JP2006196054A - Optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the thickness of the optical pickup while mounting a front monitor to correctly monitor the output of the laser light source. <P>SOLUTION: This optical pickup has a laser light source, an objective lens to focus the light beam emitted from the above laser light source on an optical disk, a photo detector to receive the return light beam of the above light beam reflected on the optical disk, a beam splitter to pass or reflect the light beam from the laser light source and the reflected light beam, and a front monitor to receive part of the light beam from the laser light source. Further, it has a transparent substrate having a 1st area irradiated by the light beam and other 2nd areas and is disposed between the beam splitter and the objective lens. This transparent substrate changes its length in the directions of the light beam for the 1st area and for the 2nd areas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical pickup mounted on an optical disc drive, and more particularly to an optical pickup having a configuration in which a part of a light beam emitted from a laser light source is detected to control the amount of light to be constant.

  In recent years, optical disc drives capable of recording and reproducing information such as CD-R / RW and DVD-R / RW have become widespread. The optical disk drive is configured to record information by irradiating the optical disk with a light beam by a built-in optical pickup, and to read information by detecting a reflected light beam from the optical disk.

  In recording and reproducing information using an optical pickup, it is necessary to accurately control the amount of light beam applied to the optical disk in order to perform stable recording and reproduction processing. For this reason, the optical pickup has a means for detecting the light amount of the light beam emitted from the laser light source, and the detected light amount is fed back to the laser light source, so that the light amount of the light beam irradiated on the optical disk can be accurately measured. Is controlling.

  In order to detect the light amount of the light beam emitted from the laser light source, it is common to provide a light receiving element that receives a part of the light beam emitted forward from the laser light source. The light receiving element that receives the light beam emitted toward the front of the chip of the laser light source is hereinafter referred to as a front monitor.

  As a means for guiding the light beam from the laser light source to the front monitor, the configuration in which the light beam emitted from the laser light source is divided into two by a beam splitter and the vicinity of the optical axis of one of the light beams is detected by the front monitor is the most. It can be said that it is a simple configuration. However, there has been a problem that the amount of light detected by the front monitor varies greatly due to interference between the light beam emitted from the laser light source and the reflected light beam reflected from the optical disk on the detection surface of the front monitor. As a method for avoiding this interference, for example, the optical pickup shown in Patent Document 1 employs a configuration in which a light beam outside the effective diameter of the objective lens is detected by a front monitor among light beams emitted from a laser light source. The light beam outside the effective diameter of the objective lens utilizes the fact that it does not interfere with the reflected light beam on the front monitor.

  Further, the optical pickup shown in Patent Document 2 has a configuration in which a part of the light beam emitted from the laser light source is reflected by a condensing mirror in a direction different from the traveling direction of the light beam and guided to the front monitor. Similar to Patent Document 1, since the light beam outside the effective diameter of the objective lens is detected by the front monitor, interference with the reflected light beam can be avoided. In addition, the arrangement of the condensing mirror increases the degree of design freedom with respect to the position of the front monitor.

JP 2001-184709 (Section 7, FIG. 1) JP 2001-93183 (Section 6, FIG. 4)

  In recent years, in order to support high-speed recording in CDs and DVDs, it is necessary to mount a high-power laser light source on the optical pickup. When the light output of a high-power laser light source is increased, the center of the optical axis may be inclined. In the optical pickup configured to detect the light beam outside the effective diameter of the objective lens with the front monitor as in Patent Documents 1 and 2, when the center of the optical axis is tilted, for example, the amount of light applied to the optical disk decreases, The amount of light on the front monitor increases, and there is a problem that the amount of light cannot be monitored accurately.

  In recent years, mobile notebook PCs have been further reduced in weight and thickness so that they can be easily carried. In order to mount an optical disc drive on such a thin notebook personal computer, it is necessary to make the optical pickup thinner as the optical disc drive becomes thinner. However, in the configuration in which a light beam outside the effective diameter of the objective lens is guided to the front monitor as in Patent Documents 1 and 2, there is a problem that it is very difficult to cope with the reduction in thickness.

  The present invention has been made in view of the above problems, and an object thereof is to monitor an accurate light amount of a laser light source.

  To achieve the above object, a laser light source, an objective lens for condensing a light beam emitted from the laser light source on an optical disc, a photodetector for receiving a reflected light beam of the light beam from the optical disc, and In an optical pickup comprising: a beam splitter that transmits or reflects a light beam emitted from a laser light source and the reflected light beam; and a front monitor that receives a part of the light beam emitted from the laser light source; A transparent substrate having a first region and a second region other than the first region, wherein the transparent substrate is disposed between the beam splitter and the objective lens, and the transparent substrate includes the first region and the second region. The length is different in the traveling direction of the light beam from the second region.

  According to the present invention, it is possible to monitor the exact light amount of the laser light source.

  Hereinafter, modes for carrying out the invention will be described in Examples 1 to 8.

  In the first embodiment, an optical pickup corresponding to an optical disc drive capable of recording and reproducing a DVD will be described.

  FIG. 1 is a diagram showing an optical system configuration of the optical pickup 1. A light beam is emitted from the laser light source 2 as divergent light. A one-dot chain line 3 in the figure indicates the optical path of the light beam. In order to record information or reproduce information on a DVD-type optical disk, a semiconductor laser having a wavelength of about 660 nm is generally used, and the laser light source 2 also emits a light beam having a wavelength of about 660 nm. Is assumed. The light beam emitted from the laser light source 2 enters the diffraction grating 4. The light beam is split into three beams by the diffraction grating 4 and used for a tracking servo signal (hereinafter referred to as TES) of the optical disk by the differential push-pull method (hereinafter referred to as DPP method). Since the DPP method is a very general TES detection method, description thereof is omitted. The light beam that has passed through the diffraction grating 4 is reflected by the beam splitter 5, guided to the collimating lens 6, and converted into a substantially parallel light beam. The light beam emitted from the collimating lens 6 is transmitted through the optical path length changing plate 7, reflected from the rising mirror 8 in the z direction in the figure, and collected on the optical disk (not shown) by the objective lens 10 mounted on the actuator 9. Lighted. The effect of the optical path length changing plate 7 will be described in detail later.

  The light beam is reflected by the optical disk, and reaches the photodetector 12 through the objective lens 10, the raising mirror 8, the optical path length changing plate 7, the collimator lens 6, the beam splitter 5, and the detection lens 11. The light beam is given predetermined astigmatism when passing through the beam splitter 5, and is used for detecting a focusing servo signal (hereinafter referred to as FES) of the optical disk by the astigmatism method. Since the astigmatism method is a very general FES detection method, its description is omitted. The detection lens 11 serves to determine the size of the light spot on the photodetector 12 while rotating the direction of astigmatism in a predetermined direction. The light beam guided to the light detector 12 is used for detection of an information signal recorded on the optical disk and detection of a position control signal of a light spot collected on the optical disk such as TES and FES.

  The light beam that has passed through the diffraction grating 4 passes through the beam splitter 5 and is guided to the front monitor 13. In the optical disk drive, as described above, when recording a signal on the optical disk, it is necessary to accurately control the light amount of the laser light source in order to irradiate the optical disk with a predetermined light amount. Is installed to control the amount of light emitted from the laser light source 2. The output signal of the front monitor 13 is fed back to a drive circuit (not shown) of the laser light source 2, and the desired amount of light can be irradiated onto the optical disk by controlling the amount of light emitted from the laser light source 2.

  The front monitor 13 is arranged so that the center of the light beam emitted from the laser light source 2 coincides with the center of the light receiving surface of the front monitor 13. Thus, in the configuration in which the center of the light beam is detected by the front monitor 13, the light beam emitted from the laser light source 2 and transmitted through the beam splitter, and the light beam emitted from the laser light source 2 through the beam splitter and the objective lens There is a problem in that the amount of light detected on the front monitor fluctuates due to interference between the light beam reflected from the optical disc on the front monitor and the amount of light on the optical disc cannot be accurately controlled. The optical path length changing plate 7 is arranged to eliminate interference on the front monitor 13. The optical path length represents the traveling distance of the light beam, and is represented by multiplying the traveling distance and the refractive index of the optical path.

  FIG. 2 shows an example of an outline of an optical path guided to a front monitor in an optical system of a conventional optical pickup. For the sake of simplicity, the optical parts are given the same names as those of the optical pickup 1. There are two optical paths, optical paths 15 and 16, through which the light beam emitted from the laser light source 2 reaches the front monitor 13. The optical path 15 passes through the beam splitter 5 and proceeds directly to the front monitor 13. The optical path 16 reflects the beam splitter 5 to reach the optical disk 14 and reflects the optical disk 14, and the reflected light beam is reflected again by the beam splitter 5 and further reflected by the end face of the laser light source 2. The light passes through the beam splitter 5 and reaches the front monitor 13.

  The traveling distance of the light beam from the laser light source 2 to the front monitor 13 indicated by the optical path 15 is the optical path length L1, and the traveling distance of the light beam from the laser light source 2 to the front monitor 13 indicated by the optical path 16 is the optical path length L2. Then, the complex amplitudes u1 (optical path 15) and u2 (optical path 16) of the light beam on the front monitor 13 can be expressed by the normal number 1. In addition, the intensity distribution on the front monitor 13 can be expressed by Equation 2.

  Here, A and B indicate the square root of the intensity of each light beam, and k (= 2π / λ) indicates the wave number. In the optical disk system, since the optical disk 14 is rotated and used when recording or reproduction is performed, the optical disk 14 is shaken and fluctuates in the direction of the arrow in the figure. In other words, the optical path length L2 of the optical path 16 changes as it becomes longer or shorter. For this reason, the intensity distribution of the light beam on the front monitor 13 expressed by Equation 2 varies greatly. This fluctuation is so-called interference of the light beam, which makes it difficult to accurately control the amount of light applied to the optical disk 14.

  FIG. 3 is a conceptual diagram of an optical path guided to the front monitor 13 in the optical system of the optical pickup 1, and parts unnecessary for explanation are omitted. The optical pickup 1 is different from the conventional optical pickup in that the number of optical path length changing plates is increased. There are three optical paths, optical paths 15, 17 a, and 17 b, through which the light beam emitted from the laser light source 2 reaches the front monitor 13.

  The optical path 15 passes through the beam splitter 5 and proceeds directly to the front monitor 13. 17 a and 17 b reflect the beam splitter 5, pass through the optical path length changing plate 7, reach the optical disc 14, reflect the optical disc 14, and the reflected light beam passes through the optical path length changing plate 7 again and passes through the beam splitter 5. , And further reflected on the end face of the laser light source 2, passes through the third beam splitter 5, and proceeds to the front monitor 13.

  The travel distance of the light beam from the laser light source 2 indicated by the optical path 15 to the front monitor 13 is the optical path length L1, and the travel distance of the light beam from the laser light source 2 indicated by the optical path 17a to the front monitor 13 is the optical path length L3a. If the traveling distance of the light beam from the laser light source 2 to the front monitor 13 indicated by the optical path 17b is an optical path length L3b, the complex amplitudes u1 (optical path 15), u3a (optical path 17a), u3b of the light beam on the front monitor 13 are set. (Optical path 17b) can be generally expressed by Equation 3. In addition, the intensity distribution on the front monitor 13 can be expressed by Equation 4.

  Here, A and C indicate the square root of the intensity of each light beam. Since it is assumed that the light path 17a and the light path 17b have the same light intensity distribution, the light beam intensity of u3a has a coefficient C equal to u3b.

  The optical path length changing plate 7 is a transparent substrate having a length L and a refractive index N, and a region 18 near the center of the light beam is longer by δ than the other regions. For this reason, since the optical path 17a passes through the center of the light beam with respect to the optical path 17b, the optical path 17a travels through the transparent substrate having a refractive index, and the optical path length L3a and the optical path length L3b are different. Become.

  For example, when the difference between the optical path length L3a and the optical path length L3b is equal to ½ of the wavelength, the intensity distribution on the front monitor 13 is a coefficient as shown in Equation 4. This indicates that the intensity distribution on the front monitor 13 is constant, and it can be said that the amount of light beam condensed on the optical disk 14 can be accurately controlled. That is, the length δ of the region 18 of the optical path length changing plate 7 may be given so that the difference between the optical path length L3a and the optical path length L3b coincides with an odd multiple of ½ of the wavelength.

  The difference between the optical path length L3a and the optical path length L3b is the difference between whether or not it passes through the region 18 of the optical path length changing plate 7. Here, attention is paid to the optical path length when the optical paths 17a and 17b travel along the optical path δ. Since the optical path 17b passes through the region 18 of the optical path length changing plate 7 having a refractive index N, the optical path length is δ × N. On the other hand, since the optical path length 17a travels in air with a refractive index of 1, the optical path length is δ. When the optical path 17a and the optical path 17b pass through the optical path length changing plate 7 once, an optical path length difference of δ × N−δ is generated. Since the optical path length 17a and the optical path length 17b pass through the optical path length changing plate 7 twice, the optical path length difference is 2 × δ (N−1).

  When the difference between the optical path length L3a and the optical path length L3b coincides with an odd multiple of ½ of the wavelength, the interference on the front monitor can be eliminated, so δ only needs to satisfy the condition of Equation 5.

  Next, the optical path length changing plate 7 will be described with reference to FIG. FIG. 4 shows a schematic diagram of the optical path length changing plate 7. The left figure shows the optical path length changing plate 7 viewed from the yz plane, and the right figure shows the optical path length changing plate 7 viewed from the zx plane. The optical path length changing plate 7 is a transparent substrate composed of a region 18 having a width p and other regions, and the region 18 has a length different from that of other regions by δ in the traveling direction of the light beam (y direction in the figure). Is. The length δ of the region 18 has an optical path difference that is an odd multiple of ¼ of the wavelength in the region other than the region 18 as expressed by Equation 5. The center of the region 18 is assumed to coincide with the optical axis. The width P of the region 18 is such that the light beam transmitted through the region 18 and the light beam transmitted through the other region, that is, the amount of light reaching the front monitor 13 by the light beams of the optical path 17a and the optical path 17b are equal. The width is optimal.

  Further, by aligning the center of the region 18 with the optical axis in this way, the light beam transmitted through the optical path length changing plate and directed to the objective lens, and the reflected light beam reflected from the optical disk and transmitted through the optical path length changing plate. Are considered to pass through the same optical path. If they do not pass through the same optical path, a desired difference cannot be given to the optical path length L2 and the optical path length L3, and the effect of interference cannot be reduced.

  The objective lens is usually used by moving in the radial direction of the optical disk when accessing a predetermined position of the optical disk. This is generally referred to as objective lens shift. In the present invention, since a longitudinal band is assumed in the radial direction of the optical disc, the effect of interference can be reduced without any problem even if such objective lens shift occurs. Can do.

  In the optical pickup 1, the optical path length changing plate 7 is disposed independently. For example, the collimator lens 8, which is a component between the beam splitter 5 and the objective lens 10, has a width P and a light beam traveling direction. A protruding region having a length δ may be provided instead of the region 18. By doing so, the amount of light on the optical disk can be accurately controlled with the same number of parts as the conventional optical pickup.

  In addition, since the amount of light at the center of the optical axis is used, there is an effect that the front monitor can be arranged in a thin optical pickup as compared with the conventional front monitor configuration that takes light outside the effective diameter of the objective lens.

  In the first embodiment, the optical pickup corresponding to the optical disk drive capable of recording and reproducing the DVD has been described. Of course, the optical pickup is compatible with a next-generation high-density optical disk drive (BD or HD-DVD) using a CD or a blue semiconductor laser. It can also be applied to compatible optical pickups.

  In the second embodiment, the configuration of the optical path length changing plate 7 is different from that of the optical pickup 1 of the first embodiment. Except for the optical path length changing plate 7, the optical pickup 1 is the same as the optical pickup 1 and will not be described.

FIG. 5 is a schematic view of the optical path length changing plate 7 mounted on the optical pickup 1.
The left figure shows the optical path length changing plate 7 viewed from the yz plane, and the right figure shows the optical path length changing plate 7 viewed from the zx plane. The optical path length changing plate 7 has a length L and is a transparent substrate composed of a region 19 having a width p and other regions. The region 19 has a refractive index different from that of the other regions by dN.

  If the refractive index of the region 19 is N1, and the refractive index of the region other than the region 19 is N2, the optical path length of the light beam passing through the region 19 is N1 × L, and the optical path length of the light beam passing through the region other than the region 19 is N2 × L. The optical path length difference between the region 19 and other regions is (N1−N2) × L, that is, dN × L. Since the light beam passes through the optical path length changing plate 7 twice, the difference in optical path length given by the optical path length changing plate 7 is 2 × dN × L, and when this is an odd multiple of ½ of the wavelength, And the influence of interference can be eliminated. For this reason, dN is preferably set so as to satisfy Equation 6.

  The width P of the region 19 is such that the light beam transmitted through the region 18 and the light beam transmitted through the other region, that is, the amount of light reaching the front monitor 13 by the light beams in the optical path 17a and the optical path 17b are made equal. The width is optimal.

  In addition, by making the center of the region 19 coincide with the optical axis in this way, a light beam that passes through the optical path length changing plate and travels toward the objective lens, and a reflected light beam that reflects from the optical disk and passes through the optical path length changing plate. Are considered to pass through the same optical path. If they do not pass through the same optical path, a desired difference cannot be given to the optical path length L2 and the optical path length L3, and the effect of interference cannot be reduced.

  Of course, N2 may be larger than N1 or N1 may be larger than N2 to give a desired optical path length difference.

  As described above, an effect of eliminating the influence of interference can be obtained even with an optical path length changing plate having a configuration different from that in FIG.

  In Example 3, a combination optical pickup corresponding to an optical disk drive capable of recording and reproducing DVD and CD will be described.

FIG. 6 is a diagram showing an optical system configuration of the optical pickup 20.
A light beam is emitted from the DVD laser light source 21 as divergent light. It is assumed that a light beam having a wavelength of about 660 nm is emitted from the DVD laser light source 21 in order to record information on or reproduce information from a DVD optical disk. A one-dot chain line 22 in the figure indicates the optical path of the light beam. The light beam emitted from the DVD laser light source 21 enters the DVD diffraction grating 23. The light beam is split into three beams by the DVD diffraction grating 23 and used for TES of an optical disk by the DPP method. The light beam that has passed through the DVD diffraction grating 23 passes through the prism 24, is reflected by the beam splitter 25, is guided to the collimator lens 26, and is converted into a substantially parallel light beam. The light beam emitted from the collimating lens 26 passes through the optical path length changing plate 27, reflects the rising mirror 28 in the Z direction in the figure, and is condensed on the optical disk (not shown) by the objective lens 30 mounted on the actuator 29. The The light beam is reflected by the optical disk, and reaches the photodetector 32 through the objective lens 30, the rising mirror 28, the optical path length changing plate 27, the collimator lens 26, the beam splitter 25, and the detection lens 31. A predetermined astigmatism is given to the light beam when passing through the beam splitter 25, and it is used for detecting the FES of the optical disk by the astigmatism method. The detection lens 31 functions to determine the size of the light spot on the photodetector 32 while rotating the direction of astigmatism in a predetermined direction. The light beam guided to the light detector 32 is used for detection of an information signal recorded on the optical disk and detection of a position control signal of a light spot collected on the optical disk such as TES and FES.

  A light beam is emitted from the CD laser light source 33 as divergent light. In order to record information or reproduce information on a CD-type optical disk, a semiconductor laser having a wavelength of about 780 nm is generally used, and the CD laser light source 33 also emits a light beam having a wavelength of about 780 nm. Assume a laser. The light beam emitted from the CD laser light source 33 enters the CD diffraction grating 34. The light beam is split into three beams by the CD diffraction grating 34 and used for TES of an optical disk by the DPP method. The light beam that has passed through the CD diffraction grating 23 passes through the correction lens 35, the prism 24, and the beam splitter 25, is guided to the collimator lens 26, and is converted into a substantially parallel light beam. A CD that does not need to narrow the light spot on the optical disc more than necessary as compared with a DVD generally has a lower optical magnification than a DVD and increases the efficiency up to the optical disc. Therefore, the correction lens 35 is arranged to change the divergence angle of the light beam emitted from the CD laser light source 33 in order to set the optical magnification of the CD optical system lower than that of the DVD optical system. The light beam emitted from the collimator lens 26 passes through the optical path length changing plate 27, reflects the rising mirror 28 in the Z direction in the figure, and is condensed on the optical disk (not shown) by the objective lens 30 mounted on the actuator 29. The The light beam is reflected by the optical disk, and reaches the photodetector 32 through the objective lens 30, the raising mirror 28, the optical path length changing plate 27, the collimator lens 26, the beam splitter 25, and the detection lens 31. The light beam is given a predetermined astigmatism when passing through the beam splitter 25, and is used for detecting the FES of the optical disc by the astigmatism method. The detection lens 31 has the function of rotating the astigmatism direction in a predetermined direction and determining the size of the light spot on the photodetector 32. The light beam guided to the light detector 32 is used for detection of an information signal recorded on the optical disk and detection of a position control signal of a light spot collected on the optical disk such as TES and FES.

  The light beam emitted from the DVD laser light source 21 and the beam emitted from the CD laser 33 are emitted from the prism 24, pass through the beam splitter 25, and are guided to the front monitor 36. In the optical disk drive, as described above, when recording a signal on the optical disk, it is necessary to accurately control the light quantity of the laser light source in order to irradiate the optical disk with a predetermined light quantity. It is installed to detect changes and control the amount of light emitted from the laser light source 2. The output signal of the front monitor 13 is fed back to the drive circuit (not shown) of the laser light source 2.

  The front monitor 36 is arranged so that the center of the light beam emitted from the DVD laser light source 21, the center of the light beam emitted from the CD laser light source 33, and the center of the light receiving surface of the front monitor 36 coincide. Thus, in the configuration in which the center of the light beam is detected by the front monitor 36, the optical path length changing plate 27 is used in order to eliminate interference caused on the front monitor by the light beam reflected from the optical disk and reflected from the end face of each laser light source. Is provided. The optical path length changing plate 27 is different from the optical path length changing plate 7 of FIG. Since the two laser light sources of the DVD laser light source 21 and the CD laser light source 33 are mounted, the optical path length changing plate 27 is an area when the emission wavelength of the DVD laser light source 21 is λ1 and the emission wavelength of the CD laser light source 33 is λ2. The length δ of 18 is expressed as in Expression 7.

  When two laser light sources having different wavelengths are mounted, the interference between the wavelengths can be eliminated by multiplying the two wavelengths. That is, it can be said that the present invention is effective also in an optical pickup of an optical system sharing a DVD and CD front monitor.

  In the third embodiment, the optical system sharing the DVD and CD front monitor has been described. Of course, the front monitor of the next generation high-density optical disk drive (BD and HD-DVD) using the CD and the blue semiconductor laser is of course. It can also be applied to the common use of the system.

  Of course, in the case of three combinations, the interference of the three wavelengths can be eliminated by multiplying the three wavelengths, and the next-generation high-density optical disk drive (BD) using DVD, CD, and blue semiconductor laser. And HD-DVD) can be used in common with three front monitors.

  In the fourth embodiment, a combination optical pickup corresponding to an optical disk drive capable of recording and reproducing DVD and CD will be described.

  FIG. 7 is a diagram showing an optical system configuration of the optical pickup 40. The first embodiment is that a two-wavelength multi-laser light source 41 having two laser chips mounted on a laser light source is disposed. The two-wavelength multi-laser light source 41 is equipped with laser chips that oscillate at wavelengths of 660 nm and 780 nm, respectively, in order to support recording and reproduction of DVD and CD. A light beam is emitted from the two-wavelength multi-laser light source 41 as divergent light. In the figure, a one-dot chain line 42 indicates the optical path of the light beam. The light beam emitted from the two-wavelength multi-laser light source 41 is converted into a substantially parallel light beam by the collimator lens 43. The light beam transmitted through the collimator lens 43 enters the DVD / CD shared diffraction grating 44. The DVD / CD shared diffraction grating 44 splits the light beam into three DVDs / CDs, which are used to detect the TES of the optical disk by the DPP method. The light beam transmitted through the DVD / CD shared diffraction grating 44 is reflected by the beam splitter 45 and transmitted through the wideband 1 / 4λ wavelength plate 46. The wideband wave plate 46 has the effect of rotating the polarization of the DVD and CD light beams by ¼ wavelength. The optical path length changing plate 47 is affixed to the wideband wavelength plate 46, and the interference on the front monitor 54 can be removed by changing the optical path length of the reflected light from the optical disk without increasing the number of optical components. Further, since there are two-wavelength light beams of DVD and CD, the thickness of the protruding portion may be set as shown in Equation 6. The light beam transmitted through the wideband wavelength plate 46 to which the optical path length changing plate 47 is attached is reflected on the rising mirror 48 in the z direction in the figure and is optical disc (not shown) by the objective lens 50 mounted on the actuator 49. Focused on top. The light beam is reflected by the optical disk, and reaches the photodetector 53 through the objective lens 50, the rising mirror 48, the wideband wavelength plate 46, the beam splitter 45, and the detection lens 52. The light beam is given a predetermined astigmatism when passing through the beam splitter 45, and is used for detecting the FES of the optical disk by the astigmatism method. The detection lens 52 functions to determine the size of the light spot on the photodetector 53 while rotating the direction of astigmatism in a predetermined direction. The light beam guided to the photodetector 53 is used for detection of an information signal recorded on the optical disc and a position control signal of a light spot collected on the optical disc such as TES and FES.

  The light beam transmitted through the DVD / CD shared diffraction grating 44 passes through the beam splitter 45 and is guided to the front monitor 54. In the optical disk drive, as described above, when recording a signal on the optical disk, it is necessary to accurately control the light amount of the laser light source in order to irradiate the optical disk with a predetermined light amount. Is installed in order to detect a change in the amount of light and control the amount of light emitted from the two-wavelength multi-laser light source 41. The output signal of the front monitor 54 is fed back to a drive circuit (not shown) of the two-wavelength multi-laser light source 41.

  The front monitor 54 is arranged so that the center of the light beam emitted from the two-wavelength multi-laser light source 41 and the center of the light receiving surface of the front monitor 54 coincide. The optical path length changing plate 47 is arranged to eliminate interference on the front monitor 54 that occurs in the configuration in which the center of the light beam is detected by the front monitor 54, and the light amount of the light beam collected on the optical disc Can be accurately controlled.

  In the fifth embodiment, an optical pickup corresponding to an optical disk drive capable of recording and reproducing a DVD will be described.

  FIG. 8 is a diagram showing an optical system configuration of the optical pickup 60. The difference from the first embodiment is that the optical module 61 is used. The optical module 60 is an optical element in which an optical element capable of detecting a laser chip, a photodetector, TES, and FES is provided in one package.

  A light beam is emitted from the optical module 60 as divergent light. A one-dot chain line 3 in the figure indicates the optical path of the light beam. In order to record information or reproduce information on a DVD-type optical disk, it is common to use a semiconductor laser having a wavelength of about 660 nm, and the optical module 60 also emits a light beam having a wavelength of about 660 nm. Is installed. The light beam emitted from the optical module 60 is guided to the collimating lens 6 and converted into a substantially parallel light beam. The light beam emitted from the collimating lens 6 is transmitted through the beam splitter 5 and the optical path length changing plate 7, reflected from the rising mirror 8 in the z direction in the figure, and optical disc (not shown) by the objective lens 10 mounted on the actuator 9. ) Condensed on top. The light beam is reflected by the optical disk, and reaches the optical module 60 through the objective lens 10, the raising mirror 8, the optical path length changing plate 7, the beam splitter 5, and the collimating lens 6.

  The light beam reflected from the beam splitter 5 is guided to the front monitor 13. In the optical disk drive, as described above, when recording a signal on the optical disk, it is necessary to accurately control the light quantity of the laser light source in order to irradiate the optical disk with a predetermined light quantity, and the front monitor 13 changes the light quantity of the light beam. It is installed to detect and control the amount of light emitted from the optical module. The output signal of the front monitor 13 is fed back to a drive circuit (not shown) of the optical module 60.

  The front monitor 13 is arranged so that the center of the light beam emitted from the optical module 60 coincides with the center of the light receiving surface of the front monitor 13. The optical path length changing plate 7 is disposed to eliminate interference on the front monitor 13 that occurs when the front monitor 13 detects the center of the light beam. It becomes possible to control the amount of light accurately.

  In the sixth embodiment, an optical disk system equipped with the optical pickup described so far will be described.

  FIG. 9 shows a schematic block diagram of an optical disk system for recording and reproduction in which the optical pickup 1 is mounted. A signal detected from the optical pickup 1 is sent to a servo signal generation circuit 71, a front monitor circuit 72, and an information signal reproduction circuit 75 in the signal processing circuit. The servo signal generation circuit 71 generates FES and TES suitable for each optical disk from these detection signals, and drives the objective lens actuator in the optical pickup 1 via the actuator drive circuit 70 based on this FES and TES. Take control. The front monitor circuit 72 detects the light amount monitor signal of the laser light source from the detection signal from the front monitor, and drives the laser light source control circuit 73 based on this to control the light amount on the optical disk 14 accurately. The information signal reproduction circuit 75 reproduces the information signal recorded on the optical disk 14 from the detection signal, and the information signal is output to the information signal output terminal 79.

  When recording information is input from the recording information input terminal 80, the recording information signal conversion circuit 76 converts the recording information into a predetermined laser driving recording signal. The recording signal for driving the laser is sent to the control circuit 78, the laser light source control circuit 73 is driven to control the amount of light of the laser light source, and the recording signal is recorded on the optical disc 14. An access control circuit 74 and a spindle motor drive circuit 77 are connected to the control circuit 78, and position control in the access direction of the optical pickup 1 and rotation control of the spindle motor 81 of the optical disk 14 are performed.

  The seventh embodiment is different from the optical pickup 1 of the first embodiment in the configuration of the optical path length changing plate 7, and other than the optical path length changing plate 7 is the same as the optical pickup 1, so the description thereof will be omitted.

FIG. 10 is a schematic view of the optical path length changing plate 7 mounted on the optical pickup 1.
The left figure shows the optical path length changing plate 7 viewed from the yz plane, and the right figure shows the optical path length changing plate 7 viewed from the zx plane. Compared with the region 18 in FIG. 5, the region 100 is simply shorter than the other regions by the length δ. Even in the optical path length changing plate having this configuration, if δ satisfies Equation 5, a desired optical path length difference can be added, and the effect of interference can be eliminated.

  In addition, the optical path length changing plate 7 is not disposed independently, but, for example, the collimating lens 8 which is a component between the beam splitter 5 and the objective lens 10 has a width P and a length δ in the traveling direction of the light beam. It does not matter at all if a recessed area is provided instead of the area 100. This also makes it possible to accurately control the amount of light on the optical disc with the same number of parts as a conventional optical pickup.

  In the eighth embodiment, the configuration of the optical path length changing plate 7 is different from that of the optical pickup 1 of the first embodiment. Except for the optical path length changing plate 7, the optical pickup 1 is the same as the optical pickup 1 and will not be described.

FIG. 11 is a schematic view of the optical path length changing plate 7 mounted on the optical pickup 1.
The left figure shows the optical path length changing plate 7 viewed from the yz plane, and the right figure shows the optical path length changing plate 7 viewed from the zx plane. Compared with the region 18 in FIG. 5, the region 101 is simply formed by doubling the length δ and doubling the width p and aligning the center of the optical axis with the lower portion of the region 101. Even in the optical path length changing plate having this configuration, if δ satisfies Equation 5, a desired optical path length difference can be added, and the effect of interference can be eliminated.

  In addition, the optical path length changing plate 7 is not disposed independently, but, for example, the collimating lens 8 that is a component between the beam splitter 5 and the objective lens 10 has a width 1 / 2P and a length 2δ in the traveling direction of the light beam. It does not matter at all if a protruding region having a ridge is provided instead of the region 101. This also makes it possible to accurately control the amount of light on the optical disc with the same number of parts as a conventional optical pickup.

  As described above, the optical pickup of the present invention is most suitable for thinning, in which the light beam near the optical axis emitted from the laser light source is divided into two by the beam splitter and one of the light beams is detected by the front monitor. With the optical system configuration, it is possible to avoid interference between the light beam emitted from the laser light source and the reflected light beam reflected from the optical disk, and to monitor the exact light amount of the laser light source.

1 is a diagram illustrating a configuration of an optical system of an optical pickup in Embodiment 1. FIG. It is a figure which shows the optical path guide | induced to the front monitor 13 among the optical systems of the conventional optical pick-up. FIG. 3 is a diagram illustrating an optical path guided to a front monitor 13 in the optical system of the optical pickup in the first embodiment. FIG. 3 is a diagram showing an outline of an optical path length changing plate in Example 1. FIG. 6 is a diagram showing an outline of an optical path length changing plate in Example 2. 6 is a diagram illustrating a configuration of an optical system of an optical pickup in Embodiment 3. FIG. 6 is a diagram illustrating a configuration of an optical system of an optical pickup in Embodiment 4. FIG. FIG. 10 is a diagram illustrating a configuration of an optical system of an optical pickup according to a fifth embodiment. FIG. 10 is a diagram showing a schematic block of an optical disc system in Embodiment 6. It is a figure which shows the outline of the optical path length change board in Example 7. FIG. It is a figure which shows the outline of the black length change board in Example 8. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical pick-up 2 ... Laser light source 7 ... Optical path length change board 12 ... Photo detector 13 ... Front monitor 73 ... Laser light source control circuit

Claims (6)

A laser light source, an objective lens for condensing a light beam emitted from the laser light source on an optical disc, a photodetector for receiving a reflected light beam of the light beam from the optical disc, a light beam emitted from the laser light source, and In an optical pickup comprising a beam splitter that transmits or reflects the reflected light beam, and a front monitor that receives a part of the light beam emitted from the laser light source,
A transparent substrate having a first region irradiated with the light beam and a second region other than the first region;
The transparent substrate is disposed between the beam splitter and the objective lens;
2. The optical pickup according to claim 1, wherein the transparent substrate has a different length in the traveling direction of the light beam in the first region and the second region.   2. The optical pickup according to claim 1, wherein the transparent substrate has the region 1 and the region of the transparent substrate, where λ is a wavelength of the laser light source, m is an integer, and N is a refractive index of the transparent substrate. 2 is an optical pickup characterized in that the length differs in the traveling direction of the light beam by 1/4 × (2 × m + 1) × λ / (N−1). A laser light source, an objective lens for condensing a light beam emitted from the laser light source on an optical disc, a photodetector for receiving a reflected light beam of the light beam from the optical disc, a light beam emitted from the laser light source, and In an optical pickup comprising a beam splitter that transmits or reflects the reflected light beam, and a front monitor that receives a part of the light beam emitted from the laser light source,
A transparent substrate having a first region irradiated with the light beam and a second region other than the first region;
The transparent substrate is disposed between the beam splitter and the objective lens;
The optical pickup according to claim 1, wherein the transparent substrate has a refractive index different between the first region and the second region.   4. The optical pickup according to claim 3, wherein the transparent substrate has the first region, where λ is a wavelength of the laser light source, m is an integer, and L is a distance in the traveling direction of the light beam of the transparent substrate. And an optical pickup having a refractive index different from that of the second region by ¼ × (2 × m + 1) × λ / L.   5. The optical pickup according to claim 2, wherein in the transparent substrate, the first region has a strip shape, and the center of the first region is substantially the same as the optical axis center of the light beam emitted from the laser light source. The optical pickup is characterized in that the longitudinal direction of the band of the first region is the radial direction of the optical disc. 6. An optical disc system comprising: the optical pickup according to claim 1; and a laser light source control circuit for controlling an emitted light amount of the laser light source using a signal output from the front monitor of the optical pickup. .

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