JPS6227364B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical switch that has the function of switching a propagation optical path to another optical path in an optical communication system or an optical information processing system, and in particular electrically controlled optical This invention relates to an optical switch capable of switching.

In optical communication systems and information propagation systems using light, signal speeds are being increased with the aim of expanding transmission capacity. However, in reality, there are limits to the modulation speed of light and to the broadband optical fiber, and sufficient capacity cannot be obtained just by increasing the signal speed. Therefore, optical wavelength division multiplexing transmission systems are attracting attention as a method for increasing capacity. In an optical wavelength division multiplexing transmission system, light waves of multiple wavelengths are modulated independently and transmitted simultaneously, so it can be used for terminal equipment,
A receiving device requires a device that separates transmitted light for each wavelength and couples it to different optical paths. Furthermore, a switch between the optical paths is required to electrically switch between the optical paths and connect the optical paths to multiple terminal devices at high speed.

Conventionally, known devices with wavelength separation mechanisms include interference filters made of multiple layers of dielectric films, prism-shaped duplexers that utilize refractive index wavelength separation, and duplexers that utilize diffraction gratings. There is. However, in all of the above devices, the optical path is fixed for each wavelength, and a separate device is required to switch between optical paths. Furthermore, a device is required to switch the optical path for each wavelength. Such an increase in the number of devices increases the number of devices and reduces their reliability. In order to reduce the size and cost of the device, it is desirable to have as few devices as possible.

The purpose of the present invention is to provide an optical wavelength separation switch that is different from the above-mentioned simple optical wavelength separation device and is capable of separating incident light into each wavelength and at the same time electrically switching to different optical paths at high speed. be.

The optical wavelength separation switch of the present invention has a plurality of electrodes each having a different period along the light transmission direction on a crystal surface exhibiting an electro-optic effect in which an optical index ellipsoid rotates when an electric field is applied. These electrodes are provided one after the other, a voltage generator is provided on the electrode, and a birefringent substance is provided on the output side of the crystal.

Generally, when an electric field is applied in the X-axis or Y-axis direction of a lithium tantalate crystal, the optical index ellipsoid of the crystal rotates due to the electrical optical constant Υ ₅₁ or Υ ₄₂ , and in the plane perpendicular to the Z-axis. The polarization component of the light wave traveling parallel to the crystal principal axis is slightly converted into the polarization component perpendicular to it. The direction of the above electric field is periodically reversed along the light traveling direction, and the period Λ is
When a value that satisfies equation (1) is selected, the conversions between the mutually orthogonal polarization components are added, and the conversion efficiency increases.

2π/Λ=2π/λ(ne − n _p )……(1) Here, λ is the wavelength of light in _vacuum , and n _p and _ne are the refractive index of the crystal for ordinary light and extraordinary light, respectively. .

The detailed principle of the above conversion is described in Japanese Patent Application No. 82095/1982. In the present invention, the conversion of the polarization component described above is performed using the wavelength λ of the incident light.
This method takes advantage of the fact that it depends on the value of . Note that the above operation is not limited to lithium tantalate crystals, but can also be obtained with other crystals having similar electro-optic effects.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of an optical wavelength separation switch according to the present invention.

In Figure 1, 1 is cut out parallel to the X plane,
It is a lithium tantalate crystal (LiTaO ₃ ) formed to transmit light in the Y-axis direction. Incident light 2
is a composite wave that is transmitted by independently modulating light waves with center wavelength λ ₁ and center wavelength λ ₂ , and is a light wave that passes through a polarizer and has only a polarization component in the Z-axis direction. . An interdigital electrode 3 having a period Λ ₁ and an interdigital electrode 4 having a period Λ ₂ are placed on the crystal 1 as shown in FIG.

Here, Λ ₁ is a value obtained by substituting λ ₁ into the value of λ in equation (1), and Λ ₂ is a value obtained by similarly substituting λ ₂ . By applying a voltage to the electrode 3 by a voltage generator 13 and by applying a voltage to the electrode 4 by a voltage generator 14, an electric field in the X-axis direction is periodically generated in the crystal 1 in the Y-axis direction. be able to. A birefringent material is provided on the output side of the crystal.

When no voltage is applied to the electrodes 3 and 4, the emitted light 5 from the crystal has only the original polarization component in the Z direction. However, when a voltage is applied to the electrode 3, only the component of the wavelength λ ₁ of the incident light 2 is converted into a polarized component in the X direction, and when a voltage is applied to the electrode 4, only the component of the wavelength λ ₂ is polarized in the X direction. converted into components. The voltage applied in the above operation is selected to a value that allows 100% conversion of the polarization component at each wavelength.

The values of λ ₁ and λ ₂ must be separated by at least a separable width. For example, if λ ₁ = 8500 Å and the number of electrodes 3 is 200, the wavelength width in which polarization components are effectively converted is 150 Å or less, that is, the separation width is 150 Å or more, so in this case, λ ₂ <
It is sufficient if 8150 Å or 8650 Å<λ ₂ . When a voltage is applied to both electrodes 3 and 4, all incident light 2 is converted into polarized light components in the X direction. The light 5 that has passed through the crystal 1 passes through a birefringent substance 6 such as calcite or rutile, which has an optical axis in a direction other than the Y-axis or Z-axis direction in the Y-Z plane, thereby changing the polarization component in the Z-axis direction. is the output light 7, and the polarization component in the X-axis direction is the output light 8.
separated into

Due to the above operation, when a voltage is applied only to the electrode 3, the light wave with wavelength λ ₁ becomes the emitted light 8, and the light wave with wavelength λ
_{The two} light waves are separated into output light 7. Conversely, when a voltage is applied only to the electrode 4, the light wave with wavelength λ ₁ becomes output light 7 and the light wave with wavelength λ ₂ becomes output light 8. Since the above conversion is performed electrically, in this embodiment it is possible to separate the wavelengths and switch the propagation optical path at high speed.

FIG. 2 is a diagram showing the principle configuration of another embodiment according to the present invention. In FIG. 2, incident light 22 is a light wave polarized in the Z-axis direction including three wavelength components of ₁ , λ ₂ , and λ ₃ that are each independently modulated. Periods Λ ₁ and Λ are formed on the lithium tantalate crystal 21, respectively.
₂ , three types of interdigital electrodes 23 of Λ ₃ ,
24, 25 are installed and voltages are applied to them by voltage generators 33, 34, 35, respectively. Λ
₁ and λ ₁ , Λ ₂ and λ ₂ , Λ ₃ and λ ₃ are each (1)
satisfies the expression. When a voltage is applied to the electrodes 23, 24, and 25, the light wave components of wavelengths λ ₁ , λ ₂ , and λ ₃ are respectively converted into polarized light components in the X-axis direction. The light wave converted in the X-axis direction passes through a birefringent material 26 provided on the output side of the lithium tantalate crystal 21, is separated from the polarized light component in the Z-axis direction, and enters the optical fiber 30 through a microlens 28.
On the other hand, the polarized light component in the Z-axis direction that has passed through the crystal 21 enters the optical fiber 31 through the microlens 29 . In this embodiment, when a voltage is applied to any of the electrodes 33, 34, and 35, only the wavelength corresponding to that electrode, for example, λ ₁ for the electrode 33, enters the optical fiber 30, and the other wavelength components are The light enters the optical fiber 31.

In the present invention, by reducing the thickness of the modulation medium and making the modulation medium thin, the voltage required for modulation can be lowered and higher modulation efficiency can be obtained.

The above-mentioned means for thinning include a method of mechanically polishing the modulation medium to make it thin, a method of placing the modulation medium on another substrate by vapor deposition, sputtering, etc., a method of diffusing metal etc. on the surface of the modulation medium, There are methods to pass light waves there, methods to grow crystals of a modulation medium thin film on another substrate, etc. When the thickness of the modulation medium thin film is reduced to several tens of microns or less using the above method, it is usually called a thin film optical waveguide, and it is known that light waves propagate while being confined within the thin film. At this time, since the light wave is separated into a plurality of propagation modes, the optical modulator must be designed in consideration of the equivalent refractive index of the target propagation mode.

As described above, according to the present invention, it is possible to separate a light wave containing a plurality of wavelength components into different propagation optical paths for each wavelength, and to switch the propagation optical paths electrically and at high speed. A separate switch can be obtained.

The configuration for implementing the present invention is not limited to the above-described embodiments. For example, it is also possible to use a plurality of crystals and provide electrodes with different periods. Further, the crystal material, the means for separating orthogonal polarization components, and the shape thereof are not limited to the above-mentioned embodiments. For example, a mixed crystal of lithium tantalate and lithium niobate, a lead niobate crystal, or the like can be used as the crystal material, and a prism-shaped birefringent substance can be used as the means for separating orthogonal polarization components.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the optical wavelength separation switch according to the present invention, and FIG. 2 is a diagram showing the principle configuration of another embodiment of the optical wavelength separation switch according to the invention. In the figure, 1 is a lithium tantalate crystal,
2, 22 are incident lights, 3, 4, 23, 24, 25 are interdigital electrodes, 13, 14, 33, 3
4 and 35 are voltage generators, and 6 and 26 are birefringent substances.

Claims (1)

[Claims] 1 An electro-optic crystal exhibiting an electro-optic effect in which the principal axis of an optical index ellipsoid rotates when an electric field is applied, and an electric field perpendicular to the light transmission direction of the crystal is applied periodically in the light transmission direction. a plurality of periodic electrodes placed on the crystal for applying voltage into the crystal;
comprising a plurality of voltage generators connected to the electrodes in a 1:1 ratio, and a birefringent material for changing the propagation optical path of the light emitted from the electro-optic crystal according to its polarization direction, An optical wavelength separation switch characterized in that the periods of the plurality of periodic electrodes are different from each other.