JPS6047238A - Optical head - Google Patents

Abstract

PURPOSE:To attain ease of beam position adjustment with less components by separating optical path of a collimator lens collimating radiated light from plural semiconductor lasers from plural beams making incident to a recording medium via a condenser lens and reflecting from the recording medium. CONSTITUTION:Irradiated lights 20a, 20b from semiconductor lasers 21a, 21b are collimated by a common collimater lens 22 and made incident to a polarized beam splitter 23. The light is not polarized by the polarized beam splitter 23 but straight-forwarded, the P polarized light is converted into circularly polarized light through a lambda/4 plate 24 and condensed on a recording medium through the condenser lens 26 fitted to an actuator 25. The interval in the (y) direction of two beams on the recording medium 27 is decided by magnification of the converged optical system and is 1-1/2 of the array interval of the semiconductor laser normally. Since the converged position shift between two beams in the focus direction is shared in common to the collimeter lens and the converged lens, the shift is not almost caused and a problem in a conventional constitution collimating plural beam with separte collimator lens is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical head of an optical information recording/reproducing apparatus that converges a light beam onto a disk-shaped recording medium to record or reproduce information.

In recent years, technology has advanced for optically reproducing information such as images and audio recorded as a series of concentric or spiral micro pits on disk-shaped recording media, and video discs, digital audio discs, etc. It is still being put into practical use. Furthermore, no effort has been made to develop an optical disk memory that can be used not only for playback but also for recording and as a memory. Optical disk memory devices capable of such recording and playback are smaller and smaller than conventional magnetic disc memory devices, etc.
It has characteristics such as high reliability, high recording density, and stability of signal quality, and is expected to be applied not only to information sources such as video and music in the home, but also to file devices and file memories in terminals. .

Semiconductor lasers (LDs), which are smaller and more efficient than conventional gas lasers, have come to be used as optical sources for such optical disk memory devices. This LD, a converging optical system, an information servo signal detection system, and a beam driving means for minute displacement for positioning a light spot on a track according to a servo signal are integrated into one to form an optical head, A mechanism in which this optical head is mounted on an actuator that performs coarse movement during track tracking selectively tracks information tracks and reproduces recorded information. An optical head having many functions such as t has become a reasonable component of an optical disk memory device.

Conventional optical heads use one T and one D as light sources, and when recording on this LD, an electric pulse is used to generate a beam power sufficiently higher than the recording threshold of the medium. CWf1 at an optical output level that is sufficiently lower than the recording threshold value during self-generation and that ensures a good S/N ratio.
I am making one work. However, with this method, it is impossible to maintain the recorded state immediately after recording, and therefore, when performing error correction, it takes two revolutions. In addition, when performing focus control during recording, in order to use high-output pulses during this recording, a low output level is set to prevent saturation in the detection system and the servo signal is sampled, and the servo signal is sampled at the recording signal level. It is necessary to compensate the gain of the control system accordingly, which has the disadvantage that the detection system becomes difficult. Therefore, it is desirable to perform recording and reproduction using beams from separate LDs, that is, to use a recording beam for recording only, and a reproduction beam for reproducing information signals and detecting servo signals during recording and reproduction.

Conventionally, multi-beam optical heads generally collimate the emitted light from two semiconductor lasers with different wavelengths using separate collimator lenses, and then combine them using a beam splitter or polarizing beam splitter to form a convergent lens, as shown in Figure 1. The configuration is such that the light is incident. lla and llb in the figure are semiconductor lasers (LD) for reproduction and recording, and 12a
, 12b is a collimator lens, 13 is a beam splitter or polarizing beam splitter, 14 is a quarter wavelength plate,
15 is an actuator, 16 is a converging lens, 17 is a recording medium, 18a and 18b are interference filters, and 19 is a detection system. The emitted light from the semiconductor lasers lla and flb, whose polarization directions are orthogonal to each other and whose oscillation wavelengths are different, is first transmitted to separate collimators 12a, 12. Collimated by b, only the light having the oscillation wavelength of the oscillation wavelength is transmitted through interference filters 18a and 18b, which transmit only the light having the oscillation wavelength of the oscillation wavelength, and the wavelengths other than the 9' are reflected, and are combined by the polarizing beam splitter 13. When transmitted through the λ/4 plate 14, the linearly polarized light becomes circularly polarized light and enters the recording medium 17 through a converging lens 16 not attached to the actuator 15. The light reflected from the recording medium 17 travels back along almost the same optical path, and when it passes through the λ/4 plate 14, it becomes 2
Each circularly polarized light is converted into a linearly polarized light that is orthogonal to the polarization direction of the emitted light from the prior injection. The light emitted from the recording semiconductor laser 11α is sent to the polarizing beam splitter 1.
3, it travels straight and is deflected by the interference filter 18b.

On the other hand, the emitted light from the reproducing semiconductor laser llb is deflected by the polarizing beam splitter 13, and then enters the deflection tongue detection system 19 by the interference filter 18a. This configuration requires two collimating lenses and two interference filters, so there are many components, and since the oscillation wavelengths of the two light sources are usually close to each other (50 nm), the angle of incidence of the beam cannot be determined by the interference filter. Separation performance is high (varies, difficult to adjust, and requires a lot of effort).

Furthermore, in a multi-beam optical head, it is necessary to suppress the relative convergence position deviation of the two beams in the focal direction to about 1 μm at most, and if there is a deviation of t1 or more, the medium will be located at the focal position of one beam. When photodynamics is applied, the other beams become itchy on the medium and the recording or keratinization properties deteriorate. In order to avoid fidgeting, it is necessary to use separate collimating lenses to achieve a perfect thousand line ratio for both rows of 5LD synchrotron radiation, but a converging lens with a focal length of 4mm and an aperture of 4mm When using this, the divergence angle of the beam transmitted through the frimate lens is about 0007°, and the convergence position in the focal direction is shifted by about 17+m.

Therefore, it is difficult to adjust the collimation of a plurality of beams to the same degree and to make the convergence positions in the focal direction substantially converge. Also, the beam spacing is determined by setting the incident angle of the beam to the converging lens as 1A, but if the focal length of the converging lens is 4 degrees, an oblique incidence of 0.14 degrees corresponds to a beam spacing of 10 μm. , the adjustment accuracy is strict and the reproducibility is poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide a multi-beam optical head that solves the stiffness problem, allows easy beam adjustment, and has fewer components.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the optical head according to the present invention, in which two AlGaAs semiconductor lasers 21a and 21b, which are close to each other, have the same emission direction, and both have an oscillation wavelength of 0.7871 m are used as light sources. This is an optical head.

Emitted light 20a from semiconductor lasers 21a and 21b,
20 b is collimated by the common frimeter lens 22 and enters the polarizing beam splitter 23 . 20a is a beam for reproduction, and 20b is a beam for distribution, and the electric field component exists almost only in the y direction (P polarized light). Polarized beam splinter 2
In 3, the P-polarized light goes straight to the polarized it'1', passes through the λ plate 24, is converted into circularly polarized light, and is condensed onto the top 27 of the recording medium 27 through the converging lens 26 attached to the actuator 25. . The spacing in the y direction of the beams at 27 degrees δ on the recording medium is determined by the magnification of the converging optical system, and is usually
This is about 1 to 1/2 of the array spacing. The convergence position difference between the two beams in the focal direction (y direction) rarely occurs because the merging lens and converging lens are shared, and this is a problem with the conventional configuration in which multiple beams are collimated using separate collimator lenses. The points are cleared. Furthermore, the beam spacing on the recording medium is determined by multiplying the spacing between the semiconductor lasers (light sources) by the imaging magnification of the optical system. Therefore, the crystal growth, the interval between the light sources, and the interval between the beams on the medium can be set with good reproducibility and accuracy. The light reflected by the recording medium X27 travels back along almost the same optical path,
When passing through the quarter-wave plate 24, the circularly polarized light changes into polarized light (S-polarized light) that is perpendicular to the polarization direction of the oscillation light of the semiconductor laser 21.
Therefore, the polarizing beam splitter 23 deflects the light in the y direction. Further, the reflected light 20C containing the reproduction signal and the reflected light 20d of the recording beam transmitted through the lens 28 are converged at a point at approximately the same distance from the lens. Convergent lens 2
7. If the focal length of the lens 28 is 40 m, the diameter of the convergent beam on the recording medium 27, and the beam interval are 1.5 μm and 50 μm, then the light that passes through the lens 28 and converges. The convergent beam diameter and beam spacing are 15μ.
m.

The width is about 500 μmm. A knife edge 2 is located at the focal position of the two reflected beams 20C and 20d from the recording medium 27.
9, the optical power is almost zero at the first point about 100 μm thin from the beam center, and the knife edge 29 can also be aligned by about 100 μm, so the reflected light 20d of the recording beam is transferred by the knife edge. A reproduced signal can be obtained by separating the optical path and allowing only the opposite light 20C to enter the detection system 30.

As described above, this configuration has the advantage that it is easy to adjust the beam position, which was a drawback of the conventional grain beam optical head, and that the number of parts is small.

In this example, AlGaAs semiconductors with the same oscillation wavelength of 078 μm were used as the two semiconductor lasers serving as the light sources, but even if semiconductor lasers with other wavelengths or different wavelengths were used, the cost would be around ¥111. I can say it. Further, although a two-beam optical head is shown as a multi-beam optical head, the same can be said of optical heads using more beams.

As described above, according to the present invention, a multi-beam optical head with fewer components and easy beam position adjustment can be realized.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional general multi-beam optical head that collimates two beams with separate frimeter lenses and then combines them.
a and 12b are collimator lenses, 13 is a beam splitter or polarizing beam splitter, 14 is a quarter wavelength plate, 15 is an actuator, 16 is a converging lens, 17 is a recording medium 18a, 18b is an interference filter, and 19 is a detection system. . 21 is a diagram showing an embodiment of the optical head according to the present invention, and 21a and 21b are semiconductor lasers 20a and 2.
0b, 20c, 20d are laser beams, 22 is a frimate lens, 23 is a polarizing beam splitter, 24 is a quarter wavelength plate, 25 is a 7-wave plate, 26 is a converging lens, 27 is a recording medium, 28 is a lens, 29 is a Knife edge 30 is a detection system. +1 Patent Attorney Uchihara

Claims (1)

[Claims] a plurality of semiconductor lasers having the same emission direction and located close to each other; one collimating lens for collimating the light emitted from the plurality of semiconductor lasers; and a collimating lens for collimating the light emitted from the semiconductor lasers, the light emitted from the semiconductor lasers being substantially perpendicular to the recording medium. a converging lens installed so that 1. An optical head comprising: optical means for separating optical paths of a plurality of beams reflected from a medium.