JP2005072737A - Optical transmitting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high-speed optical transmission at a distance longer than conventional distance by suppressing deterioration in wavelength due to mode dispersion of a multi-mode optical transmission path. <P>SOLUTION: Using a graded index type optical transmission path as an optical path, an excitation mechanism capable of exciting a specific mode is provided between an optical transmission section and an optical transmission path or midway along the optical transmission path, and a transmissive mechanism for allowing a specific mode to transmit is provided midway along the optical transmission path or between the transmission path and an optical receiver. According to this configuration, excitation of a specific low order mode is possible at a low loss, as well as the component of the low order mode can be selectively transmit at a low loss immediately before the optical transmitter even if one part is converted to the high order mode midway along the transmission path. Accordingly, the deterioration in wavelength due to mode dispersion of the multi-mode optical transmission path can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical transmission system including an optical transmission unit, an optical reception unit, and an optical transmission line connecting between them, and in particular, can suppress waveform deterioration due to mode dispersion in a multimode optical transmission line. Thus, the present invention relates to an optical transmission system that realizes high-speed optical transmission over a longer distance than before.

  Conventionally, multimode optical fibers, which are optical transmission lines capable of propagating in a plurality of modes, have been widely used in building floors, between floors, and LAN (local area network) wiring between buildings. This is due to the fact that the core diameter is as large as about 50 μm or 62.5 μm, so that the connection work is easy and the peripheral devices and parts are inexpensive.

  As described above, in the conventional optical transmission system, as shown in FIG. 8, the multimode optical fiber 1 which is an optical transmission path capable of propagating in a plurality of modes is used between the optical transmitter 11 and the optical receiver 12. Connected.

  In recent years, with an increase in performance of computers and an increase in image data, it is required to increase the speed of these optical transmission lines. In the case of an optical transmission system having a conventional configuration as shown in FIG. Because of waveform deterioration due to propagation delay difference (mode dispersion) between multiple modes propagating in the wavelength range, the transmission distance is about 65 m at 10 Gbit / s, and the latest broadband (2000 MHz-km) multimode optical fiber is used. However, it was limited to about 300m.

  For this reason, in buildings where old optical fibers have already been installed, the transmission distance is not sufficient when trying to increase the network speed from 100 Mbit / s or 1 Gbit / s to 10 Gbit / s. In many cases, a single mode optical fiber or a broadband multimode optical fiber has to be laid again, and there is a problem that a large amount of money is required.

  On the other hand, when a multimode optical fiber is used, as a method of avoiding the influence of mode dispersion, a single mode optical fiber 2 is connected to the entrance portion of the multimode optical fiber 1, for example, as shown in FIG. An invention is disclosed in which the lowest-order mode is excited on the transmission side by the structure (see, for example, Non-Patent Document 1).

As a mode restriction on the receiving side, a single mode transmission characteristic is shown at a long wavelength of 1.2 to 1.7 μm, but a multimode transmission characteristic is shown at a short wavelength of 0.6 to 1.0 μm. When a step index type optical fiber having a core diameter of about 10 μm is used as an optical transmission line, the core diameter is about 6 μm, which exhibits single mode transmission characteristics even for short wavelengths of 0.6 to 1.0 μm. An invention is disclosed in which a step index type optical fiber is connected to the exit portion to perform transmission over a wider band than before using light having a short wavelength of 0.6 to 1.0 μm (for example, Patent Document 1).
US Patent US6185346 JP2003-21723

  However, according to the invention described in Non-Patent Document 1, even if only the lowest order mode is excited at the entrance portion, the optical fiber is bent or stressed in the middle of the optical transmission line, so It is unavoidable to occur. However, in the present invention, no consideration is given to the higher-order mode on the receiving side, and from this, waveform dispersion is unavoidable due to the effect of mode dispersion due to the higher-order mode generated during propagation. There was a problem.

  On the other hand, in the invention described in Patent Document 1, a step index type so-called single mode optical fiber (multimode operation at a short wavelength) with a core diameter of about 10 μm is assumed as an optical transmission line. If this is applied to a step index type multimode optical fiber having a larger core diameter (multimode operation at both long and short wavelengths), the following problems arise.

  That is, for example, when a step index type multimode optical fiber having a core diameter of 50 μm is used as an optical transmission line, the excited fundamental mode has a large diameter of about 40 μm, so that a so-called single mode optical fiber having a mode diameter of about 10 μm ( The coupling loss with the optical fiber for excitation) is not practical because the coupling loss is 6 dB or more per connection point and cannot be ignored. On the other hand, the graded index type multimode optical fiber having a core diameter of 50 μm has a small fundamental mode diameter of about 16 μm, and the coupling loss when this is connected to a so-called single mode optical fiber (excitation optical fiber) is It can be almost ignored at 1 dB or less per connection point. Such knowledge is not described at all in Patent Document 1, but is a technique newly presented by the present invention.

  The present invention has been made to solve such a problem, and its purpose is to suppress waveform deterioration due to mode dispersion in a multimode optical transmission line, so that it can be performed at a longer distance than before. It is to realize high-speed optical transmission. Another object is to speed up an existing local area network composed of graded index type multimode optical fibers.

  In order to achieve this object, the optical transmission system of the present invention uses a graded index optical transmission line as the optical transmission line, and is specified between the optical transmission unit and the optical transmission line or in the middle of the optical transmission line. And a transmission mechanism capable of transmitting a specific mode in the middle of the optical transmission path or between the optical transmission path and the optical receiver.

  Thus, the optical transmission system of the present invention differs from the prior art in that a mechanism capable of transmitting a specific mode is introduced even on the optical receiver side, which has not been considered in the prior art.

  By adopting such a configuration, it is possible to avoid the problem that the mode dispersion is affected by the higher-order mode that occurs during propagation through the optical transmission line.

  Further, in the optical transmission system of the present invention, instead of using a step index type multimode optical transmission line as an optical transmission line for preventing waveform degradation due to mode dispersion, a graded index with a small mode diameter of the base mode is used. This is different from the prior art in that a multimode optical transmission line is used.

  Conventionally, since a step index type multimode optical fiber is used as the optical transmission line, the diameter of the fundamental mode is as large as about 40 μm, and the coupling loss with the single mode optical fiber is as large as 6 dB or more and cannot be ignored. Not practical. On the other hand, in the present invention, since a graded index type multimode optical fiber is used as an optical transmission line, the diameter of the fundamental mode is as small as about 16 μm, and when this is connected to a single mode optical fiber. The coupling loss is as small as negligible at 1 dB or less. Therefore, high-speed transmission over a long distance is possible.

  According to the optical transmission system of the present invention, waveform deterioration due to mode dispersion in a multimode optical transmission line can be suppressed, so that high-speed optical transmission over a longer distance than before can be realized.

  By applying the present invention to an existing local area network composed of graded index multimode optical fibers, it is possible to increase the speed of the existing local area network. Can be realized at low cost.

  The optical transmission system according to the present invention is composed of an optical transmission unit, an optical reception unit, and an optical transmission line connecting them, and uses a graded index optical transmission line as the optical transmission line. Further, an excitation mechanism capable of exciting a specific mode (for example, a base mode) is provided between the optical transmission unit and the optical transmission path or in the middle of the optical transmission path, and in the middle of the optical transmission path or the optical transmission path. A transmission mechanism capable of transmitting a specific mode (for example, a base mode) is provided between the optical receiver and the optical receiver.

  As this graded index type optical transmission line, a standardized graded index type optical fiber having a core diameter of 50 μm or 62.5 μm can be used, but the core diameter is not limited to 50 μm or 62.5 μm. It may be 40 μm or more and 100 μm or less which is a practical value in the vicinity.

  As the excitation mechanism, a single mode type optical transmission line composed of a single mode optical fiber or a single mode plane light wave circuit, an optical system including a lens, or a specific position of the core part of the optical transmission line is used. A diaphragm having an opening can be used.

  As the transmission mechanism, a single-mode optical transmission line composed of a single-mode optical fiber or a single-mode planar lightwave circuit is used, an optical system including a lens is used, or an optical transmission line core is specified. A diaphragm having an opening at the position can be used.

  FIG. 1 shows a first embodiment of an optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 11 is an optical transmitter, 12 is an optical receiver, 13 is a single-mode optical fiber for excitation, and 14 is a single-mode optical fiber for transmission.

  In this embodiment, a graded index type multimode optical fiber 10 (core diameter 50 μm, bandwidth 500 MHz-km) having a length of 300 m is used as an optical transmission line.

  As a mechanism capable of exciting a specific mode between the graded index type multimode optical fiber 10 and the optical transmitter 11 incorporating a light source having a wavelength of 1.3 .mu.m, an excitation of 2 m in length is used. A single-mode optical fiber 13 (core diameter 9 μm) is used, and the two fibers are connected via a connector so that the core centers coincide with each other.

  As a mechanism capable of transmitting a specific mode between the graded index type multimode optical fiber 10 and the optical receiver 12, a single-mode optical fiber for transmission 14 having a length of 2 m (core diameter 9 μm) is used. ) And are connected via a connector so that the core centers of both fibers coincide.

  As described above, in the present invention, the graded index type multimode optical fiber 10 in which the power of the low-order mode is concentrated near the center of the core is used, so that the graded index type multimode optical fiber 10 and a single unit are used. By connecting the mode optical fibers 13 and 14, good mode coupling can be realized between the two, and the loss can be reduced compared to the conventional method of connecting the step index type optical fibers. The connection is realized.

  In the present invention, by providing the excitation single mode optical fiber 13, it is possible to excite a specific low-order mode with low loss, and by providing the transmission single mode optical fiber 14, Even if a part of the transmission path is converted to a higher-order mode, the lower-order mode component is selectively transmitted with low loss immediately before the optical receiving unit 12, and unnecessary higher-order mode components are removed. In addition, since the low-order mode component with sufficient strength can be received, there is an effect that the waveform deterioration due to the delay time difference between the modes does not occur, and the transmission distance of the high-speed signal can be greatly expanded as compared with the conventional configuration. Is possible.

  For example, in the conventional configuration, the transmission distance of a 10 Gbit / s signal is about 65 m, but according to the present invention, the distance is at least four times as long, or ten times or more when a transmission line in good condition is used. Can be transmitted error-free, so the old multimode optical fiber with a bandwidth of 500 MHz-km or less already used can be used as it is, without re-installing a new wideband multimode optical fiber or single mode optical fiber. There is an advantage that the network can be speeded up with cost.

  In the present embodiment, the case where the graded index multimode optical fiber 10 having a core diameter of 50 μm is used has been described. However, when this is a graded index multimode optical fiber 10 having a core diameter of 62.5 μm, for example. The same effect is obtained, and the present invention is effective.

  In this embodiment, the case where the lengths of the single mode optical fibers 13 and 14 are 2 m has been described. However, the same effect can be obtained when the length is 1 m or 5 m, and the present invention is effective. It is. However, according to the experimental results, it has been found that when the lengths of the single mode optical fibers 13 and 14 are 1 cm or less, a remarkable effect cannot be obtained.

  In the present embodiment, the case where the specific mode is excited and transmitted has been described. However, even if a component other than the mode is slightly included at this time, all the modes are excited and transmitted although there is a difference in degree. Since the waveform deterioration due to mode dispersion is suppressed as compared with the conventional configuration, the present invention is effective.

  Further, in this embodiment, a light source having a wavelength of 1.3 μm is used, but mode dispersion is suppressed even when a light source of 1.55 μm is used, and the present invention is effective. Further, when a 0.85 μm band light source is used, the same effect can be obtained by setting the core diameter of the single mode optical fibers 13 and 14 to 6 μm, and the present invention is effective.

  FIG. 2 shows a second embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 11 is an optical transmitter, 12 is an optical receiver, 13 is an excitation single mode optical fiber, 14 is a transmission single mode optical fiber, and 15 is a relay. Single mode optical fiber.

  In this embodiment, transmission of a total length of 600 m is realized by using two graded index type multimode optical fibers 10 having a length of 300 m, and the optical transmitter 11 and the graded index type multimode optical fiber 10 are realized. In addition to providing a single-mode optical fiber 13 for excitation between the two and a single-mode optical fiber 14 for transmission between the graded index type multi-mode optical fiber 10 and the optical receiver 12, As a mechanism that can transmit and excite a specific mode between the graded index type multimode optical fiber 10, a relay single mode optical fiber 15 having a length of 2 m is provided to transmit unnecessary modes in the middle of transmission. The relay process is carried out.

  In the present embodiment, the case where the number of relays is one has been described. For example, by using three graded index type multimode optical fibers 10 having a length of 300 m, the total length is 900 m, and each single unit used for relaying is used. The same effect can be obtained even when the mode optical fiber is 2 m long and the number of times of relaying is 2, and the present invention is effective. Here, the relay distance and the number of relays should be optimized and determined for each system in consideration of the loss due to relay and the sensitivity margin of the optical receiver 12.

  FIG. 3 shows a third embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 10a is a graded index type multimode optical fiber for connection, 11 is an optical transmitter, 12 is an optical receiver, 13 is a single mode optical fiber for excitation, 14 Is a single-mode optical fiber for transmission, and 15 is a single-mode optical fiber for relay.

  In this embodiment, a relatively short graded index for connection between the optical transmitter 11 and the excitation single-mode optical fiber 13 and between the optical receiver 12 and the transmission single-mode optical fiber 14. A type multimode optical fiber 10a is disposed.

  Originally, between the optical transmitter 11 and the excitation single mode optical fiber 13 and between the optical receiver 12 and the transmission single mode optical fiber 14, both are inserted without inserting a multimode optical fiber. Although direct connection is desirable, if the length of the multimode optical fiber is short enough to ignore the transition to the higher-order mode, the same effect as in the first and second embodiments can be obtained. As a result, the present invention is effective.

  FIG. 4 shows a fourth embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 10a is a graded index type multimode optical fiber for connection, 11 is an optical transmitter, 12 is an optical receiver, 16 is a single-mode planar lightwave circuit for excitation, Reference numeral 17 denotes a transmission single mode planar lightwave circuit.

  In this embodiment, a single mode planar lightwave circuit 16 for excitation having a waveguide length of 1 m is used as a mechanism for exciting a specific mode, and a transmission having a waveguide length of 1 m is used as a mechanism for transmitting a specific mode. Single-mode planar lightwave circuit 17 is used, and such single-mode planar lightwave circuits 16 and 17 are connected to graded index type multimode optical fiber 10.

  In the present embodiment, on the transmission side, when an optical signal is incident on the graded index type multimode optical fiber 10 from the excitation single-mode planar lightwave circuit 16, only a specific low-order mode is excited and received. On the side, a component that partially transits to a higher-order mode during transmission is removed by the transmission single-mode plane lightwave circuit 17, and only a specific lower-order mode is selectively guided to the optical receiver 12. For this reason, waveform deterioration due to the delay time difference between modes is suppressed, and a high-speed optical signal can be transmitted over a longer distance than before.

  In the present embodiment, the case where the waveguide length of the single-mode planar lightwave circuits 16 and 17 is 1 m has been described, but the same effect can be obtained when the waveguide length is 2 m, and the present invention is effective. is there.

  FIG. 5 shows a fifth embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 10a is a graded index type multimode optical fiber for connection, 11 is an optical transmitter, 12 is an optical receiver, 18 is an optical system for excitation, and 19 is for transmission. It is an optical system.

  In this embodiment, since an optical system composed of two lenses and a diaphragm is used as a mechanism capable of exciting a specific mode, only a low-order mode component having a small incident angle is selectively condensed. be able to.

  Therefore, on the transmission side, only the specific low-order mode is excited in the graded index type multimode optical fiber 10 connected thereto. On the receiving side, by using a similar optical system, a component that has shifted to a higher-order mode in the middle of the transmission path is removed, and only a specific lower-order mode component can be selectively received. According to this configuration, transmission in a longer distance section than before can be performed.

  FIG. 6 shows a sixth embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 10a is a graded index type multimode optical fiber for connection, 11 is an optical transmitter, 12 is an optical receiver, 20 is a diaphragm for excitation, and 21 is a diaphragm for transmission. It is.

  In the present embodiment, as a mechanism capable of exciting a specific mode, a connection point between the graded index multimode optical fiber 10a for connection and the graded index multimode optical fiber 10 connected to the optical transmitter 11 is used. In addition, as a mechanism capable of transmitting a specific mode while using an excitation diaphragm 20 having an opening diameter of 10 μm and a thickness of 50 μm, a graded index type multimode light for connection connected to the optical receiver 12 is used. A transmission aperture 21 having an opening diameter of 10 μm and a thickness of 50 μm is used at a connection point between the fiber 10 a and the graded index multimode optical fiber 10.

  When the diaphragms 20 and 21 are used, a specific low-order mode component having a small incident angle with respect to the central axis and concentrated power in the vicinity of the core center in the graded index type multimode optical fiber 10 can be excited and transmitted. it can.

  In this embodiment, by using such diaphragms 20 and 21, higher-order mode components can be removed, and waveform deterioration due to the delay time difference between modes can be suppressed. Therefore, transmission in a longer distance section than before is possible. Is possible.

  In the present embodiment, it is not always easy to separate only the 100% specific mode component, but the relative intensity of components other than the specific mode to be mixed can be suppressed to a level that does not cause a problem in practice. Therefore, a clear waveform deterioration suppressing effect can be obtained.

  In the present embodiment, the case where the diaphragms 20 and 21 are used alone has been described. However, various applications such as a structure in which the diaphragm is built in the connection point in the fiber connector are conceivable. .

  FIG. 7 shows a seventh embodiment of the optical transmission system according to the present invention.

  In the figure, 10 is a graded index type multimode optical fiber, 11 is an optical transmitter, 12 is an optical receiver, 13 is a single-mode optical fiber for excitation, and 19 is an optical system for transmission.

  Some graded index type multimode optical fibers 10 have a dip (dent) in the vicinity of the center of the core, depending on the manufacturing method.

  When the graded index type multimode optical fiber 10 having such a refractive index dip is used, as shown in the present embodiment, the core central axis of the excitation single mode optical fiber 13 is set to the graded index. The multi-mode optical fiber 10 is arranged so as to be decentered by about 10 μm from the core central axis.

  In this case, the higher-order mode component is increased and the loss is slightly increased as compared with the case where incidence can be made with the central axis perfectly aligned, but only a specific low-order mode is used on the receiving side using the transmission optical system 19. Since it can be selectively received, transmission in a longer distance section than before is possible.

  The present invention can be applied to an optical transmission system including an optical transmission unit, an optical reception unit, and an optical transmission path connecting them.

It is a figure which shows an example of the system configuration | structure of a 1st Example. It is a figure which shows an example of the system configuration | structure of a 2nd Example. It is a figure which shows an example of the system configuration | structure of a 3rd Example. It is a figure which shows an example of the system configuration | structure of a 4th Example. It is a figure which shows an example of the system configuration | structure of a 5th Example. It is a figure which shows an example of the system configuration | structure of a 6th Example. It is a figure which shows an example of the system configuration | structure of a 7th Example. It is explanatory drawing of a prior art. It is explanatory drawing of a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Graded index type | mold multimode optical fiber 10a Graded index type | mold multimode optical fiber for connection 11 Optical transmission part 12 Optical receiving part 13 Single mode optical fiber for excitation 14 Single mode optical fiber for transmission 15 Single mode for relay Optical fiber 16 Single-mode plane lightwave circuit for excitation 17 Single-mode plane lightwave circuit for transmission 18 Excitation optical system 19 Transmission optical system 20 Excitation stop 21 Transmission stop

Claims (14)

An optical transmission line provided between the optical transmission unit and the optical reception unit, configured by a graded index type optical transmission line;
An excitation mechanism provided between the optical transmitter and the optical transmission line or in the middle of the optical transmission line, and capable of exciting a specific mode;
An optical transmission system comprising a transmission mechanism that is provided in the middle of the optical transmission path or between the optical transmission path and the optical receiver, and is capable of transmitting a specific mode. The optical transmission system according to claim 1,
An optical transmission system, wherein the optical transmission line is composed of a graded index type optical fiber having a core diameter of 40 μm or more and 100 μm or less. The optical transmission system according to claim 1,
An optical transmission system, wherein the optical transmission line is composed of a graded index optical fiber having a core diameter of 50 μm or a core diameter of 62.5 μm. The optical transmission system according to claim 1,
An optical transmission system, wherein the specific mode is a base mode. The optical transmission system according to claim 1,
An optical transmission system using a single mode type optical transmission line as the excitation mechanism. The optical transmission system according to claim 5,
An optical transmission system using a single mode optical fiber as the single mode optical transmission line. The optical transmission system according to claim 5,
An optical transmission system using a single-mode planar lightwave circuit as the single-mode optical transmission line. The optical transmission system according to claim 1,
An optical transmission system using an optical system including a lens as the excitation mechanism. The optical transmission system according to claim 1,
An optical transmission system using a diaphragm having an opening at a specific position of the optical transmission path core as the excitation mechanism. The optical transmission system according to claim 1,
An optical transmission system using a single-mode optical transmission line as the transmission mechanism. The optical transmission system according to claim 10.
An optical transmission system using a single mode optical fiber as the single mode optical transmission line. The optical transmission system according to claim 10.
An optical transmission system using a single-mode planar lightwave circuit as the single-mode optical transmission line. The optical transmission system according to claim 1,
An optical transmission system using an optical system including a lens as the transmission mechanism. The optical transmission system according to claim 1,
An optical transmission system using an aperture having an opening at a specific position of the optical transmission path core as the transmission mechanism.

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