JP2982836B2 - Manufacturing method of waveguide type isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reciprocal TE-TM 50%
The present invention relates to a method for manufacturing an isolator having two regions (a two-region isolator) in which a mode converter and a non-reciprocal TE-TM 50% mode converter are connected in series on one waveguide circuit, and particularly to a reciprocal / non-reciprocal mode conversion. The device portion is devised to be formed by a single crystal growth.

[0002]

2. Description of the Related Art As a method of manufacturing this type of waveguide type isolator (two-region isolator), conventionally, a region where a reciprocal mode converter and a non-reciprocal mode converter are grown in the same crystal orientation using a film. A method has been proposed in which the region of the non-reciprocal converter is locally laser-annealed after the film is grown, so that only the portion is magnetized in the in-plane direction (Reference: K. Ando, T. Okoshi and N. Kosh
izuka, Applied PhysicsLetter, Vol.53, No.1,1988, P.4
~ P.6).

The conventional manufacturing method will be further described with reference to FIG. In such a method, for example, Gd ₃ Ga ₅
The substrate 01 is used in which the perpendicular direction of the O ₁₂ (GGG) crystal is inclined from the (111) direction to the (112) direction by θ _C ８8 °. Then, the garnet film 02 is formed on the inclined substrate 01 by the liquid phase epitaxial growth method (LPE method). The composition of the garnet film 02 is, for example, (Bi
GdLu) ₃ (FeGa) ₅ O _{12 and the} like. In this case, when the garnet film 02 is magnetized by applying an external magnetic field (represented by H in the drawing), the magnetization (represented by M in the drawing) is inclined by θ _{m to} 27 ° from the perpendicular direction of the substrate 01. It will be designed to operate as a 50% converter for TE and TM modes. The garnet film 02 magnetized in this way exhibits the Cotton-Mouton effect known as the magnetic birefringence effect of transmitted light, and can function as a reciprocal mode converter. On the other hand, the non-reciprocal mode converter is formed by locally heating a part of the garnet film 02 with an Ar laser or the like to eliminate the dependence of the magnetization in the film growth direction and using the part 03 which is magnetized in the plane. . That is, the portion 03 that is magnetized in the plane is magnetized (indicated by M) in the plane along the external magnetic field (H), and exhibits a Faraday effect known as a magnetic rotatory effect of transmitted light.
It can act as a non-reciprocal mode converter. In this way, reciprocal / non-reciprocal mode converters can be connected in series on the same substrate 01.

[0004]

However, the two-region isolator according to the conventional manufacturing method has the following problems.

First, the first problem is caused by the fact that when irradiating a laser beam, the irradiated portion is not heated uniformly, but a temperature distribution occurs due to heat diffusion, that is, heat transfer. This temperature distribution is such that the temperature decreases exponentially from the garnet film surface, so that a relatively thin garnet film has a small temperature gradient, and the laser-irradiated portion is relatively uniformly non-reciprocal. It can be operated as a mode converter. But,
When the film thickness is several μm or more, the temperature gradient cannot be ignored, and although the upper layer of the garnet film shows the Faraday effect, the magnetization of the lower layer is still in the perpendicular direction and the cotton-Mouton effect appears. For this reason, the light incident on the non-reciprocal mode converter region has the disadvantage that the upper layer receives the effect of non-reciprocity and the lower layer receives the effect of reciprocity, and the performance as a non-reciprocal mode converter is extremely poor. Was. The thickness of the garnet film is required to be ５5 μm or more in consideration of connection with an optical fiber or a quartz waveguide. On the other hand, for a film thickness of about 1 μm or less, a prism or the like is used for coupling with the outside, but in this case, it is difficult to take advantage of the waveguide type isolator.

[0006] A second disadvantage relates to confinement of light. Normally, the waveguide is covered with a cladding having a refractive index slightly smaller than that of the waveguide itself, so that light is totally reflected at the interface between the waveguide and the cladding to confine light.
The performance of the waveguide circuit is secured. When such a clad layer is formed on a waveguide garnet film, usually, a garnet film having a changed composition is epitaxially grown on the waveguide. Here, when a non-reciprocal mode converter is formed by laser annealing, if laser annealing is performed after forming the cladding layer, the heating by the laser is almost limited to the cladding layer, and the annealing effect of the waveguide garnet film. Becomes significantly worse. Also, when forming a cladding layer after performing laser annealing,
Since the growth temperature is as high as 900 ° C., the laser-annealed portion undergoes a solid-phase reaction, and the magnetization again has a component perpendicular to the substrate surface. That is, it is difficult to form a waveguide having a cladding layer in the conventional manufacturing method, and there is a disadvantage that propagation loss due to light leakage increases.

As described above, in the conventional manufacturing method, it was not possible to sufficiently utilize the advantage of forming the two-region waveguide type isolator.

In view of such circumstances, the present invention has a film thickness of several μm or more that allows easy connection to an external optical fiber or a waveguide, and furthermore, the growth of a cladding layer before and after the waveguide film crystal growth. It is an object of the present invention to provide a method of manufacturing a waveguide type isolator capable of obtaining a possible two-region type isolator.

[0009]

A method of manufacturing a waveguide type isolator according to the present invention which achieves the above object, comprises a reciprocal mode conversion region in which magnetization is perpendicular to a direction in which light is guided and a magnetization in which light is guided. In a method of manufacturing a waveguide type isolator having a basic structure in which a non-reciprocal mode conversion region parallel to a direction and a non-reciprocal mode conversion region are connected in series, the substrate crystal in a region located immediately below each of the reciprocal mode conversion region and the non-reciprocal mode conversion region Using a single bicrystal substrate with different orientations,
After growing a thin film or a thick film crystal constituting an isolator on each region having different crystal orientations of the bicrystal substrate according to the crystal orientation of each region, these crystal films are parallel to the bicrystal substrate and It is characterized in that it is magnetized in a direction perpendicular to the boundary of the region.

[0010]

A material having a magneto-optical effect by ordinary crystal growth using a single substrate (bicrystal substrate) having different orientations of substrate crystals in regions constituting a reciprocal mode converter and a non-reciprocal mode converter. Grow. That is,
If a waveguide material crystal is epitaxially grown on the bicrystal substrate according to the orientation of the substrate crystal, waveguides having different crystal orientations can be connected in series simultaneously with the crystal growth. The easy axes of magnetization of the two regions of the waveguide can be easily made to depend on the crystal orientation, and can be a perpendicular magnetization region and an in-plane magnetization region. The perpendicular magnetization region can be used as a reciprocal mode converter showing the Cotton-Mouton effect, and the in-plane magnetization region can be used as a non-reciprocal mode converter showing the Faraday effect.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.

FIG. 1 shows a manufacturing process of one embodiment. First,
A gadolinium gallium garnet bicrystal substrate 10 as shown in FIG. 1A is prepared. The numbers in parentheses in the figure indicate the crystal orientation. Θ _c , θ _m
Indicates the angle between the (111) direction or the direction of magnetization and the perpendicular direction of the film. This bicrystal substrate 10 has two regions 11 and 12 having different crystal directions, and an interface 1
3 is very steep. Here, the region 11 has the (111) plane oriented in a direction inclined by about 4 degrees in a plane parallel to the interface 13 from a perpendicular direction of the substrate (indicated by ⊥ in the figure).
3 in the direction (112) parallel to the direction, and perpendicular to the interface (11).
0) There is a direction. On the other hand, in the region 12, the (110) direction is parallel to the interface 13 and the (112) direction is perpendicular to the interface 13. The (111) direction in the region 12 is
About 1 in the plane perpendicular to the interface 13 from the perpendicular direction (垂) of the substrate
It is inclined about 4 degrees.

In such a bicrystal substrate 10, for example, after the crystals forming the regions 11 and 12 are polished, the crystal orientations are aligned and joined as described above.
It can be obtained by performing a solid phase reaction by treating at a high temperature and a high pressure for a long time, followed by slicing and polishing.

On such a bicrystal substrate 10,
As shown in FIG. 1B, the substitution type magnetic garnet film 20 is formed.
Of 5 μm by liquid phase epitaxy (LPE)
m. Here, the LPE growth temperature is about 9
The temperature is 00 ° C., and the substitution type magnetic garnet is obtained by substituting yttrium with bismuth, gadolinium, and lutetium, and replacing part of iron with gallium. The magnetic garnet film 20 grown on the bicrystal substrate 10
Are epitaxially grown on the regions 11 and 12 having different crystal orientations according to the respective crystal orientations.
Had become. Moreover, the interface 23 was located at a position corresponding to the crystal interface 13 of the substrate 10 and was almost in the same plane up to the garnet 20 surface.

Next, in order to magnetize the grown magnetic garnet film 20, as shown in FIG.
2 in a direction perpendicular to the interface 23 and parallel to the substrate 10.
A magnetic field of 00 Oersted (represented by H in the figure) was applied. At this time, the magnetizations of the region 21 and the region 22 were respectively as shown in FIG. In the region 21, the magnetization (denoted by M in the drawing) is parallel to the interface 23 (1
It was in a plane including the 11) and (112) directions, and was in a direction inclined about 22.5 degrees from the perpendicular direction of the film surface. On the other hand, the magnetization in the region 22 has the (111) direction and the (11) direction.
2) Although it was in the plane including the direction, the direction was almost (11)
2) It was found that the magnetization was in-plane parallel to the direction and perpendicular to the region interface 23, that is, parallel to the applied magnetic field (H). It is clear from the description of the prior art that the regions 21 and 22 magnetized in this way can be used as a reciprocal mode converter and a non-reciprocal mode converter of a two-region isolator, respectively. In addition, since the magnetization directions of the regions 21 and 22 are both along the easy axis of magnetization, they are stable.
It goes without saying that a clad film crystal can be further grown thereon.

Next, in each of the regions 21 and 22, the length parallel to the magnetic field of the region, that is, the length in the waveguide direction is experimentally determined so that the rotation angle of the polarization plane becomes about 45 degrees.
The basic characteristics as an isolator were confirmed. When light having a wavelength of about 1.15 μm is guided from the region 22 to the region 21, the extinction ratio is at least 15 dB.
It turns out that it can take above. Further, the propagation loss was 1 dB or less, and it was confirmed that the scattering loss at the region interface 23 was extremely small.

In the embodiment described above, the substitution type magnetic garnet film is used. However, the present invention is not limited to this. For example, the magnetic garnet film and the like can be obtained by selecting the substrate material and its crystal orientation. It can be easily analogized that the same effect as that of the embodiment can be obtained.

[0018]

As described above, according to the present invention,
By using a waveguide type two-region isolator and a bicrystal substrate having two regions having different substrate crystal orientations, the reciprocal mode conversion region and the non-reciprocal mode conversion region can be changed by the substrate crystal orientation in one crystal growth. 2 different
It can be easily formed on one area. Therefore, according to the present invention, it is possible to have a film thickness of several μm or more and to grow a clad film crystal before and after the waveguide film crystal growth.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a manufacturing process of one embodiment.

FIG. 2 is a conceptual diagram for explaining a manufacturing method according to a conventional technique.

[Explanation of symbols]

Reference Signs List 10 bicrystal substrate 11, 12 region 13 interface 20 substitution type magnetic garnet film 21 region (reciprocal mode conversion region) 22 region (non-reciprocal mode conversion region) H external magnetic field M magnetization θ _c , θ _m (111) direction or magnetization Angle between the direction and the perpendicular direction of the membrane

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akiyuki Tate 1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Atsushi Shibukawa 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (58) Fields surveyed (Int.Cl. ⁶ , DB name) G02B 27/28 G02B ⁶ /126-6/13

Claims (1)

(57) [Claims] 1. A waveguide type having a basic structure in which a reciprocal mode conversion region whose magnetization is perpendicular to the direction of light propagation and a non-reciprocal mode conversion region whose magnetization is parallel to the direction of light propagation are connected in series. In a method for manufacturing an isolator, a single crystal substrate having different crystal orientations in regions located immediately below a reciprocal mode conversion region and a non-reciprocal mode conversion region is used, and the crystal orientations of the bicrystal substrates are mutually different. On each of the different regions, a thin film or a thick film crystal constituting the isolator is grown in accordance with the crystal orientation of each region, and these crystal films are magnetized in a direction parallel to the bicrystal substrate and perpendicular to the boundary of each region. A method of manufacturing a waveguide type isolator.