JPS59188605A - Waveguide type light mode filter - Google Patents

Abstract

PURPOSE:To enable fabrication of a waveguide type light mode filter irrespective of crystalline and amorphous media and to increase freedom of selection of materials and manufacturing methods by forming at least one of the core and clad of the waveguide path with a prescribed structural birefringence material. CONSTITUTION:A structural birefringence medium 7 is formed by the vapor deposition method or the like on a substrate of SiO2 or the like, and a core material 6 is formed by the vapor deposition method or the like on the medium 7. Then, a desired core material 6 is left and the other core material 6 is cut off. At that time, a part of the structural birefringence medium 7 is cut off, and said medium 7 is formed to complete a waveguide structure. A refractive index ne in the direction of an anisotropic axis is always smaller than the in- plane refractive index no intersecting said axis rectangularly, and isotropic media 9, 10 different in refractive index from each other (irrespective of crystalline or amorphous media) are alternately laminated to form an intended filter. Therefore, freedom of selection of materials and manufacturing methods is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a waveguide optical mode filter having selective transmission characteristics for two orthogonal polarization planes.

(Background Art) Conventional mode filters are broadly classified into bulk type and waveguide type. The bulk mode filter is realized by once emitting light within a waveguide into the air and passing it through an analyzer 2, as shown in FIG. At this time, the transmitted polarization direction can be selected depending on the optical axis direction of the analyzer 2. In this method, the light in the waveguide is radiated into the air once, so it needs to be focused again.The analyzer is relatively large, for example, at the Loim angle, and the overall size of the mode filter is large. There were drawbacks such as:

As a waveguide type TM mode filter, a metal thin film clad waveguide shown in FIG. 2 is known. That is, a thin metal film 3 such as aluminum is placed in contact with the core 1 of the waveguide to a thickness of 1 μm.
? By attaching about n over several generations in the light traveling direction 4, there is an effect of attenuating the TE mode power, which is one of the fundamental waveguide modes, to 1/1000 or less. At this time, the TE mode, which is another fundamental waveguide mode, suffers only a few percent loss, so...
T.E.

The separation effect of TM mode can be obtained. However, this structure has drawbacks such as the effect is small unless the metal thin film 3 is in contact with the core 1 of the waveguide, and a structure that only attenuates the TE mode cannot be obtained. As another waveguide mode filter, as shown in Fig. 3, a birefringent crystal is used as the core,
Alternatively, a waveguide structure with a cladding is known. For example, in FIG. 3, the core 1' is made of a birefringent crystal such as ZINbO5, and the substrate 5 and upper layer 5' are made of an isotropic medium. At this time, when the refractive index of '+5, 5' is n, the ordinary refractive index of 1' is n, and the extraordinary refractive index is n, then n (n(n -).

Alternatively, if the conditions n)n)n are satisfied, this waveguide will be TE or TM according to the axial direction of the birefringent crystal 1'.
Acts as a mode filter. The above effects can be similarly obtained when 1' is an isotropic medium and 5 and 5' are birefringent crystals. However, in these configurations, it is necessary to optically bond the interface between 5 and 1' or 1' and 5', and there is a need to precisely control the degree of area, the refractive index of the adhesive, etc. This method has serious drawbacks, such as the limited number of types of birefringent crystals that can be produced, which imposes severe constraints on the structural design conditions for the waveguide.

(Problems to be solved by the invention) In order to eliminate these drawbacks, the present invention uses a structured birefringent medium as the birefringent medium, and is devised to create a three-dimensional waveguide structure with a high electromagnetic field confinement effect. The drawings will be explained in detail below.

(Structure and operation of the invention) FIG. 4 shows an embodiment of the invention, in which 6 is an isotropic core;
7 is a cladding part, in which a structured birefringent medium whose anisotropy axis is perpendicular to the substrate surface is used, and 8 is a substrate. In the structured birefringent medium 7, which will be described in detail later, the refractive index n in the anisotropy axis direction is
e is the in-plane refractive index n perpendicular to this. Yoshi is also always small.

Therefore, if the core medium is selected so that the refractive index n of the isotropic core 6 satisfies ne<n<no, a waveguide structure will be formed in the anisotropic axis direction, but in the plane perpendicular to this (substrate In this case, only the TM mode (polarization mode perpendicular to the substrate plane) can propagate, and the TE mode (
The polarization mode (parallel to the substrate plane) is radiated.

Here, the structured birefringent medium 7 has a fine structure shown in FIG. That is, isotropic media 9 and 10 (which may be crystalline or amorphous) having different refractive indexes are stacked alternately in layers.

Here, it is sufficient that the thickness of each layer is sufficiently smaller than the wavelength (for example, 1/10 of the wavelength), and that the total layer thickness is approximately equal to or greater than the wavelength. The fact that such a medium exhibits birefringence with an anisotropy axis perpendicular to the layers has been shown, for example, by M, Born, E,
Co-authored by Wolf “Pr1nciples of 0pti
cs J (Pergamon Press, Oxfor
D, U., 1975), or its Japanese translation ``Principles of Optics'' (Tokai University Press), and is well known. As a specific example of the isotropic medium 9.1°, for example, S]
02 (n dust 15) and T ] 02 (n dust 2.o
) etc. can be used.

An example of the procedure for creating a TE mode filter, which is not shown in FIG. 4, is shown in FIG. 6. The substrate 8 shown in FIG. 6(A) is made of, for example, quartz (
S ] 02 ) can be used. Next, as shown in (B), a structured birefringent medium 7 having the fine structure shown in FIG. It is deposited by vapor deposition, sputtering, or CVD. Next, as shown in FIG. 6(C), the other core material is removed, leaving the desired core portion 6.

Techniques such as cross-cutting, etching, etc. are used for this process. These processes are described in, for example, Technical Report OQE 80-135 (1980) of the Institute of Electronics and Communication Engineers,
6-199490 etc. At this time, generally, a part of the structural birefringent medium 7 (other than the lowest part of the core part 6) is removed at the same time, as shown in FIG. 6(C).

Finally, the structured birefringent medium 7 having the fine structure shown in FIG. 5 is deposited again by vapor deposition or sputtering, thereby completing the waveguide structure. Figure 6(D) shows the birefringent medium 7 deposited in the final process, and Figure 6('
Although a boundary line 11 is shown between the birefringent media 7 deposited by the process shown in B), this boundary actually has no physical meaning. In other words, the boundary line 11, which is different from the boundary when bonding birefringent crystals using an adhesive, is due to the deposition process by vapor deposition or sputtering, so the medium 9 and the boundary line 11 generated in the microstructure shown in FIG. As with the 10 border, good optical adhesion is achieved.

FIG. 7 shows another production procedure. That is, after depositing (B) the structural birefringent medium 7 on the (A) substrate 8, a groove for the core portion is dug using a drilling method, etc.

Next, (C) the core material 6 is deposited by vapor deposition, sputtering, or the like. At this time, make sure that the groove shown in figure (B) is not completely filled. Next, (D) the structured birefringent medium 7 is deposited again. The structure shown in FIG. 7(D) differs from that in FIG. 4 in that core material is left in the parts 6' and 6// in addition to the original core 6, but the electromagnetic waves propagating through the original core 6 are It is known that the 6', 6// portion has almost no influence on the field, and it operates as a good TE mode filter as long as 6 and 6', 6// are not continuous.

With the structure described above, if a structured birefringent medium is used in the core part 6 and an isotropic medium is used in the club and dome parts 7, it will operate as a TM mode filter based on almost the same argument l). Exactly the same fabrication process as described above is then used. A TE mode filter can be manufactured by the manufacturing process shown in FIG. 6 using a structured birefringent medium whose principal axis of birefringence lies within the plane of the substrate for the core portion 6. However, in this case, the structured birefringent medium is manufactured by the procedure shown in FIG. That is, as shown in FIG. 8(A), first the substrate 8 is
A cladding 7 is created using an isotropic medium on top of the cladding 7, and one material 9 of the structural birefringent medium is further deposited on top of the cladding 7.

Next, as shown in Figure (B), periodic grooves are carved in the medium 9. In this 70 process, photoresist interference exposure,
Processing techniques such as lift ax and plasma etching are used.

Next, as shown in Figure (C), another one for the structural birefringent medium.
The other material 10 is filled into the grooves cut in the previous 70 processes. In this process, for example, Japanese Patent Application No. 57-10975
The technique disclosed in can be used. At this time, generally the material 10 not only fills in the grooves but also covers the entire substrate surface, so by uniformly removing the entire surface (D)
The structure shown in the figure is obtained. Focusing on the fact that the region where materials 9 and 10 coexist is equivalent to the structured birefringent medium shown in Figure 5, this shows that the structure is the same as that in Figure 6 (B) except for the difference in the axial direction of birefringence. You can see it. Therefore, by following the steps shown in FIGS. 6(C) and 6(D), it is possible to create a TE mode filter using a structural birefringent material in the core. We have explained the case where either one of the core and the cladding is composed of a structural birefringent medium, but even when both the core and the cladding are composed of a structural birefringent medium, the axial direction of birefringence and the magnitude of birefringence are By doing so, effects similar to those described above can be obtained. Although the above explanation mainly focuses on a structured birefringent medium composed of an amorphous medium that has never been used before, it is of course possible to use crystals as the constituent materials 9 and 10. . Therefore, for example, GaAs with small optical anisotropy
By imparting large birefringence to an optical waveguide using an InP crystal or an InP crystal, it is possible to impart a function as an I) TE or TM mode filter according to the present invention. Furthermore, although the operation of a general three-dimensional waveguide has been explained in the following explanation, the same effect can be obtained even with a slough waveguide (FIG. 3) having a much simpler structure.

(Effects of the Invention) As explained above, by configuring at least one of the core or cladding of the waveguide with a structurally birefringent material, a waveguide optical mode filter can be used regardless of whether it is a crystalline or amorphous medium. can be created, dramatically increasing the degree of freedom in selecting materials and manufacturing methods.

Furthermore, by selecting the axial direction of birefringence or whether the core or cladding is used as a birefringent medium, it is possible to create a mode filter that transmits TE mode or TM mode.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional bulk mode filter;
The figure shows the configuration of a conventional waveguide TM mode filter, and Figure 3 shows the structure of a waveguide mode filter using a birefringent crystal.
FIG. 4 is an embodiment of the present invention, FIG. 5 is a block diagram of a structured birefringent medium, FIG. 6 is a diagram showing an example of the manufacturing method of the device of the present invention, and FIGS. 7 and 8 are diagrams of the present invention. It is a figure which shows another manufacturing method of a device. ■ Core of waveguide, 2: analyzer, 3: metal thin film, 4: direction of propagation of light, 5: substrate, 6: core, 7 Nikrad, 82 substrate, 9, material for structured birefringent medium, 10 structure Material for birefringent medium, layer boundary in 1. Patent applicant Nippon Telegraph and Telephone Public Corporation Patent application agent Megumi Yamamoto - Figure 7 Figure 8 (A) (B) 29

Claims (1)

[Claims] In an optical waveguide consisting of a core and a cladding surrounding the core, at least one of the core and the cladding is composed of a structural birefringent medium having a multilayer structure made of materials with different refractive indexes, and the refractive index of the core and the refractive index of the cladding are different from each other. A waveguide optical mode filter characterized in that the magnitude relationship is reversed between the anisotropy axis direction of a structured birefringent medium and a direction orthogonal thereto.