JPH0721597B2 - Optical switch - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical switch for modulating a light wave, switching an optical path, etc. in optical communication and the like, and particularly to a waveguide type using an optical waveguide formed on the upper surface of a substrate. It relates to an optical switch.

[Conventional technology]

Optical communication systems are being put to practical use, and development is being advanced to higher-level systems with large capacity and multiple functions. New functions such as a switching function for optical transmission line networks, high-speed connection between terminals in an optical data bus, and switching are required, and the need for an optical switching network that enables them is increasing. Currently used optical switches mechanically move prisms, mirrors, fibers, etc., and have drawbacks such as low speed, insufficient reliability, large shape, and unsuitable for matrix formation. There is. What is being developed as a means for solving these drawbacks is a waveguide type optical switch using an optical waveguide installed on a cut plate, which is capable of high speed, integration of multiple elements, high reliability, etc. There are features. In particular, a material using a ferroelectric material such as LiNbO ₃ crystal is characterized by high efficiency because it has small light absorption and low loss and has a large electro-optical effect.

FIG. 3 shows a perspective view of a directional coupling type optical switch which is an example of a conventional waveguide type optical switch. Optical waveguides 31 and 32 are formed by diffusing a metal such as Ti on a LiNbO ₃ crystal substrate 10 which is cut out and shaped perpendicular to the optical axis. These optical waveguides 31,
32 forms an optical directional coupler 35 by being installed close to each other with an interval of about several μm, and a SiO ₂ film (not shown in FIG. ₂ is a buffer layer on the optical waveguides 31 and 32. ) Via the control electrodes 33 and 34.

The basic operation principle of this optical switch is as follows.First, the optical wave 16 incident from one end face of the optical waveguide 31, for example, propagates in the optical waveguide 31, and the optical waveguides close to each other at the optical directional coupler 35 portion. Energy transfer to 32, optical directional coupler 35
When the length of is matched with the full bond length L _C , almost 100%
Energy is transferred to the optical waveguide 32 and becomes emitted light 37. On the other hand, when a voltage is applied between the control electrodes 33 and 34, the refractive indexes of the optical waveguides 31 and 32 change due to the electro-optical effect, and the refractive indexes of the both become asymmetric, and the phase between the light waves propagating through them is increased. A mismatch occurs and the coupling state changes, and under an appropriate applied voltage, energy is transferred to the original optical waveguide 31 and the emitted light 38
Becomes

Conventionally, there are methods such as total reflection type, balanced bridge type, and Y-branching type in the waveguide type optical switch in addition to the directional coupling type as described above. It is known that the directional coupling type can be lowered relatively easily and has the simplest configuration. Among them, an electric field is applied in the depth direction of a crystal having an electro-optical effect cut out perpendicularly to the optical axis. It is also known that by means a low switch voltage is obtained and is easy to manufacture.

[Problems to be solved by the invention]

However, the directional coupling type optical switch has a coupling length L
And an applied voltage V are in inverse proportion to each other, and there is a drawback that a predetermined action cannot be obtained unless the coupling length L is increased in order to further lower the applied voltage.

An object of the present invention is to provide an optical switch having a low applied voltage V with respect to the same conventional coupling length L, except for the drawbacks of the conventional waveguide type optical switch described above.

[Means for solving problems]

The optical switch of the present invention comprises an optical directional coupler formed of two optical waveguides adjacent to each other formed on a crystal substrate having an electro-optical effect cut out perpendicularly to the optical axis,
A pair of main control electrodes respectively installed on the two optical waveguides via a buffer layer, and a pair of main control electrodes opposed to the one pair of main control electrodes and close to the two optical waveguides, respectively. It is characterized by comprising a pair of secondary control electrodes.

[Action]

In the conventional directional coupling type optical switch, the control electrode is provided only on the two waveguides forming the directional coupler, and the electric field caused by the control electrode causes a change in the refractive index. Can realize the same refractive index change at a low voltage by combining the respective electric fields of the main control electrode and the secondary control electrode. A buffer layer typified by a SiO ₂ film or the like is provided between the crystal substrate and the main control electrode and between the crystal substrate and the secondary control electrode to reduce absorption loss due to light leakage from the crystal substrate. However, by removing the buffer layer from under the secondary control electrode, the electric field can be concentrated on the crystal by the rate at which the layer where the electric field is likely to be concentrated due to the low dielectric constant is removed, and the voltage can be reduced.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the optical switch according to the present invention, and FIG. 2 is a sectional view thereof.

The optical switch of the present embodiment has a thickness of several hundred to 1,000 Å and a width of several to several thousand Å on a Z-axis cut LiNbO ₃ crystal substrate 10 having the same shape as the conventional directional coupling type optical switch shown in FIG. The optical waveguides 11 and 12 formed by thermally diffusing a Ti film pattern of ten and a few μm are arranged close to each other to form an optical directional coupler 15. A buffer layer 21 made of, for example, a SiO ₂ film is provided on the crystal substrate 10 having the optical directional coupler. Main control electrodes 13 and 14 are provided on the optical waveguides 11 and 12 via a buffer layer 21, respectively. Further, the main control electrodes 13 and 14 are opposed to the main control electrodes 13 and 14, respectively. Control electrodes 19 and 20 are provided on crystal substrate 10 with buffer layer 21 interposed therebetween. The length of the optical directional coupler 15 is set to be substantially equal to the complete coupling length L _C for both TM and TE modes, as in the conventional example. Its length is usually several mm to several tens of mm.

The basic operation principle of the optical switch configured as described above is the same as that described with reference to FIG. First, one optical waveguide, for example, the light wave 16 incident from the end face of the optical waveguide 11 propagates in the optical waveguide 11, energy is transferred to the optical waveguide 12 which is close to the optical directional coupler 15, and the optical directional coupling is performed. Bowl 15
Since the length of the match to the complete coupling length L _C, almost 100%
Energy is transferred to the optical waveguide 12 and becomes the emission hole 17.

On the other hand, when a voltage is applied between the secondary control electrode 19 and the main control electrode 13, between the main control electrodes 13 and 14, and between the main control electrode 14 and the secondary control electrode 20, the electro-optical effect Due to this, the refractive indices of the hole waveguides 11 and 12 are changed and the refractive indices of the two become asymmetrical, phase mismatch occurs between the light waves propagating through them, and the coupling state changes, and even under an appropriate applied voltage. Energy is transferred to the optical waveguide 11 and becomes emitted light 18.

The directional coupling type switch of the present embodiment is different from the conventional directional coupling type optical switch shown in FIG. 3 in that the conventional directional coupling type optical switch is on two waveguides constituting a directional coupler. The control electrode is disposed only on the first control electrode, and the change in the refractive index is caused by the electric field caused by the control electrode. On the other hand, in the present embodiment, the respective electric fields caused by the main control electrodes 13 and 14 and the secondary control electrodes 19 and 20 are changed. By synthesizing them, it is possible to realize the same change in refractive index at a low voltage.

For example, as shown in FIG. ₂ , if voltages V ₁ , V ₂ and V ₃ having different polarities are alternately applied between the electrodes, the electric field strength is higher than that of the conventional optical switch shown in FIG. Is increased and the electric field distribution can be made symmetrical as shown by the arrow in the figure, and an optical switch with a reduced applied voltage can be obtained.

In the above embodiments, the buffer layer 21 is provided below the secondary control electrodes 19 and 20, but by removing this buffer layer from under the secondary control electrodes, it is possible to concentrate the electric field on the crystal, Further lower voltage can be achieved.

[Effects of the Invention] As described above, according to the present invention, it is possible to obtain an optical switch that has a lower switch voltage than the conventional optical switch and is easy to manufacture.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an optical switch according to the present invention, FIG. 2 is a sectional view of the optical switch of FIG. 1, and FIG. 3 is a perspective view showing an example of a conventional optical switch. 10 …… Z-axis cut LiNbO ₃ crystal substrate 11,12,31,32 …… Optical waveguide 13,14 …… Main control electrode 15,35 …… Optical directional coupling group 19,20 …… Secondary control electrode 16… … Light wave 17,18,37,38 …… Outgoing light 21 …… Buffer layer 33,34 …… Control electrode

Claims (3)

[Claims] 1. An optical directional coupler composed of two optical waveguides adjacent to each other formed on a crystal substrate having an electro-optical effect cut out perpendicularly to an optical axis, and a buffer on the two optical waveguides. A pair of main control electrodes, each of which is disposed via a layer; and a pair of secondary control electrodes, which are respectively opposed to the one pair of main control electrodes and are disposed close to each of the two optical waveguides. Optical switch characterized by being composed of. 2. The optical switch according to claim 1, wherein the pair of secondary control electrodes are provided on the crystal substrate via a buffer layer. 3. The optical switch according to claim 1, wherein the pair of secondary control electrodes are directly arranged on the surface of the crystal substrate.