JPS6263913A - Optical isolator - Google Patents

Abstract

PURPOSE:To intercept completely the reflected return light even if the ambient temperature is changed, by providing a wedge-shaped magnetooptic element, whose thickness is changed gradually in the direction vertical to the optical axis, for a piezoelectric element which has one end part fixed and is displaced by a voltage. CONSTITUTION:When the ambient temperature rises, the polarized light component whose rotation in the polarization direction is shifted from 45 deg. in an analyzer 7 is not transmitted through the analyzer 7 and becomes a reflected component. This reflected component is received by a photodetector 20, and the electric output after photoelectric conversion is amplified by an amplifier 21 and is led to a piezoelectric element controller 22, and a voltage corresponding to the reception power of the photodetector 20 is outputted from the piezoelectric element controller 22. This voltage is led to an electrode part 23 of a piezoelectric element 10, whose one end part is fixed by a fixing part 11, to displace the piezoelectric element 10. The thickness on the optical axis of a wedge-shaped magnetooptic element 1 which is provided for the piezoelectric element 10 and is joined with a magnet 9 into one body is changed along a guide 12 in accordance with said displacement, and the rotation angle of the polarization direction of the light transmitted through the wedge-shaped magnetooptic element 1 is increased and is corrected to 45 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application Page 2 The present invention relates to an optical isolator used for optical signal transmission such as optical communication.

Conventional Technology When a semiconductor laser is used as a light source for an optical signal transmission system such as optical communication, a part of the light emitted from the semiconductor laser is reflected at the transmission path or at each connection of the transmission optical components, causing the semiconductor laser to emit light. If it returns to , it causes instability of the oscillation characteristics of the semiconductor laser and an increase in noise. An optical isolator is generally used to prevent this reflected light from returning.

Conventional optical isolake is disclosed in Japanese Patent Application Laid-Open No. 66-2111, for example.
As shown in Publication No. 3, the structure was as shown in Figure 2 a and b. 2A shows a fiber type optical isolator, and FIG. 2A shows a semiconductor laser-coupled optical insulator.

That is, as shown in FIG. 2, the optical isolator consists of optical fibers 2. Or semiconductor laser 3. Lens 4° and 6. Polarizer 6. Magneto-optical element 14. Analyzer 7° optical fiber 2',
It is well structured. Now, Hikari 73 - Aiba 2. Or the light 13 emitted from the semiconductor laser 3
becomes semi-linear light at the lens 4, only the linearly polarized component is transmitted by the polarization +6, the polarization direction is rotated by 46 degrees by the magneto-optical element 14, transmitted by the analyzer T-7, and the light is transmitted by the condensing lens 5, The light is focused onto an optical fiber 2'. Here, the axes of the analyzer 7 are aligned so that the light after passing through the magnetic optical element -f14 is transmitted with almost no loss. - The reflected return light follows the same path as described above in the opposite direction through the lens 5. After passing through the analyzer 7 and passing through the magneto-optical element 14, the polarization direction is further rotated by 45 degrees, so that the polarization component becomes orthogonal to the polarization axis direction of the polarizer 6.
It is completely blocked and does not return to the optical fiber 2 or semiconductor laser 3. Problems to be Solved by the Invention However, the general magneto-optical element 14 has a problem in that the direction of polarization changes due to changes in ambient temperature. It has the property of changing the rotation angle. An example of YIG is shown in FIG. 3 (Materials of the Japan Society of Applied Magnetics, Research Group, Melon, MSJ38-7°P42).

That is, near room temperature, the rotation angle decreases against the rise in temperature. Therefore, even if the thickness of the magneto-optical element 14 is determined so that the rotation angle is 45 degrees at a certain temperature, the rotation angle will change due to temperature changes. deviates from 45°, and as a result, the polarization direction of the reflected return light deviates from 90° with respect to the polarization direction of the polarizer 6, and a portion of the reflected return light passes through the polarizer 6. 2 optical fiber 2. Otherwise, it becomes a semiconductor and returns to -v'3.

Means for Solving the Problems In order to solve the above problems, the present invention provides a wedge-shaped magneto-optical element whose thickness gradually changes in the direction of force perpendicular to the optical axis. The wedge-shaped magneto-optical element is disposed in a piezoelectric element that changes with a fixed voltage, and the wedge-shaped magneto-optical element is displaced in a direction perpendicular to the optical axis due to changes in reflected light from the polarization separation element.

According to the force method described in Section 2, the amount of light reflected from the polarized light splitting element changes as the ambient temperature changes, and in response to this, the wedge-shaped magneto-optical element is In other words, in response to changes in ambient temperature, the magneto-optical element is displaced in a direction perpendicular to the axis so that the rotation angle of the polarization direction of the light after passing through the magneto-optical element is always 45 degrees. The thickness can be controlled, even when the ambient temperature changes.
This makes it possible to completely block reflected return light.

Embodiment FIG. 1 shows an embodiment of the optical isolator of the present invention. Figure 1a shows an optical fiber type optical isolator;
The figure shows a semiconductor laser coupled optical isolator. Generally, the light emitted from the semiconductor laser is TE linearly polarized light, and the light reflected back to the semiconductor laser is a straight line orthogonal to the light emitted from the semiconductor laser. If the light is polarized, it will not have an adverse effect on the semiconductor laser itself, so the configuration does not include a polarizer.

In FIG. 1a, the light emitted from the optical fiber 2 becomes parallel light by the collimating lens 4, and only the linearly polarized component is transmitted by the polarizer 6, which is a polarization separation element, and then the magnet 9
a wedge-shaped magneto-optical element 1 whose thickness in a magnetic circuit gradually changes in the force direction perpendicular to the optical axis; a wedge-shaped magneto-optical element 1 having a refractive index equal to that of the wedge-shaped magneto-optical element 1; and a magneto-optic effect. The light passes through a magneto-optical component that integrates an optical element 8 such that the light incident surface and light exit surface are parallel to each other,
The polarization direction is rotated by 45 degrees, and the analyzer 7 is a polarization separation element.
After passing through, the light is focused onto the optical fiber 2' by the focusing lens 6. Also, the reflected return light follows the same path in the opposite direction and passes through lens 5. After passing through the analyzer 7 and passing through the integrated magneto-optical component, the polarization direction is further rotated by 45 degrees to become a polarization component perpendicular to the polarization direction of the polarizer 6, at which point the light is completely blocked.

If the ambient temperature changes here, for example, now the temperature is −j
- When the magneto-optical element is raised, the rotation of the polarization direction of the light after passing through the magneto-optical element is less than 45 degrees. At this time, in the analyzer 7, the polarized light component whose rotation of the polarization direction deviates from 45 degrees does not pass through the analysis ear and becomes a reflected component.

This reflected component is determined by the rotation of the polarization direction or by 45° or 7/
-5 The more it shifts, the more it increases. This reflected component is received by the light-receiving element 2o, and the electrical output after optical-to-electrical conversion is amplified by the amplifier 21, and then guided to the piezoelectric element controller 22 to generate a voltage corresponding to the power received by the photo-receiving element 20. The piezoelectric element controller 22
The piezoelectric element 10 is outputted from and guided to the electrode part 23 of the piezoelectric element 10 whose one end is fixed by the fixing part 11, so that the piezoelectric element 10 is displaced in the direction of the arrow in the figure as the temperature rises.

Along with this, the wedge-shaped magneto-optical element 1 integrated with the magnet 9 installed on the piezoelectric element 10 is also displaced in the direction perpendicular to the optical axis along the guide 12, and the thickness on the optical axis is reduced. (in the case of this embodiment, the action is in the direction of increasing the thickness), increasing the rotation angle of the polarization direction of the light after passing through the wedge-shaped magneto-optical element 1, and making it possible to correct it to 45 degrees. . Furthermore, when the temperature drops, the rotation angle of the polarization direction can be corrected by the opposite effect described above.

Note that the wedge-shaped magneto-optical element 1 has a refractive index equal to that of the wedge-shaped magneto-optical element 1 that is integrated with the wedge-shaped magneto-optic element 1 even when the optical axis moves in the vertical direction, Due to the effect of the optical element 8 having no magneto-optic effect, the focal position with respect to the optical fiber 2' does not change, and good coupling characteristics are exhibited.

Further, as shown in FIG. 1, the light emitted from the semiconductor laser 3 is focused onto a light receiving fiber 2' by a lens 4, and a magneto-optical element 1 is placed between the lens 4 and the optical fiber 2'.

Another example in which an analyzer 7 and a magnet 9 are installed will be shown. In this case as well, due to the same effect as in the case of Figure 1a,
Deterioration of the ainlation ratio (reverse direction loss) due to temperature changes can be prevented.

Effects of the Invention As described above, according to the present invention, the wedge-shaped magneto-optical element is displaced in the direction perpendicular to the optical axis as the ambient temperature changes. The thickness of the magneto-optical element can be controlled so that the rotation angle of the polarization direction of the subsequent light is always 45°, and even if the ambient temperature changes, it is possible to completely block reflected light. It is what it is.

9′″′・

[Brief explanation of the drawing]

FIG. 1a is a schematic diagram of the essential parts showing one embodiment of the optical isolator of the present invention, FIG. 1 is a schematic diagram of the essential parts showing another embodiment of the invention, and FIGS. FIG. 3 is a schematic diagram showing the main part of an optical isolator, and FIG. 3 is a characteristic diagram showing the temperature characteristics of the Fade rotation angle (rotation angle of the polarization direction of light) of YIG as an example of a magneto-optical element. 1... Wedge-shaped magneto-optical element, 2, 2'...
...Optical fiber, 3...Semiconductor laser, 4,
5... Lens, 6... Polarizer, 7...
... Analyzer, 8... Optical element having a refractive index equal to that of the wedge-shaped magneto-optical element and having no magneto-optic effect, 9... Magnet, 1o... Piezoelectric element, 11
...Fixing part that fixes one end of the piezoelectric element,
12...-Guide, 13... Outgoing beam, 20... Light receiving element, 21... Amplifier, 22... Piezoelectric element control Vessel, 23...
Piezoelectric element electrode part.

Claims (2)

[Claims] (1) The magneto-optical element is provided with a polarization separation element, a magneto-optic element, a beam conversion lens, a magnetic circuit material, and an optical fiber, and is shaped like a wedge and whose thickness gradually changes in a direction perpendicular to the optical axis. , installed on a piezoelectric element whose one end is displaced by a fixed voltage, so that the wedge-shaped magneto-optical element is displaced in a direction perpendicular to the optical axis due to a change in reflected light from the polarization separation element. optical isolator. (2) As a magneto-optical element, an optical element having a refractive index equal to that of the wedge-shaped magneto-optical element and having no magneto-optic effect, and the wedge-shaped magneto-optical element are used as a light incident surface and a light exit surface. 2. The optical isolator according to claim 1, which uses magneto-optical components that are integrated so that they are parallel to each other.