JPH0253852B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for reproducing signals by bright spot scanning.

Traditionally, fixed magnetic heads have been used as devices for writing information to and reading information from recording media.
There is a VTR (video tape recorder).

FIG. 1A shows a system generally called the Newell system, in which the tape T rotates in reverse at high speed and the magnetic head MH moves, for example, from top to bottom.

That is, when track T1 is recorded, tape T
The tape T runs to the right, and when the tape T finishes being wound around the roller R1, it reverses and runs to the left. At this time, the magnetic head MH moves downward and the track T
Record 2. Next, when the tape T is wound around the roller R2, it again runs to the right and records a track T3.

In the example shown in Fig. 1B, the tape T is stored endlessly, runs at high speed in only one direction, and when one rotation is completed, the magnetic head MH moves downward to record the next track. .

Both methods are common helical scan type
This is a method proposed to make VTRs more compact.

However, in both the examples shown in FIGS. 1A and 1B, a method is adopted in which the magnetic head MH moves in the vertical direction.

The drawback of this method is tracking during playback. That is, the tape must run at a higher speed than in the helical scan type, which causes the problem of tape flapping. Particularly when the head oscillates vertically on the paper, the reproducing head will be off track, making it difficult to reproduce the signal.

Therefore, it is necessary to detect this vibration and move the reproducing head so as to always trace the signal track.

In the above two methods, since the magnetic head is moved mechanically, tracking at high frequencies is difficult. In order to solve this problem, it is necessary to improve the accuracy of the tape running system in order to minimize the vibration of the tape, and as a result, the equipment becomes expensive.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a signal reproducing device capable of high-speed tracking control.

Embodiments of the signal reproducing device according to the present invention will be described below.

The present invention is an apparatus for reproducing signals recorded on a recording medium without mechanically moving the head.
Such a feature resides in the use of a scanning element as disclosed in the specification of Japanese Patent Application No. 12939/1983 by the present applicant. As detailed in the above specification, the device has the following properties: 1. It is capable of high-speed scanning. 2. It has high resolution. 3. It can obtain a large deflection angle. 4. It can be made compact and low-cost.

In order to clarify the advantages of the signal recording and reproducing methods of recording and reproducing heads that apply optically integrated bright spot scanning elements, we will first explain the main points of the form, principle, etc. of the bright spot scanning element proposed by the applicant. Explain.

FIG. 2 shows the appearance of the bright spot scanning element. This bright spot scanning element includes a waveguide 2 formed on a substrate 1, a prism coupler 3, a comb-teeth electrode 6, and a thin film lens 9. Now laser parallel beam 4
is guided through the prism coupler 3 into the waveguide 2 as a light beam 5. The light beam 5 propagating through the waveguide is deflected by the ultrasonic surface acoustic wave 7 excited by the comb-shaped electrode 6 of the optical polarizer provided in a portion of the waveguide 2. Furthermore, this deflected light beam 8 is focused by a thin film lens 9 so as to form a bright spot 11 on the end face 10 of the thin film waveguide. That is, the end face 10 is formed at a position that substantially coincides with the focusing plane of the thin film lens 9 having power in the xz plane (shown in the figure), and the condensed light beam is focused in the x direction on or near the end face 10. and eject. In addition, in the y direction perpendicular to the x-z plane, the waveguide thickness d
(usually a few μm). In such a configuration, the bright spot scanning element of this embodiment changes the frequency of the high-frequency voltage applied to the comb tooth-shaped electrode 6 to change the wavelength of the ultrasonic surface acoustic wave on the waveguide, thereby deflecting the ultrasonic surface acoustic wave on the waveguide. The angle is controlled to scan the bright spot on the exit end face. In this way, the bright spot scanning element has an optical deflector and a condensing lens on the same substrate, and scans by forming a bright spot at or near the exit end face of the waveguide, so it is extremely compact and precise. It has advantages such as no adjustment required.

Furthermore, each component of the bright spot scanning element will be explained in more detail.

The substrate 1 is suitably made of a material that has a piezoelectric effect and allows high-frequency ultrasonic waves to propagate efficiently, such as LiNbO ₃ ,
LiTaO ₃ , ZnO, etc. are preferable. Moreover, the waveguide 2 is
In the case of LiNbO ₃ substrate, Ti is heated at high temperature (approximately 1000℃).
Formed in-diffuse on the substrate to a thickness of several micrometers.
In addition, in the case of LiTaO ₃ substrate, Nb or Ti is in-
Obtained as diffuse. Although other examples are described in the above-mentioned book, the waveguide of this example is formed of a material that has a high refractive index and a large refractive index difference with the substrate, allowing light to propagate even if the waveguide is thin. things are desirable.
Furthermore, since the refractive index of the waveguide is high, the bright spot formed by the condenser lens on the end face can have a very small diameter, that is, a sharp spot.

The deflector preferably utilizes ultrasonic surface acoustic waves, and as shown in FIG. 3, ultrasonic waves are excited by a comb-shaped electrode 6 formed on a piezoelectric waveguide surface. The pitch a of the comb tooth-shaped electrode is set to 1/2 of the center wavelength of the ultrasonic wave to be excited. for example
If you set the electrode pitch a = 8.7μm on a LiNbO ₃ substrate, when a high frequency voltage of 200MHz is applied, the wavelength will be
17.5μm ultrasound can be excited. (The speed of ultrasonic waves is approximately 3.5 x 10 ⁶ mm/sec.) The band of the deflector obtained with this one electrode is determined by the angular selection width of the Black diffraction grating created by the excited ultrasonic waves and the piezoelectric It is limited by the band of the transducer itself, which consists of material and electrodes. The former band limited by black diffraction is defined in Proc IEEE64779 (1976) E.
G. Lean et al. “Thin Film Acoustooptic Devices”
It is given by the following equation.

△υ ₁ = 2nυ/λ Λ/W (1) where n; refractive index of the waveguide λ; incident light wavelength υ; ultrasonic velocity W; ultrasonic width When the number of scanning points is further expanded, according to CSTsai et al. The broadband deflector shown can be used. (SPIE vol 139, P139, 1978) As shown in Figure 3, multiple electrodes with different pitches are arranged at angles that satisfy the black diffraction condition with respect to the incident light according to each wavelength band, and each The transducer 12 is made to share a part of the wide band, and a so-called chirp signal whose frequency changes continuously is inputted to the electrode to change the wide band of 500 MHz. This makes it possible to obtain 1250 scanning points.

Next, as the thin film lens 9, IEEE Quantum
Elect vol QE―13, P129, 1977 (by DWVakey
Suitable lenses include the mode index lens, Luneburg lens, and geodesic lens, which are also shown in E. & Van E.Wood. These latter two types of lenses provide performance close to the theoretical resolution limit.

The size (diameter) δ _x of the bright spot in the x direction focused by the thin film lens is given by the following equation.

δ _x =1.27λo f/nD (2) where n: refractive index of the waveguide λo: wavelength of the incident light beam D: beam width of the incident light beam f: focal length of the thin film lens.

For example, f=30mm, λo=820mmn=2.2, D=10
mm, δ _x = 1.4 μm. In this case, by forming the waveguide with a film thickness of approximately 1.4 μm, a substantially circular bright spot can be obtained at the exit end face 10.

Further, the deflection angle Δφ when the applied frequency is eccentric by Δν is given by the following equation.

Δφλo/nvΔν (3) Therefore, continuous bright spot scanning can be performed by repeatedly and continuously changing the applied frequency.

The number N of scanning points that can be separated from each other within this deflection angle is given by the following equation.

N=△ν・D/v (4) For example, △ν=50MHz, D=10mm, v=3.5×
At 10 ⁶ mm/sec, N=143 points.

In this way, in the integrated optical brightness scanning element, since the deflector and the condensing lens are formed on the same substrate, the element becomes compact and stable without misalignment.

The above is one form of the bright spot scanning element and the scanning principle.

An embodiment of the present invention using the above element will be explained with reference to FIG. In FIG. 5A, the optical integrated bright spot scanning element 12 includes a light source 13 (for example, a semiconductor laser), a thin film lens 14 for collimating light, a light deflecting means (light polarizer) 15, and a thin film lens 1 for focusing light.
6. It is composed of an optical waveguide section 17.

By deflecting the light beam continuously or intermittently as the recording tape 18 runs, it is possible to record signals with recording tracks parallel or nearly parallel to the tape running direction.

Now, with the chirp signal, the frequency band is 700M.
Hz deflection, the deflection angle △φ is approximately
It becomes 0.0745rad.

However, n=2.2, v=3.5×10 ⁶ mm/sec, λo=
0.82 μm was used. Tape width is 1/8 inch (approx. 3.2 mm)
Then, if a thin film lens 16 with a focal length of about 40 mm is used, the light spot 19 will be
This results in a scan of about 3 mm, which means that almost the entire width of the tape can be scanned.

Furthermore, if the width of the light beam crossing the surface acoustic wave is 5 mm, the diameter of the bright spot focused by the thin film lens is approximately 3 μm according to equation (2), and approximately 1000 points can be resolved.
Therefore, if the signal track width and track interval are set to 3 μm each, 500 signal tracks can be recorded. Note that since the diameter of the bright spot 19 in the recording signal direction is determined by the thickness of the waveguide, the signal recording density is not affected even if the track is made thicker. For example, if the thickness of the waveguide is 1 μm, the pattern of the bright spots 19 in the above example is a slit shape of 3 μm×1 μm.

Furthermore, since the response time τ is given by τ=D/V (5), in the above example, τ=2 μm, which makes it possible to deflect light at about 500 KHz.

Furthermore, the signal recording is performed by recording a bright spot 1 at an angle θ with respect to the direction perpendicular to the tape running direction, as shown in FIG. 5B.
It is preferable in terms of signal reproduction to perform the operation so that 9 is tilted.

Furthermore, it is desirable for the reproducing means described below to also provide the light splitting means 20 used during reproduction in the bright spot scanning element.

Signal recording is performed using a light source 13 (for example, a semiconductor laser)
is subjected to brightness modulation using a desired signal (for example, a TV signal), and at the same time, a start signal is applied to the optical deflection means 15 as described above to deflect the light, and the bright spot 19 is
is scanned as described above. As a result, signals can be recorded on recording tracks parallel or nearly parallel to the tape running direction.

For example, a block diagram of the above control is shown in FIG. 5C. In the figure, DET is a detector. If it is the type shown in Figure 1A, it detects an inverted signal and generates a pulse. If it is the type shown in Figure 1B, it outputs a signal every time the tape rotates once. It detects the signal and generates a pulse.

The CNT is a counter that counts pulses from the detector DET, and when it reaches a predetermined count, that is, the number of tracks recorded on the tape, it generates a pulse and returns to the initial state again.

CONT is a deflection control circuit that includes an integrating circuit and a voltage-controlled oscillator.The integrating circuit integrates the pulses of the detector DET, and the integrated output is applied to the voltage-controlled oscillator.

Every time the integrator circuit receives a pulse from the detector DET, its output voltage increases, and the output voltage from the counter CNT increases.
The output returns to the initial state. Therefore, a recording track parallel to the running direction of the recording tape 18 can be created in the optically integrated bright spot scanning element.

On the other hand, FG is an image information output device, which outputs, for example, a TV signal. MOD converts TV signal to FM with FM modulator
Modulate. A power amplifier P is used to amplify the FM modulated signal and modulate the brightness of the light source 13.

There are preferable reproduction systems depending on the type of recording material. When the recording medium is a light-transmitting type, that is, when the recording tape material is a light-transmitting material and the recording material is a heat mode type recording material such as silver salt, dye, metal thin film, amorphous thin film, etc., as shown in FIG. Perform playback with configuration.

FIG. 6A shows an example of a reproduction system.

The reproduction system includes a bright spot scanning element 12, a lens 21, and long photodetectors 22, 23, and 24.

During reproduction, a DC signal is applied to the light source 13 to cause it to emit light with uniform brightness. Also, the light splitting means 20, which was not used during recording, is activated. The light splitting means 20 utilizes a surface acoustic wave diffraction grating similarly to the light deflecting means. The light polarizing means utilizes the Black diffraction phenomenon, whereas the light splitting means utilizes the Raman-Nath diffraction phenomenon to generate high-order diffracted light and perform light splitting. Further, the applied signal is a start signal in the optical deflection means, but the optical splitting means gives a signal of a constant frequency. For example, in order to generate bright spots 25, 26, and 27 that are 5 μm apart from each other, a signal of approximately 1.2 MHz may be applied according to equations (3) and (4).

The lens 21 transmits the images of the bright spots 25, 26, 27 through the tape to the elongated photodetectors 23, 24, respectively.
22. Bright spots 25, 26, 2 in figure B
7, the signal pattern, and the relative positions of the detectors 22, 23, and 24.

The bright spot 25 traces on the signal track, and the bright spots 26 and 27 trace between the tracks. The photodetectors 22, 23, and 24 are arranged at an angle θ with a straight line formed by the three bright spots so that each bright spot is imaged independently on the light receiving surface.

When the bright spot 25 is tracing on the track, the bright spots 26 and 27 are partly tracing on adjacent tracks and partly between the tracks at the same time. Now, if the bright spot 25 causes mistracking upward in the figure, the RF signal component will increase in the receiver 22 that receives the bright spot 26, and the detector 24 that receives the bright spot 27 will have a bias The component (the RF signal component decreases) increases, a tracking error signal can be detected, and the optical deflection means is controlled using this error signal. FIG. 6C is a block diagram for carrying out the above-mentioned control. In this figure, the same parts as in FIG. 5C are given the same reference numerals. Let me explain what will appear in this explanation.

DET1, DET2, and DET3 are photodetectors, which correspond to photodetectors 22, 23, and 24.

EA is an error amplifier, photodetector DET1,
It receives the output of DET3 and outputs an error signal as described above.

The deflection control circuit CONT is a differential amplifier DA that receives the output of the integration circuit INT and the output of the error amplifier EA.
The output is applied to the voltage controlled oscillator OSC to control the oscillation frequency of the oscillator OSC.

CONT1 is a control circuit that generates a frequency signal to be applied to the light splitting means 20, and is applied to the element 12 by switching the switch SW1.

CONT2 is a control circuit whose output is applied to the semiconductor laser 13 by switching the switch SW2.
This output is for causing the semiconductor laser 13 to emit light with a constant brightness.

As described above, even when the light beam output from the element 12 is not correctly traced, it is detected by the photodetectors DET1 and DET3, which is determined by the error amplifier EA, and an error signal is output. The differential amplifier DA is the output of the integrating circuit INT and the error amplifier EA
Input the output of , output a voltage that traces correctly, and input it to the oscillator OSC. The oscillator OSC changes its frequency and controls the deflection of the light beam of the element 12.

The information on the recording tape 18 is taken out from the photodetector DET2 and reproduced.

As described above, the imaging lens 21 is not disposed, and the photodetector 2 is placed directly behind the tape as shown in FIG. 6D.
2, 23, and 24 may be arranged.

The recording material is MnBi, GdCo, GdFe, TbFe,
In the case of amorphous magnetic thin films such as GdTbFe, light
Magnetic domain reversal recording using energy can be performed in a similar manner, and reproduction can utilize the magneto-optical effect known as the Fraday effect or the Kerr effect.

FIG. 7 shows a regeneration system based on the Fraday effect due to permeation.

When the light beam propagates in a single mode in the optical waveguide, the light that illuminates the magnetic material maintains a good polarization state.

When light passes through a magnetic material, the polarization angle is rotated depending on the orientation of the magnetic domains (Fraday effect). As shown in FIG. Polarization angle modulation can be detected as brightness modulation.

In addition, playback using the Kerr effect is possible.

FIG. 8 shows an example of a reproducing head based on the Kerr effect. A magnetic transfer film layer 40 made of an amorphous magnetic material such as DyFe, TbFe, or GdCo is provided at the tip of the element by sputtering, and a protective film layer 41 is further provided for protection (protection against mechanical wear and oxidation). This protective film layer consists of Ta ₂ O ₅ , SiO ₂ , ZnO ₂ ,
TiO ₂ Cr ₂ O ₃ etc. can be used.

The magnetic signals of the tape are transferred to the magnetic transfer film 40 by bringing it close or close to the tape 42 on which magnetic signals are recorded.

The light from the light source 43 is transmitted through the lens 44, the light splitting means 45, the light deflecting means 46, and the lens 47 to the transfer film 4 onto which the signal has been transferred from the tape.
Connect the three spots on 0.

Due to the Kerr effect, the polarization angle of the reflected light is rotated according to the signal magnetic pattern, but the reflected light with the rotated polarization angle is not propagated within the optical waveguide. (It is well known that the conditions for propagation in an optical waveguide are related to the polarization state.) When the polarization angle is not rotated due to the recording pattern, the reflected light returns to the original optical path, but the optical polarization It is deflected by a beam splitter 48 which is a grating structure provided within the means 46 and the light splitting means 45 . Furthermore, a new thin film lens 49 forms a bright spot for signal detection and a bright spot for tracking detection on the photodetectors 50, 51, and 52. Signal reproduction is possible with the above configuration.

Other embodiments are shown in FIGS. 9 and 10. These embodiments are examples in which a coupler is used for introducing light into an optical waveguide or leading out light from an optical waveguide.

In FIG. 9, numerals 53 and 54 are light introducing or light guiding elements generally called prism couplers. The light flux 55 is a coupler 53
The light is introduced into the waveguide 56 and propagates within the waveguide while being totally reflected. The light is deflected by the light deflection means 57 as explained in the previous example. The polarized light is guided out from within waveguide 56 by coupler 54 .

In the case of signal recording, the recording material 5 is
9, and modulates the light and dark;
A start signal is applied to the optical deflection means to scan the bright spot 60. In the case of reproduction, a phase grating 61 is placed in front of the lens 58 to split the light, and a bright spot 60 on the recording material 59 is detected by the lens 62 on the photodetector 6.
This is done by forming an image on 3.

It is also possible to arrange a beam splitter between the prism 54 and the recording material 57 and read out signals by reflection.

Further, if the recording material uses the above-mentioned opto-magnetic effect, signal reading is possible by placing a polarizing plate between the recording material 59 and the photodetector.

FIG. 10 shows another embodiment in which light 70 is introduced into the waveguide by a hologram coupler 71 with a low refractive index material layer 72 placed on the optical waveguide as an intermediate layer. The hologram coupler basically has a grating structure, but it can also have a lens effect, such as the hologram coupler 74.
By converging the light beam taken out from inside the optical waveguide onto the recording material 75, a bright spot 76 can be created without an external lens.

The waveguide 73 is provided with a light splitting means 77 and a light deflecting means 78, and is capable of light splitting and bright spot scanning.

When recording a signal, a start signal is applied to the light splitting means 78 to modulate the light in a blinking manner. When reading a signal, in the case of reflective reading, the light beam passing through the bright spot scanning element is focused onto the photodetector 80 by the lens 79.

In this case, as in the above example, other elements such as a polarizing plate can be used depending on the type of recording material.

As explained above, the present invention uses an optically integrated bright spot scanning element and performs recording/reproduction, thereby making it possible to reduce the precision of the tape running system, which was a problem in the past, and to produce small, inexpensive signals. Enable playback equipment.

As mentioned above, the main reason for this is that the bright spot scanning element is capable of high-speed scanning and tracking control can be easily performed.

[Brief explanation of drawings]

Figures 1A and B are diagrams explaining the conventional signal recording system, Figure 2 is an example of a bright spot scanning element, Figure 3 is a diagram showing light deflection by surface acoustic waves, and Figure 4 is a diagram showing surface acoustic waves. Diagram showing how to increase the angle of light deflection by waves,
Figures 5a, b, and c are explanatory diagrams for recording using a bright spot scanning element, and Figures 6A, B, C, and D are diagrams for explaining an embodiment of the signal reproducing device of the present invention. An explanatory diagram, FIG. 7 is an explanatory diagram showing another embodiment of the present invention,
FIG. 8 is a diagram showing a bright spot scanning element for reproduction using a magnetic transfer film, and FIGS. 9 and 10 are diagrams showing a signal recording and reproducing method of the bright spot scanning element using a coupler. 20...Light splitting means.

Claims (1)

[Scope of Claims] 1. A light source, an optical system that irradiates a track formed on a recording medium with a light beam emitted from the light source, and receives light reflected or transmitted by the medium of the light beam,
A signal reproducing device comprising: a photodetector for reproducing a signal recorded on the track and detecting a tracking error signal; and means for controlling tracking of the luminous flux using the detected error signal; The means includes a thin film waveguide that propagates light emitted from the light source and guides it to a medium, a transducer that generates a surface acoustic wave that deflects the light propagating in the waveguide by diffraction, and the transducer. an oscillator that applies a high frequency signal to the user, and according to the tracking error signal,
A signal reproducing device characterized in that tracking control is performed by changing the oscillation frequency of the oscillator and controlling the deflection direction of the light beam.