JPH07209533A - Optical function device - Google Patents

Abstract

PURPOSE:To obtain a mode conversion device which can give large wavelength variation width with a relatively low applied voltage by forming an inter digital electrode formed by connecting one-end sides of electrode pieces to a common electrode and a heating electrode which faces the other end sides of the electrode pieces and generates heat by being fed with electricity. CONSTITUTION:The inter-digital electrode 5 formed by connecting one-end sides of the electrode pieces 51, arrayed at equal intervals, to the common electrode 5 respectively and the heating electrode 7 which has one side opposite to the other/end sides of the electrode pieces 51 and generates heat by being fed with electricity are formed on a substrate 1 which is made of an electrooptic material having a light guide 2 formed on a surface; and the heating electrode 7 is arranged in parallel to the light guide 2. Consequently, mode switching can be performed by periodically applying an electric field to the light guide 2 by applying a voltage between the inter-digital electrode 5 and heating electrode 7. Further, the heating electrode 7 is fed with the electricity to generate the heat, and then the large wavelength variation width can be obtained with the relatively low voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical functional device for reversibly converting the polarization mode of light by applying an electric field periodically to an optical waveguide via a comb-shaped electrode, and in particular, for heating by energizing a heating electrode. The present invention relates to a mode conversion device that makes it possible to select the wavelength of light that is mode-converted by.

A polarization mode of light passing through the optical waveguide is changed from TM to TE by periodically applying an electric field to an optical waveguide of a substrate made of an electro-optical material via comb-shaped electrodes formed on the substrate. , TE to TM for converting mode is well known.

In general, such a device has a mode selection function as well as a wavelength selection function capable of arbitrarily selecting the wavelength of light to be mode-converted. For example, a voltage is applied to a tuning electrode provided in parallel with an optical waveguide on a substrate. May be applied and used as a wavelength filter.

However, in the method of applying a voltage to the tuning electrode and selecting the wavelength, the applied voltage increases as the wavelength tunable width is expanded. Therefore, it is desired to realize a mode conversion device that can obtain a large wavelength tunable width by applying a relatively low voltage.

[0005]

2. Description of the Related Art FIG. 8 is a perspective view showing a conventional mode converter. The conventional mode converter is as shown in Fig. 8 (a).
The optical waveguide 2 is formed on the substrate 1 made of an electro-optical material such as LiNbO _3, and the surface of the substrate 1 on which the single mode linear optical waveguide 2 is formed by diffusing Ti is covered with the buffer layer 3. Has been done.

The ground electrode 4, the comb-shaped electrode 5, and the tuning electrode 6 which are parallel to the optical waveguide 2 are arranged on the substrate 1 via the buffer layer 3.
At least a part of the ground electrode 4 formed on the above and sandwiched between the comb-shaped electrode 5 and the tuning electrode 6 is formed at a position facing the optical waveguide 2.

The comb-shaped electrode 5 is composed of a plurality of electrode pieces 51 arranged at equal intervals and a common electrode 52 connecting one end of the electrode piece 51, and arranged in the longitudinal direction of the ground electrode 4. The other ends of the electrode pieces 51 are opposed to the sides of the ground electrode 4 with a predetermined gap therebetween.

As shown in FIG. 8 (b), a voltage V _MC is applied between the ground electrode 4 and the comb-shaped electrode 5 to apply a periodic electric field to the optical waveguide 2 to polarize the light transmitted through the optical waveguide 2. The mode can be converted from TM mode to TE mode or from TE mode to TM mode.

Where Λ is the arrangement pitch of the electrode pieces 51,
Assuming that N _TE and N _TM are effective refractive indices in the TE mode and TM mode, respectively, the light having the wavelength λ satisfying the following condition is mode-converted from the light polarized and incident on the mode converter and is extracted through the analyzer. .

Λ = Λ | N _TE −N _TM | Further, a voltage V _T between the ground electrode 4 and the tuning electrode 6
Is applied, | N _TE −N _TM | changes corresponding to the applied voltage V _T, and when the change of | N _TE −N _TM | at this time is ΔN, the wavelength tunable width Δλ is calculated by the formula Δλ = ΛΔN. can do.

[0011]

However, when a voltage is applied to the tuning electrode and the electro-optic effect is applied, | N _TE -N _TM |
The conventional mode conversion device that controls the voltage has a problem that the wavelength variable width Δλ is smaller than the change width of the applied voltage and that a relatively high voltage must be applied.

For example, in a conventional mode converter utilizing the electro-optic effect, a wavelength variable width of 10 nm is obtained with a light having a wavelength of 1.55 μm, so that the voltage applied between the ground electrode and the tuning electrode is about 100 V and the insulation is achieved. It becomes extremely difficult to configure the device, such as ensuring security.

An object of the present invention is to provide a mode conversion device which can obtain a large wavelength tunable width by applying a relatively low voltage.

[0014]

FIG. 1 is a perspective view showing an optical functional device according to the present invention. Note that the same object is denoted by the same symbol throughout the drawings.

The above problem is a comb type in which one end of each of a plurality of electrode pieces 51 arranged at equal intervals is connected to a common electrode 52 on a substrate 1 made of an electro-optical material having an optical waveguide 2 formed on the surface thereof. The electrode 5 and the heating electrode 7 whose side faces the other end of the electrode piece 51 and generates heat when energized are formed,
This is achieved by the optical functional device of the present invention in which the heating electrode 7 is arranged in parallel with the optical waveguide 2.

[0016]

In FIG. 1, a comb-shaped electrode in which one end of each of a plurality of electrode pieces arranged at equal intervals is connected to a common electrode on a substrate made of an electro-optical material having an optical waveguide formed on the surface, By forming a heating electrode that is arranged parallel to the waveguide and has its side facing the other end of the electrode piece, a voltage is applied between the comb-shaped electrode and the heating electrode to apply a periodic electric field to the optical waveguide. It becomes possible to change the mode. Further, by energizing the heating electrode to generate heat, it is possible to obtain a large wavelength tunable range with a relatively low voltage. That is, it is possible to realize a mode conversion device that can obtain a large wavelength tunable width by applying a relatively low voltage.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 2 is a schematic view showing another embodiment of the present invention, FIG. 3 is a plan view showing the structure of a general heating electrode, and FIG.
FIG. 7 is a plan view showing a structure of a heating electrode according to the present invention, FIG. 5 is a plan view showing another embodiment of the present invention, FIG. 6 is a view showing an arrangement example of the heating electrode and the comb-shaped electrode of the present invention, FIG. FIG. 8 is a diagram showing an application example of the heating electrode according to the present invention.

In FIG. 1 (a), the mode converter of the present invention has a linear optical waveguide 2 formed by diffusing Ti into a substrate 1 made of LiNbO _3, and the surface of the substrate 1 on which the optical waveguide 2 is formed is It is covered with a buffer layer 3 formed by depositing SiO ₂ and having a thickness of about 0.5 μm.

Unlike the conventional device, the mode converter according to the present invention has a thickness of 0.1 μm deposited on the buffer layer 3.
By having the Si coat layer 31 and depositing the Si coat layer 31 on the buffer layer 3, the pyroelectric effect when heated is suppressed and the operation is stabilized.

A heating electrode 7 is disposed on the substrate 1 in parallel with the optical waveguide 2 via a buffer layer 3 and generates heat when energized, and a plurality of electrode pieces 51 arranged at equal intervals.
And the comb-shaped electrode 5 composed of the common electrode 52 connecting one end of the electrode piece 51 with the electrode.

In the present embodiment, both the heating electrode 7 and the comb-shaped electrode 5 are made of gold plated on the Si coating layer 31 so that the thickness thereof is 10 μm. The other ends of the electrode pieces 51 arranged in the length direction face each other with a gap of 7 μm therebetween.

Here, the wavelength λ of the light whose mode is converted is 1.55.
If it is around μm, | N _TE −N _TM |, that is, ΔN is 0.072
Therefore, by substituting λ = 1.55 and ΔN = 0.072 in the formula λ = Λ | N _TE −N _TM |, the array pitch Λ of the electrode pieces 51 becomes 21.5 μm.

As shown in FIG. 1B, when a control voltage V _MC of about 20 V is applied to the heating electrode 7 and the comb-shaped electrode 5 and a periodic electric field is applied to the optical waveguide 2, the light transmitted through the optical waveguide 2 is The polarization mode is converted from the TM mode to the TE mode or from the TE mode to the TM mode.

The power applied to the heating electrode 7 is P (W / c
m), and the wavelength tunable width is Δλ (nm), it is expressed by the following equation: Δλ = 2 × 10 ^-2 P, and the length of the heating electrode 7 is 2 cm
By applying the electric power of W to the heating electrode 7, a wavelength variable width of 10 nm can be obtained.

When the width of the heating electrode 7 is 15 μm, the resistance value becomes about 20Ω, and when the heating voltage V _{H of} 6.3 V is applied to the heating electrode 7 as shown in the figure, 2 W of electric power is applied and an extremely low voltage is applied. By applying it, it becomes possible to obtain a large wavelength variable width.

A comb in which one ends of a plurality of electrode pieces arranged at equal intervals are respectively connected to a common electrode via a buffer layer on a substrate made of an electro-optical material and provided with a linear optical waveguide. By forming a mold electrode and a heating electrode that is arranged in parallel with the optical waveguide and has its side facing the other end of the electrode piece, a voltage is applied between the comb-shaped electrode and the heating electrode to periodically cycle the optical waveguide. It becomes possible to perform mode conversion by applying a general electric field.

Further, by energizing the heating electrode to generate heat, it is possible to obtain a large wavelength tunable range with a relatively low voltage. That is, it is possible to realize a mode conversion device that can obtain a large wavelength tunable width by applying a relatively low voltage.

Although the above embodiment uses the Z-cut substrate 1 having the optical waveguide 2 on the surface orthogonal to the Z axis as in the conventional mode converter, the optical waveguide 2 is provided on the surface orthogonal to the X axis. When the X-cut substrate 1 is used, the electrode arrangement on the substrate is different as shown in FIG.

In FIG. 2A, another embodiment of the mode converter according to the present invention is a substrate 1 made of LiNbO ₃ and an optical waveguide 2.
The surface of the substrate 1 on which the optical waveguide 2 is formed is covered with a buffer layer 3 having a thickness of about 0.5 μm formed by depositing SiO ₂ .

As in the previous embodiment, the buffer layer 3 covering the entire surface on which the optical waveguide 2 is formed has a thickness of 0.1 μm.
By having the Si coat layer 31 and depositing the Si coat layer 31 on the buffer layer 3, the pyroelectric effect when heated is suppressed and the operation is stabilized.

Unlike the above-mentioned embodiment, the heating electrode 7 which generates heat when energized is placed at a position facing the optical waveguide 2.
A plurality of electrode pieces 51 arranged on both sides of the heating electrode 7 in parallel with
And a pair of comb-shaped electrodes 5 composed of a common electrode 52 connecting one end of the electrode piece 51.

As shown in FIG. 2B, when a control voltage V _MC of about 20 V is applied to the heating electrode 7 and the comb-shaped electrode 5 and a periodic electric field is applied to the optical waveguide 2, the light transmitted through the optical waveguide 2 is The polarization mode is converted from the TM mode to the TE mode or from the TE mode to the TM mode.

Further, as shown in the drawing, by applying the heating voltage V _{H of} 6.3 V, the electric power of 2 W is applied to the heating electrode 7 as in the above-mentioned embodiment, and the high voltage is not applied unlike the conventional case.
It is possible to realize a mode conversion device which can obtain a large wavelength variable width of about 10 nm.

As shown in FIG. 2 (c), the buffer layer 3 and the Si coat layer 31 are formed only on the area where the heating electrode 7 is formed on the substrate 1, and the plurality of electrode pieces 51 and one end of the electrode piece 51 are connected. The pair of comb-shaped electrodes 5 composed of the common electrodes 52 to be connected may be directly formed on the substrate 1.

In each of the above-mentioned embodiments, the structure of the heating electrode, which is linearly formed but generates heat when energized, will be described in detail. As shown in FIG. 3, both ends of the linear heating electrode 7 are connected to a pair of feeding electrodes 8 as shown in FIG.

However, if the linear heating electrode is broken even at one place, its function will not be fulfilled, and the reliability as a device will be poor. In addition, if an electrode for applying an electric field is near, there is a problem that a sufficient electro-optical effect cannot be obtained due to the interaction with the heating electrode.

As shown in FIG. 4, the optical functional device of the present invention comprises a plurality of heating electrode pieces 72 in which the heating electrodes 7 are arranged in series at intervals, and the heating electrode pieces 72 arranged in parallel with the optical waveguide 2. Both ends of each are connected to the power supply electrode 8 via the dedicated power supply conductor 81.

In another embodiment of the optical functional device of the present invention, as shown in FIG. 5, a pair of power feeding electrodes 8 each comprises a plurality of power feeding conductors 81, and the power feeding conductors 81 are connected to different power feeding electrodes 8. The other end is alternately connected to the lateral side of the heating electrode 7 which is linearly formed.

As described above, the heating electrode is composed of a plurality of heating electrode pieces, and the opposite end portions of the adjacent heating electrode pieces are connected to the same feeding electrode, or one heating electrode is provided with different feeding electrodes laterally. The above problem is solved by alternately connecting the feed conductors that are connected.

That is, the heating electrode is divided into a plurality of regions, and each region is connected in parallel to the power feeding electrode. For example, even if a part of the electrode is broken, the voltage is applied to the other regions, so that the function is achieved. Is lost only in the broken area, and the function is not lost in all areas.

Moreover, since adjacent heating electrode pieces or opposite ends of continuous areas are connected to the same power supply electrode, they are at the same potential, which causes discharge breakdown due to an increase in potential at the connection portion and potential distribution in the heating electrode. Unnecessary electric field components to the optical waveguide based thereon are suppressed.

In the above embodiment, the heating electrode which generates heat when energized is used as a ground electrode and is formed of gold, but the heating electrode which generates heat when energized is simply used as a heater. The device may be formed of a metal thin film such as chromium.

Further, although not shown in the drawing, which is a known technique, by forming a groove on the substrate so as to sandwich the heating electrode, the heat escaping to the area other than the optical waveguide is reduced and the heat loss is suppressed. Therefore, the voltage applied to the heating electrode can be further reduced.

FIG. 6 shows an arrangement example of the heating electrode 7 and the comb-shaped electrode 5 on the substrate 1 when the heating electrode is applied to a mode converter, and the substrate 1 is provided with an optical waveguide (not shown) and made of SiO ₂ . The surface is covered with a buffer layer 3 formed by depositing about 0.5 μm.

A metal thin film of chromium or the like is formed on the buffer layer 3 by a vacuum vapor deposition method or the like, and the heating electrode 7 and the comb-shaped electrode 5 arranged in parallel with the optical waveguide are also provided by the photolithography method or etching together with the feeding electrode 8a. And a plurality of feeding conductors 81a are formed.

Since the heating electrode 7 is provided with the comb-shaped electrode 5 on its side, a part of the power feeding electrode 8a and the power feeding conductor 81a is covered with an insulating layer 82 made of SiO _2, and the power feeding electrode 8b and the power feeding conductor 8a are provided thereon.
A plurality of feeding conductors 81b connected to the side of the heating electrode 7 alternately with 81a are formed.

In order to make the resistance values of the power supply electrodes 8a and 8b sufficiently smaller than that of the heating electrode 7, the power supply electrodes 8a and 8b are plated with gold, for example. Further, the heating electrode 7 can be used as a ground electrode by applying the heating voltage V _H having the same absolute value of ± to the power supply electrodes 8a and 8b.

Furthermore, the arrangement pitch of the electrode pieces 51 in the comb-shaped electrode 5 is adjusted to the arrangement pitch of the power supply conductors 81a and 81b connected to the heating electrode 7, and the electrode pieces 51 are heated between the power supply conductors 81a and 81b. An electric field can be effectively applied to the optical waveguide by making it oppose.

That is, the voltage distribution in the heating electrode 7 is
The voltage becomes 0 in the middle of 81a and 81b, and the voltage of the electrode piece 51 becomes 0.
To face the part. As a result, harmful interaction between the electrodes is reduced, and it becomes possible to realize an optical functional device that combines the thermo-optic effect and the electro-optic effect.

The heating electrode can be applied to an optical functional device such as a Mach-Zehnder type optical switch in addition to the mode converter. In FIG. 7, in the Mach-Zehnder type optical switch, a Mach-Zehnder type optical waveguide 92 is formed on a substrate 91 made of LiNbO ₃ .

Although not shown, the surface of the substrate 91 on which the optical waveguide 92 is formed is covered with a buffer layer formed by depositing SiO _2, and two parallel optical waveguides 93 of the optical waveguide 92 are provided. The heating electrode 7 is formed on either one of them via a buffer layer.

The heating electrode 7 formed on the substrate 91 via the buffer layer is composed of a plurality of heating electrode pieces 72 arranged in series at intervals, and the heating electrode pieces 72 arranged in parallel with the optical waveguide 93. Both ends of each are connected to the power supply electrode 8 via the dedicated power supply conductor 81.

When the heating electrode 7 is energized, a difference in refractive index occurs between the optical waveguide 93 arranged directly below the heating electrode 7 and the other optical waveguide 93, and the optical waveguide 93 is bisected in the same phase at the branch point. A phase difference occurs during the propagation of the generated light waves in the two parallel optical waveguides 93.

For example, when the temperature coefficient of the refractive index N _TM for TM mode light with a wavelength of 1.5 μm is about 4 × 10 ⁻⁵ / ° C. and the heating section length is 10 mm, two light waves generated by raising the temperature by 1.9 ° C. Has a phase difference of π, and the emitted light is in the off state even if they are combined again.

[0055]

As described above, according to the present invention, it is possible to provide a mode conversion device which can obtain a large wavelength tunable width by applying a relatively low voltage.

[Brief description of drawings]

FIG. 1 is a perspective view showing an optical functional device according to the present invention.

FIG. 2 is a schematic view showing another embodiment of the present invention.

FIG. 3 is a plan view showing the structure of a general heating electrode.

FIG. 4 is a plan view showing the structure of a heating electrode according to the present invention.

FIG. 5 is a plan view showing another embodiment of the present invention.

FIG. 6 is a diagram showing an arrangement example of heating electrodes and comb-shaped electrodes of the present invention.

FIG. 7 is a diagram showing an application example of the heating electrode according to the present invention.

FIG. 8 is a perspective view showing a conventional mode conversion device.

[Explanation of symbols]

1 substrate 2 optical waveguide 3 buffer layer 5 comb-shaped electrode 7 heating electrode 8, 8a, 8b feeding electrode 31 Si coating layer 51 electrode piece 52 common electrode 72 heating electrode piece 81, 81a, 81b feeding conductor 82 insulating layer 91 substrate 92, 93 Optical waveguide V _MC control voltage V _H Heating voltage

Claims (4)

[Claims] 1. A common electrode (52) is provided on one end of a plurality of electrode pieces (51) arranged at equal intervals, on a substrate (1) made of an electro-optical material on the surface of which an optical waveguide (2) is formed. A comb-shaped electrode (5) connected to the electrode and a heating electrode (7) facing the other end of the electrode piece (51) and generating heat when energized are formed. An optical functional device characterized by being arranged in parallel with a waveguide (2). 2. Comb-shaped electrodes (5) and heating electrodes (7) facing each other
A mode that reversibly converts the polarization mode of the light by changing the phase difference of the light passing through the optical waveguide (2) by periodically applying an electric field to the optical waveguide (2) by applying a voltage between The optical functional device according to claim 1, wherein the optical functional device has a conversion function and makes it possible to select the wavelength of the light by controlling the electric power applied to the heating electrode (7). 3. A plurality of heating electrode pieces (72) in which heating electrodes (7) parallel to the optical waveguide (2) are arranged in series at intervals.
Both ends of the heating electrode piece (72) are
The optical functional device according to claim 1, which is connected to the power feeding electrode (8) via 1). 4. A pair of power supply electrodes (8) provided to energize the heating electrode (7) each comprises a plurality of power supply conductors (81), and the other end of the power supply conductors (81) is alternately heated. The optical functional device according to claim 1, which is connected to the electrode (7).