JP2000147577A - Acoustooptical deflector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acoustooptical deflector in which failure such as optical damage or the like are never generated by deflecting light propagating in a light guide layer while exciting a Sezawa wave in the light guide layer with comb-line electrode. SOLUTION: A ZnO film (piezo-electric thin film light guide layer) 5 is provided on the surface of a sapphire substrate 1. Moreover, an IDT(inter-digital- transducer) 6 and gratings 7, 8 as an input-output means are formed on the ZnO film 5. In such constitution, a laser beam LB from a light source in which a semiconductor laser is made to be a light source is made incident on this deflector. This laser beam LB is inputted from the grating 7 to the ZnO film 5 to be propagated. At this time, a high frequency signal is impressed on the IDT 6 from a power source 10 and a surface acoustic wave (Sezawa wave) SA propagating in a direction roughly orthogonal to a guided light in the ZnO film 5 is excited. Then, the guided light (laser beam LB) is deflected by the mutual action with this elastic wave to be emitted to the outside from the grating 8. Thus, a high electromechanical coupling coefficient is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an acousto-optic deflector,
More specifically, the present invention relates to an acousto-optic deflector that deflects light propagating in a waveguide by surface acoustic waves excited in the waveguide.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus using a laser beam as a light source, a system is employed in which a laser beam is deflected by rotation of a polygon mirror called a polygon mirror to scan a photosensitive member. I have. However, in recent years, a higher scanning speed has been demanded, and various waveguide-type acousto-optical deflectors have been developed as a countermeasure.

An acousto-optic deflector of this type has a structure in which a piezoelectric thin-film waveguide layer such as ZnO is deposited on a glass substrate.
A structure is known in which Ti is diffused on the surface of a bO ₃ substrate or proton exchange is performed on the substrate surface to form a waveguide layer. A surface acoustic wave (Rayleigh wave) is excited in these waveguide layers, and interacts with guided light (laser beam). Light deflection is performed by Bragg diffraction of the guided light when the guided light and the elastic wave intersect at an angle satisfying the Bragg condition.

However, in the structure using the glass substrate, the electromechanical coupling coefficient is small, and it is necessary to input a large electric power to the electrodes, which is inefficient. Further, in the structure using the LiNbO ₃ substrate, although the electromechanical coupling coefficient is large, the process of forming the waveguide layer is complicated, and the waveguide layer itself is damaged by light (wave propagation of the crystal by guiding light). (Decrease in efficiency).

Accordingly, an object of the present invention is to provide an acousto-optic deflection device that can form a waveguide layer without requiring a complicated process, as well as having a large electromechanical coupling coefficient, and does not cause problems such as optical damage. To provide equipment.

[0006]

To achieve the above object, an acousto-optic deflector according to the present invention has a piezoelectric thin-film waveguide layer formed on a sapphire substrate and a comb tooth in contact with the waveguide layer. An electrode was formed. The comb-like electrode excites a Sezawa wave in the waveguide layer to deflect light propagating through the waveguide layer. A Sezawa wave is a surface acoustic wave corresponding to a higher-order mode of a Rayleigh wave.

According to the present invention, a high electromechanical coupling coefficient can be obtained by oscillating a Sezawa wave using a sapphire substrate. In particular, when the R-plane and C-plane sapphire substrates are used, the waveguide layer can be formed with good crystallinity.

Further, in the acousto-optic deflector according to the present invention, the waveguide layer is formed of a ZnO film, and the relationship between the film thickness h and the wavelength λ of the surface acoustic wave is defined as 0.2 <h. /Λ<0.4
Is preferably set within the range. Under these setting conditions, experimentally, the electromechanical coupling coefficient of the Sezawa wave takes a satisfactory value, and the light deflection efficiency is improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an acousto-optic deflector according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows an acousto-optic deflector according to an embodiment of the present invention.
A film (piezoelectric thin-film waveguide layer) 5 is provided. Further, an IDT (inter-digital-transducer) is formed on the ZnO film 5.
er, comb-shaped electrode) 6 and gratings 7, 8 as light input / output means.

The ZnO film 5 functioning as a waveguide layer was deposited to a thickness of 1.2 μm by a sputtering method.
Zn with good crystallinity is placed on the R-plane or C-plane sapphire substrate.
An O film 5 can be formed. IDT6 has a film thickness of 10
A normal electrode finger having a width and a gap of 1.0 μm is provided by depositing a 00 Å Al film on the ZnO film 5 and then patterning the film by exposure with a stepper and a lift-off method.

A laser beam LB is incident on the acousto-optic deflector from a light source unit (not shown) using a semiconductor laser as a light source. This laser beam LB is input from the grating 7 to the ZnO film 5 and propagates. At this time, a high-frequency signal is applied to the IDT 6 from the power supply 10, and a surface acoustic wave (Sezawa wave) SA that propagates in the ZnO film 5 in a direction substantially orthogonal to the guided light is excited. The guided light (laser beam LB) is deflected by the interaction with the elastic wave and exits from the grating 8 to the outside.

Incidentally, the wavelength λ of the surface acoustic wave excited by the IDT 6 is four times the electrode finger width, and is therefore 4.0 μm.
m, and the thickness h of the ZnO film 5 is configured to be h / λ = 0.3. With such a configuration, ZnO
A Sezawa wave can be excited in the film 5. The electromechanical coupling coefficient K ² , which is the excitation efficiency, depends on h / λ, and as shown in FIG.
The maximum value is obtained when /λ=0.3. FIG. 2 shows the characteristics of the Rayleigh wave together with the characteristics of the Sezawa wave for comparison.

The electromechanical coupling coefficient of the deflector is very large as compared with the case where a Rayleigh wave is used using a glass substrate, and is substantially equal to the case where a LiNbO ₃ substrate is used. The use of a sapphire substrate is advantageous in that it does not cause problems such as easy fabrication of the waveguide layer and optical damage, and can realize a low-cost and highly durable deflector having a large electromechanical coupling coefficient. .

As shown in FIG. 2, when the Sezawa wave is used, the electromechanical coupling coefficient K ² is about 4%.
, Where h / λ is 0.2
What is necessary is just to set in the range of -0.4.

The acousto-optic deflector according to the present invention is not limited to the above embodiment, but can be variously modified within the scope of the invention. In particular, the comb-shaped electrode may be formed at the interface between the substrate and the waveguide layer, and may be a chirp type or a chirp tilt type. As a light input / output unit, a coupling unit such as a prism may be used in addition to the grating.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an acousto-optic deflector according to the present invention.

FIG. 2 is a graph showing an electromechanical coupling coefficient in the acousto-optic deflector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 5 ... ZnO film (piezoelectric thin film waveguide layer) 6 ... Comb-shaped electrode 7, 8 ... Grating LB ... Laser beam SA ... Sezawa wave

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Makoto Minakata 1-222-6 Hirosawa, Hamamatsu-shi, Shizuoka Prefecture Joint lodging 5-52 (72) Inventor Michio Kadota 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside of Murata Manufacturing Co., Ltd. (72) Inventor Takeshi Iwamoto 2-13-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2K002 AA06 AB06 AB07 AB08 BA12 CA02 CA22 DA05 EB07 HA10

Claims (4)

[Claims] 1. A sapphire substrate, a piezoelectric thin-film waveguide layer formed on the substrate, and a comb-shaped electrode formed in contact with the waveguide layer. An acousto-optic deflector that excites a Sezawa wave in the wave layer and deflects light propagating in the waveguide layer. 2. The method according to claim 1, wherein the waveguide layer is a ZnO film, and the relationship between the film thickness h and the wavelength λ of the surface acoustic wave is 0.2 <h / λ <.
2. The acousto-optic deflector according to claim 1, wherein the value is set within a range of 0.4. 3. The acousto-optic deflector according to claim 1, wherein said substrate is an R-plane sapphire substrate. 4. The acousto-optic deflector according to claim 1, wherein said substrate is a C-plane sapphire substrate.