JPH118591A - Optical transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of level difference in a light-receiving level on the side of a master station for receiving an optical signal synthesized by an up optical branching filter inside a slave station group. SOLUTION: This device has a master station 10, plural slave station groups 20A (20B) respectively having plural slave stations 20, a down optical transmission line 30 connected via plural down optical branchers 21a-21e to slave stations by multidrop topology, so as to transmit the optical signals from the master station 10 to the slave stations 20, and plural up optical transmission lines 40 connected via up optical branching filters 26a, 26b, 26d and 26e to slave stations inside respective slave station groups by the multidrop topology for each slave station group, so as to transmit optical signals from the slave stations in the respective groups to the master station 10. In this case, light-emitting elements mutually separating light-emitting wavelengths at prescribed intervals are respectively arranged at the respective slave stations, so as to minimize the level difference of optical signal reception from each slave station to the master station 10, after synthesis at the optical branching filters 26a and 26b (or 26d and 26e), while considering the transmission loss of the up optical transmission line 40 and the wavelength characteristics of optical branching ratios at the up optical branching filters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission apparatus for an optical communication network, and more particularly to a master station, a plurality of slave stations for performing two-way communication with the master station by optical signals, and a slave station from the master station. The present invention relates to an optical transmission device of a multi-branch type optical transmission system having a downstream optical transmission line for transmitting an optical signal to a slave station and an upstream optical transmission line for transmitting an optical signal from the slave station to the master station.

[0002]

2. Description of the Related Art Conventionally, when such a multi-branch type optical transmission system adopts a multi-drop topology connection structure, it is used for a downstream optical transmission line for transmitting an optical signal from a master station to each slave station. In consideration of the number of branches of each optical splitter, transmission loss between transmission lines, and the like, the branching ratio is set so that the light reception levels of the respective slave stations are equal. If sufficient, the topology does not affect the transmission performance, and the transmission characteristics are uniform among the stations.

However, when an upstream optical transmission line for transmitting an optical signal from each slave station to the master station is constructed with the same connection configuration as the downstream optical transmission line, a light emitting element (for example, The optical signal from the laser diode is combined by an upstream optical splitter on the upstream optical transmission line, and the combined optical signal is finally received by a light receiving element (for example, a photodiode) inside the master station. In such a case, optical signals from the slave stations may interfere with each other and generate optical beat noise.

Further, the optical beat noise increases noise in a transmission signal band, and eventually degrades signal quality such as a carrier-to-noise ratio and a bit error rate.

In order to prevent such deterioration in signal quality, a multi-branch type optical transmission system employing a wavelength control multi-drop topology has been devised.

According to the multi-branch optical transmission system employing the wavelength control multi-drop topology, optical beat noise is detected from the upstream optical branching device in the upstream optical transmission line, and the light emission of each slave station is determined based on the detection result. Since the emission wavelength of the element is controlled, it is possible to avoid occurrence of optical beat noise in the upstream optical transmission line.

However, since the configuration and algorithm are complicated, the system is complicated, and the cost of the whole system is greatly increased.

In order to avoid such a situation, the present applicant has developed an optical transmission device as described below as such a multi-branch type optical transmission system.

An optical transmission apparatus of such a multi-branch optical transmission system includes a master station, at least one slave station group having a predetermined number of slave stations, and a multi-drop optical splitter through a plurality of downstream optical splitters. A downstream optical transmission line that connects to a slave station with a topology and transmits an optical signal from the master station to the slave station, and for each slave station group, a multi-drop topology through an upstream optical splitter within each slave station group. And a plurality of upstream optical transmission lines for transmitting optical signals from the slave stations in each slave station group to the master station.

[0010] Each upstream optical splitter of such an optical transmission apparatus determines an optical splitting ratio in accordance with the number of slave stations in each slave station group. The optical branching ratio is determined according to the number of stations.

When the branching ratio of the upstream optical branching device is almost the same as the branching ratio of the downstream optical branching device, the downstream optical branching device can be used as the upstream optical branching device, and the number of components can be reduced. Cost can be reduced.

According to such an optical transmission apparatus, the slave stations in the slave station group connected to each upstream optical transmission line emit light to emit an optical signal in each slave station in order to suppress optical beat noise. The emission wavelengths of the devices need to be spaced from each other by a predetermined distance.

For example, if the number of slave stations in the slave station group is three, it is necessary to use three types of light emitting elements, and the wavelength interval between the light emitting elements is a half width of the light emitting element, It is determined based on the noise specification and the like of the optical transmission device.

Generally, the optical branching ratio of the optical branching device is set based on the center wavelength of the wavelength band used in the optical branching device. It is widely known that the optical splitting ratio of an optical splitter depends on the wavelength.

That is, the light branching ratio of the light branching device has a wavelength dependency, and therefore differs depending on the emission wavelength of each light emitting element.

[0016]

However, according to such an optical transmission apparatus, for example, the number of slave stations in the slave station group is three, the number of slave stations is two, and the upstream optical transmission line When the number of the light emitting elements in each slave station is two, the wavelength interval between the light emitting elements in each slave station is 25 nm, and a system configuration in which three types of light emitting elements are used in each slave station group, the center wavelength of the used wavelength band is 1. Even if the optical branching ratio of the upstream optical branching device is selected based on the center wavelength, the light receiving level of the optical signal received by the master station is reduced to 31 μm because there is a light emitting element having a wavelength different from the center wavelength. A difference occurs. Further, in order to reduce costs, when the branching ratio of the upstream optical branching device is substantially the same as the branching ratio of the downstream optical branching device, and when the downstream optical branching device is diverted to the upstream optical branching device, the upstream optical branching device has Since the design is not exclusively for the upstream, a level difference occurs in the light receiving level of the optical signal received on the master station side.

That is, according to such an optical transmission device,
Even if the light splitting ratio of the optical splitter is selected based on the center wavelength of the used wavelength band, and each light emitting element emits the same output,
Due to the wavelength dependence of the characteristics of the optical splitter, the light splitting ratio of the optical splitter differs depending on the emission wavelength of each light emitting element. However, there is a problem that a large level difference occurs in the light receiving level of each slave station on the master station side, and the level difference sometimes makes it impossible to demodulate on the master station side.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a base station, which combines optical signals from upstream and downstream optical splitters in a group of mobile stations, from each of the local stations. An object of the present invention is to provide an optical transmission device in which a difference in signal reception level is minimized.

[0019]

In order to achieve the above object, an optical transmission apparatus according to the present invention comprises a master station, at least one slave station group having a plurality of slave stations, and a plurality of downstream optical splitters. Connected to the slave station in a multi-drop topology via
A downlink optical transmission line for transmitting an optical signal from the master station to each slave station, and for each slave station group, connected to each slave station in each slave station group in a multi-drop topology via an upstream optical splitter. An optical transmission device comprising an upstream optical transmission path for transmitting an optical signal from each slave station to a master station, wherein each slave station in each slave station group has a different emission wavelength at a predetermined interval from each other. A light-emitting element that emits an optical signal, and when both of the light-emitting elements output an optical signal of the same level, an optical signal reception level from each slave station in the master station after being combined by the upstream optical splitter. Each light emitting element is arranged in each slave station in consideration of the transmission loss of the upstream optical transmission line and the wavelength characteristics of the optical branching ratio of the upstream optical splitter so that the difference is minimized.

Therefore, according to the optical transmission apparatus of the present invention, it is possible to minimize the difference in the light receiving level of the optical signal from each slave station in the master station after being combined by the upstream optical splitter in the slave station group. Can be.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical transmission device according to a first aspect of the present invention provides at least one optical transmission device having a master station and a plurality of slave stations.
One slave station group, a downstream optical transmission line connected to the slave station in a multi-drop topology via a plurality of downstream optical splitters, and transmitting an optical signal from the master station to the slave station, To
An optical transmission device comprising an upstream optical transmission line connected to each slave station in each slave station group in a multi-drop topology via an upstream optical splitter and transmitting an optical signal from each slave station to a master station. hand,
Each of the slave stations in each slave station group has a light emitting element that emits an optical signal having a different emission wavelength at a predetermined interval from each other, and when each of the light emitting elements outputs an optical signal of the same level, The transmission loss of the upstream optical transmission line and the wavelength of the optical branching ratio of the upstream optical splitter are set such that the optical signal reception level difference from each slave station at the master station after being combined by the optical splitter is minimized. It is characterized in that each light emitting element is arranged in each slave station in consideration of characteristics.

The downstream optical transmission line and the upstream optical transmission line are:
For example, it is equivalent to an optical fiber.

The multi-drop topology is a configuration in which a master station and each slave station are connected in a bus shape with a single optical fiber via a plurality of optical splitters. Is determined.

Each of these optical splitters has a cross port and a through port. The through port is a port through which an optical signal propagates through the same optical transmission line, and the cross port is a port through which an optical signal is transmitted through another optical transmission line. It is equivalent to a port that propagates while being coupled to a road.

The cross port and the through port of these optical splitters have different polarities of the wavelength coefficient in the optical splitting ratio, and their absolute values also differ depending on the optical splitting ratio.

For example, when there are three slave stations in the slave station group, the optical signal emitted from the slave station closest to the master station is an optical branch that combines the cross port and the through port at a ratio of approximately 1: 2. Propagating through the cross port of the container and reaching the master station. The optical signal emitted from the slave station immediately before the final end propagates through the cross port of the optical branching device that combines the cross port and the through port almost at 1: 1, and then the cross port and the through port have a ratio of approximately 1: 2. The signal propagates through the through port of the optical branching device to be synthesized in step (1) and reaches the master station. The optical signal emitted from the terminal station at the final end propagates through the through port of the optical branching device that combines the cross port and the through port almost at 1: 1 and then crosses the cross port and the through port at a ratio of about 1: 2. The light propagates through the through port of the optical branching device to be combined and reaches the master station.

The light emitting element provided in each slave station in the slave station group emits an optical signal having an emission wavelength separated by a predetermined interval, for example, 25 nm, for each slave station. If there are three slave stations in the group, the slave station group has three types of light emitting elements.

Therefore, according to the optical transmission device of the first aspect of the present invention, each of the slave stations is connected to the slave station in each slave station group in a multi-drop topology via the upstream optical splitter. In the upstream optical transmission line for transmitting an optical signal, the slave stations in each slave station group have light emitting elements that emit optical signals of different emission wavelengths separated by a predetermined interval from each other, and In consideration of the loss and the wavelength characteristics of the optical splitting ratio of the upstream optical splitter, each light emitting element is arranged in each slave station, so that when each light emitting element outputs an optical signal of the same level, the upstream optical branching is performed. It is possible to minimize the difference in the light reception level of the optical signal from each of the slave stations in the master station after being combined by the device.

According to a second aspect of the present invention, in the optical transmission device according to the first aspect, the upstream optical splitter is the same as at least one of the downstream optical splitters. Features.

For example, the number of slave stations in the slave station group is three, the number of slave station groups is two, the number of upstream optical transmission lines is two, and the number of downstream optical transmission lines is one. In the case of an optical transmission system assuming the distance between the slave stations closest to the master station and the distance between the slave stations to be 500 m, an upstream optical branching device arranged at the final end of the upstream optical transmission line in each of the local station groups; The downstream optical splitter disposed at the last end of the downstream optical transmission line has substantially the same optical branching ratio,
Furthermore, since the upstream optical branching device arranged in front of the final end of the slave station group and the downstream optical branching device arranged in front of the final end of the downstream optical transmission line have substantially the same optical branching ratio, these are almost the same. The same optical splitter is adopted for the upstream optical splitter and the downstream optical splitter having the optical splitting ratios described above.

Therefore, according to the optical transmission apparatus of the second aspect of the present invention, the upstream optical splitter is the same as at least one of the downstream optical splitters. In addition to the effects described above, the number of types of optical splitters can be reduced, so that the cost of the optical splitter can be reduced, and the system can be kept inexpensive.

According to a third aspect of the present invention, in the optical transmission device, the light emitting element is a Fabry-Perot laser diode in addition to the first or the second aspect.

The Fabry-Perot laser diode has a larger half-width of the envelope due to the multi-mode, but is lower in cost than a DFB (Distributed Feedback) laser diode, for example. When a Fabry-Perot laser diode is placed in each slave station, the cost can be reduced. However, in order to suppress beat noise, the DFB laser diode is placed at a predetermined interval between the emission wavelengths of each slave station because the half width is wide. You have to make it bigger than you did. For this reason, the difference in the optical signal reception level from each slave station in the master station after being combined by the upstream optical splitter greatly depends on the arrangement of the light emitting elements in each slave station.

Further, when the same one of at least one of the downstream optical splitters is used as the upstream optical splitter, the design of the upstream optical splitter is not exclusive to the upstream. A level difference occurs in the light receiving level of the optical signal received by the master station.

However, when a Fabry-Perot laser diode is used, since the predetermined intervals of the emission wavelengths of the respective slave stations are relatively large, the optical signal from each slave station in the master station after being combined by the upstream optical branching device. The light receiving level difference can be made larger or smaller depending on the arrangement of the light emitting elements in each slave station, so that the light receiving level difference on the master station side caused by the design of the upstream optical branching device is not dedicated to the upstream. It is also possible to arrange lasers in each slave station.

Therefore, according to the optical transmission device of the third aspect of the present invention, the light emitting element is a Fabry-Perot laser diode, so that the system cost can be reduced in addition to the effects of the first or second aspect. Even if a large level difference occurs in the light receiving level of the optical signal received by the master station, the same level difference is generated by using at least one of the downstream optical branching devices as the upstream optical branching device. Can compensate.

In the optical transmission apparatus according to claim 4 or 5 of the present invention, in addition to the configuration according to claim 1, 2, or 3, in the upstream optical transmission line, the connection order of each slave station is set to the master station. The emission wavelengths of the light emitting elements of the slave stations are arranged in order from the closest to the center wavelength defining the optical splitting ratio of the upstream optical splitter.

In general, a light emitting element that emits an optical signal having an emission wavelength close to the center wavelength of an optical branching device is standard and its cost is low.

For example, in the case of a system configuration designed to have a maximum of six slave stations with respect to one master station, the number of slave stations actually installed is necessarily six depending on the size of the installation location. It is not necessarily installed only in Therefore, since the possibility of installation is higher for a slave station closer to the master station, a light emitting element that emits an optical signal having an emission wavelength close to the center wavelength of the optical branching device is installed in the slave station closer to the master station. For example, when the number of slave stations is less than 6, the system cost can be reduced.

Therefore, according to the optical transmission apparatus of the fourth or fifth aspect of the present invention, the emission wavelength of the light emitting element of each slave station increases from the one in which the connection order of each slave station is closer to the master station. Since the optical splitters are arranged in the order close to the center wavelength that defines the optical splitting ratio, the system cost can be reduced even when the number of slave stations is smaller than the maximum number of installations.

Hereinafter, an optical transmission system according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of the optical transmission system shown in the present embodiment.

The optical transmission system 1 shown in FIG. 1 has one master station 10, two slave station groups 20A (20B) each having three slave stations 20, and a plurality of downstream optical splitters 21a (2
1b to 21e), connected to the slave station 20 in a multi-drop topology to transmit an optical signal from the master station 10 to the slave station 20, and a slave station group 20A (20)
B), the upstream optical splitters 26a, 26b (26d, 26
e) connecting the master station 10 and the slave stations 20 in each slave station group 20A (20B) in a multi-drop topology via
A plurality of upstream optical transmission lines 40 (40A, 4A) for transmitting optical signals from the slave station 20 in each slave station group 20A (20B) to the master station 10.
0B).

The slave station group 20A (20B) comprises a first slave station group 20A and a second slave station group 20B. The first slave station group 20A includes a first slave station 20a and a third slave station 20A. The second slave station group 20B includes a second slave station 20d, a fourth slave station 20e, and a sixth slave station 20f.

The upstream optical transmission line 40 connects the master station 10 to the first slave station 20a, the third slave station 20b and the fifth slave station 20c of the first slave station group 20A in a multi-drop topology. A second slave station in which a slave station group upstream optical transmission line 40A is connected to the master station 10 and the second slave station 20d, the fourth slave station 20e, and the sixth slave station 20f of the second slave station group 20B in a multi-drop topology. And a station group upstream optical transmission path 40B.

The master station 10 is connected to the downstream optical transmission line 30 via the downstream optical transmission line 30.
A master station E / O12 for converting an electric signal input to the signal input terminal 11 into an optical signal for transmitting the optical signal to the optical signal;
It is connected to the first slave station group upstream optical transmission line 40A,
First slave station group for converting optical signals from the first slave station 20a, third slave station 20b and fifth slave station 20c of the first slave station group 20A into electrical signals via the slave station group upstream optical transmission line 40A. O / E13
A and the second slave station group 2 via the second slave station group upstream optical transmission path 40B.
0B second slave station 20d, fourth slave station 20e, and fifth slave station 2
In order to transmit an optical signal from 0f to the master station 10, a second slave station group O / E13B for converting the optical signal into an electric signal, and the first slave station group O / E13A and the second slave station group O / E13B. E13B
And a synthesizing circuit 15 for synthesizing the electric signal obtained in step (1) and outputting the synthesized electric signal to the signal output terminal 14.

The first slave station 20a of the first slave station group 20A splits an optical signal from the master station 10 obtained through the downstream optical transmission line 30 with an optical splitting ratio of approximately 1/6. A 1-downstream optical splitter 21a, a first O / E 23a that converts an optical signal split by the first downstream optical splitter 21a into an electric signal, and outputs the electric signal to a signal output terminal 22a;
The first E / O 25a having a light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24a and the first slave station group upstream optical transmission line 40A are connected to the first E / O 25a.
A first upstream optical splitter 26a that combines the optical signals of the E / O 25a with an optical splitting ratio of approximately 1/3.

The second slave station 20d of the second slave station group 20B transmits an optical signal obtained through the first down-link optical splitter 21a of the down-link optical transmission line 30 to an optical branching ratio of about 1/5. A second downstream optical branching device 21d that branches off the optical signal and converts the optical signal optically branched by the second downstream optical branching device 21d into an electric signal;
The second O / O which outputs this electric signal to the signal output terminal 22d
E23D, and a second E / O having a light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24d.
25d and a second upstream optical splitter 26d which is connected to the second slave station group upstream optical transmission line 40B and splits the optical signal of the second E / O 25d at an optical splitting ratio of approximately 1/3. Have.

An optical signal obtained through the second downstream optical splitter 21d of the downstream optical transmission line 30 is supplied to the third mobile station 20b of the first mobile station group 20A with an optical branching ratio of approximately 1/4. A third downstream optical branching device 21b that branches off the optical signal and converts the optical signal branched by the third downstream optical branching device 21b into an electric signal;
A third O / O for outputting this electric signal to the signal output terminal 22b
E23B and a third E / O having a light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24b.
25b and a third upstream optical splitter 26b which is connected to the first slave station group upstream optical transmission line 40A and combines the optical signal of the third E / O 25b at an optical splitting ratio of approximately 1/2. Have.

The optical signal obtained via the third downstream optical splitter 21b of the downstream optical transmission line 30 is supplied to the fourth mobile station 20e of the second mobile station group 20B with an optical branching ratio of approximately 1/3. And a fourth O / O for converting the optical signal branched by the fourth downstream optical splitter 21e into an electrical signal and outputting the electrical signal to the signal output terminal 22e. E
23E and a fourth E / O2 having a light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24e.
5e and a fourth upstream optical splitter 26e that is connected to the second slave station upstream optical transmission line 40B and splits the optical signal of the fourth E / O 25e at an optical splitting ratio of approximately 1/2. Have.

An optical signal obtained through the fourth downstream optical splitter 21e of the downstream optical transmission line 30 is supplied to the fifth mobile station 20c of the first mobile station group 20A with an optical splitting ratio of approximately 1/2. A fifth downstream optical branching device 21c that branches off the optical signal and converts the optical signal branched by the fifth downstream optical branching device 21c into an electric signal;
The fifth O / O which outputs this electric signal to the signal output terminal 22c
E23c, and a light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24c. The light emitting element is connected to the first slave station group upstream optical transmission line 40A to emit an optical signal by the light emitting element. 5E / O25c.

The sixth slave station 20f of the second slave station group 20B converts an optical signal obtained through the fifth downstream optical splitter 21c of the downstream optical transmission line 30 into an electrical signal, and converts the optical signal into an electrical signal. A sixth O / E 23f that outputs a signal to the signal output terminal 22f;
A light emitting element that emits an optical signal corresponding to an electric signal obtained from the signal input terminal 24f, and is connected to the second slave station group upstream optical transmission path 40B to emit an optical signal from the light emitting element; / O25f.

Since the master station 10 and each of the slave stations 20a, 20b, and 20c are connected in a multi-drop topology in the first slave station group upstream optical transmission line 40A, the fifth slave station 20c has The optical signal from the 5E / O25c and the third
The third upstream optical splitter 26b combines the optical signal from the third E / O 25b of the slave station 20b with an optical splitting ratio of approximately 1: 1 and the third upstream optical splitter 26b. The optical signal thus obtained and the optical signal from the first E / O 25a of the first slave station 20a are almost 2:
The first upstream optical splitter 26a is combined at an optical splitting ratio of 1.
The optical signal split at the first station O / E1
3A.

Further, the second slave station group upstream optical transmission line 40B
, The master station 10 and each of the slave stations 20d, 20e, 20f
And are connected in a multi-drop topology,
The optical signal from the sixth E / O 25f of the sixth slave station 20f and the optical signal from the fourth E / O 25e of the fourth slave station 20e are converted into a fourth signal.
The upstream optical branching unit 26e combines the optical signals at an optical branching ratio of approximately 1: 1. The optical signal combined by the fourth upstream optical branching unit 26e and the second E / O 25d of the second slave station 20d. And the optical signal from the second upstream optical branching device 26d at an optical branching ratio of approximately 2: 1.
The optical signal combined at d is sent to the second slave station group O / E of the master station 10.
13B.

Further, the first slave station group upstream optical transmission line 40A
A third upstream optical branching device 26b disposed at the last end of the second substation group, a fourth upstream optical branching device 26e disposed at the last end of the second slave station group upstream optical transmission line 40B, and the downstream optical transmission line. The fifth downstream optical branching device 21c disposed at the last end of the optical fiber 30 has the same optical branching ratio, that is, approximately 1: 1, and further has a first upstream optical branching device 26a and a second upstream optical branching device. Since the optical splitter 26d and the fourth downstream optical splitter 21e have the same optical splitting ratio, that is, approximately 2: 1, the same optical splitter has the same optical splitting ratio. Was adopted. This makes it possible to reduce the types of optical splitters and reduce the cost of the optical splitter.

Each of these optical splitters 21a to 21e, 26
a, 26b, 26d, and 26e each have a cross port and a through port. For example, in the case of the first upstream optical splitter 26a, the through port is connected to the third upstream optical splitter 26b.
The cross port corresponds to a port for inputting an optical signal from the first E / O 25a, and as shown in FIGS. 2A and 2B,
The polarities of the wavelength coefficients in the light branching ratio are different.
At the center wavelength that defines the optical branching ratio of the upstream optical branching devices 26a, 26b, 26d, and 26e, the value of the wavelength coefficient at the optical branching ratio of the optical branching device is, as shown in FIGS. Is different.

Further, the first slave station 2 of the first slave station group 20A.
0a, the third slave station 20b, and the fifth slave station 20c each have a light emitting element that emits an optical signal having a different emission wavelength. For example, the first slave station 20a includes a light emitting element LD-B, and the third slave station 20a. The light emitting element LD-C and the fifth slave station 20
c has a light emitting element LD-A.

Each of the slave stations 20a in the first slave station group 20A
The light emitting elements provided at (20b, 20c) emit light signals of emission wavelengths separated at predetermined intervals, for example, 25 nm intervals for each slave station, and three types of slave stations are included in the slave station group 20A. Having a light emitting element of

Further, the second slave station 2 of the second slave station group 20B.
0d, the fourth slave station 20e, and the sixth slave station 20f also have light emitting elements having different emission wavelengths, the second slave station 20d has a light emitting element LD-B, and the fourth slave station 20e has a light emitting element LD-. C
The sixth slave station 20f has a light emitting element LD-A.

That is, the first slave station 20a of the first slave station group 20A and the second slave station 20d of the second slave station group 20B are the same light emitting element LD-B, and the third slave station 20b and the fourth slave station 20b are the same. The slave station 20e is the same light emitting element LD-C, and the fifth slave station 20c and the sixth slave station 20f are the same light emitting element LD-A.

The light emitting elements LD-A, LD-B, LD
For -C, a Fabry-Perot laser diode is used.

In the downstream optical transmission line 30 and the upstream optical transmission line 40, the fourth downstream optical splitter 21e of the fourth slave station 20e and the first upstream of the first slave station 20a of the first slave station group 20A. The optical splitter 26a and the second upstream optical splitter 26d of the second slave station 20d of the second slave station group 20B are the same, and the fifth
The fifth downstream optical splitter 21c of the slave station 20c, the third upstream optical splitter 26b of the third slave station 20b, and the fourth slave station 20
The fourth upstream optical splitter 26e of e is the same.

The wavelength coefficients of the through-port and cross-port optical splitters of the upstream optical splitter 26b are-
0.1 dB / 10 nm and +0.1 dB / 10 nm, and the wavelength coefficients of the through-port and cross-port optical splitters of the upstream optical splitter 26 a are −0.05 dB /
10 nm, +0.15 dB / 10 nm.

Further, the downstream optical splitter 21e is diverted to the upstream optical splitters 26a and 26d, and the upstream optical splitters 26b and 26e are used.
Since the downstream optical splitter 21c is diverted to the sub-station, even if the light-emitting elements of the sub-stations in the respective sub-station groups have the same emission wavelength, the optical signal emitted from the sub-station 20a (20d) is transmitted to the sub-station on the master station 10 side. Based on the level received by the group O / E 13A (13B), the light reception levels of the optical signals emitted from the slave stations 20b (20e) and 20c (20f) are 0.2 dB and 0.4 dB, respectively. And low.

The light emitting element provided in each slave station of each slave station group 20A (20B) depends on the wavelength of the light splitting ratio in the upstream optical splitters 26a, 26b (26d, 26e) of each slave station group 20A (20B). Transmission loss between master and slave stations and between slave stations,
When the light emission wavelength of the light emitting element of each slave station is the same, the master station 10
When the emission wavelengths of the light-emitting elements of each slave station are separated from each other by a predetermined distance in consideration of the difference in the light receiving level on the side, the slave station group O / E13A on the master station 10 side that receives the optical signal of each slave station group.
(13B) is selected so that the difference between the light receiving levels is minimized.

That is, when selecting the light emitting element of the slave station in each slave station group, the polarity of the wavelength coefficient in the optical branching ratio differs between the cross port and the through port of the optical branching device.
The value of the wavelength coefficient of the optical branching ratio varies depending on the optical branching ratio of the optical branching unit, the emission wavelength intervals of the three types of LDs are separated by 25 nm, and the transmission loss between the master station and slave stations and between slave stations. (The level difference between transmission and reception is 0.6 dB), and since the upstream optical branching device is the same as the downstream optical branching device, even if the light emission wavelength of the light emitting element of each slave station is the same, the maximum value is 0 at the master station side. Considering that there is a light receiving level difference of .4 dB, and the like.

As a result, the light emitting elements LD-B, LD-C, LD-A, (LD-B, LD) installed in the slave stations 20a to 20c (20d to 20f) in the slave station group 20A (20B).
-C, LD-A) are arranged such that LD-A, LD-B, LD-C are arranged in ascending order of the emission wavelength of the light-emitting element.
The emission wavelength of DB was 1.31 μm.

Next, the operation of the optical transmission system 1 according to the present embodiment will be described.

The fifth slave station 20c of the first slave station group 20A converts the optical signal corresponding to the electric signal obtained from the signal input terminal 24c from the fifth E / O 25c to the third upstream optical branch of the third slave station 20b. To the device 26b. The third upstream optical splitter 26b includes:
The optical signal of the fifth slave station 20c and the optical signal from the third E / O 24b are combined at an optical branching ratio of approximately 1: 1 and the combined optical signal is transmitted to the first upstream optical splitter 26a. .

The first upstream optical splitter 26a is connected to the optical signal combined by the third upstream optical splitter 26b and the first E / O2
5a is combined with the optical branching ratio of about 2: 1 and the combined optical signal is transmitted via the first slave station group upstream optical transmission line 40A to the first slave station group O of the master station 10. / E13A. The first slave station group O / E 13A converts an optical signal into an electric signal and transmits the electric signal to the combining circuit 15.

The sixth slave station 20f of the second slave station group 20B
Transmits the optical signal corresponding to the electric signal obtained from the signal input terminal 24f from the sixth E / O 25f to the fourth upstream optical splitter 26e of the fourth slave station 20e. Fourth upstream optical splitter 2
6e is the optical signal of the sixth slave station 20f and the fourth E / O 25e
Are combined with an optical signal having an optical branching ratio of approximately 1: 1 and the combined optical signal is transmitted to the second upstream optical branching device 26d.

The second upstream optical splitter 26d is connected to the optical signal combined by the fourth upstream optical splitter 26e and the second E / O2
5d is combined with the optical branching ratio of approximately 2: 1 and the combined optical signal is transmitted to the second slave station group of the master station 10 via the second slave station group upstream optical transmission line 40B. Transmit to O / E13B. The second slave station group O / E 13B converts an optical signal into an electric signal and transmits the electric signal to the synthesizing circuit 15.

The synthesizing circuit 15 is provided with the first slave station group O /
The electric signals from E13A and the second slave station group O / E13B are combined and output to the signal output terminal 14.

According to the present embodiment, the first slave station group 20A
And the upstream optical splitters 26a and 26b in the second slave station group 20B
(26d, 26e) and the downstream optical splitters 21e, 21c employ optical splitters having the same optical splitting ratio, and each of the slave stations in each slave station group 20A (20B) transmits its upstream optical signal. LD-B, LD-
C and LD-A are arranged in this order, so that the level difference of the light receiving level of the master station 10 that receives the optical signal combined by each optical branching device in each slave station group 20A (20B) is minimized. Can be limited.

According to the present embodiment, the upstream optical splitters 26a, 26a in the first slave station group 20A and the second slave station group 20B.
26b (26d, 26e) and downstream optical splitters 21e, 21
Since an optical splitter having the same optical splitting ratio as that of the optical splitter c is employed, the types of optical components can be reduced and the system cost can be reduced.

According to the present embodiment, the slave station 20a
Since an inexpensive Fabry-Perot laser diode is used for the light emitting element of ~ 20f, the system cost can be kept low, and each child in the master station which occurs when a downstream optical splitter is diverted to an upstream optical splitter. The station output level difference can be compensated.

Further, according to the present embodiment, in the upstream optical transmission line, the order of connection of the slave stations is closer to the master station, and the emission wavelength of the light emitting element of each slave station is equal to the upstream optical splitter. Since they are arranged in the order close to the center wavelength that defines the optical branching ratio of
Even when the installation location is small and the number of slave stations installed is small, the system cost can be reduced.

[0077]

According to the optical transmission apparatus of the present invention configured as described above, the light emitting elements in which the slave stations in each slave station group emit light signals of different emission wavelengths separated by a predetermined distance from each other. In consideration of the transmission loss of the upstream optical transmission line and the wavelength characteristics of the optical branching ratio of the upstream optical splitter, the light emitting elements are arranged in the respective slave stations, so that the light emitting elements are all at the same level. Is output, it is possible to minimize the difference in the light reception level of the optical signal from each slave station in the master station after being combined by the upstream optical splitter.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration inside an optical transmission system showing an embodiment of an optical transmission device of the present invention.

FIG. 2 is an explanatory diagram showing that the polarity of the wavelength coefficient of the optical branching ratio differs between the cross port and the through port of the optical branching device in the present embodiment.

FIG. 3 is an explanatory diagram showing that the optical branching device according to the present embodiment has different wavelength coefficient values depending on the optical branching ratio at the center wavelength. a) The central wavelength is 1.55 μm. The optical branching ratio is 8: 2. b) The central wavelength is 1.3 μm. The optical branching ratio is 9: 1.

[Explanation of symbols]

 Reference Signs List 1 optical transmission system (optical transmission device) 10 master station 20 slave station 20A first slave station group (slave station group) 20B second slave station group (slave station group) 21a first downstream optical splitter (downlink optical splitter) 21b 3rd downstream optical splitter (downstream optical splitter) 21c 5th downstream optical splitter (downstream optical splitter) 21d 2nd downstream optical splitter (downstream optical splitter) 21e 4th downstream optical splitter Unit (downstream optical splitter) 26a first upstream optical splitter (upstream optical splitter) 26b third upstream optical splitter (upstream optical splitter) 26d second upstream optical splitter (upstream optical splitter) 26e Fourth upstream optical branching device (upstream optical branching device) 30 downstream optical transmission line 40 upstream optical transmission line 40A first slave station group upstream optical transmission line (upstream optical transmission line) 40B second slave station group upstream optical transmission line ( Upstream optical transmission line)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/12 10/02 (72) Inventor Susumu Tsubosaka 3-1, Tsunashimahigashi 4-chome, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Matsushita Communication Industrial Inside (72) Inventor Manabu Tanabe 4-3-1 Tsunashima Higashi, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Inside Matsushita Communication Industrial Co., Ltd. (72) Inventor Hiroshi Fukuya 2-1-1 Toranomon, Minato-ku, Tokyo (72) Inventor Yoshio Ebine 2-10-1 Toranomon, Minato-ku, Tokyo Inside NTT Mobile Communication Network Co., Ltd.

Claims (5)

[Claims] 1. A master station, a group of at least one slave station having a plurality of slave stations, and a plurality of downstream optical splitters connected to the slave stations in a multi-drop topology, and each of the slave stations is connected to the slave station from the master station. A downstream optical transmission line for transmitting an optical signal to a station, and for each slave station group, connected to each slave station in each slave station group in a multi-drop topology via an upstream optical splitter, and from each slave station, An optical transmission device comprising an upstream optical transmission line for transmitting an optical signal to a master station, wherein each of the slave stations in each of the slave station groups emits an optical signal having a different emission wavelength at a predetermined interval from each other. A light-emitting element, and when each light-emitting element outputs an optical signal of the same level, the difference in the light-receiving level of the optical signal from each of the slave stations in the master station after being combined by the upstream optical splitter is minimized. Thus, the wavelength characteristics of the transmission loss of the upstream optical transmission line and the optical branching ratio of the upstream optical splitter In view, an optical transmission apparatus characterized by disposing the light emitting elements respectively to each child station. 2. The optical transmission device according to claim 1, wherein the upstream optical splitter is the same as at least one of the downstream optical splitters. 3. The optical transmission device according to claim 1, wherein the light emitting element is a Fabry-Perot laser diode. 4. In the upstream optical transmission line, the emission wavelength of the light emitting element of each slave station is determined by the center wavelength that defines the optical branching ratio of the upstream optical splitter, from the connection order of the slave stations closer to the master station. The optical transmission device according to claim 1, wherein the optical transmission devices are arranged in an order close to the distance. 5. In the upstream optical transmission line, the emission wavelength of the light emitting element of each slave station is determined by the center wavelength that defines the optical branching ratio of the upstream optical splitter, in the order of connection of the slave stations from the one closer to the master station. 4. The optical transmission device according to claim 3, wherein the optical transmission devices are arranged in an order close to.