JPH04123018A - Waveguide type optical parts - Google Patents

Abstract

PURPOSE:To drop a driving voltage by providing electrodes for impressing alternating electric fields on the side faces of the region of phase modulating parts of a ridge type optical waveguide and as well specifying the relation between the width and height of the ridge type optical waveguide. CONSTITUTION:The above optical parts have a rectangular parallelepiped substrate 2 which consists of an LiNbO3 crystal, the ridge type optical waveguide 3 which is formed atop this substrate 2 and is thermally diffused with Ti, the electrodes 4 which are disposed along the side faces of the optical wavelength 3 in order to impress the alternating electric fields on this optical waveguide 3 and an AC power source 5 which impresses a prescribed AC voltage to the electrodes 4. The phase modulating parts 3c, 3d of the optical waveguide 3 are formed to >=0.1 ratio of the height dL to width W thereof and are set at 90+ or -10 deg., more preferably 90 deg. ridge anglebeta. An electro-optical effect is effectively exhibited in this way and the correction factor of the electric field is increased. The driving voltage is thus dropped.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a waveguide type optical component, and more particularly, to an optical switch, a weak electromagnetic field sensor for electromagnetic environment, and furthermore, The present invention relates to a waveguide type optical component suitable for application to high-speed optical modulators and the like in optical fiber communication systems.

(Prior Art) As an optical component in the technical field as described above, the one shown in FIG. 7 is conventionally known.

The figure shows a planar optical component 30, for example, LiNb0. A flat channel waveguide 32 and electrodes 33a, 33b are disposed on a substrate 31 made of aluminum.

33c.

However, this planar optical component 30 has an electric field correction coefficient r(
(details will be described later) is approximately 0.4 (hereinafter usually r=o,
1 to 0. It shall mean 4. ), and for this reason, there is a problem that the drive voltage for driving the planar optical component 30 cannot be reduced.

And an electrode 33a to reduce the driving voltage.

33b and the spacing between the electrodes 33b and 33c is narrowed,
The value of the electric field correction coefficient F also decreases according to the interval (see May 1988, 2 Incorporated Association, Transactions of the Institute of Electronics, Information and Communication Engineers C, Vol. J71. Na5r Microdirectional Microdirectional Optical Switch, page 666 ).

In view of the difficulty in reducing the drive voltage in such a planar optical component 30, three-dimensional optical components have been proposed, and research on ridge-shaped optical components is in particular progressing.

Conventional waveguide type optical components will be explained below based on the relationship between the drive voltage (half-wavelength voltage) Vπ and the electric field correction coefficient F.

The waveguide type optical component 40, as shown in FIG.
b A planar optical waveguide is fabricated on an O3 crystal substrate 41 by a method such as thermal diffusion of a Ti thin film or an epitaxial film formation method, and the planar optical waveguide is formed into a ridge waveguide 42 using a mask and ion etching technology. That is.

In this case, it is known that the relationship between the ridge angle β and the electric field correction coefficient F shown in FIG. 8 is that the closer the ridge angle β approaches 90 degrees, the closer the electric field correction coefficient F approaches 1.0 (
October 24, 1977 1 Incorporated Association, Institute of Electronics and Communication Engineers Materials, 0
QE77-57. (see page 17 of Waveguide J).

Further, the distribution state of the applied electric field in the ridge-shaped optical waveguide 42 is shown in FIGS. 10(a) and 10(b).

In the case of the leading waveguide 42 with a ridge angle of 90 degrees as shown in FIG. 10(b), the electric field in the propagation region of the guided light is uniform, whereas It is known that in the case of the leading waveguide 42', the above-mentioned uniformity is reduced and the average electric field strength is also reduced (see "Ridge-type optical waveguide", page 16).

Note that FIGS. 10(a) and 10(b) show the electrode 43a.

This is an example in which a voltage of 1 (V) is applied between 43b, and
The numbers in the figure represent the electric field strength in 11 levels.

(Problem to be Solved by the Invention) As mentioned above, it is conventionally known that the closer the ridge angle is to 90 degrees, the closer the electric field correction coefficient F is to 1.0. The relationship between the width and height of and the electric field correction coefficient F is unresolved, and experimentally,
The ridge angle β decreases from 90 degrees as the height dL changes,
For example, when dL is 2 μm or more, the angle is about 75 to 70 degrees (see pages 13 and 14 of the above-mentioned “Ridge-type optical waveguide”).

Therefore, the current situation is that it is still difficult to reduce the driving voltage.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a waveguide-type optical component in which the relationship between the width and height of the ridge-type optical waveguide can be specified, and the driving voltage can be reduced.

[Structure of the Invention (Means for Solving the Problems) The present invention provides a phase modulation section on a substrate which has an electro-optic effect and whose crystal orientation with the largest electro-optic effect is perpendicular to the light guiding direction. In a waveguide type optical component having a ridge type optical waveguide formed therein, an electrode for applying an alternating electric field is provided on the side surface of the phase modulation region of the ridge type optical waveguide, and the width of the ridge type optical waveguide is set to W, and the height of the ridge type optical waveguide is set to W. sawo d
When L, it is formed so that dL/W=0.1 or more, and the ridge angle β is set in the range of 90±10 degrees.

The ridge-shaped optical waveguide has Y in the phase modulation region.
It is formed into a branched shape or a divided shape.

The width W is determined so as to be a single mode depending on the refractive index of the ridge-shaped optical waveguide and the optical wavelength used, and is approximately 4 to 8 μm in the case of a Ti-diffused LiNbO3 waveguide.

(Function) According to the waveguide type optical component having the above-described configuration, the crystal orientation of the substrate having an electro-optic effect and the alternating electric field applied to the electrode formed on the side surface of the phase modulation region of the ridge type optical waveguide are controlled. Since the directions coincide with each other, a large electro-optic effect can be obtained, and the ratio of the width W to the height dL of the ridge-shaped optical waveguide is 0.1 or more.

By setting the ridge angle β to 90±10 degrees, the electric field correction coefficient becomes larger than that of the planar type, thereby making it possible to reduce the driving voltage.

Further, the ratio of the width W to the height dL is set to about 0.1, for example, W
=8. If czm, dL=0.8 to 1 μm,
This facilitates etching of the phase modulation region.

The light intensity adjustment region in the ridge-shaped optical waveguide can have a Y-shaped branched shape or a divided shape to exhibit the above-mentioned effect.

(Example) Examples of the present invention will be described in detail below.

The waveguide type optical component 1 shown in FIG. 1 is, for example, L i Nb
An alternating electric field is applied to a rectangular parallelepiped substrate 2 of O3 crystal, a ridge-shaped optical waveguide (hereinafter referred to as "optical waveguide") 3 formed on the upper surface of this substrate 2 in which Ti is thermally diffused, and this optical waveguide 3. For this purpose, an electrode 4 arranged along the side surface of the optical waveguide 3 and an AC power source 5 for applying a predetermined AC voltage to the electrode 4 are provided.

The optical waveguide 3 includes a light entrance part 3a and a light exit part 3 formed linearly at one end and the other end of the substrate 2, respectively.
b, and phase modulation parts 3c and 3d, which are branched in a Y-shape from the light incidence part 3a and the light emission part 3b, and are arranged parallel to each other, and are parallel to the light incidence part 3a and the light emission part 3b, respectively. Equipped with

Of the optical waveguide 3, the phase modulation sections 3c and 3d are
As shown in the figure, the height d1. + width W, and the ridge angle β is set to 90±10 degrees, preferably 90 degrees, as shown in FIG.

The electrode 4 consists of side electrode patterns 4a, 4b and a center electrode pattern 4c arranged in contact with each side of the linear portion of the phase modulation parts 3c, 3d, and each electrode pattern 4a,
The lengths of 4b and 4c in the direction in which the light travels are set to 1.

Note that a phase modulation section 3c is provided for the purpose of preventing light attenuation.

In some cases, an electric field relaxing thin layer made of an insulator is inserted at the boundary between the electrode 3d and the electrode 4.

Further, the crystal orientation of the substrate 2 is such that when the three axes of X, Y, and Z are taken as shown in FIG. It is pre-formed to look like this.

Next, a phase modulation section 3c using the AC power source 5.

The explanation will be made with reference to the drive voltage Vπ and electric field correction coefficient 1 and 2 of 3d.

It is known that the drive voltage Vπ can be expressed by the following equation (1).

Vx=λW/ 2 n e r 33 r J
-(1) Here, λ is the wavelength of light, ne is the optical waveguide 3c
.

3d is the refractive index, r33 is an electro-optical constant, l is the length of the electrode 4, and W is the width of the phase modulation portions 3c and 3d as described above.

Further, the electric field correction coefficient F can be expressed by the following equation (2).

(Left below) - W/2 ffE(x.z)・e(x,z)dx・dz-or
-W/2...(2) Here, E (X, Z) is the optical electric field, e (X, Z)
is the applied electric field, and T is the average electric field in the phase modulation sections 3c and 3d.

From equation (1) above, it can be seen that the drive voltage Vπ is inversely proportional to the electric field correction coefficient r, and the larger the electric field correction coefficient F becomes, the smaller the drive voltage Vπ becomes.

Next, the height dL, width W, and electric field correction coefficient F.

Table 1 shows the results of calculations and experiments regarding the relationship between the drive voltage Vπ and the light wavelength λ=1.3 μm. Also, dL/W
The relationship between F and the electric field correction coefficient F is shown in FIG.

(Margin below) Table 1 (λ=1 3 μl) As is clear from Table 1 and Figure 2, the width W is 8 μl.
m, 6 μm, the larger the height dL, the more dt/
It can be seen that as the value of W increases, the value of the electric field correction coefficient r increases accordingly, and conversely, the value of the drive voltage Vπ becomes significantly smaller than in the case of the planar optical component.

In particular, when W=6 μm, dt=0.84 μm, and by simply etching the light modulating parts 3c and 3d to form a ridge, the electric field correction coefficient F can be reduced to 0.8 μm when J=14 mm.
6, and at this time, the driving voltage Vπ is 1.4 V, which is approximately ⅔ of that in the case of the planar type. Also, W=6 μm, d
In the case of L=3μ, 1=140 and the driving voltage Vπ is 0.8
5V, which can be reduced to 215 for planar type. This is extremely effective in high frequency operation.

Furthermore, in terms of power, since it is proportional to the square of the drive voltage Vπ, in this embodiment, it is possible to significantly reduce the power supply capacity compared to the planar type.

Next, the manufacturing process of the waveguide type optical component 1 will be explained with reference to FIGS. 3 to 5.

First, as shown in FIG. 3, a planar optical waveguide layer is formed on a substrate 2 of L i N b O3 crystal by Ti thermal diffusion or epitaxial film formation. Next, a mask using λTi or the like is formed by photolithography, and an ion etching process is performed using an etching apparatus that introduces a CF-based etching gas, so that the ridge angle β=
An optical waveguide 3 having an angle of 90±10 degrees was obtained.

Furthermore, an electrode 4 consisting of side electrode patterns 4a, 4bs and a center electrode pattern 4C is formed on the side surfaces of the phase modulation parts 3c and 3d of the optical waveguide 3, and an AC power source 5 is connected to this electrode 4, as shown in FIG. A waveguide type optical component 1 was obtained.

Next, the other side of this embodiment will be explained with reference to FIG.

The waveguide type optical component IA shown in the figure includes phase modulation sections 3c, 3
A feature is that d is formed into a shape divided into a light entrance part 3a and a light output part 3b.

Also in the case of this waveguide type optical component IA, the width W and the height dL+
By making the ridge angle β similar to that of the waveguide type optical component 1, it is possible to reduce the driving voltage Vπ.

According to the waveguide type optical component 1 of the present embodiment described in detail above, by setting the relationship between the width W and the height dL of the phase modulation portions 3c and 3d and the range of the ridge angle β as described above, , the drive voltage Vπ can be significantly reduced compared to the planar type.

In particular, the value of dL/W is practically 0.0, as is clear from FIG. In the range of 1 to 0.7, preferably 0.2 to 0. 5, the optimal value is 0. The electric field correction coefficient F is preferably about 3. In this case, the electric field correction coefficient F is 0.5 to 0.9, preferably 0.6 to 0.8, and the optimum value is about 0.7.

Further, since the direction of the crystal axis (C axis) of the substrate 2 and the direction of the alternating electric field by the electrode 4 match, the phase modulation parts 3c, 3
The electro-optic effect at d can be appropriately exhibited, and the drive voltage Vπ can be reduced.

Furthermore, for example, the height dL of the phase modulation sections 3c and 3d is also 1μ.
The driving voltage Vπ can be reduced by an etching process of about 1, and the etching process can be facilitated.

In addition to the embodiments described above, the present invention can be modified in various ways within the scope of its gist. For example, the material of the substrate 2 is L
i N b O3 as well as L i T a O3.

It can also be implemented using PLZT, GaAs, or InP.

[Effects of the Invention] According to the present invention described in detail above, the above-described configuration allows the relationship between the width, height, and ridge angle of the optical waveguide to be appropriate, and to effectively exhibit the electro-optic effect. As a result, it is possible to provide a waveguide type optical component that has a large electric field correction coefficient and can reduce the driving voltage.

The above-described effects can be achieved by forming the phase modulation region of the optical waveguide in a Y-shape or in a divided shape.

Furthermore, if the ratio between the height dL and the width W of the optical waveguide is about 0.1, processing can be facilitated.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the waveguide type optical component of the present invention, FIG. 3 and 4 are perspective views showing the manufacturing process of each embodiment, FIG. 5 is a sectional view of the same as above, FIG. 6 is a perspective view showing the other side of this embodiment, and FIG. 7 is a conventional planar type. A perspective view of the optical component, FIG. 8 is a cross-sectional view showing a ridge-shaped optical component, FIG. 9 is a graph showing the relationship between the ridge angle and the electric field correction coefficient, and FIG. 1O (a) is a ridge angle of 45 degrees. FIG. 10(b) is an electric field distribution diagram when the ridge angle is 90 degrees. 1. IA... Waveguide type optical component, 2... Substrate, 3.
...Optical waveguide, 3c, 3d... Phase modulation section, 4...
Electrode, 5...AC power supply. dL/W Figure Figure Figure Figure Figure ＼ 3b (b)

Claims (3)

[Claims] (1) In a waveguide-type optical component in which a ridge-shaped optical waveguide including a phase modulation section is formed on a substrate that has an electro-optic effect and has a crystal orientation with the largest electro-optic effect in a direction perpendicular to the light guiding direction, An electrode for applying an alternating electric field is provided on the side surface of the phase modulation region of the ridge-shaped optical waveguide, and when the width of the ridge-shaped optical waveguide is W and the height is d_L, d_L/W
1. A waveguide-type optical component, characterized in that the ridge angle β is set in the range of 90±10 degrees. (2) The waveguide-type optical component according to claim 1, wherein the ridge-shaped optical waveguide is formed within the phase modulation region substantially parallel to the two Y-shaped branched waveguides. (3) The waveguide-type optical component according to claim 1, wherein the ridge-type optical waveguide is formed into a shape divided in a phase modulation region.