JPH0287103A - Optical coupler - Google Patents

Abstract

PURPOSE:To decrease the light loss by the scattering, reflecting, mode unmatching, etc., which arise at the time of coupling with the optical coupler which has a 1st light guide and a 2nd light guide to be optically coupled to the 1st light guide by forming the optical coupler in such a manner that the 1st light guide has the propagation constant equal to the propagation constant of an optical fiber. CONSTITUTION:The three-dimensional light guide 12 and a groove 13 are provided on the surface of a substrate 11 and optical coupling is effected between the single-mode optical fiber 14 embedded in the groove 13 and the three- dimensional light guide 12. A grating 15 for executing phase matching is formed atop the three-dimensional light guide 12. The 1st light guide 12 coupling to the optical fiber 14 has the propagation constant equal to the propagation constant of the optical fiber 14 in this case and, therefore, the optical coupling of the low coupling loss is executed between the optical fiber 14 and the 1st light guide 12. The coupling loss to the optical fiber 14 is decreased in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical coupler for receiving an optical signal from an optical fiber in an optical communication system such as an optical LAN or an optical CATV.

[Conventional technology]

In optical communication systems, optical signal information is transmitted via optical fibers, which are transmission paths for optical signal information, and various terminals, controllers, repeaters, etc.

It is very important to perform coupling with receiving equipment (hereinafter collectively referred to as terminal equipment) with low loss. This is because optical communication systems have network configurations such as bus and loop types in which information is transmitted in a relay manner through nodes, and as the number of terminal devices increases, the coupling loss at each node increases to a power. If the number of terminals increases, this becomes a particular problem because the number of terminal devices that can be accommodated within the optical communication system will be limited. In recent years, optoelectronic ICs (hereinafter referred to as 0EICs) and optical ICs have attracted attention as terminal devices that connect to optical fibers. These 0EICs and optical ICs have new functions, high-speed operation, This is aimed at achieving effects such as low power consumption.

Conventionally, optical waveguides have been used as optical couplers that optically couple optical fibers with lasers and photodetectors built into 0EICs and optical ICs.

In other words, the photodetector, grating, etc.
Optical coupling is performed with an external optical fiber via an optical waveguide configured inside an IC or optical IC, and the means for connecting the optical fiber and the optical waveguide is a butt coupling that brings the end of the optical fiber into close contact with the end surface of the optical waveguide. Alternatively, this has been achieved by polishing the end of the optical fiber diagonally or by adding a grating to couple it to the top surface of the waveguide.

[Problem to be solved by the invention]

In the conventional optical coupler mentioned above, 0EIC and optical IC
Since the refractive index, refractive index distribution, and shape of the optical waveguide and the optical fiber constituting the optical fiber are significantly different from each other, there is a drawback that coupling loss increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical coupler that performs optical coupling with an optical fiber with low coupling loss.

[Means to solve the problem]

The optical coupler of the present invention includes: a first optical waveguide that optically connects to an optical fiber; and a second optical waveguide that optically couples the first optical waveguide; The optical waveguide has a propagation constant equivalent to that of the Makki optical fiber.

The first optical waveguide may be the optical fiber itself, or f
, the first optical waveguide and the second optical waveguide may be provided close to each other to form a directional coupler.

Further, the first optical waveguide and the second optical waveguide may be T-shaped optical waveguides in which a grating is provided on the interconnecting section.

Furthermore, the first optical waveguide and the second optical waveguide are connected to each other through a T, which is provided with a beam splitter in the interconnecting part.
It may also be a letter-shaped optical waveguide.

The first optical waveguide section and the second optical waveguide may be branched optical waveguides.

[Effect]

Since the first optical waveguide coupled to the optical fiber has a propagation constant equivalent to that of the optical fiber, optical coupling with little coupling loss is performed between the optical fiber and the first optical waveguide.

〔Example〕

FIG. 1 is a diagram showing the appearance of a first embodiment of the present invention.

In this embodiment, a three-dimensional optical waveguide 12 and a groove 13 are provided on the surface of a substrate 11, and optical coupling is performed between a single mode optical fiber 14 embedded in the groove 13 and the three-dimensional optical waveguide 12. It is. Incidentally, a grating 15 for performing phase matching is formed in a bunn on the upper surface of the three-dimensional optical waveguide 12.

The manufacturing procedure of this example is described below.

First, a crystalline substrate 11 (
A mask was formed using a Ti film with a Cr base on the top surface (10mm x lomm x 2mmt), and this was
By immersing the substrate 11 in benzoic acid for 30 minutes to perform proton exchange, and then removing the Ti film, a three-dimensional light guide connecting opposite sides of the substrate 11 with slightly curved ends as shown in FIG. 1 is formed. A wave path 12 was created. Next, using the same mask, linear grooves 13 were formed by ion sputtering in one row and close to the long plane direction of the three-dimensional optical waveguide 12. Next, a part of the optical fiber 14 is made into an embedded part, which is a core and a cladding several μm thick around the core, over a length of 10 m+n (opposite sides of the substrate 11), and the embedded part is placed in the groove 13 described above. Filled with refractive index adhesive. At this time, since the optical fiber 14, which is an optical waveguide, and the three-dimensional optical waveguide 12 are formed close to each other at intervals of 2 μm to 5 μm over a length of 1 mm to 5 mm, optical directional coupling may occur. Since the refractive index of the optical fiber 14 and the substrate 11 are different from each other, it is necessary to perform phase matching using a grating. The lattice constant Δ of the grating is λ, which is the wavelength used for optical transmission. , the refractive index of the substrate 11 and the optical fiber 14 is given by the following equation.

Here λ. =0.83μm, nLN=2.23, n
, = 1.49, Δ~1.12 μm is obtained. There are various methods for forming a grating, but in this example, a relief-shaped grating 15 was formed on the three-dimensional optical waveguide 12 using an ion sputtering method.

Next, the operation of the optical coupler created through the above steps was confirmed using the following procedure.

Semiconductor laser light with a wavelength of 0.83 μm and other light are sequentially input to one end of the optical fiber 14, and in each case, the output light intensity at the other end of the optical fiber 14 and the light coupled to the three-dimensional optical waveguide 12 are determined. The strength was measured. In the case of semiconductor laser light, it has been confirmed that the incident light transitions to the optical waveguide 12 with a coupling efficiency of several percent, and in the case of other lights, most of the incident light is output from the other end of the optical fiber 14. It was confirmed that This shows that the loss of light due to scattering, absorption, etc. is extremely small. Therefore, it can be confirmed that the optical coupler of this example is an extremely effective element that can suppress optical attenuation to the necessary minimum when used in a passive optical node that does not perform amplification during relaying. Ta.

FIG. 2 is a diagram showing the appearance of a second embodiment of the present invention.

In this embodiment, a ridge-type optical waveguide 22 and a buried optical waveguide 24 are provided on a substrate 21 in the same positional relationship as the three-dimensional optical waveguide 12 and groove 13 shown in the first embodiment, and optical coupling is performed between them. It is something that allows you to do this.

The manufacturing procedure of this example is as follows.

Si-doped n”-GaAs substrate 21 (10 mm x
G with a thickness of about 1μa+ on
A cladding layer of a, -XAl, AS (X is 0.05 or less) and an optical waveguide layer of n--GaAs with a thickness of approximately 5 μm are epitaxially grown in this order, and then a width of 7 μm is formed by photolithography and ion beam milling.
A ridge-type optical waveguide 22 was formed. Next, a grating for phase matching was loaded on the upper surface of the ridge type optical waveguide 22, as in the case of the first embodiment. This is the lattice constant A
=0.647 (μm) AI@.

Then, by selective etching, a width of 12 μm and a depth of 10
A μm groove 23 was formed at a position close to the ridge type optical waveguide 23. After that, a 2 μm thick 5i film which becomes the cladding layer
O7 was formed in the groove 23 by sputter deposition, and then polymethyl methacrylate (hereinafter referred to as PMMA) serving as a core was filled in the groove 23 to form a buried optical waveguide 26. This embedded optical waveguide 26 has substantially the same propagation characteristics as the optical fiber 14 shown in the first embodiment, and its end surfaces are flush with each surface of the substrate 21. After this, a single-mode optical fiber 24. which has the same propagation characteristics as the optical fiber 14 with its tip polished. , 24
2 were aligned and brought into contact with both ends of the buried optical waveguide 26 so that the cores coincided with each other, and in this state, they were bonded and fixed using an adhesive that performs refractive index matching.

Therefore, an optical coupler having an external shape substantially similar to that of the first example was manufactured.

In this example, most of the optical loss occurs in the optical fiber 24.
．． , 242 and the PMMA waveguide layer in the buried optical waveguide 26, but since the propagation characteristics of both are very similar, losses such as reflection and scattering are extremely small, and the alignment accuracy can be improved. Only the optical loss caused by the positional deviation depending on was caused, and the value was about O11 to 0.2 dB, which was a sufficiently low value.

In this embodiment, as in the first embodiment, the optical fiber 25. Semiconductor laser light with a wavelength of 1.3 μm and other light were incident on one end of the ridge type optical waveguide 22, and the coupling efficiency and optical loss with the ridge type optical waveguide 22 were measured.

As a result, good results were obtained as in the case of the first example.

In this embodiment, the optical fiber used is a single-mode optical fiber, but a multi-mode optical fiber having substantially the same propagation characteristics as the PMMA waveguide layer portion may be used. The PMMA waveguide layer is multimode and n-
Since the optical waveguide layer portion of the ridge-type optical waveguide 22 made of GaAs is close to a single mode, the coupled mode is PMM.
This becomes some of the propagation modes of the A waveguide layer section, and other mode light passes through the PMMA waveguide layer section.

As explained above, in this embodiment, the transmission mode of each waveguide making up the directional coupler is different, so regardless of the type of optical fiber used, low loss and high efficiency transmission can be achieved. can be done. Therefore, by arranging a semiconductor laser or the like at the end of the ridge-type optical waveguide 22, optical signals can be easily transmitted.

FIG. 3 is a diagram showing the appearance of a third embodiment of the present invention.

In this embodiment, a ridge type optical waveguide 3:l, :14 and a photodiode:12 are used for optical coupling to a Si substrate 31-.
121, and detects the optical signal obtained by optical coupling.

The manufacturing procedure of this example is described below.

First, a Si substrate 31 on which a photodiode 32 had been previously formed was thermally oxidized in an oxygen atmosphere humidified with water vapor to form a Si02 layer that would become a buffer layer. Next, a composite film of 5in2 and 'ra,05 was formed with the refractive index adjusted to 1.49, and the film thickness was 8 μm.
A leading wave layer was formed. Next, using photolithography and ion beam etching, the width and height were both 8 μm.
Ridge-type optical waveguides (1) and 35, which are the first and second optical waveguides of m, were formed.

The ridge type optical waveguide 33 is created in a form in which opposite sides of the Si substrate 31 are connected in a straight line, and one end of the ridge type optical waveguide 35 is in contact with the photodiode 32, and the other end is in contact with the ridge type optical waveguide 3.
ridge type optical waveguide 3 so that optical directional coupling occurs with 3.
3 at intervals of 3 μm. After creating this ridge, a cladding layer was formed by sputter depositing 5in2. Next, the end faces of the optical fibers 34, 34□, which have approximately the same refractive index and diameter as the ridge-type optical waveguide 33, are polished,
Butt coupling was made to both ends of the ridge type optical waveguide 33. In this case, the optical fiber 34. , 342 is extremely unlikely to be lost at the junction with the ridge-type optical waveguide 33.

A part of the optical signal that enters the ridge-type optical waveguide 33 from the optical fiber 34+ is directionally coupled to the ridge-type optical waveguide 35 installed nearby, and enters the photodiode 32 formed on the substrate 51. This makes it possible to detect optical signals. In this example, since the propagation characteristics of the ridge-type optical waveguides : ] : ], : ] 5 constituting the directional coupler are the same, there is no need for phase matching using a grating, and the first and second optical waveguides are the same. The optical loss was further reduced compared to the bK example.

FIG. 4 is a diagram showing the appearance of a fourth embodiment of the present invention.

In this embodiment, in the third embodiment, the waveguides formed on the substrate are T-shaped, and are used as first and second optical waveguides.

In this embodiment, a substrate 41 .on which a photodetector 42 is formed. ) The step of configuring the ridge type optical waveguide 43 in 1 is the same as that in the third embodiment, and will therefore be omitted.

This ridge-type optical waveguide 43 is provided in a straight line in a direction connecting opposite sides of the substrate 41 (hereinafter referred to as the first direction),
An optical fiber 44. .
2, which is a second optical waveguide formed so as to be in contact with
It is composed of parts. After forming the ridge-type optical waveguide 43, a grating 45 is formed on the interconnecting part where the first part and the second part are connected to each other so that the grating 45 is inclined at 45 degrees with respect to the first direction. Light of a specific wavelength is Bragg-reflected and made incident on the second portion of the ridge-type optical waveguide 43. For this reason, the optical fiber 44. Since a part of the optical signal input to the photodetector 42 is input to the photodetector 42, the optical signal can be detected.

Note that in this embodiment, a grating is used to split a specific wavelength, but the same effect can be obtained by forming a narrow gap in the interconnecting portion and using it as a beam splitter.

FIG. 5 is a diagram showing the appearance of a fifth embodiment of the present invention.

In this embodiment, the wedge-type optical waveguides shown in the third and fourth embodiments are changed to a branched structure as shown in the figure, and are used as first and second optical waveguides.

In this example, a ridge type optical waveguide 5X is formed on a substrate 53 on which a photodetector 52 is formed by photolithography and ion beam etching so that both the width and height are 8 μm, and then 5i02 is sputter-evaporated. A cladding layer was formed. The ridge-type optical waveguide 51 includes a first portion that is a linear first optical waveguide connecting opposite sides of the substrate 53, and gradually branches from the first portion.
It is composed of a second portion that is a curved waveguide-shaped second optical waveguide whose open end is in contact with the photodetector 52 . After forming the ridge type optical waveguide 51, optical fibers 441, 442, 541, 542 were attached to the first portion using the same procedure as in the third and fourth embodiments.

Therefore, the portion of the optical signal input to the optical fibers 441, 442, 541 is input to the photodetector 42 as in the third and fourth embodiments, so that the optical signal can be detected.

In each embodiment of the present invention, GaAS was used as an example of the substrate to be coupled to the optical fiber, but Li
NbO3, InP, Si, glass, organic thin film, ZnO
1PLZT etc. are suitable. Furthermore, examples of optical waveguides that can have propagation characteristics equivalent to those of optical fibers include the fiber itself, 5in2, glass, and organic thin films.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

In the optical coupler according to the first aspect, by using the first optical waveguide whose propagation characteristics are equivalent to those of an optical fiber, optical loss due to scattering, reflection, mode mismatch, etc. occurring during coupling is reduced.

In the optical coupler according to the second aspect, since the optical fiber itself is used for the first optical waveguide, the above-mentioned effect is further increased.

In the optical coupler according to claim 3, since a directional coupler is configured, in addition to the above effects, it is easy to configure eight transmitters or receivers using the second waveguide section. becomes.

In the optical coupler according to claim 4, since the first and second optical waveguides are constituted by T-shaped optical waveguides with gratings provided on the upper part, the first and second optical waveguides are
Compared to the case where the optical waveguides are configured separately, the manufacturing process can be omitted, and optical signals of specific wavelengths can be selectively detected.

In the optical coupler according to claim 5, the first and second
Since the optical waveguide is constructed, manufacturing steps can be omitted as in the case of the optical coupler according to claim 4, and optical signals of all wavelengths can be detected.

In the optical coupler according to the sixth aspect, by configuring the first and second optical waveguide sections with branched optical waveguides, the degree of freedom in design can be increased when forming the optical coupler together with a photodetector etc. on a substrate.

[Brief explanation of the drawing]

1 to 5 are diagrams showing the appearance of first to fifth embodiments of the present invention. ++, 2+, :11.41.51...Substrate, 1
2...Three-dimensional optical waveguide, 1:l, 23...Groove, +4.24. ．． 24□, 341, 342, 441, 44
2,541.54□...Optical fiber, 15, 25.45...Grating, 22, 33
．． 35.43.51...Ridge type optical waveguide, 32.
...Photodiode, 42, 52...Photodetector. Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1. Optical fiber (14, 24_1, 24_2, 34_1
, 34_2, 44_1, 44_2, 54_1, 54_2
), a first optical waveguide (26, 33) optically connected to the second optical waveguide (26, 33), and a second optical waveguide (
12, 22), wherein the first optical waveguide has a propagation constant equivalent to that of the optical fiber. 2. The optical coupler according to claim 1, wherein the first optical waveguide is the optical fiber (14) itself. 3. The optical coupler according to claim 1, wherein the first optical waveguide and the second optical waveguide are provided close to each other to form a directional coupler. 4. In the optical coupler according to claim 1, the first optical waveguide and the second optical waveguide are T-shaped optical waveguides (43) provided with a grating (45) on the interconnecting part. An optical coupler featuring: 5. The optical coupler according to claim 1, wherein the first optical waveguide and the second optical waveguide are T-shaped optical waveguides in which a beam splitter is provided in the interconnecting part. coupler. 6. The optical coupler according to claim 1, wherein the first optical waveguide and the second optical waveguide are branched optical waveguides (51).