JPS59144057A - Photomagnetic reproduction head - Google Patents

Abstract

PURPOSE:To attain the miniaturization and reduced electric power consumption of a photomagnetic reproduction head by detecting photoelectrically the Kerr revolving angle of the reflected light sent from a vertically magnetized recording medium through irradiation of the polarized and modulated light via a liquid crystal polarization element. CONSTITUTION:The laser light sent from a semiconductor laser 16 of a photomagnetic reproduction head is turned into parallel beams through a collimator lens 17 and then into the linear polarized light by a polarizer 18. This linear polarization is carried out with no generation of heat by a polarization modulator 19 using the chiral smetic liquid crystal. Therefore the polarization and modulation is possible in a small-sized constitution and reduced power consumption. Then detectors 24 and 27 detect photoelectrically the Kerr revolving angle of the reflected polarized and modulated light sent from a vertically magnetized recording medium 13, and the recorded contents are reproduced. In such a constitution, a photomagnetic reproduction head is miniaturized with reduced power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reproducing head for a magnetic recording device using a perpendicular recording medium. More specifically, the present invention relates to an apparatus using a polarization modulation method for reproducing data from a perpendicular recording medium.

FIG. 1 shows a head for optically reproducing data from a perpendicular recording medium, which employs a polarization modulation method using a Faraday cell. The emitted light from the He-He laser 1 is converted into linearly polarized light by the polarizer 2 and enters the Faraday cell 3. The Faraday cell 3 imparts polarization modulation to the incident laser light, and provides a polarization amplitude proportional to the cell length and magnetic field. In the experiment, a polarization amplitude of 1° and a modulation frequency of l MHg were taken. The light that has been modulated by the Farade cell is partially reflected by the camera 4, and is not subjected to Kerr rotation from the perpendicular recording medium 5, but is sent to the analyzer 6. The light passes through the condenser lens 7 and is received by the photodetector 8.

On the other hand, the light that has passed through the half mirror 4t is transmitted to the perpendicular recording medium 5.
It is reflected again by No-Fumi-wo-4, and then reflected by Analyzer 9. The light passes through the condenser lens IO and is received by the photodetector 11. At this time, when this light is reflected from the perpendicular recording medium 5, it undergoes a Kerr rotation of +θ or -0 depending on whether the magnetization of the reflecting surface is upward or downward.

Therefore, the output of the photodetector 11 includes vibrations of the modulated polarized light and changes in polarized light due to Kerr rotation. Therefore, by multiplying the difference between the detector output Il and the signal 3 by a signal amplifier, a signal signal from which harmonic components and the like have been removed can be obtained. The results of the mathematical analysis of this method are listed below. However, P: laser power is 1 r K1 's K, l: proportionality constant α0 including loss of optical system and circuit system; modulation polarization amplitude ω0: modulation frequency θ: defined as force-rotation angle.

1(θat) = PtK15in”(θ+αgai
nωot): P(Kxao”/2+2P(K1a6θ
8in Goo 1-(PzK1a6tomi/2)cos'
lωo1 工＠(o,t) = PiK2sin”(a6 sin
ωat)z P(Kg a6”/2 (PjK1α0
Tomi/2) cos2ωo1 工(θμ) ” K1'11(
θwe) -Ka' kos (o*') = 2p7x□IK
1α. θ5ifLω. Therefore, if the operational amplifier output signal is detected at the frequency ω0, the Kerr rotation angle θ on the signal can be read correctly. An example of the output signal is shown in FIG.

The features of this method are that the minute rotation angle θ can be read with high precision, and that high-speed reproduction is possible using an operational amplifier. However, Faraday cells have practical problems. That is, the rotation angle φ due to the Faraday cell is φ=R7H
It is expressed as the length of the cell! , and is proportional to the applied magnetic field HK. R-Keverdet constant is called Gaos phosphate, or
TOol min/ca at wavelength 700 for lead glass
r Oe. Therefore, to obtain a modulation amplitude of 6 oz = l1 with a cell length of 1 m, H = 60008),
Even if the solenoid wound on the Farade cell has 100 turns, a current of 5 A is required. In other words, the power and heat required for modulation are large and are a major obstacle in miniaturizing the device.The present invention takes this into consideration and provides a new modulation element that uses low power, does not generate heat, and allows for miniaturization of the device. The present invention provides a reproducing optical head equivalent to the polarization modulation method using a Faraday cell.

FIG. 3 shows a magneto-optical recording and reproducing apparatus incorporating an optical reproducing head according to the present invention. The disk 13 is a two-layer medium using a co-cr film, and the backing layer is permalloy. The recording is of the auxiliary magnetic pole excitation type, in which the magnetic field generated by the auxiliary magnetic pole 14 is focused on the tip of the main magnetic pole 15 to magnetize the medium 4-. For reproduction, the light emitted from the semiconductor laser 16 is converted into parallel light by a collimating lens 17 and converted into linearly polarized light by a polarizer 8. The linearly polarized light is transmitted through a liquid crystal polarization modulator 19 according to the present invention, with a polarization amplitude α0 and a modulation frequency f.
o is given. The next modulated light is a half mirror 2D
The optical path is divided into two by K. The reflected light is focused onto the perpendicular recording medium 13 by the objective lens 21, and returns to pass through the half mirror again. The annizer 22 transmits the modulated component of the returned light, and the condenser lens n guides this to the detector U. On the other hand, the light that has passed through the half-light filter as it is is similarly detected by the analyzer δ and the detector n via the lens section. A differential amplifier 28Fi amplifies the difference in optical output between the two. The reproduction principle of this method is exactly the same as that of the conventional example described above, and the difference from the present invention lies in the liquid crystal modulator 19. This will be explained in detail below.

FIG. 4 shows the configuration of a liquid crystal polarization modulator according to the present invention. This modulator aligns chiral smectic liquid crystals with optically active groups as shown in Figure 2, and applies voltages of different polarities to change the alignment direction by 2φ to modulate polarization. The chiral smectic liquid crystal used here usually has a smectic phase as shown in FIG. 5, and the director of each layer rotates in a spiral. Specifically, J′iP-decyloxybenzylidene-pl-aminol 2-methyluptylene cinname) (DOBAMB C), HOBACP, C, D-
In P-7, dF-shenzylidene-p+-amino-2-methylbutyl-cinnamate, or L-P-alkoxybenzyritine-pl-amino-2-chlorophyll-cinnamate exhibits ferroelectricity. , is characterized in that the permanent dipole is located in a direction perpendicular to the molecular axis, as shown in Figure 4. Therefore, this has led to the ability to change the arrangement of molecules with low electric fields. Next, to briefly explain how to make the cell, first, the glass with the transparent electrode (Rhos) is cleaned, and then rubbed with cotton in the direction that aligns the liquid crystal. After these two substrates are placed facing each other with a spacer of 3 to 10μ in between and the periphery is sealed, e-tropic smectic liquid crystal is vacuum-filled through a liquid crystal injection hole 6- provided in advance. Next, when the injection hole is sealed with epoxy resin and left to stand, the liquid crystal is oriented in the rubbing direction and a cell with uniform molecular directions as shown in FIG. 45 is formed. The orientation at this time uses chiral smectic, but it is characterized by not having a helical orientation, and the torsional energy is effectively used during orientation transition.

Furthermore, in order to orient the liquid crystal, a strong magnetic field may be used instead of waving, and the liquid crystal may be injected in the magnetic field.

Now, in the cell made in this way, the permanent dipoles are perpendicular to the glass substrate and aligned in one direction as shown in Figure 4, and optically, it easily transmits polarized light parallel to the long axis of the liquid crystal molecules. let When an electric field is applied to the cell in this state in the opposite direction to the direction of the dipole, the dipole rotates the liquid crystal molecules in an attempt to become parallel to the electric field. Transition to the state shown in Figure 4 ■. In the state (2), the direction of the transmitted polarized light makes an angle of 20 with respect to the initial state.

Furthermore, since the states ■ and ■ are energetically equivalent and stable states, the transitions from ■→■ and ■→■ can be reversed by reversing the applied voltage 7-. That is, the polarization state of the incident light can be changed by 2θ (o<2θ<45°), which is the same as the molecular arrangement. In addition, the transition response time is less than 1 μ8 when the applied voltage is 10-20 V.
oc y (However, P: spiral pitch.

d: cell thickness, v: applied voltage τr: response time) Therefore, by making the cell thickness even thinner or using a liquid crystal with a longer helical pitch, it is possible to further increase the response speed to a modulation frequency of 10 MHz. . The present invention uses this liquid crystal cell as a polarization modulator.

Returning to FIG. 3, the configuration shown in the diagram will now be described in detail. First, the polarizer 18 is installed with its vibration plane aligned with the center of two stable alignment positions of the liquid crystal modulator.

That is, it is placed at the center of 2φ in FIG. By pressing the button like this, the polarization plane has an amplitude of 2φ due to the reversal of the electric field, and the output intensity is cog.
It is possible to obtain different modulated polarized light. Next, analyzer 22.25
#iThe Kerr rotation angle received from the perpendicularly magnetized film as shown in Figure 6.
Set so that it is perpendicular to θk.

8- That is, the bow fuser is placed so as to form an angle of 90-θ. Then, the component of the Kerr rotation angle that can be extracted from the angle is sin for each of the magnetic field directed to the medium and the downward direction @ upward direction.
At 2θ, it becomes 0 and the change becomes large, so the playback B/N
It will improve. Incidentally, the present invention is based on the configuration shown in FIG.
It is possible to read out Kerr rotation angles of -CrH from 6 to 91 at 8 AaodB or more, similar to the conventional Faraday method.

As described above, the present invention uses a liquid crystal polarizer based on a new principle in place of the conventional Faraday cell, and by applying modulation, it is possible to obtain an effect equal to or greater than that of the conventional method. In addition, liquid crystal polarizers are low voltage, low power, thin, compact, and inexpensive, making them far more practical than conventional Faraday cells. Furthermore, since the modulation amplitude can be made sufficiently larger than that of a Faraday cell, the resolution is theoretically higher.

As described above, the present invention can be applied to all devices that use perpendicular magnetization recording format, and can be applied to any device that uses a photothermal magnetic material (Tb).

711, G(1co etc, ) to CQ -Cf
Perpendicular magnetization 1ift can be widely applied.

[Brief explanation of drawings]

FIG. 1 shows a conventional optical regeneration method using a Faraday cell, and FIG. 2 shows its output waveform. FIG. 3 shows an optical reproducing device according to the present invention. FIG. 4 is a diagram showing the principle of a liquid crystal polarization modulator used in the present invention. Figure 5 shows the molecular arrangement of chiral smectic liquid crystal. FIG. 6 shows the relationship between the powerizer and analyzer used in the present invention. Numbers in the figure 1...H, -M-Laser 2.180-Polarizer 3--7 Awoday cell 4.20...Half mirror 5,13...Perpendicular recording medium 6, 9.22, 25...Antizer 7, lrl, 23.26...Lens-1〇-8, 11, 24, 27...Detector 12, 2
8... Operational amplifier 14... 1 Auxiliary magnetic pole 15... Main magnetic pole 16... Semiconductor laser 17... Collimating lens 21... Objective lens processing... Actuator and above Applicant Suwa Seikosha Co., Ltd. -1]- Figure 4 Figure 5 Figure 6 305-

Claims (1)

[Claims] In reproducing data written on perpendicular magnetization recording media,
A magneto-optical reproducing head characterized in that a polarization modulator using chiral smectic liquid crystal provides polarization modulation in a light source, photoelectrically detects the Kerr rotation angle of light reflected from a recording medium, and reproduces data.