JP2002176392A - Passive optical network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the number of stations without losing the effect of reducing the number of fibers and a low cost property which are the merits of a PON and to execute a fault countermeasure without increasing the number of coated optical fibers. SOLUTION: This passive optical network is provided with an optical fiber 4 for transmitting the light of a plurality of wavelength bands, a plurality of couplers 5 and 6 provided in the optical fiber and a plurality of stations 7 and 8 connected through the respective couplers to the optical fiber. The number of the stations is larger than the number of the wavelength bands and the couplers are provided with a prescribed branching ratio for the light of the wavelength band used by the station connected to the coupler and provided with the characteristics of transmitting the light without practically branching it from one port connected to the optical fiber to the other port connected to the optical fiber for the light of the other wavelength band.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a passive optical network, and more particularly to a bus-type passive optical network which is low-cost and has high core-line utilization efficiency and can cope with a failure.

[0002]

2. Description of the Related Art One type of optical communication system is a passive optical network (PON). PON is passive such as optical coupler
This is an optical communication system that connects a plurality of communication stations using (passive) components. FIG. 18 shows a bus type PON which is one of the typical modes. An optical fiber 4 is connected to the master station 1, and a plurality of couplers 3-x (x = 1,... N-1) are inserted in the optical fiber 4. Downlink optical signals are connected to each coupler 3-x
At the branching ratio of the coupler, the slave station 2-x (x = 1, ...
n) is entered. The upstream optical signal output from each of the slave stations 2-x joins the optical fiber 4 while receiving a branch loss corresponding to the branch ratio of the coupler at the coupler 3-x.
To reach.

[0003] The characteristic of the PON is that branching and joining are performed at the optical level in this manner. The advantage is that a plurality of slave stations are connected to one optical fiber, so that the number of optical fiber cores for forming a network can be reduced, and the slave stations are connected to the optical fiber by low-cost parts such as the coupler. System cost is low. However, since there is a lower limit to the received optical power required to satisfy the transmission specifications, the number of slave stations that can be connected to one fiber is limited in a system such as a PON where the optical power suffers a branch loss due to the coupler. ing. By using a high-density wavelength multiplexing (DWDM) system that requires an advanced control mechanism using an expensive optical Add / Drop multiplexer instead of using the coupler, it is possible to dramatically increase the number of slave stations. It is. However, systems to which PON is applied are usually systems that require low cost, and methods that greatly increase costs such as DWDM are not suitable.

[0004] The importance of information communicated over a network varies. Even if temporary communication is interrupted due to network failure, it may not be a big problem depending on the type of information, but if communication is interrupted, business, life,
It can have a significant impact on safety. A network that communicates the latter type of information requires high reliability, and a system that can immediately back up when a failure occurs must be established.

[0005] Just because a PON is a low-cost system does not mean that reliability is not required. The simplest countermeasure is to completely duplicate the system. However, complete redundancy impairs the benefits of PON, such as the reduction in the number of optical fiber cores and the low cost.

[0006]

SUMMARY OF THE INVENTION A first object of the present invention is to increase the number of accommodated slave stations without impairing the effect of reducing the number of cores and the low cost, which are the advantages of PON. A second object of the present invention is to provide a measure against a failure without increasing the number of optical fiber cores.

[0007]

A first invention of a first invention group includes an optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided in the optical fiber, and A passive optical network having a plurality of stations connected via the coupler, wherein the number of the stations is larger than the number of the wavelength bands, and the coupler is the wavelength used by the stations connected to the coupler. Band light has a predetermined branching ratio, and for light of the other wavelength band, from one port connected to the optical fiber to the other port connected to the optical fiber. A passive optical network having a characteristic of transmitting light without substantially branching.

A second invention of the first invention group is the passive optical network according to the first invention of the first invention group, wherein the number of the wavelength bands is two.

A first invention of a second invention group is an optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided in the optical fiber, and each of the optical fibers being connected to the optical fiber via the coupler. A passive optical network having a plurality of optical transmitters, optical receivers are provided at both ends of the optical fiber, the wavelength of output light output from the plurality of optical transmitters is the plurality of wavelengths Band, the number of optical transmitters is greater than the number of wavelength bands,
The coupler has a predetermined branching ratio for light in the wavelength band to which the wavelength of output light output from the optical transmitter connected to the coupler belongs, and has a predetermined branching ratio for light in the other wavelength band. Has the property of transmitting light without substantially branching from one port connected to the optical fiber to the other port connected to the optical fiber, and the optical transmitter is capable of receiving the light. A passive optical network comprising a selection unit for selecting one or the other of the devices and outputting light, wherein each of the optical receivers has at least one or more light receiving units.

A second invention of a second invention group is directed to an optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided in the optical fiber, and each of the optical fibers being connected to the optical fiber via the coupler. A passive optical network having a plurality of optical receivers provided, an optical transmitter is provided at each end of the optical fiber, the wavelength of the light received by the plurality of optical receivers is any one of the plurality of wavelength bands. The number of the optical receivers is greater than the number of the wavelength bands, and the coupler has a predetermined branching ratio for the light of the wavelength band received by the optical receiver connected to the coupler. A characteristic that transmits light without substantially branching from one port connected to the optical fiber to the other port connected to the optical fiber for light in the other wavelength band. With Each of the optical transmitters has a light emitting unit that outputs light corresponding to each of the plurality of wavelength bands, and the optical receiver is transmitted from both of the optical transmitters via the optical fiber. A passive optical network, comprising a selective receiving means for selecting and receiving at least one of the lights.

A third invention of the second invention group is the invention according to the first invention of the second invention group or the second invention of the second invention group, wherein the number of the wavelength bands is two. It is a passive optical network.

[0012] In order to increase the number of accommodated slave stations without impairing the effect of reducing the number of core wires and the low cost, which are the advantages of PON,
In the first invention group of the present invention, wavelength multiplexing with a large wavelength interval is performed in a bus-type PON. At this time, a coupler having a special branching ratio is used.

[0013] A coupler of the type that branches and joins by using the coupling of the propagation modes between a plurality of optical waveguides close to each other has a wavelength dependence in the branching ratio. For example, an optical fiber coupler manufactured by melt drawing which is the most common method of manufacturing a coupler is used. In this type of coupler, the branching ratio changes periodically with respect to the coupling length, but the period depends on the wavelength. The coupler used in the conventional bus-type PON shown in FIG. 18 is manufactured by specifying the branching ratio only in one wavelength band, and the branching ratio for light of wavelengths other than that wavelength band is completely different. Not stipulated. On the other hand, a simple wavelength multiplexer / demultiplexer has been commercialized based on the principle of the wavelength dependence. For example, it is a wavelength multiplexer / demultiplexer that demultiplexes and combines light in the 1.55 μm band and light in the 1.31 μm band. The shorter the wavelength interval for multiplexing / demultiplexing becomes, the stricter the requirement for the manufacturing accuracy becomes. Therefore, the wavelength interval that can be manufactured with a high yield is at most 50 nm to 100 nm. Therefore, such a wavelength multiplexer / demultiplexer is used for wavelength division in a wide range of about 50 nm. In addition, the wavelength multiplexer / demultiplexer based on this principle can be manufactured in a manufacturing process that is not much different from a simple optical coupler, so that the cost is low. A commercially available wavelength multiplexer / demultiplexer splits one wavelength (eg, 1.55 μm) substantially at 10: 0, and splits the other wavelength (eg, 1.31 μm) substantially at 0:10.
It branches at. That is, 1.55 μm and 1.31 μm
When both lights are input to the input port, only 1.55 μm is output from one of the output ports, and only 1.31 μm is output from the other output port.

By utilizing the wavelength dependency of the coupling period as described above, a coupler having a special branching ratio having different branching ratios for several wavelength bands can be manufactured. For example, it is possible to manufacture a coupler that splits light in the 1.55 μm band at a branching ratio of 7: 3 and splits light in the 1.31 μm band into a 10: 0 splitting ratio, that is, does not split. Note that these branching ratios such as 7: 3 and 10: 0 are approximate branching ratios, and in practice, an error of about 10% usually occurs due to the problem of manufacturing accuracy. At present, such products are not commercially available because there is no particular demand. If the branching ratio is defined for only two wavelength bands, it can be manufactured as easily as a wavelength multiplexer / demultiplexer (WDM coupler) that separates two wavelength bands, and can be manufactured at low cost.

In the second invention group of the present invention, by using a coupler having such a special branching ratio, a PON with high core utilization efficiency and low cost is provided, and further, a measure against its failure is provided.

In the second invention group, light in a plurality of wavelength bands is used in a bus-type PON. In addition, a coupler for connecting each slave station to the optical fiber has a predetermined branching ratio (except 10: 0) for a wavelength band used by the slave station, and a special wavelength that does not branch other wavelengths. A coupler having a branching ratio is used.

For example, a case where light in the 1.55 μm band and light in the 1.31 μm band are used will be described. The first coupler for connecting the slave station using the light in the 1.55 μm band to the optical fiber splits and combines the light in the 1.55 μm band at, for example, 7: 3 and the light in the 1.31 μm band. Transmits light without substantially branching. The second coupler for connecting the slave station using the light in the 1.31 μm band to the optical fiber branches and joins the light in the 1.31 μm band at, for example, 7: 3 and the light in the 1.55 μm band. Substantially transmits light without branching. as a result,
Light in the 1.55 μm band suffers a branch loss only when passing through the first coupler, and does not suffer a branch loss when passing through the second coupler, but only suffers a loss due to excess loss of the coupler described later. It is.

The coupler used in the conventional PON has a substantially equal splitting ratio for all the lights used in the PON. Compared with such a conventional PON, the number of slave stations connectable to the PON provided by the present invention simply increases to the number obtained by multiplying the number of wavelength bands to be used. In the present invention, the number of slave stations is increased by utilizing the wavelength dependency of a very low-cost component such as a coupler (for example, the above-described melt-drawing coupler). As a result, it is possible to increase the core wire utilization efficiency at low cost.

As described above, the branching ratio of the coupler utilizing the coupling of the propagation modes by bringing the optical waveguides close to each other changes periodically with respect to the coupling length, and the period depends on the wavelength. For two wavelengths (bands), one does not substantially branch (branch ratio 10: 0) and the other has a predetermined branch ratio (for example, 7: 3)
Since there are many coupling lengths within the range in which the coupler can be manufactured, the manufacturing is easy.

However, for three wavelengths (bands), a coupling is such that one has a predetermined branching ratio and the other two have substantially no branching (branch ratio 10: 0). The length is much less frequent than in the case of two wavelength bands, so if you try to make a coupler with such characteristics for three wavelengths, the width of the wavelength band becomes narrower and higher There is a possibility that the cost may increase, for example, the production accuracy is required, or an optical fiber having a special diameter or a refractive index distribution needs to be used. Therefore, in order to maintain low cost, which is one of the advantages of the present invention, it is desirable to limit the number of wavelength bands used in the same PON to two.

The present invention has the following structural features in order to take measures against a failure without increasing the number of optical fiber cores for such a PON. First, a configuration corresponding to an upstream optical signal will be described. In a conventional bus-type PON, an optical receiver is connected to only one end of an optical fiber, and when transmitting light from an optical transmitter at a slave station to an optical receiver at the end of the fiber,
Light propagates only in a specific direction of the optical fiber. In the present invention, optical receivers are connected to both ends of the optical fiber so as to cope with a failure in which the optical fiber is broken halfway. Further, the optical transmitter provided in the slave station is provided with a means for determining the direction of transmission to the optical fiber. If the optical fiber is disconnected and the path from the optical transmitter of the slave station to the optical receiver connected before the disconnection is broken, the slave station switches the output direction of the output light from the optical transmitter and switches the optical fiber. To the optical receiver at the opposite end.

For example, eight slave stations are connected to the PON, a first optical receiver is connected to one end of the optical fiber, and a second optical receiver is connected to the other end. And First
The optical transmitter of the four slave stations closer to the optical receiver is 1.55 μm
The first optical receiver transmits light to the first optical receiver using the band, and the optical transmitters of the four slave stations closer to the second optical receiver use the 1.31 μm band to receive the second optical receiver. Assume that light is being sent to the vessel.

If the optical fiber is disconnected in such a network, for example, if any part between four slave stations transmitting light in the 1.55 μm band is disconnected, the following is performed. A slave station that has lost connection with the first optical receiver, that is, a slave station that is closer to the second optical receiver from the disconnection point among the four slave stations that have sent light to the first optical receiver Switching the output direction of the output light of the optical transmitter to the direction of the second optical receiver,
Connect to the second optical receiver. An optical coupler for connecting four slave stations that have transmitted light to the second optical receiver before disconnection transmits light in the 1.55 μm band with almost no branch loss.
Therefore, the light of the slave station switched from the communication to the first optical receiver to the communication to the second optical receiver can reach the second optical receiver with a small loss. That is, for 1.55 μm light, it can be considered that there are almost no four couplers close to the second optical receiver.

In such a configuration, not only is a new core wire not required for failure countermeasures, but also if the number of couplers passing therethrough increases because the slave station changes the direction in which light is sent to the optical fiber, Most of the couplers do not provide branch loss. Therefore, even if the number of slave stations is increased and the core wire utilization efficiency is increased, deterioration of transmission quality is small, and a backup system can be constructed with good quality. The receivers provided at both ends of the optical fiber may receive the 1.55 μm light and the 1.31 μm light collectively in one light receiving unit, or separate each of them with a wavelength multiplexer / demultiplexer to separate them. The light may be received by the light receiving unit.

Next, the case of a downlink signal will be described. Bus type
Optical transmitters are provided at both ends of the optical fiber forming the PON. Each optical transmitter has its bus-type PON
There are provided a plurality of light emitting units for outputting light in a wavelength band used therein. The slave station connected to the bus-type PON has a predetermined wavelength band of the received light. A coupler for connecting each slave station to an optical fiber has a characteristic that only light in that wavelength band is branched and light in other wavelength bands is transmitted. Each of the slave stations has means for receiving light from any direction of the optical fiber. If the optical fiber breaks and the optical receiver of the slave station cannot receive light from the optical transmitter with which it was communicating, the slave station changes the light receiving direction, and Receives light from a transmitter. The optical transmitter at the end of the optical fiber transmits light from the light emitting unit corresponding to the wavelength band, and transmits data to the slave station whose connection direction has been changed. The optical transmitters connected to both ends of the optical fiber are connected, for example, via separate lines, and can exchange data and switch communication paths.

Specifically, for example, when one end of an optical fiber is connected to a first optical transmitter, the other end is connected to a second optical transmitter, and eight slave stations are connected to the optical fiber. Will be described. The optical receivers of the four substations closer to the first optical transmitter have a receiving wavelength band of 1.55 μm, and the optical receivers of the four substations closer to the second optical receiver have their receiving wavelengths of 1.55 μm. 1.31 wavelength band
μm. 1.55 for normal operation with no faults
The slave station receiving the μm band communicates with the first optical transmitter, and the slave station receiving 1.31 μm communicates with the second optical transmitter. For example, if the optical fiber is broken at any point between four slave stations receiving the 1.55 μm band, a slave station farther from the break point with respect to the first optical transmitter is transmitted from the first optical transmitter. Light cannot be received. Therefore, the slave station that has lost communication with the first optical transmitter changes the light receiving direction to the direction of the second optical transmitter, and switches to communication with the second optical transmitter. No. 2
In response to the occurrence of a failure, the optical transmitter transmits light to the slave stations whose communication directions have been switched.

At this time, 1.55 μm transmitted by the second optical transmitter
The light in the m band passes through four couplers for connecting slave stations that receive the 1.31 μm band. These couplers are 1.55
Light in the μm band is transmitted with almost no branching loss. Therefore, for light in the 1.55 μm band, those couplers can be regarded as absent.

By doing so, it is possible to take measures against a failure without increasing the number of core wires. Further, even if the number of couplers through which light passes by switching the receiving direction increases, many of them do not cause branch loss. Therefore, even in the case of a PON having a large number of slave stations and improved core line utilization efficiency, deterioration in transmission quality is small and good transmission is possible.

[0029]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a passive optical network according to a typical embodiment of the present invention. Optical fiber 4
Are inserted with a plurality of couplers 5-x (x = 1, 2, 3) and 6-y (y = 1, 2). The wavelength band of light used by the slave station 7-x connected to the coupler 5-x is the slave station 8-y connected to the coupler 6-y.
Is different from the wavelength band of light used. This passive optical network can be regarded as an almost independent network for each wavelength band because the loss due to a coupler for connecting a slave station using another wavelength band is small.

The wavelength band used in the network of FIG.
Two cases of the 1.55 μm band and the 1.31 μm band will be described. Coupler 5-x has slave station 7-x, coupler 6-y has slave station 8
-y are connected respectively. The coupler 5-x is a 1 × 2 coupler, and the light in the 1.55 μm band has a predetermined branching ratio, for example, 7:
The light is branched at 3, and light in the 1.31 μm band is not substantially branched. That is, the transmittance from the port on the first side of the coupler 5-x to the port connected to the optical fiber 4 among the ports on the second side is about 70% for light in the 1.55 μm band and about 70% for light in the 1.31 μm band. The transmittance to the port connected to the slave station 7-x is about 30% for light in the 1.55 μm band and about 0% for light in the 1.31 μm band. The coupler 6-y is a 1 × 2 coupler, and branches light in the 1.31 μm band at a predetermined branching ratio, for example, 7: 3, and does not substantially branch light in the 1.55 μm band. That is,
The transmittance from the port on the 1 side of the coupler 6-y to the port connected to the optical fiber 4 among the ports on the 2 side is 1.31 μm
About 70% for light in the band, about 100 for light in the 1.55 μm band
%, Transmittance to the port connected to slave station 8-y is 1.31μ
Approximately 30% for light in the m band, approximately 0% for light in the 1.55μm band
It is.

As described in [Means for Solving the Problems], the couplers 5-x,
6-x can be manufactured by melt drawing, which is a general method of manufacturing a coupler. However, the coupler generally has a relatively large branching ratio manufacturing error of about 5% to 10%. Therefore, even if it is manufactured with a target of a 7: 3 branching ratio, it may actually be 6: 4 or 7.5: 2.5. The above-mentioned "predetermined branching ratio" has such a variation. Similarly, in a case where the light is transmitted without being substantially branched, the branch ratio may not be 10: 0, but may be 9.5: 0.5 or 9: 1. Further, the coupler has excess loss in addition to branch loss. The branch loss refers to, for example, in a 7: 3 coupler, a decrease in the optical power by 30% (about 1.5 dB) at the port on the output side of 7. Excess loss is a loss caused by imperfections inside the coupler and at the connection, and is not output to either port.
Excess loss is typically on the order of 10% (0.5 dB). Therefore, in a coupler with a predetermined branching ratio of 7: 3, the transmittance to one port does not become exactly 70% even if the error of the branching ratio is removed, and it is reduced by the excess loss to about 63% become. “Approximately”, “substantially”, and “almost” indicate that the numerical values may not actually be the same due to errors in the branching ratio or excessive loss.

The slave station 7-x communicates with light in the 1.55 μm band. That is, if the signal is a downstream signal, the light in the 1.55 μm band branched by the coupler 5-x is received, and if the signal is an upstream signal, the light output from the slave station 7-x is transmitted to the optical fiber 4 by the coupler 5-x. Join. Similarly, slave station 8-y uses 1.31μ for communication.
m-band light is used. That is, if the signal is a downstream signal, the light in the 1.31 μm band that has been branched by the coupler 6-y is received, and if the signal is an upstream signal, the light output from the slave station 8-y is transmitted to the optical fiber 4 by the coupler 6-y. Join.

Further, for example, 1.5 times output from the slave station 7-3 is output.
The upstream optical signal in the 5 μm band joins the optical fiber 4 at the coupler 5-3, and then passes through the couplers 6-2 and 6-1 with almost no branch loss. “Almost” means that a branching error deviated from 10: 0 is incurred due to a branching ratio error. The excess loss of the coupler is incurred regardless of the wavelength. Therefore, although it is difficult to transmit light with no loss at all, it does not suffer from a branch loss of about 1.5 dB when passing through a normal 7: 3 coupler. Since the couplers 5-1 and 5-2 act as a 7: 3 coupler for the 1.55 μm band, each of them experiences about 1.5 dB of branch loss.

Similarly, the 1.31 μm band light output from the slave stations 8-1 and 8-2 passes through the couplers 5-1 and 5-2 almost without branch loss.

In the case of a downstream optical signal, light in the 1.55 μm band is split by couplers 5-1 and 5-2 at a split ratio of 7: 3 and input to slave stations 7-1 and 7-2, respectively. . The remainder passes through couplers 6-1 and 6-2 with almost no branch loss, and is again branched by coupler 5-3 at a branch ratio of 7: 3 and input to slave station 7-3. The 1.31-μm band light passes through couplers 5-1 and 5-2 with almost no branching loss, and is branched by couplers 6-1 and 6-2 at a branching ratio of 7: 3, respectively.
Enter 8-1,8-2. The rest passes through coupler 5-3.

As described above, since the loss due to the coupler for connecting the slave station using another wavelength band is small, a network almost independent for each wavelength band can be formed. As a result, it is possible to increase the number of slave stations that can be connected to one optical fiber, and the core wire utilization efficiency increases. Also, since the components used to construct such a wavelength division multiplexing network simply utilize the wavelength dependence of ordinary couplers, a network can be constructed at low cost.

FIG. 2 shows a configuration of an upstream signal system, and shows a configuration in a case where an upstream signal is transmitted from an optical transmitter corresponding to the slave station in FIG. 1 to an optical receiver connected to an end of an optical fiber. .
Optical transmitters 10-1, 10-2, 1 connected to couplers 5-1, 5-2, 5-3
Optical transmitters 0-3 each emit light in the 1.55 μm band.
The optical transmitters 11-1 and 11-2 connected to the couplers 6-1 and 6-2 are optical transmitters that emit light in the 1.31 μm band. Coupler 5-
The branching ratio of 1,5-2,5-3,6-1,6-2 is the same as that in FIG.

The light output from the optical transmitter is transmitted to an optical fiber 4 via a coupler to which each optical transmitter is connected.
To join. When propagating through an optical fiber, a coupler connecting an optical transmitter that outputs a wavelength band different from the wavelength band of its own station does not suffer from branch loss. The combined light is received by the optical receiver 9 installed at the end of the optical fiber. The configuration around the light receiving section of the optical receiver is, for example, as shown in FIG. Fig. 3 (a)
In the figure, there is only one light receiving unit, and the optical fiber 4 has been transmitted 1.
The light in the 55 μm band and the light in the 1.31 μm band are photoelectrically converted by the same light receiving unit 12 in a mixed state. At this time, for example, frequency division so that signals from all slave stations can be separated after reception
(Subcarrier division) It is necessary to take measures such as multiplexing.

In FIG. 3B, the light transmitted through the optical fiber 4 is separated into a 1.55 μm band and a 1.31 μm band by a WDM (Wave Division Multiplexing) coupler 13 and then separated into another optical receiver 12-1. , 12-2. In this case, measures should be taken against beat noise and signal interference in each wavelength band.

FIG. 4 is also a configuration example of an upstream signal system. The difference from FIG. 2 is that the direction in which light joins from the optical transmitter to the optical fiber 4 varies, and that optical receivers are installed at both ends of the optical fiber. The optical receivers 9-1 and 9-2 in FIG. 4 each have one light receiving unit as shown in FIG. 3 (a). The optical transmitters 10-1, 10-2, and 10-3 each emit light of 1.55 μm, and join the optical fiber 4 by the couplers 5-1, 5-2, and 5-3, respectively. These propagate to the left as viewed in the figure and are received by the optical receiver 9-1. Optical transmitter 10-3
The couplers 6-1 and 6-2 through which light from the optical fiber 4 passes when propagating through the optical fiber 4 transmit light in the 1.55 μm band almost without branch loss. The optical transmitters 11-1 and 11-2 emit light in the 1.31 μm band, merge into the optical fiber 4 by the couplers 6-1 and 6-2, and propagate toward the optical receiver 9-2. Coupler 5-3
Light in the 1.31 μm band is transmitted with almost no branching loss. Thus, in FIG. 4, light in the 1.55 μm band is directed toward the optical receiver 9-1,
The light in the 1.31 μm band propagates toward the optical receiver 9-2. Light in each wavelength band is hardly split by a coupler for connecting an optical transmitter using another wavelength band.
Therefore, even if the traveling directions are different in the respective wavelength bands, the problem due to the return light to the optical transmitter hardly occurs.
For example, the light output from the optical transmitter 11-1 and propagating rightward in the optical fiber as viewed in the drawing is hardly split by the coupler 5-3. Even if a small amount of light is branched due to a coupler manufacturing error or the like, since the optical transmitter 10-3 is a 1.55 μm band optical transmitter, even if 1.31 μm band light is input, there is no adverse effect.

In FIGS. 2 and 4, 1.55 μm band optical transmitter and 1.
Although the configuration is such that the optical transmitters in the 31 μm band are intricate, they may of course be installed collectively for each wavelength band as shown in FIG. The optical transmitters 10-1 to 10-4 output light in the 1.55 μm band,
Each of them joins the optical fiber 4 by the couplers 5-1 to 5-4. The optical transmitters 11-1 to 11-4 output light in the 1.31 μm band and join the optical fiber 4 by the couplers 6-1 to 6-4, respectively. Light in the 1.55 μm band is received by the optical receiver 9-1, and light in the 1.31 μm band is received by the optical receiver 9-2.

At first glance, it appears that the configuration as shown in FIG. 5 can be easily realized with the same performance even if only light of one wavelength band is used without using wavelength multiplexing. However, when wavelength division multiplexing is not performed, the light from the four slave stations connected to one optical receiver and the light connected to the other optical receiver are used because of the return light generated by Rayleigh scattering of the optical fiber. It becomes impossible to take isolation between light from two slave stations. Therefore, it is necessary to totally monitor the light emitted from the eight slave stations, which complicates the control of the system. By using wavelength division multiplexing, it is possible to regard each of the four slave stations as an independent network, which facilitates system control.

FIG. 6 shows a configuration of a downstream signal system, in which a downstream signal is transmitted from an optical transmitter connected to an end of an optical fiber to an optical receiver corresponding to a slave station in FIG. The optical transmitter 14 has a light emitting unit 17-1 for outputting light in the 1.55 μm band and a light emitting unit 17-2 for outputting light in the 1.31 μm band as shown in FIG. The light is coupled by the coupler 18 and sent to the optical fiber 4. The coupler 18 may be a WDM coupler or a normal coupler depending on power requirements such as the output power of the light emitting unit and cost requirements. Optical fiber 4
Are transmitted to couplers 5-1, 5-2, 5-3, 6-1, and 6-2, respectively. In couplers 5-1, 5-2, and 5-3, light in the 1.55 μm band is branched at a branch ratio of, for example, approximately 7: 3, and 1.31 μm
Light in the m-band is transmitted substantially without branch loss. Optical receiver
15-1, 15-2, and 15-3 receive the 1.55 μm band light split by the couplers 5-1, 5-2, and 5-3. 1.3 for coupler 6-1 and 6-2
The light in the 1μm band is nominally split at a 7: 3 split ratio to 1.55μm
The band light is transmitted substantially without branch loss. Optical receiver 16
-1,16-2 receives the 1.31 μm band light split by the couplers 6-1 and 6-2.

In this way, similar to the upstream system, simple wavelength multiplexing for each wavelength band is performed by utilizing the wavelength dependency of the low-cost coupler, and the number of optical receivers connected to the bus-type PON is increased. Can be increased, and core wire utilization efficiency is improved.

FIG. 8 is also a configuration example of a downstream signal system, in which two optical transmitters 14-1 and 14-2 are connected to both ends of the optical fiber 4. Each of the optical transmitters 14-1 and 14-2 has one light emitting unit 17 as shown in FIG. Optical transmitter 14-1 is 1.5
The light in the 5 μm band is transmitted to the optical fiber 4, and the optical transmitter 14-2 outputs 1.
Transmits light in the 31 μm band. 1.5 sent to optical fiber 4
Light in the 5 μm band is split by couplers 5-1, 5-2, and 5-3 and input to optical receivers 15-1, 15-2, and 15-3. Light in the 1.55 μm band passes through the couplers 6-1 and 6-2 with almost no branching loss. The light not split by the coupler 5-3 is input to the optical transmitter 14-2, but the emission wavelength of the optical transmitter 14-2 is in the 1.31 μm band and interacts with the light in the 1.55 μm band. There is no effect because there is no Similarly, the 1.31 μm band light output from the optical transmitter 14-2 is split by the couplers 6-1 and 6-2 and input to the optical receivers 16-1 and 16-2. The couplers 5-1, 5-2, and 5-3 pass with almost no branching loss and are finally input to the optical transmitter 14-1, but have no effect because the wavelength bands are different. Since a network is configured using light in two independent wavelength bands, it is possible to easily construct a system in which the traveling direction in the optical fiber 4 differs for each wavelength band.

As in the case of the upstream signal system, as shown in FIG.
Optical receivers may be installed together for each wavelength band. The optical transmitters 14-1 and 14-2 are as shown in FIG. 10, and the optical transmitter 14-1 is 1.55.
The light in the μm band is transmitted, and the optical transmitter 14-2 transmits the light in the 1.31 μm band. The light output from the optical transmitter 14-1 is coupled to the coupler 5-
The signals are branched at 1 to 5-4 and input to the optical receivers 15-1 to 15-4. The light that has passed through the coupler 5-4 passes through the couplers 6-1 to 6-4 with almost no branch loss, and is input to the optical transmitter 14-2. Since the emission wavelength of the optical transmitter 14-2 is in the 1.31 μm band, it is 1.55 μm.
There is no effect even if m-band light is input. The 1.31 μm band light output from the optical transmitter 14-2 is branched by couplers 6-1 to 6-4 and input to the optical receivers 16-1 to 16-4. Coupler 6-
The light passing through 1 passes through the couplers 5-1 to 5-4 almost without branch loss, and is input to the optical transmitter 14-1. Since the output light wavelength of the optical transmitter 14-1 is in the 1.55 μm band, there is no effect even if light in the 1.31 μm band is input.

In the above embodiment, even if light having a wavelength band different from that of the output light is input to the optical transmitter, there is usually no effect. However, depending on the structure of the light emitting unit in the optical transmitter,
For example, in the case where reflection occurs at the end face of the light emitting element and returns to the optical fiber 4 and adverse effects occur, a simple wavelength filter is inserted in front of the optical transmitter so that light of another wavelength band to be input to the optical transmitter is transmitted. May be removed.

Next, an embodiment for coping with an optical fiber disconnection fault in such a system will be described. An embodiment of the downlink system is as shown in FIG. FIG. 11 is based on the configuration of FIG. 9, but of course, as shown in FIG. 6 and FIG.
A configuration in which a μm optical receiver and a 1.55 μm optical receiver are involved can be handled in exactly the same manner.

FIG. 11 shows that the 1.55 μm band and 1.31
In the example using light in two wavelength bands in the μm band, optical transmitters 14-1 and 14-2 are connected to both ends of an optical fiber 4. Each of the optical transmitters 14-1 and 14-2 has a light emitting unit corresponding to both wavelength bands as shown in FIG. The difference from Fig. 7 is that
Since there is a possibility that light in the same wavelength band as the respective light-emitting units propagates through the optical fiber 4 and enters the light-emitting units, a means for removing them is provided. That is, in FIG. 13, the optical isolators 26-1, 2 corresponding to the light including the output wavelength of each light emitting unit are provided at the output end of each light emitting unit.
6-2 is provided. The coupler 18 may be either a WDM coupler or a coupler having no wavelength dependency.

The optical fiber 4 has eight optical receivers 15-1 to 15-
4, 16-1 to 16-4 are connected via couplers 19-1 to 19-4 and 20-1 to 20-4. The optical receivers 15-1 to 15-4 are optical receivers that receive the 1.55 μm band, and the optical receivers 16-1 to 16-4 are 1.31.
It is an optical receiver that receives the μm band. Couplers 19-1 to 19-4
Splits light in the 1.55 μm band at a split ratio of approximately 7: 3,
μm band light is transmitted without being substantially branched, and the couplers 20-1 to 20-4 branch the 1.31 μm band light at a branching ratio of about 7: 3 and substantially convert the 1.55 μm band light. The light is transmitted without branching. The coupler is 2x2, but its basic characteristics are the same as those described above. Since the port numbers are assigned to the couplers 19-1 in FIG. 11, a brief description will be made using these numbers. Coupler 19-1 converts 1.55μm band light
The light is branched into 7: 3, and the light in the 1.31 μm band is transmitted without being substantially branched. In the case of 2 × 2, between port A and port B connected to optical fiber 4, light in the 1.55 μm band is approximately 70%, 1.31 μm.
Approximately 100% of light in the m band, between port A and port D and between port B and port C, approximately 30% of light in the 1.55 μm band, 1.31 μm
Approximately 0% of m-band light is transmitted. The meaning of “approximately” is as described above.

The optical receivers 15 and 16 connected to the coupler are provided with means for receiving light from any direction of the optical fiber 4. For example, FIG.
It seems as shown. FIG. 12A shows a configuration in which the two light receiving units 21-1 and 21-2 are switched by the switch 22. The light receiving unit 21-1 receives light from the left side of the optical fiber 4, that is, light from the optical transmitter 14-1. The light receiving section 21-2 receives light from the optical transmitter 14-2. By switching these outputs with the switch 22, the optical transmitter of the receiving party is selected. In the figure, the switch 22 is a 2 × 1 switch, and the output of the light receiving unit that is not selected is not connected to anywhere, but this is set to a 2 × 2 switch, and the output of the light receiving unit that is not selected is always monitored. A configuration may be adopted. FIG. 12B shows a configuration in which an optical switch 23 is inserted in front of the light receiving unit 21 and an optical transmitter to be connected by the optical switch is selected. As in the case of FIG. 12 (a), a configuration may be adopted in which the optical switch is set to 2 × 2 and the one not selected is also monitored. Although not shown, either one of the two light receiving unit outputs may not be selected but both may be received at all times. These are matters to be determined in relation to the usage form of the optical transmitter, that is, whether or not all the light emitting units are always lit or only when necessary.

In such a configuration, the optical receivers 15-1 to 15-4 normally receive light from the optical transmitter 14-1,
It is assumed that the optical receivers 16-1 to 16-4 are receiving light from the optical transmitter 14-2. Here, it is assumed that the optical fiber is disconnected at the disconnection point 24 shown in FIG. Optical receivers 15-1, 15-2 and 16-1
16-4 can receive light from the optical transmitter 14-1 or the optical transmitter 14-2 as before the disconnection. But the optical receiver 15
-3 and 15-4 cannot receive light from the optical transmitter 14-1 with which they were communicating. Therefore, the optical receivers 15-3 and 15-4 switch the direction of receiving light so as to receive the light from the optical transmitter 14-2. If the optical receiver always receives light from both, the communication destination is switched to the optical transmitter 14-2. At this time, 1.55 μm output from the optical transmitter 14-2
The light in the band passes through couplers 20-1 to 20-4 with almost no branching loss and reaches coupler 19-4. Therefore, it is as if the optical transmitter 14- is not affected by the four couplers on the right side of the drawing.
The same quality can be ensured as when 2 is adjacent to the coupler 19-4.

As a result, high-performance communication is possible even after switching the communication direction, despite the large number of optical receivers connected to the same optical fiber. Moreover, these are configured using low-cost couplers utilizing their wavelength dependence. By doing so, it is possible to construct a low-cost, high-quality, fault-tolerant network without increasing the number of core wires for troubleshooting.

It is assumed that the optical transmitters 14-1 and 14-2 are configured to be able to communicate with each other by any method. For example, as shown in FIGS. Fig. 14
(a) shows a mode in which the optical transmitters 14-1 and 14-2 are connected by a communication line 25. When a disconnection occurs, the optical transmitter 14-1 transfers data to be transmitted to the optical receivers 15-3 and 15-4 to the optical transmitter 14-2 via the communication line 25. FIG. 14 (b) shows a configuration in which the optical receiver 15- is connected via a communication network 27.
Data to be sent to 3,15-4 is sent from communication network 27 to communication line 25-1.
Is transmitted to the optical transmitter 14-1 via the communication network 27, but is transmitted from the communication network 27 to the optical transmitter 14-2 via the communication line 25-2 after the disconnection. FIG. 15 shows an example in which the optical transmitters 14-1 and 14-2 are installed together in the same station 28 in the network, and the network is ring-shaped. At this time, the optical transmitters 14-1 and 14
-2 is supplied with the same data at the same time, or the destination of the data is switched by the switch 29 as shown in FIG.

In order to switch, a process for detecting a failure is required. The means and procedure of fault detection are known,
There are various possibilities including new ones. As means of fault detection,
For example, in the case of FIG. 11, if the intensity of the light transmitted from the optical transmitter 14-1 becomes weak or is interrupted, the optical receiver 15-1
-3 is weakened by using up fiber etc.
There is a means for informing the optical transmitter 14-1 or the optical transmitter 14-2.

Next, the case of an upstream optical signal will be described. FIG.
Is one form thereof. It is based on the configuration of FIG.
The output light wavelength of the optical transmitters 30-1 to 30-4 is in the 1.55 μm band,
The output light wavelength of the optical transmitters 31-1 to 31-4 is in the 1.31 μm band.
The couplers 19-1 to 19-4 and 20-1 to 20-4 are couplers having the same wavelength dependence as in FIG. Optical receivers connected to both ends of the optical fiber 4 are the same as in FIG. Each optical transmitter has a light emitting unit 32 and an optical switch 23 at its output end as shown in FIG. 17 (a) so that the output direction of the output light of the light emitting unit can be switched. Alternatively, as shown in FIG. 17 (b), two light emitting units may be prepared and switched by an electric stage (that is, electric switch 22). Also, FIG.
In (a), a 1 × 2 coupler may be inserted instead of the optical switch 23 so that a signal is always output in both directions. However, in the latter two methods, since light in the same wavelength band is input to the light emitting unit, it is necessary to connect an optical isolator to the light emitting unit output terminal and protect the light emitting element as described in FIG. . The optical transmitters 30-1 to 30-4 are normally connected to the optical receiver 9-1, and the optical transmitters 31-1 to 31-4 are connected to the optical receiver 9-2.

In such a configuration, when the disconnection point 24 shown in FIG. 16 is disconnected, the optical transmitters 30-1, 30-2 and 31-1 to 3-1
1-4 can communicate with the optical receiver 9-1 or 9-2 as before the disconnection. However, the light from the optical transmitters 30-3 and 30-4 does not reach the optical receiver 9-1. Therefore, the optical transmitters 30-3 and 30-4 are connected to the optical receiver 9-
Switch to send a signal to 2. The light in the 1.55 μm band transmitted from the optical transmitters 30-3 and 30-4 passes through the couplers 20-1 to 20-4 and reaches the optical receiver 9-2, but the couplers 20-1 to 20- Four
Has almost no branch loss for light in the 1.55 μm band. Therefore, the loss suffered is small and the optical receiver 9-
You can reach up to 2. That is, even if the number of optical transmitters connected to the network is large, it is possible to maintain high quality and cope with disconnection without increasing the number of core wires. In addition, since it is configured using a simple coupler, a network can be constructed at low cost.

[0059]

As described above, the first effect of the present invention is to increase the number of connector stations by using light in a plurality of wavelength bands in a bus-type passive optical network, and to improve the efficiency of optical fiber core wire utilization. It is to improve. At this time,
As a coupler for connecting slave stations, a coupler having a specific branching ratio for one wavelength band and having a characteristic of transmitting light of another wavelength band without being substantially branched is used. Since such a coupler can be manufactured by a simple process, a network can be constructed at low cost.

A second effect of the present invention is to take measures against a failure without increasing the number of optical fiber cores.

[Brief description of the drawings]

FIG. 1 is a diagram showing a typical embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of the present invention.

FIG. 3 is a schematic diagram of an optical receiver applied to the present invention.

FIG. 4 is a diagram showing an embodiment of the present invention.

FIG. 5 is a diagram showing an embodiment of the present invention.

FIG. 6 is a diagram showing an embodiment of the present invention.

FIG. 7 is a schematic diagram of an optical transmitter applied to the present invention.

FIG. 8 is a diagram showing an embodiment of the present invention.

FIG. 9 is a diagram showing an embodiment of the present invention.

FIG. 10 is a schematic diagram of an optical transmitter applied to the present invention.

FIG. 11 is a diagram showing an embodiment of the present invention.

FIG. 12 is a schematic diagram of an optical receiver applied to the present invention.

FIG. 13 is a schematic diagram of an optical transmitter applied to the present invention.

FIG. 14 is a diagram for explaining auxiliary functions for implementing the present invention.

FIG. 15 is a diagram for explaining auxiliary functions for implementing the present invention.

FIG. 16 is a diagram showing an embodiment of the present invention.

FIG. 17 is a schematic diagram of an optical transmitter applied to the present invention.

FIG. 18 is a diagram illustrating a conventional bus-type passive optical network.

[Explanation of symbols]

 Reference Signs List 1 master station 2 slave station 3 coupler 4 optical fiber 5 coupler 6 coupler 7 slave station 8 slave station 9 optical receiver 10 optical transmitter 11 optical transmitter 12 light receiving unit 13 WDM coupler 14 optical transmitter 15 optical receiver 16 optical receiver 16 Device 17 Light-emitting unit 18 Coupler 19 Coupler 20 Coupler 21 Light-receiving unit 22 Switch 23 Optical switch 24 Disconnection location 25 Communication line 26 Optical isolator 27 Communication network 28 Station 29 Switch 30 Optical transmitter 31 Optical transmitter 32 Light-emitting unit

Claims (5)

[Claims] An optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided in the optical fiber, and a plurality of stations each connected to the optical fiber via the coupler. A network, wherein the number of the stations is greater than the number of the wavelength bands, and the coupler has a predetermined branching ratio for light in the wavelength band used by the stations connected to the coupler;
For light of the other wavelength band, it has a property of transmitting light without substantially branching from one port connected to the optical fiber to the other port connected to the optical fiber. A passive optical network. 2. The passive optical network according to claim 1, wherein the number of said wavelength bands is two. 3. An optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided on the optical fiber, and a plurality of optical transmitters respectively connected to the optical fiber via the coupler. A passive optical network, wherein an optical receiver is provided at each end of the optical fiber, and a wavelength of output light output from the plurality of optical transmitters belongs to any of the plurality of wavelength bands; The number of the transmitters is greater than the number of the wavelength bands, and the coupler has a predetermined branching ratio with respect to the light of the wavelength band to which the wavelength of the output light output from the optical transmitter connected to the coupler belongs. For transmitting light of the other wavelength band without substantially branching from one port connected to the optical fiber to the other port connected to the optical fiber Special The optical transmitter includes a selection unit that selects one or the other of the optical receivers and outputs light, and each of the optical receivers has at least one or more light receiving units. And passive optical network. 4. An optical fiber for transmitting light in a plurality of wavelength bands, a plurality of couplers provided on the optical fiber, and a plurality of optical receivers connected to the optical fiber via the couplers, respectively. A passive optical network, wherein an optical transmitter is provided at each end of the optical fiber, a wavelength of light received by the plurality of optical receivers is set to any of the plurality of wavelength bands, and the optical receiver Is greater than the number of the wavelength bands, the coupler has a predetermined branching ratio with respect to the light of the wavelength band received by the optical receiver connected to the coupler, and the other of the other wavelength bands. The optical transmitter has a characteristic of transmitting light without substantially branching from one port connected to the optical fiber to the other port connected to the optical fiber. Yes It has a light emitting unit that outputs light corresponding to each of the plurality of wavelength bands, and the optical receiver has at least one of the light transmitted from the two optical transmitters via the optical fiber. 1. A passive optical network, comprising: a selection receiving means for selecting and receiving a signal. 5. The passive optical network according to claim 3, wherein the number of the wavelength bands is two.