JPH01232323A - Light guide type modulator - Google Patents

Abstract

PURPOSE:To widen the modulation band of the modulator by a simple process by forming a space part near the outside of an electrode for signals along the longitudinal direction thereof. CONSTITUTION:An earth electrode 3b and the electrode 3a for signals are formed via a buffer layer 4 on a lithium niobate substrate 11 on which light guides 2 are formed. The space part 11a is provided near the outside of the electrode 3a for signals along the longitudinal direction thereof. An air layer of a small dielectric constant is, therefore, provided by this space and the effective refractive index of the microwaves propagating in the electrode 3a is lowered by as much as the space part 11a and is approximated to the refractive index of the light waves propagating in the light guides 2. As a result, the speed difference between the light waves and the microwaves is decreased and the modulation speed is increased. The modulation band is thus widened by using the simple production process.

Description

[Detailed Description of the Invention] [Summary] With regard to waveguide type optical modulators used in optical communication systems, etc., the present invention aims to achieve a wide modulation band using a simple manufacturing process. In a waveguide type optical modulator in which a traveling wave electrode is provided on the formed lithium niobate substrate in correspondence with the waveguide, nitric acid is applied so as to form a groove near the outside of the signal electrode.

[Industrial application field]

The present invention relates to a waveguide type optical modulator used in optical communication systems and the like.

In recent years, optical communication systems with modulation speeds of several Gb/s or more have been actively researched, and for example, waveguide type optical modulator A using a LiNb0m waveguide is promising for the above-mentioned high-speed modulation. It is considered.

[Conventional technology]

As an example of a conventional waveguide type optical modulator, the configuration of a Matsuhatsu Enda type optical modulator is shown in FIG. FIG. 5(a) is a perspective view, and FIG. 2(b) is an enlarged sectional view taken along the line AA. In the figure, a substrate 1 is made of two LiNbQs plates, and a waveguide 2 is formed by diffusing Ti in a predetermined region thereof. Further, on the substrate 1, a pair of asymmetric fit poles 3a, 3b are arranged, corresponding to the two parallel waveguides 2a, 2b branched from the waveguide 2. B1.
'a pole is arranged.

In the optical modulator shown here, the length l of the traveling wave electrode is formed long, for example 21, and a micro a is formed in the same direction as the traveling direction of the light wave in the waveguide 2 with respect to one electrode 3a. propagates to perform optical modulation.

That is, depending on the modulation signal applied to the microwave, the light waves propagating in the two waveguides 2a and 2b are
” or “π”, and the source of the intensity obtained by combining (interfering) these light waves is output as modulated light.

[6pA problem to be solved by the invention] LiNb0. In an optical modulator using a waveguide, the refractive index of light waves is about 2.14, whereas the refractive index of microwaves is as large as about 4.

What makes the refractive index of microwaves a problem here is the roundness in which microwaves seep deeply from the electrodes into the substrate.

Then, due to the above refractive index difference, a speed difference will occur between the light wave and the microwave.

If there is such a speed difference, especially in a device with the above-mentioned progression e and electrode, there is a possibility that the light wave will overtake the modulation No. 16 under the long electrode. A limit had to be placed on the modulation speed to avoid this. That is, there is a problem in that the modulation band is narrow and limited.

Note that, in order to reduce the refractive index of the LiNb0m guide path for microwaves, a proposal has been made to reduce the thickness of the entire substrate to about several tens of micrometers.

However, forming the entire substrate so thinly is extremely difficult to manufacture, and furthermore, the mechanical strength becomes extremely weak, making it impossible to withstand normal use.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a waveguide type optical modulator that can achieve a wide modulation band using a simple manufacturing process.

[Means for solving ambiguity vA]

The first reason is the principle diagram for explaining the present invention, in which the light guiding slope 2 is formed, the grounding pole 3b is connected to a part of the substrate 11 via the buffer layer 4, and the signal wiring A pole 3a is formed, and a space 11a where the substrate is removed is provided near the outside of the signal electrode 2a along the direction of the attack force.

[Effect]

When a space is formed in the substrate as described above, the groove portion of the medium surrounding the bottom of the electrode becomes an air layer with a low dielectric constant instead of lithium niobate, which has a high dielectric constant. Then, the effective refractive index of the microwave becomes smaller by the amount of space (air layer) and approaches the refractive index of light waves. Therefore, since the speed difference between i[ and the microwave becomes extremely small, the modulation speed can be increased, that is, the modulation band can be widened. If the substrate is cut at the position of this space instead of the above-mentioned space, this effect will be even greater.

Furthermore, since the above-mentioned space can be easily formed using a cutting saw, the manufacturing process is also very simple.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1(a) and 1(b) are a perspective view and an enlarged BB--B sectional view of one embodiment of the waveguide type optical modulator of the present invention.

The figure shows a Tohenhadeki made by Matsuha Tsuenda.

In the figure, the substrate 11 is a Z plate LiNb019,
In the predetermined area, a waveguide 2 similar to that shown in FIG.
is formed by Ti diffusion. Through a layer of silicon dioxide (SiOz) 4, a pair of asymmetrical electrodes 3a, also similar to that shown in FIG.

A traveling wave electrode consisting of 3b is arranged. The dimensions of this electrode are set so that the effective refractive index of microwaves, which will be described later, is small. For example, the length l is about 20,
Width W is several tens of μm, gap length d is approximately 15 μm, height h
is about several μm to 10 μm.

Furthermore, the substrate 11 has a thickness of, for example, 1 to 30 μm with respect to the electrode 3a.
It has a space 11a at a position close to each other to a degree of 1. This space 11a can be obtained, for example, by cutting the end portion (fourth surface 1a side) of the substrate 1 shown in FIG. 3 along the dashed-dotted line in (b) with a cutting saw. Also,
Dry etching methods such as reactive ion etching or ion milling may also be used instead of a cutting saw. Here, the depth f of the space 11a is
For example, it is about several μm to several tens of cyim, and the space 11
The width g of a is, for example, about 10 μm to several 100 μm.

Further, the distance Q from the electrode 3a to the space 11a is, for example, from several μm to several tens of μm. Furthermore, the distance from the waveguide 2a to the space 11a is such that it has no effect on propagation through the waveguide 2a. It is set to None. Such a space 11a can be easily formed by using a cutting saw.

In the narrow path type optical FV4 device of this embodiment having the above configuration,
The micro-i propagated through the electrode 3a will seep into the substrate 11 relatively deeply, as in the conventional case. In this case, since the space 11a is formed as described above, the substrate near the electrode 3a is removed, and an air layer is created correspondingly.

Then, LiNb0. The dielectric constant of the substrate 11 is 30 to 40
Since the dielectric constant of the space 11a (air layer) is as small as 1, compared to the high degree of radiance, the effective refractive index of the microphone affji is reduced by the amount of the space 11a (air layer). Therefore, the speed of the microphone og approaches the speed of light, that is, the difference in speed between the microwave and the light wave becomes extremely small.

From this, the modulation speed can be increased beyond the conventional limit, and the modulation band can therefore be widened.

Moreover, since the space 11a can be easily formed using a cutting saw as described above, the manufacturing process becomes extremely simple.

Furthermore, compared to the conventional method in which the entire substrate is made thinner, this embodiment only forms a space near the electrode.
It has strong mechanical strength and can withstand normal use.

Next, another embodiment of the waveguide type optical modulator of the present invention is shown in FIGS. 2(a) and 2(b).

The nine embodiments shown here are configuration examples of the present invention in which the third electrode 3c is provided in the configuration shown in FIG. In this case, the space 11a is formed in the gap between the electrode 3C side where the return path 2 does not exist and the center electrode 3a. If a space is formed in the gap between the electrodes where the waveguide 2 exists, the electrical resistance of the air layer is much larger than that of lithium niobate, so the electric field is concentrated in this part and the temporary guide path is No effective electric field is applied.

Note that l + w* d + h + shown in Figure 1
' + g rQ and other dimensions are not limited to the above-mentioned numerical values, but are appropriately set in consideration of the characteristics of the optical modulator.

Moreover, between the substrate 11 and the electrodes 3a and 3b, Sio,
The back 7 layers 4 made of 3177 layers are made of LiNbQ, and are made of LiNbQ.

Since the refractive index is very small compared to the substrate, the effective refractive index of microwaves can be further reduced due to the synergistic effect with the space portion 11a described above. According to experimental results, in order to reduce the effective refractive index of microwaves, in addition to providing the buffer l- as described above,! It was confirmed that it is sufficient to increase the number of poles to 4 and narrow the wire width.

Furthermore, although the Matsuno-Zenda type was adopted in each of the above-mentioned embodiments, the present invention is not limited to this, but various types of 4IN.

It can be applied to path-type optical modulators, and particularly those using traveling electrodes can be expected to have great effects.

〔Effect of the invention〕

As explained above, according to the present invention, the air layer with a small refractive index can be reduced to 1! Since it can be provided at a distance near the other end of the spectrum, the amount of lost refraction of the microwave can be reduced by that amount, thereby making it possible to increase the modulation speed, that is, to widen the modulation band. Moreover, the manufacturing process is extremely flexible, as the grooves only need to be formed on a portion of the substrate.
Mechanical performance is also sufficient.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view of an embodiment of the waveguide type optical modulator of the present invention, and FIG. 1(b) is a perspective view of the B-BT in FIG. a) is a pP+ view of another embodiment of the waveguide type optical modulator of the present invention; FIG. 2(b) is an enlarged cross-sectional view along CC in FIG. 2(a); FIG. 3(a) is the conventional waveguide type light f? Inside the strabismus of organ A,
Figure 3(b) is the 8-person large section 1 in Figure 3(a).
It is.

Claims (1)

[Claims] A buffer layer (4) was provided over the entire area of the lithium niobate substrate (11) on which the optical waveguide (2) was formed, and a traveling wave electrode for light control was formed on a part of the buffer layer (4). In the optical modulator, the traveling wave electrode includes at least a wide ground electrode (3b) and a narrow signal electrode (3a) located opposite to the ground electrode (3b). ), a space (11a) in which the buffer layer (4) and the substrate (11) are removed is formed along the longitudinal direction of the electrode.