JPS5928413Y2 - Thin film light control element - Google Patents

Description

[Detailed description of the invention] The present invention relates to light control elements such as optical modulators and optical deflectors that utilize the diffraction effect of light caused by ultrasonic waves, and particularly to light control elements that utilize the above-mentioned effects in optical integrated circuits. It is related to.

In the fields of optical information processing and optical communications, vigorous research and development efforts are being carried out to realize optical integrated circuits for the purpose of stabilizing and downsizing optical devices.

An optical integrated circuit is a circuit in which active elements such as a light source, optical amplifier, and optical modulator, and passive elements such as an optical waveguide and an optical resonator are provided on a small substrate.

Among the elements constituting this optical integrated circuit, in order to obtain an element that temporally or spatially controls light waves propagating through a waveguide, surface acoustic waves are excited on the substrate surface, and the diffraction phenomenon of light waves caused by the surface acoustic waves is generated. It is effective to construct a thin film optical deflection element or a thin film optical control element assembly using the above.

In addition to the methods described above, various methods have been considered for obtaining optical control elements in optical integrated circuits, which make use of electro-optic effects and magneto-optic effects. Valid only when it is an optical or magneto-optical material.

However, the method of utilizing the surface acoustic waves is to provide a transducer-like electrode on the surface of a piezoelectric material, or to provide a transducer-like electrode on the surface of a non-piezoelectric material, and to provide a thin film of piezoelectric material on top of the interdigital electrode. Since surface acoustic waves can be excited by the method, there are almost no restrictions on the materials of the optical waveguide and the substrate.

In addition, the element using surface acoustic waves requires less electrical input than the conventional element using bulk acoustic waves, and the elastic wave beam can be easily controlled from the substrate surface.
It has features such as the ability to miniaturize the device.

In optical modulators and optical deflectors that utilize the diffraction effect of light caused by surface acoustic waves, it is necessary to perform mutual separation between diffracted light and undiffracted light or diffracted light caused by surface acoustic waves of various frequencies. .

The angle between the two diffracted lights is approximately proportional to the difference in frequency of the elastic waves when they are diffracted, but there is an upper limit to the frequency at which the elastic waves can be excited, and the separation angle is quite small.

Normally, the diffracted lights are separated from each other by diffracting the light and then propagating it over a long distance, or by installing an appropriate passive optical element such as a lens behind the deflector. The above method is difficult for small z5 elements.

Furthermore, in order to use the above element using surface acoustic waves as one element of an optical integrated circuit, it must be coupled with other optical integrated circuit elements.

The purpose of the present invention is to provide light control elements such as light modulation elements and light deflection elements using surface acoustic waves, which are equipped with an effective means for separating diffracted light, and which are small and can be coupled to other optical integrated circuit elements. It is about providing.

According to the present invention, a thin film optical waveguide provided on a solid substrate;
a surface acoustic wave converter for generating a surface acoustic wave sound acting on a light wave propagating in the thin film optical waveguide, and a surface acoustic wave converter for further diffracting at least one light wave component diffracted by the surface acoustic wave, At least one set of diffraction gratings that increase the angular difference in the propagation direction; A thin film light control element using a diffraction grating in which a plurality of diffraction gratings different in at least one of sizes and directions are formed overlappingly in the same area can be obtained.

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows an example of a thin film optical modulation device or a thin film optical switching device using a conventional diffraction grating and an optical waveguide.

Reference numeral 1 denotes a thin film optical waveguide provided on a substrate, and is manufactured by, for example, a method such as sputtering or ion exchange.

Reference numeral 2 denotes a surface acoustic wave converter that electrically generates surface acoustic waves 4 on the surface of the optical waveguide 1 in order to diffract the optical beam 3 incident on the optical waveguide 1.

Reference numeral 5 denotes a surface acoustic wave absorber provided to prevent the surface acoustic waves 4 from being reflected from the end surface of the substrate.

6 is a thin film diffraction grating that has the function of increasing the angular difference between diffracted light and non-diffracted light in the surface acoustic wave 4, and periodically changes the thickness of the optical waveguide to maintain an equivalent refractive index. This is a phase grating manufactured using a method that changes the angle.

Reference numerals 7 and 8 are optical waveguides that respectively independently guide the diffracted light 9 and the undiffracted light 10 whose angular difference has been increased by the diffraction grating 6, and 11 and 12 are the incident ends thereof.

In order for the thin film diffraction grating 6 to have the above-mentioned function, it is necessary to satisfy the following condition sound groove.

That is, first, the diffraction angle is sufficiently large, second, the diffraction efficiency is high, and third, the property of selectively diffracting only the light waves incident at a specific incident angle, that is, the angle selectivity is high.

A specific numerical example of a configuration that satisfies the above conditions is shown below.

The equivalent refractive index of the thin film optical waveguide 1 is i1.5Q. The wavelength in vacuum of the incident light 3 is '16328°A, and the velocity and frequency of the surface acoustic wave 4 are 3000 m/sec and 60 MHz, respectively.
shall be.

The incident light 3 is a nearly parallel light beam with a width of 0.5 mm,
The light is made incident at an angle with respect to the wavefront direction of the surface acoustic wave 4 at which the intensity of the diffracted light is maximum, the so-called Bragg angle.

The thin film diffraction grating 6 is oriented such that the light diffracted by the surface acoustic wave 4 is incident at a Bragg angle, and has a grating period of 5 μm and a width of 2 mm.

In this case, the diffraction grating 6 has an incident angle selectivity of approximately 7.5 mm r a d, and the angular difference between the diffracted light and the undiffracted light due to the surface acoustic wave 4 is 8.4 f[[[tl''ad J:]. It is possible to diffract only the light diffracted by the surface acoustic wave 4 again.

In addition, the diffraction angle of the diffraction grating 6 is approximately 84 mm with respect to the incident direction.
rad, the angular difference between the diffracted light 9 and the undiffracted light 10 after passing through the diffraction grating 6 is approximately 92 mmrad.

Since the spread angle of the incident light 3 is about 1.1 mmrad, the distance between the thin film diffraction grating 6 and the incident ends 11 and 11 of the optical waveguide is about 6 m.
By disposing them at a distance of m, the diffracted light 9 and the undiffracted light 10 can be guided independently to the optical waveguides 7 and 8, respectively.

Now, if the diffraction grating 6 is not used in the same configuration as above and the diffracted light and undiffracted light due to the surface acoustic wave 4 are spatially separated, the incident ends 11 and 12 of the optical waveguide will be the surface acoustic wave 4. This means that it must be at least 60 mm away from the part that is being excited.

In addition, in this example, the input end 11 of the optical waveguide is connected to c5, as described above.
12, the undiffracted light and the diffracted light are separated by about 0.54 mm, but the separation width is further expanded by the optical waveguides 7 and 8.

When the diffraction grating 6 is installed as described above, it becomes easier to separate the diffracted light and the undiffracted light and couple them to other optical integrated circuit elements installed on the same substrate than when the diffraction grating 6 is not installed. However, in the present invention, separation becomes easier as described below.

That is, when the present invention is used, the thin film diffraction grating 6 has the function of diffracting the diffracted light due to the surface acoustic wave and simultaneously diffracting the undiffracted light in the direction opposite to the diffracted light with respect to the incident direction of the light. can be installed.

In this case, the angular difference between the diffracted light 9 and the undiffracted light 10 is further increased than in the above configuration, and the diffraction grating 6 and the optical waveguide 7,
It is possible to further narrow the distance between the incident ends 11° and 12 of 8.

In order to do this, diffraction gratings may be arranged sequentially in the direction of propagation of the light wave for each of the diffracted light and non-diffracted light by the surface acoustic wave 4, but as in the present invention, these two diffraction gratings are placed in the same It is possible to obtain a smaller element by overlapping the elements in the area.

FIG. 2 is a plan view showing a one-dimensional optical scanning element assembly having five deflection points in one embodiment for explaining the present invention.

In FIG. 2, 1 is a thin film optical waveguide, 2 is a surface acoustic wave converter capable of electrically generating surface acoustic waves of four different frequencies, and 3 is an incident light beam.

6 is a thin film diffraction grating, which consists of four types of diffraction gratings.
Each corresponds one-to-one to four specific light waves among the diffracted light and non-diffracted light due to the surface acoustic waves of the four types of frequencies, and only the specific diffracted light or non-diffracted light enters at the Bragg angle and is diffracted. It is set up so that

Furthermore, the period of the thin film diffraction grating 6 is determined by the incident light at five different angles.
That is, it is selected so as to increase the angle formed by each of the four types of diffracted light and undiffracted light by the surface acoustic wave 4.

After passing through the thin film diffraction grating 6, the diffracted light and the undiffracted light whose angles to each other are increased are separated and guided independently to optical waveguides 21, 22, 23°24.25.

FIG. 3 shows a thin film diffraction grating 6 without using the present invention.
An example is shown in which four diffraction gratings are installed in different areas.

Equivalent refractive index k1.50 of thin film optical waveguide 1, incident light 3
The wavelength in vacuum of
MHz.

In Figure 3, 44, 43, 42, 41 are each 6
0ME(z, 120MHz, 180MHz, 240MHz
z indicates diffracted light due to surface acoustic waves, and 45 indicates undiffracted light.

46, 47, 48, and 49 collectively constitute the diffraction grating 6 in FIG.
4, 45, and diffracts only the light wave, and generates diffracted lights 51, 45 for each incident light.
52,54°55.

The incident light 43 travels without being diffracted and becomes a light wave 53.

The periods of the diffraction gratings 46, 47, 48°49 are 2.
They are 5 μm, 15 μm, 15 μm, and 2.5 μm, and the widths are all 2 mm.

The angles formed by the incident lights 41 and 42, 42 and 43, 43 and 44 degrees, 44 and 45 to the diffraction grating are all about 8-4 mrad, and the angle selectivity of the diffraction grating is about 7-5 mrad J.
It's big.

Therefore, the incident lights 4L42, 43, 44, and 45 are independently diffracted.

The angles formed by the light waves 51, 52, 52, 53, 53, 54, 54, and 55 after passing through the diffraction grating are all about 92 nmlrad.
increases to

Figure 4 shows the diffraction gratings 46, 47, 48, 49 shown in Figure 3.
4 is a diagram showing an example of a diffraction grating used in the present invention manufactured by superimposing the gratings on the same area, and the periods and orientations of the four types of gratings composing FIG. 4 are completely different from those of the diffraction grating shown in FIG. 3. If they are the same, they have the same function as the diffraction grating shown in FIG.

However, in order to obtain the same diffraction efficiency as the diffraction grating shown in Fig. 3, the length of the diffraction grating shown in Fig. 4 in the light traveling direction needs to be 1/4 of that of the diffraction grating shown in Fig. 3, so it can be made very small. There is a characteristic that

66, 67, 68, and 69 indicate one period of each of the four types of diffraction gratings.

If the width of the incident light 3 in the thin film optical waveguide is 0.5 mm in FIG. By separating them by 6 mm, the diffracted light and undiffracted light by the surface acoustic wave 4 are separated from each other and guided to the optical waveguide independently.

According to the above principle, the incident light 3 is sequentially converted into output light 31, by sequentially switching the frequency of electrical input to the surface acoustic wave 2.
32, 33, and 34, and when there is no electrical input to the converter 2, the output light is 35.

Also, depending on how the input is added to the converter 2, the output light is 31,
32, 33, 34, and 35, and the device shown in this embodiment can be used as an optical scanning element in an optical recording/reading device.

It is also possible to further increase the number of deflection points to be separated by widening the frequency range of the surface acoustic waves.

The elements shown in Figs. 1 and 2 above may be used alone as they are, but the output light obtained by separation may be used as incident light to the same element provided elsewhere, and several It is also possible to separate the deflection points, and such a method k(”J
By repeating this process several times, optical scanning elements with a large number of deflection points can be obtained.

FIG. 5 shows an example in which a plurality of elements of the present invention are used.

Reference numerals 71, 72, and 73 are optical switching elements similar to those shown in the present invention, and when an input beam is present in each element and an input is applied to the surface acoustic wave converter, the output light is 75, 77°, 79, respectively. Therefore, when there is no electrical input, the output light is 74°76.78.

However, instead of the diffraction grating 6 shown in FIG.
In order to increase the separation angle, two types of diffraction gratings that diffract diffracted light and non-diffracted light due to surface acoustic waves in opposite directions are formed overlappingly in the same region.

When a light wave is input to the element 71, any one of the four output lights 76, 77, 78, and 79 can be obtained depending on how the electrical input is applied to each element.

This embodiment uses a four-point optical scanning element and converts the encoded electrical signal (r71, 72, 73) into a frequency signal to be applied to the surface acoustic wave transducer of three elements, thereby determining the position of the light. It is also possible to use it as an adhered element that converts it into a signal.

Although some embodiments have been described above using specific numerical values, these are just examples and nothing should be taken as such.

In step 5 described in detail above, according to the present invention, even diffracted light due to relatively low frequency surface acoustic waves can be separated by forming a plurality of diffraction gratings overlappingly in the same area.
A small optical control element that can be easily coupled to other optical integrated circuit elements can be obtained.

Several of these optical control elements can be combined to form elements with complex functions, and these can be used as elements of optical integrated circuits, as well as encoders, adherents, and optical scanning elements in the field of optical information processing. used.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an optical switching element for explaining the present invention, Fig. 2 is a diagram showing a five-point optical scanning element assembly of an embodiment of the present invention, and Figs. 3 and 4 are Fig. 2. FIG. 5 is an enlarged view of a portion of a thin film diffraction grating, and FIG. 5 is a diagram showing a four-point optical scanning element according to the present invention. In the figure, 1 is a thin film optical waveguide, 2 is a surface acoustic wave converter, 3 is incident light, 6 is a thin film diffraction grating, and 7 and 8 are optical waveguides.

Claims (1)

[Scope of utility model registration request] a thin film optical waveguide provided on a solid substrate; a surface acoustic wave transducer for generating a surface acoustic wave acting on a light wave propagating in the optical waveguide; and at least one surface acoustic wave transducer diffracted by the surface acoustic wave. At least one or more sets of diffraction gratings that further diffract the above light wave components and increase the angular difference in the traveling direction between the light wave components, and an optical waveguide that independently guides each of the plurality of light wave component groups whose angular differences are increased. and further characterized in that a diffraction grating is used as the diffraction grating, in which a plurality of diffraction gratings in which at least one of the magnitude or direction of the grating vector is different from each other are formed overlappingly in the same area. Light control element.