JPH02178611A - Two-stage type optical isolator - Google Patents

Abstract

PURPOSE:To stabilize the isolator against an external temp. change and a change in the wavelength of the light to be used by using two pieces of Faraday rotating elements which are different in the change rate of the rotating angle with temp. in the same external magnetic field to constitute the isolator so that the respective saturation magnetic fields vary. CONSTITUTION:The optical isolator formed by using the Faraday rotating element having (45+alpha)deg Faraday rotating angle and the optical isolator formed by using the Faraday rotating element having (45-alpha)deg Faraday rotating angle are connected and the Faraday rotating element requiring the strong saturation magnetic field is put into the state of (45-alpha)deg Faraday rotating angle without deliberately subjecting this element to the magnetic saturation. For example, the Faraday rotating elements are a tick film 4 consisting of (GdBi)3(AlGaFe)5O12 having 200G saturation magnetic field intensity and a thick film 4 consisting of (TbBi)3Fe5O12 having 700G saturation magnetic field intensity. The material and shape of a magnet are so designed that the Faraday rotating angle attains nearly 43deg when the (TbBi)3Fe5O12 is installed in the magnet. The optical isolator is able to have the stable isolation which changes less when the temp. environment or wavelength fluctuates in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION 10. OBJECTS OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator whose isolation characteristics are stable within a certain range against changes in temperature and wavelength used.

[Conventional technology]

Conventionally, the Faraday rotation element used in this type of optical isolator uses a garnet thick film such as GdBiIG. However, the Faraday rotation angle, which is the main characteristic of this thick garnet film, becomes unstable due to changes in surrounding temperature. An optical isolator using such a thick garnet film as a Faraday rotation element will naturally deteriorate its main isolation characteristic against changes in surrounding temperature. Furthermore, the oscillation wavelength of the laser oscillator used may generally vary depending on the usage time and environment. This also changes the Faraday rotation angle of the garnet thick film, causing deterioration of optical isolation. Therefore, in order to increase the efficiency and reliability of the optical isolator, there is a problem in that it is necessary to suppress changes in isolation characteristics due to temperature changes and wavelength fluctuations.

Generally, it is known that the Faraday rotation angle of a garnet thick film changes linearly depending on the direction of the magnetic field applied in the C-axis direction of the garnet thick film due to temperature changes or wavelength fluctuations. (GdBi)3 (with respect to temperature change)
The rate of change of the Faraday rotation angle in the case of the AIGaFe) 5012 thick film is −0.08 deg/, which changes in the negative direction as the temperature increases and in the positive direction as the temperature decreases. Therefore, if magnetic fields are applied to two identical Faraday rotation elements in opposite directions, the overall Faraday rotation angle will be 4.
There is a method of stabilizing it by approaching 5deg.

In addition to this method, there is also a method in which one of the Faraday rotation angles of the same material is made smaller than 45 deg and the other is made larger by the same amount, so that either one is close to 45 deg with respect to temperature changes. etc. are known. However, in the former method, each of the two external magnetic fields requires precise fine adjustment, which requires a lot of assembly man-hours and makes it difficult to produce an efficient product. Furthermore, in the latter method, it is necessary to control the thickness of the garnet film in order to adjust each Faraday rotation element, which complicates the manufacturing process and makes it difficult to produce a highly efficient isolator at a low cost.

[Problem to be solved by the invention]

In order to solve the above-mentioned problems, the present invention proposes two types of Faraday rotary elements having different temperature change rates of rotation angle in the same external magnetic field.
The rotation angle during assembly can be adjusted by using non-uniformity in the external magnetic field to adjust the rotation angle during assembly due to the difference in the saturation magnetic field of each, and by slightly moving the position of the garnet with a constant film thickness within the magnetic field. The rotation angle can be adjusted and the structure can be assembled easily.
The object of the present invention is to provide an optical isolator that has stable characteristics against external temperature changes and changes in the wavelength of the light used.

Configuration of the Invention [Means for Solving the Problems] The present invention is characterized in that optical isolators using Faraday rotators having different saturation magnetic field strengths are connected. The two Faraday rotation elements inside the optical isolator are adjusted so that the Faraday rotation angle' is smaller than 45 degrees by applying a magnetic field that does not reach saturation on one Faraday rotation element that requires a strong magnetic field. However, the Faraday rotation angle of the other Faraday rotation element is set to 45 degrees or more, and a saturation magnetic field is applied to the other Faraday rotation element. The present invention aims to provide a device that can suppress deterioration of the overall isolation due to fluctuations in the Faraday rotation angle within a certain range by connecting optical isolators made of such Faraday rotation elements. It is.

Generally, to adjust the Faraday rotation angle of a Faraday rotation element, magnetically saturate the garnet thick film, determine the film thickness at 45 degrees from the relationship between the Faraday rotation angle and the film thickness, and then adjust the film thickness. and thereby adjust the Faraday rotation angle. However, if the Faraday rotation angle is measured without magnetically saturating the Faraday rotation element, it will be smaller than when it is magnetically saturated.

By utilizing this, the Faraday rotation angle can be controlled by controlling the magnetic field applied to the crystal without controlling the film thickness. However, with this method, since the crystal domains are not aligned, the extinction ratio tends to deteriorate slightly, but this does not pose a practical problem.

[Effect]

The optical isolator of the present invention has a Faraday rotation angle of 45+
By connecting an optical isolator using an αdeg Faraday rotation element and an optical isolator using a 45-148g Faraday rotation element, an isolator with isolation that does not change suddenly due to temperature changes or wavelength changes is constructed. However, the feature of the present invention is to use two types of Faraday rotation elements with different saturation magnetic field strengths, and to intentionally keep the Faraday rotation element that requires a strong saturation magnetic field from being magnetically saturated, so that the Faraday rotation angle is 45-148g. There is a particular thing.

〔Example〕

FIG. 1 shows a configuration diagram of an optical isolator used in an embodiment of the present invention. The polarization axes of the three polarizing crystal plates used in this example are tilted in the same direction by 45 degrees. The Faraday rotation element used in this example has a saturation magnetic field strength of 20
(GdBi)3(AIGaFe) sot2 which is 0G and (TbBi)3Fe whose saturation magnetic field strength is 700G.
It is sO12. (TbBi)sFes inside the magnet
When 012 is installed, its Faraday rotation angle is approximately 4
The material and shape of the magnet were designed to provide 3deg. Before fabrication, the (TbBi)3FesO+z chip was actually attached to a fixed position inside the magnet and the Faraday rotation angle was confirmed. Also, (GdBi)3(AI
The Faraday rotation angle of GaFe) sox2 is approximately 47de
It is g. The materials were designed as described above, the optical isolator was assembled as shown in FIG. 1, and the position of the optical isolator within the magnet was adjusted and bonded so that the extinction ratio would be a specified value.

The optical isolator fabricated in this way has an insertion loss of 1
．． 5dB, isolation ratio is 45 at 10℃-40℃
Achieved ±5dB. However, the set wavelength used by this optical isolator is 1.31 μm. Further, the variation in isolation ratio due to wavelength variation was 45±6 dB in the 1.29-1.33 μm wavelength band.

C1. Effects of the Invention As can be seen from the above results, the optical isolator with improved temperature characteristics produced using the present invention has stable isolation that does not change much when the temperature environment or wavelength fluctuates. Furthermore, since the present invention allows fine adjustment by positioning the element within the magnet after the device is completed, excellent productivity can be expected.

[Brief explanation of the drawing]

FIG. 1 shows a conceptual plan view of an optical isolator used in an embodiment of the present invention. 1... Magnet body, 2... Polarizing crystal plate, 3-(
TbBi)3Fes012 thick film, 4-(GdBi)a(
AIGaFe)so12 thick film.

Claims (1)

[Claims] In an optical isolator using Faraday rotators with 1 or 2 different compositions, the configuration uses a Faraday rotator with a Faraday rotation angle of 45+αdeg,
An optical isolator in which a Faraday rotation element is magnetically saturated, and a saturation magnetic field strength is greater than that of the Faraday element in the direction of propagation of light with respect to the optical isolator, and the external magnetic field is insufficient for the saturation magnetic field strength to cause Faraday rotation. 4 corners
An optical isolator characterized by combining optical isolators using Faraday rotation elements such as 5-αdeg into a two-stage configuration.