phase conversion element 44 are used. The multi-lens 42 constitutes a return optical system. Among these, the objective lens 34, the collimator lens 37, the phase conversion unit 43, and the multi-lens 42 contribute to the return magnification (return magnification).

  The multi-lens 42, the collimator lens 37, and the objective lens 34 return to the light beam having the first wavelength λ1 (= 405 nm) when the phase conversion element 44 is not provided in the first embodiment, for example. The system is configured so that the magnification is 18.0, and at this time, the system has the same magnification for the light beams of the second and third wavelengths λ2 (= 655 nm) and λ3 (= 785 nm). It is configured as.

In such a system, as in the optical pickup 3 to which the present invention is applied, a phase conversion element 44 is additionally provided, so that only the light beams having the second and third wavelengths λ2 and λ3 are provided. By applying the action, the return magnification M _λ1 of the light beam of the first wavelength and the return magnifications of the light beams of the second and third wavelengths in the optical system including the common objective lens 34 and the common light receiving unit 40 are provided. It is possible to provide a difference between M _λ2 and M _λ3 .

The function and action of the phase conversion element 44 will be described. As described above with reference to FIG. 6A, the phase conversion unit 43 of the phase conversion element 44 functions as a function of changing the return magnification without imparting refractive power to the light beam having the first wavelength λ1. Therefore, the return magnification M _λ1 with respect to the first wavelength λ1 is 18.0 times, which is unchanged compared with the case where the phase conversion element 44 is not provided.

On the other hand, for the light beams of the second and third wavelengths λ2 and λ3, as described above with reference to FIG. 6B, the phase conversion surface which is the phase conversion unit 43 of the phase conversion element 44 is described above. As described above, the same function as that of the lens is performed to give a condensing power, that is, a refractive power, and the return magnifications M _λ2 and M _{λ3 with} respect to the second and third wavelengths λ2 and λ3 are 13. 2 times (= M _λ2 ), and 12.5 times (= M _λ3 ) at the third wavelength.

Here, as described above, since the condensing points are different in the states of FIGS. 6A and 6B, in order to actually match the condensing points on the light receiving surface of the light receiving unit 40, As shown in FIGS. 7A and 7B, it is necessary to move the collimator lens 37. When the collimator lens 37 is moved, M _λ1 = about 17.7 times and M _λ2 = about 14. 2 times, and M _λ3 = about 13.5 times.

Also, the lens stroke amount of the collimator lens 37 required at this time is about 2.9 mm, which is a sufficiently useful size. As described above, the “outgoing magnification”, “returning magnification”, “collimator lens position”, “collimator lens lens stroke amount” and the like according to the first embodiment as the configuration example in which the optical components such as the phase conversion element 44 are configured as described above. The “phase difference coefficient C ₁ of the phase conversion element” is shown in “Table 1”.

Then, the magnification difference of the return magnification with respect to each wavelength described in Table 1 satisfies the desired target focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 . The most desirable focus pull-in range is about 2 μm (= Sji _λ1 ) for a first optical disk such as a BD, and about 5 μm (= Sji _λ2 ) for a second optical disk such as a DVD. It is about 6 μm (= Sji _λ3 ) with respect to the third optical disk. Here, as described above, the focus pull-in range Sji is represented by the relationship represented by Expression (1), where M is the return path magnification. Here, Δ is an astigmatic difference. In this optical pickup 3, as shown in FIG. 9, the focal line in the x direction (front focal line) and the focal line in the y direction (rearward) generated by the multi lens 42 are shown. The position interval in the optical axis direction with respect to the focal line. Here, as described above, the focus pull-in range Sji is made desirable by giving the return magnification M wavelength selectivity by the phase conversion unit 43. FIG. 9 schematically shows that the condensing position Px in the x direction is different from the condensing position Py in the y direction due to astigmatism provided by the multilens 42, that is, an astigmatic difference Δ is generated. FIG. Here, the x direction and the y direction are directions determined by the arrangement of the multi-lens 42 and are so-called astigmatism directions.

On the other hand, the astigmatic difference Δ and the return path magnification M have a relationship as shown by the following equation (2) with the spot radius R _pd on the light receiving unit 40 such as a photodiode as shown in FIG. In this equation (2), the magnification to the front focal line is M. Note that LT in FIG. 10 indicates a composite lens in which elements having a condensing function in the optical system in the return path, that is, the objective lens 34, the collimator lens 37, the phase conversion element 44, and the multilens 42 are combined.

In Expression (2) and FIG. 10, NA represents the numerical aperture of the objective lens 34, and _fol represents the focal length of the objective lens 34. X represents the distance in the optical axis direction from the front focal line to the position where the spot is circular. Then, by transforming this equation (2), the following equation (3) is obtained.

The size of the spot radius R _pd on the light receiving unit 40 used in the equations (2) and (3) is the light beam on the light receiving unit 40 of the first wavelength reflected by the first optical disk such as BD. the spot radius _{R pd1 is,} R pd1 = about 42.5~50μm is desirable, spot radius _{R pd2} on the light-receiving portion 40 of the second wavelength of the light beam reflected by the second optical disk such as a DVD, R _It is desirable that pd2 is about _{37.4 to} 47.5 μm, and the spot radius R _pd3 of the light beam having the third wavelength reflected by the third optical disk such as CD is R _pd3 = 32.5 to About 42.5 μm is desirable. Moreover, following Formula (4) is obtained from Formula (1) and Formula (3).

Therefore, it is necessary to obtain M so as to satisfy this equation (4), and the range of M is determined as described later. The results of calculating “R _pd ”, “Sji”, and “Δ” in the case of the return magnification as shown in Table 1, and “NA” and “f _ol ” used for the calculation are shown in Table 2. As shown in Table 2, the present solution of BD: 17.7 times, DVD: 14.2 times, CD: about 13.5 times is reasonable, and the pull-in range BD: 3.2 μm, DVD: 5 0.1 μm, CD: about 5.8 μm, and a desired range can be realized.

The focus pull-in range Sji shown in Table 2 is Sji _λ1 = 3.2 μm, Sji _λ2 = 5.1 μm, and Sji _λ3 = 5.8 μm. It will be a value that can demonstrate the performance. On the other hand, when the phase conversion element 44 is not provided, the return magnification is fixed at 18 times substantially uniformly with respect to the first to third wavelengths, and the focus pull-in range is any format. However, it becomes about 3 μm, and it becomes extremely difficult to put it to practical use. As described above, by arranging the phase conversion element 44 in the return optical system, a lens effect can be given only to a desired wavelength, thereby obtaining a desired magnification M and a desired pull-in range Sji. Can do.

  Further, the astigmatic difference Δ in Table 2 is substantially the same. This indicates that the astigmatic difference Δ does not have much wavelength dependency as described above. Then, paying attention to the fact that this astigmatic difference Δ has no wavelength dependence, if Δ at each wavelength is equal, the relationship of equation (5) needs to be established from equation (1).

Using this equation (5), for example, the focus pull-in range Sji _λ1 for the first optical disc is about Sji _λ1 = 3 μm, the focus pull-in range Sji _λ2 for the second optical disc is about Sji _λ2 = 5 μm, and the focus is on the third optical disc. In _order to make the pull-in range Sji _λ3 have a relationship of about Sji _λ3 = 6 μm, the return magnifications M _λ1 , M _λ2 , and M _λ3 for each wavelength are M _λ1 : M _λ2 : M _λ3 = 1 / ((3) ^{1 / 2} ): 1 / ((5) ^1/2 ): 1 / ((6) ^1/2 ) ≈1.00: 0.77: 0.71 It is necessary to adjust the relationship. The return magnifications M _λ1 , M _λ2 , and M _λ3 shown in Tables 1 and 2 substantially satisfy this relationship.

Further, from the relationship between the return magnifications M _λ1 , M _λ2 , and M _λ3 , the focal lengths f _pλ1 , f _pλ2 , and f _pλ3 for the light beams of the first to third wavelengths of the phase conversion element 44 at each wavelength are relationship _f pλ1> f pλ2, and it is necessary to satisfy the relationship of _{f pλ1> f pλ3.} In other words, as described above, the refractive powers P _λ1 , P _λ2 , and P _λ3 that the phase conversion element 44 imparts to the light beams having the first to third wavelengths are equal to each other, and P _λ1 <P _λ2 and P _λ1 < It is necessary to satisfy the relationship of P _λ3 .

Further, the relationship of the above-mentioned formula (4), the restrictions on the ranges of the spot radii R _pd1 , R _pd2 , R _pd3 on the light receiving part, the restriction that the astigmatic difference Δ needs to be substantially the same, and the desired Sji From the limitation of the range, a range suitable as the return magnifications M _λ1 , M _λ2 , and M _λ3 of the optical pickup 3 will be described.

Specifically, in order to obtain 1.5 ≦ Sji _λ1 ≦ 3.5 in the focus pull-in range described above, the value of Sij _λ1 every 0.1 and the return path magnification M _λ1 are 10.00 in this range. Table 3 shows Δ obtained by Equation (3) when R _pd1 is applied to _42.5 to 50 _μm from the value of M _λ1 every 0.25 in the range of ˜25.00 and Equation (4). When R _pd1 does not fall within this range, “0” is indicated. In Tables 3 to 5, each Sji value is shown in the horizontal direction, and each return magnification M value is shown in the vertical direction.

Similarly, in order to obtain 4.5 ≦ Sji _λ2 ≦ 5.5 in the focus pull-in range described above, the value of Sji _λ2 every 0.1 and the return path magnification M _λ2 are 10 in the range of 4 to 6 μm. A value obtained by the equation (3) when R _pd2 is 37.4 to _47.5 μm based on the value of M _λ2 every 0.25 in the range of .00 to 25.00 and the equation (4). When R _pd2 does not fall within this range, “0” is indicated.

Further, in _order to obtain 5.5 ≦ Sji _λ3 ≦ 6.0 in the above-described focus pull-in range, the value of Sji _λ3 and the return magnification M _λ3 every 0.1 in the range of 5 to ₇ μm are 10. Table 5 shows Δ obtained by the equation (3) when R _pd3 is applied to _32.5 to 42.5 _μm from the value of M _λ3 every 0.25 in the range of 00 to 25.00 and the equation (4). When R _pd3 does not fall within this range, “0” is indicated.

The Table 3 15.75 ≦ _M λ1 ≦ Suitable range M _.lambda.1 from 25.00 is obtained, is 12.50 ≦ _M λ2 ≦ 18.00 Suitable ranges of M _.lambda.2 obtained from Table 4 further, 11.50 ≦ _M λ3 ≦ 16.25 is obtained from Table 5 as appropriate range of M _{[lambda] 3.}

Further, as shown in Tables 3 to 5, a range of Δ is also obtained in a substantially close range at the first to third wavelengths, indicating that the above range is excellent. Here, it is possible to further improve the characteristics of the optical system by selecting a value with a close Δ value and determining the return magnification. The range of Sji _λ1 , Sji _λ2 , and Sji _λ3 described above is the same for the optical pickup 3 in which the objective lens 34 and the light receiving unit 40 as described above are common to the three wavelengths and the return magnification is adjusted by the phase conversion unit 43. This is an appropriate range for obtaining an appropriate focus pull-in range.

Here, using the ranges of Sji _λ1 , Sji _λ2 , and Sji _λ3 , the relationship between the return path magnifications M _λ1 , M _λ2 , and M _λ3 that are ranges suitable as the return path magnification of the optical pickup 3 from a different viewpoint from the above. Explain that there is.

That is, here, Sji _λ1 is 2.5 to 3.5, Sji _λ2 is 4.5 to 5.5, Sji _λ3 is 5.5 to 6.5, and the formula Each relationship is derived based on (5). That is, since (4.5 / 3.5) ^1/2 ≦ M _λ1 / M _λ2 ≦ (5.5 / 2.5) ^1/2 , 1.13 in the return magnifications M _λ1 and M _λ2 A relationship of ≦ M _λ1 / M _λ2 ≦ 1.48 is obtained as an appropriate range. In addition, since (5.5 / 3.5) ^1/2 ≦ M _λ1 / M _λ3 ≦ (6.5 / 2.5) ^1/2, at the return magnifications M _λ1 and M _λ3 1.25 The relationship of ≦ M _λ1 / M _λ3 ≦ 1.61 is obtained as an appropriate range.

The desired return magnifications M _λ1 , M _λ2 , and M _λ3 as described above are the focal lengths f _pλ1 , f _pλ2 , and f _pλ3 for the light beams of the respective wavelengths of the phase conversion unit 43, the phase conversion unit 43, and the collimator lens. This can be realized by adjusting the intervals t _p1 , t _p2 , and tp ₃ with _respect to 37.

Here, by _adjusting the focal lengths f _pλ1 , f _pλ2 , and f _pλ3 of the phase conversion unit 43 for each wavelength and the distances t _p1 , t _p2 , and tp ₃ between the phase conversion unit 43 and the collimator lens 37, the desired _values are obtained. The points where the return magnifications M _λ1 , M _λ2 and M _λ3 are obtained will be described.

First, a magnification calculation method for a general optical system composed of a plurality of lenses will be described. The magnification M of an optical system composed of a plurality of lenses is known to be the product of the division (S _on / S _in ) of the image point S _in and the object point S _on of each lens as shown in equation (6). Yes. Here, n indicates an image point or an object point of the nth lens (n = 1, 2,... N), and N indicates the number of lenses. When this is applied to the optical pickup 3, the phase conversion unit 43 of the phase conversion element 44 can also be included as a lens, n = 1 is the objective lens 34, n = 2 is the collimator lens 37, and n = 3. Is the phase conversion unit 43, and n = 4 (= N) indicates the multi-lens 42.

Further, from the image point S _{in of} a certain nth lens and the distance t _n between the nth lens and the (n + 1) th lens, (n + 1) The object point S _{o (n + 1)} of the n th lens is obtained, and the relationship as shown in the equation (8) is established between the image point S _in of the n th lens, the object point S _on and the focal length f _n. It is known that the formula holds.

From these formulas (6) to (8), the focal lengths f _pλ1 , f _pλ2 and f _pλ3 of the phase conversion element 44 and the distances t _p1 , t _p2 and t _p3 between the phase conversion element 44 and the collimator lens 37 are obtained. Thus, it is shown that the return path magnifications M _λ1 , M _λ2 , and M _λ3 can be changed and adjusted. That is, in the case where the phase conversion element 44 is not provided as described above, the phase conversion element 44 having a lens effect with respect to the second and third wavelengths as described above for a system having a return magnification of 18 times. By providing this, the return magnifications M _λ2 and M _{λ3 of} 13 to 14 times are obtained.

  Next, points to be considered when determining a specific shape of the phase conversion unit 43 provided on one surface of the phase conversion element 44 will be described.

  The phase conversion unit 43 of the phase conversion element 44 has a stepped phase structure as shown in FIG. 5 described above. Specifically, for example, the phase difference as shown in FIG. 3 to give to the wavelengths λ1, λ2, and λ3. That is, FIG. 11 shows the acquired target phase by the phase structure of the phase conversion unit 43. In FIG. 11 and FIG. 14 described later, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the radius. The phase difference amount required for the light beam of each wavelength for each position in the direction is normalized by the wavelength λ (= λ1, λ2, λ3). Note that the phase step shown in FIGS. 11 and 14 has a target phase difference within the range of 0 to λ. In FIG. 11 and FIGS. 12 to 16 to be described later, the case where the effective diameter of the phase conversion element arranged in the condensed light flux is 1 mm or less is shown. However, the effective diameter is 1 mm according to the arrangement position. If it exceeds, the acquisition target phase and the like of the part exceeding the above may be calculated.

  Here, since the acquired target phase Lλ11 for the first wavelength λ1 is set not to give a refractive power to the light beam of the first wavelength here, the center in the radial direction (horizontal axis: 0). 0 to the outermost circumference (horizontal axis: 1), and the acquired target phases Lλ21 and Lλ31 for the second and third wavelengths λ2 and λ3 are predetermined for the light beams of the second and third wavelengths. Since the objective is to provide refracting power and the phase state of the wavefront to which refracting power is generally applied is a curve proportional to the square of the radius, each curve proportional to the square of the radius is It is represented by a line folded at wavelengths λ2 and λ3.

In general, it is known that the phase difference φ (λ) imparted to the light beam having a predetermined wavelength for each position in the radial direction by the phase structure satisfies the following equation (9). In Equation (9), C ₁ , C ₂ ... Indicate optical path difference function coefficients, r indicates a radius, and λ ₀ indicates a design wavelength. Here, λ ₀ = λ ₁ .

Further, in general, the optical path difference function coefficient C _i changes according to the phase shape to be given, that is, the straight lines Lλ11, Lλ21, and Lλ31 that indicate the acquired target phase differences shown in FIG. Here, the phase desired to be imparted by this phase structure is a phase difference for achieving a state equivalent to the application of refracting power (power), and a phase state equivalent to the application of such a refracting power is set. Therefore, the it is sufficient attention is paid only to C ₁ of the optical path difference function coefficients C _i are known. Further, between the focal length f _p for a given wavelength of the light beam such phase structures are formed element (phase conversion element 44), and C _1, that there is a relationship shown in equation (10) It has been known. Here, in Equation (10), λ ₀ indicates the design wavelength, and λ indicates the wavelength of the light beam that actually passes (the light beam having a predetermined wavelength for calculating the focal length). . From this, C ₁ is determined from the focal length f _p described above.

As shown in FIG. 12, the optimum phase structure for giving the acquired target phases to the light beams of the wavelengths λ1, λ2, and λ3 is calculated by the acquired target phases Lλ11, Lλ21, and Lλ31 as shown in FIG. In FIG. 12 and FIG. 15 described later, the horizontal axis indicates the position (mm) in the radial direction, and the vertical axis indicates the height of the phase structure with respect to the reference plane for each position in the radial direction. Here, the phase structure as shown in FIG. 12 gives power in the positive direction (phase difference coefficient C ₁ = 5.67 × 10 ⁻³ ) for the light beams of the second and third wavelengths λ 2 and λ 3. A phase difference to be given is set, and the return magnifications M _λ2 and M _λ3 for the second and third wavelengths are converted to a desired value of about 13 to 14 times. On the other hand, for the light beam with the first wavelength λ1, the same phase difference as 0, that is, by giving a phase difference that is an integral multiple of λ1, It does not act on the light beam, and the return magnification M _λ1 with respect to the first wavelength is set to about 18 times as desired.

Here, a time not to move the collimator lens 37 from the state shown in Table 1 above, the change in the return magnification for the second and third wavelength when changing the C ₁ of the phase converter 43 in Table 6 .

As shown in Table 6, so that the f and M are changed by C ₁ is changed. Furthermore, as shown in Table 6, it can be seen that C ₁ = 5.67 × 10 ⁻³ is an appropriate value. As described above, the appropriate value of C ₁ varies in a complicated manner depending on other lenses in the optical system, the distance between the lenses, and the like based on the above-described series of formulas. By determining target M and f from the relationship, it is possible to calculate appropriate values.

Further, the depth d for each position in the radial direction of the phase structure of the phase conversion element 44 is designed according to the following guidelines. If the desired phase difference at each wavelength is φ1, φ2, φ3 (rad), the diffraction grating refractive indexes n1, n2, n3 at each wavelength, and the refractive index n0 in the air, the following equations (11) to (11) (13) is established. However, in these formulas (11) to (13), m ₁ , m ₂ , and m ₃ represent positive or negative arbitrary integers or 0. In this embodiment, since φ1≈0, it is necessary to satisfy the relationship such as the equation (14), and the optimum d satisfying the equations (12) and (13) may be obtained.

  Here, in practice, the height of d is limited in manufacturing, so there is no complete freedom of selection. However, here, for example, it is assumed that the manufacturing limit is d <10 μm. Yes. At this time, by setting d that gives the closest values to the desired phase differences φ1, φ2, and φ3, a phase structure as shown in FIG. 12 is obtained. It should be noted that d <10 μm is not limited as long as manufacturing problems are solved.

  FIG. 13 shows the acquired phase amount obtained by the phase structure as shown in FIG. In FIG. 13 and later-described FIG. 16, the horizontal axis indicates the radial position (mm), and the vertical axis indicates the phase difference amount given to each radial position by the phase structure as shown in FIGS. Is normalized by the wavelength λ (= λ1, λ2, λ3). In FIG. 13 and FIG. 16, Lλ11′Lλ12 ′ indicates an acquired phase imparted to the light beam having the first wavelength by this phase structure, and Lλ21 ′ and Lλ22 ′ have the second wavelength by this phase structure. The acquired phase given to the light beam is shown, and Lλ31 ′ and Lλ32 ′ show the acquired phase given to the light beam of the third wavelength by this phase structure. As shown in FIG. 13, the phase difference amount provided by the phase structure as shown in FIG. 12 is roughly the same as the initially assumed target phase difference amount as shown in FIG. Therefore, it is possible to give the assumed refractive power to the light beams of the second and third wavelengths respectively corresponding to the second and third optical disks (DVD, CD).

According to the above-described Table 1 calculated according to the first embodiment, it can be confirmed again that any value falls within a practically reasonable range and a desired return magnification difference is obtained. Thus, desired target focus pull-in ranges Sji _λ1 , Sji _λ2 , and Sji _λ3 are satisfied.

  In the first embodiment described above, the phase difference given to the light beams of the second and third wavelengths corresponding to the second and third optical disks (DVD, CD, etc.) is configured to be the same. Alternatively, a phase conversion unit may be configured in which acquisition target phases based on different refractive powers are set and a phase structure is formed so as to give the acquisition target phase. In general, if the phase difference is the same, the focal length f is proportional to the reciprocal of each wavelength from the relationship of the above equation (10), but this restriction is removed by changing the acquired target phase difference amount. Furthermore, the degree of freedom for selecting the phase structure is increased.

  Further, in this embodiment, the phase structure consisting of a predetermined step gives a phase conversion effect corresponding to the refractive power to the second and third wavelengths λ2 and λ3, and refracts only to the light beam of the first wavelength λ1. Although the phase conversion effect corresponding to the force is not given, this may be configured to have such a phase conversion function by being composed of materials having two kinds of refractive indexes.

  In the first embodiment, power (refractive power) is given to the light beams having the second and third wavelengths λ2 and λ3 to obtain a desired return magnification. However, the power is negative with respect to the first wavelength λ1. The magnification may be set to a desired value by giving the power (refractive power).

  Next, the optical pickup 3 is provided only in the optical path of the return path optical system, and a phase difference is imparted to each of the first to third wavelength light beams, and the other is applied to at least one light beam. As a phase conversion unit that converts the phase state of the wavefront to a state substantially equivalent to applying a refractive power different from that of the light beam, a negative refractive power is applied to the light beam of the first wavelength described above, and the second In the case where the phase conversion unit 43B for converting the phase state of the wavefront of the light beam of each wavelength is provided in a state substantially equivalent to that in which almost no refractive power is applied to the light beam of the third wavelength, the specific numerical values are What has been described will be described as Example 2.

<Example 2>
In the second embodiment, the return magnifications M _λ2 and M _λ3 are designed to be about 14 times with respect to the light beams of the second and third wavelengths λ2 and λ3 when this element is not provided. A desired refractive power (negative power) is given only to the light beam of the first wavelength λ1, and the return magnification M _λ1 is aimed to be about 18 times for this light beam.

  FIG. 14 shows a specific acquisition target phase similar to that shown in FIG. 11 in the second embodiment, and FIG. 14 shows the acquisition target phase shown in FIG. FIG. 15 shows the optimum phase structure given to FIG. 15, and FIG. 16 shows the acquired phase amount obtained by the phase structure shown in FIG. 15 as in FIG. Here, all of the acquisition target phase, the formation step (height), and the acquisition phase of Example 2 (giving negative refractive power) are compared with Example 1 (giving positive refractive power). Therefore, the inverted value is shown.

  As shown in FIG. 14, the acquired target phase Lλ12 for the first wavelength λ1 has a target to give a predetermined refractive power to the light beam of the first wavelength, and generally has a refractive power. Since the phase state of the applied wavefront becomes a curve proportional to the square of the radius, the curve proportional to the square of the radius is represented by a line that is folded at the wavelength λ1. Here, a negative refractive power is applied to the first wavelength, but an inverted value is shown. In addition, since the acquisition target phases Lλ22 and Lλ32 for the second and third wavelengths λ2 and λ3 are targeted to provide no refractive power to the light beams of the second and third wavelengths, It is 0 from the center to the outermost periphery.

  As shown in FIG. 16, the phase difference amount provided by the phase structure as shown in FIG. 15 is roughly the same as the initially obtained target phase difference amount as shown in FIG. To the assumed optical power can be applied to the light beam having the first wavelength corresponding to the first optical disc (BD).

Further, in this way, the “outward magnification”, “return magnification”, “collimator lens position”, “lens stroke amount of the collimator lens”, and “phase” of the second embodiment in which each optical component such as the phase conversion element 44B is configured. Table 7 shows the phase difference coefficient C ₁ of the conversion element.

As shown in Table 7, the phase conversion unit 43B of the phase conversion element 44B gives a negative refractive power to the light beam having the first wavelength λ1, and the return magnification M _λ1 is M _λ1. = 19.0 times. Further, the light beam having the second and third wavelengths λ2 and λ3 is not provided with refractive power and does not function as a function of changing the return magnification, and the return magnification M _λ2 while the collimator lens 37 is moved. , M _λ3 is M _λ2 = 14.6 times and M _λ3 = 14.6 times.

In such an example, the results of calculating “R _pd ”, “Sji”, and “Δ” in the case of the return magnification as shown in Table 7, and “NA” and “f _ol ” used for this calculation. Is shown in Table 8. As shown in Table 8, the current solution of BD: 19 times, DVD: 14.6 times, CD: 14.6 times is reasonable, and the pull-in range BD: 3.1 μm, DVD: 5.3 μm, It is possible to achieve a desired target focus pull-in range of CD: about 5.3 μm.

  In the second embodiment, the phase differences given to the second and third light beams corresponding to the second and third optical discs are the same so that no refractive power is given. Although configured, an acquisition target phase based on different refractive powers may be set, and the phase conversion unit may be configured to form a phase structure that gives this acquisition target phase.

  In the first and second embodiments, either one of the light beam having the first wavelength and the light beam having the second and third wavelengths is configured so as not to impart refractive power, but is not limited thereto. For example, different refractive powers may be applied to each of the three types of wavelengths, that is, negative refractive power with respect to the first wavelength, and second and third wavelengths. On the other hand, it may be configured as a phase conversion unit formed with a phase structure that imparts positive refractive power.

  As shown in the first and second embodiments described above, in the optical pickup 3 which uses the light beams of three different wavelengths and uses the objective lens 34 and the light receiving unit 40 in common, A phase conversion unit 43 that converts the phase state of the wavefront to a state substantially equivalent to the application of a predetermined refractive power to a desired wavelength by applying a phase difference and converting the phase state of the wavefront. By having 43B, for example, a refractive power is not given to the light beam of the first wavelength and a predetermined positive refractive power is given to the light beams of the second and third wavelengths, or the first wavelength A predetermined negative refracting power is applied to the light beam and no refracting power is applied to the light beams of the second and third wavelengths, so that the optical magnification of the return optical system is set to a predetermined magnification for each wavelength used. Can It is possible to adapt the focus pull on each format.

  That is, the optical pickup 3 including the phase conversion unit 43 or the phase conversion unit 43B as described above has a desired focus in a configuration in which only one light receiving unit 40 is disposed with respect to the objective lens 34 that realizes three-wavelength compatibility. A pull-in range can be realized. The optical pickup 3 uses the objective lens 34 and the light receiving unit 40 in common, thereby realizing cost reduction and apparatus miniaturization. As described in the first and second embodiments, the optical pickup 3 can suppress the lens stroke amount of the collimator lens 37 to be sufficiently small, and can reduce the size of the optical pickup 3.

  Further, in the optical pickup 3, a collimator lens 37 as a divergence angle conversion element is moved to a predetermined position in the optical axis direction for each type of light beam emitted from the first to third wavelength light beams. By changing the state of the light beam having the first to third wavelengths according to the moved position in the optical axis direction, the light beam of each wavelength is condensed on the same light receiving surface of the light receiving unit 40. The function of the phase conversion element 44 described above is used to make the return optical system of each wavelength the desired magnification, and the compatibility between the common objective lens 34 and the common light receiving unit 40 corresponding to the three wavelengths is achieved. It is possible to achieve both the effect of realizing.

  As described above, the optical pickup 3 realizes appropriate three-wavelength compatibility including the focus pull-in range and the like by the common objective lens 34 and the common light receiving unit 40, and the optical components of the objective lens 34 and the photodetector 41. Not only to reduce the number of parts, but also to share various optical parts arranged on the optical path between them, realizing miniaturization and cost reduction, and by sharing parts It is possible to improve the characteristics as an optical pickup by preventing the influence when there is a variation in characteristics among individual components provided for each wavelength.

  In addition, the optical pickup 3 realizes compatibility with three wavelengths by using one objective lens 34, which causes problems when using a plurality of objective lenses, such as a decrease in sensitivity of the actuator, This eliminates problems such as deterioration of characteristics when there is an error in the mounting angle of the objective lens to the actuator, and realizes good recording / reproducing characteristics. In addition, this optical pickup 3 realizes the three-wavelength compatibility by the single light receiving unit 40, which is a problem when providing a plurality of light receiving units (light receiving elements), and the configuration for routing a plurality of wirings is complicated. This eliminates the problem of obstructing or miniaturization, and realizes a simple configuration and miniaturization. Further, the optical pickup 3 as a whole reduces the number of components as described above, thereby reducing the number of adjustment steps required in manufacturing and realizing easy manufacturing and cost reduction.

  Next, the optical path of the light beam emitted from each emission part of the first and second light source parts 31 and 32 in the optical pickup 3 configured as described above will be described with reference to FIG. First, an optical path when information is read or written by emitting a light beam having a first wavelength to the first optical disc 11 will be described.

  Next, the optical path of the light beam emitted from each emission part of the first and second light source parts 31 and 32 in the optical pickup 3 configured as described above will be described with reference to FIG. In this description, an example in which the above-described phase conversion element 44 is used as the phase conversion element having the phase conversion unit constituting the optical pickup 3 will be described, and the case where the phase conversion element 44B is used. Since only the refractive power to be applied is different as described above, the description thereof is omitted. First, an optical path when information is read or written by emitting a light beam having a first wavelength to the first optical disc 11 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the first optical disc 11 emits a light beam having the first wavelength from the first emitting unit of the first light source unit 31.

  The light beam of the first wavelength emitted from the first emission unit is divided into three beams for detection of a tracking error signal or the like by the first grating 45 and is incident on the first beam splitter 38. The light beam having the first wavelength incident on the first beam splitter 38 is reflected by the separation surface 38a and emitted to the second beam splitter 39 side.

  The light beam of the first wavelength incident on the second beam splitter 39 is transmitted through the combined separation surface 39a and emitted to the collimator lens 37 side, the divergence angle is converted by the collimator lens 37, and ¼. A predetermined phase difference is given to the wave plate 47, reflected by the rising mirror 48, and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is moved to the first position by the collimator lens driving means 49 and controlled so as to emit the light beam having the first wavelength in a predetermined state.

  The light beam having the first wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident side surface. As described above, the beams are emitted so that the predetermined diffraction orders are dominant, and are incident on the objective lens 34 of the condensing optical device 36. The light beam of the first wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a predetermined aperture restriction state.

  Since the light beam having the first wavelength incident on the objective lens 34 is incident at a divergence angle such that the light beam that has passed through each of the regions 51, 52, and 53 can reduce spherical aberration, the objective lens 34 The light is appropriately condensed on the signal recording surface of the first optical disc 11.

  The light beam collected by the first optical disk 11 is reflected by the signal recording surface, and passes through the objective lens 34, the diffractive optical element 35, the rising mirror 48, the quarter wavelength plate 47, and the collimator lens 37, The light is transmitted through the combining / separating surface 39a of the second beam splitter 39, transmitted through the separating surface 38a of the first beam splitter 38, and emitted to the phase conversion element 44 side.

The light beam having the first wavelength branched from the optical path of the forward light beam by the first and second beam splitters 38 and 39 passes through the phase conversion element 44 without being affected by the refractive power, Astigmatism and a predetermined refractive power are applied by the lens 42, and the light is focused on the light receiving surface of the light receiving unit 40 of the photodetector 41 and detected. At this time, the return magnification M _λ1 in the return optical system from the first optical disk is not affected by the refractive power of the light beam of the first wavelength by the phase conversion element 44, and the second and third described later. Since the light beam with the wavelength is given a positive refractive power by the phase conversion element 44, the value is larger than the return magnifications M _λ2 and M _λ3 described later.

  Next, an optical path when information is read or written by emitting a light beam of the second wavelength to the second optical disc 12 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the second optical disc 12 emits a light beam having the second wavelength from the second emitting unit of the second light source unit 32.

  The light beam of the second wavelength emitted from the second emission part is divided into three beams for detection of a tracking error signal or the like by the second grating 46 and is incident on the second beam splitter 39. The light beam of the second wavelength incident on the second beam splitter 39 is reflected by the combined separation surface 39a, is emitted to the collimator lens 37 side, the divergence angle is converted by the collimator lens 37, and the quarter wavelength. A predetermined phase difference is given to the plate 47, reflected by the rising mirror 48, and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is controlled to be moved to the second position by the collimator lens driving means 49 and to emit the light beam having the second wavelength in a predetermined state.

  The light beam having the second wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident-side surface. The beams are emitted so that the predetermined diffraction orders are dominant as described above, and are incident on the objective lens 34 of the condensing optical device 36. The light beam of the second wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a state where an aperture limiting effect is obtained by being incident on the objective lens 34. Has been.

  Since the light beam having the second wavelength incident on the objective lens 34 is incident at a divergence angle so that the light beam that has passed through the first and second diffraction regions 51 and 52 can reduce spherical aberration, The objective lens 34 is appropriately focused on the signal recording surface of the second optical disk 12.

The return path of the light beam reflected by the signal recording surface of the second optical disk 12 is the same as that of the light beam having the first wavelength described above, and is therefore omitted. However, at this time, the return magnification M _λ2 in the return optical system from the second optical disk is given a positive refractive power by converting the phase state of the wavefront of the light beam of the second wavelength by the phase conversion element 44. Therefore, the value is smaller than the return magnification M _λ1 described above. Further, since the collimator lens 37 is moved to the second position, the phase conversion element 44 gives a different refractive power from the case of the first wavelength. However, as described with reference to FIG. Furthermore, the position of the condensing point can be set to the same position as that of the first wavelength, that is, the return light beam can be reliably received and detected by the common light receiving unit 40.

  Next, an optical path when information is read or written by emitting a light beam of the third wavelength to the third optical disc 13 will be described.

  The disc type discriminating unit 22 that discriminates that the type of the optical disc 2 is the third optical disc 13 emits a light beam having the third wavelength from the third emitting unit of the second light source unit 32.

  The light beam of the third wavelength emitted from the third emission unit is divided into three beams for detection of a tracking error signal or the like by the second grating 46 and is incident on the second beam splitter 39. The light beam of the third wavelength incident on the second beam splitter 39 is reflected by the combined separation surface 39a, is emitted to the collimator lens 37 side, the divergence angle is converted by the collimator lens 37, and the quarter wavelength. A predetermined phase difference is given to the plate 47, reflected by the rising mirror 48, and emitted to the diffractive optical element 35 side of the condensing optical device 36. At this time, the collimator lens 37 is controlled to be moved to the third position by the collimator lens driving means 49 and to emit the light beam having the third wavelength in a predetermined state.

  The light beam having the third wavelength incident on the diffractive optical element 35 is transmitted through each region by the first to third diffraction regions 51, 52, and 53 of the diffractive portion 50 provided on the incident side surface. The beams are emitted so that the predetermined diffraction orders are dominant as described above, and are incident on the objective lens 34 of the condensing optical device 36. The light beam of the third wavelength emitted from the diffractive optical element 35 is not only in a predetermined divergence angle state but also in a state in which an aperture limiting effect is obtained by entering the objective lens 34. Has been.

  Since the light beam having the third wavelength incident on the objective lens 34 is incident in a state of a divergence angle so that the light beam that has passed through the first diffraction region 51 can reduce spherical aberration, the objective lens 34 The light is appropriately condensed on the signal recording surface of the third optical disc 13.

The optical path of the return path of the light beam reflected by the signal recording surface of the third optical disc 13 is the same as that of the light beam having the first wavelength described above, and is therefore omitted. However, at this time, the return magnification M _λ3 in the return optical system from the third optical disk is given a positive refractive power by converting the phase state of the wave front of the light beam of the third wavelength by the phase conversion element 44. Therefore, the value is smaller than the return magnification M _λ1 described above. Further, since the collimator lens 37 is moved to the third position, a refractive power different from that in the case of the first wavelength is given by the phase conversion element 44, but as described with reference to FIG. In addition, the position of the condensing point can be set to the same position as that of the first wavelength, that is, the returning light beam can be reliably received and detected by the common light receiving unit 40.

  The optical pickup 3 to which the present invention is applied includes first to third emission units that emit light beams having first to third wavelengths, and first to third rays that are emitted from the first to third emission units. A condensing optical device 36 for condensing a light beam of a wavelength on the signal recording surface of the corresponding optical disc, and being movable in the optical axis direction, the first to the first in accordance with the moved position in the optical axis direction A collimator lens 37 as a divergence angle conversion element for converting the divergence angle of the light beam having the wavelength 3 to a predetermined divergence angle, and the optical paths of the returned light beams having the first to third wavelengths reflected by the optical disk. The first and second beam splitters 38 and 39 as optical path separating means for separating the optical paths of the respective light beams emitted from the first to third emitting portions, and the first and second beam splitters 38 and 39 are used. Separated from each outbound light Between a photodetector 41 having a common light receiving unit 40 between three wavelengths for receiving light beams having the first to third wavelengths, and a first beam splitter 38 and a light receiving unit 40 as optical path separating means. Provided to each of the light beams having the first to third wavelengths, and substantially the same as providing a refractive power different from that of the other light beams to at least one of the light beams. By providing the phase converters 43 and 43B that convert the phase state of the wavefront into the state, a common optical device having the common condensing optical device 36 and the common light receiving unit 40 corresponding to such three types of used wavelengths. The system is used to condense a light beam having a wavelength corresponding to each optical disc, and the reflected light from the optical disc is detected to reduce the size of the apparatus and simplify the configuration. Information on the optical disc Signal recording and / or reproduction can be performed, and the optical magnification (return magnification) of the return path is optimized by the phase converters 43 and 43B in accordance with the respective wavelengths used in such a common optical system. As a result, it is possible to set a focus pull-in range corresponding to the format of each optical disc, and to further exhibit compatibility with each optical disc, thereby simplifying the configuration. And miniaturization of the apparatus, and compatibility with each optical disc is exhibited to realize good recording and / or reproduction.

Further, in the optical pickup 3, the above-described phase conversion units 43 and 43B are provided on one surface of the phase conversion element 44 provided between the condensing optical device 36 and the light receiving unit 40. The refractive power P _{λ2 applied} to the light beam having the second wavelength is larger than the refractive power P _{λ1 applied} to the light beam having the first wavelength (P _λ1 <P _λ2 ). Refraction imparted to the light beam of the third wavelength from the refractive power P _λ1 imparted to the light beam of the first wavelength while converting the phase state of the wavefront of the light beam of the first and second wavelengths. In other words, by the configuration for converting the phase states of the light beams of the first and third wavelengths into a state substantially equivalent to the state where the force P _λ3 becomes large (P _λ1 <P _λ3 ), Focal length f for the third wavelength light beam _{pλ1, f} pλ2, _f pλ3 is, _{f pλ1>} relationship _{f pλ2,} and _{f pλ1>} With the configuration as to satisfy the relationship of _{f pλ3,} return magnification at the first wavelength is a wavelength used for the first optical disk M _.lambda.1 On the other hand, it is possible to reduce the return magnifications M _λ2 and M _λ3 at the second and third wavelengths, which are used wavelengths of the second and third optical discs, respectively, thereby adapting the focus pull-in range to each format. Thus, it is possible to achieve a desired value, and thus, it is possible to realize a simple recording and / or reproduction by realizing the simplification of the configuration and the miniaturization of the apparatus and the compatibility with each optical disc.

  Further, the optical pickup 3 converts the divergence angle of the incident light beams having the first to third wavelengths between the first beam splitter 38 and the light receiving unit 40 to condense on the light receiving unit 40. Either or both of the angle conversion function and the astigmatism function that gives astigmatism to the incident first to third wavelength light beams to obtain a focus error signal and emits the light to the light receiving unit 40 side. In addition to the above-described effects, the structure of the optical pickup is further simplified by providing a multi-lens having one function and the phase conversion unit 43 being integrally formed on one surface of the multi-lens. And miniaturization.

The optical pickup 3 also includes a condensing optical device 36, a collimator lens 37, and a phase conversion element 44 having a phase conversion unit 43 that guide the light beams having the first to third wavelengths reflected by the optical disc to the light receiving unit 40. The return magnification for the light beam of the first wavelength by the return path optical system including the multi-lens 42 is M _λ1, and the return magnification for the light beam of the second wavelength by the return path optical system is M _λ2. When the return magnification for the light beam of the third wavelength is M _λ3 , the relationship of 15.75 ≦ M _λ1 ≦ 25.00, the relationship of 12.50 ≦ M _λ2 ≦ 18.00, and 11.50 ≦ M _λ3 Since the relationship of ≦ 16.25 is satisfied, the focus pull-in range can be set to a desired value suitable for each format. To demonstrate better recording and reproduction characteristics for click, thereby realizing that exhibits excellent compatibility than for each optical disc.

  In addition, since the objective lens 34 can be made common to the three wavelengths, the optical pickup 3 can prevent the occurrence of problems such as a decrease in sensitivity due to an increase in the weight of the movable part in the actuator. In addition, the optical pickup 3 to which the present invention is applied can sufficiently reduce the spherical aberration, which is a problem when using the common objective lens 34 for three-wavelength compatibility, by the diffractive portion 50 provided on one surface of the optical element. In addition, it is possible to prevent the problems such as the alignment between the diffraction parts when the diffractive parts for reducing spherical aberration are provided on a plurality of surfaces as in the prior art, and the decrease in diffraction efficiency due to the provision of the plurality of diffractive parts, Simplify the assembly process and improve light utilization efficiency. Further, the optical pickup 3 to which the present invention is applied has a diffractive portion 50 in place of the objective lens 34 and the diffractive optical element 35 by enabling the configuration in which the diffractive portion 50 is provided on one surface of the optical element as described above. The objective lens 34B can be configured so that the diffractive portion 50 is integrated with the objective lens, thereby further simplifying the configuration, reducing the weight of the movable portion of the actuator, and simplifying the assembly process. In addition, the light utilization efficiency is improved.

  Further, the optical pickup 3 not only realizes three-wavelength compatibility by the diffractive portion 50 provided on one surface of the diffractive optical element 35 described above, but also apertures corresponding to three types of optical disks and three types of light beams. The number of apertures can be limited by this, so that it is not necessary to provide an aperture limitation filter or the like, which has been necessary in the past, or adjustment when arranging it, and the configuration is simplified, downsized, and low in cost. Realize.

  An optical disc apparatus 1 to which the present invention is applied includes a driving unit that holds and rotates an optical disc arbitrarily selected from three types of first to third optical discs having different formats such as the thickness of a protective layer, and the driving And an optical pickup that records and / or reproduces information signals by selectively irradiating a plurality of light beams having different wavelengths onto an optical disk that is rotationally driven by the above-described optical pickup. 3 is common to three types of optical discs having different operating wavelengths by the diffractive portion provided on one surface of the optical element on the optical path of the light beam having the first to third wavelengths. A single objective lens 34 can be used to appropriately collect the corresponding light beams on the signal recording surface. It is possible to simplify the configuration and reduce the size of the device by using common parts, and to make it possible to achieve an appropriate focus pull-in range corresponding to the format of each optical disc by the phase conversion unit 43. 3 wavelength compatibility is achieved by obtaining a good servo signal and obtaining good recording / reproducing characteristics.

1 is a block circuit diagram showing an optical disc apparatus to which the present invention is applied. It is an optical path diagram showing an optical system of an optical pickup to which the present invention is applied. It is a figure for demonstrating the diffractive optical element of the condensing optical device which comprises the optical pickup to which this invention is applied, (a) is a top view of a diffractive optical element, (b) is a diffractive optical element of FIG. It is sectional drawing. It is a figure for demonstrating the example of the condensing optical device which comprises the optical pick-up to which this invention is applied, (a) is comprised with the diffraction optical element which has a diffraction part in the surface of an incident side, and an objective lens. It is sectional drawing which shows the condensing optical device of an example, (b) is sectional drawing which shows the condensing optical device of the example comprised by the objective lens by which the diffraction part was integrally formed in the surface of the incident side. is there. It is a figure for demonstrating the phase conversion part which comprises the optical pick-up to which this invention is applied, (a) is a top view of the phase conversion element provided with the phase conversion part, (b) is phase conversion. It is sectional drawing of an element, (c) is an expanded sectional view of the phase conversion element typically shown while expanding the phase structure of a phase conversion part. It is a figure for demonstrating the function of the phase conversion part of the phase conversion element which comprises the optical pick-up to which this invention is applied, (a) is that the incident light beam of the 1st wavelength receives the influence of a phase conversion part. (B) is a state in which light beams of the second and third wavelengths incident in the same state are emitted with a positive refractive power applied by the phase conversion unit. FIG. FIG. 7 is a diagram for explaining that light beams having different wavelengths given different refractive powers by the phase conversion unit described in FIG. 6 are appropriately focused on the same light receiving surface in the optical pickup to which the present invention is applied. In (a), the light beam of the first wavelength is condensed at a predetermined condensing point through the collimator lens arranged at the reference position and the phase conversion unit described in FIG. (B) is a diagram showing the phase conversion unit described in FIG. 6 by the collimator lens in which the light beams of the second and third wavelengths are moved in the optical axis direction from the reference position. It is a figure which shows being condensed on the same condensing point as the light beam of the 1st wavelength when passing. It is a figure which shows the relationship between the defocus amount of an objective lens, and a focus error signal, and a focus drawing-in range. It is a figure explaining the astigmatism difference which arises by the astigmatism provided by a return optical system, and the condensing position of the x direction by passing through the multi lens which provides astigmatism, and the condensing position of ay direction It is a figure which shows typically the astigmatic difference which is the space | interval of these positions. It is a figure for demonstrating the predetermined relational expression in a return path optical system, and the numerical aperture and focal distance of an objective lens, the synthetic lens which synthesize | combined the optical component of a return path optical system, return path magnification, astigmatism, and on a light-receiving part It is a figure which shows a spot radius typically. It is a figure which shows the acquisition target phase amount for comprising the phase conversion part of Example 1 for every position of a radial direction. It is a figure for showing the optical phase change surface shape of a phase change part of Example 1, ie, a phase structure, and is a figure showing the height of this phase structure for every position of a radial direction. It is a figure which shows the acquisition phase amount obtained by the phase structure of Example 1 shown in FIG. 12 for every position of a radial direction. It is a figure which shows what inverted the acquisition target phase amount for comprising the phase conversion part of Example 2 for every position of a radial direction. It is a figure for showing the optical phase change surface shape of a phase change part of Example 2, ie, a phase structure, and is a figure showing what reversed the height of this phase structure for every position of a radial direction. It is a figure which shows what inverted the acquisition phase amount obtained by the phase structure of Example 2 shown in FIG. 15 for every position of a radial direction. It is a figure which shows the example of the optical system of the conventional optical pick-up, and is an optical path figure which shows the optical pick-up which has two or more light receiving elements.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical disk apparatus, 2 Optical disk, 3 Optical pick-up, 4 Spindle motor, 5 Feed motor, 9 Servo control part, 22 Disk type discrimination | determination part, 31 1st light source part, 32 2nd light source part, 34 Objective lens, 35 Diffraction Optical element, 36 condensing optical device, 37 collimator lens, 38 first beam splitter, 39 second beam splitter, 40 light receiving unit, 41 photodetector, 42 multi lens, 43 phase converting unit, 44 phase converting element, 45 First grating, 46 Second grating, 47 1/4 wavelength plate, 48 Rising mirror, 49 Collimator lens driving means, 50 Diffraction unit, 51 First diffraction region, 52 Second diffraction region, 53 First 3 diffraction regions

Claims (6)

In an optical pickup that records and / or reproduces an information signal by selectively irradiating a plurality of light beams having different wavelengths to an optical disc arbitrarily selected from a plurality of types of optical discs,
A first emission part for emitting a light beam of a first wavelength;
A second emission part for emitting a light beam having a second wavelength longer than the first wavelength;
A third emission part for emitting a light beam having a third wavelength longer than the second wavelength;
A condensing optical device for condensing the light beams of the first to third wavelengths on the signal recording surface of the corresponding optical disc,
It is arranged on the optical path between the first to third emission parts and the condensing optical device and is movable in the optical axis direction. A divergence angle conversion element that converts a divergence angle of a light beam having a wavelength of 3 to a predetermined divergence angle;
A photodetector having a common light receiving portion for receiving the light beams of the first to third wavelengths reflected by the optical disc;
Provided between the condensing optical device and the light receiving unit, each of which imparts a phase difference to the light beams having the first to third wavelengths, and another light beam to at least one light beam. An optical pickup comprising: a phase conversion unit that converts a phase state of a wavefront to a state substantially equivalent to applying a refractive power different from the above. The phase conversion unit is provided on one surface of a phase conversion element provided between the condensing optical device and the light receiving unit,
When the refracting power that refracts the incident light beam in the optical axis direction is a positive refracting power, the phase conversion element has a second refracting power that is applied to the light beam having the first wavelength. The phase state of the wavefronts of the light beams of the first and second wavelengths is converted into a state substantially equivalent to the state where the refractive power applied to the light beam of the first wavelength is increased, and the light beam of the first wavelength The phase states of the wavefronts of the light beams of the first and third wavelengths are converted to a state substantially equivalent to the state where the refractive power applied to the light beam of the third wavelength is larger than the refractive power applied to the light beam. The optical pickup according to claim 1.   The divergence angle conversion element is moved to a predetermined position in the optical axis direction for each type of light beam emitted from the light beams having the first to third wavelengths, and is moved to the moved optical axis direction position. 2. The optical pickup according to claim 1, wherein the light beam having each wavelength is condensed on the same light receiving surface of the light receiving unit by changing the state of the light beam having the first to third wavelengths accordingly. Further, a divergence angle conversion function for converting a divergence angle of the incident light beam having the first to third wavelengths and condensing the light beam on the light receiving unit between the condensing optical device and the light receiving unit, and / or Or a multi-lens having an astigmatism imparting function for imparting astigmatism to the incident light beams having the first to third wavelengths and emitting them to the light receiving unit side,
The optical pickup according to claim 1, wherein the phase conversion unit is integrally formed on one surface of the multi-lens. The first optical path by the return optical system including at least the condensing optical device, the divergence angle conversion element, and the phase conversion unit that guides the light beams having the first to third wavelengths reflected by the optical disc to the light receiving unit. The return magnification with respect to the light beam of the second wavelength is M _λ1 , the return magnification with respect to the light beam of the second wavelength by the return optical system is M _λ2, and the return magnification of the light beam with the third wavelength by the return optical system is _Is M _λ3 ,
2. The relationship of 15.75 ≦ _Mλ1 ≦ 25.00, the relationship of 12.50 ≦ _Mλ2 ≦ 18.00, and the relationship of 11.50 ≦ _Mλ3 ≦ 16.25 are satisfied. Optical pickup. Driving means for holding and rotating the optical disc arbitrarily selected from a plurality of types of optical discs;
In an optical disc apparatus comprising: an optical pickup that records and / or reproduces an information signal by selectively irradiating a plurality of light beams having different wavelengths to an optical disc that is rotationally driven by the driving means.
The optical pickup includes a first emission unit that emits a light beam having a first wavelength;
A second emission part for emitting a light beam having a second wavelength longer than the first wavelength;
A third emission part for emitting a light beam having a third wavelength longer than the second wavelength;
A condensing optical device for condensing the light beams of the first to third wavelengths on the signal recording surface of the corresponding optical disc,
It is arranged on the optical path between the first to third emission parts and the condensing optical device and is movable in the optical axis direction. A divergence angle conversion element that converts a divergence angle of a light beam having a wavelength of 3 to a predetermined divergence angle;
A photodetector having a common light receiving portion for receiving the light beams of the first to third wavelengths reflected by the optical disc;
Provided between the condensing optical device and the light receiving unit, each of which imparts a phase difference to the light beams having the first to third wavelengths, and another light beam to at least one light beam. An optical disc device comprising: a phase conversion unit that converts a phase state of a wavefront into a state substantially equivalent to a state where a different refractive power is applied.

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