JPS5933431A - Device for utilizing surface acoustic wave - Google Patents

Abstract

PURPOSE:To improve characteristics of rise and fall, by providing a photocoupler which makes an optical beam incident to an optical waveguide layer formed with acoustooptic materials so that the optical beam is propagated in the position just under an inter-digital transducer which is formed on the optical waveguide layer and generates surface acoustic waves. CONSTITUTION:A substrate 1 having the acoustooptic effect consists of, for example, LiNbO3 crystal, and Ti or the like is diffused thermally to the surface of this substrate to form the optical waveguide layer having a refractive index higher than that of substrate 1. An inter-digital transducer 5 is formed in the approximate center on the optical waveguide layer 2 by the life-off method utilizing an AZ1350 resist, absorbing materials 7 are provided on both sides of this transducer 5. A photocoupler 3 is provided in such position that an optical beam P is propagated in the direction where the optical beam P crosses each linear electrode of the transducer 5 and the wave surface of surface acoustic wave generated from the transducer at the Bragg angle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that utilizes Bragg diffraction of light caused by surface acoustic waves.

The Bragg diffraction phenomenon of light caused by surface acoustic waves (hereinafter referred to as SAW) can be used for functional devices such as optical deflectors, optical modulators, and optical switches.

In addition to this, it can also be applied to the precise measurement of the shift in the frequency of light due to the interaction between SAW and light.

FIG. 1 shows a conventional optical polarizer. This optical polarizer consists of a thin film optical waveguide layer (2) fabricated on a crystal substrate (1).
, an interdigital transducer (hereinafter referred to as IDT) f51 that generates SAW is fabricated on one side of the optical waveguide layer (2), and an IDT that is fabricated on the other side of the optical waveguide layer (2). an absorber (7) that absorbs the SAW generated and propagated from the IDT (51 drive circuit (6),
The optical coupler (3) makes the optical beam tPl incident on the optical waveguide layer (2), and the polarized light is polarized by Bragg diffraction by the SAW so that the wavefront of the SAW propagating through the optical waveguide layer +211 crosses the wavefront of the SAW at the Bragg angle. The optical polarizer is composed of an optical coupler (4) that takes out the optical beam (R1) to the outside. Such an optical polarizer has the following problems.

(The SAW generated from jl IDTf51 is
There is a propagation path d to the position where it interacts with Pl.

Therefore, a delay time td exists between the generation of SAW and Bragg diffraction. For example, S.A.W.
When the propagation velocity V8 is 35Q Q1/sec and the distance d is IG, the delay time ta is expressed by the following equation.

'=3X10 (see) (11) By this propagation distance d, -
Since the length of the sides is longer, the degree of integration becomes smaller.

(Town: The rise and fall times of the deflected light are long.

The object of the present invention is to solve the drawbacks mentioned in item 1 and provide a surface acoustic wave utilizing device that has no delay time, good rise and fall characteristics, and is suitable for high integration. .

The surface acoustic wave utilizing device according to the present invention includes an optical waveguide layer formed of an acousto-optic material, an optical waveguide layer formed on the optical waveguide layer, and an SA
It is characterized by comprising an IDT that generates W, and an optical coupler that makes the optical beam enter the optical waveguide layer so that the optical beam propagates directly below the IDT.

Since the light beam propagates within the optical waveguide layer so that the center of the light beam coincides with the center of the IDT, the above-mentioned delay time becomes zero, and no extra space is required for SAW propagation, making it highly integrated. It is possible to aim for Because the SAW generated by the IDT75 propagates in two directions and interacts with all of the light beams, the polarized light beams are much smaller than conventional devices that propagate the light beam across the beam from one side to the other. the law of nature,
The fall time is approximately 1/2. This is a great advantage when this invention is applied to an optical switch.

Embodiments of the present invention will be described in detail below with reference to FIGS. 2 to 5. In FIGS. 2 and 5, the same components as those shown in FIG. 1 are given the same reference numerals.

In FIG. 2, a substrate (1) having an acousto-optic effect (the moon is, for example, a L i N b O3 crystal)
An optical waveguide layer (2) having a higher refractive index than the substrate (1) is produced by thermally diffusing Ti or the like onto the surface at about 1000°C. I D T (51 is formed approximately in the center of this optical waveguide layer +211 using AZi35.05 cyst or by a foot-off method. I D T (
Absorbent materials (7) are provided on both sides of 51. The optical coupler (3) propagates the light beam +p) which has entered the optical waveguide layer (2) from the optical coupler (3) directly under the I D T (51), and each line of I D T (51). The wave front of the SAW generated from the shaped electrode and the IDT f51 propagates in a direction intersecting at the Bragg angle.

As is clear from FIG. 2, the SAW generated from I D T (51 immediately interacts with the light beam tP),
Its propagation distance (corresponding to that shown by d in Figure 1)
is zero. Therefore, the delay time td as in the conventional device is zero.

Since the propagation distance is zero, only a small space is required for optical deflection, and it is also possible to integrate and arrange other optical functional elements on the substrate.

Next, we will consider the rising and falling times of polarized light, which are a particular problem when this surface acoustic wave utilization device is used as an optical switch.
This is an enlarged view of the image. In this figure ζ, the beam [IJ] of the light beam tP is represented by PW. FIG. 4 shows the response characteristics of polarized light, and tAl is the second
The apparatus shown in the figure (Bl is the conventional apparatus shown in FIG. 1).

~ In Figures 2 and 4+Ai, the drive circuit (6
), when a high-frequency pulse voltage is applied to IDT (51), the optical waveguide layer (2) directly under IDT (51
The SAW is excited. The excited SAW immediately deflects the light beam +P). As time passes, the SAW propagates in two directions away from I I) T (51, so the intensity of the light deflected by the SAW is
The distance between the tips of the SAWs becomes maximum when the distance matches rlPW of the light beam (P). At this time, when the drive circuit (6) is turned off, the SAW directly below the IDT f51 disappears, and the intensity of the deflected light decreases. Due to the propagation of the SAW that has already occurred, the area of interaction between the SAW and the light beam decreases, and finally the intensity of the deflected light becomes zero.

In the conventional device shown in FIGS. 1 and 4 (B1), after the above-mentioned delay time tcl has elapsed after the SAW is generated from I D T (51) by the drive circuit (6), the SA
W cuts across the light beam tPl. The polarized light intensity increases as the SAW traverses the light beam tP). S.A.
Since W is propagating only in one direction, the rate of increase in the intensity of the polarized light is half the rate of increase due to the propagation of the SAW in tAl in FIG. When the SAW pulse and the light beam (P) completely match, the intensity of the deflected light becomes maximum. After that, the polarized light intensity decreases monotonically. As described above, according to the present invention, the rise and fall of the deflected light becomes steep.

FIG. 5 shows a modification. In this case, the optical waveguide layer (2
) is formed on a part of the input side of the optical beam, and an optical waveguide (8) is formed in its place.In this optical waveguide (8), a Grete-coupled optical coupler (9) is formed. ) is formed, and the incident light beam is directed towards this grete ink (9
) into the optical waveguide (8). Optical waveguide (8)
is, the incident light beam tp+ is exactly I D T
(It is manufactured so that the position and direction are such that it propagates directly below 51.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing a conventional example, Fig. 2 is a perspective view showing an embodiment of the present invention, Fig. 3 is a sectional view showing an enlarged IDT, and Fig. 4 is a time diagram showing response characteristics of polarized light. ·chart,
FIG. 5 is a perspective view showing a modification. (1)...Substrate, (2)...Optical waveguide layer, +3) +
91-...Optical coupler, (5)・l・IDT1 (810-
・Optical waveguide. 2 Patent Applicants: 4 persons other than Tateishi Electric Co., Ltd. 1st drawing, 2nd drawing, 8th figure, and 4th figure (A)

Claims (1)

[Claims] An optical waveguide layer formed of an acousto-optic material, an interdigital transducer formed on the optical waveguide layer and generating surface acoustic waves, and an interdigital transducer immediately below the interdigital transducer. An optical coupler that makes a light beam enter a leading wave layer so that the light beam propagates through a certain position.