JPS6034093B2 - Manufacturing method of optical modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an optical modulation element used in an optical modulator.

In recent years, strong electrolyte crystals such as lithium tantalate and lithium niobate, which have an electro-optic effect, have been commonly used as light modulating elements.

The conventional holding means for an optical modulator is as shown in FIG.
Electrodes 2 are placed on both royal faces of a crystal plate 1 made of lithium tantalate, etc., and one of the electrodes 2 is soldered onto the central axis of the plane of a metal semi-cylindrical column 3, using two pieces. Insert it into a metal tube 4 whose inner diameter matches the diameter of the metal semi-cylinder 3, adjust the position so that the two main surfaces are perpendicular to each other, and then connect the metal semi-cylinder 3 and the metal tube 4. It is fixed.

With this holding means, the piezoelectric effect of the crystal plate (piezoresonance in which the crystal plate is distorted when an electrode is applied to the crystal plate and an electric signal is applied to the electrode) occurs, and an optical modulator that attempts to utilize the electro-optic effect Such oscillations are unnecessary and may adversely affect the electro-optical effect.

Here, one surface of the crystal plate is fixed to a metal semi-cylinder, but the other surface is not fixed anywhere, so the structure is likely to cause vibrations due to the piezoelectric effect. Therefore, in order to produce a piezo damping effect (preventing piezo resonance due to modulation voltage), the surface of the electrode 2 of the crystal plate 1 and the metal semi-cylindrical column 3 are joined by soldering. In this soldering work, the crystal plate 1 is heated to a high temperature.
This causes thermal stress distortion inside the device, which deteriorates the extinction ratio (the ratio of the maximum amount of output light to the minimum amount of light). Furthermore,
It is very difficult to position the crystal plate 1 for bonding while performing the soldering work, making the process extremely complicated. The present invention aims to eliminate the above-mentioned drawbacks, provide a method for manufacturing an optical modulator that exhibits a piezo damping effect, and prevents deterioration of the extinction ratio.

To achieve the above object, the present invention provides a light modulation element in which electrodes are arranged on two surfaces facing and parallel to a strong electromagnetic crystal plate, the outer shape of the strong electromagnetic crystal plate being The electrically insulating tube is made of a material having a coefficient of linear thermal expansion substantially equal to that of the strong electric crystal plate. A hole for filling an adhesive is provided in the side surface of the electrically insulating tube, and the adhesive passes through the hole and fills the four sides of the light modulation element other than the plane of the light transmission axis. This is a method of manufacturing an optical modulator, characterized in that an optical modulating element is individually held inside the electrically insulating tube.

That is, the present invention provides the piezo damping effect as follows:
The four surfaces of the light modulation element other than the light transmission axis are coated and fixed by filling the adhesive without requiring high-temperature heating.

The heat shrinkage rate of the adhesive used here should be selected appropriately, but is preferably 1% or less. If this thermal shrinkage rate is large, distortion will be applied to the crystal plate, resulting in a deterioration of the extinction ratio. According to experiments, when the extinction ratio is 1 when the thermal contraction rate is 3% and 6%, the extinction ratio becomes 0.7 and 0.05, respectively, and a deterioration of the extinction ratio appears. . Hereinafter, the present invention will be explained in detail using drawings of embodiments.

FIG. 2 is a perspective view showing an embodiment that is the basis of the present invention. Figure A shows the opposing surfaces of a crystal plate 5 made of lithium tantalate crystal, in which electrodes 6 are arranged on the main surfaces that are parallel to each other, and a connecting wire 7 is connected near the center of this main surface. The light modulation element 8 shown in FIG. The fusion direction is not limited to the direction shown in the figure, but as described later, in the case of a temperature-compensated optical modulator using two optical modulation elements, the fusion direction is It is necessary to unify the surface (same, Z-axis surface). B in the figure shows a cylindrical electrically insulating tube having an inner diameter that matches the outer shape of the light modulating element 8 shown in A, a hole 9 in the center, and a coefficient of thermal expansion approximately equal to the coefficient of thermal expansion of the crystal plate 5. 10 (for example, a glass tube), the connecting wire 7 is pulled out from the hole 9, and the heat shrinkage rate is 1.
% or less adhesive 11 (e.g., silicone resin, synthetic polyester adhesive, etc.) is filled in a sufficient amount for adhesion, and the four sides (Y plane and An optical modulator is shown in which the Z plane) is fixed to an electrically insulating tube 10. Here, the position of the hole 9 in the electrically insulating tube 10 is arbitrary, and does not need to be provided in the center as shown in the figure.

Further, although the number of holes 9 is two in the illustration, it may be three or more if necessary for the adhesive filling operation. Connection line 7
The outlet of the electrically insulating tube 10 does not need to pass through the hole 9.
It may be a closed part. In this case, the electrode 6 of the connecting wire 7
The extraction position is preferably at the electrode 6 near the opening □. It is preferable that the adhesive tensile coefficient and the crystal plate's thermal expansion coefficient are close to each other, but even if they are different, the crystal plate is filled with adhesive on all four sides other than the light transmission axis, and Since the thermal expansion coefficients of the insulating tube and the crystal plate are approximately equal, almost no stress such as warpage is applied to the surface of the crystal plate.

FIG. 3 is a perspective view showing a temperature compensated optical modulator which is an application example of the present invention.

Note that although electrodes and adhesives are used in the figure, they are not shown. Here, the light modulation elements 8', 8'' correspond to the light modulation element 8 shown in FIG. 2, and are inserted into the electrically insulating tubes 10', 10''. The electrically insulating tubes 10', 10'' compete with the electrically insulating tube 13, which has an inner diameter that matches the outer shape of the electrically insulating tube 13, and the connecting wires 7', 7'' from the light modulation elements 8', 8'' are electrically Insulation tube 10
When the connecting wires 7', 7'' are pulled out from the holes 9', 9'' in the electrically insulating tubes 10', 10'', corresponding holes 9', 9'' are provided in the electrically insulating tube 13, and the connecting wires 7', 7'' are connected to the electrically insulating tubes 10', 10''. (not shown), both optical modulators 12
', 12'' are connected in parallel and a modulation voltage is applied between both terminals.Next, the optical transmission axes of the optical modulators 12', 12'' are aligned, and the electrode surfaces are orthogonal. This orthogonal positioning means that one optical modulator 12'
Or, while rotating the 12'', pass the light through the optical modulator and adjust the extinction state to accurately determine the extinction state.And,
Fix the electrical insulation tubes 10' and 10'' with adhesive.
The crystal plates 5' and 5'' have distances of 1 and 1, respectively, at opposing points.
is the rotation work of the crystal plate by adjusting the extinction state, and since both crystal plates 5' and 5'' do not touch, the length of the latter is 1.
2 is to prevent the adhesive from adhering to the surface of the light transmission axis. In the above configuration, if the optical modulators 12' and 12'' are 1' and r, respectively, the phase change due to temperature is 2 (
n.

-n8) (1'-r)/in. (Here, no and ne are the refractive indexes for ordinary and extraordinary rays determined by each crystal material (lithium tantalate crystal in the example), and in is the wavelength of the passing light.) Therefore, 1'= 1″
If set to , a temperature-compensated optical modulator can be obtained. that's all,
As described above, according to the present invention, in the means for holding an electric crystal plate as a light modulating element, the inner diameter and the brace are aligned within an electrically insulated tube having a coefficient of linear thermal expansion substantially equal to the linear thermal expansion coefficient of the crystal plate. A crystal plate with the same external shape is inserted, and adhesive is filled through the hole in the electrically insulating tube to cover and fix all four sides of the crystal plate other than the plane of the light transmission axis. Not only can it be fixed without further heating, but it can also be resistant to changes in ambient temperature during and after fixing due to heat shrinkage from the bush adhesive and heat from the electrically insulated tube. Since stress due to expansion is not applied to the crystal plate, a stable optical modulator that does not deteriorate the extinction ratio can be provided.

The present invention makes it easy to adjust the fusion of two crystal plates, which affects the extinction ratio, which is the lifeblood of an optical modulator. Good optical modulators can be manufactured.

Furthermore, in terms of manufacturing operations, the installation position and fusion of the crystal plates can be easily determined using a simple jig, and the fixation of the crystal plates is also filled with adhesive, reducing the number of man-hours and making it easier than conventional methods. It can be provided at a comparatively low price.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a conventional optical modulator, FIG. 2 is a perspective view showing an embodiment of the present invention, and FIG. 3 is a perspective view showing an application example of the present invention. 5... Crystal plate, 6... Electrode, 8... Light modulation element, 9
...... Hole, 10... Electrical insulation tube. Little brother's figure 2nd figure

Claims (1)

[Claims] 1. A light modulation element in which electrodes are arranged on two surfaces facing a ferroelectric crystal plate and parallel to each other, with the outer shape of the ferroelectric crystal plate fitting into the inner diameter of an electrically insulating tube, The electrically insulating tube is inserted into the electrically insulating tube, and the electrically insulating tube is made of a material selected to have a coefficient of linear thermal expansion approximately equal to that of the ferroelectric crystal plate, and an adhesive is applied to the side surface of the electrically insulating tube. A hole for filling is prepared in advance, and the adhesive passes through the hole and fills all four sides of the light modulation element other than the plane of the light transmission axis to firmly hold the light modulation element inside the electrically insulating tube. A method of manufacturing an optical modulator, characterized in that: