JPH01225904A - Optical waveguide enclosing side of stripe - Google Patents

Abstract

PURPOSE:To enclose rays of light in the lateral direction without performing deep etching by providing thin intermediate layers having a low refractive index in a medium in the lateral direction of cores which become optical lines in the form of stripes. CONSTITUTION:A core layer 12 which guides rays of light, clad layers 11 and 14 which enclose the rays of light in the direction perpendicular to the surface of the core layer 12, and intermediate layer 13 which are formed in the core layer in the form of stripes are provided. Then the rays of light in the core layer 12 are enclosed in the direction parallel to the interfaces between the core layer 12 and clad layers 11 and 14 by making the refractive index of the intermediate layer 13 lower than that of the core layer 12. Therefore, even with a waveguide whose core layer 12 is as thick as the diameter of an optical fiber core, a difference in refractive index can easily be formed without performing any deep etching. Therefore, rays of light can easily be enclosed laterally and, since the unevenness on the surface of the waveguide is small, this waveguide can be applied to a laminated waveguide type optical integrated circuit.

Description

[Detailed Description of the Invention] (Summary) In a guiding waveguide formed on a substrate, a low refractive index intermediate layer film is inserted between a part of a core layer that confines light in the vertical direction,
By controlling the equivalent refractive index that light perceives.

This is an optical waveguide that confines light in the lateral direction by making the equivalent refractive index of a portion with an intermediate layer lower than the equivalent refractive index of a portion without an intermediate layer.

[Industrial application field]

The present invention relates to an optical waveguide, and particularly to a striped horizontal recessed optical waveguide that enables a three-dimensional waveguide structure with multilayered guiding waveguides.

(Prior art) -a. A guiding waveguide fabricated on a specific substrate such as a semiconductor or glass has some kind of optical confinement mechanism in the vertical direction (film thickness direction) and the horizontal direction (direction parallel to the substrate surface). is installed to guide the light.

In the vertical direction, for example, there are various types of refraction, such as those that utilize total internal reflection due to the difference in refractive index between the core (layer through which light passes) and the kraft, and those that utilize interference reflection of a multi-layer kraft. It can be easily manufactured by successively laminating transparent materials with a high density.

On the other hand, in the lateral direction, various optical confinement methods have been devised that combine photolithography and etching techniques.

FIG. 6 shows an example of a conventional Nori-Fuji type leading waveguide.

In the figure, 1 is a substrate such as a semiconductor, and 2 is a substrate l.
The cladding layer formed above, 3 is a core layer formed on the cladding layer 2 and has a higher refractive index than the cladding layer 2, and 4 is a ridge formed by etching the core layer 3 so as to create a step in the thickness direction. (ridge portion), 5 is a light path provided along the ridge 4.

In the Fuji-type leading waveguide shown in FIG. 6, the film thickness of the core N3 is slightly different between the ridge 4 portion and its surrounding portion, thereby causing a difference in the 9-equivalent refractive index. Performs lateral light confinement.

FIG. 7 shows an example of a conventional rectangular buried optical waveguide. In the figure, 1 is a substrate such as a semiconductor.

2 is a cladding layer; 6 is a core having a higher refractive index than the cladding layer 2;

The core 6 is formed by etching the film formed on the cladding layer 2 in a strip shape to the cladding layer 2 or the substrate 1, and then burying the strip-shaped core with a low refractive index medium to achieve lateral optical confinement. is being carried out.

[Problem to be solved by the invention]

The aforementioned Fuji-type leading waveguide and rectangular buried optical waveguide have been widely used in the past, but these generally have a core diameter of 10
When considering high-efficiency coupling with a single mode optical fiber close to μm, the core size of the optical waveguide needs to be the same size, and in that case, the etching depth required for lateral optical embedding also ranges from several μm to 108 m. It goes beyond that.

In order to etch such a thickness, non-directional chemical etching is impossible, and it is necessary to use anisotropic dry etching techniques such as reactive ion beam etching, which has rapidly progressed in recent years. Even so, it currently takes considerable precision and time to obtain a low-loss optical waveguide.

In the future, we will also focus on high-density integration of optical devices.

Layering multiple optical paths in the film thickness direction as shown in Figure 8,
It is believed that the importance of laminated waveguide type optical integrated circuits that exchange optical signals three-dimensionally will increase. To briefly explain the diagram, 30 is a substrate such as a semiconductor, 31 is a light input port, and 32 is a leading waveguide.

33 is a light output boat, 34 is a light merging/branching circuit, 35
36 is a vertical optical coupling circuit, and 36 is a photodetector. However, in the optical lateral folding method as described above, the unevenness remains on the surface after the optical waveguide is formed.

It is impossible to construct a multi-layered optical integrated circuit using this method.

The present invention alleviates the etching precision required when laterally confining a leading waveguide with a large core thickness.

The purpose of this invention is to realize a horizontally recessed optical waveguide that can be manufactured much more easily than conventional methods and leaves almost no steps on the surface.

[Means to solve the problem]

The present invention effectively lowers the refractive index by providing a striped thin intermediate layer with a low refractive index in the medium in the lateral direction of the core, which serves as the optical path, and allows the light to pass through without the need for deep etching. This realizes lateral confinement.

FIG. 1 is a diagram illustrating the principle of a striped horizontally recessed leading waveguide according to the present invention.

In the figure, 11 is a cladding layer, 12 is a core layer of a guiding waveguide, 13 is an intermediate layer of a medium whose refractive index is lower than that of the core layer 12, and 14 is a cladding layer opposite to the cladding layer 11.

Reference numeral 15 represents a core portion that serves as a light path. Further, A is a region where the intermediate layer is removed, and B is a region where the intermediate layer is present.

[For production]

The present invention will be explained in detail with reference to FIG.

A very thin intermediate layer 13 as shown in region B is sandwiched between the core layers 12 of the leading waveguide stacked in the vertical direction (thickness direction) in FIG. Since this intermediate FJ13 has a lower refractive index than the material used for the core, it has the function of slightly lowering the equivalent refractive index that acts on light. Therefore, an equivalent difference in refractive index occurs in the lateral direction with region A from which the intermediate 1113 is removed, and light is totally reflected at the boundary between 1wi regions A and B, so that light is confined in region A.

This lateral confinement method is the same as the lateral confinement method in conventional Fuji-type leading waveguides in that part of the core material is replaced with a low refractive index medium, but the low refractive index medium is placed in the middle of the core layer. By placing it in place, even a thin layer can increase the effect from several times to more than 10 times.

Therefore, in the present invention, the etching depth can be reduced to about 1/10 of that of the conventional glue Fuji type.

By chemical etching, it is possible to form track patterns in extremely rough areas. The pattern formed here does not have clear steps (strips) unlike other lateral confinement methods, and is close to two-dimensional stripes (stripes). It's called opening. Therefore, since the level difference caused by etching is small, the level difference that ultimately remains on the surface can be kept small.

Application to laminated waveguide type optical integrated circuits becomes possible.

〔Example〕

The present invention is applicable to any optical waveguide formed on a substrate such as a semiconductor or glass, and is effective when the core is as thick as a single mode optical fiber.

In particular, the resonant reflective optical waveguide (iffi name A) shown in FIG.
This is especially true for waveguides such as single-mode waveguides (RROW), which have strong optical confinement within the core even though they are single-mode waveguides, and it is difficult to obtain a lateral confinement effect with processing that causes only minute external changes such as ridges. It is considered effective. FIG. 3 shows an example in which lateral confinement is performed using such a resonant reflection type optical waveguide.

In FIG. 3, 10 is a substrate, lla is a first cladding layer, llb is a second cladding layer, 12 is a core layer, 13 is an intermediate layer, and 15 is a core portion.

In addition, the refractive index and thickness of each layer are expressed as follows.

1m-Dish rice eny vertical substrate ns-1st cladding layer nl dl2nd cladding layer
n□ 6837 layers nc
dc middle layer n Ic
d Ic Here, the resonant reflective guiding waveguide (ARRO
Due to the structural characteristics of W), a linear relationship is set between the refractive indices of each layer. Note that the refractive index of the upper medium (usually air) of the core layer is set to no.

nc　　　　　　　　　＞n・ n,>n.

nl>nz n(≧n=nl<n=Furthermore, 5 conditions for performing the stripe lateral opening according to the present invention are nlc<nc.

As a result, as shown by the arrows in Figure 2, the light incident on the core layer is confined in the vertical direction and in the horizontal direction due to interference reflection caused by appropriately setting the thickness of the second cladding layer. It propagates while being confined by total internal reflection due to the difference in the equivalent refractive index.

FIG. 4 shows the relationship between the position ID of the intermediate layer from the surface of the core layer and the lateral equivalent refractive index difference ΔΩ when the thickness dlc of the intermediate layer is used as a parameter.

As a specific example of the lateral confinement design according to the embodiment shown in FIG. = 1.54), T i Ox is applied to the first kraft layer 11a.

If S i 0x (nlc""1.46) is used for the intermediate layer 13, an equivalent refractive index difference of 0.25% in the lateral direction can be obtained even if the thickness dlc of the intermediate layer 13 is as thin as 0.4 μm. .

In addition, in manufacturing, the clad layer and core layer.

The sputtering method is used to form each layer such as the intermediate layer, and the core part 15 is
BHF (buffered hydrofluoric acid) is used to remove the intermediate layer in (area A).
Etching was used. Since the depth of etching only needs to be about several thousand layers, manufacturing is easy.

In addition, based on the present invention (according to the striped horizontal recessed optical waveguide), the level difference remaining on the surface after forming the leading waveguide is very small, so after forming one waveguide circuit on the substrate, It is possible to stack another waveguide circuit with a separation layer in between. Figure 5 shows an example of this. By providing an optical coupling section for exchanging optical signals at the part where the upper and lower waveguides overlap .

A three-dimensional laminated waveguide type optical integrated circuit can be constructed.

In FIG. 5, 16 is a substrate, 17 is an interference reflection craft that separates the substrate and waveguide, and 18 is a lower waveguide.

19 is an interference reflection craft that separates the upper and lower waveguides.

20 is an upper waveguide, 21 and 22 are intermediate layers, 23 and 24 are core parts, and 25 is an optical device such as an optical switch or a modulator.

In this way, an arbitrary plurality of waveguides can be multilayered to form a three-dimensional structure.

〔Effect of the invention〕

According to the present invention, even in a waveguide whose core layer is as thick as the core of an optical fiber, a refractive index difference can be easily formed without deep etching.

Optical horizontal opening can be achieved extremely easily. Also.

Since the surface of the waveguide has small irregularities, it can be applied to laminated waveguide type optical integrated circuits.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is an explanatory diagram of a resonant reflection type optical waveguide in which a particularly large effect can be obtained when the present invention is used, and Fig. 3 is an explanatory diagram of a resonant reflection type optical waveguide which is an embodiment of the present invention. FIG. 4 is a diagram illustrating the relationship between the intermediate layer and the lateral equivalent refractive index difference; FIG. 5 is a diagram showing the structure of a laminated waveguide type optical integrated circuit according to an embodiment of the present invention; FIG. 7 is a structural diagram of an example of a conventional ridge-type guided waveguide, FIG. 7 is a structural diagram of an example of a conventional rectangular buried optical waveguide, and FIG. 8 is an explanatory diagram of an example of a conventional laminated waveguide type optical integrated circuit. be. In Figure 1. 11: Land layer 12: Core layer 13: Intermediate layer 14: Land layer 15: Core part

Claims (1)

[Claims] A core layer (12) that guides light, a cladding layer (11, 14) that confines light within the core layer (12) in a direction perpendicular to the plane of the core layer (12), and a core layer (12) that guides light; The layer (12) has an intermediate layer (13) provided in a stripe shape, and the refractive index of the intermediate layer (13) is lower than the refractive index of the core layer (12). A striped lateral confinement optical waveguide characterized by confining light in a direction parallel to the interface between a core layer (12) and cladding layers (11, 14).