JPS59147322A - Optical modulating element - Google Patents

Abstract

PURPOSE:To constitute a photodetecting element in one body and to form an extremely small optical element easily by composing a light guide of a ridge part consisting of the projection part of a PLZT thin film provided on the surface of a substrate. CONSTITUTION:The optical modulating element branches at least one input light guide 111 into two control light guides 113 by a Y type branch 112 and holds those two control light guides 113 in parallel at a specific interval. Then, the optical modulating element 10 is provided with a light guide 11 which connects the two light guides to one output light guide 115 at the other-side terminals by a Y type branch 114 and a phase control electrode 12 provided to at least one control light guide 113, and the ridge part 221 consisting of the projection part is provided on the surface of the PLZT thin film 22 having the light guides on the substrate 21. Consequently, the photodetecting element is constituted in one body and the extremely small optical element is formed easily.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light modulation element, and in particular to a PLZ
The present invention relates to a light modulation element for optical integrated circuits made of a T-based thin film.

Conventional configuration and its problems A Mannha-Zender type light modulation element is known as a light modulation element.

Conventionally, this type of optical modulation element has been constructed from a T1 diffusion type LiNbO3 optical waveguide. This Ti-diffused LiNb
In the O5 optical waveguide, phase modulation is performed by the photoacoustic electro-optic effect propagating through one of the Y-branched waveguides, and the Y
Intensity modulation is performed by the interference effect of light that is returned to a single waveguide by branching.

However, in the T1 diffusion type LiNbO3 optical waveguide.

A single-layer structure consisting of a graded index structure (a structure in which the refractive index distribution changes approximately quadratically in the area surrounding the optical waveguide) makes it difficult to couple the propagating light with other optical elements and to miniaturize the element dimensions. If it is not a mode, the mode conversion is large, so the optical propagation loss increases, and the degree of modulation cannot be increased. Another drawback is that it is not possible to integrate photodetecting diodes, which are individual semiconductor components, for example, from the -2 group. In addition, when forming microscopic optical components such as microlens prisms, the boundary of the waveguide expands due to diffusion treatment during heat treatment at a high temperature of 1100°C, making miniaturization difficult. The drawback was that it lacked practicality.

The present inventors have succeeded in eliminating all the drawbacks of conventional light modulation devices by using a PLZT thin film optical thin film optical waveguide in this type of light modulation device, and have invented a new light modulation device.

OBJECTS OF THE INVENTION The present invention provides a light modulation element that can be integrated with a single photodetection element and is easily miniaturized and integrated. Therefore, the present invention provides the structure and constituent materials of an optical modulation element comprising a thin film optical waveguide. In particular, the present invention provides the structure and constituent materials of an optical modulation element made of a PLZT thin film optical waveguide. , an optical waveguide that holds the two control optical waveguides fully parallel at a predetermined interval and connects them to one output optical waveguide again by a Y branch at the other end, and a phase control provided in either of the control optical waveguides. In this light modulation element, the above-mentioned optical waveguide is constructed from a ridge portion consisting of a convex portion of a PLZT thin film provided on the surface of the substrate, and the substrate is made of sapphire (α - Alumina) zero-sided substrate, the PLZT thin film consists of at least oxides of lead, titanium, and lanthanum, and the molar ratio of lead (pb) and titanium (ri) is Pb/T.
i is in the range of 0.65 < Pb 7 Ti (0.90).

Description of examples Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are sectional views of the planar structure of the main part of the optical modulation element according to the present invention and the main part of the optical waveguide that constitutes the entire modulation element. Note that the buffer layer is omitted in FIG. 1, and FIG. 2 shows a cross section taken along line XX' in FIG. 1.

In the figure, an optical modulation element according to the present invention branches at least one input optical waveguide 111 into two control optical waveguides 113 by a Y branch 112 at a predetermined interval.

The two control optical waveguides 113 are held in parallel, and one output optical waveguide 11 is formed by Y-branching 114 again at the other end.
In the light control element 10 in which a phase control electrode 12 is provided on at least one of the optical waveguide 11 connected to the optical waveguide 6 and the control optical waveguide 113, the optical waveguide is provided on the surface of the PLZT thin film 22 provided on the substrate 21. A ridge portion 22 consisting of
1.

In this structure, unlike the graded index structure of conventional optical modulators which have a single mode, the inventors discovered that the optical waveguide structure with a ridge part using a PLZT thin film has less mode conversion and less optical propagation loss. It was discovered that the light modulation element can be put to practical use as a light modulation element, and based on these discoveries, the light modulation element according to the present invention was realized.

That is, as shown in FIGS. 1 and 2, the present invention differs from the Ti-diffusion type LiNb0+ optical waveguide with a Grachy-index structure in the conventional optical modulation element, and has a film thickness of 0.5 mm, which is normally used as an optical waveguide. With a PLZT thin film of 1 to 2 μm, the optical waveguide width is 3 to 3 μm (the film thickness between the 1-IJ edge part and the peripheral part, i.e., the step height edge part is less than h of the PLZT thin film), making it possible to create a multimode optical waveguide. Even if the
The inventors discovered that the light modulation element can be put to practical use as a device at a wavelength of dB/cm or less (wavelength 1.06 μm), and based on these findings, the light modulation device according to the present invention was realized. It was confirmed that the degree of optical modulation was 90% or more, which poses no practical problem, and since it is multi-mode, it is easy to combine with other optical components. In this case, the step height edge part P
If the length of the LZT yarn thin film is 4 or more or the leading waveguide width is less than 3 μm, the optical propagation loss will exceed 20 dB/crn, and if the optical waveguide width exceeds 30 μm, the device size will increase and the control electrode gap will also widen, resulting in a higher operating voltage. Not practical.

Furthermore, it was confirmed that in the above structure, minute microlenses could be easily incorporated because the optical waveguide does not expand due to thermal diffusion.

In this type of modulation element, as shown in FIG. 2, the phase control electrode is directly applied to the optical waveguide, which increases optical propagation loss. Therefore, a buffer layer 23 has been provided to separate the phase control electrode from the optical waveguide. However, although conventional PLZT-based materials are known to have a larger electro-optic effect than the LiNb05 single crystal currently used in the manufacturing process, they have a large dielectric constant, and therefore the buffer layer is usually a low dielectric material, so the electric field is It was believed that a high voltage had to be applied to the phase-controlled @A] electrode for modulation, rather than being sufficiently applied to the optical waveguide. In this case 1, for example, PL with a dielectric constant of 2000 and a film thickness of 0.36 μm
If a tantalum oxide layer with a dielectric constant of 20 and a thickness of 0.2 μm is provided on a ZT-based thin film, and a phase control electrode with a gap width of 6 to 20 μm is provided, only about 10 to 60% of the voltage will be applied to the optical waveguide. However, in the modulation element according to the present invention, it was unexpectedly discovered that a voltage of 60 to 80% or more was applied in an expiring manner, and it was confirmed that the modulation element is practically effective.

The inventors studied the constituent materials of this type of structure in more detail, discovered all new constituent materials, and invented a more effective light modulation element based on these discoveries.

That is, as shown in FIG. 2, the base plate 21 is composed of a sapphire 0-sided (○O○1) substrate.

It has been found that a PLZT thin film with a (111) plane can be grown by ion bombardment evaporation, such as magnetron sputtering. One semiconductor thin film 1, for example, Si.

It was confirmed that the (111) plane of eaAs also grows on this (0001) plane by, for example, a vapor phase growth method. These semiconductor thin films can be used to completely form, for example, a p-n or p-1-〇 structure using a normal semiconductor process, and can be used to form, for example, a photodetector element.
r can be integrated.

Furthermore, the inventors mentioned the above 4-on? They discovered that when a PLZT thin film was formed using the 15-silicon vapor deposition method, there existed a compositional region with a large electro-optic effect.Based on this discovery, they invented a more effective modulation element.

That is, the inventors set the composition of the target for S.S.I.C. at a molar ratio of Pb and Ti of Pb/Ti of 75:0.
66/Pb/Ti (We found that the electrochemical effect is large in the range of 0.90. In Figure 3, Pb/Ti
The actual measured values of the electro-optic effect when changing the Ti ratio are shown. In the same figure, one curve 31 is 2 of the PLZT thin film.
Electro-optical effect of Pb/Ti when applying an electric field of KV/mm
For comparison with this curve, curve 32 shows the characteristics of a LiNbO3 single crystal.

From the same figure, the -Pb/7i ratio is o, 6es
<pb/ri<0.90, LiNbo 3
A larger electro-optic effect can be obtained, and the half-wave voltage of modulation in the optical modulation element of the present invention is 2 Kv/mm).
Confirmed that it is a fishing device for optical modulation elements consisting of O5 optical waveguides 1~/ζ.

Example 1 As shown in FIG. 2, a surface-polished sapphire (alpha-alumina) 0-face substrate (0001) was used as the substrate 21, and a high-frequency magnetron was applied to the sapphire 0-face substrate 21. 0.4 μm PLZT thin film 2
In this case, the target L7J Ml composition is PLZT (2a10/1oo) - the rough 1 during sputtering.
The temperature of the ear substrate was 680°C and the sputtering power was 200W. The structure of the deposited PLZT film 22 is (111
) plane is a single crystal.

The refractive index is He-Na laser (wavelength 0.6328μ
m) was 2.6. Next, the surface of this PLZT-based thin film is masked with a photoresist to form the structure shown in FIG. 1 with an optical waveguide width of 20 μm, for example, and the PLZT-based thin film 22 is etched by, for example, 65 nm with an ion beam to form a ridge portion 221. Formed.

The effective refractive index generally used in optical waveguide analysis is larger in the ridge portion, that is, in the high film thickness region 221, than in the convex thickness region, so light is confined in the high film thickness region and is You can say that you should not be used. next,
'ra2o, between at least the phase control electrode and the optical waveguide on these thin films.

8th recruitment to Magnetrons Hanota/Banonoa layer 23 due to departure
It was deposited as The deposited Ta205 film is amorphous, and its refractive index is determined by Ha-Ne laser (wavelength 0.6328 Hr).
n) was 2.1. Next, the phase control electrode 12 is formed by vapor deposition A/A, and the light modulation element shown in FIG. 1 is constructed.

FIG. 4 shows the measurement results of optical intensity modulation when a voltage is applied to only one optical waveguide, for example, the waveguide 113, in the above configuration. In the same figure, the curved whip 41 shows a change due to the voltage of 90%, and when a bias voltage of 60V is applied, the half-wave voltage of one intensity modulation (tJloV) is shown.

This is a T1 diffused LiNb composed of elements of the same size.
The performance is about the same as that of a conventional optical modulation element composed of an O3 optical waveguide, and exceeds the performance of a conventional LiNbO3, and the size of the conventional element can be reduced by 1 h.

Example 2 Although the above example was described using the optical waveguide having the configuration shown in FIG. 2, it was confirmed that the same effect could be obtained using the optical waveguide having the configuration shown in FIG. That is, in the same figure (in the same figure, PLZ
By loading the surface of the T-based thin film 22 with a loading layer 51 having a refractive index smaller than that of the PLZT-based thin film, a portion of the thin film 22 immediately below the layer 61 can be used as an optical waveguide. In this case, it has been confirmed that the same effect can be obtained even if the optical modulator of the present invention is configured by, for example, forming tantalum oxide on the load layer 51 by sputtering and forming a waveguide by patterning. Effects of the Invention As described above, in the optical modulator of the present invention, t,
It is possible to integrate a photodetector element that could not be formed in the conventional RI diffusion type waveguide, and it is also possible to easily form a microscopic optical element in a part of it. Therefore, it is easy to integrate optical ICs, and its industrial value is improved. is expensive.

[Brief explanation of the drawing]

FIG. 1 shows the main parts of the light modulation element according to the present invention [S plan view,
Figure 2 is a sectional view of the main part taken along line x-x' in Figure 1 - Figure 3
The figure shows the change in birefringence of the PLZT thin film in the present invention when a voltage of 2 Kv/mm is applied, and Figure 4 shows the voltage dependence of the light intensity of the light modulation element in the example of the present invention. FIG. 5 is a sectional view of a main part of an optical waveguide according to another embodiment of the present invention. Input optical waveguide, 112, 114-
...Y branch. 113... Control optical waveguide, 115... Output optical waveguide, 12... Control electrode-21... Substrate,
22...PLZT thin film, 221...Ridge part-23...Buffer layer, 31...PLZT
A curve showing the change in birefringence when a voltage of 77 mm is applied to system thin film composition pair 2, 32- = 2Kv/mn of -LiNbO3
Straight line showing the change in birefringence when a voltage of 1 is applied -41...
...Curve showing luminous intensity versus applied voltage according to one example.
61...Load layer. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 2 Figure 3 Pb/ra: molar ratio a4 diagram

Claims (3)

[Claims] (1) At least one input optical waveguide is divided into two by Y branching.
branched into the main control optical waveguide, and the two above at predetermined intervals.
Hold the control optical waveguides in parallel. an optical waveguide connected to one output optical waveguide by a Y branch again at the other end, and a phase control electrode provided on at least one of the control optical waveguides;
A light modulation element characterized in that it is constructed by providing a ridge portion consisting of a convex portion on the surface of a PLZT thin film provided on a substrate. (2) The light modulation element according to claim 1, wherein the substrate is a Zapphire (α-alumina) zero-sided substrate. (3) The PLZT-based thin film consists of lead, titanium, and lanthanum oxidants, and contains lead (pb) and titanium (T).
i) molar ratio Pb/Ti is 0.65 < Pb/T
The light modulation element according to claim 1, characterized in that i (in the range of 0.90).