JP2006185474A - Optical power modulation element and optical pickup equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make super resolution effects variable and to make a monitored light amount variable without changing the area of the light receiving surface of a monitoring detector. <P>SOLUTION: A luminous flux branching element 12 is disposed in an optical path between a light source and an optical disk. The luminous flux branching element 12 is provided with a phase plate 16 constituted of phase plates 16a and 16b, and a PBS 17. First luminous flux A including its center among light source luminous fluxes is made incident on the phase plate 16a, and for example, a polarized state is converted into elliptic polarized light to be emitted. Remaining second luminous flux B among the light source luminous fluxes is made incident on the phase plate 16b, and emitted while a polarized state at the incident time is maintained. In the PBS 17, the synthesized luminous flux of the first and second luminous fluxes A and B obtained via the phase plate 16 is separated according to the polarized state. From the PBS 17, a part of the first luminous flux A and the second luminous flux B are directed in the direction of an objective lens, and the remaining first luminous flux A is directed to the monitoring detector. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light intensity modulation element that guides a light beam from a light source to an objective lens by changing its intensity distribution, and an optical pickup including the light intensity modulation element.

  In the field of optical pickups and printers, in order to stabilize the amount of light emitted from the laser light source, an automatic power control (APC) that monitors the laser light emitted from the rear end face of the laser light source and controls the amount of emitted light according to the result. ) May be used. However, with this method, the amount of laser light emitted from both the front side and the rear side of the laser light source is strictly different, so that accurate light amount control is difficult to perform by feedback. Further, since the light is emitted also on the side opposite to the desired direction (front) (back), the amount of light emitted from the laser light source cannot be used effectively.

  Therefore, in recent years, a front monitor system in which a part of laser light emitted forward from a laser light source is used as monitor light has been widely used (see, for example, Patent Documents 1 and 2). FIG. 16 shows a schematic configuration of the optical pickup of Patent Document 1. In this optical pickup, the laser light emitted from the semiconductor laser element 101 is converted into parallel light by the coupling lens 102, passes through the separation surface 103 a of the beam splitter 103, and is converged by the objective lens 104. It is focused on. Reflected light from the optical disk 105 is converted into substantially parallel light by the objective lens 104, reflected by the separation surface 103a of the beam splitter 103, and guided to a detection optical system (not shown).

  On the other hand, a light shielding member 106 is disposed in the optical path between the coupling lens 102 and the beam splitter 103, and a light receiving element 107 for monitoring is provided on the surface of the light shielding member 106 on the semiconductor laser element 101 side. It is arranged. As a result, the amount of emitted light can be monitored in front of the semiconductor laser element 101, and the above-described front monitor system is realized.

FIG. 17 shows a schematic configuration of the optical pickup of Patent Document 2. In this optical pickup, when S-polarized laser light emitted from the laser diode 201 is incident on the half-wave plate 202, P-polarized laser light is emitted from the half-wave plate 202, and PBS (polarized beam). It enters the splitter 203. In the PBS 203, about 90% of the incident light is reflected by the reflecting surface 203a and travels toward the optical disc. On the other hand, about 10% of the incident light passes through the reflection surface 203a of the PBS 203 and enters the front monitor 204, where the amount of light is detected. Therefore, even with the configuration of Patent Document 2, the amount of emitted light can be monitored in front of the laser diode 201.
JP-A-7-296414 JP 2004-259376 A

  By the way, in Patent Document 1, since the central portion of the light beam emitted from the semiconductor laser element 101 is shielded by the light shielding member 106 and the light receiving element 107, the light with reduced light intensity near the optical axis is applied to the optical disk 105. Can be irradiated. As a result, the diameter of the light spot irradiated onto the optical disk 105 can be reduced, and a so-called super-resolution effect corresponding to high-density recording can be obtained.

  However, since the central portion of the light beam is completely shielded by the light shielding member 106 and the light receiving element 107, the light applied to the optical disk 105 is always light whose light intensity near the optical axis becomes zero. Therefore, with the configuration of Patent Document 1, the super-resolution effect cannot be made variable.

  Since the light receiving element 107 is disposed in the optical path between the coupling lens 102 and the beam splitter 103, the amount of light incident on the light receiving element 107 is not changed unless the area of the light receiving surface of the light receiving element 107 is changed. It is constant. That is, unless the area of the light receiving surface is changed, the monitor light quantity at the light receiving element 107 cannot be made variable.

  On the other hand, in Patent Document 2, by appropriately setting the angle formed by the polarization direction (vibration direction) of the laser light emitted from the laser diode 201 and the crystal optical axis of the half-wave plate 202, the reflection of the PBS 203 is performed. The laser beam incident on the surface 203a can be separated into two laser beams having a predetermined light intensity by the reflection surface 203a. Therefore, the laser light incident on the reflective surface 203a is transmitted with a predetermined transmittance and utilized as monitor light on the front monitor 204 without being affected by the wavelength dependency of the optical multilayer film constituting the reflective surface 203a. be able to.

  However, in the configuration of Patent Document 2, it is not possible to adjust the intensity of light applied to the optical disc via the PBS 203 so as to drop only near the optical axis. As a result, the above-described super-resolution effect cannot be obtained, and the super-resolution effect cannot be made variable.

  The present invention has been made to solve the above-described problems, and its purpose is to make the super-resolution effect variable and without changing the area of the light receiving surface of the monitor detector. An object of the present invention is to provide a light intensity modulation element capable of changing the amount of monitor light and an optical pickup provided with the light intensity modulation element.

  The light intensity modulation element of the present invention is a light intensity modulation element that guides a light beam from a light source to an objective lens by changing its intensity distribution. The light beam is a first light beam including the central portion thereof and the remaining light beam. And splitting the first luminous flux into different directions by transmission and reflection, and supplying one of the branched first luminous flux and the second luminous flux to the objective lens. It is characterized by comprising a light beam branching element for guiding.

  The first light beam may be a light beam that includes at least the optical axis of the light source light beam, and may include a part of the periphery of the light source light beam. That is, the cross-sectional shape of the first light beam is not limited to a circle centered on the optical axis.

  According to the above configuration, the light source beam is separated into the first beam and the second beam by the beam splitter, and the first beam is further branched in different directions by transmission and reflection. Then, one of the branched first light fluxes and the second light flux are guided from the light flux separation element to the objective lens. Thereby, the intensity distribution of the light beam applied to the optical disc through the objective lens is not included because it does not include the light beam (part of the first light beam) branched in the direction different from the objective lens direction by the light beam branching element. Changes. That is, the light beam applied to the optical disk has an intensity distribution in which the light intensity near the optical axis of the light beam incident on the light beam splitting element is reduced. By realizing such an intensity distribution, the spot diameter of the light condensed on the optical disc can be narrowed down, and a super-resolution effect compatible with high-density recording can be obtained.

  Further, since the light beam branching element further branches the first light beam by transmission and reflection, the light amount (intensity) of the light transmitted through the light beam branching element or the light amount (intensity) of the light reflected by the light beam branching element is adjusted. A possible configuration can be easily realized. Therefore, by adjusting the amount of light, for example, the degree of decrease in light intensity near the optical axis can be changed in various ways, and the intensity distribution of the light beam guided to the optical disk via the objective lens can be changed in various ways. Can do. As a result, the super-resolution effect can be made variable by adjusting the spot diameter of the light applied to the optical disk.

  In addition, the amount of light that is branched in a direction different from the direction of the objective lens through the light beam splitting element also changes due to the light amount adjustment described above. Therefore, if the light is used as monitor light, the monitor detector receives light. The amount of monitor light can be made variable without changing the surface area.

  Here, the light beam branching element includes (1) a polarization conversion unit (for example, a phase plate (including a phase difference film)) that changes a polarization state of only the first light beam, and (2) the polarization conversion unit. A polarization separation unit (for example, a polarization beam splitter) that separates a combined light beam of the first light beam and the second light beam obtained via the light beam according to a polarization state may be used. .

  In this configuration, the polarization state of only the first light beam is converted from, for example, linearly polarized light to elliptically polarized light by the polarization conversion unit. Then, the combined light beam of the first light beam and the second light beam whose polarization state has changed is separated by the polarization separation unit according to the polarization state. For example, in the combined light beam, a component in the same direction as the polarization direction (vibration direction) of the light source light beam is reflected, for example, by the polarization separation unit and travels toward the objective lens. On the other hand, in the composite light beam, the component in the direction perpendicular to the polarization direction of the light source light beam passes through the polarization separation unit, for example, and travels in a different direction from the objective lens.

  At this time, since the polarization state of only the first light beam is changed by the polarization conversion unit, the polarization separation unit particularly determines the first light beam among the combined light beams in the direction of the objective lens according to the polarization state. Are separated in different directions. On the other hand, since the second light beam maintains the polarization state of the light source light beam (because the polarization direction is the same as that of the light source light beam), the second light beam itself is not separated by the polarization separation unit and is directed to the objective lens direction. Is emitted.

  As described above, since the polarization separation unit can emit a part of the first light beam and the second light beam in the direction of the objective lens, the light emitted from the polarization separation unit to the optical disc through the objective lens. The light intensity near the optical axis can be reduced. In addition, the light intensity in the vicinity of the optical axis of the light can be adjusted according to the degree of change of the polarization state in the polarization converter. As a result, according to the above configuration, both the super-resolution effect and the monitor light quantity can be easily made variable.

  In particular, if the polarization conversion unit is configured to convert the polarization state of the first light beam from linearly polarized light to elliptically polarized light, the elliptically polarized light has a component in the same direction as the polarization direction of the light source light beam, and the polarization direction. Since it has a component in the vertical direction, the combined luminous flux can be reliably separated into the objective lens direction and a different direction while changing the light intensity near the optical axis according to the state of elliptically polarized light. it can. As a result, both the super-resolution effect and the monitor light amount can be reliably varied.

  The polarization conversion unit may be configured to convert the polarization state of the first light flux into linearly polarized light different from the polarization direction of the first light flux. As such a polarization conversion unit, for example, a half-wave plate or an optical rotation plate can be considered. Even with this configuration, linearly polarized light having a component in the same direction as the polarization direction of the light source beam and a component in a direction perpendicular to the polarization direction can be obtained. While changing the light intensity near the axis, the combined light beam can be reliably separated into the objective lens direction and a different direction. As a result, both the super-resolution effect and the monitor light amount can be reliably varied.

  The light beam branching element may further include a phase adjusting unit that adjusts the phase of the second light beam. By such phase adjustment by the phase adjustment unit, it is possible to suppress a phase shift between the first light beam obtained through the polarization conversion unit and the second light beam not incident on the polarization conversion unit. it can. As a result, it is possible to suppress disturbance of the wave front of the combined light beam of the first light beam and the second light beam.

  Here, it is desirable that the polarization conversion unit and the phase adjustment unit be formed adjacent to each other on a plane perpendicular to the optical axis of the incident light beam. In this case, the polarization conversion unit and the phase adjustment unit can be easily obtained by integral formation.

  Moreover, it is desirable that the polarization conversion unit and the phase adjustment unit are each configured by a phase plate. That is, the optical axes of the polarization conversion unit and the phase adjustment unit are in a plane perpendicular to the optical axis of the incident light beam, the optical axis of the phase adjustment unit is parallel to the polarization direction of the incident light beam, and the polarization The optical axis of the conversion unit is preferably inclined with respect to the polarization direction of the incident light beam.

  As described above, by configuring the polarization conversion unit and the phase adjustment unit with the above-described phase plate, the polarization conversion unit can surely have the function of changing the polarization state of the first light flux, and the second The phase adjusting unit can surely have a function of adjusting the phase of the light beam.

  In addition, the polarization conversion unit is composed of a phase plate (for example, a retardation film), and is bonded to the polarization separation unit via an adhesive, and the adhesive is an ordinary ray of the phase plate. A configuration having a refractive index equal to the refractive index or the refractive index of extraordinary rays may be used.

  In this configuration, the phase shift between the first light beam obtained via the polarization converter and the second light beam can be achieved without providing a means (for example, a phase plate) for adjusting the phase of the second light beam. These light beams can be incident on the polarization splitting part via an adhesive without causing them to occur. Therefore, it is possible to suppress the wavefront of the luminous flux from being disturbed without providing the adjusting means.

  Further, the polarization conversion unit may be composed of an optical rotation plate. The optical rotatory plate emits the incident linearly polarized light by rotating its polarization direction, so that linearly polarized light having a component in the same direction as the polarization direction of the light source beam and a component perpendicular to the polarization direction is obtained. be able to. Accordingly, it is possible to reliably separate the combined light beam into the objective lens direction and a direction different from the above while changing the light intensity near the optical axis in accordance with the rotation angle of the polarization direction on the optical rotation plate. As a result, both the super-resolution effect and the monitor light amount can be reliably varied.

  In addition, the light beam splitting element includes a first region that transmits the first light beam with a predetermined transmittance, and a second region that reflects the second light beam with a predetermined reflectance and guides it to the objective lens. May be composed of reflective optical elements formed on the same plane (substrate).

  As described above, since the light beam branching element is configured by the reflective optical element, most of the first light beam is transmitted through the first region, while the rest is reflected by the first region and is reflected on the objective lens. In addition to being guided, it is possible to realize a configuration in which most of the second light flux is reflected by the second region and guided to the objective lens.

  At this time, the amount of transmitted light in the first region can be adjusted by adjusting the optical characteristics (transmittance, reflectance) of the first region. Thereby, if the light which permeate | transmits a 1st area | region is utilized as monitor light, the light quantity of the monitor light can be made variable. Moreover, since the light quantity (intensity) of the light reflected in the first region is also adjusted by adjusting the optical characteristics of the first region, the intensity distribution of the reflected light in the first region and the second region. Can be adjusted in various ways, for example, so that the light intensity near the optical axis decreases. As a result, the super-resolution effect can be made variable by adjusting the spot diameter of the light applied to the optical disk. That is, by adjusting the optical characteristics of the first region, both the monitor light amount and the super-resolution effect can be easily made variable.

  The optical pickup according to the present invention includes a light source that emits light, a light intensity modulation element that changes an intensity distribution of a light beam from the light source, and condenses light obtained through the light intensity modulation element on an optical disk. An optical pickup provided with an objective lens to be operated, wherein the light intensity modulation element is composed of the light intensity modulation element of the present invention described above.

  According to the above configuration, the intensity distribution of the emitted light from the light source is changed by the light intensity modulation element, and is condensed on the optical disk by the objective lens. At this time, since the light intensity modulation element is composed of the light intensity modulation element of the present invention described above, the above-described effects such as the ability to vary both the super-resolution effect and the monitor light amount can be obtained.

  Further, the optical pickup of the present invention further includes a monitor detector for controlling the output of light emitted from the light source, and the monitor detector is arranged in the direction of the objective lens by the light intensity modulation element. It may be configured to receive light branched in a different direction from the light source and control the light output of the light source based on the amount of light received.

  As described above, if the light branched in the direction different from that of the objective lens by the light intensity modulation element is used as the monitor light, the monitor light quantity can be made variable by the light intensity modulation element. Thus, it is possible to appropriately control the light output of the light source by the monitor detector.

  According to the present invention, the light beam branching element that constitutes the light intensity modulation element branches the first light beam by transmission and reflection, so that the light amount (intensity) of the light transmitted through the light beam branching element or the light beam branching element is reflected. It is possible to easily realize a configuration that enables adjustment of the light amount (intensity) of the emitted light. Therefore, by adjusting the amount of light, the intensity distribution of the light beam guided to the optical disc through the objective lens can be changed in various ways so that, for example, the light intensity near the optical axis decreases. As a result, the super-resolution effect can be made variable by adjusting the spot diameter of the light applied to the optical disk.

  In addition, the amount of light that is branched in a direction different from the direction of the objective lens through the light beam splitting element also changes due to the light amount adjustment described above. Therefore, if the light is used as monitor light, the monitor detector receives light. The amount of monitor light can be made variable without changing the surface area.

[Embodiment 1]
(1. Configuration of optical pickup)
An embodiment of the present invention will be described below with reference to the drawings.
FIG. 2 is an explanatory diagram showing a schematic configuration of the optical pickup according to the present embodiment. This optical pickup includes a first light source unit 1, a second light source unit 2, a dichroic prism 3, a rising mirror 4, a quarter wavelength plate 6, and an objective lens 7.

  The first light source unit 1 includes a light source 11, a light beam splitting element 12, a collimator lens 13, a light receiving element 14, and a monitor detector 15.

  The light source 11 emits laser light (blue laser) having a wavelength of 405 nm, for example, as a light beam. The beam splitter 12 separates linearly polarized laser light emitted from the light source 11 into a direction of the objective lens 7 and a direction different from the direction (for example, the direction of the monitor detector 15). Specifically, the beam splitter 12 is composed of a phase plate 16 and a polarization beam splitter (hereinafter abbreviated as PBS) 17, and changes the intensity distribution of the beam from the light source 11. A light intensity modulation element led to the objective lens 7 is configured, and details thereof will be described later.

  The collimator lens 13 converts the laser light incident through the PBS 17 into parallel light. The light receiving element 14 receives the return light from the optical disk D incident through the PBS 17. The light received by the light receiving element 14 detects a servo signal (focus error signal, tracking error signal), an information signal, an aberration signal, and the like during recording and reproduction of a high density recording optical disc corresponding to a blue laser.

  The monitor detector 15 receives the light branched from the light source 11 in a direction different from the direction of the objective lens 7 by the light beam splitting element 12, and the light of the light source 11 based on the amount of the received light. For controlling the output, for example, it is composed of a photodiode and a control unit. In the present embodiment, since the laser light emitted forward (in the direction toward the optical disc D) from the light source 11 is monitored by the monitoring detector 15 via the light beam splitting element 12, the front monitor system is used.

  The second light source unit 2 includes a light source 21, a light beam splitting element 22, a collimator lens 23, a light receiving element 24, and a monitor detector 25.

  The light source 21 emits, for example, laser light having a wavelength of 660 nm (for DVD) and laser light having a wavelength of 785 nm (for CD) as light beams. That is, the light source 21 is a light source that emits laser light having two wavelengths. The beam splitter 22 separates the linearly polarized laser beam emitted from the light source 21 into a direction of the objective lens 7 and a direction different from the direction (for example, the direction of the monitor detector 25). Specifically, the beam splitter 22 is composed of a phase plate 26 and a PBS 27, and constitutes a light intensity modulator that guides the beam from the light source 21 to the objective lens 7 by changing its intensity distribution. The details will be described later.

  The collimator lens 23 converts laser light incident through the PBS 22 into parallel light. The light receiving element 24 receives the return light from the optical disc D that enters through the PBS 22. The light received by the light receiving element 24 detects a servo signal (focus error signal, tracking error signal), information signal, aberration signal, and the like during recording / reproduction of a DVD or CD.

  The monitor detector 25 receives the light branched from the light source 21 in a direction different from the direction of the objective lens 7 out of the light emitted from the light source 21, and the light from the light source 21 based on the amount of the received light. For controlling the output, for example, it is composed of a photodiode and a control unit. In the present embodiment, the laser light emitted forward (in the direction toward the optical disc D) from the light source 21 is monitored by the monitoring detector 25 via the light beam branching element 22, so that the front monitor method is used.

  The dichroic prism 3 reflects the laser light supplied from the first light source unit 1 and guides it to the rising mirror 4 and transmits the laser light supplied from the second light source unit 2 to the rising mirror 4. Lead. That is, the dichroic prism 3 is an optical path conversion element that emits the laser light incident from different directions with the same traveling direction.

  The rising mirror 4 is disposed between the light sources 11 and 21 and the optical disc D, more specifically, in the optical path between the dichroic prism 3 and the objective lens 7, and reflects the incident light, thereby allowing the optical path of the incident light. It has a function to bend.

  The quarter wavelength plate 6 converts the linearly polarized light reflected by the rising mirror 4 into circularly polarized light, and converts the return light (circularly polarized light) from the optical disc D into linearly polarized light. The objective lens 7 collects the light reflected by the rising mirror 4 and obtained through the quarter-wave plate 6 on the optical disc D.

  In the above-described configuration, the component (for example, S-polarized light) having the same polarization direction as the polarization direction of the linearly polarized laser light emitted from the light source 11 is reflected by the beam splitter 12 and enters the collimator lens 13. On the other hand, the component perpendicular to the polarization direction of the incident light (for example, P-polarized light) passes through the light beam splitting element 12 and enters the monitor detector 15 where it is monitored. The laser light converted into parallel light by the collimator lens 13 is reflected by the dichroic prism 3 and enters the rising mirror 4.

  On the other hand, of the linearly polarized laser light emitted from the light source 21, a component having the same polarization direction as the polarization direction (for example, S-polarized light) is reflected by the beam splitter 22 and enters the collimator lens 23. A component perpendicular to the polarization direction of the light (for example, P-polarized light) is transmitted through the beam splitter 22 and incident on the monitor detector 25, where it is monitored. The laser light converted into parallel light by the collimator lens 23 passes through the dichroic prism 3 and enters the rising mirror 4.

  The laser light incident on the rising mirror 4 is reflected and incident on the quarter-wave plate 6, converted into circularly polarized light by the quarter-wave plate 6, and then collected on the optical disk D by the objective lens 7. Lighted.

  The return light from the optical disk D is incident again on the quarter-wave plate 6 through the objective lens 7, where it is converted into linearly polarized light (for example, P-polarized light), then reflected by the rising mirror 4 and dichroic. Incident on the prism 3. At this time, if the return light is the return light of the laser light emitted from the light source 11, the return light incident on the dichroic prism 3 is reflected by the dichroic prism 3 and is passed through the collimator lens 13 to the PBS 17 of the beam splitter 12. Is received by the light receiving element 14 through the PBS 17.

  On the other hand, if the return light is the return light of the laser light emitted from the light source 21, the return light incident on the dichroic prism 3 passes through the dichroic prism 3 and passes through the collimator lens 23 to the PBS 27 of the light beam splitting element 22. Incident light passes through the PBS 27 and is received by the light receiving element 24.

(2. Details of beam splitter)
Next, the details of the beam splitters 12 and 22 will be described. Since the basic structures of the light beam branching elements 12 and 22 are the same, the light beam branching element 12 will be described below, and the light beam branching element 22 will also be described.

  FIG. 1 is an explanatory view schematically showing a schematic configuration of the light beam branching element 12. As described above, the beam splitter 12 includes the phase plate (wave plate) 16 and the PBS 17. In FIG. 1, the polarization direction of the incident light beam and the direction of the optical axis of the phase plate 16 are indicated by solid arrows. In the present embodiment, the phase plate 16 and the PBS 17 are separated from each other, but they may be in close contact with each other. The beam splitter 22, the phase plate 26 and the PBS 27 in FIG. 2 correspond to the beam splitter 12, the phase plate 16 and the PBS 17 in FIG. 1, respectively.

  The phase plate 16 is disposed between the light source 11 (see FIG. 2) and the PBS 17, and includes a phase plate 16a and two phase plates 16b. The phase plate 16a and the two phase plates 16b are formed adjacent to each other so that the two phase plates 16b are sandwiched from both sides on a plane perpendicular to the optical axis of the incident light beam. Thereby, among the light beams from the light source 11, the first light beam A including the central portion (the light beam including the optical axis) is incident on the phase plate 16a, and the second light beam B that is the remainder of the light beam is The light enters each phase plate 16b. From this, it can be said that the phase plate 16 has a function of separating the light source light beam into the first light beam A and the second light beam B according to the incident position.

  The optical axis of the phase plate 16a is in a plane perpendicular to the optical axis of the incident light beam and is inclined with respect to the polarization direction of the incident light beam. Thus, when the first light beam A is incident on the phase plate 16a, the first light beam A is emitted from the phase plate 16a in the direction of the PBS 17 with the polarization state converted from linearly polarized light to elliptically polarized light. . Therefore, it can be said that the phase plate 16a constitutes a polarization conversion unit that changes the polarization state of the first light beam A including the central portion of the light beam from the light source 11 to elliptically polarized light.

  By adjusting the tilt angle of the optical axis of the phase plate 16a with respect to the polarization direction of the incident light beam, elliptically polarized light corresponding to the tilt angle can be obtained. Further, when the phase plate 16a functions as, for example, a half-wave plate, if the angle between the optical axis of the phase plate 16a and the polarization direction of the incident light is θ, the polarization direction of the incident light is relative to the incident state. It is converted into linearly polarized light inclined by 2θ. Therefore, in this case, the phase plate 16a functions as a polarization conversion unit that converts the polarization state of the first light flux A into linearly polarized light different from the polarization direction.

  On the other hand, the optical axis (high-speed axis and low-speed axis) of the phase plate 16b is in a plane perpendicular to the optical axis of the incident light beam, and is parallel and perpendicular to the polarization direction of the incident light beam. As a result, when the second light beam B is incident on the phase plate 16b, the polarization direction of the second light beam B does not change, but only its phase changes. Therefore, it can be said that the phase plate 16b constitutes a phase adjusting unit that adjusts the phase of the second light beam B. By providing such a phase plate 16b, the phase shift between the first light beam A obtained via the phase plate 16a and the second light beam B obtained via the phase plate 16b can be reduced, It can suppress that the wave front of the synthetic | combination light beam of the 1st light beam A and the 2nd light beam B is disturb | confused.

  The phase plate 16 having the above-described configuration can be manufactured as follows. For example, as shown in FIG. 3, the plate-like phase plate 16 a is sandwiched between two plate-like phase plates 16 b so that the optical axes of the phase plates 16 a and 16 b are in a predetermined direction, and this is fixed by a cutter 41. The phase plate 16 can be obtained by slicing to a thickness of.

  The PBS 17 reflects light (for example, S-polarized light) having the same polarization direction as the incident light to the phase plate 16 out of the light obtained through the phase plate 16 and guides it in the direction of the objective lens 7, while directing it to the phase plate 16. The incident light and the light whose polarization direction is perpendicular (for example, P-polarized light) are transmitted and guided to the monitor detector 15. That is, the PBS 17 separates the combined light beam of the first light beam A obtained through the phase plate 16a and the second light beam B obtained through the phase plate 16b in different directions depending on the polarization state. A polarization separation unit is configured.

Next, the optical path of light in the light beam splitting element 12 having the above configuration will be described.
FIG. 4 shows the optical path of the second light beam B incident on the phase plate 16b. As shown in the figure, the two second light beams B (S-polarized light) enter the respective phase plates 16b, but the polarization direction does not change in the phase plates 16b, so the same polarization as the polarization state at the time of incidence. The light is emitted from the phase plate 16 b while maintaining the direction, and enters the PBS 17. The light (S-polarized light) incident on the PBS 17 is reflected and travels toward the objective lens 7 via the collimator lens 13 (see FIG. 2). That is, all of the second light beam B is reflected by the light beam branching element 12 and travels toward the objective lens 7.

  On the other hand, FIG. 5 shows the optical path of the first light flux A incident on the phase plate 16a. As shown in the figure, when the first light beam A (S-polarized light) enters the phase plate 16a, it is converted from linearly polarized light into elliptically polarized light. Among the elliptically polarized light, a component (S-polarized light) having the same polarization direction as the light incident on the phase plate 16a is reflected by the PBS 17 and travels toward the objective lens 7 via the collimator lens 13 (see FIG. 2). On the other hand, of the elliptically polarized light, the component (P-polarized light) whose polarization direction is perpendicular to the incident light to the phase plate 16 a passes through the PBS 17 and enters the monitor detector 15.

  As described above, since the light beam splitter 12 of the present embodiment includes the phase plate 16a and the PBS 17, a part of the first light beam A obtained through the phase plate 16a is transmitted through the PBS 17, and the object is obtained. Since it is separated in a direction different from the direction of the lens 7, the intensity distribution of the light applied to the optical disc D through the objective lens 7 is finally shown by the amount of the part of the first light flux A. As shown in FIG. 1, the intensity distribution is such that the light intensity near the optical axis is reduced (the blackened portion is the intensity reduction). Therefore, the so-called super-resolution effect that can narrow down the spot of light condensed on the optical disc D via the beam splitter 12 in the radial direction or the circumferential direction of the optical disc D, and can cope with high-density recording / reproduction. Can be obtained.

  Further, the polarization state of the phase plate 16a to elliptically polarized light can be easily adjusted by changing the tilt angle of the optical axis of the phase plate 16a as described above. Therefore, since the amount of light (intensity) of the first light flux A transmitted through the PBS 17 can be adjusted by adjusting the polarization state, the amount of light (monitor light) incident on the monitor detector 15 can be varied. Can be. Further, the adjustment of the light amount of the first light beam A transmitted through the PBS 17 results in the adjustment of the light amount (intensity) of the remaining first light beam A reflected by the PBS 17 and guided to the optical disc D. Therefore, it is possible to variously adjust how the intensity of the light irradiated to the optical disc D is reduced near the optical axis. As a result, the above-described super-resolution effect can be made variable.

  Because of such an effect, the light beam splitting element 12 of the present embodiment separates the light source light beam into the first light beam A including the central portion and the remaining second light beam B, and the first It can be said that it has a function of branching one light beam A in different directions by transmission and reflection and guiding one of the branched first light beam A and the second light beam B to the objective lens 7. .

  By the way, although this embodiment demonstrated the case where the light beam which injects into the phase plate 16 from the light source 11 is S polarized light, the said light beam may be P polarized light. For example, FIG. 6 shows a schematic configuration of the optical pickup when the light beam incident on the phase plate 16 from the light source 11 is P-polarized light. In this case, the arrangement of the light source 11, the light receiving element 14, the monitor detector 15 and the phase plate 16 with respect to the PBS 17 is only different from that in FIG. 2, and even with this configuration, the same effects as in this embodiment can be obtained. There is no change.

  In the present embodiment, the example in which the phase plate 16a is used as the polarization conversion unit has been described. However, an optical rotation plate may be used. Since the optical rotation plate can rotate the polarization direction of the incident linearly polarized light, the amount of light (monitor light) incident on the monitor detector 15 and the super-resolution effect can be varied according to the rotation angle. Can do. As such an optical rotatory plate, for example, a TN (Twisted Nematic) liquid crystal, an optical rotatory liquid crystal, and an optical rotator film can be used.

  In the present embodiment, a phase plate 16b that adjusts the phase of the second light beam B is provided, and the first light beam A obtained through the phase plate 16a and the second light beam obtained through the phase plate 16b. Although the phase shift with respect to B is suppressed, for example, by adopting the configuration of FIG. 7, the phase shift between the two light beams can be eliminated without providing a phase plate corresponding to the phase plate 16b.

  FIG. 7 is an explanatory diagram showing another configuration of the beam splitter 12. The light beam splitting element 12 is configured by bonding a retardation film 19 (phase plate) formed on a flat substrate 18 and a PBS 17 via an adhesive 20.

  The retardation film 19 is a polymer film having refractive index anisotropy created by stretching or the like, and has a function equivalent to that of the phase plate 16a. A thin plate such as quartz may be used instead of the retardation film 19. The retardation film 19 is formed on the flat substrate 18 so as to be covered with the adhesive 20. Thereby, only the first light beam A of the light source light beam is incident on the phase difference film 19, while the second light beam B is not incident on the phase difference film 19 but is incident on the surrounding adhesive 20.

  The adhesive 20 can be composed of, for example, an ultraviolet curable resin, a thermosetting epoxy resin, or an acrylic adhesive. In the configuration of FIG. 7, the adhesive 20 has a refractive index equivalent to the ordinary light refractive index no or the extraordinary light refractive index ne in the retardation film 19. Thereby, it is possible to prevent the optical length due to the difference in refractive index from changing between a portion where the retardation film 19 is present and a portion where the retardation film 19 is not present, and to suppress the wavefront of light incident on the PBS 17 from being disturbed.

  When the retardation film 19 is made of a general polycarbonate-based material, the refractive indices no and ne vary depending on the manufacturing method, etc., but the refractive index no is approximately 1.590. The refractive index ne seems to be about 1.592 (refractive index difference Δn = 0.002). Further, when the retardation film 19 is composed of a liquid crystalline polymer, it is possible to realize the refractive indexes no and ne of about 1.510 and 1.620 (refractive index difference Δn = 0.11), respectively. .

  By matching the refractive index of the adhesive 20 with the refractive index no or ne of the retardation film 19, the optical length due to the refractive index difference is not changed between the portion with and without the retardation film 19. Therefore, the difference between the refractive index of the adhesive 20 and the refractive index no or ne of the retardation film 19 needs to be smaller than Δn, specifically, 1/100 or more and 1/1000 or less. It is thought that it is necessary to make it.

  Further, when the retardation film 19 is used as shown in FIG. 7, there is almost no problem of thickness error, which is a problem with the crystalline phase plate, and it is easy to control the retardation for a plurality of wavelengths. is there.

  More specifically, in the case of a crystalline phase plate, the phase difference δ is expressed by δ = 2πΔn · d / λ. In addition, Δn represents a refractive index difference (ne-no) between extraordinary rays and ordinary rays, and d represents the thickness of the phase plate. For example, since the refractive index difference Δn of quartz is about 0.009, the phase difference δ corresponds to nine wavelengths (wavelength 0.5 μm) (multi-order) in a phase plate having a thickness of 0.5 mm (500 μm). Therefore, the phase difference δ varies greatly with a slight difference in the thickness d of the phase plate. On the other hand, the retardation film has a single order, and the influence of the retardation error hardly occurs.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to the drawings. For convenience of explanation, the same components as those in the first embodiment are denoted by the same member numbers, and the description thereof is omitted.

  FIG. 8 is an explanatory diagram showing a schematic configuration of the optical pickup according to the present embodiment. This optical pickup differs from the configuration of FIG. 6 of the first embodiment in the following points, and is otherwise the same as the configuration of FIG. That is, in the present embodiment, a raising mirror 4 'is arranged instead of the raising mirror 4 in FIG. Then, in the first light source unit 1 and the second light source unit 2, the phase plates 16 and 26 and the monitor detectors 15 and 25 are deleted, and instead, the monitor detectors are disposed behind the raising mirror 4 ′. 5 is arranged.

  The rising mirror 4 ′ is a light beam branching element that branches the light beam from the light sources 11 and 21 into a light beam traveling in the direction of the objective lens 7 and a light beam traveling in a different direction. The details will be described later. To do.

  The monitor detector 5 receives a part of the laser light emitted from each of the light sources 11 and 21, and is composed of, for example, a photodiode and a control unit. In this embodiment, the monitor detector 5 receives light branched in a direction different from the direction of the objective lens 7 by the rising mirror 4 ′ (for example, light transmitted through the rising mirror 4 ′), and The light output of the light sources 11 and 21 is controlled based on the amount of received light. Therefore, also in this embodiment, the laser light emitted forward from each of the light sources 11 and 21 (in the direction toward the optical disk D) is monitored by the monitor detector 5 via the rising mirror 4 ′. It is a monitor method.

  In the configuration of the present embodiment, of the linearly polarized laser light emitted from the light source 11, for example, P-polarized light passes through the PBS 17 and enters the collimator lens 13. Then, the laser light converted into parallel light by the collimator lens 13 is reflected by the dichroic prism 3 and enters the rising mirror 4 '. On the other hand, of the linearly polarized laser light emitted from the light source 21, for example, P-polarized light passes through the PBS 27 and enters the collimator lens 23. The laser light converted into parallel light by the collimator lens 23 passes through the dichroic prism 3 and enters the rising mirror 4 ′.

  In the rising mirror 4 ′, part of the laser light emitted from the light sources 11 and 21 is guided to the monitor detector 5 and monitored by the monitor detector 5. On the other hand, the remainder of the laser light emitted from the light sources 11 and 21 is reflected by the rising mirror 4 ′ and is circularly polarized by the quarter wavelength plate 6, and then condensed on the optical disk D by the objective lens 7. Is done.

  The return light from the optical disk D again enters the quarter-wave plate 6 through the objective lens 7, where it is converted into linearly polarized light (for example, S-polarized light), and then enters the rising mirror 4 ′. The light is reflected by the raising mirror 4 ′ and enters the dichroic prism 3. At this time, if the return light is the return light of the laser light emitted from the light source 11, the return light incident on the dichroic prism 3 is reflected by the dichroic prism 3 and enters the PBS 17 via the collimator lens 13. In the PBS 17, the incident return light is reflected and received by the light receiving element 14.

  On the other hand, if the return light is the return light of the laser light emitted from the light source 21, the return light incident on the dichroic prism 3 passes through the dichroic prism 3 and enters the PBS 27 through the collimator lens 23. In the PBS 27, the incident return light is reflected and received by the light receiving element 24.

Next, details of the rising mirror 4 ′ will be described.
FIG. 9 is a plan view schematically showing a schematic configuration of the rising mirror 4 ′ of this embodiment. FIG. 10 shows the intensity distribution of incident light and the intensity distribution of reflected light of the rising mirror 4 ′. It is explanatory drawing shown typically. The rising mirror 4 'has a first region 31 and a second region 32 having different optical characteristics (for example, reflection characteristics), and constitutes a reflective optical element. In FIG. 9, the first region 31 is shown in black for the purpose of clearly distinguishing the first region 31 and the second region 32 (the same applies to FIG. 13).

  The first region 31 is a region for guiding a part of the laser light emitted from the light sources 11 and 21 to the monitor detector 5. In the present embodiment, the first region 31 includes a transmission region that transmits incident light with a predetermined transmittance. It has become. The first region 31 is inside (inside) the second region 32 on the glass substrate 4a, and in the plane intersecting with the optical axis of the laser light emitted from the light sources 11 and 21, the center of the optical axis. Are formed in one spot shape. Accordingly, the first region 31 can transmit the central portion of the light source light flux with a predetermined transmittance. The first region 31 can be formed by, for example, forming a general antireflection film (AR (Anti Reflection) film) on the glass substrate 4a which is a transparent substrate, but as shown in FIG. In addition, it is possible to allow light to pass through without providing an antireflection film on the glass substrate 4a, that is, to form the first region 31 only by the glass substrate 4a.

  FIG. 11 shows the spectral reflectance of the first region 31. In the first region 31, the reflectance of light in the vicinity of wavelengths of 405 nm, 660 nm, and 785 nm is set to be as low as 2% or less, and it is possible to monitor by transmitting laser light of these wavelengths. .

  On the other hand, the second region 32 is a region that guides the remainder of the laser light emitted from the light sources 11 and 21 (for example, the periphery of the light source beam) to the optical disc D. In FIG. 9, the line representing the outer edge of the second region 32 represents the outer edge of the laser light beam incident on the rising mirror 4 ′. The second region 32 is a reflective region that reflects incident light with a predetermined reflectance, and in this embodiment, a dielectric multilayer film 32a as a reflective film is formed on the glass substrate 4a. Is formed. The second region 32 may be formed by forming a composite of the dielectric multilayer film 32a and the metal film on the glass substrate 4a.

  FIG. 12 shows the spectral reflectance of the second region 32. Thus, in the second region 32, the reflectance of light in the vicinity of wavelengths 405 nm, 660 nm, and 785 nm is set to 96% or more. As a result, the laser beams having the respective wavelengths incident on the second region 32 are almost reflected by the second region 32 and directed to the optical disc D to be used for recording / reproduction of the optical disc D.

  Here, when the reflective film of the second region 32 is formed of, for example, aluminum only, the reflectance is only about 93% and the reflection is weak (the intensity of the reflected light is low). In addition, if the reflective film in the second region 32 is made of, for example, silver, corrosion progresses quickly with long-term use, so that the reliability is inferior. Therefore, by forming the reflective film in the second region 32 including at least the dielectric multilayer film 32a, there is almost no fear of corrosion due to long-term use, and a highly reliable rising mirror 4 ′ is realized. Can do.

  As described above, since the first region 31 and the second region 32 having the above-described characteristics are formed on the glass substrate 4a, the rising mirror 4 ′ has a plurality of regions having different reflection characteristics. It can be said that they are the structure currently formed on the same plane.

  In the above configuration, the central portion of the light beam emitted from the light sources 11 and 21 transmits the first region 31 with a predetermined transmittance. The light transmitted through the first region 31 is monitored by the monitor detector 5. In addition, the light reflected by the first region 31 in the central portion of the light flux travels toward the objective lens 7. On the other hand, the peripheral portion of the light beam emitted from the light sources 11 and 21 is reflected by the second region 32 with a predetermined reflectance and travels toward the objective lens 7. Both of the above light beams traveling toward the objective lens 7 are irradiated onto the optical disc D through the objective lens 7.

  As described above, in the raising mirror 4 ′, a plurality of regions (first region 31 and second region 32) having different reflection characteristics are formed on the same plane. Of the laser light guided to the optical disk D, light near the optical axis can be extracted (transmitted at a predetermined transmittance) in the direction of the monitor detector 5 through the first region 31. As a result, the intensity of the laser light applied to the optical disc D can be reduced only in the vicinity of the optical axis. At this time, as shown in FIG. 10, the intensity distribution of the light reflected by the rising mirror 4 ′ is such that the intensity in the vicinity of the optical axis of the intensity distribution of the incident light having a Gaussian distribution is slightly reduced. Distribution. As a result, the spot of the light condensed on the optical disc D via the rising mirror 4 ′ can be narrowed down in the radial direction and the circumferential direction of the optical disc D, and so-called super solution that can cope with high-density recording / reproduction. An image effect can be obtained.

  Further, since the light spot on the optical disk D can be further narrowed down, for example, even when there is a slight design error in the objective lens 7 or the like, the light spot with an appropriate diameter can be applied to the optical disk D, and recording on the optical disk D is possible. Reproduction can be performed reliably. That is, the design error of the optical element constituting the optical pickup can be absorbed by the above design of the rising mirror 4 '.

  Since the super-resolution effect as described above is obtained, the rising mirror 4 ′ of FIGS. 9 and 10 transmits the first region 31 that transmits the central part of the light beam from the light sources 11 and 21 with a predetermined transmittance. And the second region 32 that reflects the peripheral portion of the light beam with a predetermined reflectance and guides it to the objective lens 7 is a reflective optical element formed on the same plane (glass substrate 4a), and the light beam The central portion and the peripheral portion of the light beam are separated by the first region 31 and the second region 32, and the central portion of the light beam is further branched in different directions depending on the optical characteristics of the first region 31 (due to transmission and reflection) In other words, it can be said that a light beam branching element for guiding one branched light beam and the peripheral portion of the light beam to the objective lens 7 is configured.

  Further, since the rising mirror 4 ′ constitutes the light beam splitting element, the amount of transmitted light in the first region 31 can be adjusted by adjusting the optical characteristics (transmittance, reflectance) of the first region 31. can do. Thereby, if the light which permeate | transmits the 1st area | region 31 is utilized as monitor light like this embodiment, the light quantity of the monitor light can be changed without changing the area of the light-receiving surface of the detector 5 for monitoring. can do.

  Furthermore, since the amount of light (intensity) of light reflected by the first region 31 can also be adjusted by adjusting the optical characteristics of the first region 31, the reflected light from the first region 31 and the second region 32 can be adjusted. As shown in FIG. 10, the intensity distribution can be adjusted so that the light intensity near the optical axis decreases, and the intensity distribution can be adjusted according to the adjustment of the optical characteristics of the first region 31. You can also adjust the street. As a result, the super-resolution effect can be made variable by adjusting the spot diameter of the light applied to the optical disc D.

  That is, in the present embodiment, since the rising mirror 4 ′ constitutes the above-described light beam branching element, both the monitor light quantity and the super-resolution effect can be easily changed by adjusting the optical characteristics of the first region 31. Can be.

  As described above, the rising mirror 4 ′ of the present embodiment can change the intensity distribution of the incident light flux and guide it to the objective lens 7 by setting the optical characteristics of the first region 31. It can be said that the light intensity modulation element which guides the light flux from the light beam to the objective lens 7 by changing the intensity distribution is also constituted.

  By the way, the raising mirror 4 'is not limited to the configuration shown in FIG. For example, FIG. 13 is a plan view showing another configuration of the raising mirror 4 '. In the rising mirror 4 ′, the first region 31 is formed in a single slit shape passing through the center of the optical axis in a plane intersecting with the optical axis of the laser light emitted from the light sources 11 and 21. . In addition, the 1st area | region 31 may be formed with the slit which passes along the said optical-axis center, and the some slit arrange | positioned in the position which becomes left-right symmetric about the slit as an axis of symmetry.

  Even when the first region 31 is formed in this way, the central portion of the light source light beam and a part of the peripheral portion of the light source light beam are branched in the first region 31 in different directions by transmission and reflection. Therefore, as long as at least the central portion of the light source light beam is incident on the first region 31, the same effect as the configuration of FIG. 9 can be obtained. In particular, in the configuration of FIG. 13, since the first region 31 is formed in a slit shape passing through the center of the optical axis, the diameter of the light spot collected on the optical disc D is set to the radial direction or the circumferential direction of the optical disc D. There is an advantage that a super-resolution effect according to the optical disk D to be used can be obtained.

  As described above, the rising mirror 4 ′ according to the present embodiment may have the configuration shown in FIG. 9 or 13, and can be expressed as follows. That is, the rising mirror 4 ′ of the present embodiment is a light intensity modulation element that guides the light flux from the light sources 11 and 21 to the objective lens 7 by changing the intensity distribution thereof. A first region 31 and a second region 32 that are separated into a first light beam and a remaining second light beam, and the first light beam depends on the optical characteristics of the first region 31. Is further divided into different directions by transmission and reflection, and is constituted by a light beam branching element that guides one of the branched first light beam and the second light beam to the objective lens 7.

  By the way, in the rising mirror 4 ′ of the present embodiment, in order to suppress the disturbance of the wave front of the reflected light in the first region 31 and the second region 32, the phase adjustment layers for adjusting the phase of the reflected light are provided as described above. It may be provided in at least one of the regions. This point will be further described as follows.

  FIG. 14 schematically shows how the incident light beam is reflected by the rising mirror 4 '. Note that it is assumed that the rising mirror 4 ′ in FIG. 14 is not provided with a phase adjustment layer. Further, in the figure, the quarter wavelength plate 6 is not shown.

Consider a case where linearly polarized light is incident on the surface of the glass substrate 4a of the rising mirror 4 ′ at an incident angle of 45 °, for example. When this linearly polarized light is P-polarized light, the phase delay of the reflected light with respect to the incident light is caused by Pp1 for the reflected light in the first region 31 and Pp2 for the reflected light in the second region 32. Further, in the first region 31 and the second region 32, as shown in FIG. 14, a physical step d corresponding to the thickness of the dielectric multilayer film 32a occurs. The phase delay caused by the step d is represented by 2d · cos 45 °. Therefore, in order to prevent the wavefront of the entire light reflected by the first region 31 and the second region 32 from being disturbed, that is, to prevent an optical step from occurring.
2mλ = (2d · cos 45 ° + Pp2) −Pp1
It is sufficient to satisfy the above relationship. Note that m is an integer and λ is a wavelength used. In order to satisfy such a relational expression, a phase adjustment layer is provided on the glass substrate 4a of the rising mirror 4 ′, and the layer thickness of the phase adjustment layer may be set appropriately.

  For example, as shown in FIG. 15, in the second region 32, a phase adjustment layer 33 that adjusts the phase of reflected light in the region is provided below the dielectric multilayer film 32 a, and the layer of the phase adjustment layer 33 is provided. What is necessary is just to set thickness appropriately. If the layer thickness of the phase adjustment layer 33 is appropriately set, the phase adjustment layer 33 may be provided in the first region 31 and in both the first region 31 and the second region 32. It may be provided. That is, the phase adjustment layer 33 may be provided in at least one of a plurality of regions having different reflection characteristics.

  In each of the embodiments described above, the case where a plurality of light sources are provided has been described. However, the present invention can also be applied to an optical system having one light source.

It is explanatory drawing which shows the schematic structure of the light beam branching element used for the optical pick-up which concerns on one Embodiment of this invention. It is explanatory drawing which shows the schematic structure of the said optical pick-up. It is explanatory drawing which shows 1 process at the time of manufacturing the phase plate of the said light beam splitting element. It is explanatory drawing which shows the optical path of the 2nd light beam which injects into the said phase plate. It is explanatory drawing which shows the optical path of the 1st light beam which injects into the said phase plate. It is explanatory drawing which shows the other structure of the said optical pick-up. It is explanatory drawing which shows the other structure of the said light beam splitting element. It is explanatory drawing which shows the schematic structure of the optical pick-up which concerns on other embodiment of this invention. It is a top view which shows the schematic structure of the raising mirror used for the said optical pick-up. It is explanatory drawing which shows typically the intensity distribution of the incident light of the said raising mirror, and the intensity distribution of reflected light. It is a graph which shows the spectral reflectance of the 1st area | region of the said raising mirror. It is a graph which shows the spectral reflectance of the 2nd area | region of the said raising mirror. It is a top view which shows the other structure of the said raising mirror. It is explanatory drawing which shows typically a mode that an incident light beam is reflected by the said raising mirror. It is sectional drawing which shows other structure of the said raising mirror. It is explanatory drawing which shows the schematic structure of the conventional optical pick-up. It is explanatory drawing which shows the other structure of the conventional optical pick-up.

Explanation of symbols

4 'Rising mirror (light intensity modulation element, beam splitting element, reflection optical element)
5 Monitor Detector 7 Objective Lens 11 Light Source 12 Beam Splitting Element (Light Intensity Modulating Element)
15 Monitor detector 16a Phase plate (polarization converter)
16b Phase plate (phase adjustment unit)
17 PBS (polarization separator)
19 Retardation film (phase plate, polarization converter)
20 Adhesive 21 Light source 22 Beam splitting element (light intensity modulation element)
25 Monitor Detector 26 Phase Plate (Polarization Conversion Unit)
27 PBS (polarization separator)
31 1st area | region 32 2nd area | region A 1st light beam B 2nd light beam D Optical disk

Claims (13)

A light intensity modulation element that guides a light beam from a light source to an objective lens by changing its intensity distribution,
The light beam is separated into a first light beam including a central portion thereof and a remaining second light beam, and the first light beam is further branched in different directions by transmission and reflection, and the first light beam is branched. A light intensity modulation element comprising a light beam branching element for guiding one of the light beams and the second light beam to the objective lens. The luminous flux branching element is
A polarization converter that changes the polarization state of only the first light beam;
2. A polarization separation unit that separates a combined light beam of the first light beam and the second light beam obtained through the polarization conversion unit according to a polarization state. 2. The light intensity modulation element according to 1.   The light intensity modulation element according to claim 2, wherein the polarization conversion unit converts the polarization state of the first light flux into elliptically polarized light.   The light intensity modulation element according to claim 2, wherein the polarization conversion unit converts the polarization state of the first light flux into linearly polarized light different from the polarization direction of the first light flux.   5. The light intensity modulation element according to claim 2, wherein the light beam branching element further includes a phase adjusting unit that adjusts a phase of the second light beam.   6. The light intensity modulation element according to claim 5, wherein the polarization conversion unit and the phase adjustment unit are formed adjacent to each other on a plane perpendicular to the optical axis of the incident light beam.   The light intensity modulation element according to claim 5, wherein the polarization conversion unit and the phase adjustment unit are each configured by a phase plate. The optical axes of the polarization conversion unit and the phase adjustment unit are in a plane perpendicular to the optical axis of the incident light beam,
The optical axis of the phase adjustment unit is parallel to the polarization direction of the incident light beam,
8. The light intensity modulation element according to claim 5, wherein an optical axis of the polarization conversion unit is inclined with respect to a polarization direction of an incident light beam. The polarization conversion unit is composed of a phase plate, and is bonded to the polarization separation unit via an adhesive,
5. The light intensity modulation element according to claim 2, wherein the adhesive has a refractive index equivalent to a refractive index of ordinary light or extraordinary light in the phase plate. .   The light intensity modulation element according to any one of claims 4 to 6, wherein the polarization conversion unit is constituted by an optical rotation plate.   The beam splitter includes a first region that transmits the first beam with a predetermined transmittance, and a second region that reflects the second beam with a predetermined reflectance and guides it to the objective lens. The light intensity modulation element according to claim 1, comprising a reflection optical element formed on the same plane. A light source that emits light;
A light intensity modulation element that changes the intensity distribution of the light beam from the light source;
An optical pickup comprising an objective lens for condensing light obtained through the light intensity modulation element on an optical disc,
An optical pickup comprising the light intensity modulation element according to any one of claims 1 to 11. A monitor detector for controlling the output of light emitted from the light source;
The monitor detector receives light branched in a direction different from the direction of the objective lens by the light intensity modulation element, and controls the light output of the light source based on the amount of received light. The optical pickup according to claim 12.

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