JPH01114830A - Optical circuit element applying electro-optical effect - Google Patents

Abstract

PURPOSE:To effectively control a signal light with a low voltage by constituting the title element so that the polarization component of a signal light which cannot be controlled by a first optical switch is made incident on a second optical switch as a polarization component which can be controlled by the second optical switch. CONSTITUTION:Under a low control voltage, a signal light R is made incident on the optical waveguide 80 of a substrate 31a from an input fiber 34a, and reaches an optical switch 33a of the right end. Also, the signal light R is refracted in the left direction by an optical switch 90 of the first stage of the optical switch 33a brought to two-stage connection. In this case, the horizontal polarization component of the signal R can be controlled completely by the optical switch 90, but a vertical polarization component cannot be controlled completely, and a part there of is made incident on an optical switch 33b through an optical switch 92 and a polarized wave maintaining fiber 32. The vertical polarization component of this signal light R rotates by 90 deg. in conformity with the torsion of the fiber 32 in the course of advancing through the polarized wave maintaining fiber 32, therefore, becomes a horizontal polarization component against a crystal axis C of a substrate 31b. Therefore, said component can be controlled completely by the low control voltage, and it does not occur that this polarization component is superposed on other signal light.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical circuit element, and particularly to an optical circuit element to which an electro-optic effect is applied, which is applied to an optical switch.

(Prior Art) An optical matrix switch, in which an optical waveguide is formed on a dielectric crystal substrate and electrodes are provided for switching light by utilizing the electro-optic effect of this substrate, can be formed relatively compactly. Furthermore, it can operate at low operating voltage. When a voltage is applied to the electrodes of the optical switch, the refractive index of the dielectric crystal changes due to the electro-optic effect. Therefore, the signal light incident on the optical waveguide can be refracted along the optical waveguide by the optical switch. However, the electro-optic effect of dielectric crystals is
It has the characteristic that its effect is large only for specific electric field directions and light polarizations. In other words, even if the voltage applied to the optical switch is constant, the degree of change in the refractive index of the dielectric crystal varies depending on the relationship between the direction of the voltage and the orientation of the crystal.Therefore, the optical switch is able to detect polarized light with a large refractive index. It was unable to function adequately except for signal light.

In order to solve these shortcomings, for example, James
E. Watson, et al. “A Po1a
rization l X113 Guided-Wa
ve 0ptical 5w1tch Integra
ted an Lithium N1obate”, J
our own'of LightwaveTecbno
lag2. Val, LT-4, No, 11. 17th
Pages 17 to 1721 (Novesber 198B)
There are some things mentioned in .

This applies a high voltage to an optical switch to refract even polarized light components with a small electro-optic effect.゛(Problem that the invention seeks to solve).

However, in this case, when the dielectric crystal substrate is, for example, lithium niobate, it is necessary to apply a voltage approximately 5 to 6 times higher to the optical switch than when refracting a specific polarized light having a large refractive index. By applying such a voltage to the dielectric crystal substrate, it is possible to prevent polarized light components with a small electro-optic effect from proceeding to other optical waveguides instead of proceeding to a predetermined optical waveguide and adversely affecting other signal lights. It is possible. However, because a high voltage is applied, the advantage of an optical switch that utilizes the electro-optic effect, which is a low operating voltage, is lost.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks of the prior art and to provide an optical circuit element that uses an electro-optic effect and has a low operating voltage and can control signal light having a plurality of polarization components.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention includes a crystal material having anisotropy in the electro-optic effect, and an optical waveguide through which signal light is transmitted is formed. a first optical switch means disposed on the main surface of the first substrate and guiding the signal light to a desired optical waveguide by changing the refractive index of the first substrate; a second optical switch means disposed on the main surface of the second substrate and controls the path of the signal light by changing the refractive index of the second substrate; A connection for connecting the first and second optical switch means such that the polarized light component that is not guided to the desired optical waveguide is input to the second optical switch means as a polarized light component that can be controlled by the second optical switch means. means.

(Function) According to the present invention, the signal light incident on the optical waveguide of the first substrate is guided to the desired optical waveguide by the first optical switch means. The polarized light component of the signal light that is not guided to this optical waveguide is input to the second optical switch means and is controlled so as not to affect other signal light.

(Example) Next, an example of an optical circuit element to which the electro-optic effect according to the present invention is applied will be described in detail with reference to the accompanying drawings.

With reference to FIG.
A perspective view of an embodiment applied to a 7-board of AN) is shown. This node includes two substrates 1a and 1b each having an optical switch for switching light,
Two input/output fibers 4a to 4d are connected to each of these substrates, forming a 2×2 switch.

The substrates 1a and 1b are formed of dielectric crystals such as lithium niobate (LiNb03) or tantalum tantalate (LrTa03), which have a large electro-optical effect. These substrates are in the shape of rectangular parallelepiped plates, and are connected in a cross shape by connecting surfaces 2 such that the substrate 1a is vertical and the substrate 1b is horizontal, and the crystal axes C are different from each other by 90 degrees. The electro-optic effect is a phenomenon in which the refractive index of a crystal changes depending on the relationship between the direction of an applied electric field and the direction of the crystal axis C. The polarization components differ by 80 degrees.

An optical waveguide 70 is formed on the substrate 1a, and an optical waveguide 74 is formed on the substrate 1b. Further, an optical waveguide 72 is formed spanning the substrate 1a and the substrate 1b. The optical waveguides 70, 72 and 74 are formed by depositing a light-diffusing material, such as titanium oxide, on a substrate and then heating and oxidizing it to infiltrate the titanium into the substrate. .

The optical waveguide 70 is formed on the right side portion 8 of the substrate 1a and is an optical path connecting the input fiber 4a connected to the center of the front portion 10 and the output fiber 4C connected to the upper portion of the rear portion 12. As shown in Figure 1, the optical waveguide 70 extends from the front part 10 parallel to the upper surface of the substrate 1a to the center, and connects to the fiber 4C connected to the rear part 12 with the electrode 50 of the optical switch 3a disposed in the center as a boundary. It is slanted upwards.

The optical waveguide 74 is formed on the upper surface part 9 of the substrate 1b, and connects the input fiber 4d connected to the right side of the front part 14 and the rear part 1.
This is an optical path connecting the output fiber 4b connected to the center of the optical fiber 6. The optical waveguide 74 is inclined toward the center from the right side of the front part 14 as shown in the figure, and is connected to the optical switch 3b disposed at the center.
The fiber 4b is bent parallel to the side surface of the electrode 62.
It is growing up to. The optical waveguide 72 is located between the optical waveguide 70 and the optical waveguide 72, and is formed between the electrode 52 of the optical switch 3a and the electrode 82 of the optical switch 3b.

The optical switch 3a is composed of electrodes 50 and 52, and these electrodes are arranged so that optical waveguides 70 and 72 are sandwiched between them. Further, the optical switch 3b is composed of electrodes 60 and 62, and these electrodes are also arranged so that optical waveguides 72 and 74 are sandwiched therebetween. The switches 3a and 3b utilize the electro-optic effect of dielectric crystals, and when a voltage is applied to the electrodes of these switches,
The refractive index of the dielectric crystal portion changes. For this reason,
An optical signal that has traveled straight through an optical waveguide does not travel straight, but instead bends and travels along the optical waveguide.

The fiber 4aΦ4C connected to the substrate 1a and the fibers 4b to 4d connected to the substrate 1b are media for transmitting signal light between each mate of the local area network, and are centered around a high refractive index core. This is an optical fiber in which a cladding with a low refractive index is formed.

A voltage is normally applied to the switch 3a disposed on the substrate 1a and the switch 3b disposed on the substrate 1b. Therefore, the signal light incident on the input fiber 4a is outputted to the output fiber 4C via the optical waveguide 70, and the signal light incident on the input fiber 4d is outputted to the output fiber 4b via the optical waveguide 74. Furthermore, when no voltage is applied to the switches 3a and 3b, the signal light incident on the fiber 4a travels straight as it is, leading to the optical waveguide 7.
0. Fiber 4 via optical waveguide 72 and optical waveguide 74
It is output from b.

FIG. 2 is a diagram showing the operating principle of the node in FIG. 1. Using the figure, a signal light 24 having two polarized components inputted from an input fiber 4a is transmitted to a switch 3a and a switch 3a.
It will be explained that the signal is controlled by b and is output to the output fiber 4C. Note that it is assumed that a voltage is applied to the switches 3a and 3b.

The signal light 24 has a polarization component 22 parallel to the crystal axis C and a polarization component 23 perpendicular to the crystal axis C. When the signal light 24 travels straight through the optical waveguide 70 and reaches the switch 3a, the signal light 24 passes through the electrode 5 of the switch 3a.
0 and 52, the refractive index of the crystal of the substrate 1a changes and bends along the waveguide 70. At this time, the polarization component 22 is completely controlled by the switch 3a because it is parallel to the crystal axis C, but the polarization component 23 is not completely controlled by the switch 3a because it is perpendicular to the C axis. Therefore, as shown by the dotted line in the figure, a part of the polarized light component 23 travels along the optical waveguide 70 as a polarized light component 23a, but the other polarized light component 23b continues straight through the optical waveguide 70.
It leaks.

As described above, the direction of the crystal axis C of the substrate 1b is 80 degrees with respect to the crystal axis C of the substrate 1a. Therefore, when the polarized light component 23b travels through the optical waveguide 72 and reaches the substrate 1b, it becomes a polarized light component parallel to the crystal axis C thereof. The polarization component 23b is therefore fully controllable by the switch 3b.

Therefore, even if another signal light is transmitted from the input fiber 4d to the output fiber 4b, the polarization component 23b of the signal light 24 will not be superimposed on this signal.

Note that if a voltage that is, for example, twice as much as required to refract the polarized light component parallel to the crystal axis C is applied to the switch 3a, most of the polarized light component 23 perpendicular to the crystal axis C is directed to the optical waveguide 70. can be refracted along. If there is no switch 3b, in order to prevent the polarized light component 23b from having any effect on the signal light passing through the optical waveguide 74, it is necessary to apply a voltage about 5 to 6 times higher to the switch 3a. However, in this embodiment, the leaked polarized light component 23b can be completely controlled by the switch 3b so as not to be superimposed on the signal light passing through the optical waveguide 74 as described above. For this reason, it is sufficient to apply to the switch 3a a voltage that is, for example, about twice the voltage required to refract the polarized light component 22.In this way, in this embodiment, the switch 3a and the switch 3b are provided on the substrate 1a and the substrate tb, respectively. Furthermore, by arranging the directions of the crystal axes C of both substrates to be 90 degrees, it is possible to completely control both polarization components 22 and 23 of the signal light 24 with a low voltage.

FIG. 3 shows an embodiment in which the optical circuit element according to the present invention is applied to a 3×3 optical switch 100. switch 1
00 has substrates 31a and 31b, and these substrates are connected by nine polarization maintaining fibers 32.

A cross-sectional view of the polarization maintaining fiber 32 is shown in FIG. Cross section 38a is a cross section of connection surface 35a with substrate 31a, and cross section 313b is a cross section of connection surface 35b of substrate 31b.
This is a cross section of As is clear from the figure, the connecting surfaces 35a and 35b of the polarization maintaining fiber 32 are connected such that their axes are 80 degrees apart from each other.

The polarization maintaining fiber 32 has a high refractive index core 3B at the center, and two birefringent bodies 38 having a birefringence inducing structure are disposed on both sides of the core 3B. The birefringent body 38 is provided to rotate the polarization component of the signal light incident on the polarization maintaining fiber 32 accordingly. As mentioned above, the axes of the connecting surface 35a and the connecting surface 35b are 90 degrees apart from each other.
Since the polarized light component is parallel to the C-axis of the substrate 31a at the connection surface 35a, the signal light with the polarization component horizontal to the C-axis of the substrate 31a is
1b as a polarized component perpendicular to the C axis. Note that the core 36 and the birefringent body 3B are surrounded by a cladding 37 having a low refractive index.

The substrate 31a is a rectangular plate made of dielectric crystal, and has an optical waveguide 80 and three sets of 1×3 optical switches 33.
It has a. The substrate 31b is a rectangular plate made of dielectric crystal like the substrate 31a, and has an optical waveguide 82.
and three sets of 3X'1 corresponding to the optical switch 33a.
It has an optical switch 33b. Note that these are the substrate 31a
and 31b, and the crystal axis C of these substrates is
is perpendicular to the top surface.

The optical waveguides 80 and 82 are, for example, the optical waveguide 7 described above.
They are formed on each substrate by the same method as 0.

The optical switch 33a is a 1×2 optical switch 80 and 92
By connecting them in two stages, a 1×3 optical switch is formed. Similarly, the optical switch 33b forms a 3×1 optical switch by connecting 2×1 optical switches 94 and 9B in two stages. The optical switches 90 to 88 are optical switches that utilize the electro-optic effect in a dielectric crystal having a set of electrodes, similar to the optical switch 3a described above.

The operation in which signal light R having two polarization components horizontal and perpendicular to the crystal axis C of the substrate 31a is input from the input fiber 34a at the right end and output from the output fiber 34b at the left end will be described. The signal light R is input from the input fiber 34a to the optical waveguide 80 of the substrate 31a, and is passed through the optical switch 3 at the right end.
Reach 3a. The @ light R is refracted to the left by the first optical switch 90 of the optical switches 33a connected in two stages. At this time, the horizontal polarization component of the signal R can be completely controlled by the optical switch 90, but the vertical polarization component cannot be completely controlled as described above, and some of it is controlled by the optical switch 3.
2 and the optical switch 33b via the polarization maintaining fiber 32.
incident on .

The vertical polarization component of the signal light H is rotated by 90 degrees according to the twist of the polarization maintaining fiber 32 while traveling through the polarization maintaining fiber 32, and thus becomes a horizontal polarization component with respect to the crystal axis C of the substrate 31b. Therefore, it can be completely controlled by the switch 33b, and this polarized light component will not be superimposed on other signal lights.

In this embodiment, the polarization component of the signal light is rotated by 80 degrees using the polarization maintaining fiber 32, so that the switch
The switch 33b converts the vertically polarized light component which cannot be controlled by the switch 33a into a horizontally polarized light component, thereby making it possible to control the vertically polarized light component. Therefore, it is possible to control the signal light without applying a high voltage to the optical switch to refract the vertically polarized component as in the prior art. Although the same embodiment used a 3×3 type optical matrix switch, the present invention is not limited to this.
It is applicable to XN type optical matrix switch, NXN type optical matrix switch and MXN type optical matrix switch.

(Effects of the Invention) According to the present invention, the polarization component of the signal light that cannot be controlled by the first optical switch disposed on the first substrate can be controlled by the polarization component of the signal light that cannot be controlled by the first optical switch disposed on the first substrate. The light is input to a second optical switch as a polarized light component that can be controlled by an optical switch. Therefore, it is possible to control signal light with multiple polarization components, and compared to controlling multiple signal lights with a single-stage optical switch, signal light can be controlled with a voltage of about 173 to 273. It is possible to do so.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a node of a local area network to which an optical circuit element applying the electro-optic effect according to the present invention is applied, and FIG. FIG. 3 is a perspective view showing an embodiment of a 3X3 type optical matrix switch to which an optical circuit element applying the electro-optic effect according to the present invention is applied. FIG. FIG. 4 is a cross-sectional view of the polarization maintaining fiber used in the embodiment of FIG. 3; The storage of signs of the parts la, lb, 31a, 31b, , substrates 3a, 3b,
33a, 33b, , 'Optical switches 4a, 4d, 3
4a , , , , inputry 7 Iha 41), 4
c, 34b , , , Output fiber 32 , , ,
, , polarization maintaining fiber 50, 52, 80, 82
, , ,electrode? 0,72,74,80,82. ,
, Optical waveguide patent applicant Oki Electric Industry Co., Ltd. Representative Takao Katori Takao Maruyama Optical node using optical circuit elements Figure 1 Operating principle of node Figure 3 Cross section of polarization maintaining fiber Figure 4

Claims (1)

[Claims] 1. A first and a second waveguide including a crystal material having anisotropy in an electro-optic effect and forming an optical waveguide through which signal light is transmitted.
a first optical switch means disposed on the main surface of the first substrate and guiding the signal light to a desired optical waveguide by changing the refractive index of the first substrate; and a second substrate. a second optical switch means disposed on the main surface of the second substrate for controlling the path of the signal light by changing the refractive index of the second substrate; connecting means for connecting the first and second optical switch means so that the polarized light component not guided to the optical waveguide is input to the second optical switch means as a polarized light component that can be controlled by the second optical switch means; An optical circuit element applying an electro-optic effect characterized by comprising: