JP3535937B2 - Optical transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical CATV, an optical I.
The present invention relates to an optical transmission system such as a TV, an optical transmission monitoring system, and a subscriber optical communication system, and more particularly to an optical transmission system having a function of transmitting transmission signals from a plurality of points to a master station.

[0002]

2. Description of the Related Art An optical transmission system shown in FIG. 13 is one of those used in the field of optical transmission systems such as an optical CATV, an optical ITV, an optical transmission monitoring system and a subscriber optical communication system. The optical transmission system of FIG. 13 is a system for transmitting the images of the slave stations 1301 to 130n at a plurality of different points to the master station 132, and 133 is a slave station 1301 at each point.
, 130n are television cameras, and 134 is a modulator for modulating an electric signal from the television camera 133. Examples of the modulator 134 include an FM modulator and an AM.
A modulator is used. The electric signal modulated by the modulator 134 is subjected to optical intensity modulation by the electrical-to-optical converter 135 such as a DFB laser, and the transmission signal light subjected to the optical intensity modulation is combined by the optical coupler 136 to the optical fiber trunk line 137. And is led to the master station 132.

The master station 132 has slave stations 1301 ...
The transmission signal light from 130n is transmitted via the optical fiber trunk line 137. The master station 132 is the slave station 13 at each point it has reached.
The transmission signal light from 01 to 130n is collectively converted into an electric signal by a light-to-electrical converter 138 such as a semiconductor photodetector, and this electric signal is demodulated by a demodulator 139 for each carrier frequency assigned to each modulator 134. Demodulate to TV monitor 200
The images of the slave stations 1301 to 130n at the respective points are displayed by.

By the way, as described above, a plurality of slave stations 130 are provided.
It is known that when the transmission signal lights from 1 to 130n are collectively received by the optical-to-electrical converter 138, beat noise is generated at a frequency position corresponding to the wavelength difference of the light of each slave station 1301 to 130n. . Therefore, in order to prevent the influence of this beat noise from affecting the transmission signal light located at the carrier frequency, the optical wavelengths of the semiconductor lasers or the like, which are the electrical-to-optical converters 135 in the slave stations 1301 to 130n, are set to different values. Set to. Usually, this wavelength difference is set to a value of 0.1 nm or more. Further, when the optical amplifier 141 is provided on the optical fiber trunk line 137 as shown in FIG. 14, the optical transmission loss can be compensated by the optical amplifier 141, so that a plurality of transmission signal light from the slave stations 1301 to 130n at each point can be compensated. Can be transmitted over a longer distance. Since other configurations are similar to those in FIG. 13, the same components are designated by the same reference numerals, and detailed description thereof will be omitted.

Further, the one shown in FIG. 15 is an example of a so-called wavelength division multiplexing optical transmission system in which signal light is distinguished by positively utilizing the difference in wavelength. Here, the same symbols as those in FIG. 13 indicate the same components as those in FIG.
Transmission signals such as video signals and data signals emitted from the slave stations 1301 to 130n at the respective points are converted into transmission signal lights having different wavelengths by the same means as in FIG.
The optical fiber trunk line 137 is multiplexed by 6 and the master station 132A
Be led to. In the master station 132A, the multiplexed transmission signal light is separated for each wavelength by the wavelength division multiplexer 151 composed of an optical filter or the like, and each transmission signal light is converted into an optical → electrical converter 138 such as a semiconductor light receiving device, The demodulator 139 is used to extract the transmission signal.

The optical transmission system shown in FIG. 15 is similar to that shown in FIG.
Unlike the optical transmission system of FIG. 3 and FIG. 14, it is not necessary to distinguish the signals by using the carrier frequency and the like, and various kinds of signals such as a digital baseband signal can be selected as the signals to be transmitted. That is, in addition to the signal identifying means based on the frequency of the electric signal, the wavelength of light can be used for the signal identifying means, and a larger number of signals can be transmitted at the same time as compared with the conventional case.

Furthermore, the optical transmission system shown in FIG. 16 is also capable of transmitting signals of slave stations at multiple points using one optical fiber trunk line. The optical transmission system shown in FIG. 16 transmits signals from multiple points to repeater type slave stations 1601 to 16
By 0n, the transmission signal light of the own station is multiplexed to the optical fiber trunk line 137 and the transmission signal light of the optical fiber trunk line 137 is simultaneously transmitted and transmitted to the master station 132. Relay type slave station 16
01 to 160n are optical-to-electrical converters 163, such as a semiconductor photodetector that extracts the transmission signal light from the upstream in the form of electric signals.
Modulator 164 that modulates the signal of its own station, optical-to-electrical converter 1
63 and an electric signal composed of a signal multiplexer 165 for multiplexing an electric signal of a modulator 164 for modulating the signal of its own station and a semiconductor laser for converting the combined signal into an optical signal and transmitting it to the optical fiber trunk line 137. An optical converter 166 is provided. Figure 1
6, the same reference numerals as those in FIG. 13 denote the same components as those in FIG.

[0008]

The above-described optical transmission system of FIGS. 13 to 15 can transmit signals of slave stations at multiple points by using one optical fiber trunk line, and is used as an infrastructure. Although the optical fiber network can be effectively used, the conventional optical transmission system described above has the following problems. The optical transmission systems of FIGS. 13 to 16 are systems that require a plurality of wavelengths, and require electrical-to-optical converters (semiconductor laser light sources) having different wavelengths for the number of slave stations. Particularly, when the number of slave stations is increased, it is difficult to secure light sources of different wavelengths, and it is complicated to adjust and manage the light source wavelength of each slave station.

Further, by using the optical amplifier 141 as in the optical transmission system shown in FIG. 14, long distance transmission becomes possible. On the other hand, when an erbium-doped optical fiber amplifier is used for the optical amplifier 141, the optical amplification factor thereof has wavelength dependence, so that the number of wavelengths increases and the wavelength band of light passing through the optical amplifier 141 is increased. When spread, there is a problem that a level difference occurs in the transmission signal light, which hinders good optical transmission. Furthermore, FIG.
In the above optical transmission system, it is necessary to design and manufacture the wavelength of the wavelength division demultiplexer 151 in accordance with the wavelength of the light source, and it is difficult to design and manufacture the same when the number of slave stations increases as described above. was there. In the optical transmission system of FIG. 15, if the light source of the slave station 1301 fails, for example, it is necessary to replace it with a light source having a wavelength substantially equal to that of the failed light source. Alternatively, it is necessary to remanufacture the wavelength division multiplexer / demultiplexer 151 in accordance with the wavelength of the light source of the exchanged slave station 1301, and these operations may involve stopping the system, which requires a great deal of labor.

As described above, the optical transmission system shown in FIGS. 13 to 15 has a problem mainly due to the need for a multi-wavelength light source. On the other hand, in the optical transmission system of FIG. 16, these problems are solved. That is, in the optical transmission system of FIG. 16, since the transmission is performed while repeating the relay, the light of only one wavelength is always transmitted to the optical fiber trunk line 137, so that the light source of a plurality of wavelengths is unnecessary. Further, by repeating the relay, it is possible to perform transmission while electrically amplifying the optical loss, and it is possible to perform transmission over a relatively long distance.

However, the optical transmission system of FIG. 16 has the following problems. First, each relay slave station 160
Since the relay is repeated at 1 to 160n, if any one slave station has a trouble, all the signals transmitted from the upstream side cannot reach the master station 132, so that the reliability of the system is as described above. It is far inferior to the system.

Second, all the signals from the upstream are collected in the relay type slave station 1601 at the final stage, which is the closest to the master station 132, and this is an electric-to-optical converter 166 composed of a semiconductor laser.
Is converted into an optical signal by, for example, each relay type slave station 1
A so-called subcarrier multiplex transmission system (SCM system) in which a different carrier frequency is allocated to each of 601 to 160n
In the case of adopting, the optical modulation degree for each carrier frequency is limited. In addition, since the load on the light source increases, modulation distortion becomes a problem, and there is a problem that the transmission distance is limited.

Thirdly, there is a problem that the C / N ratio (signal-to-noise ratio) is deteriorated because the noise of the repeater is added to the signal by repeating the repeating. As described above, the optical transmission system of FIGS. 13 to 15 has a problem associated with the increase in the wavelength of the light source, and the optical transmission system of FIG. 16 has a problem associated with the relay. In particular, when trying to transmit information of a large number of points over a long distance by using as few optical transmission lines as possible, a new system design idea has been demanded.

The present invention solves the above problems, minimizes the number of wavelengths of light sources to be used, improves the reliability of the system which was a problem in the relay system, and minimizes the use of infrastructure. It is an object of the present invention to provide an optical transmission system capable of transmitting signals from multiple points with good quality over a long distance through an optical transmission line.

[0015]

The present invention has the following means in order to solve the above problems.

The optical transmission system according to claim 1 of the present invention is an optical transmission system for transmitting transmission signals from slave stations at a plurality of points to a master station by using optical fiber trunks, wherein one or more optical fiber trunks are provided. Has a repeater, and the repeater collects transmission signals from a plurality of slave stations collected in the repeater,
The wavelength of the transmission signal light transmitted from the upstream side of the repeater on the optical fiber trunk line is converted into light having a wavelength unique to the repeater, which is multiplexed into the optical fiber trunk line and transmitted downstream. Characterize.

In the optical transmission system according to claim 2 of the present invention, the transmission signal light from the plurality of slave stations which is collected in the repeater is transmitted through the optical fiber trunk line and collected in the repeater, and these transmission signals are collected. The light wavelength of the light is different from the wavelength of the transmission signal light transmitted from the upstream side of the optical fiber trunk line.

In the optical transmission system according to claim 3 of the present invention, the transmission signal light from a plurality of slave stations transmitted through the optical fiber trunk line and collected in the repeater, and the other transmissions transmitted through the optical fiber trunk line. The signal light is an optical signal having a different wavelength band.

In the optical transmission system according to claim 4 of the present invention, the transmission signal light from a plurality of slave stations transmitted through the optical fiber trunk line and collected in the repeater is an optical signal in the 1.3 μm band, and other than that. Is characterized in that it is a 1.55 μm band optical signal.

In the optical transmission system according to claim 5 of the present invention, the repeater reflects a specific wavelength of the transmission signal light transmitted on the optical fiber trunk line from the upstream of the repeater,
This is characterized in that an optical fiber grating for transmitting transmission signal light from the plurality of slave stations having different wavelengths is used as a wavelength division multiplexer.

According to the optical transmission system of claim 1 of the present invention, the wavelength of light required for the optical fiber trunk line is reduced to the same number as the number of repeaters, and the load on the system design and securing of the light source is reduced. Is reduced, and system construction and system management become easier. In addition, it is not necessary to repeat electrical relay for all transmitted signals, and it is possible to avoid concentrating many signals on one light source. Problems such as limitation and increase of noise are alleviated, and at the same time, the system can be constructed without sacrificing the reliability of the system so much.

According to the optical transmission system of the second aspect of the present invention, effective utilization of the optical fiber trunk line can be further promoted.

According to the optical transmission system of the third aspect of the present invention, it becomes easy to design the wavelength of the light source and secure the light source.

According to the optical transmission system of claim 4 of the present invention, it becomes possible to perform long-distance transmission along the optical fiber trunk line at a wavelength in the 1.55 μm band where the loss of the optical fiber is smaller. In addition to facilitating the application of erbium-doped optical amplifiers, it also enables clear wavelength separation from optical signals used for short-distance transmission to repeaters, making system design and securing light sources easy. Becomes

According to the optical transmission system of claim 5 of the present invention, the wavelength division demultiplexer used for the repeater has a simpler structure as compared with the conventional one, thereby facilitating the design and manufacture. it can.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to embodiments. (Embodiment 1) FIGS. 1 to 6 show an embodiment of the present invention. An optical transmission system according to the present embodiment will be described with reference to FIGS. 1 to 6. Note that FIG.
Throughout FIG. 6, the same components are designated by the same reference numerals. The optical transmission system shown in FIG. 1 is a system for transmitting images of slave stations 10i (i = 1 to m + n ...) at a plurality of different points to a master station 20, and 2 denotes slave stations 101 to 10m at each point.
TV cameras installed at + n-, 3 is a TV camera 2
The modulator 3 is a modulator for modulating the electric signal from, and as the modulator 3, for example, an FM modulator or an AM modulator is used. The electric signal modulated by the modulator 3 is subjected to optical intensity modulation by an electrical-to-optical converter 4 such as a DFB laser, and the transmission signal light subjected to this optical intensity modulation is combined by the optical coupler 5 to the optical fiber trunk line 6. And is led to the master station 20.

The parent station 20 has a child station 10i (i =
The transmission signal light from 1-m + n-) is transmitted through the optical fiber trunk line 6. The master station 20 is the slave station 10 at each arrived point
The transmission signal light from i (i = 1 to m + n) is separated for each wavelength by the wavelength division multiplexer 21 composed of an optical filter or the like,
A transmission signal is extracted from each transmission signal light by using an optical-electrical converter 22 and a demodulator 23 such as a semiconductor light receiver.

A feature of the present invention is that the repeaters 30-1 to 30-N are provided for each of a predetermined number of slave stations between the slave stations 10i (i = 1 to m + n) at the respective points multiplexed on the optical fiber trunk line 6. Is located. As shown in FIG. 2, the repeater 30-N includes a wavelength division multiplexer 31, an optical-to-electrical converter 32, an electric amplifier 33, an electric-to-optical converter 34, and a wavelength multiplex wave multiplexer 3.
It is equipped with 5.

The operation of the repeater 30-N will be described below. For example, to the repeater 30-2, the transmission signal light H3 in which the transmission signal is multiplexed with the light of wavelength λ3 output from the repeater 30-3 is input. On the other hand, in the repeater 30-2,
In addition, the slave stations 10m to 10m + upstream of the repeater 30-2
Each of the transmission signal lights from n to is the transmission signal light H3.
Is input through the same optical fiber trunk line 6. Here, the wavelength of the transmission signal light from the slave stations 10m to 10m + n is the wavelength λ of the transmission signal light H3 from the repeater 30-3.
3 is different from that of the repeater 30-, as shown in FIG.
The transmission signal light H3 and the transmission signal light from the slave stations 10m to 10m + n are separated by the wavelength division multiplexing / demultiplexing device 31 provided in No. 2. The transmission signal light from each of the separated slave stations 10m to 10m + n is converted into an electric signal by a light-to-electrical converter 32 composed of a semiconductor light receiving element or the like, amplified by an electric amplifier 33, and then a semiconductor laser. The transmission signal light H2 having a wavelength .lambda.2 different from that of the transmission signal light H3 is multiplexed by the electrical-to-optical converter 34 composed of the above.

A plurality of slave stations 10m to 10m performed here
The multiplexing of the transmission signal light from + n to is easily realized by the conventionally used subcarrier multiplexing system. When the transmission signal light is a digital signal, a time division multiplexing system may be used. The transmission signal light H2 and the transmission signal light H3 are wavelength-multiplexed by the wavelength multiplex multiplexer 35 provided in the repeater 30-2, and are guided to the optical fiber trunk line 6. Further, as a repeater 30A shown in FIG. 3 as the structure of the repeater, the multiplexed transmission signal light after the multiplexing after the wavelength multiplex wave multiplexer 35 is amplified by an optical amplifier 36 made of an erbium-doped fiber or the like, It is also possible to compensate for the transmission loss expected in the downstream optical fiber trunk line 6.

As another configuration of the repeater, as in the repeater 30B shown in FIG. 4, only the transmission signal light H3 demultiplexed by the wavelength division multiplexer 31 may be amplified by the optical amplifier 37. Further, as another configuration of the repeater, the repeater 3 shown in FIG.
0C, the transmission signal light demultiplexed by the wavelength division multiplexer 31 is amplified by the optical → electrical converter 38, the electric amplifier 37 and the electric → optical converter 39, and the transmission signal light H3 is provided upstream thereof. It is also possible to compensate for the optical loss incurred.

Next, for example, the repeater 30-1 will be described. The transmission signal light H from the upstream to the repeater 30-1.
3 and transmission signal light H2 and plural slave stations 102 to 10m-
Each transmitted signal light from 1 arrives, and the repeater 3
Similar to 0-2, the transmission signal light is separated and multiplexed. The wavelength division demultiplexer 31 has a function of demultiplexing into the transmission signal light H3, the transmission signal light H2, and the transmission signal light H1 from the plurality of slave stations 102 to 10m-1, and
The wavelength multi-multiplexer 35 includes a transmission signal light H1 and a transmission signal light H2 in which signals from a plurality of slave stations 102 to 10m-1 are multiplexed.
It may be designed to have a function of multiplexing the transmission signal light H3 with.

The wavelength division multiplexer / demultiplexer 3 of the repeater 30-N
1 can be easily constructed by a conventional technique such as an optical filter or a wavelength division multiplexer, but can be further easily constructed by using an optical fiber grating 41 as shown in FIG. The wavelength division multiplexer 3 shown in FIG.
1 is adopted in the repeater 30-2, for example, the transmission signal light H3 of the wavelength λ3 from the repeater 30-3 is reflected by the optical fiber grating 41, demultiplexed by the optical coupler 42 and ported. It is output to P1. Plural slave stations having different wavelengths from the transmission signal light H3 10 m to 10 m +
The transmission signal light from n is the optical fiber grating 41.
And is output to the port P2.

In FIG. 6, reference numeral 43 is an optical isolator. Further, the case where the wavelength division multiplexer / demultiplexer 31 of FIG. 6B is adopted for the repeater 30-1, for example, will be described. The transmission signal light H3 of the wavelength λ3 from the repeater 30-3 is explained.
Is reflected by the optical fiber grating 41A, demultiplexed by the optical coupler 42, and output to the port P1. The transmission signal light H2 having the wavelength λ2 from the repeater 30-2 is reflected by the optical fiber grating 41B, and the optical coupler 4 similarly.
It is demultiplexed by 2 and output to the port P1.

The transmission signal light H1 from a plurality of slave stations 102 to 10m-1 having different wavelengths from the transmission signal light H3 and the transmission signal light H2 passes through the optical fiber grating 41A and the optical fiber grating 41B and is output to the port P2. It The optical fiber grating 41 is
By irradiating the optical fiber with ultraviolet light from an excimer laser, etc., it can be produced by forming a periodic refractive index distribution along the longitudinal direction in the core of the optical fiber, and compared with conventional optical filters and wavelength multiplexing couplers. There is a merit that it can be manufactured at low cost by simple and simple process. The optical transmission system of the present embodiment has the following merits as compared with the conventional optical transmission system.

For example, in the optical transmission system of FIG. 13 to FIG. 15, it is necessary to have the same number of light sources of electric-to-optical converters having different wavelengths as the number of slave stations. However, in the optical transmission system of the present embodiment, a repeater is used. The number of light sources can be greatly reduced because the system is composed only of the light sources of the same number as the different wavelengths and the light sources used for the transmission signal light from the plurality of slave stations that are collected in each repeater. Further, the transmission signal light of the slave station accommodated in each repeater does not cause any problem even if the wavelengths overlapping between the repeaters are used. Therefore, the number of light sources does not increase significantly.

Specifically, for example, in the conventional optical transmission system having 50 slave stations, it was necessary to prepare light sources of 50 different wavelengths, but in the optical transmission system of the present embodiment, there are 10 repeaters. If the slave stations are installed in each relay station and each relay station accommodates five slave stations, light sources with different 10 wavelengths corresponding to the relay stations and light sources with different 5 wavelengths accommodated by each relay station may be prepared. For example, the repeater 30-1 of the optical transmission system according to the above-described embodiment collects the five wavelengths of the slave station and the repeater 3
Since there is no problem even if the 5 wavelengths of the slave stations 0-2 are overlapped, no problem occurs. Therefore, if a light source of at least 15 different wavelengths is prepared, the system can be constructed.

Therefore, it is easy to secure the light source, and when the repeater 30A of FIG. 3 or the repeater 30B of FIG. 4 is used as the repeater of the optical transmission system of the above embodiment, for example, The optical wavelength band that passes through the optical amplifier 36 or 37 can be narrowed, and problems such as a level difference related to the wavelength dependence of the amplification factor can be greatly reduced. Further, in the optical transmission system of the above-described embodiment, the transmission signal light transmitted from the repeater 30-N and transmitted through the optical fiber trunk line 6 and the transmission signal light transmitted from the plurality of slave stations have different wavelength bands. By using the transmission signal light, the design and manufacture of the wavelength division multiplexer / demultiplexer 31 used in the repeater 30-N can be further simplified. That is, the wavelength division multiplexer / demultiplexer 31 does not need to be designed to demultiplex light having a small wavelength difference, and it is sufficient if only the lights having different wavelength bands can be distinguished and demultiplexed.

Furthermore, the transmission signal light transmitted from the optical repeater 30-N and transmitted through the optical fiber trunk line 6 is changed to light in the 1.55 μm band, and the transmission signal light transmitted from a plurality of slave stations is set to 1.
The same effect can be obtained by using light in the 3 μm band. At the same time, the transmission signal light transmitted from the repeater 30-N over a long distance can be set to a wavelength in the 1.55 μm band in which the transmission loss of the optical fiber is smaller, and an erbium-doped fiber amplifier is used. And can be easily amplified. Next, for example, when the optical transmission system of FIG. 16 and the optical transmission system of the present embodiment are compared, the following advantages occur.

For example, in the case of transmitting signals from 50 different slave stations, in the conventional optical transmission system of FIG. 16, the relay type slave station 1601 closest to the master station 132 transmits the 50 transmitted signal lights as one signal. It is necessary to multiplex the electricity into the optical converter (light source) 166. Here, for example, if the subcarrier multiplexing method is adopted, the optical modulation degree assigned to each subcarrier wave is 5.7%. This means that when a semiconductor laser or the like is used as an electrical-to-optical converter, the effective modulation degree given by m√N (m is the optical modulation degree per wave, N is the number of multiplexed signal waves) is 40% or less. Therefore, it is necessary to suppress the signal distortion generated in the semiconductor laser or the like.

On the other hand, in the optical transmission system of this embodiment, 5
When transmitting signals from 0 different slave stations, the repeater 30
If -N is set at 10 locations and each relay 30-N accommodates five slave stations, subcarrier multiplexing is performed at each slave station.
It is sufficient to consider multiplexing of waves, and at this time, the optical modulation degree per wave can be set to about 18%. In general, the signal-to-noise ratio (CNR) in the receiver is proportional to the square of the optical modulation index m when the received light level is the same, and therefore it is 5.7% per wave of the conventional optical transmission system of FIG. In the optical transmission system of the present invention, the optical modulation degree is 18% per wave, and the CNR is about 10 times, that is, about 10 dB larger than the optical modulation degree. Therefore, good signal transmission with a small amount of noise is realized.

The signal multiplexing need not be limited to the subcarrier multiplexing system of this embodiment. For example, when the transmission signal light of the slave station is time division multiplexed, the time slot given to one slave station is used. Becomes inversely proportional to the number of multiples,
In this case as well, the effectiveness of the optical transmission system of the present invention is exhibited similarly.

Furthermore, in the conventional optical transmission system of FIG. 16, for example, the relay type slave station 160 closest to the master station 132 is provided.
If 1 stops due to an electrical trouble, transmission of all signals transmitted from upstream becomes impossible. On the other hand, in the optical transmission system of the present invention, for example, when the repeater 30-1 closest to the master station 20 is stopped due to an electrical trouble, the repeater 30-1 shows the repeater shown in FIG. Three
If it is 0-N, the relay device 30-N will be used when an electrical trouble occurs.
Although it becomes impossible to transmit signals from a plurality of slave stations accommodated in the optical fiber, the transmission signal light transmitted from the upstream of the optical fiber trunk line 6 from the upstream side of the slave stations is a wavelength division multiplexer 31 and a wavelength multiplexor which are passive components. It only passes through the wave device 35 and is transmitted without being affected by electrical trouble. That is, according to the optical transmission system of the present invention, the spread of trouble is limited to a smaller area, which is also advantageous in terms of system reliability.

Furthermore, when the repeater of FIGS. 2 to 4 is used as the configuration of the repeater of the optical transmission system of the present invention, optical-to-electrical conversion and electrical conversion are performed as in the conventional optical transmission system of FIG. Since it is not necessary to repeat amplification and electrical-to-optical conversion, it is possible to avoid accumulation of electrical noise in these steps, and also in this respect, signal transmission with good quality can be realized.

(Other Embodiments) FIG. 7 shows another embodiment of the optical transmission system of the present invention. The feature of the optical transmission system of the present embodiment is that the repeaters 70-1 to 70-7
0-N. In the first embodiment, signals from a plurality of slave stations 101 to 10m + n contained in the repeater 30-N are
Although supplied in the form of optical signals, in the optical transmission system shown in FIG. 7, the repeaters 70-1 to 70-N have a plurality of slave stations 7.
The signals from 01 to 70n + m are received in the form of electric signals. For example, the repeater 70-N collectively combines the electric signals from the slave stations 701 to 703 by the signal combiner 71 and amplifies by the amplifier 72 as shown in FIG. The amplified electric signal is subjected to light intensity modulation by an electricity → optical converter 73 such as a DFB laser, and the transmission signal light subjected to this light intensity modulation is wavelength-multiplexed by the wavelength multiplex wave multiplexer 35, and the optical fiber trunk line 6 And is guided to the master station 20.

In the optical transmission system of FIGS. 7 and 8, the same components as those of the optical transmission system of FIGS. 1 to 5 are designated by the same reference numerals and detailed description thereof will be omitted. Similar to the first embodiment, even when signals from a plurality of slave stations 701 to 70n + m are received by the repeater 70-N in the form of an electric signal and multiplexed into the optical fiber trunk line 6 as in the present embodiment. The effect is obtained. Further, in the first embodiment, a plurality of slave stations 10m
Signals from 10m + n to 10m + n are transmitted to the repeater 30-N using the optical fiber trunk line 6 to enable more effective use of the infrastructure. However, depending on the installation conditions of the system, the optical transmission system shown in FIG. So that, for example, a plurality of slave stations 1
The signal from 0 m to 10 m + n is transmitted to the repeater 90 using another optical fiber transmission line 91 different from the optical fiber trunk line 6.
May be transmitted to.

In this case, the repeater shown in FIGS. 10 to 12 in which the wavelength multiplex wave multiplexer 31 in the repeaters 30-N, 30A and 30B shown in FIGS. 2 to 4 used in the first embodiment is omitted. By using the repeaters such as the devices 90, 90A, and 90B, the same effect as that of the first embodiment can be obtained. In addition, in the optical transmission system of FIG. 9 to FIG.
The same components as those of the optical transmission system of FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted.

In the above-described embodiment of the optical transmission system of the present invention, the electrical-to-optical conversion is described mainly with respect to the direct intensity modulation method using a semiconductor laser or the like, but lithium niobate is used. Other modulators such as the Mach-Zehnder type external modulator and the electro-absorption type semiconductor external modulator may be used, and the effect of the optical transmission system of the present invention is not impaired at all.

Further, in the above-described embodiment of the optical transmission system of the present invention, the transmission signal light transmitted through the optical fiber trunk line and reaching the master station is wavelength-separated by the wavelength division multiplexer in the master station. Although the optical receiver converts light to electricity later, wavelength separation by this wavelength division multiplexer is not always necessary.As with the conventional example, the light is collectively collected by one receiver without wavelength separation. → Even if the signal is separated at the electric signal level after the electric conversion, the basic effect of the present invention is not hindered, and rather, the wavelength division multiplexer can be omitted, and the system configuration is further simplified. .

[0050]

As described above, according to the optical transmission system of claims 1 to 5 of the present invention, the number of wavelengths of the light source to be used is minimized and the conventional relay system has a problem. The reliability can be improved. In addition, it is possible to transmit signals from multiple points over a long distance with good quality by using the minimum number of optical transmission lines to effectively use the infrastructure, and to achieve a large transmission capacity optical fiber communication network with a simpler design. Easy to implement.

According to the optical transmission system of claim 1 of the present invention, the wavelength of the light required for the optical fiber trunk line is reduced to the same number as the number of repeaters, and the load for securing the system design and the light source is reduced. Is reduced, and system construction and system management become easier. In addition, it is not necessary to repeat electrical relay for all transmitted signals, and it is possible to avoid concentrating many signals on one light source. Problems such as limitation and increase of noise are alleviated, and at the same time, the system can be constructed without sacrificing the reliability of the system so much.

According to the optical transmission system of the second aspect of the present invention, the effective utilization of the optical fiber trunk line can be further promoted.

According to the optical transmission system of claim 3 of the present invention, it becomes easy to design the wavelength of the light source and secure the light source.

According to the optical transmission system of claim 4 of the present invention, it becomes possible to perform long-distance transmission along the optical fiber trunk line at a wavelength in the 1.55 μm band in which the loss of the optical fiber is smaller. In addition to facilitating the application of erbium-doped optical amplifiers, it also enables clear wavelength separation from optical signals used for short-distance transmission to repeaters, making system design and securing light sources easy. Becomes

According to the optical transmission system of claim 5 of the present invention, the wavelength division demultiplexer used for the repeater has a simpler structure than the conventional one, thereby facilitating the design and manufacture. it can.

[Brief description of drawings]

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

2 is a block diagram showing an embodiment of a repeater used in the optical transmission system of FIG.

3 is a block diagram showing another embodiment of a repeater used in the optical transmission system of FIG.

FIG. 4 is a block diagram showing another embodiment of a repeater used in the optical transmission system of FIG.

5 is a block diagram showing another embodiment of a repeater used in the optical transmission system of FIG.

6A and 6B are block diagrams showing an embodiment of a wavelength division multiplexer / demultiplexer of a repeater used in the optical transmission system of FIG. 1.

FIG. 7 is a block diagram showing another embodiment of the optical transmission system of the present invention.

8 is a block diagram showing an embodiment of a repeater used in the optical transmission system of FIG.

FIG. 9 is a block diagram showing another embodiment of the optical transmission system of the present invention.

10 is a block diagram showing an embodiment of a repeater used in the optical transmission system of FIG.

11 is a block diagram showing another embodiment of a repeater used in the optical transmission system of FIG.

12 is a block diagram showing another embodiment of the repeater used in the optical transmission system of FIG.

FIG. 13 is a block diagram showing an example of a conventional optical transmission system.

FIG. 14 is a block diagram showing another example of a conventional optical transmission system.

FIG. 15 is a block diagram showing another example of a conventional optical transmission system.

FIG. 16 is a block diagram showing another example of a conventional optical transmission system.

[Explanation of symbols]

2 TV camera 3 modulator 4 Electricity-> optical converter 5 Optical coupler 6 Optical fiber trunk line 101 ~ 10m + n ~ Slave station 20 parent station 21 WDM 22 Optical to electrical converter 23 Demodulator 30-1 to 30-N Repeater 31 WDM 32 optical to electrical converter 33 Electric amplifier 34 Electric to optical converter 35 Wavelength Multiplex Wave H1, H2, H3 transmission signal light

Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00-14/08 H04N 7/22

Claims (5)

(57) [Claims] 1. An optical transmission system for transmitting transmission signals from slave stations at a plurality of points to a master station by using an optical fiber trunk line, wherein the optical fiber trunk line has one or more repeaters, and the repeater comprises: Converts transmission signals from a plurality of slave stations collected in this repeater into light having a wavelength peculiar to the repeater different from the wavelength of the transmission signal light transmitted on the optical fiber trunk line from upstream of this repeater. The optical transmission system is characterized in that it is multiplexed with an optical fiber trunk line and transmitted downstream. 2. Transmission signal light from a plurality of slave stations collected in a repeater is transmitted through an optical fiber trunk line and collected in a repeater, and the optical wavelengths of these transmission signal lights are on the optical fiber trunk line. 2. The optical transmission system according to claim 1, wherein the wavelength is different from the wavelength of the transmission signal light transmitted from the upstream thereof. 3. An optical signal in which a transmission signal light from a plurality of slave stations transmitted through an optical fiber trunk line and collected in a repeater and another transmission signal light transmitted through the optical fiber trunk line have different wavelength bands from each other. The optical transmission system according to claim 1 or 2, wherein 4. The transmission signal light from a plurality of slave stations transmitted through an optical fiber trunk line and collected in a repeater is an optical signal of 1.3 μm band, and the other optical signals are optical signals of 1.55 μm band. The optical transmission system according to any one of claims 1 to 3, wherein 5. A repeater reflects a specific wavelength of a transmission signal light transmitted on an optical fiber trunk line from the upstream of the repeater, and a transmission signal light from the plurality of slave stations having a different wavelength from this. 5. The optical transmission system according to claim 1, wherein the optical transmission system is configured by using an optical fiber grating for transmitting as a wavelength division multiplexer.