JP3487664B2 - Optical function device and driving method thereof - Google Patents

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 made of an electro-optical material and a driving method thereof. As the construction of multimedia information networks by optical transmission progresses, it is desired to improve the practicality of optical functional devices such as mode converters, wavelength filters and optical modulators. Particularly for mode converters, it is desired to expand the variable range of the selected wavelength and reduce crosstalk.

[0002]

2. Description of the Related Art A polarization mode of light propagating in an optical waveguide is changed from a TE mode to a TM mode by periodically applying an electric field to an optical waveguide formed in a substrate made of an electro-optical material by using comb electrodes. Alternatively, the TM mode can be converted to the TE mode. Then, by appropriately selecting the arrangement period Λ of the electrode fingers of the comb-shaped electrode, it is possible to selectively perform mode conversion of the light of the wavelength λi expressed by the equation (1). At the rear end of the optical waveguide, an analyzer that transmits a polarization mode orthogonal to the polarization mode of the incident light is provided, and the device with the configuration that the light after mode conversion is sent to the latter stage through the analyzer is a wavelength filter. Function.

Λi = Λ | N _TE −N _TM | (1) N _TE : Effective refractive index of TE mode light N _TM : Effective refractive index of TM mode light For example, in lithium niobate (LiNbO ₃ ), the refractive index is The difference | N _TE −N _TM | is about 0.072, and the wavelength is 1.5.
When selecting the light of μm, the arrangement period Λ of the electrode fingers may be set to about 20.8 μm.

FIG. 7 is a diagram showing the configuration of a conventional mode converter 80. Note that FIG. 7B is a sectional view taken along the line BB of FIG. 7A. The mode converter 80 includes a substrate 81 made of an electro-optical material having an optical waveguide 82 formed on the surface layer thereof, two comb-shaped electrodes 84 and 85 for mode conversion, an electrode 86 for tuning, and the light formed by the comb-shaped electrodes 84 and 85. It is composed of an insulating film layer 83 for preventing absorption.
The illustrated substrate 81 is made of X-cut LiNbO ₃ ,
The optical waveguide 82 is provided in the direction along the Y axis.

A power source 87 having a constant voltage V _MC is connected between the two comb-shaped electrodes 84 and 85 to keep the voltage between the comb-shaped electrodes 84 and 85 constant. A voltage variable power source 88 is connected to the tuning electrode 86, and the voltage V _T applied to the electrode 86 is changed to change the refractive index in the optical waveguide 82. That is, tuning is performed to change the selected wavelength λi for mode conversion.

[0006]

The conventional mode converter 8
In 0, since the selection wavelength is tuned by the electro-optical effect, the change amount of the refractive index difference | N _TE −N _TM | is small, and the change width of the selection wavelength is smaller than the change width of the voltage V _T. There was a problem.

Generally, the wavelength variable width Δλ required as an optical functional device is about 10 to 100 nm. For example, in order to obtain the wavelength variable width Δλ of 10 nm, the variable width of the voltage V _T needs to be about 200V. However, when such a high voltage is applied, dielectric breakdown occurs in the substrate 81 or the insulating film layer 83, an overcurrent flows, and the heat generated thereby melts the electrodes 85 and 86. Therefore, the voltage V _T
The maximum variable range is several tens of V, and the obtained variable wavelength range Δλ is extremely insufficient.

Further, in the conventional mode converter 80, the difference between the main peak output level and the side peak output level of the selected wavelength λi in the wavelength filter characteristic is small, that is, the side peak output level is not sufficiently suppressed. There was also a problem. Therefore, when the mode converter 80 is used for optical communication, it is difficult to reduce crosstalk.

By the way, it is known that the refractive index also changes due to the thermo-optic effect. For example, in the case of LiNbO ₃ , the temperature dependence of the refractive index n ₀ for ordinary light can be ignored, but the temperature coefficient dn _e of the refractive index n _e for extraordinary light is negligible.
/ Dt is about 4 × 10 ⁻⁵ / ° C. in the wavelength band of 1.5 μm, and the refractive index n _e can be greatly changed by slightly changing the temperature.

Therefore, conventionally, in order to perform tuning by utilizing such a thermo-optical effect, a method has been proposed in which the entire mode converter is placed in a constant temperature bath to adjust the temperature of the optical waveguide. However, this method is not practical because the device including the mode converter and its drive system becomes enormous.

The present invention has been made in view of the above problems, and an object thereof is to utilize a thermo-optical effect with a simple structure to obtain a large wavelength tunable range with a low voltage and to improve wavelength selectivity. I am trying.

[0012]

According to a first aspect of the present invention, there is provided a device for producing a periodic electric field distribution in an optical waveguide on a substrate made of an electro-optic material on which the optical waveguide is formed. An optical functional device in which electrodes are arranged, which has a heating element for heating the optical waveguide, and has a window function along the light propagation direction in the optical waveguide during heating by the heating element. It is configured so that a temperature distribution in which the temperature changes at a rate according to

[0013]

In the device according to the second aspect of the present invention, as a heat source for heating the optical waveguide, a heat generating element whose heat generation amount changes along the light propagation direction is arranged on the substrate.

In the device according to the invention of claim 3 , a groove extending along the optical waveguide and having a varying width is provided on the surface of the substrate, and a heating element is arranged between the groove and the optical waveguide. It becomes.

A device according to a fourth aspect of the present invention has a heating element for heating the optical waveguide, and a strip-shaped insulating layer that extends along the optical waveguide and has a variable width on the surface of the substrate. Is provided.

According to a fifth aspect of the present invention, the optical waveguide and the heating element are covered with an insulating layer. According to a sixth aspect of the present invention, there is provided an optical functional device driving method, wherein a current is passed through the heating element to heat the optical waveguide,
A voltage is applied between the heating element and the electrode in a state where a temperature distribution in which the temperature changes in the optical waveguide along the light propagation direction at a rate according to a window function is generated. This is a method of generating an electric field distribution.

[0018]

The heating element generates heat by passing an electric current, and the optical waveguide is thereby heated. The temperature of the optical waveguide can be controlled by adjusting the current passed through the heating element. Since the refractive index of the optical waveguide changes depending on the temperature change due to the thermo-optical effect, the selection wavelength λi can be tuned by controlling the temperature of the optical waveguide. When the optical waveguide and heating element are covered with an insulating layer,
The heat storage effect increases the heating efficiency of the optical waveguide.

At this time, when a temperature distribution in which the temperature changes along the light propagation direction is generated in the optical waveguide, a mode due to the electro-optical effect is generated as compared with the case where the temperature of the optical waveguide is substantially uniform regardless of the location. The wavelength selection characteristic in conversion can be improved.

That is, the conversion efficiency η of the mode conversion is expressed by the equations (2) to (4), for example.

[0021]

[Equation 1]

In the equations (2) to (4), L is the electrode length (length in the light propagation direction of the electrode for applying an electric field to the optical waveguide), λ is an arbitrary wavelength, and Γ is the distribution of the applied electric field. And the field distribution of light (electric field strength distribution), the value of the integral (0 ≦ Γ ≦
1) and r ₅₁ are electro-optic constants.

Since the refractive indexes N _TE and N _TM depend on temperature,
If there is a temperature distribution, the coupling coefficient κ varies depending on the position in the light propagation direction, as is clear from the equation (4). Therefore,
For example, by changing the temperature in the light propagation direction at a rate according to the window function (Hamming function, Hanning function, Blackman function, Sink function, etc.) used to optimize the shape of the directional coupler, The selection characteristics can be optimized.

[0024]

1 is a schematic view showing the structure of a mode converter 1 of the first embodiment, and FIG. 1 (b) is a sectional view (end view) taken along the line BB of FIG. 1 (a). .

The mode converter 1 includes a substrate 11 made of an electro-optical material, an optical waveguide 12, a comb-shaped electrode 13 for applying an electric field to the optical waveguide 12, a tuning electrode 14 for heating the optical waveguide 12, and an insulating layer. It is composed of 15.

In the mode converter 1, as the substrate 11, Z
Cut LiNbO ₃ (lithium niobate) crystals are used. The external dimensions of the substrate 11 are, for example, 5 mm
It is (X) x 30 mm (Y) x 1 mm (Z).

The optical waveguide 12 is a single-mode linear waveguide extending in the Y direction in the crystal structure of the substrate 11, and is formed on the surface layer portion (surface in the −Z direction) of the substrate 11. The comb-shaped electrode 13 includes a large number of electrode fingers (comb teeth) 13a arranged at a constant pitch Λ along the light propagation direction (Y direction) of the optical waveguide 12 and a connecting conductor portion that connects one end of each electrode finger 13a. 13b and. The comb-shaped electrode 13 serves as an optical waveguide 12.
It is arranged so that it does not overlap.

The tuning electrode 14 includes the electrode pieces 14a arranged at equal intervals in the light propagation direction and the optical waveguide 12.
It is a conductive thin film having a two-layer structure composed of a pair of connecting conductor portions 14b extending along. In plan view, the tuning electrode 14 is patterned, for example, into a shape in which a ladder is folded in two with the middle portion of each step being a fold line.

Each electrode piece 14a is an L-shaped lower layer piece 141.
And a linear upper layer piece 142, and are arranged so as to face each electrode finger 13a of the comb-shaped electrode 13 with the optical waveguide 12 interposed therebetween. The lower layer piece 141 and the upper layer piece 142 are integrated by superimposing the end portions on the optical waveguide side.

One connecting conductor portion 14b connects one ends of the lower layer pieces 141 of the electrode pieces 14a, and the other connecting conductor portion 1
4b connects one ends of the upper layer pieces 142 of the electrode pieces 14a. The insulating layer 15 is provided to insulate the lower layer side and the upper layer side of the tuning electrode 14 from each other.

Here, it should be noted that the shape of the tuning electrode 14 in plan view is selected so that a temperature distribution in which the temperature changes in the optical waveguide 12 along the light propagation direction is generated.

That is, each connecting conductor portion 14b of the tuning electrode 14 is not parallel to the optical waveguide 12 and is curved so that the central portion in the light propagation direction is closer to the optical waveguide 12 than the end portion. Along with that, the tuning electrode 14
The lengths of the electrode pieces 14a are not uniform, and are the shortest at the central portion in the light propagation direction, and gradually increase toward both ends.

In the present embodiment, the change in the length of each electrode piece 14a is based on the Hamming function represented by the equation (5). However, in this case, the variable p in the equation (5) indicates the position in the light propagation direction, and the origin (the position where p = 0) is the comb-shaped electrode 13.
At the center position in the light propagation direction.

[0034]

[Equation 2]

The mode converter 1 having the above configuration is manufactured by the following procedure. The thickness of the substrate 11 is 10 by vapor deposition.
A titanium (Ti) film of 00Å is provided, and the thin film has a width of
Patterning is performed in a band of μm. Then, the substrate 11 is heated to 1050 ° C. in a wet oxygen atmosphere, and the state is kept at 10 ° C.
The optical waveguide 12 is formed by a thermal diffusion process of holding for a time.

By forming and patterning a thin film made of a conductive material, a part of the tuning electrode 14 (the lower layer piece 1) is formed.
41 and one connecting conductor portion 14b) are formed. As the conductive material, various metals or non-metal heating element materials such as molybdenum silicide can be used.

Then, by a lift-off method, for example, the thickness of silicon dioxide is 0.5 to 1 μm so that the tip end of each lower layer piece 141 and one end of the connecting conductor portion 14b are exposed.
The insulating layer 15 having a thickness of about m is formed, and an annealing process is performed if necessary.

Then, a thin film made of a conductive material is formed again and patterned to form the remaining portion of the tuning electrode 14 (the upper layer piece 142 and the other connecting conductor portion 14b) and the comb-shaped electrode 13 at the same time.

The mode converter 1 manufactured in this way
Are housed in a suitable metal housing (not shown). Next, the driving method and operation of the mode converter 1 will be described.

The pair of connecting conductors 14b of the tuning electrode 14 is connected to a voltage variable power source 52. As a result, the common voltage V _H is applied between both ends of the electrode piece 14a of the tuning electrode 14, a current flows through the electrode piece 14a, and the electrode piece 14a generates heat. Then, the temperature of the optical waveguide 12 rises due to heat conduction. That is, the tuning waveguide 14 heats the optical waveguide 12.

At this time, since the length of each electrode piece 14a is set according to the Hamming function as described above, the resistance value between both ends of each electrode piece 14a is from the end portion in the light propagation direction. It becomes smaller toward the center. As a result, the amount of heat generated in the central portion in the light propagation direction is larger than that in the end portion, and as shown in FIG. 2, the temperature distribution is such that the temperature gradually decreases from the central portion in the light propagation direction to the end portion. Occurs within.

The power supply 52 is constructed so that the midpoint potential of the voltage V _H becomes the ground potential. Therefore, the electric potential at the central position of each electrode piece 14a, that is, the electric potential at the position where the distance from one end is half the total length is almost the ground potential.

By controlling the temperature of the optical waveguide 12 by changing the voltage V _H , the refractive index of the optical waveguide 12 can be changed and the selected wavelength λi for mode conversion can be adjusted. According to the thermo-optic effect, a large change in the refractive index can be obtained with a slight change in temperature, so that the maximum value of the voltage V _H is 1
Wavelength variable width Δ sufficient for practical use, even if it is about 0 to 20 V
λ can be obtained.

On the other hand, the connecting conductor portion 13b of the comb-shaped electrode 13
Is connected to a power supply 51 that outputs a constant voltage V _MC .
As a result, each electrode finger 13a is kept in a state where the potential difference from the ground potential is equal to the voltage V _MC .

Since the potential at the center of the electrode piece 14a of the tuning electrode 14 is the ground potential, the optical waveguide 12
An electric field in the x direction corresponding to the voltage V _MC is generated between the electrode finger 13a and the electrode piece 14a that are opposed to each other with the electrode sandwiched therebetween. That is, a periodic electric field distribution in the light propagation direction occurs in the optical waveguide 12.

The light propagating in the optical waveguide 12 rotates its polarization direction by an angle corresponding to the electric field strength each time it passes through the electric field. Therefore, by setting the voltage V _MC according to the electrode length L of the comb-shaped electrode 13, it is possible to realize the mode conversion between the TE mode and the TM mode for the light of the selected wavelength λi.

FIG. 3 is a diagram showing the wavelength selection characteristics of the mode converter 1. The characteristics of Fig. 3 are the calculation method (RCALFERNESS and PETER S.CROS proposed by Alphanes et al.
S, “FILTER CHARACTERISTICS OF CODIRECTIONALLY COUP
LED WAVEGUIDES WITH WEIGHTED COUPLING ", IEEE J.Quan
tum Electron., vol.QE-14, No.11, shows the results of simulation by reference pp843-847,1978). Figure 3
The solid line indicates the characteristic when the optical waveguide 12 has a temperature distribution conforming to the Hamming function, and the broken line indicates the characteristic when the temperature (refractive index) of the optical waveguide 12 is uniform. The value of the parameter of the simula- Les <br/> Shon are shown in Table 1, the selected wavelength λi is selected to be 1.55 .mu.m.

[0048]

[Table 1]

In FIG. 3, when there is a temperature distribution,
The output level of the side peak of wavelength 1.5525 μm is −29 dB with respect to the output level of the main peak of wavelength 1.55 μm. However, when the temperature is uniform, the output level of the side peak at the wavelength of 1.5517 μm is −9 dB. That is, it is understood that the wavelength selectivity can be significantly improved by changing the temperature of the optical waveguide 12 along the light propagation direction.

FIG. 4 is a schematic diagram showing the structure of the mode converter 2 of the second embodiment, and FIG. 4 (b) is a sectional view taken along the line BB of FIG. 4 (a).
It is a cross-sectional view (end view). The mode converter 2 heats a substrate 21 made of Z-cut LiNbO ₃ crystal, an optical waveguide 22 formed on the surface layer of the substrate 21, a comb-shaped electrode 23 for applying an electric field to the optical waveguide 22, and an optical waveguide 22. The tuning electrode 24 and the insulating layer 25 are provided.

In the mode converter 2, before forming the comb-shaped electrode 23 and the tuning electrode 24 on the substrate 21, two grooves 28 and 29 extending in the light propagation direction are formed on the surface of the substrate 21 by etching. Has been done,
The optical waveguide 22 is arranged between the grooves 28 and 29.

The widths of the grooves 28 and 29 are not constant but change along the light propagation direction. That is, the groove 28 is formed such that the width (length in the X direction) w of the surface layer portion 21a sandwiched between the grooves 28 and 29 in the substrate 21 is narrow near the center in the light propagation direction and gradually widens toward both ends. , 29 widths have been selected.

The comb-shaped electrode 23 is a connecting conductor that connects a large number of electrode fingers 23a arranged at a constant pitch Λ along the light propagation direction of the optical waveguide 22 (Y direction in this example) and one end of each electrode finger 23a. And part 23b.

The tuning electrode 24 comprises a ladder-shaped lower layer portion 24a and a comb-shaped upper layer portion 24b.
Is a conductive thin film having a two-layer structure in which the tips of the comb teeth are joined to the lower layer portion 24a. The tuning electrode 24 is arranged so that the straight line portion 241 passes between the groove 28 and the optical waveguide 22. The straight line portion 241 is a portion of the lower layer portion 24a that extends in the light propagation direction and is in contact with the upper layer portion 24b.
The insulating layer 25 is provided to insulate the lower layer portion 24a and the upper layer portion 24b.

When the mode converter 2 is used, the voltage V _H is applied to the tuning electrode 24 by the power supply 62. The power supply 62 is variable in voltage and is configured so that the midpoint potential of the voltage V _H becomes the ground potential.

By applying the voltage V _H , the tuning electrode 24 generates heat and the optical waveguide 12 is heated. At this time, the heat generation amount of the linear portion 241 of the tuning electrode 24 is substantially uniform regardless of the position in the light propagation direction, but the heat capacity around the optical waveguide 22 changes according to the width w of the surface layer portion 21a of the substrate 21. Therefore, in the optical waveguide 22, a temperature distribution occurs in which the temperature gradually decreases from the center to the end in the light propagation direction.

On the other hand, when the voltage V _MC is applied to the comb-shaped electrode 23 by the power supply 61, the potential of the linear portion 241 of the tuning electrode 24 is almost the ground potential. And electrode piece 24
The electric field in the x direction is effectively generated between the optical waveguide 2 and
2 shows a periodic electric field distribution along the light propagation direction.

By applying such an electric field, the selected wavelength λ
Mode conversion is performed on the light of i. Selected wavelength λi
Is set to a desired value by changing the voltage V _H and adjusting the temperature of the optical waveguide 22.

In the mode converter 2, the grooves 28, 29 are provided.
As a result, an appropriate temperature distribution similar to the above-mentioned example can be obtained, whereby mode conversion with good wavelength selection characteristics can be realized.

FIG. 5 is a schematic diagram showing the structure of the mode converter 3 of the third embodiment. FIG. 5B is BB of FIG. 5A.
FIG. 5 is a cross-sectional view (end view) as viewed in the direction of the arrow, and FIG.
6 is a cross-sectional view (end view) taken along the line CC of FIG.

The mode converter 3 is an X-cut LiNbO.
_A substrate 31 made of ₃ crystals, an optical waveguide 32 formed on the surface layer of the substrate 31, and two ladder electrodes 3 made of a metal thin film.
3, 34, the insulating layer 35, and the buffer layer 36.

The ladder-shaped electrodes 33, 34 are arranged so that the electrode pieces 33a, 34a are alternately arranged in the light propagation direction (Y direction), and the central portions of the electrode pieces 33a, 34a overlap the optical waveguide 32. It is located in.

The insulating layer 35 is provided to insulate the ladder electrodes 33 and 34. In addition, the buffer layer 36
Are provided to prevent light absorption due to contact between the optical waveguide 32 and the ladder electrodes 33 and 34.

When manufacturing the mode converter 3, the optical waveguide 32 is formed by thermal diffusion of titanium, and the buffer layer 3 is formed.
6 and the ladder-shaped electrode 34 are sequentially provided. The insulating layer 3 is formed on both sides of the optical waveguide 32 so as not to cover the optical waveguide 32.
5 is provided, and then the ladder electrode 33 is formed.

In the mode converter 3, the optical waveguide 32
The insulating layer 35 is patterned so that a predetermined temperature distribution is generated therein. That is, the planar shape of the insulating layer 35 is selected such that the width (length in the Z direction) of the insulating layer 35 is narrow near the center in the light propagation direction and gradually widens toward both ends. The narrow portion of the insulating layer 35 has a smaller cross-sectional area and a smaller heat capacity per unit volume than the wide portion of the insulating layer 35, so that the temperature easily rises.

When the ladder-shaped electrode 34 is connected to a voltage variable power source 72 and a common voltage V _H1 is applied across both ends of each electrode piece 34a of the ladder-shaped electrode 34, each electrode piece 34a uniformly generates heat. Since the power source 72 is configured such that the midpoint potential of the voltage V _H1 becomes the ground potential, the potential at the center position of each electrode piece 34a becomes substantially the ground potential. By controlling the temperature of the optical waveguide 32 by changing the voltage V _H1 ,
The refractive index of the optical waveguide 32 can be changed.

Further, the ladder-shaped electrode 33 is connected to the power source 7 with variable voltage.
When the common voltage V _H2 is applied across both ends of each electrode piece 33a of the ladder-shaped electrode 33, the electrode pieces 33a uniformly generate heat. At this time, the potential at the central position of each electrode piece 33a becomes approximately the midpoint potential of the voltage V _H2 . Voltage V _H2
The refractive index of the optical waveguide 32 can be changed by changing the temperature and controlling the temperature of the optical waveguide 32.

That is, in the mode converter 3, the optical waveguide 32 is heated by both the ladder-shaped electrode 33 and the ladder-shaped electrode 34, and the refractive index of the optical waveguide 32 is efficiently changed to select the selected wavelength λi for mode conversion. Can be adjusted.

On the other hand, a power source 71 which outputs a constant voltage V _MC
By shifting the midpoint potential of the voltage V _H1 from the ground potential, the ladder-shaped electrode 33 is formed in the vicinity of the optical waveguide 32.
The voltage V _MC is applied between the electrode piece 33a of No. 3 and the electrode piece 34a of the ladder electrode 34. As a result, an electric field in the X direction (thickness direction of the substrate 31) is generated as indicated by a broken line in FIG. 5C, and a periodic electric field distribution along the light propagation direction is generated in the optical waveguide 32. Then, the mode conversion for the light of the selected wavelength λi is performed by applying such an electric field.

In the mode converter 3, by setting the width of the insulating layer 35, an appropriate temperature distribution similar to that in the above-described example can be obtained, and thereby mode conversion with good wavelength selection characteristics can be realized.

It should be noted that the ladder electrode 33 may be used only for applying an electric field without passing a heating current through the electrode piece 33a of the ladder electrode 33. Further, the ladder electrode 33 may be used for heating the optical waveguide 32, and the ladder electrode 34 may be used for applying an electric field.

FIG. 6 is a sectional view of the mode converter 4 of the fourth embodiment. In FIG. 6, the components corresponding to those in FIG. 1B are designated by the same reference numerals. The configuration of the mode converter 4 is basically the same as that of the mode converter 1 of FIG.
However, in the mode converter 4, the uppermost layer is SiO ₂
Insulating film layer 17 having a small thermal conductivity of about 1 μm
Is provided. Since the insulating film layer 17 exerts a heat storage effect and effectively heats the optical waveguide 12, the power consumption of the power supply 52 can be reduced.

According to the above-described embodiment, the optical waveguides 12, 2 are set by setting the planar shape such as the shape of the tuning electrode 14, the shape of the grooves 28, 29, or the shape of the insulating layer 35.
Since an appropriate temperature distribution is generated in Nos. 2 and 32, it is easier to realize a temperature distribution that changes smoothly as compared with the case where the temperature distribution is generated by changing the film thickness or the material.

In the embodiment shown in FIGS. 4 and 5, the coating for heat storage is applied as in the example shown in FIG.
The efficiency of heating 2, 32 can be improved. In the embodiment of FIG. 1, the heat generation amount of the tuning electrode 14 may be changed along the light propagation direction by changing the film thickness or material of the tuning electrode 14.

In the above-mentioned embodiments, the temperature distribution conforming to the Hamming function is explained, but window functions other than the Hamming function (Hanning function, Blackman function, Sink function, etc.) and other suitable functions are used. The wavelength selection characteristics may be optimized by generating a temperature distribution according to

In the above-mentioned embodiment, as the substrate material,
Various electro-optic materials other than LiNbO ₃ can be used. The electrode structure may be appropriately selected according to the application and the material of the substrate. In addition, the configuration (shape, size, material) of the mode converters 1 to 4, the connection form with the power source, and the like can be variously changed in accordance with the gist of the present invention.

[0077]

According to the inventions of claims 1 to 6 ,
The thermo-optic effect can be utilized with a simple structure, a large wavelength tunable range can be obtained with a low voltage, and the wavelength selectivity can be improved.

According to the invention of claim 5 , it is possible to effectively heat the optical waveguide and reduce power consumption. According to the invention of claim 6 , since the heating element is used both for heating the optical waveguide and for applying an electric field, the electrode structure can be simplified.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a mode converter according to a first embodiment.

FIG. 2 is a diagram showing an example of a temperature distribution of an optical waveguide.

FIG. 3 is a diagram showing wavelength selection characteristics of a mode converter.

FIG. 4 is a schematic diagram showing a configuration of a mode converter according to a second embodiment.

FIG. 5 is a schematic diagram showing a configuration of a mode converter according to a third embodiment.

FIG. 6 is a sectional view of a mode converter according to a fourth embodiment.

FIG. 7 is a diagram showing a configuration of a conventional mode converter.

[Explanation of symbols]

1, 2, 3, 4 mode converter (optical functional device) 11, 21, 31 substrate 12, 22, 32 optical waveguide 13, 23 comb-shaped electrode (electrode for generating electric field distribution) 14, 24 tuning electrode (heat generation) Body 17 Insulating layer (insulating layer covering heating element) 28, 29 Groove 33 Ladder type electrode (electrode for generating electric field distribution) 34 Ladder type electrode (heating element) 241 Linear portion (groove and optical waveguide Heating element) 35 Insulating layer

Continuation of the front page (56) References JP-A-63-300217 (JP, A) Tadao Nakazawa, Shinji Taniguchi, Minoru Seino, Examination of tunable wavelength filters using thermo-optic effect, Proceedings of IEICE Conference , September 1994, C-160 (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/035 G02F 1/03 502 G02B 6/12

Claims (6)

(57) [Claims] 1. An optical functional device comprising an electrode for generating a periodic electric field distribution in the optical waveguide, which is arranged on a substrate made of an electro-optical material having an optical waveguide formed thereon. It has a heating element for heating the optical waveguide, and in the optical waveguide during heating by the heating element, a temperature distribution in which the temperature changes along the light propagation direction at a rate according to the window function is generated. An optical functional device comprising: 2. An optical functional device in which an electrode for generating a periodic electric field distribution in the optical waveguide is arranged on a substrate made of an electro-optical material in which the optical waveguide is formed. An optical functional device characterized in that a heat-generating body whose amount of heat generation changes along the light propagation direction is arranged on the substrate as a heat source for heating the optical waveguide. 3. An optical functional device comprising an electrode for generating a periodic electric field distribution in the optical waveguide, which is arranged on a substrate made of an electro-optical material having the optical waveguide formed thereon. An optical functional device, characterized in that a groove extending along the optical waveguide and having a variable width is provided on a surface of a substrate, and a heating element is arranged between the groove and the optical waveguide. 4. An optical functional device comprising an electrode for generating a periodic electric field distribution in the optical waveguide, which is arranged on a substrate made of an electro-optical material having an optical waveguide formed thereon. An optical functional device having a heating element for heating the optical waveguide, wherein a strip-shaped insulating layer extending along the optical waveguide and having a variable width is provided on the surface of the substrate. 5. The optical waveguide and the heating element are covered with an insulating layer.
4. The optical functional device according to any one of 4 above. 6. A method of driving the optical functional device of claim 1 Symbol placement, law to said electric current to the heating element to heat the optical waveguide, a window function along the light propagation direction in the optical waveguide A method for driving an optical functional device, characterized in that a voltage is applied between the heating element and the electrode to generate the electric field distribution in a state in which the temperature distribution in which the temperature changes at the ratio is generated.