HK1069486A - Single fibre bidirectional optical transmission system and single fibre bidirectional optical amplifier - Google Patents

Description

Single-fiber bidirectional optical transmission system and single-fiber bidirectional optical amplifier

Technical Field

The present invention relates to a single-fiber bidirectional optical transmission system and a single-fiber bidirectional optical amplifier, and more particularly, to a single-fiber bidirectional optical amplifier for collectively amplifying bidirectional optical signals using one optical amplifier in single-fiber bidirectional optical transmission using a single optical fiber for bidirectional transmission.

Background

In a single-fiber bidirectional optical transmission technique for performing bidirectional transmission using one optical fiber, the number of optical fibers to be used is reduced by half compared with a double-fiber bidirectional transmission in which two optical fibers perform unidirectional transmission, respectively. Thus, when a new optical fiber needs to be laid, the laid optical fiber is reduced by half, and when a bare optical fiber (dark fiber) is used, the optical fiber cost is reduced by half. Thus, an economical system can be constructed.

In optical communication, in order to realize long-distance transmission, an optical amplifier amplifies an optical signal attenuated due to transmission path loss as it is as an optical beam without performing photoelectric (O/E) conversion and electro-optical (E/O) conversion. The optical amplifier is characterized in that it does not depend on a bit rate and a signal format, and can collectively amplify wavelength-multiplexed signals, thereby enabling a flexible and low-cost network.

In general, for an optical amplifier, an erbium-doped fiber amplifier is used, which makes excited light incident into an erbium-doped fiber together with a signal beam and amplifies the signal beam. Such an optical amplifier is manufactured so that it amplifies a light beam transmitted in one direction, and its configuration is less complicated. Therefore, the optical fiber amplifier cannot be simply inserted into a single-fiber bidirectional transmission path in which an optical signal is bidirectionally transmitted in a single optical fiber.

Thus, various techniques of single-fiber bidirectional transmission optical amplifiers have been proposed, although the configuration is complicated. For example, as shown in fig. 17, a method may be used in which signals 252, 262, 272, and 282 that advance in different directions up and down in single-fiber bidirectional transmission paths 84 and 89, respectively, are separated by optical circulators (optical circulators) 83, 85, 88, and 90, and amplified in the up and down directions by using conventional optical amplifiers 86 and 87, respectively, and thereafter multiplexed again by the circulators 83, 85, 88, and 90.

At this time, in the optical amplifiers 86 and 87, an optical multiplexer for multiplexing the excited light and the signal beam is required. Furthermore, in order to separate the signals 252, 262, 272 and 282 upstream and downstream in the single fiber bi-directional transmission paths 84 and 89, optical demultiplexers are required. A technique of sharing the optical multiplexer and the optical demultiplexer by an optical circulator having four ports has been proposed (for example, refer to patent document 1).

Further, a configuration in which sharing of the optical multiplexer and the optical demultiplexer is attempted by using a reflector when multiplexing the excited light and the signal beam in the optical amplifier has been proposed (for example, refer to patent document 2), and a configuration similar thereto has been proposed (for example, refer to patent document 3).

On the other hand, as for a method of amplifying the upstream and downstream optical signals without separating them, a technique may also be used in which an erbium-doped fiber is connected to one bidirectional transmission path to add up the upstream and downstream bidirectionally excited light, thereby bidirectionally amplifying the upstream and downstream optical signals (for example, refer to patent document 4).

[ patent document 1 ]

Japanese patent laid-open publication No. Hei 6-342950 (pages 4 to 6, FIG. 1)

[ patent document 2 ]

Japanese patent laid-open publication No. Hei 11-274625 (pages 7 and 8, FIG. 1)

[ patent document 3 ]

Japanese patent laid-open publication No.2002-118313 (pages 5 and 6, FIG. 1)

[ patent document 4 ]

Japanese patent laid-open publication No. Hei 3-92827 (bottom right column on page 161, top left column on page 162, FIG. 6)

When an optical communication system is dedicated to metropolitan areas, it is given the highest priority in cost, and therefore it is desirable to use low-cost products. According to a technique of separating and independently amplifying uplink and downlink optical signals, similar to those described in patent documents 1, 2, and 3, two sets of uplink and downlink optical amplifiers are required among conventional single-fiber bidirectional optical amplifiers. This makes the cost expensive and the device large in size, and causes problems such as large power consumption.

Further, according to this technique, the optical multiplexing and demultiplexing element is shared by combining two functions of separating uplink and downlink signals transmitted in both directions and multiplexing the signal beam of the optical amplifier and the excited light. Therefore, there is a need to newly develop an element specifically for use with a single-fiber bidirectional optical amplifier, which poses a problem that the cost becomes expensive.

On the other hand, as for a technique of amplifying an optical signal without separating an upstream optical signal and a downstream optical signal, although a technique is disclosed in patent document 4, an optical amplifier must be inserted with an optical isolator so that oscillation inside the optical amplifier is not generated by reflection occurring at a connection point of an erbium-doped fiber and a transmission path and in the transmission path. Therefore, there is a problem that such a configuration is impossible to realize.

Further, according to the conventional single-fiber bidirectional optical amplifier, vertically symmetrical transmission paths are designed so that the upstream and downstream optical signals are equally amplified. Thus, it is necessary to install the optical amplifier at the center of the single-fiber bidirectional transmission path, and therefore, there is a problem that the installation condition is limited.

Further, in the case where the transmission distance exceeds 60km and the transmission rate is not lower than 10Gbps per wavelength, not only optical amplification but also dispersion compensation is required. However, the problem is that this has not been considered so far.

Disclosure of Invention

It is therefore an object of the present invention to solve the above-mentioned problems and to provide a single-fiber bidirectional optical transmission system and a single-fiber bidirectional optical amplifier which are capable of achieving bidirectional long-distance extension of a single fiber at a moderate cost.

The single-fiber bidirectional optical transmission system of the present invention is a single-fiber bidirectional optical transmission system for multiplexing a plurality of optical signals having different wavelengths and performing bidirectional transmission between a first optical terminal and a second optical terminal through a single-fiber bidirectional transmission path, the single-fiber bidirectional optical transmission system including an optical amplifier for amplifying the bidirectional wavelength multiplexed optical signals collectively.

The single-fiber bidirectional optical amplifier of the present invention is a single-fiber bidirectional optical amplifier for a single-fiber bidirectional optical transmission system for multiplexing a plurality of optical signals having different wavelengths and performing bidirectional transmission between a first optical terminal and a second optical terminal through a single-fiber bidirectional transmission path, the single-fiber bidirectional optical amplifier including an optical amplifier for amplifying the bidirectional wavelength multiplexed optical signals collectively.

That is, in order to achieve the above object, a first single-fiber bidirectional optical transmission system according to the present invention is characterized in that a plurality of optical signals having different wavelengths are multiplexed, bidirectional transmission is performed between a first optical terminal and a second optical terminal through a single-fiber bidirectional transmission path, and the bidirectional wavelength-multiplexed optical signals are collectively amplified by an optical amplifier.

A second single-fiber bidirectional optical transmission system according to the present invention is characterized in that, in the above-described single-fiber bidirectional optical transmission system, an optical amplifier is provided only for the first optical terminal or the second optical terminal.

A third single-fiber bidirectional optical transmission system of the present invention is characterized in that in the above-described first optical terminal and second optical terminal, the wavelength-multiplexed light beam transmitted through the single-fiber bidirectional transmission path is separated in each direction by a directional separator.

A fourth single-fiber bidirectional optical transmission system of the present invention is characterized in that the above-mentioned directional separator is any one of an optical circulator, an optical blue/red filter and an optical interleaver.

A fifth single-fiber bidirectional optical transmission system of the present invention is characterized in that the above-mentioned optical amplifier includes an optical amplification section, an optical multiplexer and a first optical dispersion compensator provided on an input side of the optical amplification section, and an optical demultiplexer and a second optical dispersion compensator provided on an output side of the optical amplification section, and the first optical dispersion compensator is connected to an optical transmitter and an optical multiplexer in a first or second optical terminal equipped with the optical amplifier, and the second optical dispersion compensator is connected to an optical receiver and an optical multiplexer in a first or second optical terminal equipped with the optical amplifier, an optical signal output from the optical transmitter and having passed through the first dispersion compensator, and an optical signal having passed through a single-fiber bidirectional transmission path are multiplexed and amplified collectively, and thereafter demultiplexed into a signal to be output to the optical receiver through the second dispersion compensator, And a signal to be output to the single-fiber bidirectional transmission path.

A sixth single-fiber bidirectional optical transmission system of the present invention is characterized in that the above-mentioned optical multiplexer and optical demultiplexer are any one of an optical blue/red filter and an optical interleaver.

A seventh one of the single-fiber bidirectional optical transmission systems of the present invention is characterized in that the optical amplifier in the above-mentioned single-fiber bidirectional optical transmission system comprises an optical amplification section, an optical multiplexer provided on an input side of the optical amplification section, an optical demultiplexer provided on an output side of the optical amplification section, an optical dispersion compensator, and optical directional splitters provided at both ends of the optical dispersion compensator, wherein an optical signal output from an optical transmitter in a first or second optical terminal equipped with the optical amplifier and an optical signal having propagated through a single-fiber bidirectional transmission path are multiplexed and subjected to dispersion compensation and joint amplification, thereafter demultiplexed and output to an optical receiver in the first or second optical terminal equipped with the optical amplifier, and further output to the single-fiber bidirectional transmission path.

An eighth single-fiber bidirectional optical transmission system of the present invention is characterized in that the optical multiplexer and the optical demultiplexer are at least one of an optical blue/red filter and an optical interleaver.

A ninth single-fiber bidirectional optical transmission system according to the present invention is characterized in that the above-mentioned optical directional separator is any one of an optical circulator, an optical blue/red filter and an optical interleaver.

A tenth single-fiber bidirectional optical transmission system according to the present invention is characterized in that the optical amplifier is provided at the center of the transmission path.

As described above, the present invention inserts an optical amplifier into either end of a single-fiber bidirectional transmission path and realizes a single-fiber bidirectional optical amplifier for collectively amplifying bidirectional optical signals by one optical amplifier.

Drawings

Fig. 1 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a first embodiment of the present invention;

FIG. 2 illustrates the optical circulator of FIG. 1;

FIG. 3 shows the optical blue/red filter of FIG. 1;

fig. 4 shows the characteristics of the optical blue/red filter;

fig. 5 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a second embodiment of the present invention;

fig. 6 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a third embodiment of the present invention;

FIG. 7 shows the optical interleaver of FIG. 6;

fig. 8 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a fourth embodiment of the present invention;

fig. 9 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a fifth embodiment of the present invention;

FIG. 10 shows the characteristics and wavelength settings of an optical blue/red filter;

FIG. 11 shows the construction and wavelength arrangement of an optical interleaver;

fig. 12 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a sixth embodiment of the present invention;

fig. 13 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a seventh embodiment of the present invention;

fig. 14 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to an eighth embodiment of the present invention;

FIG. 15 shows the characteristics and wavelength settings of an optical blue/red filter;

FIG. 16 shows the construction and wavelength arrangement of an optical interleaver; and is

Fig. 17 shows a conventional single-fiber bidirectional optical transmission system.

Detailed Description

Embodiments of the present invention will be described next with reference to the drawings. Fig. 1 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a first embodiment of the present invention. In fig. 1, one optical terminal a of a transmission path is composed of a single-fiber bidirectional optical amplifier 1, a first optical transmitter (Tx)2 and a first optical receiver (Rx)3, and the optical terminal a is connected to a single-fiber bidirectional transmission path 5 through an optical circulator 4.

The other optical terminal B of the transmission path is constituted by a second optical transmitter (Tx)7 and a second optical receiver (Rx)8, and the optical terminal B is connected to the single-fiber bidirectional transmission path 5 by a single-mode optical fiber through an optical circulator 6.

The single-fiber bidirectional optical amplifier 1 includes an optical amplifying section 11 (e.g., an erbium-doped fiber amplifying section), an optical blue/red filter 12 immediately before the optical amplifying section 11, and an optical blue/red filter 13 immediately after the optical amplifying section 11. Dispersion Compensators (DCFs) 14 and 15 are interposed between the optical blue/red filter 12 and the first optical transmitter 2, and between the optical blue/red filter 13 and the first optical receiver 3, respectively.

Fig. 2 shows the optical circulator 4 of fig. 1. In fig. 2, the optical circulator 4 is an element that performs multiplexing or demultiplexing according to the direction of an optical signal. The insertion loss (isolation) from the port 4a to the port 4b is 1dB, and the isolation (isolation) from the port 4a to the port 4c is not less than 40 dB. Thus, the light beam from the port 4a is transmitted only to the port 4b, and not to the port 4 c.

Similarly, the insertion loss from port 4b to port 4c is 1dB, while the isolation from port 4b to port 4a is not less than 40 dB. Thus, the optical signal from the port 4b is transmitted only to the port 4c without proceeding to the port 4 a. Thus, bidirectional transmission is performed on the port 4b side, and unidirectional transmission is performed at the ports 4a and 4 c. Although not shown, the same applies to the optical circulator 6 similarly to the optical circulator 4.

Fig. 3 shows the optical blue/red filter 12 of fig. 1, and fig. 4 shows the characteristics of the optical blue/red filter. The optical blue/red filter 12 is an element that multiplexes and demultiplexes light beams according to the wavelength band of an optical signal. Ports 12a, 12b and 12c are used as blue, common and red ports, respectively.

The transmission characteristics of the blue port 12a and the red port 12c are shown in fig. 4, respectively. The insertion loss between the blue port 12a and the common port 12b, or between the red port 12c and the common port 12b is 1dB, and the isolation between the blue port 12a and the red port 12c is not less than 30 dB.

Also, the pass bands of the blue port 12a and the red port 12c are 1530.0 to 1543.2nm and 1547.4 to 1561.0nm, respectively. The blue port 12a and the red port 12c transmit only signals having wavelengths within the pass band, while the common port 12b transmits signals independent of the optical signal wavelength, thereby performing multiplexing and demultiplexing according to the band.

Assuming that the transmission speed of the optical signal from first optical transmitter 2 is 10Gbps, wavelength λ 1 is 1558.98nm, and the transmission speed of the optical signal from second optical transmitter 7 is 10Gbps, wavelength λ 2 is 1540.56nm, since the optical signal of wavelength λ 1 can be transmitted only in red port 12c and the optical signal of wavelength λ 2 can be transmitted only in blue port 12a, multiplexing and demultiplexing according to wavelength is performed at optical blue/red filter 12. Although not shown, the same applies to the optical blue/red filter 13 similarly to the optical blue/red filter 12.

Although the optical amplifier 11 gives an equal gain to an optical signal of each channel of a WDM (wavelength division multiplexing) signal having an input level of-30 to-15 dBm/ch and a wavelength range of 1535.11 to 1559.48nm, level differences between channels of a plurality of input signals are large, and when a power level exceeds the range of-30 to-15 dBm, there is often a case where the power level reaches a gain saturation region so that the output level becomes constant and thus a sufficient gain is not obtained, or the gain of the channel in the WDM signal fluctuates. Therefore, it is preferable that the difference in optical signal level between the channels in the WDM signal is small.

In the single-fiber bidirectional optical amplifier 1 of the present invention, by inserting the dispersion compensator 14 immediately after the first optical transmitter 2, the difference between the power level of the optical signal input from the first optical transmitter 2 to the optical amplification section 11 and the power level of the optical signal input from the second optical transmitter 7 to the optical amplifier 11 can be made small.

The optical signal output from the second optical transmitter 7 passes through the optical circulator 6, the single-fiber bidirectional transmission path 5, the optical circulator 4, and the optical blue/red filter 12, and is then incident on the optical amplification section 11. Assuming that the loss of the single optical fiber bidirectional transmission path 5 is 0.25dB/km and the distance is 80km, the total loss received by the optical signal output from the second transmitter 7 until it is incident on the optical amplification section 11 is 23 dB.

On the other hand, the optical signal output from the first optical transmitter 2 passes through the dispersion compensator 14 and the optical blue/red filter 12, and is then incident on the optical amplifying section 11. At this time, assuming that the dispersion compensation amount is-1360 ps/nm, which is dispersion at the time of transmission of 80km, and assuming that the loss is 10dB, the total loss experienced by the optical signal output from the first transmitter 2 until it is incident on the optical amplifying section 11 is 11 dB.

Thus, when the output of the first optical transmitter 2 and the output of the second optical transmitter 7 are simultaneously-5 dBm, the power levels of the optical signals when the optical signals are incident on the optical amplifying section 11 become-16 dBm and-28 dBm, respectively, and the power level difference is 12 dB. Thus, it is within a range in which sufficient bidirectional uplink and downlink gains can be secured.

Also, when the gain of the optical amplifying section 11 is 25dB, since the power at the first optical receiver 3 and the second optical receiver 8 becomes-14 dBm, which exceeds the reception sensitivity of-18 dBm of the optical IF (interface) of 10Gbps, no problem is caused.

Further, since the input from the optical circulator 4 to the single-fiber bidirectional transmission path 5 is 7dBm, there is no problem in the influence of the nonlinear optical effect. As described above, by using the single-fiber bidirectional optical amplifier 1 of the first embodiment of the present invention, single-fiber bidirectional transmission of 10Gbps and 80km can be realized.

Fig. 5 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a second embodiment of the present invention. In fig. 5, a single-fiber bidirectional optical transmission system according to a second embodiment of the present invention has the same configuration as that of the first embodiment of the present invention shown in fig. 1, except that the system is configured to multiplex and demultiplex upstream and downstream optical signals by replacing the optical circulators 4 and 6 with optical blue/red filters 16 and 17. Also, the operation of the same components is the same as that of the first embodiment of the present invention.

The pass bands of the optical blue/red filters 16 and 17 have the same wavelength as the pass bands of the optical blue/red filters 12 and 13. Thus, in the second embodiment of the present invention, similar to the above-described first embodiment of the present invention, single-fiber bidirectional transmission of 10Gbps and 80km can be realized by using the single-fiber bidirectional amplifier 1.

Fig. 6 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a third embodiment of the present invention. In fig. 6, a single-fiber bidirectional optical transmission system according to a third embodiment of the present invention has the same configuration as that of the first embodiment of the present invention shown in fig. 1, except that the system is configured to use optical interleavers (optical interleavers) 18 and 19 instead of the optical circulators 4 and 6, thereby multiplexing and demultiplexing the upstream and downstream optical signals. Also, the operation of the same components is the same as that of the first embodiment of the present invention.

Fig. 7 shows the optical interleaver 18 of fig. 6. In fig. 7, a plurality of signals having a wavelength interval of 100GHz in the port 18b are demultiplexed into even-numbered channels and odd-numbered channels having a wavelength interval of 200GHz for the port 18a and the port 18c by the optical interleaver 18.

On the other hand, the plurality of signals at intervals of 200GHz input from the ports 18a and 18c are multiplexed into the plurality of signals at intervals of 100GHz at the port 18b by the optical interleaver 18. Since the frequencies of wavelengths λ 1 ═ 1558.98 and λ 2 ═ 1540.56 are 192.30THz and 194.60THz, respectively, λ 1 is transmitted in port 18a of optical interleaver 18, and λ 2 is transmitted in port 18b of optical interleaver 18.

Since the loss of the optical interleaver 18 is 1dB, the optical signal powers of the wavelength λ 1 and the wavelength λ 2 input to the optical amplification section 11 become-16 dB and-28 dB, respectively, which is within the range in which the optical amplification section 11 operates linearly, like the above-described first embodiment of the present invention. Thus, in the present embodiment, by using the single-fiber bidirectional optical amplifier 1, single-fiber bidirectional transmission of 10Gbps and 80km can be realized. Although not shown, the same applies to the optical interleaver 19, similarly to the optical interleaver 18.

Fig. 8 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a fourth embodiment of the present invention. In fig. 8, a single-fiber bidirectional optical transmission system according to a fourth embodiment of the present invention has the same configuration as that of the first embodiment of the present invention shown in fig. 1, except that the system is configured to perform multiplexing and demultiplexing by using optical interleavers 21 and 22 instead of the optical blue/red filters 12 and 13. Also, the operation of the same components is the same as that of the first embodiment of the present invention.

The optical interleavers 21 and 22 have the same characteristics as the optical interleavers 18 and 19 in the third embodiment of the present invention described above. Thus, in the present embodiment, similarly to the above-described first embodiment of the present invention, by using the single-fiber bidirectional amplifier 20, single-fiber bidirectional transmission of 10Gbps and 80km can be realized.

At this time, similarly to the above-described second embodiment of the present invention, the present embodiment can be performed by replacing the optical circulators 4 and 6 with optical blue/red filters. Also, similarly to the above-described third embodiment of the present invention, this embodiment can be realized by replacing the optical circulators 4 and 6 with optical interleavers.

Fig. 9 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a fifth embodiment of the present invention. In fig. 9, the single-fiber bidirectional optical transmission system according to the fifth embodiment of the present invention is configured to perform WDM transmission of a plurality of unidirectional channels by multiplexing and demultiplexing using optical multiplexers 36 and 45 and optical demultiplexers 35 and 46 of a plurality of channels.

The present embodiment is configured to perform bidirectional transmission of 2 waves per direction for a total of 2 × 2 wavelengths. The optical signal wavelengths from each of the optical transmitters 31, 32, 41, and 42 are λ 11-1558.98 nm, λ 12-1557.36 nm, λ 13-1540.56 nm, and λ 14-1538.98 nm, respectively, and the optical output power is-1 dBm.

Fig. 10 shows the characteristics and wavelength settings of the optical blue/red filter, while fig. 11 shows the construction and wavelength settings of the optical interleaver. In fig. 10, the relationship between the wavelength settings of the signal beams λ 11 to λ 14 and the frequency bands of the optical blue/red filters 12 and 13 is shown.

The passband bandwidths of the blue band and the red band are the same as in the above-described first embodiment of the present invention. The optical signals of the wavelengths λ 11 and λ 12 are transmitted only in the red band, and the optical signals of λ 13 and λ 14 are transmitted only in the blue band. Thus, the optical signals of the wavelengths λ 11 and λ 12 and the optical signals of the wavelengths λ 13 and λ 14 are multiplexed and demultiplexed according to the wavelengths.

Assuming that the loss of the optical multiplexers 36 and 45 and the optical demultiplexers 35 and 46 is 3dB and the loss of the single-fiber bidirectional transmission path 5 is 80km and 20dB, the power input to the optical amplification section 11 is-15 dBm per channel for the wavelengths λ 11 and λ 12 and-27 dBm per channel for the wavelengths λ 13 and λ 14, and the power level difference of the input optical signal is 12dB, and thus, it is within the range in which the optical amplification section 11 operates linearly, like the above-described first embodiment of the present invention.

Also, since the gain is 25dB, the optical power at the optical receivers 33, 34, 43 and 44 becomes-16 dBm, at an acceptable level. Thus, in the present embodiment, by using the single-fiber bidirectional amplifier 30, four-channel single-fiber bidirectional transmission of 10Gbps and 80km can be realized.

At this time, in the present embodiment, similar to the above-described second embodiment of the present invention, the optical circulators 4 and 6 may use optical blue/red filters having the same frequency band as the optical blue/red filters 12 and 13.

Also, the frequency of each signal from the wavelength λ 11 to the wavelength λ 14 is 192.30THz, 192.50THz, 194.60THz, and 194.40THz, respectively. The frequency setting of the signal beams λ 11 to λ 14 is shown in fig. 11, and since the wavelengths λ 11 and λ 12, and the wavelengths λ 13 and λ 14 can be divided into different ports by the optical interleaver 37, the optical circulators 4 and 6 can be implemented even with an optical interleaver, similarly to the above-described third embodiment of the present invention. Also, in this embodiment, the optical blue/red filters 12 and 13 in the single fiber bidirectional amplifier 30 may be optical interleavers, similar to the fourth embodiment of the present invention described above.

Fig. 12 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a sixth embodiment of the present invention. In fig. 12, a single-fiber bidirectional optical transmission system according to a sixth embodiment of the present invention is constructed by installing optical circulators 51 and 52 before and after a dispersion compensator 15, multiplexing and demultiplexing upstream and downstream optical signals before and after the dispersion compensator 15, and performing bidirectional common dispersion compensation on a dispersion compensation fiber, thereby constructing a single-fiber bidirectional optical amplifier 50 using the dispersion compensator 15 instead of the two sets of dispersion compensators 14 and 15 used in the above-described first to fifth embodiments of the present invention.

Similarly to the first embodiment of the present invention described above, the output wavelengths of the first optical transmitter 2 and the second optical transmitter 7 are λ 1 ═ 1558.98nm and λ 2 ═ 1540.56 nm. Similar to the first embodiment of the present invention described above, the dispersion compensator 15 has a dispersion compensation amount of-1360 ps/nm and a loss of 10 dB.

Assuming that the outputs of the first and second optical transmitters 2 and 7 are-5 dBm, the optical powers of the wavelengths λ 1 and λ 2 input to the optical amplification section 11 are-18 dBm and-28 dBm, respectively, which is within the range in which the optical amplification section 11 operates linearly, similar to the above-described first embodiment of the present invention. Also, the power at the first optical receiver 3 and the second optical receiver 8 becomes-16 dBm at a receivable level. Thus, in the present embodiment, by using the single-fiber bidirectional optical amplifier 50, single-fiber bidirectional transmission of 10Gbps and 80km can be realized.

Even here, the optical circulators 4, 6, 51, and 52 may use optical blue/red filters and optical interleavers having the same frequency band as the optical blue/red filters 12 and 13, similarly to the above-described second and third embodiments of the present invention.

Also, in this embodiment, the optical blue/red filters 12 and 13 within the single fiber bi-directional optical amplifier 50 may be optical interleavers, similar to the fourth embodiment of the present invention described above. Also, in the present embodiment, similarly to the above-described fifth embodiment of the present invention, WDM transmission of a plurality of unidirectional channels can be performed by using an optical multiplexer and an optical demultiplexer.

Fig. 13 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to a seventh embodiment of the present invention. In fig. 13, a single-fiber bidirectional optical transmission system according to a seventh embodiment of the present invention is configured such that a single-fiber bidirectional optical amplifier 1 is inserted in the middle of a transmission path.

By installing the optical circulators 4, 61, and 62 before and after the single fiber bidirectional optical amplifier 1, the amplifier 1 can be inserted not only into the terminal part of the transmission path in the above-described first to sixth embodiments of the present invention but also into the middle of the transmission path.

Similarly to the first embodiment of the present invention described above, the output wavelengths of the first optical transmitter 2 and the second optical transmitter 7 are λ 1 ═ 1558.98nm and λ 2 ═ 1540.56 nm. Similar to the first embodiment of the present invention described above, the dispersion compensator 15 has a dispersion compensation amount of-1360 ps/nm and a loss of 10 dB.

In the present embodiment, the distances from the single-fiber bidirectional optical amplifier 1 to the optical terminal a and the optical terminal B are taken as 20km and 60km, respectively, and the losses of the single-fiber bidirectional transmission paths 5 and 63 at this time are taken as 5dB and 15dB, respectively.

Assuming that the outputs of the first and second optical transmitters 2 and 7 are-5 dBm, the optical powers of the wavelengths λ 1 and λ 2 input to the optical amplification section 11 are-23 dBm and-23 dBm, respectively, which is within the range in which the optical amplification section 11 operates linearly, similar to the above-described first embodiment of the present invention. Also, the power at the first optical receiver 3 and the second optical receiver 8 becomes-16 dBm at a receivable level. Thus, in the present embodiment, it is possible to realize single-fiber bidirectional transmission of 10Gbps and 80km without restricting the installation position of the single-fiber bidirectional optical amplifier 1 to the center of the transmission path.

At this time, in the present embodiment, the optical circulators 4, 6, 61, and 62 may be replaced with optical blue/red filters and optical interleavers, similarly to the above-described second and third embodiments of the present invention.

Also, in this embodiment, the optical blue/red filters 12 and 13 in the single fiber bi-directional optical amplifier 1 may be optical interleavers, similar to the fourth embodiment of the present invention described above. Also, in the present embodiment, similarly to the above-described fifth embodiment of the present invention, WDM transmission of a plurality of unidirectional channels can be performed by using an optical multiplexer and an optical demultiplexer.

Fig. 14 is a block diagram showing the configuration of a single-fiber bidirectional optical transmission system according to an eighth embodiment of the present invention. In fig. 14, a single-fiber bidirectional optical transmission system according to an eighth embodiment of the present invention is constructed such that a single-fiber bidirectional optical amplifier 70 including an optical amplifying section 11 and optical blue/red filters 12 and 13 disposed before and after the amplifier does not use a dispersion compensator because of a short transmission distance.

In the present embodiment, the transmission distance is taken to be 60km, the loss thereof is taken to be 15dB, and the system is configured to perform bidirectional transmission of 4 waves per direction for a total of 4 × 2 wavelengths. For the optical multiplexer 74, a low-priced coupler is used, and the loss thereof is 9dB, whereas the loss of the optical multiplexer 77 and the optical demultiplexers 73 and 78 is 5dB, respectively.

The optical signal wavelengths from each of the optical transmitters 71-1 to 71-4 and 75-1 to 75-4 are λ 21-1558.98 nm, λ 22-1557.36 nm, λ 23-1555.75 nm, λ 24-1554.13 nm, λ 25-1540.56 nm, λ 26-1538.98 nm, λ 27-1537.40 nm, and λ 28-1535.82 nm, respectively, and the optical output power is-5 dBm.

Fig. 15 shows the characteristics and wavelength settings of the optical blue/red filter, and fig. 16 shows the configuration and wavelength settings of the optical interleaver. Fig. 15 shows the relationship between the wavelength settings of the signal beams λ 21 to λ 28 and the frequency bands of the optical blue/red filters 12 and 13.

The passband bandwidths of the blue band and the red band are the same as in the above-described first embodiment of the present invention. The optical signals of wavelengths λ 21 to λ 24 are transmitted only in the red band, and the optical signals of wavelengths λ 25 to λ 28 are transmitted only in the blue band. Thus, the optical signals of the wavelengths λ 21 to λ 24 and the optical signals of the wavelengths λ 25 to λ 28 are multiplexed and demultiplexed according to the wavelengths.

The power of the wavelengths λ 21 to λ 24 and λ 25 to λ 28 input to the optical amplification section 11 is-15 dBm and-28 dBm per channel, respectively, and since the power level difference of the input signals is 13dB, it is within the range in which the optical amplification section 11 operates linearly, like the above-described first embodiment of the present invention.

Also, since the gain is 25dB, the optical power at the optical receivers 72-1 through 72-4 and 76-1 through 76-4 becomes-8 dBm and-13 dBm, at acceptable levels. Thus, in this embodiment, 8-channel single fiber bidirectional transmission at 10Gbps and 60km can be achieved by using the single fiber bidirectional amplifier 70.

At this time, in the present embodiment, similarly to the above-described second embodiment of the present invention, the optical circulators 4 and 6 may be optical blue/red filters having the same frequency band as the optical blue/red filters 12 and 13.

Also, in the present embodiment, the frequency of each signal from the wavelength λ 21 to the wavelength λ 28 is 192.30THz, 192.50THz, 192.70THz, 192.90THz, 194.60THz, 194.80THz, 195.00THz, and 195.20THz, respectively. The frequency setting of the signal beams λ 21 to λ 28 can be divided into different ports for the wavelengths λ 21 to λ 24 and the wavelengths λ 25 to λ 28 by the optical interleaver 79 shown in fig. 16, and therefore the optical blue/red filters 12 and 13 and the optical circulators 4 and 6 can be realized even with an optical interleaver similarly to the above-described third embodiment of the present invention. Also, the optical blue/red filters 12 and 13 in the single fiber bi-directional optical amplifier 70 may be optical interleavers, similar to the fourth embodiment of the present invention described above.

In the above description, although the optical amplification section 11 employs an erbium-doped fiber amplification section, the section may be an optical amplification section using an optical fiber to which other rare earth elements are added or a semiconductor optical amplification section depending on the wavelength of an optical signal to be amplified.

Also, the optical blue/red filter employs a C-band blue/red filter, but the filter may be a filter used in other bands depending on the wavelength range used.

Also, in the configuration of the present invention, an element depending on the transmission speed is not used, and for example, the transmission speed may be 2.4Gbps or 10 Gbps. Thus, in the above configuration, the optical signal wavelength, the transmission speed, and the transmission distance are not limited as long as the above functions are satisfied, and the above description does not limit the present invention.

Thus, the single-fiber bidirectional optical amplifier of the present invention can be realized at a moderate price. Since in the single-fiber bidirectional transmission path 5 for bidirectional transmission over a single conductor fiber, the optical amplifier 11 is inserted only into either end of the transmission path, and the upstream and downstream bidirectional optical signals can be collectively amplified by one optical amplifier 11, the long-distance extension of the single-fiber bidirectional can be realized at moderate cost. Also, since the single-fiber bidirectional optical amplifier of the present invention can be realized with a simple configuration in which only passive components are added to a general optical amplifier, it can be manufactured at a moderate price.

As described above, the present invention has an advantage in that a bidirectional long-distance extension of a single optical fiber is achieved by the above-described configuration and processing operation.

Claims (20)

1. A single-fiber bidirectional optical transmission system in which a plurality of optical signals having different wavelengths are multiplexed and bidirectional transmission is performed between a first optical terminal and a second optical terminal through a single-fiber bidirectional transmission path, the single-fiber bidirectional optical transmission system having an optical amplifier that collectively amplifies the bidirectional wavelength multiplexed optical signals.

2. A single fiber bidirectional optical transmission system as defined in claim 1 wherein one of said first optical termination and said second optical termination is provided with said optical amplifier.

3. The single fiber bi-directional optical transmission system of claim 1, wherein said first optical termination and said second optical termination include directional splitters that split said wavelength multiplexed light transmitted through said single fiber bi-directional transmission path for each direction.

4. The single fiber bi-directional optical transmission system of claim 3, wherein said directional splitter is at least one of an optical circulator, an optical blue/red filter, and an optical interleaver.

5. The single fiber bidirectional optical transmission system according to claim 1, wherein the optical amplifier includes an optical amplification section, an optical multiplexer and a first optical dispersion compensator provided at an input side of the optical amplification section, and an optical demultiplexer and a second optical dispersion compensator provided at an output side of the optical amplification section,

wherein the first optical dispersion compensator is connected to an optical transmitter in any one of the first and second optical terminals equipped with the optical amplifier and also connected to the optical multiplexer,

wherein the second optical dispersion compensator is connected to an optical receiver in any one of the first and second optical terminals equipped with the optical amplifier, is further connected to the optical demultiplexer, and

wherein the optical signal output from the optical transmitter and having passed through the first dispersion compensator and the optical signal having propagated through the single-fiber bidirectional transmission path are multiplexed and amplified in common, and thereafter demultiplexed into a signal to be output to the optical receiver through the second dispersion compensator and a signal to be output to the single-fiber bidirectional transmission path.

6. The single fiber bi-directional optical transmission system of claim 5, wherein said optical multiplexer and said optical demultiplexer are at least one of an optical blue/red filter and an optical interleaver.

7. The single-fiber bidirectional optical transmission system according to claim 1, wherein the optical amplifier includes an optical amplification section, an optical multiplexer disposed at an input side of the optical amplification section, an optical demultiplexer disposed at an output side of the optical amplification section, the optical dispersion compensator, and optical directional splitters disposed at both ends of the optical dispersion compensator, and

wherein an optical signal output from an optical transmitter in any one of the first and second optical terminals equipped with the optical amplifier and an optical signal having propagated through the single-fiber bidirectional transmission path are multiplexed and subjected to dispersion compensation and common amplification, thereafter demultiplexed, and then output to an optical receiver in any one of the first and second optical terminals equipped with the optical amplifier and also output to the single-fiber bidirectional transmission path.

8. The single fiber bi-directional optical transmission system of claim 7, wherein said optical multiplexer and said optical demultiplexer are at least one of an optical blue/red filter and an optical interleaver.

9. The single fiber bi-directional optical transmission system of claim 7, wherein said optical directional splitter is at least one of an optical circulator, an optical blue/red filter, and an optical interleaver.

10. A single fiber bidirectional optical transmission system as defined in claim 5 wherein said optical amplifier is provided in the middle of said transmission path.

11. A single-fiber bidirectional optical amplifier for a single-fiber bidirectional optical transmission system, in which a plurality of optical signals having different wavelengths are multiplexed and bidirectional transmission is performed between a first optical terminal and a second optical terminal through a single-fiber bidirectional transmission path, has an optical amplifier for collectively amplifying the bidirectional wavelength multiplexed optical signals.

12. A single fiber bi-directional optical amplifier as defined in claim 11 wherein said amplifier is provided for either of said first optical termination and said second optical termination.

13. The single fiber bi-directional optical amplifier of claim 11, wherein said first optical termination and said second optical termination include directional splitters that split said wavelength multiplexed light transmitted through said single fiber bi-directional transmission path for each direction.

14. A single fiber bi-directional optical amplifier as set out in claim 13, wherein said directional splitter is at least one of an optical circulator, an optical blue/red filter and an optical interleaver.

15. The single fiber bidirectional optical amplifier of claim 11, wherein the optical amplifier includes an optical amplification section, an optical multiplexer and a first optical dispersion compensator provided at an input side of the optical amplification section, and an optical demultiplexer and a second optical dispersion compensator provided at an output side of the optical amplification section,

wherein the first optical dispersion compensator is connected to an optical transmitter in any one of the first and second optical terminals equipped with the optical amplifier and also connected to the optical multiplexer,

wherein the second optical dispersion compensator is connected to an optical receiver in any one of the first and second optical terminals equipped with the optical amplifier, is further connected to the optical demultiplexer, and

wherein the optical signal output from the optical transmitter and having passed through the first dispersion compensator and the optical signal having propagated through the single-fiber bidirectional transmission path are multiplexed and amplified in common, and thereafter demultiplexed into a signal to be output to the optical receiver through the second dispersion compensator and a signal to be output to the single-fiber bidirectional transmission path.

16. The single fiber bi-directional optical amplifier of claim 15, wherein said optical multiplexer and said optical demultiplexer are at least any one of an optical blue/red filter and an optical interleaver.

17. The single fiber bidirectional optical amplifier of claim 11, wherein the optical amplifier includes an optical amplification section, an optical multiplexer disposed at an input side of the optical amplification section, an optical demultiplexer disposed at an output side of the optical amplification section, the optical dispersion compensator, and optical directional splitters disposed at both ends of the optical dispersion compensator, and

wherein an optical signal output from an optical transmitter in any one of the first and second optical terminals equipped with the optical amplifier and an optical signal having propagated through the single-fiber bidirectional transmission path are multiplexed and subjected to dispersion compensation and common amplification, thereafter demultiplexed, and then output to an optical receiver in any one of the first and second optical terminals equipped with the optical amplifier and also output to the single-fiber bidirectional transmission path.

18. The single fiber bi-directional optical amplifier of claim 17, wherein said optical multiplexer and said optical demultiplexer are at least any one of an optical blue/red filter and an optical interleaver.

19. A single fiber bi-directional optical amplifier as set out in claim 17, wherein said optical directional splitter is at least any one of an optical circulator, an optical blue/red filter and an optical interleaver.

20. A single fiber bi-directional optical amplifier as defined in claim 15 wherein said optical amplifier is provided in the middle of said transmission path.