JPS61249004A - Optical multiplexer and demultiplexer - Google Patents

Abstract

PURPOSE:To form an optical multiplexer and demultiplexer of the light module integrated with light emitting elements and photodetectors with simple constitution by providing the elements which receive and emit the light signal leaking under the cut-off condition of a propagation mode onto a tapered optical waveguide. CONSTITUTION:The tapered optical waveguide 2 having the refractive index larger than the refractive index of a substrate 3 is formed on the substrate and the width (f) of the waveguide 2 is selected at the value to guide the light when the light signal of wavelengths lambda1-lambda3 is made incident to the waveguide. The light signal of the wavelength lambda1 is made into the leak mode in the part 2a and is radiated from the waveguide; similarly the light of the waveguides lambda2, lambda3 are successively demultiplexed in the parts 2b, 2c. The waveguide acts therefore as the optical demultiplexer when the photodetectors are disposed in the parts 2a-2c and the waveguide acts as the optical multiplexer and demultiplexer when the light emitting elements are provided thereto in conjunction with the optical multiplexer. The monolithic constitution of the optical multiplexer and demultiplexer with single chip is thus made possible, by which the simpler and more economical constitution thereof is made possible. Since there are no adjusting points, the considerable reduction of the cost is attained by mass production.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an optical multiplexer/demultiplexer, and particularly to an optical multiplexer, an optical demultiplexer, an optical multiplexer/demultiplexer, etc. used for optical wavelength multiplexing transmission in optical fiber communication. with optical devices.

The present invention relates to optical modules in which semiconductor light emitting/light receiving elements and the like are incorporated into these devices.

[Background of the invention]

Important elements in the transmission characteristics of optical fibers are transmission loss and frequency band, and depending on the type of light emitting element, the coupling characteristics with the fiber are also important. When used for relatively short distances such as optical information transmission, optical control, and optical measurement, coupling with the light emitting element is more important than transmission loss, so optical fibers with as large a numerical aperture (NA) as possible, such as multi-band optical fibers, are used. Mode fibers are advantageous. On the other hand, long wavelength optical fiber has low loss.

Because it has the feature of wideband, long-distance, large-capacity transmission can be realized, and reliability, economy, and maintainability can be expected to be improved by reducing the number of repeaters. In particular, single mode fibers without mode dispersion are attracting attention as broadband fibers. Single-mode fiber transmission is the ultimate form of optical fiber communication in the future, and is an important technology for making optical wavelength division multiplexing transmission economical and expanding services in optical fiber communication.

In other words, optical wavelength division multiplexing, which propagates multiple signal lights in one optical transmission path, not only increases the amount of transmission, but also expands the range of applications of optical communications by improving the freedom and flexibility of system configuration. It is considered an important method for measuring Furthermore, in optical wavelength division multiplexing transmission, an optical multiplexer/demultiplexer becomes an essential device.

For conventional optical demultiplexers, configurations using interference film filters, configurations using diffraction gratings, configurations using prisms, etc. are being considered (Hisayoshi Yanai, "Optical Communication Handbook", published by Chokoku Shoten, September 1, 1982). Day.

(See p. 324-331). Those using interference film filters utilize the wavelength selectivity of the interference filter film, which is a stack of high/low refractive index dielectric films with an optical thickness close to 1/4 wavelength or 1/2 wavelength. It realizes a duplexer. but,
In this type of optical demultiplexer, it is necessary to increase the number of filters as the number of channels increases, and therefore insertion loss tends to increase as the number of channels increases. Also,
As a diffraction grating, a blazed diffraction grating is used, which concentrates diffracted light on a specific order.

With this type of optical demultiplexer, there is almost no increase in loss as the number of channels increases up to a considerable degree of multiplicity.

Suitable for optical demultiplexing circuits with a relatively large number of channels.

Also, those using a prism are used in the initial stage before using a diffraction grating, and like those using a single diffraction grating, this is also an angular dispersion type optical demultiplexer. but,
These optical multiplexers/demultiplexers have a hybrid configuration made of a combination of individual parts, so they have a complex structure and a large number of parts, and it takes time to assemble and adjust the optical axis, making it impossible to reduce costs and downsize. However, both mass productivity and reliability are extremely poor. These problems make it difficult to expand the scope of application of optical communication systems.

[Purpose of the invention]

The purpose of the present invention is to solve such conventional problems and to integrate an optical demultiplexer, an optical multiplexer, an optical multiplexer/demultiplexer, a semiconductor light emitting/light receiving element, etc., which can be simpler and more economical than the conventional ones. An object of the present invention is to provide an optical multiplexer/demultiplexer such as an optical module.

[Summary of the invention]

In order to achieve the above objects, the optical multiplexer/demultiplexer of the present invention includes an optical waveguide having a tapered shape whose width is gradually narrowed, a plurality of optical signals having different wavelengths propagated on the optical waveguide, and a plurality of optical signals having different wavelengths propagated on the optical waveguide. It is characterized by comprising a plurality of light-receiving elements each receiving an optical signal leaked from the optical waveguide according to the cut-off condition of the propagation mode, or a semiconductor light-emitting element in which all or a part of the light-receiving elements are replaced. .

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 9 is a diagram showing the principle of light propagation in an optical fiber. The refractive index of core 2, which is the center of the optical fiber, is nl,
If the refractive index of the outer cladding 9 is nl, then the core 2
When light is incident on the cladding 9 at an angle θ1, and the light is transmitted through the cladding 9 at an angle θ2, the following relationship holds between these refraction angles according to Snell's law.

Now, if nt>nl, θl>θ2.

As the angle θl becomes smaller, θ2 becomes 0 and total reflection occurs. In order to connect the phenomenon of waveguiding expressed by total reflection of light with wave motion, which is another property of light, it is convenient to express it as a specific set of light called a mode. That is, for light traveling within the core 2 at an angle θ1 with respect to the boundary, the propagation constant kO is expressed by the following equation, assuming that the wavelength in vacuum is λ.

This value is because the refractive index is nl in the core 2.
The wavelength becomes λ/n L, and the propagation constant becomes kon
It becomes large as l. If the component of the propagation constant of a plane wave traveling in the horizontal direction is γ, then γ=(ko nr) sin θ.

The lateral distribution of light intensity does not change along the axis. This form is called a mode, and is formed only when the angle between the light and the boundary surface is a special value. If the width of the core 2 is 28, the phase change of one period in the lateral direction of the waveguide is λ
It is expressed as the sum Δφ of ×2aX2 and the phase change −2φ caused when the light is further totally reflected twice at the upper and lower boundary surfaces.

If the amount of phase change Δφ is an integral multiple of 2π, for example, N times, all the multiple reflected waves overlap at the same position, resulting in a type of standing wave. N=1.2,3
．． The superposition of plane waves corresponding to . If this value is set to NMAX, total reflection will not occur for N larger than this, and the light will escape to the cladding 9. Modes with angles greater than the maximum number of waveguide modes NMAX cannot propagate, so they are said to be cut off.

The optical multiplexer/demultiplexer of the present invention demultiplexes or multiplexes light by utilizing the cutoff characteristics of an optical waveguide. For three-dimensional optical waveguides such as shapes.

It is a configuration of an optical demultiplexing element, an optical multiplexing element, or an optical multiplexing/demultiplexing element. Furthermore, on this optical waveguide, semiconductor light emitting devices (semiconductor lasers, light emitting diodes, etc.) and light receiving devices,
Functional elements such as a light modulation element and an optical switch are also integrated.

Specifically, by gradually tapering the optical waveguide, the wavelength λ1. λ2. ...λ.

The light of (λl>λ2>...λn) is sequentially leaked under cutoff conditions. An optical demultiplexer can be constructed by sequentially arranging light-receiving elements in the leaky portions of the optical waveguide. Moreover, instead of the above-mentioned light receiving element, the wavelength is λ1. λ2. By arranging n semiconductor light emitting elements of λn, an optical multiplexer can be constructed. Furthermore, by mixing semiconductor light-emitting elements and light-receiving elements, an optical multiplexer/demultiplexer can be constructed. Note that the shape distribution of the tapered optical waveguide includes the parabolic distribution type tapered optical waveguide shown in FIG. 10(a), the linear gradient distribution type tapered optical waveguide shown in FIG. A horn-type tapered optical waveguide, etc. can be used. Also, the width (or thickness) of the optical waveguide to become a cutoff mode at wavelength λn
fn is selected so as to satisfy the following equation.

Here, np is the refractive index of the optical waveguide, and nc is the refractive index of the cladding surrounding the optical waveguide.

FIG. 1 is a configuration diagram of an optical demultiplexing element that utilizes the cutoff characteristics of an optical waveguide, showing a first embodiment of the present invention. 1st
FIG. 1(a) is a top view, and FIG. 1(b) is a left side view. Substrate 3 (e.g. Ga AI As, LiNb
C)1. Materials such as glass and polymers, refractive index ns)
Optical waveguide 2 tapered upward (refractive index nF, however, nF
>ns) is formed.

Here, the tapered optical waveguide 2 has a parabolic distribution type. Now, from the arrow 1 side, the wavelength λ1. Consider the case where an optical signal of λ2°λ3 (where λ3>λ2>λl) is incident on the optical waveguide 2. The width f of the optical waveguide is determined by the above λ1. λ2.
a 2 a is selected as a value that allows light with a wavelength of λ3 to be guided.
The width f3 of the optical waveguide at the portion is set to satisfy the following equation.

However, nc:1.

As a result, the optical signal of wavelength λ3 meets the cut-off condition at the portion 2a, so it becomes a leakage mode, leaks as shown by arrow 4, and is radiated from the optical waveguide. However, λ2.
f3 is set so that the optical signal of λ1 is guided through the portion 2a. Specifically, make it so that, similarly,
The width f2 of the optical waveguide in the portion 2b is set to satisfy the following equation.

As a result, the optical signal of wavelength λ2 is cut off at the portion 2b, becomes a leaky mode, and is emitted from the optical waveguide as shown by arrow 5. In this case as well, the width f1 of the optical waveguide of the 0th-order 20th part is set so that the optical signal of λ1 is guided through the part 2b, and the width f1 of the optical waveguide of the 20th order part is also set to satisfy the following equation.

As a result, the optical signal 2c having the wavelength λ1 is cut off, becomes a leaky mode, and is emitted from the optical waveguide as shown by the arrow 6. In this way, the wavelength λ3. which was propagating through the optical waveguide. λ2. Each optical signal of λl is 2 a
It is sequentially demultiplexed at the e 2 b * 2 c portion. Therefore, by arranging semiconductor light-receiving elements at portions 2a, 2b, and 2c, an optical demultiplexer is constructed. Furthermore, if a semiconductor light emitting element is placed in place of the light receiving element, an optical multiplexer can be constructed. Furthermore, if a semiconductor light emitting element and a light receiving element are mixed, an optical multiplexer/demultiplexer can be obtained. In addition, in FIGS. 1 to 8.

Although embodiments of tapered optical waveguides are shown.

It can be applied to any of the parabolic distribution type, linear gradient distribution type, and horn type (see Fig. 10).

FIG. 2 is a perspective view of waveguides of various shapes showing an embodiment of the present invention.

In addition to the ridge-type configuration of the optical waveguide shown in FIG. 1, there are other configurations of the optical waveguide shown in FIGS. A shape as shown in l (d) can be used. FIG. 2(a) shows the core part 2 and the clad part 3.
It is a buried waveguide embedded in the

The demultiplexed optical signal is brought close to the core part 2 and sent to another core part (
(not shown), and the leaked light is extracted by propagating through this separately provided core section. FIG. 2(b) shows a diffused optical waveguide. The core portion 7 is configured such that the refractive index decreases from the center toward the periphery, so that light leakage can be more easily performed.

In this case, the light can be extracted by embedding a core part for propagation of demultiplexed light close to the core part 7, or by arranging core parts formed by a diffusion method in parallel in the same way as the core part 7. conduct. Next, FIG. 2(c) shows a loaded groove waveguide. This is constructed by forming a cladding part 9 on a substrate 3 (refractive index n3) and providing a core part 8 (refractive index ncwnc>ns) thereon. Next, FIG. 2(d) shows an embankment type waveguide. A core portion 10 is formed on the substrate 3.

FIG. 3 is a configuration diagram of an optical demultiplexing element showing a second embodiment of the present invention.

Note that λ1 to λ3 are λn〉 in all examples.
The relationship is λn-1>...λ3>λ2>λ1. In FIG. 3, a tapered curved optical waveguide 2d is provided on the substrate 3 to promote leakage and at the same time to provide a sufficient distance between the light receiving elements 11, 12, and 13. That is, by using a tapered curved optical waveguide, it is possible to prevent the optical signal with the wavelength λ3 from leaking into the light receiving element 12, and to suppress the optical signal with the wavelength λ2 from leaking into the light receiving element 13. can. In addition, element 1
1, 12, all or part of 13,
It can also be replaced with a semiconductor light emitting device. Light receiving element 11
, 12.13 is also advantageous in that a large amount of optical and electrical crosstalk attenuation can be achieved. Also, when considering the size of the light-receiving elements, it is advantageous to leave space between the elements.

FIG. 4 is a configuration diagram of an optical demultiplexing element showing a third embodiment of the present invention.

FIG. 4 shows an example in which one-minute wavelength light is extracted to opposite sides. That is, the optical waveguide 2e has an asymmetric structure,
An optical signal with a wavelength λ2 is transmitted from the upper side of the optical waveguide section 14,
An optical signal with a wavelength λl is transmitted from the lower side of the optical waveguide section 15,
Take out each.

Therefore, the optical waveguide 2d has a structure that is bent downward above the portion 14 and bent upward below the portion 15. In this way, by extracting optical signals from opposite sides, it is possible to increase the amount of optical and electrical crosstalk attenuation between the optical signals of λ1 and λ2. Furthermore, a sufficient space for arranging a light receiving element (or one light emitting element) can be secured, and a light emitting element driving circuit and a light receiving element receiving circuit can be integrated on the same substrate.

FIG. 5 shows a fourth embodiment of the present invention, and is a configuration diagram of an optical demultiplexer that allows leakage light to be extracted more easily.

In contact with the optical waveguide 2e (refractive index nE), the optical waveguide 2g (
refractive index nc) + optical waveguide 2h (refractive index nH), and the cut-off wavelength λ2 . This makes it easier to extract the optical signal of λl. Here, ncwn
l( is a value almost equal to nE (however, nE>nc+n
H), the more effective light extraction becomes. In addition, 1
2.13 is a light receiving element.

FIG. 6 is a configuration diagram of an optical demultiplexing element showing a fifth embodiment of the present invention, and shows a case where lenses 16 and 17 are provided in front of the light receiving element. The optical signals leaked through these lenses 16 and 17 are taken into the light receiving elements 11 and 12.

Thereby, leaked light can be efficiently coupled to the light receiving elements 11 and 12. In addition, in FIG. 6, it is configured for bidirectional use, and from the direction of arrow 1, the wavelength λ2
An optical signal with a wavelength of λ3 enters the optical waveguide 21, and from the direction of the arrow 18, an optical signal of the light emitting element with a wavelength of λ1 enters the optical waveguide 21.
1 and exits in the direction of arrow 19. That is, if an optical fiber (single mode) is connected to the end face 20,
Wavelength λ1. λ2. The optical signal of λ3 will be wavelength-multiplexed and bidirectionally transmitted within the optical fiber.

FIG. 7 is a structural diagram of an optical demultiplexer showing a sixth embodiment of the present invention, in which the thickness of the tapered optical waveguide 2j is changed in an inclined manner. Figure 7(a) is a top view, Figure 7(a) is a top view;
b) is a right side view. As shown in (b), when the thickness of the optical waveguide 2j changes in an inclined manner, the leakage light emitted from the optical waveguide force due to the cutoff condition propagates in the direction where the optical waveguide is thinner, From the optical waveguide, arrows 4, 5.
It is radiated like 6. Of course, the width of the optical waveguide and the wavelength λ1
゜λ2. By configuring the relationship with λ3 to satisfy both equations (4) to (8), arrows 4 and 5 can be
．． 6 separately λ[, λ2 . An optical signal with a wavelength of λ3 is extracted in leaky mode. Such a structure is effective when extracting one-minute wavelength light only from one side (the upper side in the figure). As shown in Figure 7(b), if the thickness of the thin part at the tip of the part that slopes from thick to thin is made too thin, the insertion loss will increase, so single mode optical fiber transmission Select the thickness dimension from within the range of conditions.

FIG. 8 is a structural diagram of an optical demultiplexer showing a seventh embodiment of the present invention, and shows a modification of FIG. 7. That is, by providing a thin film 2k (refractive index n K +, where nK is extremely close to nJ, the relationship nK < nJ) on the tapered optical waveguide 2j (refractive index nJ), the arrow The propagation of the demultiplexed light in directions 4 and 5 is promoted and guided to the light receiving elements 11 and 12. In addition, in FIGS. 7 and 8, substantially the same characteristics can be expected even if the refractive index n of the optical waveguide is provided with a slope as described above instead of providing a slope in the thickness of the optical waveguide.

Although various shapes of the embodiments have been described above, the present invention is not limited to these embodiments.

For example, it goes without saying that the configurations shown in FIGS. 1 to 8 can be combined in various ways. In other words, as mentioned above, the shape distribution of the tapered optical waveguide includes waveguides of the parabolic distribution type, the linear slope distribution type, the horn distribution type (see Figure 10), as well as combinations of these waveguides, and There are various types of waveguides such as bent waveguides (see Figures 3, 4 and 5), variable thickness waveguides (see Figures 7 and 8), and graded index waveguides (see Figure 8). A combination of can be used. In addition, these tapered optical waveguides can undergo continuous and discontinuous shape changes (for example, continuous changes include first
See Figure 3, and Figures 4 to 7 for discontinuous items.
(see figure). Moreover, it goes without saying that either a symmetrical structure or an asymmetrical structure may be used (see FIG. 1 and FIG. 10 for a symmetrical structure, and FIGS. 3 to 8 for an asymmetrical structure). A Fresnel lens can be used as the lenses 16 and 17 shown in FIG. Furthermore, optical switches, optical modulators, electrical circuits, etc. can also be formed on the optical waveguide. Note that the wavelength multiplexing number can be applied to two or more waves, and can be applied to either unidirectional or bidirectional transmission.

〔Effect of the invention〕

As explained above, according to the present invention, an optical waveguide type optical demultiplexer, an optical multiplexer, an optical multiplexer/demultiplexer, and a semiconductor light emitting/demultiplexer can be used.
Optical devices with built-in photodetectors, optical switches, etc. can be constructed monolithically on a single chip, making them simpler and more economical.

Moreover, since there are no adjustment points, significant cost reductions can be expected through mass production. Furthermore, if electric circuits are also integrated on optical waveguides, costs and yields comparable to those of semiconductor integrated circuits can be expected.

[Brief explanation of drawings]

Fig. 1 is a structural diagram of an optical demultiplexer showing the first embodiment of the present invention, Fig. 2 is a diagram showing the structure and shape of the optical waveguide of the invention, and Figs. FIG. 9 is a diagram showing the principle of light propagation in an optical fiber; FIG. 10 is a basic configuration diagram of an optical waveguide of the present invention. . 1: Direction of incidence of light into the optical waveguide, 2, 2a to 2: Optical waveguide, core part, 3 = substrate, 9: Clad part, 11 to 13
: Light receiving element or light emitting element, 16° 17: Lens, 7,
8, 10, 14. ．． 15: Part of optical waveguide. Figure 1 (b) (a) Figure 2 (a) Figure 3 Figure 5 Figure 6 @ Figure 7 (a) (1))
Figure 8 (&) (b) Figure 9 Figure 1O

Claims (5)

[Claims] (1) An optical waveguide with a tapered shape whose width gradually becomes narrower, and a plurality of optical signals with different wavelengths propagated on the optical waveguide, and leakage from the optical waveguide due to the cutoff condition of the propagation mode at the tapered part. What is claimed is: 1. An optical multiplexer/demultiplexer comprising: a plurality of light-receiving elements each receiving an optical signal; or a semiconductor light-emitting element in which all or a portion of the light-receiving elements are replaced. (2) A tapered shape consisting of a parabola, straight line, or horn shape with a narrow width, a partial bend, a partial thickness change, or a combination of shapes with a refractive index distributed in the thickness direction. an optical waveguide, and a plurality of light receiving elements that propagate a plurality of optical signals of different wavelengths on the optical waveguide and each receive an optical signal leaked from the optical waveguide according to a cutoff condition of a propagation mode at a tapered portion. An optical multiplexer/demultiplexer comprising a semiconductor light emitting element in which all or part of the light receiving element is replaced. (3) The optical multiplexer/demultiplexer according to claim 2, wherein another optical waveguide is provided close to the tapered optical waveguide at a position where an optical signal leaks from the optical waveguide. (4) The optical multiplexer/demultiplexer according to claim 2, wherein a lens is provided close to the tapered optical waveguide at a position where an optical signal leaks from the optical waveguide. (5) A patent characterized in that the optical waveguide is configured by integrating an optical demultiplexer, an optical multiplexer, an optical demultiplexer/multiplexer, a semiconductor light emitting element/light receiving element, an optical switch, or an electric circuit. An optical multiplexer/demultiplexer according to claim 2.