JPH01520A - Acousto-optic device with amorphous hard carbon film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Madarago Momme I The present invention relates to an acousto-optic device.

When using optical transmission for optical communications and optical information processing, optical deflection technology is essential. Light deflection is accomplished by mechanical means, vt
The optical means is realized by an acousto-optic means or the like. In the case of mechanical means or electro-optical means, it is possible to increase the deflection efficiency and the deflection angle, but on the other hand,
Problems arise in that the device itself becomes larger and the production cost increases. Therefore, light deflection elements that utilize acousto-optic deflection have attracted attention because although the deflection angle of light cannot be large, the device is smaller, the deflection efficiency is high, and the deflection speed is faster.

Conventionally, optical waveguide materials for acousto-optic light deflection elements include, for example,
LiTaO3, L+NbO3, Tio2, etc. are used. When this conventional optical waveguide material is used, there is a problem in that the polarization efficiency deteriorates because the intensity of the polarized light cannot be increased very much. As a result, a problem has arisen in that the accuracy of the optical deflector and switching element is reduced.

, ILJ It is an object of the present invention to eliminate such drawbacks of the prior art and to provide an acousto-optic element with good deflection efficiency and high intensity of deflected light.

En-1 In order to achieve the above object, the present invention includes a substrate, an optical waveguide layer forming an optical waveguide on the substrate, and a conversion method that generates surface acoustic waves in the optical waveguide layer and deflects light in the optical waveguide layer. The optical waveguide layer is characterized in that it contains an amorphous material containing carbon atoms and hydrogen atoms as main structure-forming elements. Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

The present invention uses a so-called "amorphous hard carbon film" synthesized by a low-pressure vapor phase film deposition method using hydrocarbon plasma as an optical waveguide material.

"Amorphous hard carbon film" (hereinafter referred to as 1-carbon) is an amorphous material whose main structure-forming elements are carbon atoms and hydrogen atoms. It is a strong and hard material that also has a diamond-like bond structure (SP3 bond).In other words, tocarbon is an amorphous, hard material with excellent electrical insulation and chemical stability. This i-carbon is also called, for example, diamond-like carbon or hard carbon.

FIG. 1 shows an example in which the guiding waveguide material according to the present invention is applied to a surface acousto-optic device.

Ml 2 of i-carbon, which is a guiding waveguide material, is formed on a flat substrate 1 made of Y2O3, ZnO1S e 03, etc., a piezoelectric material film 3 such as ZnO is formed on the i-carbon film 2, and the piezoelectric material Above the membrane 3 are an interdigital transducer 4, prism coverrs 5 and 6, a polarizer 7, a photomultiplier tube 8. Sound absorbing materials 9 and the like are arranged.

The input beam lO is polarized in a polarizer 7,
The light is inputted via the prism coupler 5 to the i-carbon@2 which is the optical waveguide of the element. By applying a high frequency wave to the interdigital transducer 4, a surface acoustic wave is generated on the carbon film 2, and the input beam 10 is optically deflected, and the diffracted light 12 that is diffracted by the optical deflection operation is separated from the diffracted light 12 that is not diffracted. The non-refracted lights 13 are outputted to photomultiplier tubes 8 via prism coverrs 6, respectively.

The i-carbon film 2 in this example has physical properties as shown in FIG. 2, and was synthesized by the plasma GVD method described later.

? Figure 53 shows the principle of Bragg diffraction due to surface i-waves. θB in Figure 0 is the Bragg diffraction angle,
The relationship between the wavelength of light and the wavelength λ8 of the surface acoustic wave is given by the following equation.

sin θB=in 72λS (1) Also, the intensity of the diffracted light at this time! d is Id-sin2(kΔnL/2) (2) In this equation (2), k is the wave number of light, and L is the width of the surface acoustic wave packet.

In order to obtain high deflection efficiency, it is important to obtain a large Δn in terms of materials. The surface acoustic wave power Pa per unit wavelet cross-sectional area propagating in a medium is Pa□1/2, where the speed of sound is V, the density of the medium is ρ, and the strain is S. It is expressed as ov3S2(3). In addition, the refractive index of the medium changes due to strain caused by surface acoustic waves, and the change is Δ(1/n2)=
PS (4). This formula (
P in 4) is a photoelastic constant.

From the above, Δn is.

28 31/2 Δn=(P N /p v ) ・(Pa/2) 1
/2(5). In this formula (5), M2-n P
/ρ is called a figure of merit, and the larger the figure of merit M2, the greater the Bragg diffracted light intensity can be obtained with the same power of surface acoustic wave input. In addition to surface acoustic wave optical deflection, it is also possible to change W when used as a modulation layer.
The figure of merit M1 takes into account the IJ bandwidth, and the figure of merit M3 when the beam diameter and the height H of the superbeam are made equal is defined as follows, taking into account the configuration of the two-dimensional optical deflector.

Mt-n7P2/ρv (8)M
=n7P2/p v2 (7) Looking at FIG. 4, the physical property values and performance index of conventionally used optical waveguide materials such as L+Ta0a and carbon used in this example are shown. A comparison of the figures of merit shows that i-carbon is far superior to other conventionally used optical waveguide materials. Especially when comparing M2, which is an important performance index for this device,
For example, LiTaO3 is 1.37X 10"s/g, while i-carbon is 30.9X 10"s/g.
It can be seen that it exhibits superior detection properties compared to other materials.

7JIJ5 shows an example in which the optical waveguide material according to the present invention is applied to a broadband deflector.

The broadband deflector in this embodiment has a film 2 of i-carbon, which is an optical waveguide material, formed on a flat substrate l of Y2O3, and a piezoelectric material I1 such as ZnO on the i-carbon [2]. 3 is formed, and a plurality of broadband transducers 22 having different center frequencies are arranged on the piezoelectric material film 3 at an angle so as to satisfy the Bragg condition. By adopting such a structure, it is possible to expand the elastic surface area.

By applying high frequency to the broadband transducer 22 to the laser beam 21 input to the i-carbon 115!2, which is the leading wave path of the element, a surface acoustic wave is generated on the i-carbon film 2, and the input laser beam 21 The diffracted light convergent beam 23 diffracted by the light deflection operation is transmitted to the array 24 and the high-speed photodetector 2.
5 and output as an optical signal.

According to the above embodiments, since i-carbon is used as the optical waveguide material of the surface acousto-optic element, the light intensity is higher than that of the conventionally used guiding waveguide material, and the deflection efficiency can be increased. can. Therefore, the accuracy of the optical deflector and the switching element can be improved.

Next, an example of a method for producing i-carbon used in the optical waveguide material of the above embodiments will be shown.

In this example, a case will be described in which an i-carbon film having the physical properties shown in FIG. 2 is synthesized by the plasma GVD method.

FIG. 7 shows a schematic diagram of a plasma CVD reactor. The substrate 1 is attached to the RF power supply side electrode 70 in the vacuum apparatus, and a raw material gas such as CH4/H2 consisting of hydrocarbons and hydrogen is introduced. In this gas atmosphere, a negative bias is applied to the RF power feeding side electrode 70 and a high frequency power source 72 is applied to the parallel plate electrode to generate plasma. Radicals and ions dissociated and excited during this plasma generation are deposited on the substrate, and a carbon film is deposited. This is the i-carbon film.

Details of pressure and other conditions are shown in FIG.

The optimum conditions for synthesizing the i-carbon film in the present invention are a pressure of 0.0 OITorr and a gas composition of H2/CCH4-H2)-80%.

The temperature is room temperature and the RF power is 50%1.

According to this film-forming method, a hydrocarbon gas is used as a raw material gas, and film-forming can be performed at low pressure and at room temperature, so that elements can be manufactured at low cost.

As described above, by using carbon as the optical waveguide material of an acousto-optic device, the accuracy of optical deflectors, switching devices, etc. can be improved, and the device can be manufactured at low cost.

The present invention is applicable not only to optical deflectors, optical modulators, and switching elements when using optical transmission such as optical communications and optical memories as shown in the above embodiments, but also to optical dynamometers, optoelectronic integrated circuits, etc. It can also be applied to

Antibody-1 According to the present invention, the optical waveguide material of the one-surface acousto-optic element
Since i-carbon is used, the light intensity is greater than that of conventionally used optical waveguide materials, and the deflection efficiency can be increased. Therefore, the accuracy of the optical deflector and the switching element can be improved.

[Brief explanation of the drawing]

FIG. 1 is an external perspective view showing an embodiment of the acousto-optic device according to the present invention. FIG. 2 is a diagram showing the physical properties of the optical waveguide material of the embodiment shown in FIG. 1. FIG. 3 is a diagram showing surface elasticity. An explanatory diagram explaining the principle of Bragg diffraction due to waves, Figure 4 is a diagram comparing the physical properties of the optical waveguide material of the example shown in Figure 1 and a conventionally used optical waveguide material, and Figure 5 is a diagram of the book. Fig. 6 is a diagram showing the film forming conditions of the optical waveguide material of the embodiment shown in Fig. 1; It is a schematic diagram showing an example. Part 1 10. , substrate 2, ,i-carbon film 380. Piezoelectric material film 411. Interdigital transducer 22,...
Broadband transducer 70, RF power supply side electrode 72, RF main power supply license applicant Ricoh Co., Ltd. agent Kamasu Takao Maruyama Takabu, Figure 1, Figure 5

Claims (1)

[Claims] 1. A substrate, an optical waveguide layer forming an optical waveguide on the substrate, and a converter that generates a surface acoustic wave in the optical waveguide layer and deflects light in the optical waveguide layer. 1. An acousto-optic element having an amorphous hard carbon film, wherein the optical waveguide layer contains an amorphous material having carbon atoms and hydrogen atoms as main structure-forming elements.