JPH04214242A - Optical head - Google Patents

Abstract

PURPOSE:To reduce the noise of emitted light and to prevent the deterioration of a reproducing signal by deviating the polarized direction of incident light at a prescribed angle from the polarized direction of a semiconductor laser by the rotational angle of a transmitted light quantity correcting means. CONSTITUTION:When the main axis direction of a 1/2 wavelength plate 21 is rotated in the polarized direction of the semiconductor laser 1 only at the angle of, the polarized direction of a laser beam Btheta which is transmitted through the 1/2 wavelength plate 21 is changed only by the amount of 2, and the beam is made incident on a polarized beam splitter 24 with keeping the light quantity I d. This beam can be resolved into a vertical axis component I b1 (transmitted and polarized beam) and a horizontal axis component I d2 (total reflection polarized beam) by light vector Btheta. That means, the transmitted light quantity in the polarized beam splitter can be corrected by the transmitted light quantity correcting means 20, the transmitted light quantity in the apparent polarized beam splitter can be corrected, and the bonding efficiency of the apparent polarized beam splitter can be matched with a prescribed design value, the noise of the emitted light of the semiconductor laser can be reduced and the deterioration of the reproducing signal can be prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention aims to improve the quality of optical heads, especially beam splitters, of optical storage devices that record and reproduce information at high density by irradiating an information storage medium with a laser beam focused on a minute spot. The present invention relates to an optical head that suppresses variations in the intensity of a light beam caused by variations in the intensity of the light beam.

0002

[Background Art] Magneto-optical storage devices that utilize magneto-optical effects have recently appeared, and their use in the computer field is attracting attention as large-capacity rewritable external storage devices that replace hard disks and floppy disks. There is. Additionally, phase change optical storage devices and the like are being developed that utilize reversible phase change from crystalline to amorphous due to changes in the temperature of the storage medium.

[0003] Recording and reproduction of information in these storage devices,
Operations such as rewriting are performed by irradiating the storage medium with a laser beam focused on a minute spot using an optical head, but in order to perform high-quality recording and playback, the intensity of the laser beam must be stable and It is required that the light emission noise is not included.

FIG. 4 is a schematic configuration diagram showing a conventional optical head. Light emitted from a semiconductor laser 1 is converted into a parallel laser beam B1 by a collimating lens 2, and shaped into a circular beam B2 by a beam shaping prism 3. Ru. The laser beam B2 passes through the beam splitter 4, changes direction with the mirror 5, is focused by the objective lens 7 held by the actuator 6, and forms a light spot 9 of about 1 μm on the recording medium surface of the magneto-optical disk 8. It is irradiated and, for example, information is recorded.

The reflected light B2 that has been modulated and reflected on the recording medium surface is reflected laterally by the beam splitter 4 via the objective lens 7 and the raising mirror 5 again, and is then reflected to the side by the beam splitter 4 and then passed through the 1/2 wavelength plate 10 and the convex lens. 11, the light is focused on a six-segment photodiode 13 through a cylindrical lens 12, and a data signal on the surface of the recording medium is detected.

In addition to the data signal, the 6-divided photodiode 13 receives a focus error signal from the objective lens 7;
Tracking error signals are detected, and based on these error signals, the actuator 6 is driven by the actuator drive circuit 14, and the optical spot 9 is moved onto the magneto-optical disk 8.
Control is performed to move in the vertical direction and radial direction to track data tracks on the surface of the storage medium.

The amount of light emitted from the semiconductor laser 1 is determined by monitoring the light reflected by the beam splitter 4 with a monitoring photodiode 15.
is detected, the semiconductor laser drive circuit 16 controls the drive current of the semiconductor laser 1, and the light intensity of the laser beam B1 is stabilized, thereby stabilizing the recording signal and the reproduction signal, so that recording and reproduction can be performed. .

[0008]

[Problems to be Solved by the Invention] In the above-mentioned optical head, the coupling efficiency α of the beam splitter 4, that is, the ratio of the amount of transmitted light to the amount of incident light, is determined to a predetermined value in design, but in reality it varies for each individual product. There is considerable variation in the amount of light transmitted through the beam splitter 4, and the amount of light transmitted through the beam splitter 4 varies from optical head to optical head. Therefore, a measure is usually taken to adjust the amount of light emitted from the semiconductor laser 1 for each product to maintain the amount of transmitted light at a predetermined value. However, when the coupling efficiency of the beam splitter 4 is greater than a predetermined value and the amount of light emitted from the semiconductor laser 1 is reduced,
The driving current of the semiconductor laser becomes smaller, and conversely the emission noise of the semiconductor laser becomes larger. Therefore, the noise in the reproduced signal detected by the photodiode 13 when reproducing information increases, and the signal-to-noise ratio (S/ N) deteriorates, so-called deterioration of the reproduced signal occurs, and this causes a problem in that it becomes difficult to reproduce high-quality recorded information.

An object of the present invention is to eliminate the influence of variations in the coupling efficiency of beam splitters and to obtain an optical head that does not cause deterioration of reproduced signals even when the coupling efficiency is higher than a predetermined value.

[Means for Solving the Problems] In order to solve the above problems, according to the present invention, light emitted from a semiconductor laser is made into parallel light by a collimating lens, transmitted through a beam splitter, and made incident on a converging lens. Information is recorded by optically or optically irradiating a recording medium on which information is recorded as convergent light, and the reflected light from the information recording section is reflected by the beam splitter via the converging lens, and the reflected light is In a device that guides light to a light receiving element and detects changes in light intensity and polarization state to reproduce and control recorded information, the beam splitter transmits polarized light in a direction perpendicular to the polarization direction of the light emitted from the semiconductor laser. The polarized beam is composed of a polarized beam splitter that performs total reflection, and is rotatably arranged on the incident side optical path of the parallel light of this polarized beam splitter, and controls the polarization direction of the parallel light incident on the polarized beam splitter by its rotation angle. It is assumed that a beam splitter transmitting light amount correcting means is provided.

It is also assumed that the transmitted light amount correcting means includes a 1/2 wavelength plate and a rotation mechanism that supports the 1/2 wavelength plate so as to be rotatable within a predetermined angular range.

[0011] Furthermore, the rotation mechanism section includes a lens barrel that supports the 1/2 wavelength plate on its outer circumferential side, and a bearing portion that rotatably surrounds the lens barrel and has a notch in a predetermined angular region.
It consists of an arm that protrudes from the lens barrel into the notch and is biased by a spring to one side in the rotational direction, and an adjustment screw that engages with the arm within the notch to adjust the rotation angle. shall be taken as a thing.

0012

[Operation] In the configuration of the present invention, the conventional beam splitter is replaced with a polarizing beam splitter that totally reflects polarized light in a direction perpendicular to the polarization direction of the semiconductor laser, and the polarization direction of the incident light is adjusted by the rotation angle of the transmitted light amount correction means. is configured to be shifted by a predetermined angle from the polarization direction of the semiconductor laser, and as the angle increases, the amount of reflected light from the polarizing beam splitter increases and, conversely, the amount of transmitted light decreases, so that the coupling efficiency of the polarizing beam splitter is greater than a predetermined value. case,
It is possible to obtain a function of reducing the amount of light transmitted through the polarizing beam splitter and correcting it to a predetermined light amount without reducing the amount of light emitted from the semiconductor laser. Therefore, it is possible to drive the semiconductor laser with a sufficiently large drive current to reduce emission noise, and it is possible to prevent deterioration of the reproduced signal.

Further, if the transmitted light amount correcting means is a 1/2 wavelength plate supported by the rotation mechanism, the polarization direction of the laser beam incident on the polarization beam splitter can be easily changed by a predetermined amount by adjusting the rotation angle. The amount of transmitted light can be corrected to a predetermined value.

[0014] Furthermore, in the rotation mechanism part, a half-wave plate supported by the lens barrel is supported by a bearing part having a notch,
If the positioning is performed using an adjustment screw, the rotation angle of the main axis of the half-wave plate can be easily and precisely adjusted, and the function of positioning can be obtained.

[0015]

EXAMPLES The present invention will be explained below based on examples. FIG. 1 is a block diagram schematically showing an optical head according to an embodiment of the present invention, and the same parts as in the conventional device are designated by the same reference numerals, and detailed explanation thereof will be omitted. In the figure, 24 is a polarizing beam splitter that totally reflects polarized light in a direction perpendicular to the polarization direction of the semiconductor laser 1, and between the beam shaping prism 3 and the collimating lens 2 arranged on the incident optical path, For example, the rotation mechanism section 31
and a 1/2 wavelength plate 21 rotatably supported thereon, a transmitted light amount correcting means 20 is provided, and correction means 20 for correcting the amount of transmitted light of the polarizing beam splitter 24 achieves a predetermined coupling efficiency of the polarizing beam splitter 24. This is done in response to deviations from the value.

FIG. 2 is a vector diagram showing the effect of correcting the amount of transmitted light by the amount of transmitted light correcting means. In the figure, the vertical axis is the polarization direction of the laser beam emitted by the semiconductor laser 1,
The horizontal axis is the polarization direction of the polarized light totally reflected by the polarizing beam splitter 24, the amount of light emitted from the semiconductor laser 1 is Id, the coupling efficiency of the polarizing beam splitter is α, and the amount of transmitted light is Io. Here, when the main axis direction of the 1/2 wavelength plate 21 is rotated by an angle Θ with respect to the polarization direction of the semiconductor laser, the polarization direction of the laser beam Bθ transmitted through the 1/2 wavelength plate 21 changes by 2Θ, and the light amount Id and enters the polarizing beam splitter 24. The light vector Bθ is
This can be decomposed into a vertical axis component Id1 (transmitted polarized light) and a horizontal axis component Id2 (totally reflected polarized light). For example, the light amount Id1 of the transmitted polarized light is Id1=Id ・Cos
It is expressed as 2Θ. Further, the amount of transmitted light Io of the polarizing beam splitter 24 becomes Io =Id.α.Cos2Θ, which is smaller than Id1 by the coupling efficiency α, and conversely, the amount of total reflected light increases by α and becomes Id2/α.

As described above, according to the embodiment, the transmitted light amount correcting means 20 can correct the amount of transmitted light of the polarizing beam splitter in accordance with the deviation of the coupling efficiency α of the polarizing beam splitter 24 from a predetermined value, and the apparent amount of transmitted light can be corrected. The coupling efficiency of the upper polarizing beam splitter can be made to match a predetermined design value. At this time, there is no need to change the light intensity Id of the laser beam emitted from the semiconductor laser 1, and therefore the semiconductor laser can be driven with a sufficiently large drive current, reducing the emission noise of the semiconductor laser and preventing deterioration of the reproduced signal. can.

FIG. 3 is a plan view showing the configuration of a rotating mechanism section according to an embodiment of the present invention, and the rotating mechanism section 31 has a 1/2
A lens barrel 33 that supports the wavelength plate 21 , a bearing portion 34 that rotatably supports the lens barrel 33 , a notch portion 35 formed in a predetermined angular region thereof, and a portion from the lens barrel 33 into the notch portion 35 . Consisting of a protruding arm 32, a spring 37 that biases the arm 32 in one direction of rotation, and an adjustment screw 36 coupled to a bearing portion 34 so as to engage within a notch on the side opposite to the spring of the arm 32. The aperture angle of the notch 35 is determined within a range that can correct variations in the amount of transmitted light due to variations in the coupling efficiency of the polarizing beam splitter.

[0019] A 1/2 wavelength plate 21 is attached to the rotation mechanism section 31 described above.
The transmitted light amount correcting means 20 supporting the 1/2 wavelength plate can be easily rotated by a desired angle Θ and positioned using the adjustment screw 36.

[0020]

Effects of the Invention As described above, the present invention replaces the conventional beam splitter with a polarizing beam splitter that totally reflects polarized light in a direction perpendicular to the polarization direction of a semiconductor laser, and adjusts the angle of rotation of the transmitted light amount correction means to The polarization direction of the light is shifted by a predetermined angle from the polarization direction of the semiconductor laser. As a result, as the angle increases, the amount of reflected light from the polarizing beam splitter increases and the amount of transmitted light decreases, so if the coupling efficiency of the polarizing beam splitter is greater than a predetermined value, the polarizing beam splitter can be The ability to reduce the amount of transmitted light and correct it to a predetermined light amount eliminates the conventional problem of increased light emission noise due to reducing the amount of light emitted from the semiconductor laser, and allows the semiconductor laser to be driven with a sufficiently large drive current. Therefore, it is possible to provide an optical head that can reduce light emission noise and prevent deterioration of reproduced signals.

Furthermore, if the transmitted light amount correcting means is a 1/2 wavelength plate supported by the rotation mechanism, the polarization direction of the laser beam incident on the polarization beam splitter can be easily changed by a predetermined amount by adjusting the rotation angle. Since the amount of transmitted light can be corrected to a predetermined value, the coupling efficiency of the polarizing beam splitter, which varies individually, can be made to match the design value in appearance.

[0022] Furthermore, the rotation mechanism section is supported by the lens barrel.
If the 1/2 wavelength plate is supported by a bearing with a notch and positioned using an adjustment screw, the rotation angle of the main axis of the 1/2 wavelength plate can be precisely and easily adjusted and positioned. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an optical head according to an embodiment of the present invention.

[Fig. 2] A vector diagram showing the correcting action of the transmitted light amount by the transmitted light amount correction means in the embodiment.

FIG. 3 is a plan view showing a rotation mechanism according to an embodiment of the present invention.

[Figure 4] A schematic configuration diagram of a conventional optical head.

[Explanation of symbols]

1 Semiconductor laser 2 Collimating lens 3 Beam shaping prism 4 Beam splitter 5 Stand-up mirror 6 Actuator 7 Objective lens 8 Magneto-optical disk 9. Light spot 10 1/2 wavelength plate 13 6-segment photodiode 20 Transmitted light amount correction means 21 1/2 wavelength plate 24 Polarizing beam splitter 31 Rotating mechanism section 32 Arm 33 Lens barrel 34 Bearing part 35 Notch part 36 Adjustment screw Id Emitted light amount of semiconductor laser Io Transmitted light amount Θ Rotation angle α Coupling efficiency

Claims (3)

[Claims] Claim 1: Light emitted from a semiconductor laser is made into parallel light by a collimating lens, transmitted through a beam splitter, and incident on a convergent lens, and irradiated as convergent light onto a recording medium on which information is recorded magneto-optically or optically. to record information, and to reflect the reflected light from the information recording section by the beam splitter via the converging lens, and to guide the reflected light to a light receiving element to detect changes in light intensity and polarization state; In the apparatus for reproducing and controlling recorded information, the beam splitter is a polarizing beam splitter that totally reflects polarized light in a direction perpendicular to the polarization direction of the emitted light from the semiconductor laser, and An optical head comprising: a means for correcting the amount of transmitted light of the polarizing beam splitter, which is rotatably disposed on the incident side optical path and controls the polarization direction of parallel light incident on the polarizing beam splitter according to the rotation angle thereof. . 2. The transmitted light amount correcting means comprises a 1/2 wavelength plate and a rotation mechanism that rotatably supports the 1/2 wavelength plate within a predetermined angular range. Light head as described. 3. The rotation mechanism includes a lens barrel that supports the 1/2 wavelength plate on its outer circumferential side, and a bearing portion that rotatably surrounds the lens barrel and has a notch in a predetermined angular region. It consists of an arm that protrudes from the lens barrel into the notch and is biased by a spring to one side in the rotational direction, and an adjustment screw that engages with the arm within the notch to adjust the rotation angle. The optical head according to claim 2, characterized in that: