JP2006140718A - Optical communications system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communications system that uses a small-sized optical amplifier. <P>SOLUTION: The optical communication system has an optical transmitter, a first optical transmission line, a semiconductor optical amplifier, a second optical transmission line, and an optical receiver. The optical transmitter outputs a signal light. The first optical transmission line receives the signal light and transmits the polarized-wave direction while holding it. The semiconductor optical amplifier amplifies the signal light transmitted by the first optical transmission line. The second optical transmission line receives the signal light amplified by the semiconductor optical amplifier. The optical receiver receives the signal light transmitted by the second optical transmission line. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical communication system.

  In a large-capacity, long-distance backbone optical communication system, submarine optical communication system, and the like, an optical amplifier is mainly used to compensate for transmission path loss. As this optical amplifier, an erbium-doped optical fiber amplifier (hereinafter referred to as EDFA) is widely known.

  With the spread of the Internet in recent years, low-capacity and short-distance optical communication systems have been installed in offices, buildings, condominiums, or homes. In such an optical communication system, it is preferable to use a small optical amplifier.

  However, since the EDFA has an excitation light source in addition to a sufficiently long erbium-doped optical fiber, a relatively large installation space is required.

  Therefore, an object of the present invention is to provide an optical communication system suitable for installation indoors, such as in a station, in a building / condominium, or in a home.

  The optical communication system of the present invention includes an optical transmitter, a first optical transmission line, a semiconductor optical amplifier, a second optical transmission line, and an optical receiver. The optical transmitter outputs signal light. The first optical transmission line receives the signal light and transmits it while maintaining its polarization direction. The semiconductor optical amplifier amplifies the signal light transmitted through the first optical transmission line. The second optical transmission line receives the signal light amplified by the semiconductor optical amplifier. The optical receiver receives the signal light transmitted through the second optical transmission line.

  The optical communication system of the present invention uses a semiconductor optical amplifier that can be reduced in size as compared with the EDFA, and is therefore suitable for installation indoors such as in a station, in a building / condominium, or in a home. In general, the gain of a semiconductor optical amplifier has polarization dependency, and its value changes according to the polarization direction of the input signal light. However, in the present invention, since the first optical transmission line maintains the polarization direction of the signal light, the polarization direction of the signal light incident on the semiconductor optical amplifier is constant. Therefore, the semiconductor optical amplifier can amplify the signal light with a constant gain regardless of the polarization dependence of the gain.

  The optical communication system of the present invention further comprises an optical branching device for branching the signal light from the semiconductor optical amplifier, and the second optical transmission line is a plurality of optical transmissions receiving a plurality of signal lights branched by the optical branching device. The optical receiver may include a plurality of optical receivers that receive signal light from the plurality of optical transmission paths. According to this configuration, the branch loss of the optical branching device is compensated by the semiconductor optical amplifier.

  The polarization direction held by the first optical transmission line may be a polarization direction in which the semiconductor optical amplifier has the maximum gain. According to this configuration, the signal light is reliably amplified with the maximum gain.

  The first optical transmission line may be a polarization maintaining optical fiber or an absolute single polarization maintaining optical fiber.

  Since the optical communication system of the present invention uses a semiconductor optical amplifier, the installation space can be reduced. Therefore, this optical communication system can be suitably installed in a station, a building / apartment, or a home.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

  FIG. 1 is a diagram illustrating a configuration of an optical communication system according to the first embodiment. An optical communication system 10 shown in FIG. 1 includes a first optical transceiver 12, a first optical transmission line 14, a semiconductor optical amplifier 16, a second optical transmission line 18, and a second optical transceiver 20. . In the present embodiment, the optical communication system 10 is installed indoors, such as in a station, in a building / condominium, or in a home. The optical communication system 10 is connected to an external optical transceiver 22, which is connected to an external optical transmission path 24. The optical transceiver 22 receives an optical signal from the optical transmission path 24 and converts it into an electrical signal, and inputs it to the optical communication system 10. The optical transceiver 22 receives an electrical signal from the optical communication system 10, converts it into an optical signal, and outputs it to the optical transmission line 24.

  The first optical transceiver 12 is connected to an external optical transceiver 22 and includes a transmission unit 26 and a reception unit 28. The transmission unit 26 includes a semiconductor light emitting element and a driver circuit for driving the semiconductor light emitting element. The semiconductor light emitting element generates linearly polarized light polarized in a predetermined direction. The driver circuit drives the semiconductor light emitting element based on the electrical signal received from the external optical transceiver 22. The first optical transmission line 14 is connected to the optical output port of the optical transceiver 12, and the linearly polarized optical signal generated by the semiconductor light emitting element is output to the optical transmission line 14. The transmitter 26 further has a pigtail (hereinafter referred to as a PMF pigtail) made of a polarization maintaining optical fiber. This PMF pigtail transmits only light in a specific polarization direction. This polarization direction coincides with the polarization direction of the light emitted from the light emitting element. The optical transmission line 14 is connected to this PMF pigtail. The receiving unit 28 includes a semiconductor light receiving element, receives an optical signal from the first optical transmission line 14, and converts it into an electrical signal. The receiver 28 outputs this electrical signal to the external optical transceiver 22.

  The first optical transmission line 14 is connected between the first optical transceiver 12 and the semiconductor optical amplifier 16, and transmits optical signals bidirectionally between the optical transceiver 12 and the semiconductor optical amplifier 16. The optical transmission line 14 transmits light while maintaining its polarization direction. In the present embodiment, the optical transmission line 14 is a polarization maintaining optical fiber that transmits only light in a specific polarization direction. The optical transmission line 14 receives an optical signal from the optical transceiver 12 and transmits it to the semiconductor optical amplifier 16 while maintaining the polarization direction. The optical transmission line 14 receives an optical signal from the semiconductor optical amplifier 16 and transmits the optical signal to the optical transceiver 12 while maintaining the polarization direction.

  In addition to the first optical transmission line 14, a second optical transmission line 18 is also connected to the semiconductor optical amplifier 16. The semiconductor optical amplifier 16 receives and amplifies the optical signal from the optical transmission line 14 and outputs it to the optical transmission line 18. The semiconductor optical amplifier 16 receives and amplifies the optical signal from the optical transmission line 18 and outputs the amplified optical signal to the optical transmission line 14.

  The second optical transmission line 18 is connected between the semiconductor optical amplifier 16 and the second optical transceiver 20, and transmits optical signals bidirectionally between the semiconductor optical amplifier 16 and the optical transceiver 20. Similar to the optical transmission line 14, the optical transmission line 18 transmits an optical signal while maintaining its polarization direction. In the present embodiment, the optical transmission line 18 is also a polarization maintaining optical fiber. The optical transmission line 18 receives an optical signal from the semiconductor optical amplifier 16 and transmits the optical signal to the optical transceiver 20 while maintaining the polarization direction. The optical transmission line 18 receives the optical signal from the optical transceiver 20 and transmits it to the semiconductor optical amplifier 16 while maintaining the polarization direction.

  The second optical transceiver 20 includes a transmission unit 30 and a reception unit 32. The transmission unit 30 receives an electrical signal for communication from a communication device (for example, a computer) installed indoors together with the optical communication system 10. The transmission unit 30 drives the semiconductor light emitting element based on an electrical signal input from an indoor communication device, and outputs an optical signal corresponding to the electrical signal. This optical signal is transmitted to the optical transmission line 18. The transmitter 30 further has a PMF pigtail. The polarization direction of the PMF pigtail coincides with the polarization direction in which the gain of the semiconductor optical amplifier 16 is maximized. The optical transmission line 18 is connected to this PMF pigtail. The receiving unit 32 has a configuration similar to that of the receiving unit 28 and generates an electrical signal corresponding to the optical signal received from the second optical transmission line 18. The transmission unit 30 has the same configuration as the transmission unit 26.

  Hereinafter, the operation of the optical communication system 10 will be described. The optical signal transmitted through the optical transmission path 24 is converted into an electrical signal by the optical transceiver 22. This electrical signal is converted into an optical signal by the transmission unit 26 of the optical transceiver 12. This optical signal propagates through the optical transmission line 14 while maintaining its polarization direction, and enters the semiconductor optical amplifier 16. The optical signal is amplified by the semiconductor optical amplifier 16 and then input to the receiving unit 32 of the optical transceiver 20 via the optical transmission line 18. Thus, the optical signal from the outside is transmitted to the optical transceiver 20.

  In the optical communication system 10, optical communication in the direction opposite to the propagation direction of the optical signal described above is also possible. The transmission unit 30 of the optical transceiver 20 converts the input electrical signal into an optical signal and sends it to the optical transmission line 18. The optical transmission line 18 transmits an optical signal while maintaining its polarization direction. The optical signal is amplified by the semiconductor optical amplifier 16 and then input to the optical transceiver 12 through the optical transmission line 14. The optical transceiver 12 converts the optical signal into an electrical signal and sends it to an external optical transceiver 22, and the optical transceiver 22 converts the electrical signal into an optical signal and outputs it to an external optical transmission line 24. To do. Thus, the optical signal generated indoors is transmitted to the outdoor optical communication network.

  The semiconductor optical amplifier 16 can be reduced in size as compared with the EDFA and has an advantage that the band is wide. By constructing the optical communication system 10 using the small semiconductor optical amplifier 16, the installation space of the optical communication system 10 can be reduced. For this reason, this optical communication system 10 can be suitably installed indoors, such as in a station, in a building or apartment, or in a home.

  In general, the gain of a semiconductor optical amplifier has polarization dependence, and its value changes according to the polarization direction of input light. However, in this embodiment, since the optical transmission lines 14 and 18 maintain the polarization direction of the optical signal, the polarization direction of the optical signal incident on the semiconductor optical amplifier is constant. Therefore, the semiconductor optical amplifier can amplify the signal light with a constant gain regardless of the polarization dependence of the gain.

  The polarization direction of the optical signal held by the optical transmission lines 14 and 18 is preferably the polarization direction in which the semiconductor optical amplifier 16 has the maximum gain. In other words, the polarization directions held by the optical transmission lines 14 and 18 are the same as the polarization directions of the optical signals generated by the transmitters 26 and 30, respectively, and the semiconductor optical amplifier 16 has the maximum gain. It is the same as the wave direction. According to this configuration, the optical signal can be reliably amplified with the maximum gain.

  The polarization maintaining optical fibers used as the optical transmission lines 14 and 18 are preferably absolute single polarization maintaining optical fibers. The polarization maintaining optical fiber can transmit the input light in two orthogonal polarization directions while maintaining the polarization directions. However, when an external pressure is applied to a polarization maintaining optical fiber, mode coupling occurs in two transmittable polarization directions, and the polarization direction of the input light cannot be maintained and the other polarization direction is changed. is there. On the other hand, an absolute single polarization maintaining optical fiber transmits only light in a single polarization direction. Even if external pressure is applied to an absolute single polarization maintaining optical fiber, there is no other polarization direction that causes mode coupling, so the absolute single polarization maintaining optical fiber ensures the polarization direction of the input light. Can be held. Therefore, if an absolute single polarization maintaining optical fiber is used as the optical transmission lines 14 and 18, a desired polarization direction can be reliably maintained.

  Next, an optical communication system according to the second embodiment will be described. FIG. 2 is a diagram showing the configuration of this optical communication system. The optical communication system 10a shown in FIG. 2 is different from the first embodiment in that it includes a plurality of second optical transmission lines 18 and second optical transceivers 20 and further includes an optical hub 36. The optical hub 36 includes a semiconductor optical amplifier 16 and an optical branching device 34, and the optical branching device 34 is connected between the semiconductor optical amplifier 16 and the plurality of second optical transmission lines 18. The optical branching device 34 and the semiconductor optical amplifier 16 are integrated on the same substrate. The optical branching device 34 branches the optical signal from the semiconductor optical amplifier 16 into a plurality of optical signals, and outputs one of them to the transmission destination optical transceiver 20. Further, when receiving the optical signal from one of the plurality of optical transmission lines 18, the optical branching device 34 outputs the optical signal to the semiconductor optical amplifier 16. If communication devices are connected to each optical transceiver 20, bidirectional optical communication is possible between these communication devices and an outdoor optical communication network.

  The optical branching device 34 in the optical hub 36 can be manufactured using a quartz waveguide, a plastic waveguide, a semiconductor waveguide, or the like. If the optical branching device 34 and the semiconductor optical amplifier 16 are integrated on the substrate in a hybrid or monolithic manner, the optical hub 36 can be reduced in size and the manufacturing cost can be reduced. The semiconductor optical amplifier 16 preferably has an active layer made of GaInNAs and is formed on a GaAs substrate. Such a semiconductor optical amplifier can be manufactured at low cost and has excellent temperature characteristics.

  Since the optical communication system 10a uses the semiconductor optical amplifier 16 similarly to the first embodiment, a small installation space is required. Further, the semiconductor optical amplifier 16 can compensate for the branching loss of the optical branching device 34. Therefore, this optical communication system 10a can be suitably installed indoors having a plurality of communication devices.

  Furthermore, in the optical communication system 10a, since the optical branching device 34 and the semiconductor optical amplifier 16 are integrated on the same substrate, the installation space can be further reduced and the price can be reduced.

  Although the above embodiment has shown that bidirectional transmission is performed with one optical transmission line, two optical transmission lines and two semiconductor optical amplifiers may be used for transmission in each direction. .

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

FIG. 1 is a diagram illustrating a configuration of an optical communication system according to the first embodiment. FIG. 2 is a diagram illustrating a configuration of an optical communication system according to the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Optical communication system, 12 ... 1st optical transmitter / receiver, 14 ... 1st optical transmission line, 16 ... Semiconductor optical amplifier, 18 ... 2nd optical transmission line, 20 ... 2nd optical transmitter / receiver, 22 ... External optical transceiver, 24 ... External optical transmission path, 26 ... Transmitter, 28 ... Receiver, 30 ... Transmitter, 32 ... Receiver, 34 ... Optical splitter, 36 ... Optical hub

Claims (5)

An optical transmitter that outputs signal light;
A first optical transmission line that receives the signal light and transmits the signal light while maintaining the polarization direction;
A semiconductor optical amplifier for amplifying the signal light transmitted by the first optical transmission line;
A second optical transmission line for receiving the signal light amplified by the semiconductor optical amplifier;
An optical receiver for receiving the signal light transmitted by the second optical transmission line;
Comprising
Optical communication system. An optical branching device for branching the signal light from the semiconductor optical amplifier;
The second optical transmission path includes a plurality of optical transmission paths that receive the plurality of signal lights branched by the optical splitter.
The optical receiver includes a plurality of optical receivers that receive the signal light from the plurality of optical transmission lines.
The optical communication system according to claim 1. The polarization direction held by the first optical transmission line is a polarization direction in which the semiconductor optical amplifier has a maximum gain.
The optical communication system according to claim 1 or 2. The first optical transmission line is a polarization maintaining optical fiber;
The optical communication system in any one of Claims 1-3. The first optical transmission line is an absolute single polarization maintaining optical fiber;
The optical communication system in any one of Claims 1-3.

Images