JPS6068320A - Waveguide type optical modulator - Google Patents

Abstract

PURPOSE:To make production easier and to improve responsiveness and uniformity of characteristic by forming plural layers of optical waveguides in tight contact with piezoelectric films and using said waveguides as at least one of branch optical paths. CONSTITUTION:Ridge-shaped optical waveguides 3a, 3b consisting of hardened photoresist having width W=50mum and height h=3mum are formed to the central part of a pair of piezoelectric films 2a, 2b consisting of PVDF (polyvinyl chloride) having, for example, length l=8.5mm. and thickness d=9mm. of an optical waveguide 1. Al electrodes 4a, 4b having length m=4mm. are formed to cover the central part. Al electrode films 5a, 5b are formed on the opposite side faces of the films 2a, 2b and the films are joined to each other by means of an adhesive agent 6.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a branching interference type optical modulator that utilizes changes in optical path length, and particularly to an optical waveguide type optical modulator that effectively utilizes expansion and contraction of a piezoelectric film to change optical path length.

With the development and diversification of optical communications, the need for optical modulation is increasing. One type of optical modulator that has been developed for this purpose is a branching interference type optical modulator. This branching interference type optical modulator splits cohesin light from a single light source into two optical paths, applies a phase change to the light passing through at least one of the two optical paths, and then recombines the light between the optical paths. Modulation is performed by interference based on phase differences.

Conventionally, in this branching interference type optical modulator, in most cases, as in many other optical modulators, in order to give a phase change to the branched light, it is necessary to pass the branched light through an electro-optic crystal. , a method is adopted in which the refractive index of the crystal is changed by electrical input applied to the electro-optic crystal to provide a phase change.

On the other hand, in the method using the electro-optic effect as described above, it is necessary to form the optical waveguide within the electro-optic crystal, and the optical waveguide material is not arbitrary. In order to eliminate drawbacks such as the inability to modulate the wavelength of light and the fact that the crystal itself is relatively expensive, methods that change the optical path length have been proposed in recent years. Such proposals include, for example, sandwiching an optical fiber that provides a branched optical path (optical waveguide) between piezoelectric films (7).
) (K, P, Koo et al., ELECTORONTC9L
ETTER9, Vol.

1? , No., pp. 11.380-3112), or those in which the optical fiber is coated with piezoelectric resin (L, J, D
onalds et al., ELECTORON[:S LETT
ER9, Vol. 18. No. 8, pp. 328-327). All of these devices apply electrical input to the piezoelectric material and transmit the resulting dimensional change to the optical fiber, thereby changing the optical path length.

However, according to research conducted by the present inventors, the system in which two optical fibers are used as an optical waveguide has problems with respect to responsiveness to electrical input and stability of characteristics. This is because optical fibers have a cladding in addition to the core that forms the optical waveguide, and the increase in mass due to the cladding prevents dimensional changes in the optical waveguide and further reduces the response speed. It depends on being. In addition, optical fibers have a wooden circular cross-sectional shape, which also causes problems such as a decrease in stress transmission efficiency or a coating with a uniform thickness when applying a piezoelectric layer to sandwich or surround the optical fibers. This may cause problems such as non-uniformity of properties due to difficulty in formation.

In view of the above-mentioned circumstances, an object of the present invention is to provide an optical waveguide type optical modulator belonging to the branching interference type optical modulator, which is easy to manufacture and has good responsiveness.

As a result of research for the above-mentioned purpose, the inventor of the present invention has found that the problems of the above-mentioned waveguide type optical modulator using an optical fiber as an optical waveguide can be solved by thinning the optical waveguide and forming it directly on a piezoelectric film. I discovered that.

The waveguide type optical modulator of the present invention is based on such knowledge, and more specifically, it recombines at least two optical waveguides branched from a single coherent light source and generates a signal by interference of transmitted light. A waveguide type optical modulator that performs modulation is characterized in that at least the - optical waveguide is a thin layer, is formed on a piezoelectric film, and is made variable in length by electrical input to the piezoelectric film. It is something.

Embodiments of the optical waveguide type optical modulator of the present invention will be described in more detail below with reference to the drawings.

FIG. 1 is an exploded perspective view of a preferred embodiment of the waveguide type optical modulator of the present invention, and FIG. 2 is a cross-sectional view including the direction in which the optical waveguide is in a bonded state.

In the optical modulator 1 of this example, each length! = about 8.5m
A pair of PVDF (polyvinylidene fluoride, manufactured by Kureha Chemical Industry ■) electrical film 2 with thickness d = approx.
In the longitudinal center of the opposing surfaces of a and 2b, rubber + bisazide resin (photoresist OMR83 manufactured by Tokyo Ohka Kogyo Co., Ltd.) with a width W = approximately 50%■ and a height h = approximately 37L11 are respectively placed. ridge-shaped optical waveguide 3 made of cured product of
a, 3b are formed, and also cover their central parts,
Length m = 4mmc7) AI electrode (thickness approximately 0.1mm) 4
a and 4b are formed. Also, the piezoelectric film 2
At electrode films 5a and 5 are provided on opposite surfaces of electrodes a and 2b, respectively.
b is formed. Further, the pair of piezoelectric films 2a and 2b are bonded to each other by an adhesive 6 applied to both ends of the optical waveguide 3a, thereby providing an optical modulator l as shown in a side view in FIG.

The modulation characteristics of the optical modulator 1 described above were evaluated using a measurement system as shown in FIG. That is, He-Ne laser 31
25) tz chopper 3
2. The light was coupled to the optical waveguide at one end of the optical modulator 1 through the mirror 33 and the condensing lens 34 . Also, a pair of electrodes 4a sandwiching one optical waveguide 3a and a piezoelectric film.

Direct current voltages of various magnitudes were applied from a variable DC power supply 35 between 5a and 5a. On the other hand, the output light from the optical modulator 1 is curved into the optical fiber 36, and the photomultiplier tube 37
The modulated light was measured by the lock-in amplifier 38.

A voltage of 0 to 200 V is applied to the optical modulator, and the relationship between the applied voltage and the relative intensity of the output light (maximum intensity is 1.0) is plotted in FIG. Applied voltage is O~20
The maximum output light intensity in the range of 0■ was 75V,
145V, and the maximum attenuation was at 35V.
V, 110V, and 180V. From this, it was found that the half-length voltage required to shift the phase of light by π radians is approximately 36V. Moreover, the maximum modulation degree was about 60%. The theoretical value of the half-wave voltage determined from the piezoelectric characteristics of PVDF is about 22 V, and it is understood that the above-mentioned optical modulator has extremely excellent responsiveness. In addition, the response is approximately 2.6 × 104 radian/(V/m)
/ m-length, which is approximately 2.3×10 as measured by Donalds et al. using the above-mentioned optical fiber as an optical waveguide.
-' Radian/(V/m)/m length It can be seen that this is greatly improved.

In Section 2, the optical modulator of the present invention has been described with reference to a preferred embodiment thereof, but the embodiment described in Section 2 can be implemented with various modifications within the scope of the present invention.

For example, although a pair of optical waveguides were used in the above example, optical modulation is generally possible using a similar principle by using an optical waveguide on an area. Also, in the above example,
A similar piezoelectric film was used as a support for a pair of optical waveguides. This is preferable in the sense of harmonizing the phase characteristics of the pair of optical waveguides in the non-voltage applied state, but it goes without saying that one of the supports can be formed of a non-piezoelectric material. On the other hand, when the pair of supports are both made of piezoelectric films, as in the example above, it is also possible to further reduce the half-wave voltage by applying voltages of opposite polarity to both. . In addition, as in the above example, it is preferable to construct the ridge-shaped optical waveguide using photoresist because it is possible to easily and precisely form a thin layer structure that follows the expansion and contraction deformation of the piezoelectric film, but it is not necessary. As long as it can provide suitable dimensional characteristics, other plastic films or other light-transmitting materials, preferably films of materials having a larger refractive index than the piezoelectric material, may be attached. Here, the optical waveguide being a thin layer means that it is substantially thinner than the piezoelectric film. To achieve sufficient interference at the output end of the optical waveguide,
It is desirable to have a single mode optical waveguide, and making the optical waveguide thinner is important from the point of view of achieving a single mode. On the other hand, it is also desirable that the width of the optical waveguide be narrow in order to achieve a single mode.

Further, in the above example, the supports forming a pair of optical waveguides are joined at the ends of the optical waveguides. Such a configuration is preferable in terms of downsizing the optical modulator and facilitating coupling at the entrance and exit of the optical modulator, but it is also possible to perform optical modulation even if the optical waveguides are completely separate. It is easy to understand that this is the case with a normal branching interference type optical modulator.

In addition, as another example, a schematic perspective view including a circuit section is shown in Fig. 5.
As shown in the figure, a pair of optical waveguides 3a and 3b can also be formed on a single piezoelectric film. In this example, the pair of optical waveguides 3a and 3b are sandwiched together with the piezoelectric film 2 between electrodes 4a and 5, or between electrodes 4b and 5, and are supplied with voltages of opposite polarity by a variable DC power source 35a or 35b. applied. As a result, the optical waveguides 3a and 3b are deformed such that one of them is extended and the other is contracted, and optical modulation is performed by the resulting optical path difference.

Further, as the piezoelectric film, it is preferable to use a polymeric piezoelectric film such as vinylidene fluoride resin including PVDF in order to provide the necessary stretching and deformation characteristics, but it is difficult to provide the necessary thin film. Inorganic piezoelectric films are used as much as possible, and polymer films in which fine inorganic piezoelectric materials are dispersed are also preferably used.

It should be noted that the dimensions of each part shown in the above embodiments are merely illustrative, and it goes without saying that they can be changed as appropriate within the spirit of the present invention.

Further, in the above description, an example has been described in which the optical waveguide is made of a material different from the piezoelectric film and is formed in a protruding or ridge shape on the piezoelectric film. Such a structure is shown in FIG.
FIG. 6 shows a cross-sectional view of a cross-section including the I-line (that is, a cross-section in the thickness direction of the piezoelectric film 2a orthogonal to the extending direction of the optical waveguide 3a). However, such a protruding or ridge-shaped optical waveguide can also be formed as a protrusion 3aa of the piezoelectric film Zaa itself, as shown in FIG. This is because the optical waveguide must be made of a material with a larger refractive index than the surrounding material (air (refractive index n.:l) in FIGS. 6 and 7) in a considerable part of its outline. For example, the necessary degree of light confinement effect can be achieved. The optical waveguide shape as shown in FIG. 7 can be obtained, for example, by removing the piezoelectric material on both sides of the waveguide by sputter etching or the like. Further, the optical waveguide may have a form in which a layer 3ab of material with a refractive index of 1 is embedded in the surface layer of the piezoelectric film 2ab, as shown in FIG.

For example, when using a PvDF piezoelectric material, such a high refractive index material layer can be formed by replacing some of the fluorine atoms by implanting atoms such as chlorine, which have a larger atomic weight, by ion sputtering or the like. It can be formed by In the specification, the expression "forming a thin-layer optical waveguide on a piezoelectric film" is used to include such a series of conditions.

As described above, according to the present invention, by forming a thin-layer leading waveguide in close contact with a piezoelectric film and using it as at least one of the branching optical paths, manufacturing is simple, and good response and uniformity can be achieved. A waveguide type optical modulator having such characteristics is provided.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of an optical modulator according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view in the thickness direction including an optical waveguide in an assembled state of the optical modulator, and FIG. 3 is an optical modulator in an assembled state. FIG. 4 is a graph showing the evaluation results; FIG. 5 is a schematic perspective view showing another embodiment of the optical modulator of the present invention together with a drive circuit; FIG. The figure is a sectional view including the V-v line in Figure 1,
7 and 8 are cross-sectional views showing examples of other cross-sectional shapes of the optical waveguide of the present invention, respectively. 1.1a... Optical modulators 2a, 2b, 2.2aa, 2ab,... PVDF piezoelectric film 3a, 3b, 3aa, 3ab... Optical waveguide 4
a, 4b ---A I electrode 5a, 5b, 5-A I electrode 6... Adhesive No. 2 Figure 4 Country I'17511 iJ pressure (V) Figure 6 弗7 @

Claims (1)

[Claims] 1. In a waveguide type optical modulator that recombines at least two optical waveguides branched from a single coherent light source and performs modulation by interference of transmitted light, at least - 1. A waveguide type optical modulator comprising a thin layer, formed on a piezoelectric film, and having a variable length by electrical input to the piezoelectric film. 2. The optical waveguide is a pair of thin layers, each formed on a pair of support films, and at least one of the support films forming the optical waveguide is a piezoelectric film. The optical modulator according to range 1. 3. The optical modulator according to claim 2, wherein a pair of support films each having an optical waveguide formed thereon are joined at each optical waveguide extension end with the optical waveguide forming surface inside. 4. The above-mentioned double optical waveguide is formed on a single piezoelectric film, and an electrical input is applied to at least a portion of the piezoelectric film forming the double optical waveguide. The optical modulator according to range 1. 5. The optical modulator according to any one of claims 1 to 4, wherein the thin-layer optical waveguide essentially consists of plastic. 6. The optical modulator according to any one of claims 1 to 5, wherein the thin-layer optical waveguide is formed in a ridge shape on a piezoelectric film. 7. The optical modulator according to claim 6, wherein the ridge-shaped thin layer optical waveguide is provided by photoresist. 8. The optical modulator according to any one of claims 1 to 5, wherein the thin-layer optical waveguide is formed in a state embedded in the surface layer of a piezoelectric film. 9. The optical modulator according to any one of claims 1 to 8, wherein the piezoelectric material is made of a polymeric piezoelectric material. 10. The optical modulator according to claim 9, wherein the piezoelectric body is made of vinylidene fluoride resin.