JPH09258115A - Optical external modulator and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to obtain a desired frequency characteristic by adjusting the resonance frequency of a suppuration substrate and an optical fiber so that the frequency coincides perfectly with the frequency of a driving ultrasonic wave. SOLUTION: The modulator 8 is manufactured by forming a piezoelectric element part 5 consisting of a lower electrode 2, a piezoelectric film 3 and an upper electrode 4, on a supporting substrate 1 and connecting lead wires 9a, 9b respectability to the upper electrode 2 and the lower electrode 4. Next the resonance frequency of the modulator 8 is measured. The measurement of the frequency is elected by the impedance measurement between the lead wires 9a and 9b. The difference between the two reference frequencies is determined and the final thickness adjustment quantify of the supporting substrate 1 is determined in the case the substrate frequency is made coincident with the fiber resonance frequency, the modulator 8 with which the frequency measurement ends is immersed into an etching liquid and is adjusted to the desired thickness,. Finally, the optical external modulator having the desired frequency characteristic is obtd. by fixing the optical fiber to the modulator 8 with which the thickness adjustment ends.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical external modulator that applies mechanical stress from the outside of an optical transmission line to modulate light propagating in the optical transmission line and a method for manufacturing the optical external modulator. .

[0002]

2. Description of the Related Art As an optical external modulator for indirectly modulating a light propagating in an optical transmission line by applying a mechanical signal from the outside of the optical transmission line, for example, the light disclosed in Japanese Patent Application No. 3-196291. External modulators have been proposed. As shown in FIG. 4, a thin film type lower electrode 2, a piezoelectric film 3, and an upper electrode 4 are laminated in this order on one surface of a support substrate 1 made of quartz glass to form a thin film type piezoelectric element portion 5. The leads 9a and 9b for introducing a modulation signal for driving the piezoelectric film 3 are connected to the lower electrode 2 and the upper electrode 4, and further, as shown in FIG. A portion of a desired length of the single mode optical fiber 6 is covered with a coating material 7 having a specific acoustic impedance close to the specific acoustic impedance of the cladding of the optical fiber 6 and fixed to the substrate 1 just below the film 3. It is a thing.

In the optical external modulator, when a modulation signal having a predetermined frequency is applied between the lead wires 9a and 9b from a driving power source (not shown), elastic waves are periodically generated from the piezoelectric film 3, and the stress is transmitted through the substrate 1. Is applied to the single-mode optical fiber 6, the internal refractive index of the single-mode optical fiber changes, and the polarization state of the passing light changes.

[0004]

Such an optical external modulator has a problem that the frequency characteristic varies even though it is manufactured under the same conditions. Therefore, a modulator having a desired frequency characteristic can be stabilized. Could not be obtained, resulting in a decrease in yield and an increase in cost.

[0005]

In view of the above technical problems, the present invention stably manufactures a modulator having a desired frequency characteristic, and provides a device at a low cost by a technically simple method. Is what you are trying to do.

The results of considering the above problems are shown below. In the optical external modulator, the generated elastic wave causes a resonance phenomenon in the support substrate, and a strong ultrasonic wave is incident on the optical fiber at this resonance frequency. Similarly, resonance also occurs in the optical fiber. Therefore, the characteristic of the entire modulator is a characteristic obtained by adding the characteristics of both the supporting substrate and the optical fiber.

The resonance frequency in the supporting substrate and the optical fiber can be obtained from the following calculation. First, the resonance frequency interval f _b0 of elastic waves in the supporting substrate is expressed by the following equation. f _b0 = v _b / (2 × t) [v _b : velocity of elastic wave in the substrate, t: substrate thickness] Further, the resonance frequency f _bn is f _bn = n × f _b0 [n: integer]
It is represented by Therefore, the substrate thickness is calculated by the following equation. t = n × v _b / (2 × f _bn ), and the resonance frequency interval f _f0 in the optical fiber is f _f0 = v
_f / (2 × d) [fiber diameter], resonance frequency f
_fn is represented by f _fn = (n−1 / 2) × f _f0 . Therefore, the fiber diameter is calculated by the following equation. d = (n−1 / 2) × v _f / f _fn

Therefore, in the optical external modulator according to the present invention, the following means are taken to achieve the intended purpose.
A desired frequency characteristic is realized by finely adjusting the resonance frequencies of the supporting substrate and the optical fiber according to the above relationship. For example, if the resonance frequency of the supporting substrate and the optical fiber is adjusted so as to be completely matched with the frequency of the driving ultrasonic wave, a high output frequency characteristic can be obtained in a narrow band, and the resonance frequency of the supporting substrate and the optical fiber can be obtained. By intentionally making a slight shift, a wide band frequency characteristic can be obtained.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The resonance frequency of the supporting substrate, the resonance frequency of the optical fiber, and the frequency of the driving ultrasonic wave are up to ± 0.9 MHz when the frequency of the driving ultrasonic wave is about 300 to 400 (MHz), respectively. It is possible to shift, and in this case, the efficiency becomes higher as the frequencies of the three are matched, and the efficiency becomes worse if the difference between the shifts becomes large. As a means for adjusting the resonance frequency of the supporting substrate and the optical fiber, since the resonance frequency of the substrate and the optical fiber are determined by the thickness of the substrate and the outer diameter of the optical fiber according to the above formula, it can be chemically treated with a hydrofluoric acid solution. There is a method in which the thickness or the outer diameter is eroded to adjust the thickness or the outer diameter. According to this method, it is possible to perform processing in the submicron order and control the resonance frequency with high accuracy.

[0010]

【Example】

(Embodiment 1) FIG. 1 is a perspective view showing the basic structure of an external optical modulator of the first embodiment of the present invention. First,
A piezoelectric element portion 5 including a lower electrode 2, a piezoelectric film 3, and an upper electrode 4 is formed on a supporting substrate 1, and lead wires 9a and 9b are connected to the upper electrode 2 and the lower electrode 4, respectively, to manufacture a modulator 8. . Here, the support substrate 1 is a quartz glass having a thickness of 0.3 mm, and the lower electrode 2 and the upper electrode 4 are made of gold (Au) having a thickness of about 0.2 μm formed by a vacuum deposition method. The lower electrode 2 and the upper electrode 4 may be formed of aluminum (Al), chromium-gold (Cr-Au), or titanium-gold (Ti-Au). The piezoelectric film 3 is made of zinc oxide (ZnO) formed by a sputtering method and has a thickness of about 5 μm. The piezoelectric film 3 is made of lithium niobate (LiNbO3), polyvinylidene fluoride (PVDF), or aluminum nitride (Al.
It may be formed of a piezoelectric material such as N).

Next, the resonance frequency of the modulator 8 is measured. The frequency can be easily measured by measuring the impedance between the lead wires 9a and 9b. For example, when matching the substrate resonance frequency with the fiber resonance frequency, 2
The final thickness adjustment amount of the support substrate 1 is determined by calculating the difference between the two resonance frequencies.

After the frequency measurement, the modulator 8 is dipped in the etching solution 10 and adjusted to a desired thickness, as shown in FIG. Here, the piezoelectric element portion 5 and the lead wire 9
Is protected by a covering material 11 such as a resin, if necessary. A buffered hydrofluoric acid solution or the like can be used as the etching solution.

Finally, by fixing the optical fiber 6 to the modulator 8 whose thickness has been adjusted, an optical external modulator having a desired frequency characteristic can be obtained.

By this method, the glass substrate was etched for the purpose of setting the resonance frequency of the modulator whose initial resonance frequency was 331.96 MHz to 334.0 MHz which is the resonance frequency of the optical fiber.
It can be set to MHz, and a desired frequency characteristic is obtained. By etching the supporting substrate in this manner, it is possible to control the desired frequency with an accuracy of ± 0.1 MHz.

Similarly, by intentionally etching the substrate so that the resonant frequency of the substrate deviates from the resonant frequency of the optical fiber, it is possible to obtain a frequency characteristic having a wider bandwidth than when both resonant frequencies are matched. You can

(Embodiment 2) In the second embodiment of the present invention, as shown in FIG. 3, the coating of the portion of the optical fiber 6 joined to the polarization plane optical external modulator is removed to expose the fiber clad. Then, the optical external modulator 8 is temporarily fixed, and the resonance frequency of the elastic wave in the fiber is measured. The final outer diameter adjustment amount is determined from the difference between the resonance frequency of the fiber measured here and the target frequency. The fiber coating may be removed mechanically by peeling it off, but considering damage to the clad surface, a method of melting the coating by heat treatment or using an organic solvent is preferable.

The optical fiber 6 from which the coating has been removed is adjusted to a desired outer diameter by an etching solution such as a buffered hydrofluoric acid solution and then fixed to the optical external modulator 8 to have an optical external modulator having a desired frequency characteristic. Is obtained.

[0019]

According to the present invention, desired frequency characteristics can be obtained by controlling the shapes of the supporting substrate and the optical fiber. Further, when chemical treatment with an etching solution or the like is performed, processing can be performed with higher accuracy and at lower cost than with mechanical processing, and manufacturing costs can be reduced.

[Brief description of drawings]

FIG. 1 is a perspective view showing a basic configuration of an external light modulator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a method of manufacturing an external optical modulator according to another embodiment of the present invention.

FIG. 3 is an explanatory view showing a method of manufacturing an external optical modulator according to still another embodiment of the present invention.

FIG. 4 is a perspective view showing an example of a conventional external light modulator.

5 is an explanatory cross-sectional view of the conventional external optical modulator shown in FIG.

[Explanation of symbols]

 1 is a support substrate 2 is a lower electrode 3 is a piezoelectric film 4 is an upper electrode 5 is a piezoelectric element part 6 is an optical fiber 7 is a coating material 8 is a modulator 9 is a lead wire 10 is an etching liquid 11 is a coating material

Claims (5)

[Claims] 1. In an optical external modulator in which a piezoelectric element and an optical fiber are formed on a support substrate, the resonance frequency of an elastic wave in the support substrate and the resonance frequency of an elastic wave in the optical fiber drive the frequency of ultrasonic waves. An optical external modulator characterized in that they are almost matched with each other. 2. A method of manufacturing an optical external modulator having a piezoelectric film and an optical fiber formed on a supporting substrate, wherein the thickness of the supporting substrate on which the piezoelectric film is formed is finely adjusted, and elastic waves in the supporting substrate are adjusted. A method of manufacturing an optical external modulator, wherein the resonance frequency of the optical modulator is substantially matched with the resonance frequency of the elastic wave in the fiber. 3. A method of manufacturing an optical external modulator having a piezoelectric film and an optical fiber formed on a supporting substrate, wherein the resonance frequency of an elastic wave in the optical fiber is supported by finely adjusting the outer diameter of the optical fiber. A method of manufacturing an optical external modulator, which is characterized in that the resonance frequency of an elastic wave in a substrate is approximately matched. 4. The method of manufacturing an optical external modulator according to claim 2, wherein the thickness of the supporting substrate is finely adjusted by chemical treatment. 5. The method of manufacturing an optical external modulator according to claim 3, wherein the outer diameter of the optical fiber is finely adjusted by chemical treatment.