JPS62200543A - Optical pickup - Google Patents

Abstract

PURPOSE:To miniaturize and lighten a device by using two hologram lenses having a function which focuses a semiconductor laser beam on an optical disk medium, and a function which introduces reflected light from the optical disk medium to a detector by adding aberration on it. CONSTITUTION:The titled device is equipped with two hologram lenses 103 and 104 which, after focusing each of laser beams 110 and 111 from two semiconductor lasers 101 and 102 at each of two focusing positions P1 and P2 locating apart from each other by a prescribed distance (d) in the groove direction of a track on an optical disk device 107, on correcting the aberration respectively, receive respectively reflected light 113 and 112 from the focusing positions P2 and P1 reversed with each other, and two detectors 106 and 105 which detect the reflected light 113 and 112 from the two hologram lenses 103 and 104. By constituting the device in such way, it is not necessary to prepare a polarizing beam splitter, and a two-beam optical pickup with a simplified structure can be offered, and the device can be miniaturized and lightened compared with a conventional device.

Description

[Detailed Description of the Invention] [Summary] The present invention is a two-beam optical pickup that uses two hologram lenses that correct aberrations and focus semiconductor laser beams of two different wavelengths onto the optical disk medium surface. are placed adjacent to each other, and the reflected light from the convergent points is received by the above-mentioned hologram lenses opposite to each other, and the light is guided to the detector with aberration added, thereby making the two-beam optical pickup smaller and lighter. The goal is to achieve lower costs and lower costs.

[Industrial application field]

The present invention relates to a two-beam type optical pickup using a hologram lens.

[Prior art] In a write-once optical disc device in which information can be written by the user of an optical disc, information is recorded on the disc in the form of bits and then read out to check whether the information has been written correctly. Although it is necessary to do this, a two-beam optical head is being researched in which the reading beam is placed near the writing beam spot so that there is no need to wait for the disk to rotate once.

On the other hand, in response to demands for smaller and lighter optical disk devices and shorter access times, it is desired that optical heads be made significantly smaller, lighter, and lower in price.

A conventional optical pickup is shown in FIG. The diverging light of the semiconductor laser 1301 is made into parallel light by the collimating lens 1302, and the beam is shaped by the prism 1303.
After passing through the polarizing beam splitter 1304, λ/
The light is circularly polarized by a four-plate 1305 and focused onto an optical disk 1307 by an objective lens 1306. The reflected signal light returns on its outward path, is made linearly polarized by a λ/4 plate 1305 in a direction orthogonal to the incident signal light, is separated by a deflection beam splinter 1304, and guided to a detector 1309 by a converging lens 1308.

In the case of a two-beam optical pickup, the optical system becomes even more complicated. FIG. 14 shows an example of conventional two-beam optical pink-up, in which semiconductor lasers 1401 and 1402 with two different wavelengths λ1 and λ2 are used to
Two beam spots SL separated by a minute distance on 03
and S2, and signal light detection uses a dichroic mirror 1404 to detect only one wavelength.

[Problem to be Solved by the Invention 1] As can be seen from FIGS. 13 and 14, conventional optical pickups, especially 2-beam type optical pickups, require many optical elements and are extremely complicated. The problem is that it is difficult to significantly reduce the weight, size, and cost of optical disc devices, and this is a factor that hinders the miniaturization, cost reduction, and shortening of access time of optical disk devices. was.

In order to eliminate the above-mentioned problems, the present invention uses two hologram lenses to simultaneously focus two semiconductor laser beams on the optical disk medium surface and receive the reflected light from the beams, thereby reducing the size and weight. The object of the present invention is to provide an optical pickup that can realize high performance and low prices.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention aims to solve each laser beam (110, 1) from two semiconductor lasers (101, 102).
11) and correct their aberrations to produce an optical disc medium (107).
It has two hologram lenses (103, 104) that respectively focus on two focusing positions (P+, Pz) separated by a predetermined distance (d) in the groove direction of the upper track, and furthermore, from the focusing position (P+ 1Pg). Each reflected light (112
, 113) and the hologram lenses (104) opposite to each other.
, 103) and guides it to each detector (105, 106).

[For production]

In the above means, first, the laser beam (110) from the semiconductor laser (101) is transmitted to the hologram lens (103).
The focusing position (P) on the optical disk medium surface (107) is
+ ).

The reflected light (112) from there is received by the other hologram lens (104) and detected by the detector (112).
05). Conversely, the laser beam (l l 1) from the semiconductor laser (102) is transmitted through the hologram lens (104).
The reflected light (113) is focused at the focusing position (P2).
is received by the opposite hologram lens (103) and guided to the detector (106). At this time, each laser beam (1
Since the wavelengths of the reflected lights (10, 111) are different, each reflected light (112
, 113) does not return to the position of each semiconductor laser (102, 101), and each adjacent detector (105, 10
6).

In the above operation, each optical path is separated in space and time, so
It does not require a polarizing beam splitter or a λ/4 plate, making it possible to significantly reduce the weight and size of the optical pickup.

〔Example〕

Examples of the present invention will be described in detail below.

(First embodiment of the optical pickup according to the present invention (FIG. 1)) FIG. 1 shows a first embodiment of the optical pickup according to the present invention. A hologram lens 103 and a semiconductor laser 1 that focus on a point PI on a medium 107 without aberration.
The light of wavelength λ2 (>λ1) diverging from point P! A hologram lens 104 that focuses the image without aberration is formed adjacently on the same transparent substrate 108. However, since the hour wheel is used here, the protective cover glass of the hologram lenses 103 and 104 and the optical disc protective layer are omitted. Although they actually need to be taken into account, there is no problem in explaining the embodiments and effects of the present invention even if they are omitted.

Laser light 110 of wavelength λ1 focused on point P1 by hologram lens 103 is reflected by optical disk medium 107 and enters hologram lens 104 as reflected light 112. When a laser beam with a wavelength λ2 emitted from P2 is incident on the hologram lens 104, it focuses the light on the position of the semiconductor laser 102, but when the wavelength is λ or shorter λ, the diffraction angle becomes smaller. reaches the position of the detector 105 on the left side. Distance d between points P and P2
is set to about 10 to 20 μm. The distance WD between the optical disk medium 107 and the hologram lenses 103 and 104 is l u ~
2 dragons are about 2 orders of magnitude larger than d.

The focusing position shift Δx1 of the laser beam 112 with wavelength λ1 with respect to the semiconductor laser 102 is not d but mainly Δλ=
This is due to λ2-λ1. The above is for the wavelength λ1, and the first
In the figure, solid lines 110 and 112 indicate the optical path.

Next, regarding the case of wavelength λ2, this can also be explained in the same way as the case of wavelength λ1. A laser beam 111 having a wavelength λ2 emitted from the semiconductor laser 102 is focused on a point P2 by the hologram lens 104. reflected light 1
13 enters the hologram lens 103, and since λ2>c, after being diffracted, it reaches the detector 106 on the left side of the semiconductor laser 101.

In the two-beam optical pickup configured as described above,
Each of the two hologram lenses formed on one substrate has two functions: forming a minute beam spot and focusing signal light, and the optical path is spatially separated for one wavelength. A major advantage of this method is that it does not require a polarizing beam block or a λ/4 plate, making it possible to significantly reduce the size and weight of the optical head.

The method of writing and reading information to and from the optical disk using the optical pickup shown in Fig. 1 is to write with a beam of wavelength λ1, read with a beam of wavelength λ2 after a distance d, and check whether the writing was performed correctly or not. Find out. In the case of only reading, it can be performed using any wavelength. In the above system, the optical pickup shown in FIG. 1 is arranged so that the left-right direction in the plane of the drawing corresponds to the track groove direction.

(Explanation of track error and focus error detection (Figures 2 to 4)) Next, track error and focus error detection will be explained. It is possible to detect tracking errors and focus errors by using this method. FIG. 2 shows an example of detector arrangement in the first embodiment (FIG. 1).

Here, the detector 105 detects a focus error, and the detector 106 detects a trunk error.

For example, two divided detectors are used as the detectors 105 and 106, and the divided detectors are arranged so that the dividing directions thereof are perpendicular to each other. 11■, ■, and ■ in Fig. 2 are the detectors 10, respectively.
5.106 isolated segments are shown.

FIG. 3 shows an example of detecting a track error (using the detector 106). The principle is the same as the conventional push-pull method, and the relative position of the beam waist with respect to the track (al-
1 to (C)-1, the intensity distribution of the signal light incident on the two-split detector changes as shown in (al-2 to (e)-2), and the output difference changes.

FIG. 4 shows an example of focus error detection using the detector 105. Since the angle of incidence of the reflected signal light on the hologram lens 103 changes depending on the amount of focus shift, the light intensity distribution of the focused beam on the detector 105 changes. By receiving this signal with a two-split detector and taking the difference in output, it is possible to detect a focus shift.

(Specific example of parameters of the first embodiment (Fig. 5.6)) When actually configuring the optical pickup of the first embodiment shown in Fig. 1, the wavelength of the semiconductor laser used is λ.
+ -780 nm and λz = 830 nm, the deviation amounts Δxl and Δx2 of the signal light focusing position will be calculated according to FIG. FIG. 5 is a schematic diagram of the head optical system showing only the optical axis, and shows the beam 110 to the optical disk medium 107.
．． The projection angle of 111 is 30 degrees, and the hologram lens 103.
The distance between 104 and the semiconductor laser °101.102 is 1
If it is 0 m, ΔX.

and Δx2 is approximately 300 μm. Since the distance of 300 μm is about the same size as the semiconductor laser itself,
It is difficult to simply arrange a conventional semiconductor laser and a detector separately and adjacent to each other.

Therefore, as shown in FIG. 6, for example, a semiconductor laser 10
It is necessary to bring the detector 105 close to the exit port 2, and to create a structure in which the detector 105 is bonded to the heat sink 601, for example. Note that since the distance between the semiconductor laser beam 102 and the detector 105 is small, there is a possibility that a part of the signal light may enter the semiconductor laser 102, but the wavelength of the reflected light 112 is different from the wavelength of the adjacent semiconductor laser 111. Since they are different, they do not interfere, and the output stability of the semiconductor laser 102 is not affected. The above configuration can be similarly considered for the semiconductor laser 101 and the detector 106.

(Second Embodiment of Optical Pickup According to the Present Invention (FIG. 7)) FIG. 7 shows a second embodiment that improves the point that ΔxI and Δx2 are small as described above in FIG. 5.

This embodiment is basically the same as the first embodiment (FIG. 1), but is characterized in that the optical paths for each wavelength are crossed so that the angle of diffraction by the hologram lenses 103 and 104 becomes large. In addition, in this embodiment, the hologram lens 1
Since the interference fringes of 03.104 are almost perpendicular to the hologram surface, there is no problem that the bra-knob angle changes due to swelling or contraction of the film during the creation of the hologram lens, which reduces the efficiency of first use. . Furthermore, since the semiconductor laser beams 110 and 111 are incident obliquely on each hologram lens, if they are made to be P-polarized light with respect to the hologram, the short axis direction of the elliptical beam will be expanded and the beam will be circular. It also has the advantage of being able to get close to it.

(Third Embodiment of Optical Pickup According to the Present Invention (FIG. 8)) FIG. 8 shows a third embodiment. This is intended to make the optical head thinner, and the basic configuration is the same as the second embodiment (FIG. 7). A mirror 801 is placed parallel to the transparent substrate on which the two hologram lenses 103 and 104 are formed, and the seventh
By bending the optical path of the optical system shown in the figure, the semiconductor laser 101.1
02 and detectors 106 and 105 are placed on the side. Note that the optical bus is a semiconductor laser 10
Only the wavelength λ1 from 1 is shown.

(Fourth embodiment of optical pickup according to the present invention (9th embodiment)
(Fig. 10)) Next, a fourth embodiment is shown in Fig. 9. In this embodiment, two hologram lenses 10 are attached to the optical disk surface 107.
3.104 is characterized by a slanted structure. In order to form a minute beam spot of about 1 μm on the optical disk medium 107, it is necessary to set the numerical aperture of the hologram lenses 103 and 104 to a large value of about 0.5. FIG. 10 shows the relationship between the optical axis when focusing the beam and the diameter of the hologram lens. Figure (a)-1 is
The optical axis is perpendicular to the hologram lens, and the numerical aperture (NA
) is given by sin θ. The minimum beam spot diameter that can be formed is determined by the diffraction limit based on NA.

In order to obtain the same beam spot diameter as in (a)-2 with a hologram lens whose optical axis is inclined to the normal to the hologram surface, as shown in (tll-1), the NA of the focused light must be the same. In order to achieve this, it is necessary to increase the aperture of the hologram lens in the horizontal direction on the paper as shown in (b) -2.When it is necessary to correct aberrations when actually creating a hologram lens, (a) ) The hologram lens of (bl) is more difficult to produce than the hologram lens of type (a). Therefore, the fourth embodiment shown in FIG. 9 is a case where the hologram lens of type (a) is used.

In the fourth embodiment, a mirror is arranged on the side surface and the optical path is bent in consideration of thinning.

This method has the advantage that it is easier to increase the NA of the hologram lens compared to the other first to third embodiments, but the working distance is slightly shorter.

(Fifth embodiment of the optical pickup according to the present invention (Eleventh embodiment)
Figure) Figure 11 shows a fifth embodiment. In this example, when the wavelength of the semiconductor laser changes by a minute amount due to mode hopping,
It is characterized in that the beam spot on the optical disc medium and the intensity distribution of the signal light on the detector do not change. As for the structure, a grating 1101 is arranged parallel to a transparent substrate on which hologram lenses 103 and 104 are formed.

From semiconductor lasers 101 and 102 to optical disk medium 107
and from the optical disk medium 107 to the detector 10
Since the optical path leading to 5.106 is zigzag, it has the effect of canceling out changes in the diffraction angle when the wavelength changes.

(Sixth embodiment of optical pickup according to the present invention (12th embodiment)
Figure) Figure 12 shows a sixth embodiment. This embodiment is characterized in that a temperature control element such as a Vertier element is added to the optical pickup in order to prevent wavelength fluctuations of the semiconductor laser. Mode hops in semiconductor lasers occur due to temperature changes due to heat generation of the semiconductor laser itself when the drive current is kept constant. Therefore, the temperature inside the optical pickup is monitored using a thermocouple 1201, etc., and the Bertier element 12 is adjusted according to the temperature change.
02 to cool or heat it and keep the temperature constant. A fin 1203 for heat radiation is attached to one end of the Beltier element 1202.

〔Effect of the invention〕

In the optical pickup according to the present invention, by using two hologram lenses that have the function of focusing the semiconductor laser light onto the optical disk medium and the function of adding aberration to the reflected light from the optical disk medium and guiding it to the detector, It is possible to provide a two-beam optical pickup with a simple structure, eliminating the need for a polarizing beam splitter, making it significantly smaller and lighter than conventional methods, and using conventional optical elements (lenses,
Since prisms, etc.) are not required, the cost can be reduced.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a first embodiment of an optical pickup according to the present invention, Fig. 2 is a diagram showing an example of the arrangement of detectors in the first embodiment, Fig. 3(a)-1, (b)-1, (C)-1, (al-
2, (b)-2, (C1-2 is an explanatory diagram of an example of track error detection in the first embodiment, Figure 4 (a)-1, (bl-1, (C)-1, (a )−
2, (bl-2, (C)-2 is an explanatory diagram of an example of focus error detection in the first embodiment, FIG. 5 is an explanatory diagram of a specific example of parameters in the first embodiment, FIG. 6 7 is a block diagram of a second embodiment of the optical pickup according to the present invention. FIG. 8 is a block diagram of a third embodiment of the optical pickup according to the present invention. 9 is a block diagram of the fourth embodiment of the optical pickup according to the present invention, and FIG. 10 is a block diagram of the fourth embodiment of the optical pickup according to the present invention.
-2 is an explanatory diagram of the relationship between how to take the optical axis and the diameter of the hologram lens. Fig. 11 is a configuration diagram of the fifth embodiment of the optical pickup according to the present invention. Fig. 12 is a diagram showing the configuration of the fifth embodiment of the optical pickup according to the present invention. FIG. 13 is a block diagram of a conventional optical pickup, and FIG. 14 is a block diagram of a conventional two-beam optical pickup. 101.102... Semiconductor laser, 103.104... Hologram lens, 105.10
6...Detector, 107...Optical disk medium, 110.111...Laser light, 112.113...Reflected light, 903.904...Optical axis, 1101...Grating, 1201...・Thermocouple, 1202... Peltier element, 1203... ・Fin,

Claims (1)

[Claims] 1) Two laser beams (110, 111) having different wavelengths from two semiconductor lasers (101, 102) are focused on each optical disk medium (107), and each reflected beam (1
In a two-beam optical pickup that records and reads information by receiving laser beams (12, 113), each laser beam (110, 111) from the two semiconductor lasers (101, 102) is corrected for aberrations. two focusing positions (P_1, P_2) separated by a predetermined distance (d) in the groove direction of the track on the optical disc medium (107).
After focusing on the respective focusing positions (P_2, P_2,
Two hologram lenses (103, 104) each receive reflected light (113, 112) from P_1), and two detectors (106, 106,
105). 2) The detector (106 or 105) has a detection area divided into two or more, and the hologram lens (103
or 104) adds aberration to the reflected light (113 or 112) and guides it to the detector (106 or 105);
05) determines two focusing positions (
2. The optical pickup according to claim 1, wherein a tracking error or a focus error of the laser beam (111 or 110) at P_2 or P_1) is detected. 3) The first detector (105) has two detection areas (I, II) in a direction perpendicular to the groove direction of the track on the optical disc medium (107), and each detection area (I, I
A focus error is detected by the detection output of the reflected light (112) from the optical disc medium (1), and the second detector (106)
07) It has two detection areas (III, IV) in the direction parallel to the groove direction of the upper track, and track errors are detected by the detection output of the reflected light (113) from each detection area (III, IV). The optical pickup according to claim 2, wherein the optical pickup performs detection. 4) A claim characterized in that the two hologram lenses (103, 104), the two semiconductor lasers (101, 102), and the two detectors (105, 106) are integrated. The optical pickup according to item 1. 5) The semiconductor lasers (101, 102) are arranged so that the laser beams (110, 111) cross each other and enter the hologram lenses (103, 104), and the two detectors (106, 105) are arranged such that the respective reflected lights (113, 112) from the respective hologram lenses (103, 104) cross each other and enter the corresponding detectors (106, 105). An optical pickup according to claim 1 or 4, characterized in that: 6) Each of the hologram lenses (103, 104) emits each of the laser beams (103, 104) from each of the hologram lenses.
10, 111) are arranged so that their optical axes (903, 904) are at an angle close to perpendicular to each of the hologram lenses. pick up. 7) Each of the hologram lenses (103, 104) has a grating (1101) at its front stage, and each of the laser beams (110, 111) and each reflected beam (113, 11)
2) is arranged such that its diffraction direction is reversed every time it passes through each of the hologram lenses (103, 104) and the grating (1101). optical pickup. 8) Adjacent to each of the semiconductor lasers (101, 102), temperature detection means (1) for detecting the temperature of each of the semiconductor lasers.
201) and temperature adjusting means (1202, 1203) for heating or cooling each of the semiconductor lasers (101, 102) based on the detection output of the temperature detecting means (1201) An optical pickup according to claim 1 or 4.