JP4969835B2 - Optical wavelength division multiplexing system - Google Patents

Description

The present invention relates to an optical wavelength multiplex transmission system that multiplex-transmits a multi-channel broadcast signal using an optical signal.

In areas where it is difficult to receive television (TV) radio waves, such as in mountainous areas, TV radio waves are received using a predetermined antenna at the top of a mountain suitable for reception, and the received TV radio signal is transmitted via a predetermined transmission line. The method of delivering to each subscriber's home is taken. In recent years, the introduction of a system using an optical fiber as a transmission path has been promoted. For example, an FTTH (Fiber To The Home) transmission system that uses an optical fiber for the transmission path to each subscriber's house has already been put into practical use. Has been.

A transmission system that distributes a TV signal to each subscriber's home using the conventional FTTH method will be described with reference to an example shown in FIG. The frequency multiplexed signal 101 of the TV signal is an electric signal obtained by multiplexing different frequencies (channels) A, B, C, and D, and is input to the optical transmitter 102 and converted into the optical signal 103 having the wavelength λ1. The optical signal 103 is transmitted to the optical distributor 105 via the optical fiber 104 while being amplified by an optical amplifier (not shown) as necessary.

The optical distributor 105 distributes the input optical signal 103 into two or more optical signals, and transmits each distributed optical signal to an optical receiver 106 provided in each subscriber's house. The optical receiver 106 converts the input optical signal into an electrical signal again, and outputs an electrical signal 107 in which the frequencies A, B, C, and D are multiplexed.

In an FTTH transmission system as shown in FIG. 7, for example, when an analog TV broadcast signal is distributed, there is a need to further distribute a satellite broadcast signal using the same transmission system. In order to realize this, a frequency-multiplexed signal of satellite broadcasting is received at a certain point by a predetermined antenna, an electric signal of the received frequency-multiplexed signal is converted into an optical signal, and this is converted into an optical signal for analog TV broadcasting. It must be mixed with the signal and transmitted.

Generally, WDM (Wavelength Division Multiplexing) is used to mix and separate optical signals that are intensity-modulated by high-frequency multiplexed signals such as analog TV signals, BS-IF signals, and CS-IF signals. A filter is used (Non-Patent Document 1).

A conventional transmission system that mixes and transmits two frequency multiplexed signals in a transmission system using the FTTH system will be described with reference to FIGS. 8 to 11 show a system in which a second frequency multiplexed signal 111 is added and transmitted to a system that initially transmits only the first frequency multiplexed signal 101.

FIG. 8 shows an example in which the second frequency multiplexed signal 111 is received at the same point as the first frequency multiplexed signal 101, and the first frequency multiplexed signal 101 is input and converted into an optical signal. The frequency multiplex signal 111 is also input. A frequency multiplexed signal obtained by mixing the first frequency multiplexed signal 101 and the second frequency multiplexed signal 111 is converted into an optical signal 112 having a predetermined wavelength λ1 by the optical transmitter 102.

The optical signal 112 is transmitted to the optical distributor 105 via the optical fiber 104, distributed by the optical distributor 105, and input to the optical receiver 106 provided in each subscriber's house. Then, the optical receiver 106 converts the first frequency multiplexed signal 101 and the second frequency multiplexed signal 111 into an electric signal 113.

FIG. 9 shows a method of receiving the second frequency multiplexed signal 111 at the same point as the first frequency multiplexed signal 101 and inputting the second frequency multiplexed signal 111 to an optical receiver 121 different from the optical transmitter 102. Is shown.

The optical transmitter 102 converts the first frequency multiplexed signal 101 into an optical signal 103 having a wavelength λ1, while the optical receiver 121 converts the second frequency multiplexed signal 111 into an optical signal 122 having another wavelength λ2. The optical signal 103 and the optical signal 122 are mixed by the WDM filter 123 and transmitted to the optical distributor 105 as a mixed optical signal 124.

The mixed optical signal 124 is distributed to each subscriber's house by the optical distributor 105 and input to the WDM filter 125 provided in each subscriber's house. The mixed optical signal 124 is demultiplexed into two waves of an optical signal 126 having a wavelength λ 1 and an optical signal 127 having a wavelength λ 2 by the WDM filter 125, and the optical signal 126 is converted into a first frequency multiplexed signal 128 by the optical receiver 106. On the other hand, the optical signal 127 is converted into the second frequency multiplexed signal 130 by the added optical receiver 129.

Next, a case where the second frequency multiplexed signal 111 is received at a point different from the first frequency multiplexed signal 101 will be described with reference to FIGS. 10 and 11. FIG. 10 shows a method of transmitting the first frequency multiplexed signal 101 and the second frequency multiplexed signal 111 with an optical signal having a wavelength λ1, and FIG. This shows a method of mixing and transmitting this.

In FIG. 10, the optical signal 103 having the wavelength λ 1 output from the optical transmitter 102 is returned to the first frequency multiplexed signal 142 of the electrical signal by the optical receiver 141 at a point in the middle of transmission through the optical fiber 104. . Then, the first frequency multiplexed signal 142 is input again to the optical transmitter 143 together with the second frequency multiplexed signal 111 of the electric signal, and is converted into the optical signal 144 having the wavelength λ1.

Similarly to the example shown in FIG. 8, the optical signal 144 is distributed by the optical distributor 105 and then input to the optical receiver 106 provided at each subscriber's house, where the first frequency multiplexed signal 101 and It is converted into an electric signal 145 including the second frequency multiplexed signal 111.

In FIG. 11, a WDM filter 123 is provided in the middle of the optical fiber 104 serving as a transmission path, and the optical signal 103 having the wavelength λ 1 output from the optical transmitter 102 is input. The second frequency multiplexed signal 111 is converted into an optical signal 122 having a wavelength λ 2 by an optical transmitter 121, and this is input to a WDM filter 123. Then, the WDM filter 123 mixes the optical signal 103 having the wavelength λ1 and the optical signal 122 having the wavelength λ2, and outputs a mixed optical signal 124.

Thereafter, similarly to FIG. 9, the mixed optical signal 124 is distributed to each subscriber's house by the optical distributor 105, and then split by the WFDM filter 125 into the optical signal 126 of wavelength λ1 and the optical signal 127 of wavelength λ2, respectively. The signals are converted into a first frequency multiplexed signal 128 and a second frequency multiplexed signal 130 by the optical receiver 106 and the optical receiver 129.
Kazutaka Nara et al., “PLC-MZI type 3-wave multiplex wideband WDM filter array for FTTH video distribution service”, Furukawa Electric Technical Report No. 16 (July 2005).

However, the conventional FTTH transmission system that transmits frequency multiplexed signals of two or more waves has the following problems.

The method shown in FIG. 8 is a method in which the second frequency multiplexed signal 111 is input to the optical transmitter 102 together with the first frequency multiplexed signal 101 and converted into an optical signal. This method is the first frequency multiplexed signal. This is applicable only when 101 and the second frequency multiplexed signal 111 are received at the same point, and is not applicable when the second frequency multiplexed signal 111 is received at another point.

If the frequency band that can be converted by the optical transmitter 102 does not include the frequency band of the second frequency multiplexed signal 111, it is necessary to replace the optical transmitter 102 with one that can handle a wider band.

Further, in the method shown in FIG. 10, after the optical receiver 141 returns to the first high frequency multiplexed signal 142 of the electrical signal, the optical transmitter 143 converts it back to the optical signal again, resulting in degradation of signal characteristics. become. Further, it is necessary to add the optical receiver 141 and the optical transmitter 143, and there is a problem that the cost increases.

In the method using the WDM filter shown in FIG. 9 and FIG. 11, not only the WDM filter is required to mix the two-wave optical signals, but also the WDM filter and the optical receiver are added to each subscriber's house. There was a problem that it was necessary and the cost was significantly increased.

Furthermore, since the optical loss during transmission increases by 2 to 3 dB by using the WDM filter, there is a problem that the transmission characteristic of the transmission system is deteriorated or the dynamic range is compressed. If it is not designed in advance in view of the loss increase due to the WDM filter, wavelength multiplexing by this method cannot be realized.

Accordingly, the present invention has been made to solve these problems, and an optical wavelength multiplexing transmission system capable of realizing high-quality optical wavelength multiplexing at low cost without adding a WDM filter, an optical receiver, or the like. The purpose is to provide.

The first aspect of the optical wavelength division multiplexing transmission system of the present invention is installed at a predetermined location suitable for receiving broadcast waves, and an electrical signal frequency-multiplexed in a predetermined frequency band is input to obtain an optical signal of a predetermined wavelength. The first optical transmitter to be converted and the predetermined wavelength input from an electrical signal that is installed in a location different from the predetermined location and frequency-multiplexed in a different frequency band different from the predetermined frequency band A second optical transmitter for converting to an optical signal having a different predetermined wavelength; a first input terminal to which the optical signal having the predetermined wavelength is input; and a second input terminal to which the optical signal having the other predetermined wavelength is input. And an optical distributor for combining the optical signal having the predetermined wavelength and the optical signal having the other predetermined wavelength respectively input to the first input terminal and the second input terminal and distributing the optical signal to two or more optical signals. And input an optical signal having two wavelengths combined by the optical distributor, and An optical receiver that converts an electric signal frequency-multiplexed in the frequency band and the other frequency band, between the first optical transmitter and the optical distributor, between the second optical transmitter and the optical distributor. And an optical transmission path for transmitting an optical signal by connecting between the optical distributor and the optical receiver, and each of the optical signal of the predetermined wavelength and the optical signal of the other predetermined wavelength And a CN ratio when only the optical signal having the predetermined wavelength is input to the optical receiver and a CN ratio when the combined optical signal having two wavelengths is input. There is substantially adjusted each of the light receiving level to be equal, the CN ratio, wherein der Rukoto following 45dB respectively when inputting the multiplexed been two wavelengths optical signal to the optical receiver This is an optical wavelength division multiplexing transmission system.

According to a second aspect of the present invention, there is provided an optical wavelength division multiplexing transmission system, wherein the optical distributor is a fused optical coupler or a planar waveguide.

A third aspect of the invention, the predetermined frequency band is 70～770MHz, the another frequency band is a light wavelength multiplex transmission system, which is a 950~2150MH z.

According to a fourth aspect of the present invention, there is provided an optical wavelength division multiplex transmission system, wherein an optical amplifier for amplifying the optical signal of the predetermined wavelength and the optical signal of the other predetermined wavelength is provided in the optical transmission line. .
According to a fifth aspect of the present invention, in order to easily realize the system shown in any one of the first to fourth aspects, the optical distributor according to the second aspect is incorporated. Is an optical transmitter.

As still another aspect of the present invention, in order to easily realize the system shown in the fourth aspect, the optical distributor according to the second aspect is incorporated in the optical transmitter or the optical amplifier. Is an optical wavelength division multiplexing transmission system.

As described above, according to the present invention, optical wavelength multiplexing transmission can be performed without causing an increase in optical loss during transmission by performing optical mixing using an existing optical distributor. A system can be provided. Since it is not necessary to use a WDM filter or add an optical receiver for two-wavelength transmission, it can be realized at low cost.

In addition, since an optical distributor such as an optical coupler has almost no wavelength dependency, a light source having a wide range of wavelengths can be used. As a result, even if the wavelength varies due to, for example, temperature variation or current variation of the laser diode used for the light source, there is no increase in optical loss.

In addition, by appropriately setting the reception level of the optical signal input to the optical receiver, it is possible to realize high-quality transmission without deterioration of the CN ratio characteristic even during two-wave transmission, and can be added. An optical wavelength division multiplexing transmission system with high expandability can be provided without greatly restricting the number of channels. Since high quality can be maintained even in transmission of two-wavelength optical signals, it is not necessary to use a filter and can be realized at low cost.

Furthermore, in the optical wavelength division multiplex transmission system of the present invention, it is possible to receive and transmit an additional broadcast wave at a point different from the conventional reception point, so that it is possible to add a device to a conventional facility and increase power consumption. Therefore, it is possible to construct a system that can be easily maintained.

A configuration of an optical wavelength division multiplexing transmission system according to a preferred embodiment of the present invention will be described in detail with reference to the drawings. In addition, about each structural part which has the same function, the same code | symbol is attached | subjected and shown for simplification of illustration and description.

FIG. 1 is a block diagram showing a schematic configuration of an optical wavelength division multiplex transmission system according to an embodiment of the present invention. The optical wavelength division multiplexing transmission system 1 of this embodiment includes an optical transmitter 2 provided at a predetermined point, an optical fiber 3 as a transmission path, an optical distributor 4 that distributes an optical signal to each subscriber's house, The optical receiver 5 is installed in each subscriber's house, and the optical transmitter 6 is provided at a point different from the predetermined point.

In FIG. 1, the configuration excluding the optical transmitter 6 is a system configuration initially installed to transmit only the broadcast wave received at the predetermined point. In the optical wavelength division multiplexing transmission system 1 of the present embodiment, Further, an optical transmitter 6 is added.

The first frequency multiplexed signal 11 received at the predetermined point is converted into an optical signal 12 of wavelength λ1 by the optical transmitter 2, and the optical signal 12 is transmitted to the optical fiber 3 and input to the optical distributor 4. The Also, the second frequency multiplexed signal 14 received at the other point is input to the optical transmitter 6 and converted into an optical signal 15 having a wavelength λ2, and the optical signal 15 is also input to the optical distributor 4.

The optical signal 12 and the optical signal 15 input to the optical distributor 4 are mixed in the optical distributor 4 and further transmitted to the optical receiver 5 installed in each subscriber's house. The mixed wave 13 of the optical signal 12 and the optical signal 15 transmitted to the optical receiver 5 at each subscriber's house is converted again to the frequency multiplexed signal 16 of the electrical signal by the optical receiver 5. The frequency multiplexed signal 16 is an electrical signal in which the first frequency multiplexed signal 11 and the second frequency multiplexed signal 14 are combined.

An example of a signal transmitted by the optical wavelength division multiplex transmission system 1 of the present embodiment is shown in FIG. Here, the first frequency multiplexed signal 11 is an electrical signal in which different frequencies (channels) A, B, C, and D are multiplexed, and the second frequency multiplexed signal 14 is changed to different frequencies (channels) F and G. Another electric signal is multiplexed. The first frequency multiplexed signal 11 can be a broadcast wave in the frequency band 70 to 770 MHz, and the second frequency multiplexed signal 14 can be another broadcast wave in the frequency band 950 to 2150 MHz or 70 to 2150 MHz.

In FIG. 2, a first frequency multiplexed signal 11 composed of four channels is converted into an optical signal 12 having a wavelength λ 1 as shown in FIG. The second frequency multiplexed signal 14 consisting of two channels is converted by the optical transmitter 6 into an optical signal 15 having a wavelength λ2 as shown in FIG. Then, the optical signal 12 and the optical signal 15 are combined by the optical distributor 4 to become a mixed wave 13 as shown in FIG. Further, the mixed wave 13 is converted into an electric signal by the optical receiver 5 and output as a frequency multiplexed signal 16 having six channels as shown in FIG.

The optical distributor 4 can use a fused optical coupler or a planar waveguide. For example, when a melting type optical coupler is used as the optical distributor 4, the melting type optical coupler is formed by bundling a plurality of optical fibers and melting the central portion, and therefore has the same number of input ends and output ends. is doing. However, when the fused optical coupler is used as an optical distributor, light is input to only a part of the input end, and the other input ends are terminated.

In the optical distributor 4 shown in FIG. 1, since only one signal of the optical signal 12 is initially input, only one input terminal is used, and all other input terminals are terminated.

Therefore, in the optical wavelength division multiplexing transmission system 1 of the present embodiment, any one of the input terminals that have been subjected to termination processing of the optical distributor 4 can be used again, and the optical signal 15 is input to the input terminal. Yes. That is, the optical signal 15 is combined with the optical signal 12 using the existing optical distributor 4. The optical signal 15 input to the optical distributor 4 is evenly distributed together with the optical signal 12 and transmitted to each subscriber's house.

The mixed signal of the optical signal 12 and the optical signal 15 transmitted to each subscriber's home is converted into an electrical signal by the optical receiver 5 and includes the first frequency multiplexed signal 11 and the second frequency multiplexed signal 14. 16 is output. If the optical receiver 5 does not support the frequency band of the second frequency multiplexed signal 14, the optical receiver 5 that does not support the predetermined frequency band is replaced.

As described above, in the optical wavelength division multiplexing transmission system 1 of the present embodiment, the existing optical distributor 4 is used to mix the optical signal 14 with the optical signal 12, so that not only the cost increase can be avoided, It is also possible to avoid an increase in optical loss of the optical signals 12 and 15.

In addition, in a conventional method of performing optical mixing using a WDM filter, only an optical signal having a specific wavelength defined by the WDM filter can be used. That is, the wavelength λ1 of the optical signal 12 and the wavelength λ2 of the optical signal 15 have to be matched with a specific wavelength defined by the WDM filter to be used.

On the other hand, in the present invention, since the optical distributor 4 such as an optical coupler is used for multiplexing the optical signal 12 and the optical signal 15, there is almost no wavelength dependence, and a light source in a wide wavelength range can be used. It becomes possible. As a result, even if the wavelength of the optical signals 12 and 15 changes due to the temperature or current fluctuation of the laser diode that is the light source provided in the optical transmitters 2 and 6, there is no risk of increasing the optical loss. .

When the optical signal 15 is combined with the optical signal 12 to transmit an optical signal of two wavelengths, the quality of the optical signal at the optical receiver 5 is degraded as compared with the case where only the optical signal 12 is transmitted. there is a possibility. FIG. 3 shows the relationship between the light reception level of each optical signal and the CN ratio in the optical receiver 5. Here, the CN ratio represents the ratio of signal to noise, and the higher the CN ratio, the higher the quality.

In FIG. 3, a graph 21 shows the relationship between the light reception level and the CN ratio when the optical receiver 5 receives only one wave of the optical signal 12, and a graph 22 shows the relationship between the optical signal 12 and the optical signal. The relationship between the light reception level and the CN ratio when receiving two waves with the signal 15 is shown.

FIG. 3 shows that when the light reception level in the optical receiver 5 is high, a large difference occurs in the CN ratio between receiving one wave and receiving two waves. Such a difference in the CN ratio affects the visibility of the TV viewer, which may cause the TV viewer to feel uncomfortable. Therefore, it is desirable that the respective CN ratios when receiving one wave and when receiving two waves are approximately the same.

Therefore, as one of transmission methods for mixing and transmitting two waves, conventionally, one optical signal is mixed with the light intensity of the other optical signal lowered by about 5 to 10 dB. By reducing the light intensity of the other optical signal, the influence on the one optical signal can be almost eliminated. Thus, when transmitting with a difference in the light intensity between the two waves, it is necessary to provide a difference in the modulation degree of each optical signal so that the signal intensity of the two waves in the optical receiver is equal.

FIG. 4 shows an example of the degree of modulation necessary to receive the two-wave optical signal with the same signal intensity when the two-wave optical signal is transmitted with the light intensity changed. In the figure, a graph 31 shows the degree of modulation of the one optical signal transmitted at a predetermined light intensity, and here it is 9% per channel. Graph 32 shows the relationship between the ratio of the light intensity of the other optical signal to the one optical signal (light level ratio) and the degree of modulation necessary to make the signal intensity of the two waves equal. .

Further, a graph 33 shows an allowable value of the modulation degree in a general direct modulation type optical transmitter. Usually, the maximum modulation degree is about 30 to 40% and the total modulation degree is 30 to 35%. It is common. The allowable value of the modulation factor is provided in order to avoid deterioration of distortion characteristics and optical clipping.

From FIG. 4, for example, when the modulation degree of the optical signal 12 is 9% per channel (graph 31) and the optical level ratio of the added optical signal 15 to the optical signal 12 is lowered by 5 dB, the modulation of the optical signal 15 is performed. The degree needs to be 28% per channel. For this reason, the number of signals that can be added becomes about 1 to 2 channels from the allowable value of the modulation degree, and the merits of the wavelength multiplexing system cannot be sufficiently exhibited.

Therefore, in the optical wavelength division multiplexing transmission system 1 of the present invention, the optical intensity of the optical signal 12 and that of the optical signal 15 are substantially equal (the optical level ratio is zero or a value close to zero), while one-wave reception and two-wave reception are performed. Therefore, the light intensity of each optical signal is lowered so that the received light level becomes almost free from the difference in CN ratio. However, the reception level at which the CN ratio is higher than a predetermined allowable value is selected as the light reception level.

As described above, by making the optical intensities of the optical signal 12 and the optical signal 15 substantially the same and lowering the light receiving level of both, the CN ratio characteristic when receiving two waves deteriorates compared with when receiving one wave. Can be suppressed. Further, since it is not necessary to increase the optical level ratio between the optical signal 12 and the optical signal 15, it is possible to transmit them with substantially the same degree of modulation. As a result, there is no need to limit the number of channels to be added, and a highly scalable system can be constructed.

When the optical signal 12 or the optical signal 15 is a digital signal, the allowable value of the CN ratio with respect to the digital signal is greatly reduced. As a result, even if the light intensity of the digital signal is lowered to increase the light level ratio shown in FIG. It is never done.

An application example of the optical wavelength division multiplexing transmission system 1 of the present invention is shown in FIG. An optical wavelength division multiplex transmission system 1 shown in FIG. 5 has an optical transmitter 2 installed on a mountain or the like suitable for receiving analog TV broadcast radio waves, and the optical transmitter 2 converts a frequency multiplexed signal 11 into an optical signal 12 for each. It is transmitted to the optical receiver 5 at the subscriber's house.

In addition, an optical transmitter 6 is provided for receiving broadcast waves such as BS broadcasts and CS broadcasts on a flat ground in the vicinity of the subscriber's house and converting them into optical signals 15. By installing the optical transmitter 6 on a flat land or the like near the subscriber's home, the addition of facilities and power consumption to the mountaintop where the optical transmitter 2 is installed is avoided. By providing the additional optical transmitter 6 on a flat ground or the like, the burden of equipment maintenance or the like can be reduced.

Another embodiment of the optical wavelength division multiplexing transmission system of the present invention is shown in FIG. In the optical wavelength division multiplexing transmission system 41 shown in FIG. 6, an optical amplifier 42 is added in the middle of the optical fiber 3 that is a transmission path. Thus, in the optical wavelength division multiplexing transmission system of the present invention, one or more optical amplifiers can be added as necessary.

Further, both the optical wavelength division multiplexing transmission system 1 shown in FIG. 1 and the optical wavelength division multiplexing transmission system 41 shown in FIG. 6 are configured to have only one optical distributor 4, but depending on the number of houses and the arrangement of the subscriber's homes, etc. A configuration in which a plurality of optical distributors are appropriately connected may be employed.

As still another embodiment of the optical wavelength division multiplexing transmission system of the present invention, the system can be easily realized by incorporating the optical distributor in the optical transmitter or the optical amplifier.

Note that the description in the present embodiment shows an example of the optical wavelength division multiplex transmission system according to the present invention, and the present invention is not limited to this. The detailed configuration and detailed operation of the optical wavelength division multiplex transmission system in the present embodiment can be appropriately changed without departing from the spirit of the present invention.

FIG. 1 is a block diagram showing a schematic configuration of an optical wavelength division multiplexing transmission system according to an embodiment of the present invention. FIG. 2 is a diagram illustrating an example of a signal transmitted by the optical wavelength division multiplex transmission system 1 of the present embodiment. FIG. 3 is a graph showing the relationship between the light reception level of each optical signal and the CN ratio in the optical receiver. FIG. 4 is a graph showing an example of the degree of modulation necessary for receiving the two-wave optical signal with the same signal intensity when the two-wave optical signal is transmitted with the light intensity changed. FIG. 5 is a block diagram showing an application example of the optical wavelength division multiplexing transmission system 1 of the present invention. FIG. 6 is a block diagram showing another embodiment of the optical wavelength division multiplexing transmission system of the present invention. FIG. 7 is an example of a transmission system that distributes a TV signal to each subscriber's home using the conventional FTTH method. FIG. 8 is a block diagram showing a conventional system in which the second frequency multiplexed signal is received at the same point as the first frequency multiplexed signal and input to the same optical transmitter. FIG. 9 is a block diagram showing a conventional system in which the second frequency multiplexed signal is received at the same point as the first frequency multiplexed signal and input to another optical receiver. FIG. 10 is a block diagram showing a conventional system in which a first frequency multiplexed signal and a second frequency multiplexed signal are received at different points and transmitted as an optical signal having a wavelength λ1. FIG. 11 is a block diagram showing a conventional system in which a first frequency multiplexed signal and a second frequency multiplexed signal are received at different points, and converted into optical signals of different wavelengths and transmitted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 41 ... Optical wavelength division multiplexing transmission system 2, 102, 143 ... Optical transmitter 3, 104 ... Optical fiber 4, 105 ... Optical distributor 5, 106, 121, 129, 141 ... Optical receivers 11, 101, 128, 142 ... first frequency multiplexed signals 12, 15, 103, 112, 122, 126, 127, 144 ... optical signals 13 ... mixed waves 14, 111, 130... Second frequency multiplexed signal 16, 113, 145... Electrical signal 21 including first frequency multiplexed signal and second frequency multiplexed signal 107... 107 Electrical signal 123, 125. .WDM filter 124 ... mixed optical signal

Claims (6)

A first optical transmitter that is installed at a predetermined location suitable for receiving broadcast waves and that converts an electrical signal frequency-multiplexed in a predetermined frequency band into an optical signal of a predetermined wavelength;
An electrical signal installed at a location different from the predetermined location and frequency-multiplexed in a different frequency band different from the predetermined frequency band is inputted into an optical signal having a different predetermined wavelength different from the predetermined wavelength. A second optical transmitter for conversion;
The first input terminal to which the optical signal with the predetermined wavelength is input and the second input terminal to which the optical signal with the other predetermined wavelength is input are input to the first input terminal and the second input terminal, respectively. An optical distributor for combining the optical signal of the predetermined wavelength and the optical signal of another predetermined wavelength and distributing the optical signal to two or more optical signals;
An optical receiver that inputs an optical signal of two wavelengths combined by the optical distributor and converts the optical signal into an electric signal that is frequency-multiplexed in the predetermined frequency band and the different frequency band;
An optical signal is transmitted between the first optical transmitter and the optical distributor, between the second optical transmitter and the optical distributor, and between the optical distributor and the optical receiver. and an optical transmission path,
The optical signal of the predetermined wavelength and the optical signal of the other predetermined wavelength have substantially the same light intensity, and the CN ratio when only the optical signal of the predetermined wavelength is input to the optical receiver And the light receiving level is adjusted so that the CN ratio when inputting the combined two-wavelength optical signal is substantially equal,
The combined by two optical wavelength multiplexing transmission system CN ratio, characterized in der Rukoto following 45dB respectively when the optical signal of the wavelength inputted to said optical receiver. 2. The optical wavelength division multiplexing transmission system according to claim 1, wherein the optical distributor is a fused optical coupler or a planar waveguide. 3. The optical wavelength division multiplexing transmission system according to claim 1, wherein the predetermined frequency band is 70 to 770 MHz, and the another frequency band is 950 to 2150 MHz. The light according to any one of claims 1 to 3 , wherein an optical amplifier for amplifying the optical signal of the predetermined wavelength and the optical signal of the other predetermined wavelength is provided in the optical transmission line. Wavelength multiplex transmission system. An optical transmitter comprising the optical distributor according to claim 2 in order to easily realize the optical wavelength division multiplexing transmission system according to any one of claims 1 to 3 . An optical amplifier comprising the optical distributor according to claim 2 in order to easily realize the optical wavelength division multiplexing transmission system according to claim 4 .

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