JPH0154686B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a non-reciprocal optical circuit element among waveguide type optical circuit elements, which has transmission characteristics that differ depending on the direction of propagation of light, and in particular, a non-reciprocal optical circuit element that can switch the directionality without having a movable mechanism, and which can dissipate energy. The present invention relates to a non-reciprocal optical circuit element that can maintain a state without dissipating. Terminal stations, terminal devices, relay devices, etc. that make up a fiber optic communication system require various optical circuit elements to branch and switch fiber light, which is a signal carrier. It is desirable that these optical circuit elements have high performance, high reliability, and small size. Attempts have been made to construct the various optical circuit elements described above by providing a layer with a high refractive index on the surface of a dielectric or semiconductor substrate and using this as an optical waveguide. These elements are smaller than conventional methods that combine optical components such as lenses and prisms, and because the light is confined within the substrate, they are stable against environmental changes such as ambient temperature and humidity. Yes, it is highly reliable. Among various optical circuit elements such as optical branching elements and optical switch elements, isolators and circulators, which are non-reciprocal circuit elements, prevent light from returning from the fiber to the light source, preventing unstable operation of the light source and noise. It is an optical circuit element with high utility value, such as as an element that prevents optical fibers from occurring, or as an element that separates signals in two directions when performing bidirectional communication using a single optical fiber. Conventionally known optical waveguide type non-reciprocal circuit elements are made by coating a single crystal layer of yttrium, iron garnet, etc., which has a slightly higher refractive index, on a (111) gadolinium garnet single crystal substrate by several micrometers. This is grown thinly and used as an optical waveguide layer, and a magnetic field is applied from the outside in the direction of light transmission, aligning the direction of magnetization in the crystal layer in this direction, and directing the TE wave of the incident light to the crystal layer. It is converted into TM waves by the Faraday effect. In the case of guided light, the TE wave and TM wave have different phase velocities, and almost no conversion occurs if this continues. For conversion to occur efficiently,
It is necessary to match the phase velocities. For this reason, a dielectric having optical birefringence is placed on the thin film layer, and this birefringence is utilized to degenerate the phase velocities of the two modes. For light traveling in the opposite direction to the direction of the magnetic field, coupling between the two modes does not occur due to the non-reciprocity of the Faraday effect, so the non-reciprocity of the element is maintained. The waveguide type non-reciprocal circuit element with such a conventional configuration is intended to be used as an element that electrically controls the directionality so that the directionality can be reversed depending on the time and the state can be maintained. In this case, dissipation of energy is required, such as by continuing to apply a current or magnetic field to maintain the state, or by rotating a permanent magnet through a mechanical mechanism to reverse the direction.
It is difficult to avoid a decrease in reliability due to the movable mechanism. This is because in the conventional configuration, (111) yttrium iron garnet, which is a magnetic material, does not have an axis of easy magnetization in a specific direction within the film plane. Yttrium iron garnet is influenced by <111>, which is located near the three equivalent <211> existing within the film surface and is at a slight angle above the film surface, and the three <211> are easily It works in the same way as an axis. In other words, it does not have an axis of easy magnetization in a specific direction within the film plane (111)
When a film such as Y ₃ Fe ₅ O ₁₂ is used, when the external magnetic field is removed, the magnetization is oriented in one of the equivalent directions in the film plane determined by the magnetocrystalline anisotropy. This is because it will be put away. SUMMARY OF THE INVENTION An object of the present invention is to provide a memory-type waveguide non-reciprocal optical circuit element which is O-type stable and which eliminates the above-mentioned drawbacks. The inventors have discovered that a small and stable waveguide non-reciprocal circuit element can be formed by using a garnet film having an axis of easy magnetization in a specific direction within the film plane, and have accomplished the present invention. That is,
The non-reciprocal optical element of the present invention employs an orthorombic anisotropic (110) film having an axis of easy magnetization in a specific direction within the film plane as a ferromagnetic garnet film, and a polarizer that transmits linearly polarized light and a polarizer that transmits linearly polarized light. The magnetic garnet film is installed between the light that passes through the polarizer and the polarizer that transmits the polarized light with an inclination of 45 degrees, so that the light passes through the polarizer-magnetic garnet film-polarizer, and the magnetic garnet film The magnetic garnet film and two polarizers are arranged so that the light propagates parallel to the easy axis of magnetization, and the magnetic garnet film is further provided with means for applying a magnetic field to the magnetic garnet film parallel to the easy axis of magnetization. did. The details of the present invention will be explained using examples. When (110) garnet films having the film compositions shown in Table 1, 1 to 6, were grown by the liquid phase epitaxial method, all of them had orthorombic magnetic anisotropy. It exhibited magnetic properties as shown. The energy E of orthorombic magnetic anisotropy is expressed by the following formula. This origin is due to growth-induced anisotropy. E=(Ku+Δ・sin ² φ)sin ² θ Here, Ku and Δ are as shown in Figure 1.
It is the difference in energy between the three principal axes, and φ and θ are the azimuth and inclination angle of the magnetization Ms. From this formula
It shows that Ku and Δ have uniaxial symmetry about three orthogonal principal axes. For the materials shown in Table 1, Ku<0, Δ>0 and Ku+
Δ>0. In other words, from the above equation, for both films, [001] in the film plane is the axis of easy magnetization, and [110]
was the difficult axis, and [110] perpendicular to the membrane surface was the intermediate axis. Using these garnet films 1, light 2 is introduced parallel to the axis of easy magnetization in the film plane as shown in Figure 2.

【table】

[Table] A waveguide circuit element was formed. These materials have orthorombic magnetic anisotropy, so when no external magnetic field is applied, the magnetization points to either [001] or the equivalent 180° opposite direction to [001]. . The hard magnetization axis [110] shown in FIG. 2 is the intermediate axis. Coil 3 wound around this element
The garnet film is magnetized in advance in parallel to [001] by passing a current through the TE wave (or TM
When a wave) is incident parallel to [001], the light travels by the optical path length determined by the Faraday rotation coefficient φ _F of the material and exits the element with a polarization direction of 45 degrees from the polarization direction of the incident light. It undergoes Faraday rotation into tilted linearly polarized light. Similar to conventional isolators, this 45°-inclined linearly polarized light traveling in the opposite direction travels through the element in the opposite direction to the direction of magnetization, so when it exits the element it becomes linearly polarized light perpendicular to the incident light. becomes. Therefore, an isolator is formed by equipping the input side with a polarizing element that transmits the polarized light of the incident light, that is, the TE wave (or TM wave), and the output side with a polarizing element that transmits the polarized light tilted by 45 degrees. It was done. Also, if the current is passed through the coil 3 in the opposite direction to the above, the magnetization will be [001]
The above-mentioned incident TE wave (TM wave) is rotated in the opposite direction and cannot pass through the output polarizer, whereas the light that passes through the output polarizer and travels in the opposite direction. was able to pass through the polarizer on the incident side due to rotation of the plane of polarization in the element. In other words, a non-reciprocal optical element as referred to in the present invention was formed. This device uses magnetic anisotropy that points in a specific direction within the plane of the (110) garnet film, so even if the magnetic field generated by the current flowing through the coil is removed, the magnetization of the garnet film will not change depending on the coil current. Since the direction of the resulting magnetic field can continue to be oriented, it has become a memory-type non-reciprocal optical element that can switch direction without having a moving mechanism and can maintain its state without dissipating energy. . Furthermore, since the garnet films with film compositions 1 to 5 in Table 1 contain Bi ³⁺ , the value of the Faraday rotation coefficient |φ _F | is large, making it possible to miniaturize the device.

[Table] Done. In addition, when using a (110) film in which the axis of easy magnetization is [110] in the film plane as shown in Table 2, the light transmission direction is set to [110] or [110].
By providing a coil to generate a magnetic field in the [110] (or [110]) direction or in the opposite direction to this axis of easy magnetization, a memory-type non-magnetic device without a movable mechanism can be created. We were able to create a reciprocal optical circuit element. When [110] is the axis of easy magnetization, Ku + Δ as shown in Table 2
It had to be <0. As described above, according to the present invention, a non-reciprocal optical element can be obtained which can switch directionality without having a movable mechanism and can maintain a state without dissipating energy.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram showing the orthorombic magnetic anisotropy in a (110) garnet film, where Ku is between [110] and [001], and Ku + Δ is Δ between [110] and [110]. indicates the difference in energy between [001] and [110]. FIG. 2 is a diagram showing the principle of construction of a non-reciprocal optical device according to an embodiment of the present invention, in which 1 is a garnet film, 2 is a laser beam, and 3 is a garnet film.
is a coil.

Claims (1)

[Claims] 1. A polarizer that transmits linearly polarized light, a polarizer that transmits polarized light that is at an angle of 45 degrees to the light transmitted through the polarizer, and a magneto-optical device that is sandwiched between these two polarizing elements in the light transmission direction. In a magneto-optical element consisting of a medium, a (110) magnetic garnet film with an axis of easy magnetization in the film plane and having orthorombic magnetic anisotropy is used as the magneto-optic medium, and the easy magnetization direction of the (110) magnetic garnet film is 1. A magneto-optical non-reciprocal optical element characterized by having means for guiding light and applying a magnetic field parallel to the easy axis of magnetization.