JPS6394205A - Optical excitation device for bidirectional transmission - Google Patents

Abstract

PURPOSE:To permit coupling of an optical integration module for bidirectional transmission and optical fiber with high efficiency by disposing an input waveguide of a refractive index n1 and optical waveguide of a refractive index n0 (n1>=n0) in parallel and contact with each other so that both the waveguide have a tapered shape. CONSTITUTION:The input waveguide 12 of the refractive index n1 and the optical waveguide 14 of the refractive index n0 are disposed in parallel and contact with each other via the layer of a refractive index nc1 on a substrate 8 (n1>=n0>nc1). The outer peripheries of the two parallel disposed waveguides 12, 14 are coated with a layer of a refractive index nc2 (n1<=n0>nc1<=nc2). An optical fiber 5 or semiconductor optical element is disposed to one end of the input waveguide 12 and the opposite side thereof is formed to the tapered shape. The waveguide 14 on one end side of the waveguide 12 is also formed to the tapered shape. A light signal repeats reflections in the tapered parts, by which the reflection angle thereof is increased and the light is efficiently coupled to the waveguide 14 or the waveguide 12. The coupling of the optical integration module for bidirectional transmission and the optical fiber 5 is thereby permitted with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for connecting an optical fiber and a waveguide, and a method for connecting a semiconductor light emitting or light receiving element to a thin waveguide.

[Conventional technology]

With the rapid development of optical fiber communications, semiconductor light emitting devices,
Research on so-called optical integrated circuits, which integrate light-receiving elements, optical switches, optical modulation elements, optical coupling/demultiplexing elements, optical waveguides that wave light, etc., has become active. An important issue in this optical integrated circuit is the coupling between the optical waveguide and the above-mentioned optical element or optical fiber. That is,
What is important is how efficiently to combine them.

Conventionally, typical examples of the above-mentioned coupling methods include the end face direct coupling method as shown in FIG. 5 and the coupling method via a tapered waveguide as shown in FIG. ).

[Problem that the invention seeks to solve]

Although the method shown in Fig. 5 has a simple structure, there is a restriction that the size of the optical waveguide 9 must be close to the diameter of the core part of the optical fiber in order to obtain high coupling efficiency, and there is freedom in designing the optical waveguide. There is no degree.

The method shown in Fig. 6 is an improved method of Fig. 5, in which the input waveguide 1
The refractive index nl of 0 is the refractive index n of the optical waveguide 9.

The refractive index of the substrate 8 is set to be equal to or larger than , and lower than the refractive index ns'@:no + nt of the substrate 8. With this configuration, the size of the optical waveguide 9 can be designed without regard to the diameter of the core portion 6 of the optical fiber 5, and instead, the thickness and width of the thin waveguide 10 are adjusted to the size of the core portion of the optical fiber. Designed to be.

Therefore, light from the optical fiber is coupled into the manual waveguide 10 with high efficiency. The light is then excited into the optical waveguide with high efficiency via the tapered portion 11 of the input thin waveguide. In FIGS. 5 and 6, a semiconductor laser may be used instead of the optical fiber. However, although the excitation method in FIG. 6 is effective as a method for excitation from an optical fiber or semiconductor laser to an optical waveguide, This method is not suitable for an excitation method in which an optical fiber 5 is connected to an optical module 1 for bidirectional transmission as shown in FIG. That is, the optical module 1 has an optical fiber 5.
In the case of FIG. 6, in which the light with wavelength λ2 propagating within the optical waveguide 9 must be coupled into the optical fiber 5, and the light with the wavelength λl from the optical module 1 must be coupled into the optical fiber 5. It is very difficult to couple the light that is in the optical waveguide 9 to the core 6 of the optical fiber 5 through the input waveguide 10 with high efficiency.
This is because it is difficult to couple to the input waveguide 10 due to propagation as shown in FIG.

This tendency is particularly strong when the size and refractive index of the optical waveguide 9 are determined for single mode or low-order mode transmission.

An object of the present invention is to solve the above problems.

That is, the object is to achieve highly efficient coupling between an optical integrated module for bidirectional transmission and an optical fiber. Another object of the present invention is to provide a method that allows a degree of freedom in design so that the size of the optical waveguide can be selected regardless of the above-mentioned improvement in efficiency.

[Means for solving problems]

The above object is achieved by the following configuration method. That is, an input thin wave path with a refractive index nl and a leading wave path with a refractive index no are arranged in parallel on the substrate via a layer with a refractive index nc1, nl, ≧-n.

>ncl), and the outer periphery of both waveguides arranged in parallel has a refractive index n
cz Cnt>no>ncsnnc2), an optical fiber or a semiconductor optical device is arranged at one end of the input waveguide, the opposite end is made into a Taber shape, and the optical waveguide at one end of the input waveguide is also This is achieved by using a tapered configuration.

[Effect]

An optical signal from an optical fiber (or a semiconductor light emitting device) is excited into an input waveguide, propagates through the input waveguide, and is repeatedly reflected in a zigzag pattern within the tapered section, increasing the reflection angle each time, and gradually transmitting light inside the optical waveguide. will be combined into. Conversely, an optical signal propagating in the opposite direction within the leading waveguide gradually increases its reflection angle as it enters the tapered part of the optical waveguide, is efficiently coupled to the input waveguide, and is then transmitted from the input waveguide to the optical fiber. The signals are combined and propagate in the opposite direction through the optical fiber.

〔Example〕

FIG. 1 shows an embodiment of the bidirectional transmission frequency excitation method of the present invention. This figure shows a part of a side view, and optical elements such as a semiconductor laser and a light receiving element are omitted. However, in reality, it naturally exists. 5 is an optical fiber, 6 is a core portion, and 7 is a cladding portion. Light is transmitted in both directions within this optical fiber. The input thin wave path (refractive index nx) 12 has a tapered portion 13 with an angle αB.

The optical waveguide (refractive index no.) 14 also has a tapered portion 15 with an angle α^
have. In this case, the refractive index of the substrate 8 is ncl. The relationship between each refractive index is determined as shown in the following equation.

. □, ≧-no>. . □ ・・・
(1) The upper surface of the input waveguide 12 is covered with air in this case. Input waveguide 12. In this case, the optical waveguide 14 is 3
Although it is a dimensional waveguide (embedded type, ridge type, etc.), it may be a slab waveguide as long as a lens is provided between the optical fiber and the input waveguide. Here, angle αB, α
The angle ^ is preferably as small as possible so that the coupling between the input waveguide 12 and the optical waveguide 14 is strong.In other words, if it is approximately expressed by a ray equation, the refraction to the waveguide on the side adjacent to the above angle is The relationship with the angle θ is expressed as follows. In the above equation, nl and no are approximately equal. The closer θ is to 90", the larger the amount of bonding can be. Therefore, from equation (2), the smaller αB is, the better. Specifically, it is preferably 10° or less. Also, the values of α^ and αB are The smaller it is, the smaller the light emitted to areas other than the waveguide can be suppressed.

FIG. 2 shows another embodiment of the bidirectional transmission moonlight excitation method of the present invention. This is the input waveguide.

It has a structure in which an optical waveguide 12 is placed below and an optical waveguide 14 is provided above. Since the upper part of the optical waveguide 14 is covered with air, the coupling efficiency from the optical waveguide to the input waveguide is better than in the case of FIG.

Figure 3 shows a low refractive index (ncx) below the input waveguide in Figure 2.
layer 16 and a low refractive index (n cz) layer 1 on top of the optical waveguide.
7, respectively. In this case, the refractive index of substrate 8 may be higher than the refractive index of 16.

FIG. 4 shows an embodiment of an optical module in which a semiconductor laser 24 is provided on a substrate 8. In the figure, 18 is an InP layer, 1
9 is an InP buffer layer, 25 is an InGaAsP active layer, 26 is an InP buffer layer, and 27 is an InP cladding layer. Reference numeral 12' denotes an input waveguide for coupling the semiconductor laser 24 and the optical waveguide 14, and its refractive index is selected so that the coupling efficiency with the semiconductor laser 24 is optimized. Therefore, the refractive index may be different from that of the 12 input waveguides.

The present invention is not limited to the above embodiments. First, the material of the substrate may be glass, sapphire, etc. in addition to semiconductors. In addition to semiconductor optical elements, the substrate may also include optical multiplexing/demultiplexing elements, optical switch elements, optical multiplexing/demultiplexing elements, and optical multiplexing/demultiplexing elements. Optical elements such as elements, lenses, etc.
It may include an electric circuit (a laser drive circuit, an amplifier circuit, etc.).

[Effects of the Invention] According to the present invention, it is possible to realize highly efficient coupling between an optical integrated module for bidirectional transmission and an optical fiber (or a semiconductor optical device). Further, since the size of the optical waveguide can be selected almost independently of the above-described high efficiency, a degree of freedom in design can be provided.

[Brief Description of the Drawings] Figures 1, 2, 3, and 4 are diagrams showing an embodiment of the bidirectional transmission moonlight excitation method of the present invention, and Figures 5 and 6 are diagrams showing conventional FIG. 7, which is a diagram showing a method of coupling a fiber (or semiconductor optical device) and an optical module, is a schematic diagram of a bidirectional transmission optical module and an optical fiber being considered by the present inventor. DESCRIPTION OF SYMBOLS 1... Optical module for bidirectional transmission, 2... Light emitting element, 3... Light receiving element, 4... Optical multiplexer/demultiplexer, 5... Optical fiber, 6... Core part, 7... ...Clad part, 8.
... Substrate, 9... Optical waveguide, 10, 12, 12'...
・Input optical waveguide, 13.13', 15,15'...
Tapered part, 14... Optical waveguide, 16.17... Clad part, 18... InP layer, 19... InP buffer layer, 24... Semiconductor laser, 25-InGaAsP
Active layer, 26 ”・I n P puff No. 117 Z 2 +] Z3 Figure/b Kura, 7 do 17 Kura・・do bitterp Name 5 Lower Cla 1. Do (p 'Hb Lower 7 run) - IP IO )sne%ikz q
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Claims (1)

[Claims] 1. An input waveguide with a refractive index n_1 and an optical waveguide with a refractive index n_0 (n_1≧n_0) are arranged in parallel and in contact with each other,
Both waveguides arranged in parallel are covered with a layer having a refractive index lower than the above refractive index, an optical fiber or a semiconductor optical element is arranged at one end of the input waveguide, and the other end has a tapered shape, Furthermore, an optical excitation device for bidirectional transmission is characterized in that the optical waveguide on the input waveguide side also has a tapered shape. 2. The optical excitation device for bidirectional transmission according to claim 1, wherein both the waveguides are formed on a substrate. 3. An optical excitation device for bidirectional transmission according to claim 2, characterized in that at least one semiconductor optical device is formed on the substrate.