JP2001042149A - Optical element with ridge type optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the optical coupling efficiency irrespective of the form of optical elements and optical waveguides to be directly coupled to a ridge type optical waveguide by forming the ridge in at least one of the input or output part of the ridge-type waveguide to transfer polaritons as tapered to gradually decrease its width to the end so that the width of the ridge becomes smaller than the cut off width. SOLUTION: In the cross section of the ridge type optical waveguide,the waveguide has a core 1 in the center and has clads 2, 3 over and under the core, respectively, to form a ridge by the upper part of the core 1 and the clad 2. In this ridge type optical waveguide, the width of the ridge is decreased toward the input or output part for light. In particular, the width is gradually decreased so that the width of the ridge becomes smaller than the cutoff width. By gradually decreasing the width of the ridge to the end, the mode profile is increased and, as a result, the coupling efficiency with an optical fiber can be significantly improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element having a ridge-type optical waveguide, and more particularly, to an optical element having a ridge-type waveguide on a substrate, the end of the ridge-type waveguide being another optical element or an optical fiber. The present invention relates to a configuration of an optical element having a ridge-type optical waveguide that forms a coupling portion that couples with the optical element.

[0002]

2. Description of the Related Art Conventionally, when a waveguide of an optical element is coupled to an optical fiber, there has been a problem that the mode spot sizes of the waveguide and the optical fiber do not match, and the optical coupling efficiency deteriorates. Because of this, a significant portion of the light from the optical element is lost at the coupling,
The intensity of the light guided to the optical fiber is reduced, and problems such as the need to send more light than necessary from the optical element occur. Similarly, the same problem occurred when light was sent from an optical fiber to an optical element.

[0003] These problems occur not only between an optical fiber and an optical element but also between optical elements. The optical element in this case may be any element as long as it includes an optical waveguide, and includes, for example, any waveguide optical switch, semiconductor laser, semiconductor amplifier, and the like.

As a method for solving these problems, the present inventors have made the width of a waveguide such as a ridge-type optical waveguide provided in an optical element gradually smaller toward an end face, that is, toward an input / output end. Invented to enlarge the mode of propagating light. Regarding the technology, Japanese Patent No. 2771162
No. "Method for manufacturing optical waveguide". The ridge type optical waveguide described in the above-mentioned patent prepares a member for forming a ridge waveguide of an optical waveguide having a light input portion and a light output portion, and a light input / output portion of the light guide and its vicinity. The optical coupling efficiency is reduced by forming the width of the optical waveguide in one portion narrower than the width of the optical waveguide in the other portion, and forming the width of the optical input / output portion of the optical waveguide and a portion in the vicinity thereof as required. It will improve.

[0005]

However, the end of the ridge-type optical waveguide is formed of a single-mode waveguide, and the width of the ridge-type optical waveguide coupled to the single-mode waveguide is gradually reduced to a minimum. The section was the same as the width of the single mode waveguide. Therefore, when the optical device having the ridge-type optical waveguide is coupled to another optical device or an optical fiber, it is effective when the other optical device or the optical fiber has a single mode waveguide. It was found that the optical coupling efficiency was reduced when no one-mode waveguide was provided.

Accordingly, an object of the present invention is to improve an optical element having the above-mentioned ridge type optical waveguide, and to improve optical coupling efficiency irrespective of the shape of the optical element and the optical waveguide directly coupled to the above-mentioned ridge type optical waveguide. An object of the present invention is to realize an optical element having a ridge-type optical waveguide.

[0007]

In order to achieve the above object, an optical element having a ridge-type optical waveguide according to the present invention includes a ridge-type optical waveguide having a tip portion, that is, at least one of an input portion and an output portion. The width of the waveguide is gradually narrowed so as to be equal to or less than the cutoff of the ridge type optical waveguide. Here, the optical element is formed on the substrate, and at least partially optically couples a ridge-type waveguide, and the optical element includes a light emitting element, a light receiving element, an optical switch, an optical transformer, and the like. .

[0008]

FIG. 1 shows an embodiment of an optical element having a ridge-type optical waveguide according to the present invention, wherein (a) and (b) are a plan view and a cross section, respectively. The figure is shown. This embodiment is the simplest optical element having a ridge-type optical waveguide. As shown in FIG. 1 (b), the ridge-type optical waveguide has a core 1 at the center, a clad 2 at the upper part, and a clad 3 at the lower part, and the upper part of the core 1 and the clad 2 Configure the ridge. In the ridge-type optical waveguide, the light is confined in the vertical (vertical) direction by total reflection based on the refractive index difference between the core and the clad, and the confinement in the horizontal direction is caused by equivalent refractive index confinement due to the presence of the ridge. . In the case of such a ridge-type optical waveguide, the width of the ridge is reduced toward the input portion or the output portion of the light, in particular, by temporarily reducing the width of the ridge toward the end so as to be equal to or less than the cutoff. It was found that the optical coupling efficiency was improved.

This is considered to be because the effect of confining the light in the lateral direction is reduced by reducing the width of the ridge, and as a result, the mode profile of the propagating light is enlarged as compared with the waveguide before the narrowing. . Further, it has been found that the reduction in the ridge width has the effect of reducing the light confinement effect in the vertical direction, and as a result, the mode profile in the vertical direction also increases. As described above, the width of the ridge gradually decreases toward the end so as to be equal to or smaller than the cutoff, so that the mode profile is expanded, and as a result, for example, the coupling efficiency with the optical fiber is greatly improved.

A specific embodiment of an optical element having a ridge type optical waveguide having the structure shown in FIG. 1 will be described. The composition is clad 2
And 3 are Al _0.17 Ga _0.83 As, and core 1 is Al _0.13 Ga _0.87 As. The thickness of the core 1 is 1.8 μm, and the thickness of the claddings 2 and 3 is 2 μm. The width w of the ridge 4 was 2 μm, and the width at the tip of the input / output portion of the waveguide was almost 0 μm. For this reason, the mode in the input / output unit is below the cutoff. The length of the portion (tapered region) where the width w of the ridge 4 gradually decreases toward the end so that the width w becomes equal to or smaller than the cutoff is set to 100 μm. The height of the ridge was 2.5 μm. For this reason, the ridge has a structure in which it extends into the core region.

The method of manufacturing the device of the above embodiment is as follows. First, a layer to be a lower clad, a core, and an upper clad was crystal-grown on a GaAs substrate by metal organic chemical vapor deposition. After that, the SiO ₂
Was formed, and the ridge was formed by vapor phase etching using this pattern as a mask.

FIG. 2 shows the results of measuring the coupling efficiency between an optical element having a ridge-type optical waveguide according to the above embodiment and a multimode optical fiber. The multimode optical fiber is a normal optical fiber having a core diameter of 10 μm and an outer diameter of 125 μm.
The wavelength of the used light is 1.3 μm. As is clear from FIG. 2, when the width of the tapered tip portion of the coupling portion of the ridge type optical waveguide with the optical fiber is close to 0, the coupling efficiency becomes 50%, and the ridge width is not reduced. The coupling efficiency is twice as high as when the width w of the ridge 4 is 2 μm. Also, the coupling efficiency is improved by 10% as compared with the case where the width of the tapered tip portion of the coupling portion is 1.4 μm, which is a cutoff.

<Embodiment 2> FIG. 3 is a structural view of an optical element having an optical waveguide according to a second embodiment of the present invention. FIG.
(A) and (b) show a plan view and a sectional view, respectively.

In this embodiment, the claddings 2 and 3 are made of A
l _0.17 Ga _0.83 As and the amplification layer 5 is Al _0.05 Ga _0.95 A
s. The cap layer 6 was provided on the upper clad layer 2. The thickness of the amplification layer 5 is 0.2 μm, the thickness of the cladding 2 is 2 μm, the thickness of the cladding 3 is 3 μm, and the thickness of the cap layer 6 is 0.5 μm. In this case, the amplification layer 5 is a non-doped layer, and the upper cladding layer 2 has C of 10 ¹⁸ cm ^−3.
And p layer is doped, the lower cladding layer 3 Si 10 ¹⁸
cm ^{−3 was} doped to form an n-layer. Also, the cap layer 6
C was doped at 10 ²⁰ cm ^-3 to form a p-layer. The width of the ridge 4 was 2 μm, and the width at the tip of the input / output portion of the ridge type optical waveguide was almost 0 μm. For this reason, the mode in the input / output unit is cut off. The length of this tapered region was 100 μm. Also, the height of the ridge is
It was 2.5 μm. For this reason, the ridge has a structure in which it extends into the region of the amplification layer 4. In this case, a p-electrode was formed on the top of the device and an n-electrode was formed on the back, and when a current was passed, the effect of amplifying light was confirmed. The same manufacturing method as in Example 1 was used.

In this embodiment, the core diameter is 10 μm and the outer diameter is 12 μm.
When the coupling efficiency with a 5 μm ordinary optical fiber was measured, the coupling efficiency was 45% at a wavelength of 0.85 μm, and 1.8 times the coupling efficiency was obtained as compared with the case where the ridge width at the output section was not narrowed. .

<Embodiment 3> FIG. 4 shows the configuration of an optical element having an optical waveguide according to a third embodiment of the present invention. FIG.
(A) and (b) show a plan view and a sectional view, respectively.

In this embodiment, the claddings 2 and 3 are made of A
_l0.17 Ga _0.83 As, and the core layer 1 is made of _{Al 0.13} Ga _0.87 A
s, the quantum well layer 7 is GaAs. The overall thickness of the core layer 1 is 1.8 μm, the thickness of the quantum well layer 7 is 100 nm,
The thickness of the clad 2 is 2 μm, and the thickness of the clad 3 is 3 μm
It is. All layers were non-doped layers. in this case,
The width of the ridge was 2 μm, and the width at the tip of the input / output portion of the waveguide was almost 0 μm. For this reason, the mode in the input / output unit is below the cutoff. The length of this tapered region was 100 μm. The height of the ridge was 2.5 μm. For this reason, the ridge has a structure in which it extends into the region of the amplification layer 4. The manufacturing method is
The same method as in Example 1 was used.

In this embodiment, after confirming that the polariton propagates at a temperature of 5K, the core diameter is 10 μm and the outer diameter is 12 μm.
When the coupling efficiency with a normal optical fiber of 5 μm was measured, the coupling efficiency was 35% at a wavelength of 0.79 μm, and the coupling efficiency was tripled as compared with the case where the ridge width at the output portion was not narrowed. Thus, the coupling efficiency was improved even in the waveguide that propagates the polariton.

<Embodiment 4> FIG. 5 is a plan view showing the structure of an optical element having an optical waveguide according to a fourth embodiment of the present invention. The configuration of this embodiment is a directional coupler type switch shown in FIG. 5 using the waveguide having the cross-sectional structure shown in the first embodiment. However, the cladding 2 was made to be p-type by doping carbon C by 10 ¹⁸ cm ⁻³ , and the cladding 3 was made to be n-type by doping Si by 10 ¹⁸ cm ⁻³ , so that an electric field could be applied to the waveguide by reverse bias. . In this case, the length of the coupling portion was 2 mm, and an electric field could be applied to only one of the waveguides. As a result, switching can be performed by applying an electric field, and the total coupling efficiency with an optical fiber coupled to both ends of the switch is 25%.
%, The coupling efficiency is 3 compared to when not narrowing both ends.
Doubled.

<Embodiment 5> FIG. 6 is a plan view showing the structure of an optical element having an optical waveguide according to a fifth embodiment of the present invention. In the configuration of the present embodiment, a Mach-Zehnder switch shown in FIG. 6 was manufactured using the waveguide having the cross-sectional structure shown in the first embodiment. However, the clad 2 is made of carbon of 10 ₁₈ c
m ^{−3 is} doped into a p-type, and the cladding 3 is
¹⁸ cm ^{−3 was} doped to make it n-type, and an electric field could be applied to the waveguide with a reverse bias. In this case, the length of the region where the waveguide is divided was 5 mm, and an electric field could be applied to only one of the waveguides. As a result, it was found that switching can be performed by applying an electric field, and that the coupling efficiency with the optical fiber coupled to both ends of the switch can be increased to 30% as a whole. In this way, the coupling efficiency is increased to four times as compared with the case where both ends are not thinned.

[0021] <Example 6> LiNbO ₃ Ti thickness was 2μm form LiNbO ₃ doped on the substrate, then Ti
A waveguide having a 1.5-μm-high ridge formed by etching LiNbO ₃ doped with GaN. In this case, the width of the ridge was 2 μm, and the width at the input / output portion of the waveguide was almost 0 μm. For this reason, the mode in the input / output unit is cut off. The length of this tapered region was 200 μm. For this reason, the ridge has a structure in which it extends into the core region.

With this structure, the core diameter is 10 μm and the outer diameter is 12 μm.
When the coupling efficiency with a 5 μm ordinary optical fiber was measured, the coupling efficiency was 70% at a wavelength of 1.5 μm, and the coupling efficiency was doubled as compared with the case where the ridge width at the output portion was not narrowed.

[0023]

According to the present invention, the optical coupling efficiency between the ridge type optical waveguide and the optical fiber is improved, and the light introduction efficiency to the polariton waveguide is improved. As a result,
Energy saving is realized by reducing the input power to the element, and the assembly yield is improved by increasing the optical coupling tolerance in modularization, so that the module can be easily modularized.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical element having a ridge-type optical waveguide according to the present invention.

FIG. 2 is a view showing a result of measuring a coupling efficiency between an optical element having a ridge-type optical waveguide and a multimode optical fiber according to Example 1.

FIG. 3 shows a second example of an optical element having an optical waveguide according to the present invention.
The figure which shows the block diagram of Example of FIG.

FIG. 4 is a diagram showing a configuration of an optical element having an optical waveguide according to a third embodiment of the present invention.

FIG. 5 is a plan view showing the configuration of an optical element having an optical waveguide according to a fourth embodiment of the present invention.

FIG. 6 is a plan view showing the configuration of an optical element having an optical waveguide according to a fifth embodiment of the present invention.

[Explanation of symbols]

 1: core 2: clad 3: clad 4: ridge 5: amplification layer

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[Procedure amendment]

[Submission date] March 24, 2000 (200.3.2.
4)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masataka Shirai 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 2H037 BA24 BA31 CA34 CA36 2H047 KA05 KA13 KB04 MA05 PA05 PA21 PA24 QA02 QA03 RA08 TA32 TA42

Claims (7)

[Claims] 1. A light guide characterized in that it is formed in a tapered shape such that the width of at least one of an input portion and an output portion of a ridge type optical waveguide gradually decreases toward an end so that a width of the ridge becomes equal to or less than a cutoff. An optical element with a wave path. 2. The optical element according to claim 1, wherein the ridge waveguide is made of a semiconductor material or a dielectric material. 3. The optical element according to claim 1, wherein the ridge waveguide is a ridge portion of a ridge amplifier. 4. An optical element having an optical waveguide according to claim 1, wherein said ridge-type waveguide is a ridge of a ridge-type quantum well waveguide. 5. An optical element having an optical waveguide according to claim 1, wherein said ridge-type waveguide is a waveguide of a ridge-type directional coupler. 6. An optical element having an optical waveguide according to claim 1, wherein said ridge-type waveguide is a waveguide of a Muff-Zehnder type coupler. 7. An element having an optical waveguide, wherein the optical waveguide is a waveguide that propagates polaritons.