JPH08171031A - Optical communication system - Google Patents

Abstract

PURPOSE: To provide an optical communication system having high availability of light and capable of performing wholly dual bidirectional communication by a single optical fiber. CONSTITUTION: A light emitting/receiving device for optical transmission 21A, provided with a grating coupler 15A provided on a waveguide arranged on a silicon substrate on which a photodiode 11 is formed and a semiconductor laser 16A opposing to the grating coupler 15A, and a light emitting/receiving device for optical transmission 21B of the same type are arranged on the respective terminals and these light emitting/receiving devices for optical transmission are connected by means of an optical fiber 17. At the time of transmission, light beams from light emitting elements 16A, 16B having different light emitting wave lengths for every terminal are totally reflected by the grating couplers 15A, 15B, respectively, and transmitted to a terminal on the other side through the optical fiber 17. At the time of reception, an optical signal transmitted from the terminal on the other side through the optical fiber 17 is coupled to a waveguide 25 by means of the grating couplers 15A, 15B and received by photoelectrically converted by means of the photodiode 11 on the silicon substrate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication system using an optical fiber cable for a transmission line.

[0002]

2. Description of the Related Art An optical communication system using an optical fiber cable as a transmission line can extend a transmission distance with low loss, can transmit a large amount of information in a wide band, and can reduce electromagnetic induction and lightning interference. Since the fiber has a small diameter, light weight, flexibility, and is easy to lay, it is expected to make great progress in the future.

In such an optical communication system, as a one-core bidirectional transmission device capable of bidirectional communication using a single optical fiber, a type using a half mirror, a directional coupler in a waveguide is used. There are known types such as a type that uses a laser diode (LD), an LD transceiver type that uses a laser diode (LD) as an element that also serves as a light receiving element, and a PD transceiver type that uses a photodiode (PD) as an element that also serves as a receiving and reflecting element.

[0004]

Among the conventional optical communication systems described above, the type using a half mirror has a relatively large number of adjustment points and two-way communication is possible, but the light utilization efficiency is high. There is a problem that Also,
There are many adjustment points in the type that uses a directional coupler in the waveguide, the LD transceiver type that uses the laser diode (LD) as the light-receiving and dual-use element, and the PD transceiver type that uses the photodiode (PD) as the receiving and dual-use element. At the same time, there is a problem that full duplex bidirectional communication is basically difficult.

The present invention has been made in view of the present situation of the optical communication system of this kind as described above, and an object thereof is high utilization efficiency of light and full duplex of a single optical fiber. An object is to provide an optical communication system capable of bidirectional communication.

[0006]

In order to achieve the above object, the invention according to claim 1 provides a semiconductor substrate on which a light receiving element is formed, a waveguide provided on the semiconductor substrate, and the waveguide. An optical transmission / reception device for optical transmission, which includes a waveguide coupling element disposed in the optical waveguide coupling element and a light emitting element disposed opposite to the waveguide coupling element, is disposed in each terminal. Is an optical communication system configured by being connected to each other by an optical fiber, the emission wavelength of the light emitting element is set to a different value for each terminal, the waveguide coupling element,
By coupling an optical signal transmitted from the other terminal via the optical fiber to the waveguide, the optical signal is photoelectrically converted by the light receiving element and received, and the light of the light emitting element is guided by the light guide element. By being totally reflected by the waveguide coupling element, the light of the light emitting element is guided to the optical fiber as an optical signal and transmitted to the other party's terminal.

Similarly, in order to achieve the above-mentioned object, the invention according to claim 2 is characterized in that, in the invention according to claim 1, the waveguide coupling element is a grating coupler.

Similarly, in order to achieve the above-mentioned object, the invention according to claim 3 is the invention according to claim 1, characterized in that the waveguide coupling element is a prism coupler.

[0009]

According to the present invention, a waveguide coupling element disposed in a waveguide provided on a semiconductor substrate on which a light receiving element is formed,
An optical transmission / reception device including a light emitting element arranged with respect to the waveguide coupling element is disposed in each terminal, and these optical transmission / reception devices are connected to each other by an optical fiber. At the time of transmission, the light from the light emitting element in which the emission wavelength different for each terminal is set is totally reflected by the waveguide coupling element and transmitted to the partner terminal as an optical signal through the optical fiber. Further, at the time of reception, the optical signal transmitted from the partner terminal via the optical fiber is coupled to the waveguide by the waveguide coupling element, and the optical signal from the partner terminal is
It is photoelectrically converted by the light receiving element of the semiconductor substrate and received.

[0010]

【Example】

[First Embodiment] First, the first embodiment of the present invention will be described with reference to FIG.
This will be described with reference to FIG. FIG. 1 is an explanatory diagram showing an overall configuration of a first embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a configuration of a main part of the present embodiment.

In this embodiment, as shown in FIG. 1, optical communication light-receiving / emitting devices 21A and 21B are provided in each terminal, and these optical communication light-emitting / receiving devices 21A and 21B are mutually connected by an optical fiber 17. It is connected to the. The optical communication light receiving and emitting device 21A includes a semiconductor substrate portion 20 and the semiconductor substrate portion 2
0 and the semiconductor laser 16A arranged with respect to the semiconductor substrate section 20.
1 has a configuration in which the waveguide 25 is formed on the silicon substrate 10 formed on one end side.

The waveguide 25 has a refractive index of 1.46, a buffer layer 12 having a film thickness of 1 μm, a refractive index of 1.52 and a film thickness of 1.4.
6 μm waveguide layer 13 and refractive index 1.46 film thickness 0.8 μ
m of the cladding layer 14, and on the other end side of the semiconductor substrate portion 20, the cladding layer 14 has a period of 0.83 μm as a waveguide coupling element for exciting the light from the optical fiber 17 into the waveguide 25. Grating coupler 15A
Are formed. Further, at the position of the photodiode 11, the thickness of the buffer layer 12 is tapered so that the thickness of the buffer layer 12 becomes 0.1 μm, and the guided light is absorbed by the photodiode 11. The thicknesses of the waveguide layer 13 and the clad layer 14 are also changed to taper at the positions where the light is guided, so that the waveguide light is prevented from being scattered.

A semiconductor laser 16A is arranged to face the grating coupler 15A, and the semiconductor laser 16A
Light having a wavelength of 780 nm from A is collimated by the lens 22 and is incident on the grating coupler 15A at an incident angle of 45 °, is totally reflected by the grating coupler 15A, is incident on the lens 23, and is converged. It is configured to be transmitted to the light transmission / reception device 21B for optical transmission via 17. In addition, the light transmitting / receiving device 21 for optical transmission
The wavelength 68 transmitted from B via the optical fiber 17
The light of 0 nm is collimated by the lens 23 and is incident on the grating coupler 15A at an incident angle of 45 °. The light is excited in the waveguide 25 by the grating coupler 15A, photoelectrically converted by the photodiode 11, and received. It is configured to be.

On the other hand, in the optical transmission / reception device 21B, the wavelength of the light from the semiconductor laser 16B is 680 nm and the period of the grating coupler 15B is 0.97 μm.
However, the configuration of the other parts is the same as that of the light transmission / reception device 21A for optical transmission described above.

The operation of this embodiment having such a configuration will be described. In the optical communication of the present embodiment, the semiconductor laser 16A of the light transmitting / receiving device 21A for optical transmission emits light having a wavelength of 780 nm, and this light is collimated by the lens 22.
The grating coupler 15A is incident on the grating coupler 15A at an incident angle of 45 ° and has a period of 0.83 μm.
Is totally reflected with a reflection probability of 100%. The light totally reflected in this way enters the lens 23, is focused, is guided to the optical fiber 17, and is transmitted to the optical transmission / reception device 21B by the optical fiber 17.

In this way, the light transmitting / receiving device 21 for optical transmission is used.
The light transmitted to B is collimated by the lens 23 and is incident on the grating coupler 15B at an incident angle of 45 °. The grating coupler 15B having a period of 0.97 μm causes the waveguide 25 to have a coupling probability of about 70%. It is excited inside and is photoelectrically converted by the photodiode 11 and is almost 90%.
It is received with the reception probability of.

On the other hand, the semiconductor laser 16B of the light transmitting / receiving device 21B for optical transmission emits light having a wavelength of 680 nm.
This light is collimated by the lens 22, is incident on the grating coupler 15B at an incident angle of 45 °, and has a period of 0.
With a 97 μm grating coupler 15B, 10
Total reflection is performed with a reflection probability of 0%. The light totally reflected in this way is made incident on the lens 23 and focused to form the optical fiber 1.
7 and is transmitted to the light transmission / reception device 21A for optical transmission by the optical fiber 17.

In this way, the optical transmission / reception device 21 is used.
The light transmitted to A is collimated by the lens 23 and is incident on the grating coupler 15A at an incident angle of 45 °. The grating coupler 15A having a period of 0.83 μm causes the waveguide 25 to have a coupling probability of about 70%. It is excited inside and photoelectrically converted by the photodiode 11,
It is received with a% reception probability.

As described above, according to this embodiment, the light having the wavelength of 780 nm emitted from the semiconductor laser 16A of the light transmitting / receiving device 21A for optical transmission is totally reflected by the grating coupler 15A having a period of 0.83 μm, and is used for optical transmission. It is not excited in the waveguide 25 of the light emitting and receiving device 21A,
The grating coupler 15 having a period of 0.97 μm is transmitted to the light transmitting / receiving device 21B for optical transmission through the optical fiber 17.
B is excited in the waveguide 25 of the optical transmission / reception device 21B, photoelectrically converted by the photodiode 11, and received.

Similarly, the light having a wavelength of 680 nm emitted from the semiconductor laser 16B of the light transmitting / receiving device 21B for optical transmission is
The light is totally reflected by the grating coupler 15B having a period of 0.97 μm, and the waveguide 2 of the light transmitting / receiving device 21B for optical transmission is used.
5 is transmitted to the light transmitting / receiving device 21A for optical transmission through the optical fiber 17 without being excited in the optical fiber 5, and the period is 0.83 μm.
The grating coupler 15A excites the light in the waveguide 25 of the light transmitting / receiving device 21A for optical transmission, photoelectrically converts it by the photodiode 11, and receives it. Therefore, according to the present embodiment, the simple configuration of the single-core optical fiber
It becomes possible to perform full duplex two-way communication under high light utilization efficiency.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram showing the configuration of the main part of the second embodiment of the present invention.

In this embodiment, as shown in FIG. 3, as the waveguide coupling element, instead of the grating coupler of the first embodiment, prism couplers 30A and 30B made of flint glass with an Appe number of 50 or less are used. Is provided.
The prism couplers 30A and 30B have a refractive index of 6
1.7936 at 80 nm, 1.785 at 780 nm
The angle of incidence on the prism coupler 30 is set to 56.8 ° for the optical transmission / reception device 21A and 57.3 ° for the optical transmission / reception device 21B. The configuration of the other parts of this embodiment is the same as that of the first embodiment already described, and therefore a duplicate description will not be given.

The operation of this embodiment having such a configuration will be described. In the optical communication of the present embodiment, the semiconductor laser 16A of the light transmitting / receiving device 21A for optical transmission emits light having a wavelength of 780 nm, and this light is collimated by the lens 22.
The light is incident on the prism coupler 30A at an incident angle of 56.8 °, and is totally reflected by the prism coupler 30A with a reflection probability of 100%. The light totally reflected in this way enters the lens 23, is focused, is guided to the optical fiber 17, and is transmitted to the optical transmission / reception device 21B by the optical fiber 17.

In this way, the light transmitting / receiving device 21 for optical transmission is used.
The light transmitted to B is collimated by the lens 23 and is incident on the prism coupler 30B at an incident angle of 57.3 °.
The prism coupler 30B excites the light in the waveguide 25 with a coupling probability of approximately 70%, photoelectrically converts it in the photodiode 11, and receives it with a reception probability of approximately 90%.

On the other hand, the semiconductor laser 16B of the optical transmission / reception device 21B emits light having a wavelength of 680 nm,
This light is collimated by the lens 22, enters the prism coupler 30B at an incident angle of 57.3 °, and is totally reflected by the prism coupler 30B with a reflection probability of 100%. The light totally reflected in this way enters the lens 23, is focused, is guided to the optical fiber 17, and is transmitted to the optical transmission / reception device 21A by the optical fiber 17.

In this way, the light transmitting / receiving device 21 for optical transmission is used.
The light transmitted to A is collimated by the lens 23 and is incident on the prism coupler 30A at an incident angle of 56.8 °, and the prism coupler 30A guides the light inside the waveguide 25 with a coupling probability of about 70%. Photodiode 1
The signal is photoelectrically converted at 1 and is received with a reception probability of almost 90%.

As described above, according to this embodiment, the light having the wavelength of 780 nm emitted from the semiconductor laser 16A of the light transmission / reception device 21A for optical transmission is totally reflected by the prism coupler 30A and guided by the light transmission / reception device 21A for optical transmission. It is not excited in the waveguide 25 but is transmitted to the light transmitting / receiving device 21B for optical transmission through the optical fiber 17, and the prism coupler 30 is used.
B is excited in the waveguide 25 of the optical transmission / reception device 21B, photoelectrically converted by the photodiode 11, and received.

Similarly, the light having a wavelength of 680 nm emitted from the semiconductor laser 16B of the light transmitting / receiving device 21B for optical transmission is
The light is totally reflected by the prism coupler 30B and is not excited in the waveguide 25 of the optical transmission / reception device 21B.
The light is transmitted to the light transmission / reception device 21A for optical transmission through the optical fiber 17, excited by the prism coupler 30A into the waveguide 25 of the light transmission / reception device 21A for optical transmission, photoelectrically converted by the photodiode 11, and received.

Therefore, according to the present embodiment, it is possible to perform full-duplex bidirectional communication with high light utilization efficiency with a simple structure using a single-core optical fiber, and further, the semiconductor laser 16A. , 16B, the bidirectional communication can be carried out in a stable state in which the reception intensity at the photodiodes 11 of the optical transmission / reception devices 21A, 21B is not attenuated even when the wavelengths of the light from the optical transmissions, 16B vary.

In each of the embodiments, the case where a silicon substrate is used as the semiconductor substrate and a semiconductor laser having a relatively short wavelength is used has been described, but the present invention is not limited to these embodiments. It is also possible to use, for example, a phosphide-indium substrate as the semiconductor substrate and to use a semiconductor laser having a longer wavelength. Also, in each example,
Although the case where the grating coupler and the prism coupler are used as the waveguide coupling element has been described, the present invention is not limited to the embodiments, and an interference film coupler can be used as the waveguide coupling element. is there.

[0031]

According to the invention described in claim 1 or claim 2, at the time of transmission, the light emitted from the light emitting element in which the emission wavelength different for each terminal is set is the waveguide provided on the semiconductor substrate. Is totally reflected by the waveguide coupling element formed on the optical fiber, transmitted as an optical signal to the partner terminal through the optical fiber, and at the time of reception, the optical signal transmitted from the partner terminal through the optical fiber is the waveguide coupling element. Since it is coupled to the waveguide by the light receiving element of the semiconductor substrate and photoelectrically converted, the single optical fiber is used, and the simple configuration with few adjustment points reduces the manufacturing cost and high light utilization efficiency. It becomes possible to carry out full duplex bidirectional communication below.

According to the third aspect of the invention, in addition to the effect obtained by the first aspect of the invention, since the waveguide coupling element is a prism coupler, there is no variation in the reception characteristic with respect to the wavelength variation of the light emitting element. Stable transmission / reception becomes possible.

[0028]

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an overall configuration of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a main part of the embodiment.

FIG. 3 is an explanatory diagram showing a configuration of a main part of a second embodiment of the present invention.

[Explanation of symbols]

 10 Silicon substrate 11 Photodiode 12 Buffer layer 13 Waveguide layer 14 Cladding layer 15A, 15B Grating coupler 16A, 16B Semiconductor laser 17 Optical fiber 20 Semiconductor substrate part 21A, 21B Optical communication light emitting / receiving device 22, 23 Lens 30A, 30B Prism Coupler

Claims (3)

[Claims] 1. A semiconductor substrate on which a light receiving element is formed, a waveguide provided on the semiconductor substrate, a waveguide coupling element disposed on the waveguide, and a waveguide coupling element opposed to the waveguide coupling element. An optical transmission / reception device including a light emitting element, the optical transmission / reception device being provided in each terminal, and these optical transmission / reception devices being connected to each other by an optical fiber. The emission wavelength of the element is set to a different value for each terminal, and the waveguide coupling element couples the optical signal transmitted from the partner terminal via the optical fiber to the waveguide, whereby the optical signal Is received by being photoelectrically converted by the light receiving element, and by totally reflecting the light of the light emitting element by the waveguide coupling element, the light of the light emitting element is guided to the optical fiber as an optical signal and is transmitted by the other party. Is transmitted to the side terminal Optical communication system characterized by being configured to. 2. The optical communication system according to claim 1, wherein the waveguide coupling element is a grating coupler. 3. The optical communication system according to claim 1, wherein the waveguide coupling element is a prism coupler.