JPH04328338A - Optical information recording/reproducing head - Google Patents

Abstract

PURPOSE:To converge an optical spot where there is no aberration and there is no bias of strength distribution on a recording medium so as to improve an information recording/reproducing signal. CONSTITUTION:A collimator lens 2, an opening diaphragm 3 and a condenser lens 5 are provided in an optical path between a light source 1 and the recording medium 4. The collimator lens 2 and the opening diaphragm 3 are fitted to an internal frame 13 and the optical axes of then are made to coincide. The internal frame 13 is position-adjusted with respect to an external frame 12, and the optical axes of the light source, the collimator lens 2 and the opening diaphragm are made to coincide. A unit 15 consisting of the internal frame 13 and the external frame 12 is position-adjusted and the position of light flux for the condenser lens 5 is adjusted.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical information recording/reproducing head (abbreviated as an optical head) used for recording and reproducing information by irradiating a light spot onto an optical information recording medium.
It is related to.

0002

2. Description of the Related Art A semiconductor laser is generally used as a light source in an optical head. The light flux from the semiconductor laser is guided onto the recording medium to record and reproduce information, but in this case, if the reflected light from the recording medium returns to the semiconductor laser, noise is likely to occur, and the S /N
The problem is that it causes deterioration.

One method for solving this problem is disclosed in, for example, Japanese Patent Application Laid-open No. 150391/1983. As shown in FIG.
This is a so-called off-axis method in which the light beam is made obliquely incident on the optical system 9. According to this, the laser beam emitted from the semiconductor laser 21 is transmitted to the collimator lens 2.
2, it becomes a parallel light beam and enters the beam shaping prism 23. Here, the light beam from the collimator lens 22 whose cross section has an elliptical intensity distribution is converted into a light beam having a substantially circular intensity distribution. Next, the aperture stop 30 limits the beam diameter, and the diffraction grating 24 generates zero-order and ±1st-order diffracted light. In this way, the three beams are collected by the condensing lens 25
The light enters off-axis and forms three focused spots on the recording medium 29.

The three beams of light reflected on the recording medium 29 are:
After entering the condenser lens 25 again and exiting as a parallel light beam, the optical path is bent by the mirror 26 and the light passes through the detection lens 27.
Three spots are formed on the photodetector 28 by radiating the beam.

[0005] With this configuration, the recording medium 2
The reflected light at 9 can be guided to the photodetector 28 without going backwards in the direction of the semiconductor laser 21.
This makes it possible to prevent the generation of noise due to the return light. This off-axis method is said to be particularly effective for recording media such as optical cards that exhibit birefringence and is widely used.

By the way, the incident light flux M and the output light flux N at the entrance pupil of the condenser lens 25 are properly arranged at positions offset from the optical axis O of the condenser lens 25, as shown in FIG. is necessary. As mentioned above, the incident light flux M is reflected by the recording medium, enters the condenser lens again, becomes the output light flux N, and is guided to the mirror. It must be located off-axis by a length A on the line. The same applies to the outgoing light flux N, which must be located at a position corresponding to the incident light flux M on the X-axis with the optical axis O in between.

Generally, in order to make the optical system compact, a prism or a mirror is provided between the condenser lens 25 and the aperture stop 30 for bending or dividing the optical path. Therefore, the optical axes of the condenser lens 25 and the collimator lens 22 may be misaligned. This adjustment is performed by moving the semiconductor laser 21 in a plane perpendicular to the optical axis of the collimator lens 22.

FIG. 5 is an explanatory diagram showing a state in which the position of the semiconductor laser 21 is adjusted. To simplify the explanation, the shaping prism, diffraction grating, optical path bending prism, etc. between the collimator lens 22 and the condensing lens 25 are omitted and not shown. The optical axis C (dotted chain line) of the collimator lens 22 and the optical axis D (dotted chain line) of the condensing lens 25 may differ depending on the arrangement position of each optical element including these omitted optical elements, mechanical processing errors of the optical head, etc. It is assumed that there is a shift s in the Y direction between them. In this case, in addition to the normal off-axis amount A, there is also a deviation in the X direction as an error, but this will be omitted for the purpose of simplifying the explanation.

Therefore, the shift in the Y direction is adjusted by moving the semiconductor laser 21 so that the light beam passing through the center of the aperture stop 30 passes through point B in FIG. This adjustment amount n is the optical axis C of the collimator lens 22.
The focal length of the collimator 22 is f, the distance from the aperture stop 30 to the focal point 31 of the collimator lens 22 is p, and the distance from the focal point 31 to the focusing lens 25 is When the distance to the pupil is m and the distance from the aperture stop 30 to the pupil of the condensing lens 25 is p+m, the deviation s is calculated by s=(p+m)n/f. Therefore, by adjusting the semiconductor laser by n, the shift s in the Y direction can be adjusted.

0010

[Problem to be solved by the invention] However, the aperture diaphragm 3
A light beam passing through the center of 0 (center beam of the luminous flux) E (Fig. 5
The solid line) does not coincide with the light beam F (broken line) emitted vertically forward from the semiconductor laser 21, but is emitted at a slight angle. Moreover, the light beam F (broken line) passes through a position slightly shifted from the center of the luminous flux.

[0011] Generally, the light emitted perpendicularly from the semiconductor laser 21 has the maximum intensity, so if only the shift adjustment in the Y direction as in the conventional example is performed, the maximum intensity position of the light beam will be shifted from the center of the light beam. Therefore, the condenser lens 2
5, the maximum intensity position of the light spot focused on the recording medium is shifted from the center of the light spot, resulting in a problem of deterioration of information recording/reproducing signals. Furthermore, since the light beam is tilted with respect to the optical axis of the condenser lens 25, the light spot becomes an off-axis image, resulting in comatic aberration, which further causes deterioration of information recording and reproduction signals. .

The present invention has been made in view of the above-mentioned problems, and it is possible to image a good light spot on the medium without deviation of the center of intensity of the light spot on the recording medium and without tilting of the light beam. An object of the present invention is to provide an optical information recording/reproducing head as described above.

[0013]

[Means for Solving the Problems] The optical information recording and reproducing head of the present invention includes a collimator lens that converts the light beam into a parallel light beam and an aperture diaphragm that adjusts the diameter of the light beam in the optical path that guides the light beam from the light source to the recording medium. and a condensing lens for condensing a light beam from an aperture stop onto a recording medium, in which the light source and a collimator lens are used to adjust the position of the light beam with respect to the condensing lens; It is characterized in that the aperture stop and the aperture stop are movable together.

[0014]

[Operation] With the above configuration, since the beam with the maximum intensity emitted perpendicularly from the light source can be adjusted while maintaining the state passing through the center of the aperture stop, a light spot with an unbiased intensity distribution can be imaged on the recording medium. be able to. Furthermore, the parallel light beam from the collimator lens can be adjusted to be parallel to the optical axis of the condenser lens, and since there is no inclination, axial imaging is possible and a good light spot without comatic aberration can be obtained.

[0015]

[Embodiment] FIG. 2 shows an optical path system in an optical head according to an embodiment of the present invention. In the figure, a light beam emitted from a semiconductor laser 1 enters a collimator lens and is emitted as a parallel light beam. . The light beam emitted from the collimator lens 2 passes through the aperture stop 3, thereby becoming a parallel light beam with a limited aperture. This parallel light beam has an elliptical intensity distribution and enters the next shaping prism 7,
It is converted into a luminous flux with an approximately circular intensity distribution. In this case, the aperture stop 3 has an elliptical aperture in consideration of the shaping ratio of the shaping prism 7.

Next, the light beam from the shaping prism 7 passes through the diffraction grating 8, becomes a required diffracted light, and enters the prism 9. This prism 9 has both the function of bending an optical path and the function of a mirror in order to make the optical head more compact. The light beam incident on the prism 9 is reflected at a point a in a direction perpendicular to the direction of incidence, as shown by the broken line, and further reflected in a perpendicular direction at a point b, and then enters the condenser lens 5. In the condensing lens 5, as explained with reference to FIG. 3, the incident light beam and the outgoing light beam at the entrance pupil are arranged at appropriate off-axis positions from the optical axis O, respectively.

A light spot is irradiated onto the recording medium 4 through the condenser lens 5, and the light beam reflected by the recording medium 4 enters the condenser lens 5 again. By passing through the condenser lens 5, the light becomes a parallel light beam and enters the prism 9. The light beam incident on the prism 9 is reflected at point c in a direction perpendicular to the direction of incidence, and further reflected in a direction perpendicular to the direction of incidence on mirror surface e (shaded area), and exits from the prism 9. After the emitted light enters the imaging lens 10, it passes through the photodetectors 11 (11a to 1).
1d), an information recording or reproduction signal is obtained.

[0018] Although the present embodiment is configured as described above,
The positional relationship between the optical axis of the collimator lens 2 and the optical axis of the condensing lens 5 deviates from the designed value due to manufacturing errors of the prism 9, dimensional errors of hardware, and the like. Therefore, it is necessary to adjust the position of the light beam incident on the condenser lens 5.

In FIG. 2, reference numeral 15 denotes an adjustment unit that performs this position adjustment, and moves the semiconductor laser 1, collimator lens 2, and aperture stop 3 integrally within the XY plane perpendicular to the optical axis to adjust the position of the condenser lens 5. Adjust the beam position relative to the light beam.

FIG. 1 shows this adjustment unit 15, which includes an inner frame 13 to which the collimator lens 2 and the aperture stop 3 are attached, and an outer frame 12 into which the inner frame 13 is inserted and to which the semiconductor laser 1 is attached. ing. These inner frame 13, outer frame 12, semiconductor laser 1, collimator lens 2, and aperture stop 3 are assembled with the following relationship.

[0021] The collimator lens 2 is fixed to the inner frame 13,
Furthermore, the aperture stop 3 is attached to the inner frame 13 so that the optical axis of the collimator lens 2 and the center of the aperture stop 3 coincide. Then, the inner frame 13 is slid along the inner wall of the outer frame 12 in the optical axis (Z-axis) direction, and the inner frame 13 is adjusted and fixed so that the light beam from the semiconductor laser 1 becomes a parallel light beam by the collimator lens 2. Next, the semiconductor laser 1 is moved within the XY plane perpendicular to the optical axis, and its position is adjusted and fixed so that the parallel light beam is not tilted, that is, parallel to the optical axis c of the collimator lens 2.

Next, as described above, the unit that has been adjusted and assembled is moved as a unit within the XY plane so that the optical axis C of the collimator lens and the optical axis D of the condensing lens coincide (actually, (As shown in FIG. 3, the unit signal is shifted by A in the X and Y directions) This unit signal is adjusted.

By performing such adjustment, the maximum intensity light ray vertically emitted from the semiconductor laser 1 is aligned with the optical axes of the collimator lens 2 and the condenser lens 5, and passes through the center of the aperture stop 3. , it is possible to image a light spot on the recording medium 4 with no bias in intensity distribution. In addition, the parallel light beam emitted from the collimator lens 2 is parallel to the optical axis D of the condenser lens and has no inclination, so it forms an axial image, and there is no coma aberration, making it possible to form a good light spot. can. Therefore, it is possible to obtain good information recording/reproducing signals, and to prevent signal deterioration.

In the above embodiment, the aperture stop 3 is attached to the inner frame 13, but it may be attached to the inner frame 12. That is, as long as the center of the aperture stop 3 coincides with the optical axis C of the collimator lens, the aperture stop may be placed at any position.

[0025]

[Effects of the Invention] The present invention adjusts the position of the light source, collimator lens, and aperture diaphragm integrally with respect to the condensing lens, so that a light spot without aberrations and with an unbiased intensity distribution is condensed onto the recording medium. It is possible to improve information recording and reproduction signals.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of essential parts in an embodiment of the present invention.

FIG. 2 is an overall perspective view of an embodiment of the present invention.

FIG. 3 is a plan view showing the function of a condensing lens.

FIG. 4 is a perspective view of a conventional optical head.

FIG. 5 is a side view illustrating position adjustment of a light source.

[Explanation of symbols]

1 Semiconductor laser 2 Collimator lens 3 Aperture diaphragm 4 Recording medium 5 Condensing lens

Claims (1)

[Claims] Claim 1: In an optical path that guides the light beam from the light source to the recording medium, there is a collimator lens that converts the light beam into a parallel light beam, an aperture stop that limits the diameter of the light beam, and an aperture stop that focuses the light beam from the aperture stop onto the recording medium. In an optical information recording/reproducing head equipped with a condenser lens, the light source, collimator lens, and aperture stop are movable integrally in order to adjust the position of the light beam with respect to the condenser lens. Characteristic optical information recording/reproducing head.