JPH02306215A - Optical isolator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical isolator, the purpose is to miniaturize the optical isolator by using a magnetic garnet element that functions as a Faraday rotator without a permanent magnet that applies an externally applied magnetic field. Two polarizers whose polarization plane selection directions are arranged at an angle of 45 degrees to each other, and a magnet that is formed on a single substrate and has stable square magnetic characteristics, and is inserted between the two polarizers. The optical isolator is configured to include both a garnet film and a magnetic shield cover that surrounds the magnetic garnet film and is arranged so as not to obstruct the optical path.

[Industrial application field] The present invention relates to improvements in optical isolators.

It is well known that laser light has come to be used for main power transmission lines, mainly undersea communication cables.

Furthermore, with improvements in optical fibers, laser light sources, optical data links, and other optical components, LAN (Local Array)
The introduction of light wave technology into buildings such as EA Netinork has become popular, and information network systems based on optical fibers are now being used in recent new intelligent buildings.

These laser light application systems require various optical devices, but for example, in semiconductor lasers, the modulation and spectral characteristics change due to reflected return light generated at the coupling system and optical fiber connection, causing noise. Therefore, it is necessary to incorporate an optical isolator into the optical system to suppress this return light, and there is a particular need for the development of an optical isolator that is small and easy to assemble and adjust.

(Prior Art) FIG. 4 is a diagram illustrating a conventional example of an optical isolator using a YIG rod, in which (A) is a configuration diagram and (B) is a cross-sectional view.

In the figure, numerals 2 and 2 denote polarizers, which are made of birefringent crystal plates such as calcite, dielectric multilayer films, etc., and are arranged so that their polarization plane selection directions are inclined at 45 degrees to each other. 11 and 12 are optical path windows, 45 is a YIG Rondo, and the length is usually several mm.
, a cylinder with a diameter of several 100 μmφ or a side of 1100 a
Form into a corner prism. 50 is a permanent magnet, for example, S
m-Co magnets are used. 100 is a package for protecting the optical isolator.

Since the YIG rod 45 is oriented (M) in its longitudinal direction by a permanent magnet 50, it acts as a Faraday rotator and rotates the plane of polarization of light passing through it.The angle of rotation is defined as θ. Then, it is expressed by the following formula.

θ=VHffi・−・・−−−−1−・・・・−−−−
・−・−・−・・−−−111・−(1) In the knee, e is the Faraday rotator, that is, the length of the YIG rod, and H
is the applied magnetic field strength (saturation magnetic field for ferromagnetic materials), and ■ is the Verdet constant (edited by the Institute of Electronics, Information and Communication Engineers: Electronics, Information and Communication Handbook, Vol. 1, see p1040).

For the optical isolator, set θ = 456.

be done.

Now, for example, when light with a wavelength of 1.3 μm is incident from the left side of the optical isolator, the light whose polarization plane is selected in a certain direction by the polarizer 1 is transmitted through the rod 45 and rotates the polarization plane by 45°. let Therefore, since its polarization plane matches the polarization plane selection direction of polarizer 2, the light is directly \polarizer 2
pass through.

Next, when the light is reflected by a reflecting surface not shown in the figure and returns, it passes through the polarizer 2 again and passes through the YIG rod 45.As is known from the action of a Faraday rotator, the plane of polarization is the same. The light beam is further rotated by 45 degrees in the direction of the light beam, that is, rotated by 90 degrees from the original polarization plane, and is transmitted through the YIG rod 45 and enters the polarizer 1.

In the end, the polarization plane of the returned light is perpendicular to the polarization plane selection direction of polarizer 1, and the light is blocked by polarizer 1 and cannot return to the light source on the left, so it can be operated as an optical isolator. .

FIG. 5 is a diagram illustrating another conventional example of an optical isolator using an LPE (FF film), in which 40 is, for example, B
This is a magnetic garnet film such as an i-substituted iron garnet film, and is formed by a liquid phase epitaxial method (LPE method) on a substrate 30 made of non-magnetic garnet such as GGG (Gd:+Ga50+z).

In this case, the Faraday rotation coefficient is about an order of magnitude larger than that of YIG, and since a thin film of good quality can be produced by the LPE method, there is an advantage that the lengthwise dimension of the element can be significantly reduced. For example, the external dimensions of the conventional example using the YIG rod shown in Figure 4 were approximately 10φ x 20mm, while the external dimensions of the conventional example using the YIG rod shown in Figure 5 were 10φ.
The size has been reduced in half in the length direction to 10 mm.

[Problems to be Solved by the Invention] However, in all of the above conventional examples, in order to use the magnetic material as a Faraday rotator with magnetic saturation, a permanent magnet 50 is required around the magnetic material, and therefore, the optical path and There is a problem in that there is a limit to reducing the dimension in the perpendicular direction, and a solution has been needed.

[Means to solve the problem]

The above problem is solved by forming two polarizers 1 and 2 whose polarization plane selection directions are arranged at an angle of 45 degrees to each other, and a single substrate 3 which is inserted between the two polarizers. This problem is solved by configuring an optical isolator to include at least a magnetic garnet film 4 having stable square magnetic properties, and a magnetic shield cover 5 surrounding the magnetic garnet film 4 and disposed so as not to obstruct the optical path. be able to.

[Function] According to the present invention, the magnetic garnet film that acts as a Faraday rotator is formed on a single substrate so as to have stable square magnetic characteristics, so a permanent magnet is not required. This allows the dimension in the direction perpendicular to the optical path to be reduced.

[Embodiment] FIG. 1 is a block diagram of an embodiment of the present invention. In the figure, reference numerals 1 and 2 denote polarizers, which are made of birefringent crystal plates such as calcite, dielectric multilayer films, etc., and are arranged so that their polarization plane selection directions are inclined at 45 degrees to each other.

11 and 12 are optical path windows, and 10 is a package for protecting the optical isolator.

4 is a Bi-substituted iron garnet film, for example (GdCa)
s(GaMgZr) sOl□ as the substrate 3, and (TbBi)+(FeA I Ga) Sol 2 on it
was formed by the LPH method.

Reference numeral 5 denotes a magnetic shield cover for preventing magnetic disturbance from the outside, and a permalloy plate with a thickness of 0.2 mm is provided inside the package 10 to avoid the optical path windows 11 and 12 and cover the magnetic garnet film 4. It is.

FIG. 2 is a diagram illustrating the formation of a magnetic garnet film according to the present invention, in which (a) is a top view and (b) is a side view. In the figure, 6 is a wafer, 60 is a substrate wafer, 4 is a magnetic garnet film forming a Faraday rotator, and 7 is a groove.

The substrate wafer 60 has a diameter of 75 mm and a thickness of 0.
5mm (GdCa):+ (GaMgZr)so+z
The (111) plane of (TbBi) 3 (FeA
I! , Ga) 5012 is melted at high temperature, and the substrate wafer is horizontally immersed and rotated for about 20 hours for liquid phase growth to form a 300 μm thick (TbBi) 3 (
FeA 1. A Ga) sol 2LPE membrane was obtained.

If the saturation magnetization of this LPE film is M, 4πMs is approximately 3
00 Gauss.

Using a rotating diamond blade cutting machine, the 20 wafer 6 was cut in the center a little deeper than the thickness of the magnetic film so that the square magnetic garnet film 4 with sides of 3 mm was separated from the surrounding magnetic films. Grooves 7 of 200 μm were formed in all directions.

Next, this wafer was exposed to phosphoric acid (H3PO4) at 150°C.
The etching process was carried out for about 10 minutes in a vacuum chamber.

Finally, in order not to damage the end face of the magnetic garnet film 4 at the center of the groove 7, each magnetic garnet film 4 was cut along with the substrate using a diamond blade that was thinner than when forming the groove to create a Faraday rotator.

As comparative samples, several chips with magnetic garnet films of similar size were cut without etching in phosphoric acid ('H: +PO4).

Figure 3 shows the hysteresis characteristics of the magnetic garnet film according to the present invention, in which (a) shows the mechanically grooved sample after processing, and (b) shows the grooved sample after processing using phosphoric acid. FIG. 3 is a characteristic diagram measured for a sample after chemical etching.

Note that the measurement was performed using a normal vibrating sample magnetometer.

As can be seen from the figure (A), in this case, the squareness of the hysteresis characteristic is poor, and the coercive force HCI is very small at about 300e (Oersted). Therefore, such a magnetic film cannot function as a stable Faraday rotator unless it is magnetized using a permanent magnet.

On the other hand, in the case of the same figure (b), the coercive force H62 is about 1
It was found that it was very large at 8000e and had very good squareness.

This is because the nucleation magnetic field (HN) for magnetization reversal at the edge portion of the magnetic garnet film is significantly improved by the defect removal effect of the chemical etching process of the magnetic garnet film.

When we manufactured an optical isolator with the configuration shown in Figure 1 using this sample, the external dimensions were 5 mm in diameter x 1 in length.
It has become possible to significantly reduce the size to 172 to 1/8 of the conventional case. Moreover, it was confirmed that the optical isolator had a return light blocking performance equivalent to or better than that of conventional optical isolators without using a permanent magnet.

In addition, since no permanent magnets are used and there are fewer restrictions on the light receiving surface,
Optical axis adjustment has become easier and can be done in less than a fraction of the time compared to conventional methods.

Note that the present invention applies to the substrate composition, magnetic film composition,
The magnetic film forming method and groove formation are not limited to processing methods, chemical etching methods, etc., and other similar groups VI, M composition, magnetic film composition, and VA film forming methods may be used.

It goes without saying that the grooves may be formed by appropriately selecting processing methods, chemical etching methods, etc. as necessary.

〔Effect of the invention〕

As explained above, according to the present invention, a Bi-substituted magnetic garnet film is formed on a non-magnetic garnet substrate by the LPE method, and the coercive force is increased by mechanically grooving and chemical etching after processing. A Faraday rotator that is large and has very good squareness in terms of hysteresis characteristics can be obtained.Therefore, there is no need for permanent magnets, the external dimensions are extremely small, and the optical axis can be easily adjusted, making it suitable for optical isolators. The performance improvement 1 contributes to the price reduction extremely.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram explaining the formation of a magnetic garnet film of the present invention, FIG. 3 is a hysteresis characteristic diagram of a magnetic garnet film of an embodiment of the present invention, and FIG. Figure 5 is a diagram explaining a conventional example of an optical isolator using a YIG rod. Figure 5 is a diagram explaining another conventional example of an optical isolator using an LPB magnetic garnet film. In the figures, 1 and 2 are polarizers, and 3 is a polarizer. A substrate, 4 a magnetic garnet film, 5 a magnetic shield cover, 6 a wafer, and 7 a groove. ℃ 3fshi (ffigo% 2l) (a) The grooved grooves are processed. Shisis Special J
Figure HFigure 3 (A)a Growth diagram

Claims (1)

[Scope of Claims] Two polarizers (1, 2) whose polarization plane selection directions are arranged at an angle of 45 degrees to each other, and a polarizer (1, 2) inserted between the two polarizers (1, 2), A magnetic garnet film (4) formed on a single substrate (3) and having stable square magnetic properties, and a magnetic shield cover (5) surrounding the magnetic garnet film (4) and arranged so as not to obstruct the optical path. ).