JPS63206920A - Optical head device - Google Patents

Abstract

PURPOSE:To always project a luminous flux on an information recording surface with the minimum fluctuation of a spot diameter by providing an aperture diaphragm into an optical path reaching an objective lens from a light source to limit the effective diameter of the luminous flux made incident on the recording surface with a fixed positional relation secured relatively to the objective lens. CONSTITUTION:It is supposed that an objective lens 3 is moved so that a recording surface 10 goes away from a light source up to a position G' and the light is condensed at a point O'. Under such conditions, an aperture diaphragm 11 is set at the focus position F'' of the lens 3 and therefore an angle psi1 formed between the luminous flux of the most outer circumference and an optical axis is equal to an angle psi0 and has no change even in case a condensing point O is shifted to the point O'. When the lens 3 is vertically displaced against its optical axis, a luminous flux 51'' passing through the most outer circumference of the diaphragm 11 is reflected on the surface 10 and made incident on the fringe of the diaphragm 11. Thus, no harmful vignetting of the luminous flux occurs even in a tracking action state. Thus, it is possible to project the luminous flux sent from the light source onto the surface 10 with the minimum fluctuation of a spot diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is for recording and recording information by irradiating light emitted from a light source onto a disc-shaped, card-shaped, or chip-shaped information recording surface.
When the non-parallel light beam emitted from the light source is focused by the objective lens and irradiated onto the information recording surface, it corresponds to the movement of the information recording surface in the optical axis direction. The present invention also relates to a device for producing light by driving the objective lens in the optical axis direction by an appropriate amount so that a focusing relationship is established to obtain a predetermined minute spot.

(Prior Art) In recent years, in optical haird devices that optically record information on an information carrier or optically read out recorded information, it has become unnecessary to use a collimator lens that converts a non-parallel light beam from a light source into a parallel light beam. A finite distance imaging system objective lens has been developed.

Since this objective lens does not require a collimator, the number of parts can be reduced, which is effective in making the device more compact and lower in price.

Figure 8 shows the light using the above-mentioned finite system objective lens.

An example of a conventional card device is shown below.

In the figure, a diverging light beam emitted from a semiconductor laser light source 1 is transmitted through a beam slit 2 and a finite objective lens 3.
After being incident on the information carrier, it converges to form a minute spot on the recording surface 10 via the transparent substrate 9 of the information carrier. Next, the light beam incident on the recording surface 10 is reflected by the recording surface 10, becomes a light beam containing information, travels backward along the optical path, and returns to the objective lens 3.
The beam passes through and enters the beam currant 2. The light flux incident on the beam splitter 2 is separated from the incident light from the light source 1 and passes through the sensor lens 5 with its optical path bent at a right angle. For example, the sensor lens 5 is composed of a combination of a concave lens and a cylindrical lens,
After astigmatism is applied here, the light is irradiated onto the four-divided light-receiving surface of the sensor 6, and focus error detection is performed using the astigmatism method.

(Problems to be Solved by the Invention) Incidentally, in the optical path from the light source 1 to the recording surface 10, the spread of the light beam emitted from the light source 1 is limited by the aperture 4. This aperture diameter is an amount set by, for example, the edge of the objective lens 3 or the support fitting of the objective lens 3. Therefore, the angle that the outermost beam passing through the objective lens 3 limited by the effective diameter 4 forms with the optical axis of the objective lens 3 is ψ. When the wavelength of the light beam from the light source is λ, and the refractive index of the transparent substrate 9 is n, the diameter d of the minute spot formed on the recording surface 10 is as follows when the aberration of the objective lens 3 is sufficiently corrected. It is determined by the formula % formula % (1).

Now, the substrate 9 is moving in the direction of the optical axis indicated by the arrow due to surface wobbling or the like.
When the objective lens 3 is displaced by a predetermined amount, the objective lens 3 is moved by a predetermined amount in the optical axis direction to form a minute spot with a predetermined diameter on the recording surface 10. At this time, since the objective lens 3 is a finite distance imaging optical system, the imaging magnification on the recording surface 9' after movement changes. At the same time, the distance from the objective lens 3' after the movement to the recording surface 10' after the movement also changes to tl, and the angle that the outermost beam of light in the objective lens 3' makes with the optical axis also changes to 9'1λ. As a result, the above equation (1) becomes d=0.8−n
gtnψ1, and the spot diameter d formed on the recording surface 10 changes. Therefore, when reading the signal, the frequency characteristics of the read signal fluctuate, resulting in a disadvantage that the quality of the reproduced signal deteriorates.

Further, when the information carrier is a carrier having a recording function, such as a write-once type or a rewritable magneto-optical record carrier, the above-described conventional optical head device has the following drawbacks. That is, the information recording carrier is generally provided with a guide groove in advance, and a minute spot narrowed to a predetermined size is imaged onto the guide groove to record or read information. Track error detection is always performed so that the spot can accurately follow the guide groove even when a track deviation occurs due to eccentricity of the carrier.However, such recording or reading and track following When performing this, it is necessary to maintain the spot size at a predetermined size, but if the spot diameter changes each time the carrier moves up and down, as in the conventional device described above, it is difficult to record information accurately. Not only is this not possible, but the S/N ratio when reading recorded information is degraded, which is an inconvenience.Furthermore, the sensitivity when detecting a track error signal changes, making the tracking and kingsage characteristics unstable. In addition, if the amount of vertical movement is constant, the change in the spot diameter due to the vertical movement of the information carrier becomes larger as the optical path from the light source 1 to the recording surface 10 becomes shorter. This poses a major obstacle to miniaturization.

Next, another conventional example is shown in FIG. 9 and will be explained.

FIG. 9(a) is a diagram schematically showing a luminous flux when a tracking operation is performed by driving only the objective lens 3 in an optical head device using a finite distance imaging system objective lens 3. .

In FIG. 9(a), the objective lens (e3) is somewhat displaced in the direction perpendicular to the optical axis due to tracking drive.

A diverging light beam 51 emitted from the light source 1 passes through the objective lens 3 and then enters the recording surface 10 while converging. In this case, as shown in FIG. 9(a), the incident light becomes asymmetrical with respect to the vertical axis of the recording surface 10, and the reflected light beam from the recording surface 10 is affected by the effect of the objective lens 3 as shown at 53. The optical path may deviate from the diameter.

FIG. 9(b) shows the positional relationship between the incident light beam and the reflected light beam on the pupil plane of the objective lens 3, and the shaded area is the light beam that can pass through the objective lens 3 again among the reflected light beams. As shown, the reflected light beam indicated by 53 is eclipsed. In this way, the amount of light varies in the reflected light flux, and harmful table drift occurs in the tracking error signal.

For this reason, in an optical head device that performs tracking using the 3-beam system, the eclipse amounts of the front and rear sub-beams are different, making it impossible to detect correct tiger and king error signals. In addition, in an optical head device using a tracking method that utilizes the intensity distribution on the pupil plane of the objective lens 3, the amount of +1st-order diffracted light incident on the photodetector from the rear and rear, and the amount of 11th-order diffracted light incident on the photodetector. The amount is different, and the correct tiger and king signals cannot be obtained.

The present invention was made in order to solve the above-mentioned problems in conventional optical head devices, and even when the information recording surface moves up and down due to surface play, etc., the light flux from the light source can be minimized by the spot diameter fluctuation. An object of the present invention is to provide an optical head device that is improved so that a recording surface is irradiated with light.

(Means for Solving the Problems) The problems of the prior art described above are solved by the method of recording information by passing the non-parallel light beam emitted from the light source of the present invention through an objective lens and condensing it onto the information recording surface. Alternatively, the light for reading recorded information 1r is incident on the information recording surface in a certain positional relationship relative to the objective lens in the optical path from the light source to the objective lens in the decoder. The problem is solved by an optical head device characterized by being provided with an aperture stop that limits the effective diameter of the light beam.

(Operation) The concept of the optical head device according to the present invention is shown in FIG. An aperture diaphragm 11 is provided near the position, and this aperture diaphragm can be moved in the optical axis direction while maintaining a constant distance from the objective lens 3 by a driving means (not shown). When the aperture stop v11 moves by a distance e, the aperture stop v11 moves to the position indicated by 11' in the figure.

Here, the operation of the optical head device having the above-mentioned configuration will be explained using FIGS. 2 and 3.

In FIG. 2, G indicates the case where the recording surface 10 is at the basic thread position, and G' indicates the case where the recording surface 10 has moved to some extent from the G position. Further, 51 is an objective lens 3 so as to irradiate a light spot with the smallest diameter onto the recording surface 10 located at the G position.
This is the luminous flux generated when is placed at the M position. Reference numeral 51' denotes a light beam generated when the objective lens 3 moves to the H' position so as to irradiate the recording surface 10 at the G' position with a light sporatra of the minimum diameter. Note that the objective lens 3 emits a light beam 51.
51' is shown as if it does not move to facilitate comparison, but in reality it moves significantly as the recording surface 10 moves. Now, when the recording surface 10 is at the reference position GK, a light beam 51 emitted from a light source (not shown) is directed to the objective lens 3.
After the effective diameter is limited by an aperture stop 11 disposed on the focal plane on the light source side, the light is focused on a point O on the recording surface 10. On the other hand, if the recording surface 10 is far from the light source at position G' or the objective lens 3 is moved to focus the light at V O/, then the aperture stop 1
1 is placed at the focal point tIt, F'# of the objective lens 3, so even when the focal point O moves to O', the angle ψ1 that the outermost luminous flux makes with the optical axis changes to be equal to ψ. do not. This is clear from the fact that the light beam incident on the objective lens is condensed to one point on the focal plane.

FIG. 3 is a diagram showing changes in the luminous flux when the objective lens 3 is displaced in a direction perpendicular to the optical axis due to a tracking operation. As shown in the figure, even if the light beam is incident at a finite angle with the optical axis of the objective lens 3, the light beam passing through the focal point Fv will be at the objective lens 3''f.

After passing through, the light enters the recording surface 1θ perpendicularly, and is then reflected by the recording surface 10, after which it travels back along the optical path again.

In addition, the light beam 51'' passing through the outermost circumference of the aperture stop 11 is reflected by the recording surface 10 and becomes a light beam that enters the edge of the aperture stop 11, causing harmful vignetting of the light beam during the tracking and king operations. Does not occur.

Furthermore, the effect of providing an aperture stop as described above is as follows.

This phenomenon is peculiar to the case where a finite-distance imaging objective lens is used as the condensing lens of a do-device, and does not occur at all in a conventional do-device that uses an infinite-distance objective lens. Even if a conventional optical head device has a diaphragm that limits the luminous flux arranged at the same position as the present invention, this is completely different from the concept of the present invention, and the optical axis of the lens is tilted. The purpose is simply to correct the axial aberrations that occur when

Due to the above-described effects of the present invention, changes in the frequency characteristics of the readout signal caused by changes in the diameter of the light spot irradiated onto the information recording surface, and the accompanying S
/N ratio deterioration or sensitivity drop when detecting track error signals, fluctuations in the amount of returned light that occur when driving with the objective lens metal tread or king actuator, and the occurrence of trough and king offsets that occur due to this, etc. To the dissolved light.

You can obtain a coded device.

(Example) Hereinafter, specific examples of the present invention will be described with reference to the drawings. In the following figures, parts having the same functions as parts in FIGS. 8 and 9 used in the description of the conventional example are given the same numbers.

FIG. 4 is a schematic cross-sectional view of a first embodiment of the present invention. Reference numeral 3 denotes an objective lens (a finite distance imaging system objective lens, the same applies to the following embodiments), which is attached to a lens barrel 12 equipped with an 11ft aperture diaphragm having a square cross section. . This lens barrel 12 is attached to an actuator substrate 13 and driven in the focusing direction and the tracking direction by a driving means (not shown). The aperture stop 11 is provided near the focal point of the lens barrel 12 on the light source side, and limits the effective diameter of the light beam emitted from the light source (not shown). Reference numeral 9 denotes a base of the information recording carrier, which has a recording surface 10.

Next, the 25th g of the present invention! An example will be explained using FIG.

11 is a mask provided on the surface of the objective lens 3 on the light source side. This mask 11 is provided along the periphery of the light source side opening of the lens barrel 12, and can be attached to the objective lens 3 by adhesively attaching an annular component thereto. Alternatively, it can also be provided by forming on the surface of the objective lens 30 by means such as silk screen printing. In this embodiment, the mask 11 limits the effective diameter of the objective lens 3. The objective lens 3 can be driven by a driving means (not shown) attached to the actuator substrate 13.

In this embodiment, the means for setting the effective diameter is not provided at the focal position of the objective lens 3 as in the first embodiment, but is provided attached to the objective lens 3. When the thickness is relatively thick, fluctuations in N and A can be effectively prevented.

Further, a third embodiment of the present invention will be described using FIG. 6.

The objective lens 3 can be molded using plastic or Kumold, and has a mounting portion 16t. The actuator substrate 13 is provided with an aperture diaphragm 11 having an edge-shaped cross section, and a lens mounting portion 15 is formed on the substrate 9 side of the information carrier.

By abutting the mounting portion 16 of the objective lens 3 against the mounting portion 15, the mutual positional accuracy between the objective lens 13 and the aperture stop 11 is maintained. In this embodiment, the effective diameter of the objective lens 3 is limited by the aperture diaphragm 11 provided on the actuator substrate 13, and the N and A of the light beam incident on the recording surface 10 of the information carrier are kept approximately constant.

The objective lenses 3 used in the above embodiments can all be easily obtained by plastic molding. Further, if these objective lenses are aspherical lenses, the necessary aberration correction can be performed, and the light receiving device can be constructed with a small number of parts.

Next, in the above embodiment, the position at which the opening for setting the effective diameter should be installed can be determined by the following calculation method. FIG. 7 (&) shows the magnification β based on the objective lens (finite distance imaging system objective lens) 3.

It is a diagram showing a state in which it is used in (-1 × β. × O). In this case, N%Athψ on the information recording surface 10 side. can be calculated using the following formula.

Now, assuming that the information recording surface 10 is displaced by e in the optical axis direction, the NA of the light beam incident on the recording surface 10 at this time can be determined by the following equation.

-ψ=-7thφ The displacement amount e and the magnification β have the following relationship.

Here, by setting m□=−1θ, m=−伜”m6+Δm, and omitting higher-order terms of Δm, the following equation is obtained.

According to the experimental results, N due to the change in the position of the information recording surface,
The change in A should preferably be kept within ±2 inches, and at worst within ±5 inches. - Allowable change in N and A on the other hand - jk
When is set to ±5%, the following relationship is obtained from equations (2), (3), and (5).

...... (6) Equation (6) clearly holds true when S = 0, and S indicates the distance from the focal position on the light source side to the objective lens 3, so the aperture 11 that sets the effective diameter is the objective lens. If it is provided at the focal position on the light source side of No. 3, fluctuations in N and A of the luminous flux incident on the information recording surface 10 can be prevented. However, in an actual device, it is desirable that the aperture stop 11 that sets the effective diameter be provided as close to the objective lens 3 as possible, so the aperture stop 11 should be set to 0≦S≦2. Of... (7)
It is necessary to install it in a position that satisfies the following. In addition, the aperture diaphragm v1
1 is too far away from the lens surface of the objective lens 3, it becomes difficult to correct off-axis aberrations, and the weight of the lens drive unit increases due to an increase in the effective diameter given to the objective lens 3 or an increase in the length of the lens barrel. It will cause an increase. Now, under the conditions of equation (7), equation (6) is solved as follows. Recording surface 10
When the amount of surface play is 6=t(t)O), Δm)O, and N and A increase, so rearrange this with respect to S to obtain the following equation.

(9) Note that when the information recording surface 10 approaches the objective lens 3 (
The same condition holds true even when e=-t).

As a result, the effect of the optical head device of the present invention becomes remarkable when the information recording surface 10 moves to such an extent that the condition of equation (8) is satisfied.

Further, calculations similar to those described above are performed for movement of the recording surface 10 in the tracking direction. However, in general, for optical discs, etc., the stroke in the track direction is ±0.31 for the stroke in the optical axis direction of ±1 m, and especially (9
) must satisfy the conditions of the formula.

(Effects of the Invention) As explained above, according to the present invention, in an optical head device using a finite distance imaging system objective lens, a light beam from a light source can be irradiated onto an information recording surface with minimum spot diameter variation. Even if vertical movement occurs due to surface wobbling of the information recording surface, accurate tiger and king error signals can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the concept of the optical head device of the present invention, and FIGS. 2 and 3 are schematic cross-sectional views explaining the operation of the optical head device shown in FIG. 4 is a schematic cross-sectional view of essential parts showing a first embodiment according to the present invention, FIG. 5 is a schematic cross-sectional view of main parts showing a second embodiment according to the present invention, and FIG.
The figure is a schematic cross-sectional view of essential parts showing a third embodiment of the present invention,
FIG. 7 is a diagram for explaining a calculation method for determining the position f of an aperture stop to be installed in an optical head device according to the present invention, FIG. 8 is a schematic cross-sectional view showing a conventional example, and FIG. FIG. 2 is a diagram for explaining a conventional example. 3...Objective lens, 9...Base of information carrier, 10.
...Information recording surface, 11...Aperture diaphragm. Agent Patent Attorney Jo Taira Yamashita Figure 2 Figure 4 Figure 5 Figure 9

Claims (2)

[Claims] (1) In an optical head device that records information or reads recorded information by passing a non-parallel light beam emitted from a light source through an objective lens and condensing it onto an information recording surface, from the light source to the objective An optical head device characterized in that an aperture diaphragm is provided in an optical path leading to a lens, forming a fixed positional relationship relative to the objective lens, and limiting the effective diameter of a beam of light incident on the information recording surface. (2) The focal length of the objective lens is f, and the imaging lateral magnification with respect to the information recording surface of the light source at the reference position is β_0(-1
<β_0<0), and the amount of surface alignment of the information recording surface is ±t(t
>0), and when the distance from the light source side focus position of the objective lens to the aperture stop is S, these t, β_0, f
Claims characterized in that: -β_0t/(1-β_0^2)f>1/20, and S satisfies the following relationship: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ The optical head device according to item 1.