JP2002311267A - Connecting type optical waveguide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a connecting type optical waveguide having low insertion loss and reflected light quantity which can be easily manufactured. SOLUTION: An optical waveguide 13 for converting the spot size as a third optical waveguide has such a structure that an InP clad 7 having a refractive index higher than that of a polyimide clad 6 is present on at least one of the sides of the core 5 and that the width of the InP clad 7 decreases in a tapered form from an embedded optical waveguide 11 to a high-mesa optical waveguide 12. The optical waveguide 13 for converting the spot size is disposed between the embedded optical waveguide 11 and the high-mesa optical waveguide 12. Because the width of the side clad of the optical waveguide for converting the spot size gently changes from the embedded optical waveguide to the high- mesa optical waveguide, the guided light can be smoothly converted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a connection type optical waveguide having less loss and reflection, and more particularly, to a connection type optical waveguide including a buried optical waveguide, a spot size conversion optical waveguide, and a high-mesa optical waveguide. .

[0002]

2. Description of the Related Art FIG. 6 is a view showing the structure of a conventional connection type optical waveguide. FIG. 7 is a sectional view taken along line AA 'of FIG. 6, and FIG.
FIG. 3 is a view showing a cross-sectional view taken along line BB ′ of FIG. Reference numeral 21 in the figure
Is a core of the buried optical waveguide 31 which is the first optical waveguide, and has a band gap wavelength of 1.55 μm.
P and 22 are left and right InP claddings, 23 is an upper and lower InP cladding.
The clad 24 is an InP substrate.

Reference numeral 25 denotes a core of a high-mesa optical waveguide 32 which is a second optical waveguide, and has an exciton peak wavelength of 1.
It is a 46 μm multiple quantum well (well: InGaAsP, barrier: InGaAsP). Reference numerals 26 denote left and right claddings in the high-mesa optical waveguide 32.
It is assumed that the material is much lower than the P clad 22.
Here, polyimide is assumed as the cladding 26, but it goes without saying that other materials may be used.

As described above, both the buried optical waveguide 31 and the high-mesa optical waveguide 32 have the InP cladding 23 on the upper and lower sides, but the InP cladding 22 and the high mesa The polyimide cladding 26 is provided on the left and right sides of the core 25 of the optical waveguide 32, and the materials of the left and right claddings are different between the embedded optical waveguide 31 and the high-mesa optical waveguide 32. The refractive indexes of InP and polyimide are about 3.17 and 1.7 in the 1.55 μm band, respectively.

FIG. 9 is a top view of the conventional connection type optical waveguide shown in FIG. 6, and FIGS. 10 and 11 show a buried waveguide 31 as a first optical waveguide and a second optical waveguide. The field distributions a and b of the eigenmode of a certain high-mesa optical waveguide 32 are indicated by dotted lines. In the embedded optical waveguide 31 shown in FIG. 10, since the refractive index of the left and right InP claddings 2 is as high as about 3.17, the guided light leaks to the left and right InP claddings 22 and spreads to the left and right.

On the other hand, a high mesa optical waveguide 32 shown in FIG.
Then, the refractive index of the left and right polyimide claddings 26 is about 1.
7, the guided light is left and right polyimide clad 26
And is confined in the core 25 in the left and right directions. That is, the buried waveguide 31 as the first optical waveguide and the high-mesa optical waveguide 32 as the second optical waveguide have different eigenmode field distributions a and b.

FIG. 12 is a top view showing another example of the conventional connection type optical waveguide. The first optical waveguide is formed by tapering the core 21 of the embedded waveguide 31 which is the first optical waveguide. Is converted into the eigenmode field distribution d of the high-mesa optical waveguide 32 that is the second optical waveguide. In the figure, “e” indicates the guided light whose spot size has been converted by the tapered core.

[0008]

As described above, since the distribution of the guided light in each region is different, the buried optical waveguide 31 which is the first optical waveguide and the high mesa which is the second optical waveguide are different. When light propagates to the optical waveguide 32, first, at the connection portion between the embedded optical waveguide 31 and the high-mesa optical waveguide 32, light loss occurs due to the mismatch of the spot size. Further, as can be seen from FIG. 9, the light having the eigenmode field distribution a in the buried optical waveguide 31 is wider than the light having the eigenmode field distribution b in the high-mesa optical waveguide 32. 31
Of the light in the eigenmode in the above, the light that has spread beyond the high-mesa optical waveguide 32 is the medium 2 having a low refractive index at the connection portion.
However, there is a problem that reflected return light is also generated due to the feeling of 6.

Further, in the example shown in FIG. 12, the core 21 of the buried waveguide 31 has to be finely processed, so that there is a problem that the production is difficult.

The present invention has been made in view of such a problem, and an object of the present invention is to provide a connection type optical waveguide which is easy to manufacture with little insertion loss and reflected return light. .

[0011]

In order to achieve the above object, the present invention provides a buried optical waveguide in which the right and left sides of a core are buried with a first medium,
A connection type optical waveguide comprising a high-mesa optical waveguide having a second medium having a lower refractive index than the first medium on the left and right sides of the core, a third medium having a higher refractive index than the second medium; Is located on at least one of the left and right sides of the core, the width of the third medium, the spot size conversion optical waveguide tapered narrower from the embedded optical waveguide toward the high mesa optical waveguide, It is provided between the embedded optical waveguide and the high-mesa optical waveguide.

The invention described in claim 2 is the first invention.
In the invention described in (1), the second medium and the third medium have the same refractive index.

[0013] The invention described in claim 3 is the first invention.
Alternatively, in the invention described in Item 2, the tapered shape includes a linear shape.

The invention described in claim 4 is the first invention.
Alternatively, in the invention described in Item 2, the tapered shape includes a curved shape.

According to the present invention, since the width of the right and left claddings of the optical waveguide for spot size conversion gradually changes from the buried optical waveguide toward the high-mesa optical waveguide, the present invention provides a smooth waveguide. Wave light can be converted. Therefore, coupling loss and reflected return light do not occur at the connection between the embedded optical waveguide and the high-mesa optical waveguide. In addition, since the cladding of the optical waveguide for spot size conversion changes in a tapered shape, the radiation loss in this portion is also small, so that there is an effect that the insertion loss as a whole can be reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an embodiment of a connection type optical waveguide according to the present invention. In FIG. 1, reference numeral 1 denotes a core of an embedded optical waveguide 11 as a first optical waveguide, and InGaAsP having a band gap wavelength of 1.55 μm. 2 is the left and right InP claddings, 3 is the upper and lower InP claddings, 4 is In
It is a P substrate.

Reference numeral 5 denotes a core of the high-mesa optical waveguide 12, which is the second optical waveguide, and has an exciton peak wavelength of 1.4.
It is a 6 μm multiple quantum well (well: InGaAsP, barrier: InGaAsP). 6 is a high-mesa optical waveguide 1
2, which is assumed to be a material such as polyimide or air whose refractive index n is much lower than that of the left and right InP claddings 2 of the embedded optical waveguide 11.

As described above, both the buried optical waveguide 11 and the high-mesa optical waveguide 12 have the InP cladding 3 on the upper and lower sides.
There is an InP cladding 2 on the left and right, and a polyimide cladding 6 on the left and right of the core 5 of the high-mesa optical waveguide 12, and the buried optical waveguide 11 and the high-mesa optical waveguide 12 have different left and right cladding materials. The refractive indexes of InP and polyimide were 3.17 and 1.57 μm, respectively.
It is about 1.7.

In such a configuration, the spot size converting light guide for converting the spot size of the guided light of the embedded optical waveguide 11 as the first optical waveguide to the spot size of the high-mesa optical waveguide 12 as the second optical waveguide. Wave path 1
3 is provided between the embedded optical waveguide 11 and the high-mesa optical waveguide 12.

That is, the spot size conversion optical waveguide 13 which is the third optical waveguide has the InP cladding 7 having a higher refractive index than the polyimide cladding 6 on at least one of the right and left sides of the core 5. The width is configured so as to taper from the embedded optical waveguide 11 toward the high mesa optical waveguide 12, and the spot size converting optical waveguide 13 is formed between the embedded optical waveguide 11 and the high mesa optical waveguide 12. It is provided in.

FIG. 2 is a sectional view of a region of the optical waveguide for spot size conversion, and FIG. 3 is a top view of FIG. As shown in FIG. 2, the spot size conversion optical waveguide 13 has an InP cladding 7 having a width W on the left and right sides of the core 5, and a polyimide 6 on the outside thereof. Therefore, the spot size conversion optical waveguide 13 has an intermediate structure between the embedded optical waveguide 11 and the high-mesa optical waveguide 12. Note that W = 0
In the case of the above, a high mesa optical waveguide is obtained. In the figure, A indicates the field distribution of the eigenmode of the buried optical waveguide 11, B indicates the field distribution of the eigenmode of the high-mesa optical waveguide 12, and C indicates the field distribution of the spot size conversion.

FIG. 4 shows the total insertion loss from the buried optical waveguide to the high-mesa optical waveguide by the three-dimensional beam propagation method (3-D
FIG. 9 is a diagram showing a result calculated by BPM) using a width W of an InP clad in a spot conversion region as a variable. Here, the width of the core in the optical waveguides 11, 12, and 13 was 2 μm, and the thickness of the core was about 0.2 μm. Here, the lengths of the spot conversion optical waveguide 13 and the high mesa optical waveguide 12 are assumed to be 15 μm and 200 μm, however, other lengths may be used.

The optical waveguide 13 for spot size conversion
The widths of the right and left claddings 7 were changed as a linear taper or a square curve taper. As can be seen from FIG. 4, when the width W of the InP cladding 7 in the spot conversion region is zero, the insertion loss is as large as slightly less than 1 dB.
It is understood that the loss can be sufficiently reduced by providing the width W of the P cladding 7 of 1 μm or more.

FIG. 5 is a graph showing the result of calculating the reflected return light returning to the embedded optical waveguide from the connection surface between the embedded optical waveguide and the high mesa optical waveguide when the light propagates from the embedded optical waveguide to the high mesa optical waveguide. FIG. 3 is a diagram showing a width W of an InP cladding in a region as a variable. As can be seen from FIG. 5, it can be seen that by providing the width W of the InP cladding 7 of 1.5 μm or more, the amount of reflected return light can be sufficiently reduced. 4 and FIG.
The case of = 0 corresponds to the conventional example.

In the above embodiment, the wavelength is 1.55
Although μm is assumed, it goes without saying that other wavelengths may be used. The core of the buried optical waveguide section 11 and the core of the high-mesa optical waveguide section 12 have a band gap wavelength of 1.0.
Although 55 μm InGaAsP and a multiple quantum well having an exciton peak wavelength of 1.46 μm are assumed, these may be cores made of other materials, or may be a buried optical waveguide 11, a high-mesa optical waveguide 12, and a spot size converting optical waveguide 13. The cores may be different from each other. Further, their cores may be the same. Further, the present invention is applicable not only to optical waveguides made of semiconductor materials, but also to any kinds of materials such as quartz-based and polymer-based materials.

In the area of the spot conversion optical waveguide 13, which is the third optical waveguide, it is assumed that claddings 7 are provided on the left and right sides of the core. However, it goes without saying that although the effect is weakened, only one of the left and right may be used. Further, the left and right claddings are the same as the left and right claddings of the buried optical waveguide 11, but the effects may be slightly different, but they may be different from each other.

The spot size conversion optical waveguide 13
The widths of the right and left claddings are changed in a straight line or a square curve, but may be changed in other curves. Further, the present invention can be applied to a direction opposite to that of the embodiment of FIG. 1, that is, a case where light propagates from the high-mesa optical waveguide to the embedded optical waveguide.

[0028]

As described above, according to the present invention, the third medium having a higher refractive index than the second medium is provided on at least one of the left and right sides of the core, and the width of the third medium is reduced.
Since the spot size conversion optical waveguide tapered and narrowed from the buried optical waveguide toward the high mesa optical waveguide is provided between the buried optical waveguide and the high mesa optical waveguide, the left and right spot size conversion optical waveguides have Since the width of the clad gradually changes from the buried optical waveguide side toward the high-mesa optical waveguide, it is possible to smoothly convert the guided light. Therefore, coupling loss and reflected return light do not occur at the connection between the embedded optical waveguide and the high-mesa optical waveguide. In addition, since the cladding of the optical waveguide for spot size conversion changes in a tapered shape, the radiation loss in this portion is also small, so that there is an effect that the insertion loss can be reduced as a whole.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a connection type optical waveguide of the present invention.

FIG. 2 is a sectional view of a region of an optical waveguide for spot size conversion.

FIG. 3 is a top view of the embodiment of the present invention shown in FIG.

FIG. 4 is a diagram showing a result of calculating a total insertion loss from a buried optical waveguide to a high-mesa optical waveguide by a three-dimensional beam propagation method (3-D BPM), using a width W of an InP cladding in a spot conversion region as a variable. is there.

FIG. 5 is a graph showing calculation results of reflected return light returning to the embedded optical waveguide from a connection surface between the embedded optical waveguide and the high mesa optical waveguide when light propagates from the embedded optical waveguide to the high mesa optical waveguide; FIG. 3 is a diagram showing a width W of a clad as a variable.

FIG. 6 is a diagram showing a structure of a conventional connection type optical waveguide.

FIG. 7 is a sectional view taken along line AA ′ of FIG. 6;

FIG. 8 is a sectional view taken along line BB ′ of FIG. 6;

FIG. 9 is a top view of a conventional connection type optical waveguide.

FIG. 10 is a diagram showing a field distribution of an eigenmode of the buried waveguide.

FIG. 11 is a diagram showing a field distribution of an eigenmode of the high-mesa optical waveguide.

FIG. 12 is a diagram showing another example of a conventional connection type optical waveguide.

[Explanation of symbols]

Reference Signs List 1 core of embedded optical waveguide as first optical waveguide 2 InP clad on left and right of first optical waveguide 3 InP clad on upper and lower sides of optical waveguide 4 InP substrate 5 core of high mesa optical waveguide as second optical waveguide 6th 2 left and right claddings of the optical waveguide InP cladding 7 left and right InP claddings of the spot conversion optical waveguide as the third optical waveguide 11 embedded optical waveguide 12 high mesa optical waveguide 13 spot conversion optical waveguide 21 embedded optical waveguide as the first optical waveguide Waveguide core 22 Left and right InP cladding of first optical waveguide 23 Upper and lower InP cladding of optical waveguide 24 InP substrate 25 Core of high mesa optical waveguide as second optical waveguide 26 Left and right cladding InP cladding of second optical waveguide 31 embedded optical waveguide 32 high mesa optical waveguide

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takaaki Kakizuka, Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Within Nippon Telegraph and Telephone Corporation (72) Yasumasa Susaki 2-3-3, Otemachi, Chiyoda-ku, Tokyo No. 1 Within Nippon Telegraph and Telephone Corporation (72) Yasuo Shibata Inventor 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Hiroaki Takeuchi 2-chome Otemachi, Chiyoda-ku, Tokyo No. 3-1 F-term in Nippon Telegraph and Telephone Corporation (reference) 2H037 CA35 CA36 2H047 KA04 KA13 QA02 QA05 TA24 TA32

Claims (4)

[Claims] 1. A buried optical waveguide in which a left and right core is buried with a first medium, and a high-mesa optical waveguide having a second medium having a lower refractive index than the first medium on both sides of the core. In the connection type optical waveguide, a third medium having a higher refractive index than the second medium is provided on at least one of the left and right sides of the core, and the width of the third medium is greater than the width of the embedded optical waveguide. A connection type optical waveguide, wherein an optical waveguide for spot size conversion tapered toward the high mesa optical waveguide side is provided between the embedded optical waveguide and the high mesa optical waveguide. 2. The connection type optical waveguide according to claim 1, wherein a refractive index of the second medium is equal to a refractive index of the third medium. 3. The connection type optical waveguide according to claim 1, wherein the tapered shape includes a linear shape. 4. The connection type optical waveguide according to claim 1, wherein the tapered shape includes a curved shape.