JPH04156430A - Optical beam scanning element - Google Patents

Abstract

PURPOSE:To attain light weight, compactness and high speed optical beam scanning by forming at least one domain wall or more for reflecting optical beams injected into a ferroelectric substance monocrystal, and moving this domain wall. CONSTITUTION:A ferroelectric substance monocrystal 1 is partitioned into a 180 deg. domain 2 and a 90 deg. domain 3, and the respective domains 2, 3 are formed laterally with 90 deg. domain wall 4 as a boundary. The light injected at a critical angle into the 90 deg. domain 3 is totally reflected by the 90 deg. domain wall 4. Accordingly, if the 90 deg. domain wall 4 is moved parallel in the direction 5, the totally reflected beams can be also scanned by the parallel migration length l part of the 90 deg. domain wall 4. The domain wall 4 for reflecting beams injected into such a ferroelectric substance monocrystal 1 can be moved in its position by applying an electric field and stress, and the beams outgoing by reflecting the incident beams can be scanned. Light weight and compactness, and high speed optical beam scanning can be thereby attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light beam scanning element constituting an optical pickup necessary for writing to and reading from a recording medium such as an optical disk.

[Prior Art] Optical desks have a much larger storage capacity than magnetic desks, so they are not as popular as magnetic desks. The reason for this is slow access time, which may be due to heavy optical pickup. That is, since the scanning of the laser beam is performed mechanically, there is a limit to the weight reduction of the mechanical parts.

In order to improve this drawback, the laser beam scanning mechanism should be made solid, specifically OE 1. Research on conversion to C is progressing. An example is shown in FIG. This is a waveguide type optical pickup, and the optical system (photodetector (S i -PD)
47, F G C (Focusing G
ratjB Coupler) 48, Beam splitter-C T G F B S (Twin Gra
tingFocusing Beam 5plitter
r) A Si chip in which 49 is integrated on a Si substrate 50 is mounted in a hybrid manner. According to this, it is smaller and lighter than conventional optical pickups. However, it has a signal detection function for focus error and tracking error, but it does not have a servo mechanism. Therefore, there is a drawback that it is necessary to separately consider the mechanism of the actuator.

Therefore, if the servo mechanism is mechanical + f/i, the weight of the optical pickup will not be reduced, and the access time will not be shortened.

On the other hand, as a solid-state laser beam scanning mechanism, acousto-optical (AO)
) Research is also underway on devices that utilize this effect. An example of this is shown in FIG. This is L i N b O3
(L N ) A planar guide waveguide 51 is formed by diffusing Ti on the single crystal surface, a laser diode (LD) 53 is disposed on the end face 52 of this waveguide, and a waveguide Fresnel lens (F L) 54 is attached to the guide waveguide 51. , a surface acoustic wave generation conversion electrode (SAW-IDT) 55 , a condensing grating coupler (FCC) 56 , and a light beam output end 57 . The laser light emitted from the laser diode 53 is made into parallel light by the waveguide lens 54, then diffracted by the acoustic grating 57 due to the ultrasonic wave from the conversion electrode 55, and condensed by the condensing grating coupler 56.
The light is emitted from the output end 57 of the waveguide 51 onto the target medium. The diffraction angle at this time is the frequency width of the supersonic wave and (LN)
+1 is determined by the speed of sound in the crystal.

Such an AO element does not contribute to miniaturization and weight reduction, but even if the diffraction angle is large, it is only a few degrees and lacks scanning ability. There is also the problem that reflected light cannot be detected, and the structure proposed so far cannot be applied to optical pickup.

[Problems to be Solved by the Invention] As described above, none of the conventional devices has been suitable as a device that is small and lightweight and can scan a light beam at high speed.

An object of the present invention is to provide a completely new optical beam scanning element that can realize the above functions based on a completely new principle, is small and lightweight, and can perform high-speed scanning.

[Means and effects for solving the problem] The basic principle of the present invention will be explained using FIG. now,
As shown in FIG. 1, a ferroelectric single crystal 1 is divided into a 180 degree domain 2 and a 90 degree domain 3, and
are formed on the left and right sides with the 90-degree area wall 4 as a boundary. Here, if the refractive index of the 180 degree domain 2 and the 90 degree domain 3 is 018 (1+n90), then the light incident on the 90 degree domain 3 at the critical angle will be totally reflected by the 90 degree domain wall 4. Therefore. , if the 90-degree domain wall 4 can be moved in parallel in the direction of the arrow 5, the total internal reflection beam can also be scanned by the parallel movement distance g of the 90-degree domain wall 4.If the ferroelectric single crystal 1 is square When it belongs to a class, its polarization axes are (1,00) in the 11 directions of x, y, and z.

There can be a total of six in the upward direction of (01,0) and (001). This means that there may be domains in which the polarization axes are orthogonal to each other. - Within the film, the domains are distributed in such a way that the sum of the electrostatic energy of the entire crystal and the elastic energy of the domain walls formed in both branch gates is minimized. Furthermore, this domain distribution can be changed by applying an electric field vector or stress vector to the ferroelectric single crystal. This situation is shown in FIG. In the upper part of Fig. 2 (a), electrodes 8a and 8b are attached to both sides of the ferroelectric single crystal 1, and a constant DC voltage V is applied through the electrodes 8a and 8b. = 6- shows what was formed [7. The upper part of FIG. 2(a) has an electrode 8a on the ferroelectric single crystal 1.

Direct current constant voltage -V in the opposite direction through 8b (1,8fl,
) As a result of applying a pulsed polarization inversion voltage - electric field),
Strong 1 dielectric single crystal 1 has a partially 180 degree inversion 81'i
This shows that region 10 was formed. Note that 11 is its boundary, and this inversion domain 10 expands in the directions of arrows 1' and 2.

-b1 FIG. 2(b) shows a state in which polarization rotation of 90 degrees is performed on the ferroelectric TLI crystal 1 by applying stress.

That is, in the upper part of FIG. 2(b), a constant DC voltage V is applied through the electrodes 8a and 8b provided on both sides of the ferroelectric material i11 and the crystal, as in the case of two series, -(]
, 80 degree domain 7 is formed. Figure 2(b)
The upper one is 90% as a result of applying stress F to the ferroelectric 111-crystal 1 from the electrodes 8a and 8b side.
A state in which a degree inversion region 14 is formed is shown. Note that the same effect can be obtained even if a tensile stress in a direction perpendicular to the stress F is applied to this -2 90 degree inversion region 14. Further, such a 90-degree inverted domain] 4 can also be formed by applying an electric field hector in the 90-degree inverted direction.

Note 1: What should be done here is the case of the 90 degree rotation mentioned above, and by slightly reducing the stress F in Fig. 2(b), the two parts can be divided as shown in Fig. 2(C). Area 7. ] 4, that is, the 90 degree domain wall 16 is formed at an angle of 45 degrees. The means for forming this domain wall is shown in Fig. 2(a).
It may also be one that applies an electric field, as in

Then, the 90-degree domain wall] 6 formed in this way is made into a ferroelectric material by, for example, applying a constant DC voltage -■ to the electrodes 8a and 8b. 1i, by means of a control means that applies an electric field to the crystal 1, the 90 degree domain wall 16 can be moved in parallel.

Note that this 90 degree domain wall surface needs to have good planar smoothness, and for this purpose, it is necessary to minimize defects in the strong 1-excellent electric material single crystal 1. requires sufficient attention.

In addition, as an initial method of forming the above-mentioned 90 degree domain wall, it is possible to completely or partially form an electrode using a ferroelectric material t11 given (-1).
The crystal is heated above its Curie point Tc to extinguish its spontaneous polarization, and in this state, it is cooled to room temperature while applying pressure to the entire surface or part in a direction perpendicular to the electrode surface, and the pressure applied part is aligned with the direction of pressure application. Spontaneous part h P s in the vertical direction
Make sure the + side faces. After that, a pulse voltage is applied to the electrode to form a vertical spontaneous polarization Ps2 of 1'Is under the electrode, resulting in the generation of a 00 degree domain wall)jn:.

The moving speed of the domain wall] 6 formed as described above is said to be about the same as the sub-speed, although it depends on the applied voltage V.

1 as the speed of sound 7000 m/see. It moves at a high speed of 1/700000 sec = 14 μs to move cm. In addition, in order to increase the ability to control this movement,
For example, if the electrodes 8a and 8b are moved along the moving direction,
), and by sequentially or alternately applying a pulse voltage to the plural pairs of electrode portions, the scanning position of the light beam can be accurately controlled by the number of pulses.

[Embodiment] FIGS. 3 to 5 show a first embodiment of the present invention.

First, the manufacturing procedure of the single crystal used in this example will be explained. Barium carbonate (purity: 99.99%) and titanium oxide (purity Nigerade 1) were weighed at a molar ratio of 35:65,
Stir and mix with a thunder crusher for 30 minutes, and mix with a high-purity pod for 10 minutes.
Calcinate at 0 DC for 2 hours. 2wt% in this calcined powder
Mix and grind polyvinyl alcohol as a binder,
After drying and granulation, a disk with a diameter of 3 cm is made using a hydraulic press, and this is calcined again at 1200° C. for 2 hours in an oxygen atmosphere, and the resulting powder is used as a starting material. The single crystal was grown using an MP furnace manufactured by ADL in the United States and a 400 kl (z
.

By high frequency induction heating using a 30kW oscillator and controller. B a T 1 in a platinum crucible that also serves as a heating element
Pour the 03 powder into the iJi crystal growth apparatus and soak the seeds in the melted powder so that the crystals will precipitate there. #L degree slope relative to the distance from the liquid level or 40
-1,c)- below the polished surface, and keep the temperature at the bottom of the crucible within 1°C in the range of 1400 to 1600°C. Seed is B a T 10
3 Butterfly crystals are used. Seeding timing (
Seed the seeds carefully (temperature), and when you see crystals precipitating, start pulling. The condition is a pulling speed of 0.3 mm/Il
r Rotation speed: 50 to 60 r Cooling rate of crucible after PI11 growth: 0.5 to 2 °C/fir Temperature gradient on liquid surface: 40 °C/cm was preferable.

The crystal obtained in this way was cut parallel to the C axis, gold was deposited as an electrode on both sides, and the dielectric properties and hysteresis properties were measured. The dielectric constant was approximately ε = 300, ε
-4000, a za approximately rectangular PE curve shown in FIG. 5 was obtained. Next, this pulled crystal 18 is cut into a size of 10*1*1 mm 3 so that a plane parallel to the C-axis and a plane perpendicular to the C-axis as shown in FIG. 3 (1)) are exposed. As shown in Figure (a), one transparent electrode 24a, 24b, 25a, 25b is attached to each end face of each pair of opposing
While heated to 00°C, a pressure of 1.0 kg/cm 2 is applied in the direction of the stress F shown in FIG. 2(b), and the temperature is lowered in that state. By these operations, the polarization can be changed as shown in Figure 2 (
A state corresponding to that shown in C) results in a single domain oriented in the direction along the electrodes 25a, 25b.

Here, when a voltage Va is applied between the electrodes 24a and 24b, polarization is directed in the direction of the electric field vector I·le, and a 90-degree domain wall 19 is formed. 90 from the end face of the electrode 24a
The laser beam 221 is incident on the domain wall 19, and the electrode 25
When a pulsed voltage vb is applied between a and 25b, the 90 degree domain wall 19 moves to the position indicated by ], 9a or 19b according to the number of pulses, and the laser beam 221 moves to the position shown by this moving domain. Total reflection from wall 19, from 23a to 23b
The range will be scanned. Note that at this time, by applying a pulsed voltage Va alternately with the pulsed applied voltage Vb to the electrodes 24a and 24b, the moving speed can be controlled and positioning for scanning can be facilitated. Further, in order to stop the movement of the 90-degree domain wall 19, the latter pulse voltage Va is made larger than the former. In order to move the 90 degree domain wall 19 in the opposite direction, a voltage in the direction as shown in FIG. 4(b) is applied to the electrodes 24a and 24b.

As can be seen from the above explanation, whether the light beam enters or exits the electrode 2
4b and 25b, it is necessary that at least the electrodes 24b and 25b be transparent. In addition, cylindrical lenses 2 are installed on the incident side and the output side, respectively.
6.27 and its pair of cylindrical lenses 2
If 6.27 are perpendicular to each other, the output beam 222 can be focused.

FIG. 6 shows a second embodiment of the invention. The method of manufacturing the crystal used in this example is the same as in the first example described above. 50*1*0.5 mm in rod shape
3 to obtain a ferroelectric single crystal 1. On both sides of this crystal piece, ITO transparent electrodes 32°, 33, 36, 37 are attached on both sides, sandwiching the crystal piece.
LZT transparent piezoelectric bodies 30 and 31 are bonded and disposed. IT
A voltage can be applied to the ferroelectric single crystal 1 and the piezoelectric material 30.31 through the O transparent electrodes 32, 33, 36, 37. Each outer portion of the PLZT transparent piezoelectric body 30°31 is mechanically fixed. In other words, the piezoelectric body 30.
By applying a voltage to 31, the ferroelectric single crystal 1
It constitutes a means for applying compressive stress to the shaft and a tensile stress to the shaft in the axial direction.

Further, a voltage can be applied to the PLZT transparent piezoelectric body 30.31 through the ITO transparent electrodes 32.3B and 36.37. When a voltage is applied, the PLZT transparent piezoelectric bodies 30 and 31 extend in the directions shown by 35, and the ferroelectric single crystal 1 receives tensile stress in the direction of the arrow shown by 34. At this time, the single crystal 1 has electrodes 32, 33, 36, 3
Polarization domain 21 showing polarization 21 oriented along direction 7
, and the 90 degree domain wall moves to the left from 16 to 17. 90 degree domain wall 1 formed at this time
The position of 6.17 is determined by the manner in which the voltages Vp and v are applied to the single crystal and the piezoelectric material 30.3, respectively. In addition,
This structure sometimes allows for a single domain.

Therefore, electrode', 36. When a voltage (2) is applied to 37 with the polarity shown in FIG. 6, a 180 degree domain 20 is easily formed, and the QOa domain wall 16 moves to the right h. In this way, the 90 degree wall 16 can be scanned left and right. In this case, since the length of crystal 1 is long, the light beam
For example, the scanning distance ρ is such that it is possible to access the optical desk in the radial direction, and a mechanical access device (14
becomes unnecessary. This defeats the conventional drawbacks of optical desks, and it will contribute to the spread of the previous desks.
It's a big deal.

In each of the above embodiments, an electric field is applied to the ferroelectric single crystal.
The ferroelectric material can be divided into multiple electrodes, stress (J"j), piezoelectric element r25 domain moving stage, or intermediate to the ferroelectric single crystal, or by dividing them into multiple pieces. It is also possible to remove the parts that act on the single crystal (for example, by sequentially or alternately applying a balloon to multiple pairs of electrodes that generate an electric field to move the domain wall). By applying pressure, more reliable scanning control can be performed.

[Effects of the Invention] As explained above, the present invention forms a domain wall that reflects a light beam in a ferroelectric single crystal, moves the position of this domain wall by applying an electric field or stress, It is possible to realize a novel forward beam scanning element that scans the outgoing light beam by reflecting the incident light beam at the domain wall. According to this, scanning can be performed at a crystal speed and the scanning range can be lengthened. Moreover,
A lightweight and compact optical beam scanning element can be constructed. Therefore, various drawbacks of conventional optical scanning devices can be solved, and optical disks, for example, can be popularized.

[Brief explanation of the drawing]

Figure 1 is a small explanatory diagram of the principle of the present invention, Figure 7 (, a) (
b) (c) is an explanatory diagram of the action, and Figure 3 is the first diagram of the present invention.
Example 611. A diagram schematically showing the Y structure, Fig. 4 (a
)(b) is an explanatory diagram of f′[ of the first embodiment, FIG. 5 is a diagram showing PE hysteresis characteristics, and FIG. 6(a) U)
) schematically shows the structure of the second embodiment of the present invention, and the sixth embodiment
Figure (a) is a front view, Figure 6 (b) is a side view, complete (7).
Figures 1 and 8 are diagrams showing the schematic configurations of different conventional optical pickups. 1... Ferroelectric single crystal, 2... 180 degree domain, 3...
90 degree domain, 7-, 180 degree domain, 8a, 8b-electrode, ]0...00 degree domain, M...00 degree domain, ■-Applied voltage. Applicant's attorney Patent attorney ISP Tsuki Jun -/;
匡1) 飄↑

Claims (6)

[Claims] (1) A ferroelectric single crystal into which a light beam is incident; a means for forming at least one domain wall that reflects the light beam incident into the ferroelectric single crystal; 1. A light beam scanning element, comprising a scanning control means for moving the light beam. (2) The light beam scanning element according to claim 1, wherein the domain wall forming means applies mechanical stress to the ferroelectric single crystal to form the domain wall. (3) The light beam scanning element according to claim 1, wherein the domain wall forming means forms the domain wall by applying an electric field to the ferroelectric single crystal. (4) The scanning control means is characterized in that it is provided with an electric field applying electrode that applies an electric field to the ferroelectric single crystal, and controls the applied voltage to move the domain wall. 1. The light beam scanning element according to 1. (5) The light beam scanning element according to claim 1, wherein the ferroelectric single crystal is a perovskite type and belongs to a tetragonal crystal, and the domain wall is a 90 degree domain wall. (6) The crystal axis (100) of the ferroelectric single crystal coincides with the C axis, and the incident light beam is incident perpendicularly to the 180 degree domain, and the 180 degree domain and the 90 degree domain are 2. The light beam scanning element according to claim 1, wherein the light beam scanning element is set to a polarized state in which the incident beam is reflected in a direction 90 degrees with respect to the direction of incidence at a 90 degree domain wall that is an interface with the light beam scanning element.