JPH0439618A - optical phase modulator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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. .

BACKGROUND OF THE INVENTION Conventionally, optical phase modulators used for such purposes include waveguide-shaped optical phase modulators in which an optical waveguide and electrodes are formed on a dielectric substrate such as lithium niobate, and circular optical phase modulators. There are two types of optical fiber-type optical phase modulators in which an optical fiber is wound around a columnar piezoelectric vibrator. Among these, optical fiber type optical phase modulators are waveguide type optical phase modulators, which are extremely easy to optically couple with optical fiber sensors such as optical fiber gyros because they both have optical fibers as their main component. It has excellent features not found in phase modulators.

Further, this optical fiber type optical phase modulator has the advantage of being simple in structure and easy to manufacture.

FIG. 3 is a conceptual diagram of the conventional optical fiber type optical phase modulator mentioned above. In the figure, reference numeral 21 denotes a cylindrical piezoelectric vibrator, which vibrates in the diameter direction. 22 is an optical fiber tightly wound several times around the outer circumference of the cylindrical piezoelectric vibrator 21;
The light to be phase modulated is inputted from one end of the optical fiber, and the phase modulated light is extracted from the other end. Further, 23 and 24 are electrodes to which a modulation signal voltage is applied, and when a modulation signal voltage is applied between these electrodes, the piezoelectric sensor 21 vibrates in the diametrical direction, and the optical fiber 22 wound around it vibrates. Inducing longitudinal stresses and strains. Therefore, as the effective refractive index and length of the optical fiber 22 change slightly due to this stress and strain, the time it takes for light to pass through the optical phase modulator changes in accordance with the modulation signal voltage, resulting in a phase change. Modulation is performed.

Problems to be Solved by the Invention Even though the fiber-type optical phase modulator has the excellent features described above, it still has the following drawbacks. That is, in a conventional fiber-type optical phase modulator, there are several resonance frequencies of vibration modes determined by its shape, 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 the piezoelectric vibrator 21 and the amplitude of the phase displacement amount of light passing through an optical phase modulator is as shown in FIG. 4, but this modulation frequency characteristic The curve includes a piezoelectric vibrator 21
Remarkable resonance characteristics related to the vibration modes of

In other words, with such an uneven modulation frequency characteristic, it is impossible to modulate the phase of light with an arbitrary waveform and perform highly accurate optical measurement using advanced signal processing.

The object of the present invention is to eliminate such drawbacks of the conventional fiber-type optical phase modulator mentioned above, to realize flat optical phase modulation characteristics, and to facilitate coupling with the optical fiber sensor that the fiber-type optical phase modulator has. The object of the present invention is to obtain a fiber-type optical phase modulator that can fully utilize its excellent features such as ease of manufacture.

Means for Solving the Problem According to the first aspect of the present invention for achieving this problem,
An optical phase modulator is provided, in which electrodes are formed on the inner and outer sides of a cylindrical piezoelectric vibrator having no axis of symmetry or plane of symmetry, and an optical fiber is wound around the outer periphery.

According to the second aspect of the present invention, a cavity different from the cylindrical cavity having the same central axis as the cylinder is formed inside the piezoelectric vibrator having a cylindrical outer shape, and the wall thickness is not uniform. There is provided an optical phase modulator characterized in that electrodes are formed on the inside and outside of a cylindrical piezoelectric vibrator, and an optical fiber is wound around the outer periphery of the piezoelectric vibrator.

Furthermore, according to a third aspect of the present invention, a cylindrical piezoelectric vibrator having a cylindrical outer shape has a cylindrical cavity formed inside the piezoelectric vibrator whose central axis is not the same as the cylinder. An optical phase modulator is provided in which an electrode is formed and an optical fiber is wound around the outer periphery of a piezoelectric vibrator.

According to the fourth aspect of the present invention, electrodes are formed on the inside and outside of the piezoelectric vibrator whose wall length is not uniform, and an optical fiber is attached to the outer periphery of the piezoelectric vibrator. A wound optical phase modulator is provided.

According to the fifth aspect of the present invention, electrodes are formed on the inner and outer sides of a piezoelectric vibrator cut along a plane that is not perpendicular to the central axis of the external cylinder, and an optical fiber is wound around the outer circumference of the piezoelectric vibrator. An optical phase modulator is provided.

Effects Each of the configurations of the present invention described above makes it possible to obtain a cylindrical piezoelectric vibrator with electrodes formed on the inside and outside of the cylindrical piezoelectric vibrator, which has no axis of symmetry or plane of symmetry and whose wall thickness is uneven. When an oscillating voltage is applied, significant resonance is less likely to occur with respect to diametrical oscillations associated with optical phase modulation due to the low symmetry. Then, as in the present invention, as a piezoelectric vibrator with low symmetry, a cavity different from a cylindrical cavity having the same central axis as the cylinder of the outer shape is formed inside the piezoelectric vibrator having a cylindrical outer shape. , if a cylindrical piezoelectric vibrator with uneven wall thickness is used,
The effect that no significant vibration mode resonance occurs is similarly obtained. Furthermore, since the optical phase modulator according to the present invention has a cylindrical outer shape, there are few manufacturing difficulties, and it is easy to wind the optical fiber. In the optical phase modulator according to the present invention, if the cavity formed inside is a cylindrical cavity having a central axis different from the central axis of the external cylinder, manufacturing of the piezoelectric vibrator becomes easier.

In other words, in the present invention, by making the wall thickness of the cylindrical piezoelectric vibrator non-uniform, it is possible to suppress the resonance of the vibration mode related to the wall thickness and obtain flat modulation frequency characteristics. However, the resonance of the diametrical 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. Such a configuration can be easily obtained by cutting a piezoelectric vibrator having a cylindrical outer shape along a plane that is not perpendicular to its central axis.

EXAMPLE Hereinafter, details of an embodiment of an optical fiber type optical phase modulator according to the present invention will be explained using FIGS. 1 and 2. FIG. 1 is a perspective view of an optical fiber type optical phase modulator according to the present invention. The reference numeral 11 in the figure is a cylindrical piezoelectric vibrator with a cylindrical outer shape made of lead titanate ceramic, and the reference numeral 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 301111, and the optical fiber 13 is wound around the outer circumference only three times. The diameter of the inner cavity is 10 dragons, and the diameter is 71+ with respect to the central axis of the outer cylinder.
It is eccentric by 11. In addition, regarding the length direction of the piezoelectric vibrator 11, it is noted that the longitudinal direction of the piezoelectric vibrator 11 is
It has a shape cut along a plane. Electrodes 14 and 16 are formed on the inside and outside of the piezoelectric vibrator 11, and by applying an oscillating voltage between the two electrodes, the piezoelectric vibrator vibrates in the diametrical direction.

In the piezoelectric vibrator 11 of this embodiment, the central axis of the inner cylindrical cavity is eccentric, so the wall thickness is non-uniform.

The piezoelectric vibrator 11 also has a shape in which the length of the wall is not uniform in the longitudinal direction, and no significant vibration mode resonance occurs. Therefore, as shown in Figure 2, the modulation frequency characteristic curve of an optical phase modulator constructed by winding an optical fiber around such a piezoelectric vibrator does not exhibit significant resonance characteristics and has a flat characteristic. can get.

The serodyne method is one of the effective methods for high-precision signal processing in optical fiber gyros, etc., but this method requires optical phase modulation using a sawtooth wave, and has a period of 10 μsec to 1 m5 ec. An optical phase modulator with a wide band that can perform optical phase modulation with a sawtooth signal with When optical phase modulation was performed using this sawtooth wave using the optical phase modulator according to the present invention, it was possible to obtain a modulated signal with no problems in practical use.

Effects of the Invention As explained above, according to the present invention, not only can flat frequency characteristics of optical phase modulation be obtained, but also the fiber-type optical phase modulator of the present invention has advantages in manufacturing piezoelectric vibrators. There are fewer problems, the optical fiber can be easily wound, and there are advantages such as not losing the characteristic of the fiber-type optical phase modulator that it is easy to couple with the fiber.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an 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 FIG. 3 is a diagram of a conventional fiber-type optical phase modulator. FIG. 4, a perspective view of the modulator, is a modulation frequency characteristic diagram of the same optical phase modulator with respect to an applied modulation signal of constant amplitude. 11... Cylindrical piezoelectric vibrator, 12... Eccentric cylindrical cavity, 13.22... Optical fiber, 14.16.23.2
4... Electrode, 21... Cylindrical piezoelectric vibrator. Name of agent Patent attorney Shigetaka Awano and one other person Fig. Fig. Fig. Modulation frequency Fig. Modulation frequency

Claims (5)

[Claims] (1) An optical phase modulator characterized in that 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 circumference of the piezoelectric vibrator. (2) Inside the piezoelectric vibrator having a cylindrical outer shape, a cavity different from the cylindrical cavity having the same central axis as the cylinder is formed, and the wall thickness is not uniform. An optical phase modulator characterized in that an electrode is formed on the outside and an optical fiber is wound around the outer periphery of a piezoelectric vibrator. (3) Electrodes are formed on the inside and outside of the cylindrical piezoelectric vibrator, which has a cylindrical cavity whose central axis is not the same as that of the cylinder, inside the piezoelectric vibrator whose external shape is cylindrical. An optical phase modulator characterized by having an optical fiber wound around its outer periphery. (4) Claim 1 characterized in that electrodes are formed on the inner and outer sides of the piezoelectric vibrator whose walls are not uniform in length, and an optical fiber is wound around the outer periphery of the piezoelectric vibrator. , claim 2
Or the optical phase modulator according to claim 3. (5) A claim characterized in that electrodes are formed on the inside and outside of a piezoelectric vibrator cut along a plane that is not orthogonal to the central axis of the external cylinder, and an optical fiber is wound around the outer periphery of the piezoelectric vibrator. 4. The optical phase modulator according to claim 2 or claim 3.