JPH04147210A - Optical phase modulator - Google Patents

Abstract

PURPOSE:To realize the modulator which is easily manufactured and has a flat frequency characteristic of optical phase modulation by forming electrodes inside and outside a cylindrical piezoelectric vibrator which has only one plane of symmetry from at most one axis of symmetry and winding the outer periphery with an optical fiber. CONSTITUTION:Lead titanate ceramic is used, a columnar cavity 12 which has a different center axis is formed in the cylindrical piezoelectric vibrator 11 whose outward shape is columnar, and the outer periphery is wound with the optical fiber 13 three times. Then the vibrator is cut along a plane which does not cross the center axis of the outward shape column at right angles in the length direction. The electrodes 13 and 14 are formed inside and outside the vibrator 11 and applied with a vibrating voltage, so that the vibrator vibrates in a dynamic diameter direction. The vibrator is irregular in thickness and further not uniform in the length of the wall, so resonance in remarkable mode never appears. Consequently, the excellent flatness of the optical phase modulation frequency characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical fiber type optical phase modulator used in optical fiber sensors such as optical fiber gyros that perform high-precision measurements using optical fibers. .

Prior Art Conventional optical phase modulators include a waveguide-shaped optical phase modulator in which an optical waveguide and an electrode are formed on a dielectric substrate such as niobium oxide, and a cylindrical piezoelectric vibrator. There are two types of optical fiber type optical phase modulators that are wound with optical fiber. Among these, optical fiber type optical phase modulators are optical waveguide type optical modulators that are extremely easy to optically couple with optical fiber sensors such as optical fiber gyros because both have optical fibers as their main components. It has excellent features not found in phase modulators. Furthermore, the structure is simple and manufacturing is easy.

A schematic structural diagram of a conventional optical fiber type optical phase modulator is shown in FIG. 21 is a cylindrical piezoelectric vibrator that vibrates in the radial direction. An optical fiber 22 is tightly wound several times around the outer circumference of the cylindrical piezoelectric vibrator.

The light to be phase-modulated is input from one end of the optical fiber, and the phase-modulated light is extracted from the other end.

23 and 24 are electrodes, and a modulation signal voltage is applied between the two electrodes.
When assembled, the piezoelectric vibrator 2 vibrates in the radial direction,
This induces longitudinal stress and strain in the optical fiber 22 wound around it. As a result, the effective refractive index and length of the optical fiber 22 change slightly ("C"), so the time it takes for light to pass through the optical phase modulator changes in accordance with the modulation signal voltage, resulting in the phase Modulation is performed.

Problems to be Solved by the Invention Although fiber-type optical phase modulators have excellent features, they also have drawbacks. First of all, in the fiber-type optical phase modulator according to the prior art, there are several resonant frequencies of vibration motes determined by the shape of the fiber-type optical phase modulator, and therefore the modulation characteristics are not flat. For example, the relationship between the frequency of a modulation signal with a constant amplitude voltage applied to a piezoelectric vibrator and the amplitude of the phase displacement amount of light passing through an optical phase modulator is as shown in FIG. This modulation frequency characteristic curve shows remarkable resonance characteristics related to the vibration mode of the piezoelectric vibrator. With such characteristics,
It is impossible to modulate the phase of light with an arbitrary waveform and perform highly accurate optical measurements using advanced signal processing.

The present invention eliminates these drawbacks of conventional fiber-type optical phase modulators, realizes flat optical phase modulation characteristics, and is easy to combine with the optical fiber sensor that fiber-type optical phase modulators have and is easy to manufacture. The purpose is to take advantage of its excellent features such as ease of use.

Means for Solving the Problems In the present invention, in order to eliminate the drawbacks of the fiber-type optical phase modulator as described above, a piezoelectric vibrator having a shape having at most one axis of symmetry or one plane of symmetry is used. At least one pair of electrodes is formed on the surface of the optical phase modulator, and an optical fiber is wound around the outer periphery of the optical phase modulator.

In particular, the optical phase modulator described above is an optical phase modulator in which electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator that does not have an axis or plane of symmetry, and an optical fiber is wound around the outer circumference. Second, the optical phase is a cylindrical piezoelectric vibrator that has no point or axis of symmetry in its cross-sectional shape and whose walls are not uniform in length, with electrodes formed on the inside and outside, and an optical fiber wrapped around the outside. To describe in more detail, first, electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator whose outer shape is cylindrical, elliptical, or prismatic with rounded corners, and whose wall thickness is not uniform. , an optical phase modulator in which an optical fiber is wound around the outer periphery, and secondly, inside a piezoelectric vibrator whose outer shape is a cylinder, an elliptical cylinder, or a prism with rounded corners, the cylinder, elliptic cylinder, or prism with rounded corners is placed inside the piezoelectric vibrator. ,
Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator, which has a cylindrical, elliptical, or prismatic cavity with rounded corners that do not have the same central axis, axis of symmetry, or plane of symmetry, and an optical fiber is wound around the outer periphery. It is an optical phase modulator, and thirdly, a piezoelectric vibrator with a cylindrical, elliptical, or prismatic shape with rounded corners has a shape in which a part of a cone, elliptical cone, or square pyramid with rounded corners is cut out. It is an optical phase modulator in which electrodes are formed on the inner and outer sides of a cylindrical piezoelectric vibrator with a cavity, and an optical fiber is wound around the outer periphery. It is an optical phase modulator in which electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator that has a stacked shape of round prisms and a cavity is formed inside, and an optical fiber is wound around the outer circumference. Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator, which has the shape of a cylinder, an elliptic cylinder, or a rectangular cylinder with rounded corners with a part cut out, and whose wall thickness is not uniform. Electrodes are formed on the inside and outside, and an optical fiber is wound around the outside. Sixthly, a cylindrical piezoelectric vibrator having a cylindrical, elliptical, or prismatic shape with rounded corners is placed in a plane that is not orthogonal to the central axis of the cylinder, elliptical, or prismatic with rounded corners. This is an optical phase modulator in which electrodes are formed on the inside and outside of a cut-shaped piezoelectric vibrator, and an optical fiber is wound around the outer circumference.

Function: When an oscillating voltage is applied between a pair of electrodes of a piezoelectric vibrator having at most one axis or plane of symmetry according to the present invention, significant resonance is unlikely to occur because the symmetry is low.

Therefore, the modulation frequency characteristic curve of an optical phase modulator constructed by winding an optical fiber around the outer periphery of such a piezoelectric vibrator does not exhibit significant resonance characteristics, and a flat characteristic is obtained.

In particular, when electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator whose wall thickness is particularly uneven, when an oscillating voltage is applied between the two electrodes, a vibration occurs that is closely related to the phase modulation characteristics of light. Significant resonance with respect to radial vibration is less likely to occur. In addition to this, the resonance of the radial vibration mode of the cylindrical piezoelectric vibrator also has a contribution from resonance related to the length of the piezoelectric vibrator.

To suppress this, it is effective to make the length of the wall of the cylindrical piezoelectric vibrator non-uniform. By doing this, it became possible to further suppress the resonance of the vibration mode related to the wall thickness, and it was possible to obtain flat modulation frequency characteristics.

If a cylindrical piezoelectric vibrator with a cylindrical, elliptical, or rounded prismatic external shape and uneven wall thickness is used as a piezoelectric vibrator with low symmetry, no significant vibration mode resonance will occur. is obtained similarly. Furthermore, since the external shape is cylindrical, elliptical, or prismatic with rounded corners,
It is easy to wind the optical fiber, and there are few manufacturing difficulties, especially in the case of a cylinder.

If the cavity provided inside is a cylindrical, elliptical cylindrical, or prismatic cavity with rounded corners that does not have the same central axis, axis of symmetry, or plane of symmetry as the external cylinder, elliptical cylinder, or prismatic cylinder with rounded corners, the present invention further provides the present invention. This makes it easy to manufacture piezoelectric vibrators. A cylindrical piezoelectric vibrator whose inner cavity is shaped like a partially cut out cone, elliptical cone, or rounded pyramid has low symmetry not only in the cross-sectional shape but also in the length direction, making it difficult to suppress resonance. The effect is strong. Further, there is no particular increase in the difficulty in manufacturing.

In a cylindrical piezoelectric vibrator whose wall thickness is not uniform, if the external shape is a circular cylinder, an elliptical cylinder, or a square cylinder with rounded corners with a part cut out, the symmetry in the length direction can be reduced. A large resonance suppression effect can be easily obtained. In particular, it is very difficult to manufacture a cylindrical piezoelectric vibrator whose external shape is a cylinder, an elliptical cylinder, or a prism with rounded corners, cut by a plane that is not perpendicular to the central axis of the cylinder, elliptic cylinder, or rectangular pillar with rounded corners. It is easy to use and can effectively suppress resonance in dogs.

If you use a cylindrical piezoelectric vibrator whose outer shape is a stack of cylinders or elliptical cylinders of different sizes or square cylinders with rounded corners and a hollow inside, it will be possible to combine cylinders or elliptical cylinders of different sizes or square pillars with rounded corners. The respective resonance characteristics of the round prisms can cancel each other out, and a flat modulation frequency characteristic can be obtained.

Embodiment FIG. 1 is a perspective view of an embodiment of an optical fiber type optical phase modulator according to the present invention. 1] is a cylindrical piezoelectric vibrator with a cylindrical outer shape made of lead titanate-based ceramic, and 12 is a cylindrical cavity having a central axis different from the central axis of the external cylinder.

The outer diameter of the cylindrical piezoelectric vibrator is 30 mm, and an optical fiber 3 is wound around the outer circumference three times. The diameter of the inner cavity is 10
M, and is eccentric by 7 mm with respect to the central axis of the external cylinder.

The shape is cut along a plane that is not perpendicular to the central axis of the external cylinder. Cylindrical piezoelectric vibrator 1
Electrodes 14 and 15 are formed on the inside and outside of 1, and by applying an oscillating voltage between the two electrodes,
The piezoelectric vibrator vibrates in the radial direction.

In the piezoelectric vibrator according to this embodiment, the central axis of the inner cylindrical cavity is eccentric, so the wall thickness is non-uniform. Regarding the length direction, since the shape is cut with an inclined surface in a direction different from the uneven flooding direction, the length of the wall is not uniform, and the resonance of the vibration mote does not appear.For this reason, the second
As shown in the figure, the good flatness of the optical phase modulation frequency characteristic can be obtained. The Seven Rod Inker method is one of the most effective methods for performing high-precision signal processing in optical fiber gyros and the like. This method requires optical phase modulation using a sawtooth wave, and an optical phase modulator with a wide band that can perform optical phase modulation using a sawtooth wave signal with a period of 10 μsec to ]m5eC must be used. No pressure. When optical phase modulation was carried out using the above-mentioned sawtooth wave using the optical phase modulator according to the present invention, it was possible to obtain a modulation I/H number that poses no problem in practice.

Next, other embodiments of the piezoelectric vibrator shape according to the present invention will be shown. FIG. 3 shows an embodiment in which a piezoelectric vibrator 41 having an elliptical external shape is provided with an elliptic cylindrical cavity 12 whose plane of symmetry and axis of symmetry do not coincide with the elliptical cylinder, and electrodes 43 and 44 are formed on the inside and outside. A notch 45 is provided in the shoulder part of the elliptical cylinder to reduce the symmetry in the height direction of the elliptical cylinder. Figure 4 shows a triangular cylinder with rounded corners. This is an embodiment in which a cavity 52 in the shape of a partially cut out cone is provided inside a piezoelectric vibrator 51, and electrodes 53 and 54 are formed on the inside and outside. The optical phase modulator according to the present invention, which is wound with optical fiber, has non-uniform wall thickness in all directions and can obtain extremely good modulation frequency characteristics. This is an embodiment in which a cylindrical cavity 62 is provided inside a piezoelectric vibrator 61 having a shape in which cylinders are stacked with their center axes shifted, and electrodes 62 and 63 are formed.
The optical phase modulator is constructed by applying all the cylinders Q a predetermined number of times. The light incident on this phase modulator is sequentially modulated by the three cylindrical parts. The size of the cylinder is determined so that the resonance characteristics of the three cylinder parts optimally cancel each other out, thereby obtaining good modulation frequency characteristics.

In addition to the embodiments mentioned above, optical phase modulators of various shapes with flat modulation frequency characteristics can be easily obtained by appropriately combining the techniques described in each claim of the present invention. is possible.

Effects of the Invention As described above (・τ), the present invention can realize a fiber-type optical phase modulator with flat frequency characteristics of optical phase modulation.
With the structure of the present invention, there are fewer problems in manufacturing the pressure-N sensor, and optical fibers can be easily wound. What's more, it does not lose the characteristic of fiber-type optical phase modulators, which is that they can be easily coupled to fibers.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the optical phase modulator according to the present invention, FIG. 2 is a modulation frequency characteristic diagram of the optical phase modulator according to the present invention for an applied modulation signal with a constant amplitude, and FIGS. 4
5 and 5 are perspective views of an embodiment of a piezoelectric vibrator of an optical phase modulator according to the present invention, FIG. 6 is a perspective view of a fiber type optical phase modulator according to the prior art, and FIG. 7 is a perspective view of an embodiment of a piezoelectric vibrator of an optical phase modulator according to the present invention. FIG. 3 is a modulation frequency characteristic diagram of an optical phase modulator according to the prior art with respect to a modulated signal. 11...Cylindrical piezoelectric vibrator, 12 Eccentric cylindrical cavity, 1
3... Optical fiber, 21-- Cylindrical piezoelectric vibrator, 2
2--Optical fiber. Name of agent: Patent attorney Akira Okaji and two others 1st
Figure 2 Modulation N Gabe Figure 3 4-44 L pole 42 Culm bar? In the cave No. 4, Figure 5, the town shrine's hat storehouse, Sashiko, Figure 5, Figure 6, Figure 23, 7.'

Claims (9)

[Claims] (1) A light characterized by forming at least one pair of electrodes on the surface of a piezoelectric vibrator having at most one axis of symmetry or one plane of symmetry, and winding an optical fiber around the outer periphery. Phase modulator. (2) The optical phase modulator according to claim 1, wherein electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator having no axis of symmetry or plane of symmetry, and an optical fiber is wound around the outer periphery. (3) Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator that does not have a symmetry point or axis of symmetry in its cross-sectional shape and whose wall length is not uniform, and an optical fiber is wound around the outer circumference. The optical phase modulator according to claim 1. (4) Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator whose external shape is cylindrical, elliptical, or prismatic with rounded corners and whose wall thickness is not uniform, and an optical fiber is wound around the outer circumference. Features of optical phase modulator. (5) Inside a piezoelectric vibrator whose external shape is cylindrical, elliptical, or prismatic with rounded corners, there is a cylindrical shape whose central axis, axis of symmetry, or plane of symmetry is not the same as the cylinder, elliptical, or prismatic with rounded corners. or an optical phase modulator according to claim 4, characterized in that electrodes are formed on the inner and outer sides of a cylindrical piezoelectric vibrator having an elliptical cylinder shape or a prismatic cavity with rounded corners, and an optical fiber is wound around the outer periphery. . (6) Cylindrical piezoelectric vibration in which a cavity in the shape of a part of a cone, elliptical cone, or rounded pyramid is provided inside a piezoelectric vibrator with a cylindrical, elliptical, or prismatic shape with rounded corners. 5. The optical phase modulator according to claim 4, wherein electrodes are formed on the inside and outside of the child, and an optical fiber is wound around the outer periphery. (7) Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator whose external shape is a cylinder, an elliptic cylinder, or a rectangular cylinder with rounded corners with a part cut out, and whose wall thickness is not uniform. An optical phase modulator characterized by a wound fiber. (8) A piezoelectric vibrator having a shape obtained by cutting a cylindrical piezoelectric vibrator having a cylindrical, elliptical, or prismatic shape with rounded corners along a plane that is not perpendicular to the central axis of the cylinder, elliptical, or prismatic with rounded corners. , an optical phase modulator characterized by forming electrodes on the inside and outside and having an optical fiber wound around the outside. (9) Electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator that has a stacked shape of cylinders, elliptical cylinders, or square cylinders with rounded corners of different sizes, and has a cavity inside. Claim 8 characterized in that an optical fiber is wound around the
The optical phase modulator described.