WO2013183439A1

WO2013183439A1 - Optical pickup device

Info

Publication number: WO2013183439A1
Application number: PCT/JP2013/064054
Authority: WO
Inventors: 章一郎豊田
Original assignee: 三洋電機株式会社
Priority date: 2012-06-05
Filing date: 2013-05-21
Publication date: 2013-12-12
Also published as: JP2015156242A

Abstract

[Problem] To achieve further cost reduction when using a ½ wavelength plate or ¼ wavelength plate made of resin film. [Solution] An optical pickup device is characterised in that it comprises: a first laser light source that emits first laser light of a first wavelength; a second laser light source that emits second laser light of a second wavelength; an object lens; a ½ wavelength plate made of resin film provided on a common optical path between the aforementioned laser light source and the object lens; a beam splitter provided on a common optical path between the ½ wavelength plate and the object lens, that reflects incident laser light in the direction of the object lens with the phase of this laser light inverted; and a ¼ wavelength plate made of resin film provided on a common optical path between the beam splitter and the object lens. The ½ wavelength plate and the ¼ wavelength plate are formed so that, in the relationship of the wavelength of the incident laser light and the phase difference applied to the emitted laser light, both of these have a characteristic with a positive gradient or both of these have a characteristic with a negative gradient.

Description

Optical pickup device

The present invention relates to an optical pickup device that performs a read operation of a signal recorded on an optical recording medium and a signal recording operation on the optical recording medium.

In an optical pickup device that optically records and reproduces signals using an optical recording medium such as a DVD (Digital Versatile Disc) or CD (Compact Disc) optical disk, the recording density is obtained by a single optical pickup device. Are compatible with different DVDs and CDs.

Such an optical pickup device compatible with DVD and CD includes a first laser light source that emits laser light in a red wavelength band of 645 nm to 675 nm suitable for DVD, and a laser light in an infrared wavelength band of 765 nm to 805 nm suitable for CD. A multi-laser unit including a second laser light source that emits light is used to switch the laser light to be used in accordance with the optical disk.

An optical pickup device compatible with DVD and CD shares an objective lens with a ring-shaped diffraction grating, and diffracts each laser beam having a wavelength suitable for each optical disk of DVD and CD with this diffraction grating. The spherical aberration is corrected for each optical disc, and the quality of each laser beam applied to each optical disc is ensured.

The optical pickup device for DVD and CD can simplify the optical path by adopting the above-mentioned laser unit corresponding to the two wavelengths and a common objective lens.

Such an optical pickup device includes, for example, a laser diode, a half-wave plate, a diffraction grating, a half mirror, a photodetector for monitoring, a collimator lens, a quarter-wave plate, a rising mirror, an objective lens, an AS (AStigmatism). ) A plate and a photodetector are arranged on the optical path.

The laser diode selectively emits laser light having a red wavelength band of 645 nm to 675 nm and laser light having an infrared wavelength band of 765 nm to 805 nm.

The half-wave plate adds a phase difference of ½ wavelength (180 degrees) to the laser light emitted from the laser diode, and converts it into linearly polarized light in the S direction with respect to the reflecting surface of the half mirror. Output.

A half-wave plate used in an optical pickup device compatible with DVD and CD is incident in a band extending from a red wavelength band used for DVD to an infrared wavelength band used for CD (hereinafter also referred to as broadband). It is formed so as to add a half-wave phase difference to the laser light.

The diffraction grating diffracts the laser light and separates it into a main beam that is 0th-order light, a + 1st-order diffracted light, and two sub-beams that are -1st-order diffracted light.

The half mirror is disposed at a position where the laser beam transmitted through the diffraction grating is incident and inclined by 45 ° with respect to the optical axis of the laser beam, and is converted into S-polarized light by the half-wave plate. A control film that reflects most of the light and transmits most of the laser light polarized in the P direction is provided.

The monitoring photodetector is provided at a position where the laser light emitted from the laser diode is irradiated with the laser light that has passed through the control film of the half mirror. Detect intensity. The detection signal output from the monitoring photodetector is used to control the output of the laser light emitted from the laser diode.

The collimating lens is provided at a position where the laser beam reflected from the control film of the half mirror is incident, and converts the incident laser beam into parallel light.

The quarter-wave plate is provided at a position where the laser beam converted into parallel light by the collimating lens is incident. The quarter-wave plate converts linearly polarized light to circularly polarized light, and vice versa, by changing the phase of the incident laser light by a quarter wavelength (90 degrees), and conversely, from circularly polarized light to linearly polarized light. To do. The laser light emitted from the laser diode is converted from S-polarized light to circularly-polarized light on the outward path from the optical disk to the optical disk by the quarter-wave plate, and from circularly-polarized light to P-polarized light on the return path from the optical disk to the photodetector. The

A quarter-wave plate used in an optical pickup device compatible with DVD and CD is 1 in the incident laser beam in a band (broadband) from a red wavelength band used for DVD to an infrared wavelength band used for CD. It is formed so as to add a phase difference of / 4 wavelength.

The rising mirror is provided at a position where circularly polarized laser light transmitted through the quarter wavelength plate is incident, and is configured to reflect the incident laser light in the direction of the objective lens.

The objective lens irradiates the incident laser light as a spot on the signal recording layer provided on the optical disc by the focusing function of the objective lens.

The laser light applied to the signal recording layer is reflected by the signal recording layer.

The reflected light reflected by the signal recording layer of the optical disk is incident on the control film of the half mirror through the objective lens, the rising mirror, the quarter wavelength plate, and the collimating lens.

Since this reflected light is changed from circularly polarized light to linearly polarized light in the P direction by the phase changing function by the quarter wavelength plate, the reflected light passes through the control film of the half mirror. The reflected light that has passed through the control film is incident on the AS plate.

The AS plate is disposed obliquely with respect to the optical axis direction of the reflected light, and adds astigmatism used for focusing control to the reflected light.

The photodetector is configured to include a light receiving unit that receives the reflected light separated into three beams by the diffraction grating, and a reproduction signal for reading information recorded on the signal recording layer of the optical disc, A focus error signal for performing focusing control and a tracking error signal for performing tracking control are generated.

Such an optical pickup device is disclosed in Patent Document 1, for example.

Japanese Patent Laid-Open No. 9-204681

A half-wave plate or a quarter-wave plate is formed by forming a control film on the surface of a glass plate for adding a desired phase difference to incident laser light. The control film is formed so as to give a desired phase difference to the laser beam in a wide band from the red wavelength band used for DVD to the infrared wavelength band used for CD.

However, with the recent strong demand for cost reduction and weight reduction of optical pickup devices, the replacement of half-wave plates and quarter-wave plates with resin films that do not use glass plates is progressing.

However, a resin film that can be used as a half-wave plate or a quarter-wave plate has a narrow wavelength band for obtaining a desired phase difference with only one film, and the wavelength of the incident laser light changes. The phase difference of the emitted laser light also changes. In other words, a desired phase difference can be obtained only in a narrow band in which the wavelength of the laser light is in the vicinity of a predetermined wavelength (for example, a band covering only a red wavelength band used for DVD, or an infrared wavelength band used for CD). In the case of laser light having a wavelength outside that band, a desired phase difference cannot be obtained.

For this reason, in order to give a desired phase difference to the passing laser beam in a wide band from the red wavelength band of DVD to the infrared wavelength band of CD, a more expensive ½ wavelength obtained by laminating a plurality of films. This can be achieved by using a plate or a quarter-wave plate. As a result, the cost reduction effect due to the replacement of the half-wave plate or quarter-wave plate from glass to resin film is reduced. End up.

The present invention has been made in view of the above problems, and reduces the cost when a single-band or a narrow-band half-wave plate or quarter-wave plate made of a resin film having a smaller number of bonded sheets than the wide-band type is used. One purpose is to further promote

An optical pickup device according to one aspect includes a first laser light source that emits a first laser beam having a first wavelength, and a second laser light source that emits a second laser beam having a second wavelength longer than the first wavelength. An objective lens for irradiating the optical recording medium with the first laser light and the second laser light, and a resin film provided on a common optical path between the first laser light source, the second laser light source and the objective lens A half-wave plate manufactured on the common optical path between the half-wave plate and the objective lens, and the incident laser beam is obtained by inverting the phase of the laser beam. A beam splitter that reflects in the direction, and a quarter-wave plate made of a resin film provided on the common optical path between the beam splitter and the objective lens, the half-wave plate and the 1 / 4 wavelength plate In relation to the phase difference to be added to the laser beam emitted from the wavelength of the incident laser beam, either positive slope or both are formed so as to have a characteristic that a negative slope.

The other problems disclosed by the present application and the solutions thereof will be clarified by the description in the column of the embodiment for carrying out the invention and the description of the drawings.

Cost reduction can be further promoted when a half-wave plate or quarter-wave plate with a narrow band such as a resin film is used.

It is a figure which shows the structural example of the optical pick-up apparatus of this embodiment. It is a figure which shows the example of a characteristic of the half-wave plate of this embodiment. It is a figure which shows the example of a characteristic of the quarter wavelength plate of this embodiment. It is a figure which shows the example of a characteristic of the phase difference of the laser beam in the optical pick-up apparatus of this embodiment. It is a figure which shows the example of a characteristic of the phase difference of the laser beam in the optical pick-up apparatus of this embodiment. It is a figure which shows the example of a characteristic of the 1/2 wavelength plate different from this embodiment. It is a figure which shows the example of a characteristic of the phase difference of the laser beam in the optical pick-up apparatus different from this embodiment. It is a figure which shows the example of a characteristic of the phase difference of the laser beam in the optical pick-up apparatus different from this embodiment.

At least the following matters will become clear from the description of this specification and the accompanying drawings.

The optical pickup device 1 of this embodiment will be described with reference to FIGS. FIG. 1 is a diagram illustrating a configuration example of an optical pickup device 1 according to the present embodiment. FIG. 2 is a diagram illustrating a characteristic example of the half-wave plate 121 of the present embodiment. FIG. 3 is a diagram illustrating a characteristic example of the quarter-wave plate 14 of the present embodiment. 4 to 5 are diagrams showing examples of characteristics of the phase difference of the laser light in the optical pickup device 1 of the present embodiment.

In order to clarify the characteristics of the optical pickup device 1 of the present embodiment, the characteristics of the phase difference of the laser light when a half-wave plate different from the present embodiment is used are shown in FIGS. An example is shown.

== Configuration of the Embodiment ==
The optical pickup device 1 of the present embodiment is configured to support recording and playback of a DVD (Digital Versatile Disc) and to support recording and playback of a CD (Compact Disc).

The laser unit 11 emits laser light having a first wavelength in a red wavelength band of 645 nm to 675 nm suitable for DVD recording / reproduction, for example, a first wavelength of 660 nm (hereinafter also referred to as first laser light). And a second laser light source 112 that emits laser light having a second wavelength in the infrared wavelength band of 765 nm to 805 nm, for example, 784 nm (hereinafter also referred to as second laser light) suitable for CD recording / reproduction.

The laser unit 11 is a so-called multi-laser unit, and the first laser light source 111 and the second laser light source 112 are formed on the same semiconductor substrate.

The laser unit 11 emits the first laser light from the first laser light source 111 and emits the second laser light from the second laser light source 112. The laser unit 11 selectively emits the first laser beam and the second laser beam.

Hereinafter, when it is not necessary to distinguish between the first laser beam and the second laser beam, these are described together with the laser beam as appropriate.

Laser light emitted from the laser unit 11 is incident on the composite optical element 12. The composite optical element 12 includes a half-wave plate 121 and a diffraction grating 122.

The diffraction grating 122 separates the laser light into three beams of a 0th order light beam, a + 1st order diffracted light beam, and a −1st order diffracted light beam.

The half-wave plate 121 is provided on a common optical path between the first laser light source 111 and the second laser light source 112 and the half mirror 13, and has a half wavelength (180 degrees) with respect to the incident laser light. Generate and output a phase difference. The half-wave plate 121 has a narrow band characteristic.

Here, the narrow band is a laser that is output only when the wavelength of the incident laser light is a band that covers a red wavelength band used for DVD, for example, or a band that covers an infrared wavelength band used for CD. This means that a half-wave phase difference is added to the light.

For example, the half-wave plate 121 is ½ wavelength (180 degrees) with respect to the laser beam only when the incident laser beam is the first wavelength (for example, 660 nm) in the red wavelength band used for DVD, for example. ) Is generated and output. The half-wave plate 121 converts incident laser light into linearly polarized light in the S direction with respect to, for example, the reflecting surface of the half mirror 13.

Note that the half-wave plate 121 of the present embodiment is a narrow-band type configured by using a single resin film or a resin film having a smaller number of laminated sheets than the broadband type, and a laser is applied to the surface of the diffraction grating 122, for example, the diffraction grating 122 It is affixed to the surface on the light incident side. The half-wave plate 121 is configured using, for example, a polycarbonate film or Arton (registered trademark) film. The half-wave plate 121 is composed of one resin film having a thickness of 100 μm or less, for example, about 70 μm.

As described above, since the half-wave plate 121 can be configured by using a single half-wave plate 121 or a resin film having a smaller number of bonded sheets than the wide-band type, the cost of the half-wave plate 121 can be reduced. Therefore, cost reduction of the optical pickup device 1 can be promoted.

In addition, since the half-wave plate 121 of this embodiment is comprised using one resin film, as shown in FIG. 2, it is the position added to the wavelength of the incident laser beam, and the emitted laser beam. It is formed so as to have a characteristic that has a negative gradient in relation to the phase difference. That is, the phase difference added to the laser light transmitted through the half-wave plate 121 has a characteristic of decreasing as the wavelength of the incident laser light becomes longer.

Since the half-wave plate 121 of the present embodiment is configured using a single resin film, the wavelength range in which a phase difference of ½ wavelength (180 degrees) is obtained is, for example, the first wavelength ( For example, it is limited to the vicinity of 660 nm) (becomes narrow band characteristics). Therefore, when the wavelength of the laser beam is, for example, the second wavelength (for example, 784 nm), the phase difference of the laser beam output from the half-wave plate 121 is 147 degrees.

The laser beam that has passed through the composite optical element 12 is a beam splitter having a reflecting surface that is tilted by, for example, 45 ° with respect to the optical axis of the laser beam. A part of the light is reflected by the half mirror 13 and guided to the collimator lens 15, and the remaining part is transmitted through the half mirror 13 and guided to the front monitor light receiving detector 30.

The half mirror 13 is provided on a common optical path between the half-wave plate 121 and the objective lens 17, inverts the phase of the incident laser light and reflects the S-polarized component in the direction of the objective lens 17. Transmits polarized components. For example, the half mirror 13 reflects a part of incident laser light, for example, 90% or 90% or more, and transmits the remaining part, for example, 10% or 10% or less.

Therefore, almost all of the laser light incident from the diffraction grating 122 is reflected by the half mirror 13 and guided to the collimating lens 15, and the rest is transmitted and guided to the front monitor light receiving detector 30.

The intensity of the laser light applied to the front monitor light receiving detector 30 changes according to the output level of the laser light emitted from the laser unit 11. Accordingly, the monitor signal generated by the front monitor light receiving detector 30 in accordance with the intensity of the laser light applied to the front monitor light receiving detector 30 is supplied to a drive circuit provided to supply a drive signal to the laser unit 11. By performing the feedback, a laser servo operation for controlling the output of the laser light emitted from the laser unit 11 to a target value can be performed.

The collimating lens 15 makes the first wavelength laser beam suitable for DVD parallel light, and narrows the spread angle of the second wavelength laser beam suitable for CD. The laser light that has passed through the collimating lens 15 is incident on the quarter-wave plate 14.

The quarter wavelength plate 14 is provided on a common optical path between the half mirror 13 and the objective lens 17, and generates and outputs a phase difference of a quarter wavelength (90 degrees) with respect to the incident laser light. . The quarter-wave plate 14 has a narrow band characteristic.

Here, the narrow band is a laser that is output only when the wavelength of the incident laser light is a band that covers the red wavelength band used for DVDs or an infrared wavelength band that is used for CDs, for example. This means that a quarter-wave phase difference is added to the light.

For example, the ¼ wavelength plate 14 is ¼ wavelength (90 degrees) with respect to the laser beam only when the incident laser beam is the first wavelength (for example, 660 nm) in the red wavelength band used for DVD, for example. ) Is generated and output.

As a result, the quarter-wave plate 14 converts the 0th-order light and the ± 1st-order diffracted light reflected by the half mirror 13 from the S-polarized light to the circularly-polarized light on the forward path from the laser unit 11 to the optical disk 100, and On the return path from 100 to the photodetector 20, the reflected light from the optical disc 100 is converted from circularly polarized light to P-polarized light.

The quarter-wave plate 14 is a narrow-band type configured by using one or a smaller number of bonded resin films than the wide-band type, like the half-wave plate 121. The quarter wave plate 14 is configured using, for example, a polycarbonate film or Arton (registered trademark) film. The quarter-wave plate 14 is composed of a single resin film having a thickness of 100 μm or less, for example, about 70 μm.

As described above, the quarter-wave plate 14 can be configured by using a single quarter-wave plate 14 or a resin film having a smaller number of bonded sheets than the wide-band type, thereby reducing the cost of the quarter-wave plate 14. Therefore, cost reduction of the optical pickup device 1 can be promoted.

Since the quarter wavelength plate 14 of the present embodiment is configured by using a single resin film, as shown in FIG. It is formed so as to have a characteristic that has a negative gradient in relation to the phase difference added to the laser beam. That is, the phase difference added to the laser light transmitted through the quarter-wave plate 14 has a characteristic that decreases as the wavelength of the incident laser light becomes longer.

In the ¼ wavelength plate 14 of the present embodiment, the wavelength range in which a ¼ wavelength phase difference is obtained is limited to, for example, the vicinity of the first wavelength (for example, 660 nm) (becomes narrow band characteristics). For this reason, when the wavelength of the laser light is, for example, the second wavelength (for example, 784 nm), the phase difference of the laser light output from the quarter wavelength plate 14 is 75 degrees.

Note that the polarization state of light is converted as follows in the forward path and the return path by the combination of the half-wave plate 121, the half mirror 13, and the quarter-wave plate 14, for example.

In the forward path, the S-polarized component of the laser light that has passed through the half-wave plate 121 is reflected by the half mirror 13 and converted into circularly polarized light by the quarter-wave plate 14.

This circularly polarized light is reflected by an information recording layer (not shown) of the optical disc 100 and converted to P polarized light by the quarter wavelength plate 14 in the return path. This P-polarized light is transmitted through the half mirror 13.

More specifically, when the laser light emitted from the laser unit 11 passes through the half-wave plate 121, a phase difference as shown in FIG. 2 is given according to the wavelength of the laser light ( (Phase difference between points A and B on the common optical path of the laser beam shown in FIG. 1). That is, a phase difference of 180 degrees is given when the wavelength is 660 nm and 147 degrees when the wavelength is 784 nm.

When the S-polarized component of the laser beam is reflected by the half mirror 13, a phase difference as shown in FIG. 4 is caused by phase inversion at the time of reflection (points A to C on the common optical path of the laser beam shown in FIG. 1). Phase difference between). That is, the phase difference is −180 degrees for 660 nm and −147 degrees for 784 nm.

Next, when this laser beam passes through the quarter wavelength plate 14, a phase difference as shown in FIG. 3 is given according to the wavelength of the laser beam (on the common optical path of the laser beam shown in FIG. 1). Phase difference between points C to D). That is, a phase difference of 90 degrees is given when the wavelength is 660 nm and 75 degrees when the wavelength is 784 nm.

For this reason, after the laser light emitted from the laser unit 11 passes through the quarter-wave plate 14, the phase difference of the laser light varies depending on the wavelength of the laser light as shown in FIG. (The phase difference between points A to D on the common optical path of the laser beam shown in FIG. 1). That is, the phase difference is −90 degrees when the wavelength is 660 nm, and −72 degrees when the wavelength is 784 nm.

The laser light after passing through the quarter-wave plate 14 is circularly polarized because the phase difference is −90 degrees when the wavelength is 660 nm. On the other hand, when the wavelength is 784 nm, the phase difference is −72 degrees, so that it is elliptically polarized light.

That is, in the case of a laser beam having a wavelength of 784 nm, when the optical disc 100 is irradiated, a deviation of 18 degrees from circularly polarized light (−90 degrees phase difference) occurs.

However, if the phase difference is elliptical polarized light of −72 degrees, it is possible to record / reproduce the CD without any trouble.

In other words, in the optical pickup device 1 according to the present embodiment, DVD and CD can be realized while realizing cost reduction by using one narrow-band resin film for the half-wave plate 121 and the quarter-wave plate 14. In either case, the polarization of the laser light applied to the optical disc 100 can be made substantially circularly polarized.

The laser light that has passed through the quarter-wave plate 14 is reflected by the rising reflecting mirror 16, the optical axis of the laser light is bent, and the optical axis and light detection of the laser light emitted from the laser unit 11. The optical axis is substantially perpendicular to the optical axis of the reflected light from the optical disc 100 received by the optical device 20 and is incident on the objective lens 17.

The objective lens 17 has an annular diffractive structure centered on the optical axis on the incident surface. The objective lens 17 collects spherical aberration caused by the thickness of the transparent substrate layer of each DVD and CD optical disc 100 when the laser light incident on the objective lens 17 is condensed on each DVD and CD optical disc 100. It corrects appropriately by the diffraction effect by this diffraction structure.

The NA (Numerical Aperture) of the objective lens 17 is designed to be 0.65 for the first wavelength laser light suitable for DVD and 0.51 for the second wavelength laser light suitable for CD. Has been.

Therefore, the laser light having the first wavelength from the first laser light source 111 is condensed by the objective lens 17 in accordance with the thickness of the transparent substrate layer of the DVD and irradiated to the signal layer of the DVD. The second-wavelength laser light from the laser beam is condensed by the objective lens 17 in accordance with the thickness of the transparent substrate layer of the CD, and irradiated to the signal layer of the CD.

By such an optical system, the first wavelength laser light suitable for the DVD generated from the first laser light source 111 of the laser unit 11 is condensed on the DVD standard optical disc 100 and the second laser light source of the laser unit 11 is collected. The laser light having the second wavelength suitable for the CD generated from the light 112 is condensed on the optical disk 100 of the CD standard.

The objective lens 17 performs a focusing control operation by displacing in the direction (focus direction) perpendicular to the signal surface of the optical disc 100, and performs a tracking control operation by displacing in the radial direction (tracking direction) of the optical disc 100. Configured to do. The objective lens 17 that performs such an operation is provided to be displaceable in the focus direction and the tracking direction by, for example, four or six support wires. When the objective lens 17 is driven in the focus direction and the tracking direction, the laser light is focused on the signal layer of the DVD or CD optical disc 100 and irradiated so as to follow the signal track 101.

The laser light applied to the signal layer of the optical disc 100 is modulated and reflected by the signal layer, returns to the objective lens 17, and is converted from circularly polarized light to P polarized light by the quarter wavelength plate 14. The P-polarized laser light passes through the half mirror 13.

Then, the laser beam that has passed through the half mirror 13 is guided to the photodetector 20 through the AS plate 18 that is tilted so as to give astigmatism used for focusing control. A control film for controlling the transmissivity of the reflected light is formed on the surface of the AS plate 18.

The photodetector 20 detects the reflected light of the laser beam from the DVD and CD. The photodetector 20 includes a light receiving unit that receives the reflected light separated into three beams by the diffraction grating 122, and reads information recorded on the signal recording layer of the optical disc 100. A reproduction signal, a focus error signal for performing focusing control, and a tracking error signal for performing tracking control are generated.

As described above, the optical pickup device 1 according to the present embodiment can cope with the recording and reproduction of the DVD and also with the recording and reproduction of the CD.

== Comparative Example ==
On the other hand, for comparison with the present embodiment, a laser in the case of using a broadband half-wave plate 1121 constructed by bonding a plurality of resin films, which is more expensive than the half-wave plate 121 of the present embodiment. The phase difference of light will be described with reference to FIGS.

Here, the term “broadband” means that a phase difference of ½ wavelength is added to the output laser light in a band from a red wavelength band used for DVD to an infrared wavelength band used for CD.

The half-wave plate 1121 different from the present embodiment is provided on the common optical path between the first laser light source 111 and the second laser light source 112 and the half mirror 13, and the wavelength of the incident laser light is from 660 nm, for example. When it is within a band including a range up to 784 nm, a phase difference of ½ wavelength (180 degrees) is generated with respect to this laser light and emitted.

The half-wave plate 1121 is formed by laminating a plurality of resin films, and is attached to the surface of the diffraction grating 122, for example, the surface on the side where the laser light is incident on the diffraction grating 122. The half-wave plate 1121 is configured using, for example, a polycarbonate film or Arton (registered trademark) film. The half-wave plate 1121 has a thickness of about 140 μm to 150 μm, for example. Since the half-wave plate 1121 is configured by laminating a plurality of resin films, the thickness is larger than the half-wave plate 121 of the present embodiment composed of a single resin film, exceeding 100 μm. Yes.

As shown in FIG. 6, the half-wave plate 1121 has a 1 / (2) wavelength of laser light that is transmitted over a wide band including the first wavelength (for example, 660 nm) of the DVD standard and the second wavelength (for example, 784 nm) of the CD standard. It is possible to give a phase difference of two wavelengths.

When the laser light emitted from the laser unit 11 passes through the half-wave plate 1121, a phase difference of 180 degrees is given as shown in FIG. 6 (on the common optical path of the laser light shown in FIG. 1). Phase difference between points A and B). A phase difference of 180 degrees is given both when the wavelength of the laser beam is 660 nm and when it is 784 nm.

The S-polarized component of this laser beam is reflected by the half mirror 13, but due to the phase inversion at the time of reflection, the phase difference of the laser beam after being reflected by the half mirror 13 is -180 degrees as shown in FIG. (Phase difference between points A to C on the common optical path of the laser beam shown in FIG. 1). That is, a phase difference of −180 degrees is obtained regardless of whether the wavelength is 660 nm or 784 nm.

For this reason, after the laser light emitted from the laser unit 11 passes through the quarter-wave plate 14, the phase difference of the laser light varies depending on the wavelength of the laser light as shown in FIG. (The phase difference between points A to D on the common optical path of the laser beam shown in FIG. 1). That is, the phase difference is −90 degrees when the wavelength is 660 nm, and −105 degrees when the wavelength is 784 nm.

The laser light after passing through the quarter-wave plate 14 is circularly polarized because the phase difference is −90 degrees when the wavelength is 660 nm. On the other hand, when the wavelength is 784 nm, the phase difference is −105 degrees, so that it is elliptically polarized light.

That is, in the case of laser light having a wavelength of 784 nm, when the optical disc 100 is irradiated, there is a 15 degree deviation from circularly polarized light (-90 degree phase difference).

However, if the phase difference is elliptical polarized light of −105 degrees, it is possible to record / reproduce the CD without any trouble.

As described above, in the comparative example, by using the half-wave plate 1121, the polarization of the laser light applied to the optical disc 100 for both DVD and CD is made almost circularly polarized.

However, since the half-wave plate 1121 is configured by bonding a plurality of resin films and is expensive, the cost reduction effect due to the replacement of the half-wave plate from glass to resin film is reduced. .

== Advantage of this embodiment ==
As described above, the optical pickup device 1 according to the present embodiment includes the narrow-band half-wave plate 121 and the quarter-wave plate 14 formed of a single film or a film having a smaller number of laminated sheets than the wide-band type. Since it uses, compared with the case where the film and glass wide-band 1/2 wave plate and 1/4 wave plate are used, cost can be restrained cheaply.

Moreover, the ½ wavelength plate 121 and the ¼ wavelength plate 14 according to the present embodiment are both positive gradients in the relationship between the wavelength of the incident laser beam and the phase difference added to the emitted laser beam, Alternatively, since both are formed so as to have a negative gradient characteristic, the characteristic that the phase difference given to the laser beam by the half-wave plate 121 is inverted by a beam splitter such as the half mirror 13 is used. Thus, the phase difference of the laser light generated by the half-wave plate 121 can be canceled by the phase difference generated by the quarter-wave plate 14.

For this reason, even if an expensive broadband resin film is not used for the half-wave plate 121 and the quarter-wave plate 14, the laser light when irradiated onto the optical disc 100 is in a state close to circular polarization over a wide band. It becomes possible to do.

Thereby, the cost reduction by using the resin film half-wave plate 121 or the quarter-wave plate 14 can be further promoted.

== Other Embodiments ==
This embodiment can be variously modified.
For example, as illustrated in FIGS. 2 and 3, the half-wave plate 121 and the quarter-wave plate 14 according to the present embodiment have a wavelength difference between an incident laser beam and a phase difference added to the emitted laser beam. In this case, not only the case of having a characteristic that has a negative gradient but also the case of having a characteristic that has a positive gradient may be used.

Further, in the ½ wavelength plate 121 and the ¼ wavelength plate 14 according to the present embodiment, the wavelength range in which the phase difference between the ½ wavelength and the ¼ wavelength is obtained is in the vicinity of the first wavelength (for example, 660 nm). Instead, for example, it may be in the vicinity of the second wavelength (for example, 784 nm) or a third wavelength different from the first wavelength or the second wavelength.

Further, the half-wave plate 121 adds a wavelength of the laser light (first predetermined wavelength) that adds a half wavelength to the laser light, and the quarter-wave plate 14 adds a quarter wavelength to the laser light. The wavelength (second predetermined wavelength) may be different. For example, the ½ wavelength plate 121 adds ½ wavelength to the laser light having the first wavelength (660 nm), and the ¼ wavelength plate 14 is 1 / wave to the laser light having the third wavelength (for example, 620 nm). You may comprise so that 4 wavelengths may be added.

In other words, the characteristics of the half-wave plate 121 and the quarter-wave plate are determined so that the laser light applied to the optical disc 100 is elliptically polarized light that is close to circularly polarized light (phase difference 90 degrees). Various changes are possible.

In addition, the optical pickup device is not limited to an optical pickup device compatible with DVD and CD, but also in an optical pickup device adapted to the Blu-ray Disc (registered trademark) standard using a laser beam (for example, 405 nm) in a blue-violet wavelength band of 400 nm to 420 nm. Is available.

As mentioned above, the embodiments of the invention described above are for facilitating understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and equivalents thereof are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 11 Laser unit 12 Compound optical element 121 1/2 wavelength plate 122 Diffraction grating 13 Half mirror (beam splitter)
14 1/4 wavelength plate 15 Collimating lens 16 Rising reflection mirror 17 Objective lens 18 AS plate 20 Photo detector 30 Front monitor light receiving detector 100 Optical disc 1121 1/2 wavelength plate

Claims

A first laser light source that emits a first laser beam having a first wavelength;
A second laser light source that emits a second laser beam having a second wavelength longer than the first wavelength;
An objective lens for irradiating the optical recording medium with the first laser beam and the second laser beam;
A half-wave plate made of a resin film provided on a common optical path between the first laser light source and the second laser light source and the objective lens;
A beam splitter that is provided on the common optical path between the half-wave plate and the objective lens, and reflects the incident laser light in the direction of the objective lens by inverting the phase of the laser light;
A quarter-wave plate made of a resin film provided on the common optical path between the beam splitter and the objective lens;
With
The half-wave plate and the quarter-wave plate are both positive slopes or negative slopes in the relationship between the wavelength of the incident laser light and the phase difference added to the emitted laser light. The optical pickup device is formed so as to have the following characteristics.
The optical pickup device according to claim 1,
The half-wave plate and the quarter-wave plate respectively have a half-wavelength and a quarter-wavelength with respect to the laser light when the incident laser light is the first wavelength. An optical pickup device characterized by adding a phase difference.
The optical pickup device according to claim 1 or 2,
The half-wave plate outputs an incident laser beam as an S-polarized laser beam.
The optical pickup device according to any one of claims 1 to 3,
Both of the thickness of the resin film of the half-wave plate and the thickness of the resin film of the quarter-wave plate are 100 micrometers or less.
The optical pickup device according to any one of claims 1 to 4,
The first laser beam is a laser beam for recording and reproducing a DVD standard optical recording medium, and the second laser beam is a laser beam for recording and reproducing a CD standard optical recording medium. Optical pickup device.
A first laser light source that emits a first laser beam having a first wavelength;
A second laser light source that emits a second laser beam having a second wavelength longer than the first wavelength;
An objective lens for irradiating the optical recording medium with the first laser beam and the second laser beam;
Provided on a common optical path between the first laser light source and the second laser light source and the objective lens, and has a phase difference of approximately ½ wavelength only in one of the first laser light and the second laser light. A narrow-band half-wave plate to be applied;
A beam splitter that is provided on the common optical path between the half-wave plate and the objective lens, and reflects the incident laser light in the direction of the objective lens by inverting the phase of the laser light;
Provided on the common optical path between the beam splitter and the objective lens, and a phase difference of ½ wavelength is given by the ½ wavelength plate of the first laser light and the second laser light. A narrow-band quarter-wave plate that imparts a phase difference of approximately ¼ wavelength only to one laser beam,
The half-wave plate and the quarter-wave plate are both positive slopes or negative slopes in the relationship between the wavelength of the incident laser light and the phase difference added to the emitted laser light. The optical pickup device is formed so as to have the following characteristics.