JPS63292428A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To stabilize a tracking control extending over a wide range by radiating a luminous flux which is made incident by an objective lens utilizing a diffraction phenomenon, onto an information carrier and a second photodetector, and detecting a moving extent of the objective lens by an output difference of the photodetector. CONSTITUTION:A luminous flux 9 which is made incident on an objective lens 8 utilizing a diffraction phenomenon irradiates two luminous fluxes, a luminous flux 11 which is not condensed onto an information carrier 4 is made incident on photodetectors 12, 13 roughly equally to each other, when the objective lens 8 is in a neutral position 810 against the tracking control direction, and the output of an operational amplifier 14 goes to about zero. On the other hand, when the objective lens 8 moves in the direction T1 by a tracking control, the incidence quantity of the photodetector 12 becomes larger and the output of the operational amplifier 14 goes to minus, and on the contrary, when said lens moves in the direction T2, the output of the photodetector 13 becomes larger and the output of the operational amplifier 14 goes to plus, and a position in the tracking control direction of the objective lens 8 can be detected.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to an optical recording/reproducing device for optically recording and reproducing information on the surface of an information carrier. This invention relates to an optical recording/reproducing apparatus equipped with a photodetector (C) for receiving light and obtaining a reproduction signal and a sub-leg signal.

[Conventional technology]

FIG. 6 shows a conventional optical recording/reproducing apparatus such as that shown in Japanese Utility Model Application Publication No. 61-68322, particularly its optical head section.
A half mirror (
2), an objective lens (3) is arranged, and an information carrier (
2-split detector (5) that receives reflected light from 4) #
(8) is connected to an operational amplifier (7).

With the above configuration, the luminous flux emitted from the light 1M (1) is deflected 90@side by the half mirror (2),
The light is projected onto the information carrier (4) by the objective lens (3), and when in focus, forms a minute light spot with a diameter of approximately 1 μm. In such an optical head, in order to accurately record or reproduce information on the information carrier (4), the objective lens (3) is always in focus on the information carrier (4). Focusing control is performed by driving the lens in the direction of the arrow (T), and tracking control is performed by driving the objective lens (3) in the direction of the arrow (T) so that the minute light spot follows the information track on the information carrier (4). FIG. 6 shows an optical path for obtaining a tracking error signal for tracking control.

The reflected light from the information carrier (4) passes through the objective lens (3) and the half mirror (2), and is processed into information by the arithmetic circuit (7) based on the distribution of the amount of light incident on the two-split photodetectors (5) and (6). A tracking error signal of a minute light spot with respect to the carrier (4) is detected. This is a tracking error signal detection method known as a push-pull method (disclosed in Japanese Patent Application Laid-open No. 49-60702).

As described above, this diffracted light tracking error signal detection method detects the positional deviation of a minute light spot with respect to the information track of the information carrier (4) due to the difference in the amount of light incident on the two-split photodetector (5), (a). In other words, it is configured to detect tracking errors.

Therefore, the objective lens (3) is
This has the disadvantage that the light flux incident on the two-split photodetector (5) 76 moves when moving in the direction of the arrow T5 in Fig. g6, and as a result, an error is superimposed on the tracking error detection signal. This situation is shown in FIG.

FIG. 7(a) shows a case where the objective lens (3) is at a neutral position with respect to the tracking control direction. Figure (b) shows the arrow (
As the objective lens (3) moves, it is reflected by the information carrier (4), passes through the objective lens body), the half mirror (2), and then the two-split photodetector (5), (6). )
Since the light flux incident on the photodetector (5), (6
) becomes unbalanced, and the output becomes a negative level in the figure.

[Problem that the invention seeks to solve]

In the conventional optical recording/reproducing device, the optical head has the sail configuration as described above, so when the objective lens moves k in the tracking direction (direction of arrow T) due to tracking control, the optical head is sent to the photodetectors (5) and (8). The incident light also moves, causing an error to be superimposed on the tracking error signal, which poses a problem in that this error becomes an obstacle when tracking control is performed over a wide range.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain an optical recording/reproducing device that can stably perform tracking control over a wide range.

[Means for solving problems]

The optical recording and reproducing apparatus according to the present invention uses a lens called a hologram lens or a grating lens, which has a lens effect due to a diffraction phenomenon, as an objective lens, and uses the objective lens to direct a beam of light incident from a light source to the objective lens in two directions. One of the light beams is focused onto the information carrier as in the conventional case, and the position of the other light beam in the tracking control direction where the light beam is focused onto the information carrier is detected.

[For production]

In this invention, a lens that utilizes a diffraction phenomenon is used as an objective lens to irradiate a light beam in two directions, and a second light detector is divided into at least two parts to receive the light beam that is not focused on the information carrier. The position of the objective lens in the tracking control direction is detected from the change in the output of this second photodetector. This detected position information is fed back to the tracking error signal obtained by the normal diffraction light method to obtain a correct tracking error signal.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3. In Fig. 1, an objective lens (8) that utilizes a diffraction phenomenon, second photodetectors (12), (13), and a second operational amplifier (14) are provided, and the light emitted from the light source (1) is The light beam is deflected upward by 90 degrees by the half-z mirror (2), becomes a light beam (9) that enters the objective lens (8) using the diffraction phenomenon, and is focused onto the information carrier (4) by the objective lens (8). The first luminous flux (lO) to be emitted, and this first luminous flux (lO)
The light beam (10) is divided into a 20th light beam (11) directed in a different optical axis direction. A second photodetector (12), (13) is provided to receive this second light beam (11), and an operational amplifier (14) is connected to the second photodetector (12), (13).
3) Find the output difference. Here, the objective lens (8) that utilizes the diffraction phenomenon moves in the tracking control direction (Fig. 1(b)).
When in the neutral position with respect to the arrow (°C direction), the second light beam (11) incident on the second photodetectors (12), (13)
) are proportioned so that they are approximately equal.

In addition, the same reference numerals as in FIG. 6 indicate the same parts.

Next, the operation will be explained. First, the operation of the objective lens (8) using the diffraction phenomenon will be explained with reference to FIG. Figure 2 shows an objective lens (8) that utilizes the diffraction phenomenon.
As an example, a case where a hologram lens is used is shown. The hologram lens (81) irradiates two light beams to form two reconstructed images when the reproduction light, that is, the light beam (9) that is incident on the objective lens, enters the hologram lens (81). The first of these beams (lO) contains most of the amount of light of the incident beam (9), and, as described above, becomes the beam that is focused onto the information carrier (4).

On the other hand, the second D light beam (11) is irradiated in a different optical axis direction from the first light beam (lO), and is shown as a light beam converging toward the upper left in the figure. Although this second light beam (11) may be a parallel light beam, there is no problem with the operation and effect of the present invention described below, but here, it is shown as a convergent light beam as an example.

Next, using the hologram lens (81) shown in FIG.
The principle of obtaining position information in the dragging control direction will be explained below.

In Figure 2, the objective lens or hologram lens (81
) is a direction perpendicular to the plane of the paper, as shown by (T) in the figure.

3113 (b) shows the second light beam (11) incident on the 20th photodetector (1z), (x3) when the hologram lens (81) is at the neutral position (810) with respect to the tracking control direction. It shows the positional relationship. As mentioned earlier, when the objective lens, that is, the hologram lens (81) is at the neutral position (810) with respect to the tracking control direction, the second light beam (11) is transmitted to the second photodetector (12).
The second photodetectors (12), (13) are arranged so that they are substantially equally incident on L(13); in this case, the second photodetectors (12), (13) C ) outputs are approximately equal to each other, and the result is .

As a result, the output of the operational amplifier (14)+2) becomes approximately zero.

On the other hand, when the hologram lens (81) moves in the direction of the arrow (Tl) due to tracking control, as shown in FIG. As it moves in the same way, the amount of light incident on the second photodetector (12), (x3) changes, and in this case, the photodetector (12) is larger than the photodetector (13), The output of the operational amplifier (14) becomes negative. Conversely, when the hologram lens (81) is moved in the direction of the arrow CT2 by tracking control as shown in FIG.
In this case, the output of the photodetector (13) is larger than that of the photodetector (12), and as a result, the output of the operational amplifier (14) becomes positive.

As described above, the second light beam (11) is created by the objective lens that utilizes the diffraction phenomenon, that is, the hologram lens (81).
is received by the second photodetector (12), (13), and the difference in output between these two detectors (12), (13) is calculated by the operational amplifier (1).
By taking it out in step 4), the position of the hologram lens (81) in the tracking control direction can be detected.

By applying correction according to the amount of movement of the hologram lens (81), that is, the position in the tracking control direction, the tracking error signal due to the movement of the objective lens (in this case, due to the movement of the hologram lens) described in the conventional example is obtained. It is possible to eliminate the superposition of errors, and it is possible to stably perform tracking control over a wide range.

In addition, tracking control generally deals with a control target of a secondary system on a servo, and when the amount of tracking is large, the residual error tends to increase.However, with this invention, the position information of the objective lens, It is possible to incorporate so-called zero-order system information into the servo, and there is also the effect that residual errors can be reduced.

In addition, in the configuration of the present invention, by using the hologram lens (81) as the objective lens, not only can the objective lens be quantified, but also other light sources,
It is possible to easily create a second beam of light that provides objective lens position information without preparing another converging lens, etc., and the purpose can be achieved simply by preparing a second photodetector in the nest. .

Note that in the above embodiment, an objective lens (
Although the example of the hologram lens (81) was shown as 8),
A so-called grating lens having diffraction grooves may be used, or a so-called microlens, which equivalently produces a diffraction phenomenon with flat glass having a refractive index distribution, may also be used to obtain the same effect.

Furthermore, in the above embodiment, the objective lens (8) that utilizes the diffraction phenomenon to create the first and second light beams was shown as one hologram lens, but as shown in FIG. A first hologram lens (
The same effect can be obtained by combining two hologram lenses, 81a) and a second hologram lens (81b) that reproduces the second beam (11) as shown in FIG. 4(C), as shown in FIG. 4(C). This effect can be obtained, and as mentioned above, a grating lens or a microlens may also be used here.

Further, in the above embodiment, position detection in the tracking control direction of the objective lens was described, but the second photodetector (1
By using 4-split photodetectors for 2) and (13), position detection in 7 orcusing control directions can also be performed, and it is also possible to improve the accuracy of 7 orcussing servos.

FIG. 5 shows the principle of position detection in the focusing control direction.

Figure 5 is a diagram corresponding to Figure 2, in which the second photodetector (12
It is divided into four parts: a) (12b) (13aM13b). The first figure in Figure 5 is when the hologram lens (81) is in the neutral position with respect to the focusing control direction, Figure 5 (al) is in the (Fs) direction, and Figure 5 (cl) is in the (P
2) shows a state in which the hologram lens (81) has moved in the direction. (Bz) and (bt)*(C:) in FIG. 5 correspond to (at)s(btL(ct)), respectively.

In this state, an operational amplifier (not shown) calculates ((x2b + 13b) - (12a + 13a
)) The hologram lens (81
) The hologram lens (81
) position information in the tracking control direction can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, a lens that utilizes a diffraction phenomenon is used as an objective lens, and a light beam incident on the objective lens is irradiated in two directions, and the other light beam that is not focused on the information carrier is received. A second photodetector is provided, and the amount of movement of the objective lens in the tracking control direction is detected based on the output difference of the second photodetector. It is possible to eliminate the superposition of errors caused by the movement of the objective lens on the system tracking error signal, and it is possible to perform stable tracking control over a wide range.

[Brief explanation of drawings]

FIG. 1 shows the main part of an embodiment of the present invention, and FIG.
is a front view, FIG. 2 is a side view, FIG. 2 is a partially enlarged front view of FIG. 5 is a front view of a main part of another embodiment, FIG. 5 is a front view of a main part and a plan view of a main part of another embodiment, FIG. 6 is a side view of a main part of a conventional optical recording/reproducing unit, and FIG. This figure is a side view of a main part for explaining the operation of the one shown in FIG. (1) - Light source, (4) - Information carrier, (5) , (
6) Fist/first photodetector, (8)...Objective V-lens using diffraction phenomenon, (81)...Hologram lens, (9
)−・Light flux incident on the hologram lens, (10)・・
The first beam of light emitted from the hologram lens, (11)
...Second light beam irradiated from the hologram lens, (1
2), (13)...second photodetector. In each figure, the same reference numerals indicate the same or corresponding parts. (0) (b) Figure 2 Figure 81 - Hologram Lens Figure 3 (C) Figure 4 (0) (b) (C) '4LL Figure 6 Figure 7

Claims (8)

[Claims] (1) A light source, an objective lens for condensing the light beam emitted from the light source onto an information carrier, a driving means for driving the objective lens, an optical means for guiding the light beam to the objective lens, and the information carrier. and a first photodetector for receiving a reflected light beam from the light source and obtaining a reproduction signal and a control signal, the light beam emitted from the light source entering the objective lens serves as the objective lens. is irradiated in two directions, a first beam of which is focused onto the information carrier, and a second beam is irradiated in an optical axis direction different from the optical axis of the first beam. Using an objective lens that utilizes the formed diffraction phenomenon, a second photodetector divided into at least two parts to receive the second light beam is provided, and the diffraction phenomenon is detected from the output of the second photodetector. An optical recording/reproducing device characterized by detecting the position of an objective lens used. (2) The optical recording and reproducing apparatus according to claim 1, wherein the objective lens that utilizes a diffraction phenomenon is a single lens. (3) An objective lens that utilizes a diffraction phenomenon includes a lens that creates a first light beam that is focused onto an information carrier, and a second light beam that is irradiated in an optical axis direction different from the optical axis of the first light beam. An optical recording and reproducing apparatus according to claim 1, which comprises two lenses. (4) The optical recording and reproducing apparatus according to claim 1, wherein the objective lens that utilizes a diffraction phenomenon is a hologram lens. (5) The optical recording and reproducing apparatus according to claim 1, wherein the objective lens utilizing a diffraction phenomenon is a grating lens having a diffraction groove. (6) The optical recording and reproducing apparatus according to claim 1, wherein the objective lens that utilizes a diffraction phenomenon is a microlens that gives a flat glass a refractive index distribution and equivalently produces a diffraction phenomenon. (7) The light source is any one of a semiconductor laser whose output light amount is constant or pulse-modulated.
The optical recording and reproducing device described in . (8) The objective lens utilizing the diffraction phenomenon is formed so that the second light beam becomes convergent light.
The optical recording and reproducing device described in .