JPH0515129U - Hologram light head - Google Patents

Abstract

(57) [Abstract] [Purpose] To reduce the assembly and adjustment man-hours by integrating optical parts. [Structure] A photodetector 18 in which four light receiving elements are arranged around a laser diode 17 is provided. A cover glass 21 is provided on the laser light emitting window 19 a of the case 19. The hologram surface 20 is formed on the cover glass 21. The hologram surface 20 is composed of four regions having different lattice patterns. The photodetector 18 receives the light beam diffracted through each of the four areas of the hologram surface 20.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 This invention relates to a hologram optical head.

[0002]

[Prior Art]

 FIG. 7 shows an example of a conventional optical head. The laser light emitted from the laser diode 1 is separated into three light beams by the diffraction grating 2, reflected at a right angle by the half mirror 3, collimated by the collimator lens 4, and directed to the disk 7 side by the rising mirror 5. It is reflected at a right angle, condensed by the objective lens 6 and focused on the signal surface of the disk 7. The return light reflected by the disk 7 passes through the objective lens 6 in the same path, is reflected in the right angle direction by the rising mirror 5, is condensed by the collimator lens 4, passes through the half mirror 3, and is further flat. The glass plate 8 for returning the deviation of the optical axis caused by passing through the half mirror 3 made of glass is transmitted, the plano-concave lens 9 is transmitted, and the photodetector 10 is irradiated. Although not shown, the photodetector 10 is a 6-division photosensor having elements on both sides of the 4-division photosensor. Focusing error detection is based on transmission through the flat half mirror 3 and the glass plate 8. The astigmatism method utilizing the accompanying astigmatism is used, and tracking error detection is performed using two of the three beams.

[0003]

[Problems to be solved by the device]

 Since the conventional optical head has a large number of parts and they are arranged independently, it is not easy to miniaturize them, and it requires a lot of man-hours for assembling each optical part and a large number of man-hours for adjusting them. I need. In addition, each optical component is often fixed with an adhesive, but since the adhesive is easily affected by temperature, there is a risk that the optical components will be displaced due to temperature fluctuations. There is also a problem in that the reliability of signal detection is reduced because the number of points used is increased.

The present invention has been made in view of the above circumstances. The number of parts of the optical head is reduced, each optical part is integrated to reduce the size, and the number of assembling steps and adjusting steps are reduced, and the temperature fluctuation is further reduced. It is an object of the present invention to provide a hologram optical head which is less likely to be affected by.

[0005]

[Means for Solving the Problems]

 The hologram optical head of the present invention for solving the above-mentioned problems is provided with a hologram element composed of four regions having different grating patterns, and the return light reflected by the disk is divided into four diffracted lights separated by the respective regions of the hologram device. Is provided with a photodetector composed of four light-receiving elements, and at least two light-receiving elements of the four light-receiving elements are divided into two.

A hologram optical head according to a second aspect of the invention has a laser diode, a photodetector composed of four light receiving elements arranged around the laser diode as a center, and a laser light emitting window, A hologram laser unit comprising: a case for accommodating a diode and a photodetector; and a cover glass attached to the laser light emitting window, the cover glass having a hologram surface composed of four regions having different grating patterns. To do.

[0007]

[Action]

 In the hologram optical head described above, the return light reflected by the disk is diffracted by the four regions of the hologram element to be separated into four light beams, and the four light receiving elements of the photodetector are individually irradiated. In this case, the tracking error can be detected by the difference in the outputs of the light receiving elements corresponding to the two areas of the hologram element consisting of four areas and the other two areas, that is, by the push-pull method. . Focusing error detection can be performed by the so-called double knife edge method based on the outputs of two two-divided photodetectors corresponding to two regions.

In the hologram optical head of the second aspect, the laser diode, the photodetector and the hologram element are highly integrated as a hologram laser unit.

[0009]

【Example】

 Hereinafter, embodiments of the present invention will be described with reference to FIGS. In FIG. 1, reference numeral 11 is a hologram laser unit for emitting laser light and receiving return light, and reference numeral 12 is for raising the laser light emitted from the hologram laser unit 11 to the disk 14 side and returning it, although details will be described later. A rising mirror that reflects light toward the hologram laser unit 11, and an objective lens 13 that focuses the laser light on the signal surface of the disk 14.

The details of the hologram laser unit 11 are shown in FIG. In this hologram laser unit 11, a laser diode 17 and a photodetector 18 are attached to a base 15 via a stem 16, these are housed in a case 19, and an inner surface is formed in a laser light emitting window 19a opened in the case 19. A cover glass 21 having a hologram surface (that is, a hologram element) 20 formed thereon is fixed.

As shown in FIG. 3, the hologram surface 20 is composed of four regions a, b, c, and d in which a circle is divided into four equal parts and different lattice patterns are formed in the respective parts. The lattice pattern of the illustrated example is such that a and d have equal pitches, b and c have equal pitches with a wider spacing than the above a and d, and in the lattice direction, a and c are in the same direction and b and d are It is perpendicular to the above a and d and is in the same direction. As shown in FIG. 4, the photodetector 18 includes four light receiving elements A, B, C, and D at positions that form an angle of 45 ° with respect to the X-Y direction. The light receiving elements A, B, C and D respectively receive the light beams transmitted through the four areas a, b, c and d of the hologram surface 20, and the light receiving elements A and C are light receiving elements each consisting of a single element. Each of the light receiving elements B and D is a two-divided light receiving element composed of two elements B ₁ , B ₂ or D ₁ , D ₂ . Further, the light receiving elements A and D are located equidistant from the optical axis Z in correspondence with the narrow equal pitch areas a and d on the hologram surface 20, and the light receiving elements B and C are wide equal pitch areas b and c. Correspondingly, the light receiving elements A and D are located equidistantly closer to the optical axis Z than the light receiving elements A and D.

Next, signal detection by the hologram optical head will be described. The laser light emitted from the laser diode 17 in the hologram laser unit 11 passes through the hologram surface 20, is reflected at a right angle by the rising mirror 12, is converged by the objective lens 17, and is focused on the signal surface of the disk 14. The return light reflected by the disk 14 follows the same path, passes through the objective lens 13, and is reflected again by the rising mirror 12 in the perpendicular direction, and passes through the cover glass 21 of the hologram laser unit 11. When passing through the hologram surface 20 of 21, the four diffracted lights (for example, only the + 1st order diffracted light is used) can be obtained by passing through the four regions a, b, c and d having different grating patterns on the hologram surface 20. can get. The light beams that have respectively passed through the regions a, b, c, d of the hologram surface 20 illuminate the respective light receiving elements A, B, C, D of the photodetector 18. Now, assuming that the jitter direction (disc tangential direction) is the Y axis, the reproduction RF signal (RF), the tracking error detection signal (TE), and the focusing error detection signal (FE) are respectively obtained by the following equations. _{RF = A + B 1 + B} 2 + C + D 1 + D 2 ...... TE = (A + D 1 + D 2) - (B 1 + B 2 + C) ...... FE = (B 1 + D 2) - (B 2 + D 1) ...... i.e., tracking The error is detected by detecting the difference in the amount of light transmitted through the semicircular portions of the regions a and d of the hologram surface 20 and the other semicircular portions of the regions b and c as the output difference between the light receiving elements A, D and B, C. This is the so-called push-pull method. Focusing error detection is a so-called double knife edge method.

Further, assuming that the jitter direction is the X axis, the reproduction RF signal (RF) and the focusing error detection signal (FE) are the same as the above, but the tracking error detection signal (TE) is expressed by the following equation: TE = (A + B ₁ + B ₂ ) − (C + D ₁ + D ₂ ) ... This detection principle is the same as the above equation.

In the hologram optical head described above, when the hologram laser unit 11 is attached to a base (not shown) of the optical head, the adjustment point comes every 90 ° by rotating about the Z axis. Therefore, as the adjustment of the attachment position, only the adjustment of one axis in the Z-axis direction (focus direction) is required. On the other hand, the conventional optical head shown in FIG. 7 requires triaxial adjustment in the focusing direction and two orthogonal directions orthogonal to the focusing direction, which greatly simplifies the adjustment. Also, when the wavelength of the laser light emitted from the laser diode 17 changes, the diffraction angle on the hologram surface 20 changes, but according to the present invention, the optical element can be made long in the direction of 45 ° with the XY axis. Therefore, it is easy to absorb the variation of the diffraction angle, that is, the variation of the wavelength of the laser light emitted from the laser diode 17.

In the present invention, the lattice pattern of the four areas of the hologram surface 20 is not limited to the example shown in the figure. For example, the lattice directions are the same as shown in FIG. It is also possible to have four different regions a, b, c, d. In this case, four light receiving elements A, B, C and D are arranged in one row as shown in FIG. The light receiving elements B and C are two-division photosensors. For the reproduction RF signal (RF), the tracking error detection signal (TE), and the focusing error detection signal (FE) in this case, the above equations can be applied.

Further, the hologram laser unit 11 may be fixed to the base of the optical head, and an objective lens actuator for controlling the objective lens 13 may be separately provided. However, the hologram laser unit 11 serves as an objective lens actuator. It is also possible to adopt a configuration in which they are provided integrally, and in this case, the integration of parts is realized at a higher level.

[0017]

[Effect of the device]

 According to the present invention, the photodetector, the laser diode, and the hologram element can be easily integrated into one unit, and it is easy to achieve high integration and miniaturization.

According to the hologram optical head of the second aspect, since the laser diode, the photodetector, and the hologram element, which are the main components of the optical head, are unitized as a hologram laser unit, the number of components is small, Very few assembly and adjustment man-hours. Further, since it is sufficiently miniaturized, it can be integrated with the optical head actuator portion, and in this case, higher integration and miniaturization are possible. Further, since the number of parts is small and the number of places where the adhesive is used is small, it is possible to prevent the reliability from being lowered due to temperature fluctuation.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical system configuration of a hologram optical head according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of the hologram laser unit in FIG.

FIG. 3 is a diagram showing a lattice pattern on the hologram surface in FIG.

FIG. 4 is a plan view of a light receiving element of the photodetector in FIG.

FIG. 5 is a diagram showing an example of another lattice pattern on the hologram surface.

FIG. 6 is a plan view of a light receiving element in the case of using the lattice pattern of the hologram surface of FIG.

FIG. 7 is a configuration diagram of an optical system of a conventional optical head.

[Explanation of symbols]

11 hologram laser unit 17 laser diode 18 photodetector A, B (B ₁ , B ₂ ), C, D (D ₁ , D ₂ ) light receiving element 19 case 19a laser light emission window 20 hologram surface (hologram element) a, b, c, d 4 areas of hologram surface 21 Cover glass

Claims (2)

[Scope of utility model registration request] 1. A light receiving element comprising a hologram element composed of four regions having different grating patterns, and which individually receives four diffracted light beams of return light reflected by a disk and separated by respective regions of the hologram element. 2. A hologram optical head, comprising a photodetector consisting of, and at least two light-receiving elements of the four light-receiving elements are divided into two. 2. A case having a laser diode, a photodetector composed of four light-receiving elements arranged around the laser diode as a center, a laser light emission window, and housing the laser diode and the photodetector. And a different lattice pattern attached to the laser beam emitting window.
2. The hologram optical head according to claim 1, further comprising a hologram laser unit including a cover glass having a hologram surface formed of three regions.