JPS6011326B2 - Branch type optical modulator - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to improvements in branch-type optical modulators. Conventionally, as shown in FIG. 1, a branching path type optical modulator has an input side common path section 3, an output side common path section 4, and an input side common path section in a substrate 1 having an electro-optic effect from its main surface 2 side. A waveguide 8 is formed between the output end 5 of the section 3 and the input device 6 of the output side common path section 4, and is composed of branch path sections 7A and 7B that can be extended in parallel, and on the main surface 2 of the substrate 1, Branch section 7 of waveguide 8
In the region 1 between A and 7B, there are electrodes 1 and 1 which can extend in the direction of extension of the branch passages 7A and 78, and branch passage parts A.
An electrode 13A that can be extended to face the electrode 11 across the branching path section 7A in a region 12A facing the area io across the area, and a region 12B facing the area 10 across the branching path section 7B.
A configuration has been proposed in which an extendable electrode 13B is formed facing the electrode 11 with the branching path portion 7B in between. According to the branched optical modulator having such a configuration, the input light L is input to the input side common path section 3 of the waveguide 8 from the side opposite to the output end 5 side. If the light is propagated as L, the branched light L is transmitted to the branched paths 7A and 7B, respectively.
A and LB (not shown) are branched and propagated toward the output side common path section 4, and then the branched lights LA and LB are combined at the output side common path section 4 and sent to its input end. In this case, if a modulation voltage V is applied from the modulation voltage source 14 between the electrode 11 and the electrodes 13A and 138, the output light L' propagates toward the side opposite to the electrode 13A.
1 and 13A; between the electrodes 11 and 138, electric fields in mutually opposite directions are obtained when viewed from the position of the electrode 11 passing through the branch section 7A: and 78 of the waveguide 8; thereby, the branch section 7A;
and the refractive index of 7B is relatively changed in the opposite direction,
For this reason, the branched lights LA and LB propagate to the branching path sections 7A and 7B.
The phase of the output light L' is changed in a relatively opposite direction, so that the output light L' is generally obtained as output light 1 whose intensity is modulated according to the modulation voltage V expressed by the following tl1 formula. , and if the branched lights LA and LB have the relationship E^:EB, which is equal to each other in terms of their optical electric fields E^ and E8, then the output light L' is as follows.

[2-Modulation voltage V expressed by equation
It is obtained as output light whose intensity is modulated according to the intensity. However, in m and (2-types), electrodes 11 and 13A and 13B are connected between electrodes 11 and 13A, and between electrodes 11 and 13
The electrodes 11, 13A and 13B are arranged one after another with an interval B and an equal interval W, and the electrodes 11, 13A and 13B exactly overlap each other with an equal extension length 1 when viewed from the side in the direction in which they are arranged. represents the modulated output light when
In addition, in the '1' and (2) formulas, entry is the wavelength of light, k is the wave number of light expressed in 2m/^, 1 is the length of the electrodes 11, 13A and 138 mentioned above, n is between the electrodes 11 and 13A, Electrode 11
Waveguide 8 when the modulation voltage V between and 13B is zero
The refractive index of the branching path portions 7A and 78,
2.........) is the electro-optic coefficient of the waveguide 8,
W indicates the spacing between the electrodes 11 and 13A, and the spacing between the electrodes 138, respectively. However, in the case of the configuration of the conventional branching path type optical modulator described above in FIG.
If the length 1 of electrodes 1, 13A and 138 is made large, and the distance W between electrodes 11 and 13A and between electrodes 11 and 13B is made small, the modulated output light L' can be changed to a lower value of the modulation voltage V. However, if the lengths of electrodes 11, 13A and 138 are increased, the overall structure becomes larger, and if the distance W between electrodes 11 and 13A and between electrodes 11 and 13B is decreased, Branching sections 7A and 78 of wave guiding wisteria 8 according to the
As the spacing between them becomes smaller and the mutual divergence angles on the input-side common path section 3 side and the output-side common path section 4 side of the branch path sections 7A and 7B become smaller, it propagates to the branch path sections 7A and 7B. Unnecessary coupling occurs in the branched lights LA and LB, making it impossible to obtain the output light L' as the desired modulated output light, and furthermore, the distance W between the electrodes 11 and 13A and between the electrodes 11 and 13B, and therefore the branching path of the waveguide 8. If the distance between the parts 7A and 78 is made small, the conductor loss with respect to the modulating voltage V at the electrode 11 position will increase,
For this reason, there are drawbacks such as the fact that the modulation voltage V cannot be used over a wide frequency band. Therefore, the present invention aims to propose a novel branch-type optical modulator which is based on the conventional branch-type optical modulator described above in FIG. It will become clearer from now on. 2 and 3 show an example of a branched optical modulator according to the present invention. Parts corresponding to those in FIG. In the above-described configuration, the electrodes 11, 13A and 13B are omitted, however, in the substrate 1, in the region 10' between the branch sections 7A and 78 of the waveguide 8, the branch sections 7A and 7B are formed. A groove 21 extending in the extension direction is formed, and the groove 21 is formed on the main surface 2 of the substrate 1.
A cladding layer 22 is applied to the branch portion 7A of the waveguide 8 including the inner surface of the waveguide 8, and corresponds to the electrode 11 (or 13A and 13B) described above in FIG. 1 via the cladding layer 22. The electrode 23 is also connected to the electrodes 13A and 138 described above in FIG.
It has the same structure as the case of FIG. 1 except that an electrode 24 corresponding to (or 11) is attached. The above is an example of the configuration of the branch optical modulator according to the present invention. According to this configuration, it is the same as the configuration shown in FIG. 1 except for the matters mentioned above. It is clear that if the input light L is propagated to the input side common path section 3, the output light L' that propagates to the output side common path section 4 will be obtained in accordance with this, but in this case, the light beam 21 exists. By this, the electrode 23
If a modulation voltage V is applied from the modulation voltage source 14 between the electrodes 23 and 24, the branch portion 7 of the waveguide 8 is applied between the electrodes 23 and 24.
Electric fields in opposite directions are obtained when looking inside the substrate 1 from the main surface 2 side of the substrate 1 passing through A and 7B. Therefore, the output light L' is obtained as output light whose intensity is modulated in accordance with the modulation voltage V in a manner similar to that shown in FIG. However, in the case of the exemplary configuration of the branch type optical modulator according to the present invention described above in FIGS. 2 and 3,
Region 10 between branch path portions 7A and 78 of waveguide 8 on substrate 1
Without providing an electrode above, the output light L' can be obtained as output light whose intensity is modulated according to the modulation voltage V in a manner similar to that shown in FIG. Assuming that the size is the same as in the case of FIG.
It can be larger than the length 1 of 3B (in the case of Fig. 1, the area 10
Since this is a region formed between the branch portions 7A and 7B of the waveguide 8, if the length of the electrode 11 provided in that region 10 is increased, the overall configuration becomes larger.) Also, even if the region 101 between the branching path portions 7A and 7B of the waveguide 8 of the substrate 1 has the groove 21, it does not have an electrode, and on the other hand, the groove 21 is smaller than the electrode when the region 10 is provided with an electrode. However, since this can be formed with a sufficiently small width,
Branch portions 7A and 78 of waveguide 8 between electrodes 23 and 24
The distance between the electrodes 23 and 24 can be made sufficiently smaller than the distance W between the electrodes 11 and 13A and between the electrodes 11 and 13B in the case of FIG. Even if the distance between the branching path portions 7A and 7B of No. 8 is small, the presence of the groove 21 between the branching path portions 7A and 7B prevents the branched light LA from propagating to the branching rocky portions 7A and 7B.
The unnecessary coupling of LB and LB is much smaller than in the case of FIG. This can be increased as needed, as long as it is
There is substantially no conductor loss with respect to the modulating voltage V as in the case of FIG. 1, and therefore a modulating voltage over a wide frequency band can be used as the modulating voltage V. Therefore, according to the configuration of an example of the branch path type optical modulator according to the present invention described above in FIGS. 7B, and the modulated output light L' can be effectively obtained with a low value of the modulation voltage V over a wide frequency band. It has the following characteristics. The above description merely shows one embodiment of the present invention, and various modifications and changes may be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing a conventional branching path type optical modulator;
FIG. 2 is a schematic perspective view showing an example of a branch type optical modulator according to the present invention, and FIG. 3 is a sectional view thereof. In the figure, 1 is a substrate having an electro-optic effect, 2 is a main surface, 3 is an input side common path, 4 is an output side common path, 5 is an output end of the input side common path, and 6 is an output side common path. 7A and 7B are branch portions, 8 is a waveguide, 10 is a region, 11, 13
A, 13B, 23 and 24 are electrodes, 21 is a groove, and 22 is a cladding layer, respectively. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1 In a substrate having an electro-optic effect, from the main surface side thereof, there is a parallel relationship between an input side common path section, an output side common path section, an output end of the input side common path section, and an input end of the above output side common path section. A waveguide is formed that includes first and second branching sections extending in the direction of extension of the first and second branching sections in the region between the first and second branching sections. 1. A branch path type optical modulator, characterized in that a groove is formed extending into the branch path portion, and first and second electrodes are disposed on the first and second branch portions with a cladding layer interposed therebetween.