JPH09233053A - Optical signal transmission method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To configure multi-transmission stations and multi-channels at a low cost by dividing optical signals subjected to wavelength multiplexing into two wavelength groups or over and allowing one light receiving device to receive each wavelength group and wavelength sets which belong to one wavelength group simultaneously. SOLUTION: Transmission stations 11-1n are grouped into a λ11 group - a λ1m group and a λ21 group - a λ2m group depending on a optical wavelength from a light source 51. A carrier of each wavelength group belongs to a different wavelength band. A video signal outputted from each signal source 31 is frequency-modulated by an FM modulator 41 and a light excited by a light source 51 which a modulated signal to be sent is intensity-modulated and converted into an optical signal and the optical signal is sent to an optical fiber transmission line 7. The light made incident to a reception station 2 is demultiplexed into an optical signal at each wavelength band by a wavelength division type optical demultiplexer 12 and respective optical signals are separated into wavelength groups by optical demultiplexers 91, 92 and received by light receiving devices 81, 82 for each wavelength group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal transmission method applicable to various optical signal transmission systems such as an optical CATV system, an optical ITV system, an optical transmission monitoring system and a subscriber optical communication system. It is suitable for use in a multiplex transmission system in which the transmitted signal is frequency-multiplexed and wavelength-multiplexed and transmitted.

[0002]

2. Description of the Related Art Conventionally, there are various optical signal transmission methods used in an optical CATV system, an optical ITV system, etc., and one of them is shown in FIG. According to this optical signal transmission method, a plurality of transmitting stations 11 to 1n arranged at intervals of several hundred meters to several km are connected by one optical fiber transmission line 7, and a video signal obtained at each transmitting station 11 to 1n is connected. The optical signal is converted into an optical signal, transmitted to the optical fiber transmission line 7, and the optical signals merged into the optical fiber transmission line 7 from the plurality of transmitting stations 11 to 1n are collectively received by the receiving station 2.

In this optical signal transmission method, the transmitting stations 11 to 1
n has one or more signal sources 31 to 3n such as a video camera, and the video signals of the signal sources 31 to 3n are modulated by the FM modulator 41 having different carrier frequencies to be multiplexed, and the frequency multiplexed signal is used as the light source 51. Light of 5n is modulated to generate an optical signal. In this case, the light source 5 of each broadcasting station 11 to 1n
1 has different emission wavelengths, for example, the wavelength band is 1.3 μm band (1.29 to 1.33 μm) and 1.5.
Two types of 5 μm band (1.53 to 1.57 μm) are used. The optical signals generated from the respective transmitting stations 11 to 1n are coupled to one optical fiber transmission line 7 by the optical multiplexer 61 of the transmitting stations 11 to 1n, wavelength-multiplexed and transmitted. On the other hand, in the receiving station 2, the frequency-multiplexed and wavelength-multiplexed optical signals transmitted through the optical fiber transmission line 7 are received by the photodetector 8 and O / E converted, and the O / E-converted electric signal is FM demodulated. In the devices 101 to 10n, the carrier frequencies are selected and then demodulated, and the video signals can be viewed on the TV monitors 111 to 11n by the transmission stations 11 to 1n.

Conventionally, there is also an optical signal transmission system as shown in FIG. This is because the transmitting stations _{11 to} 1n are the cameras 3 _{1 to} 3n,
Modulators 41 to 4n for modulating the video signals from the respective cameras 31 to 3n into subcarrier signals of different frequencies, and electro-optical converters 51 to 5n for emitting optical signals of respectively different oscillation wavelengths λ1 to λn. It is composed of In each of the transmitting stations 11 to 1n, the video signals captured by the cameras 31 to 3n are modulated into subcarrier signals of different frequencies by the modulators 41 to 4n, and the electric / optical converters 51 are respectively modulated by these subcarrier signals. Optical signals having different oscillation wavelengths emitted from 5n are modulated. As the modulator of FIG. 11, modulators of various modulation methods such as an AM modulator, an FM modulator and a QPSK modulator are used.
Various laser diodes such as DFB-LD, FP-LD and LED are used as 1 to 5n.

Optical signals of wavelengths λ1 to λn in FIG. 11 are guided to a common optical transmission line 7 by optical multiplexers 61 to 6n such as optical couplers and received by an optical / electrical converter 8 of a receiving station 2. It In this case, as the optical / electrical converter 8, a photodiode such as a pin photodiode (pin-PD) or an avalanche photodiode (APD) is mainly used. Further, each optical signal received by the optical / electrical converter 8 becomes a subcarrier signal of a different frequency and is guided to the demodulators 101 to 10n via the demultiplexer 9. Demodulators 101-10
n demodulates the sub-carrier signal having a predetermined frequency into the original video signal, and the monitors 111 to 11n display the transmitting stations 11 to 11n.
The video signal from 1n is reproduced. Although the case where the signal to be transmitted is a video signal has been described here, the signal to be transmitted is not limited thereto, and various transmitted signals such as voice and data signals are transmitted by such a system.

[0006]

In the optical signal transmission method of FIG. 10, two or more video signals are modulated by the FM modulator 41 having different carrier frequencies and multiplexed. In this case, the carrier frequency interval is usually 30. ~ 60MHz (BS or CS I
F is assumed). Therefore, when multi-channel transmission is performed by expanding the scale of optical transmission, the number of images transmitted by the transmission stations 11 to 1n and the number of the transmission stations 11 to 1n are increased, and the carrier frequency band is expanded accordingly. There must be.
However, the expansion of the carrier frequency band increases the cost of various devices in the transmission system, and the influence of the distortion generated when the optical signal is received by the photodetector 8 becomes large, which cannot be ignored.

Although the electrical / optical converters 51 to 5n of the transmitting stations 11 to 1n shown in FIG. 11 usually have the same characteristics and optical output powers, the transmitting stations 11 to 1n are used.
Since the distance between the receiving station 2 and the receiving station 2 is usually different, the amount of optical loss determined by the transmission distance is different for each transmitting station 11 to 1n. Therefore, the light receiving level of the optical signal at the receiving station differs for each transmitting station 11 to 1n, and the light receiving level differs between the optical signals. In particular, when there are many transmitting stations, there is a problem that the number of transmitting stations that can satisfy the transmission quality and can be transmitted at the same time (the number of simultaneously transmittable stations) is limited due to the difference in the light receiving level. The relationship between the received light level difference and the number of stations that can be simultaneously transmitted will be described below.

As one of the indexes of transmission quality when subcarrier signal transmission is performed, there is a ratio (CNR) of subcarrier signal power output from an optical / electrical converter to noise power. In particular, when a multi-wave optical signal having different wavelengths is received by one optical / electrical converter, CNR is a shot noise and thermal noise determined by the characteristics of the optical / electrical converter, and a frequency corresponding to the wavelength difference of light. It is dominated by beat noise generated at the position. In order to prevent the influence of beat noise from affecting the transmitted signal located at the subcarrier signal frequency, the optical wavelengths λ1 to λn of the optical signals transmitted from the respective transmitting stations are different from each other with a certain interval. Set to the value. As an example,
As the electric / optical converters 51 to 5n and the optical / electrical converter 8 shown in FIG. 11, generally used electric / optical converters and optical / electrical converters are used, and the respective transmitting stations 11 to 1n in that case.
12 shows the relationship between the wavelength arrangement of the optical signal and the light receiving level, and FIG. 13 shows the relationship between the number of transmitting stations n and the CNR of the optical signal having the lowest light receiving level in that case.

In this type of optical transmission, when the number of transmitting stations increases, it is inevitable that the set optical wavelengths are close to each other, and the influence of beat noise increases. When the light receiving levels of the respective light wavelengths are not uniform, the maximum light receiving level difference (n-
1) The larger Δp is, the larger the beat noise is, and the transmission quality of the optical signal having the lowest received light level is deteriorated. FIG. 13 assumes a case where a DFB-LD is used as the electrical / optical converter and the wavelength interval of each optical signal is set to about 0.2 nm. The CNR of the optical signal with the lowest received light level is satisfied (exceeds CNR _{spec. In the} figure) when the number of transmitting stations n is about 24 or less, and the number of stations that can simultaneously transmit in this system is It will be about 24. FIG. 13 also shows the theoretical limit value (CNR when only that noise exists) for each dominant noise component. Looking at this, comprehensive CNR (CNR
_It can be seen that _total ) is limited by the _beat noise component (CNR _beat ).

In order to reduce the influence of beat noise due to the nonuniformity of the light receiving level as described above, in the conventional optical communication system, when an optical signal is sent from each transmitting station, a large number of light is received by the receiving station side. Has been devised (controlled) so that the light reception level of the optical signal is uniform. As means for equalizing the received light level, a method of controlling the optical output level by changing the setting of the operating current value of the electric / optical converter of each transmitting station, and an optical attenuator provided after the electric / optical converter There is a method of controlling the optical output level according to the optical loss from each transmitting station to the receiving station. Recently, the stability of the system,
The demand for flexibility is increasing, and a design is being considered in which the optical trunk line is looped to provide a redundant system as an emergency measure when the trunk line is cut.

However, in the method of changing the setting of the operating current value of the electric / optical converter, not only the optical output but also other optical characteristics change, which is very inconvenient in designing the system. . Further, in the method of providing the optical attenuator in the latter stage of the electric / optical converter, it is necessary to select the parts after considering the transmission loss of the receiving station and each transmitting station, and the installation work for each transmitting station is also required. It is troublesome because it becomes indispensable. In the form in which the redundant system is provided, if the light receiving level of each optical signal is set to be uniform, the light receiving level becomes non-uniform during transmission using the redundant system, and thus resetting is necessary,
It is not preferable to set the light receiving level fixed.

[0012]

SUMMARY OF THE INVENTION A first object of the present invention is to:
An object of the present invention is to provide an optical signal transmission method capable of realizing multi-channel transmission and multi-channel transmission at low cost, and capable of constructing a large-scale optical transmission device. A second object of the present invention is to prevent the beat noise from becoming large and to prevent the light receiving level from being increased even if the transmitting station does not control a large number of optical signals transmitted from the transmitting station so that the light receiving level at the receiving station is made uniform. It is an object of the present invention to provide an optical signal transmission method capable of simultaneously transmitting optical signals from a large number of stations without impairing the transmission quality of low optical signals.

In the optical signal transmission method according to the first aspect of the present invention, as shown in FIGS. 1 to 3, a large number of transmission stations 11 to 1n are provided.
In each of the above, the signal to be transmitted from the signal source 31 is placed on a carrier wave of a specific frequency, and by this signal, each of the transmitting stations 11 to 11
In the optical signal transmission method, which modulates the optical signal generated from the 1n light source 41, sends these optical signals to the common optical transmission line 7, wavelength-multiplexes and frequency-multiplexes them, and transmits them to the receiving station 2 side, The wavelength-multiplexed optical signal is divided into two or more wavelength groups, and these wavelength groups are received by each of the wavelength groups, and the wavelengths belonging to one wavelength group are simultaneously received by one photodetector 81, 82. It was done.

In the optical signal transmission method according to the second aspect of the present invention, as shown in FIGS. 4 to 6, a large number of transmission stations 11 to 1n are provided.
In each of the above, the signal to be transmitted is placed on a carrier of a specific frequency, the optical signal generated from the light source of each of the transmitting stations 11 to 1n is modulated by this signal, and these optical signals are sent out to the common optical transmission line 7 In an optical signal transmission method for multiplexing and frequency-multiplexing and transmitting to the receiving station side, controlling so that the light receiving level of each optical signal at the receiving station 2 in each of the transmitting stations 11 to 1n is made uniform. Instead, the signal light is sent from each transmitting station, and the wavelength-multiplexed optical signals are divided into two or more wavelength groups λ1 to λn.
Wavelengths belonging to one wavelength group are simultaneously received by one light receiver 81, 8
The light is received at 2.

In the optical signal transmitting method according to the third aspect of the present invention, as shown in FIG. 7, two or more wavelength groups all belong to the same wavelength band (for example, around 1.3 μm). .

In the optical signal transmission method according to the fourth aspect of the present invention, as shown in FIG. 8, two or more wavelength groups belong to different wavelength bands (for example, around 1.3 μm and around 1.5 μm). It was done.

In the optical signal transmitting method according to the fifth aspect of the present invention, as shown in FIG. 3, the frequency arrangement of the transmitted signals is shifted so that adjacent wavelength groups do not overlap each other.

In the optical signal transmission method according to the sixth aspect of the present invention, as shown in FIG. 3, the frequency arrangement of the signals to be transmitted is equidistant within the wavelength group.

In the optical signal transmission method according to the seventh aspect of the present invention, as shown in FIG. 3, the frequency arrangement of the transmitted signals is set at equal intervals within the wavelength group so that adjacent wavelength groups do not overlap each other. It has been shifted.

In the optical signal transmitting method according to the eighth aspect of the present invention, the frequency arrangement of the transmitted signal is within one octave.

In the optical signal transmission method according to claim 9 of the present invention, two or more wavelength groups are all in the same wavelength band, and the wavelength band is around 1.3 μm or around 1.5 μm as shown in FIG. It is what

In the optical signal transmission method according to claim 10 of the present invention, two or more wavelength groups belong to different wavelength bands,
The wavelength band of one of the two or more wavelength groups is shown in FIG.
As shown in (1), the wavelength band of the other wavelength group is around 1.3 μm and around 1.5 μm.

In the optical signal transmission method according to the eleventh aspect of the present invention, as shown in FIG. 9, the optical transmission line 7 connecting two or more transmitting stations and receiving stations is formed in a loop shape, In case of trouble such as disconnection of the transmission line, the optical transmission line 7 is used to perform optical transmission from the opposite direction to the normal communication.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1 An embodiment of the optical signal transmission method of the present invention will be described below with reference to FIG. In FIG. 1, reference numerals 11 to 1n are all transmitting stations, reference numeral 2 is a receiving station, reference numeral 7 is an optical fiber transmission line, and connects each transmitting station 11 to 1n and the receiving station 2. Multiple transmitting stations 11 to 1
n is a λ ₁₁ group as shown in FIG. 2 according to the emission wavelength of the light source 51,
... λ _1m group, λ ₂₁ group, ... λ _2n group. The frequency array of the carrier waves of the transmitted signal transmitted by each of the transmitting stations 11 to 1n is set as shown in FIG. The λ ₁₁ group, ... λ _1m group belong to the wavelength band 1.31 μm, and the λ ₂₁ group, ... λ _2n group belong to the wavelength band 1.55 μm.

Below, the transmitting stations 11 to 1n and the receiving station 2
A detailed description of the above will be given together with its configuration. Transmitting stations 11 to 1
n is a signal source 31 such as a video camera, and the signal source 31
A plurality of pairs of FM modulators 41 for modulating a video signal of a carrier wave of a predetermined frequency, and a light source such as a semiconductor laser (here, a DFB (distributed feedback type) laser is used) 51 and its light source. An optical multiplexer 61 for multiplexing the light of 51 into the optical fiber transmission line 7 is provided. In these transmitting stations 11 to 1n, the video signals output from the individual signal sources 31 are frequency-modulated by the FM modulator 41, and the modulated transmitted signals have equal intervals B (30) as shown in FIG.
To a desired value between 60 MHz) and the light source 51
The intensity of the light emitted by the optical modulator 61 is modulated by the above-mentioned one or more transmitted signals, and the optical signal is converted into an optical signal.
Is coupled to the optical fiber transmission line 7 and transmitted to the optical fiber transmission line 7.

In this case, the transmitting stations 11 belonging to the same wavelength group
The modulation frequency of the FM modulator 41 of 1n is set as follows. When the first transmitting station 11 uses the 1st to mth carriers in FIG. 3, the second transmitting station 12 uses the m + 1th to nth carriers not used by the transmitting station 11 in FIG. , And the following another transmitting station 13 uses the n + 1th and subsequent carriers, and so on, so that the frequencies of the carriers do not overlap. Here, the carrier frequency band is 0.9 to 1.8 GH.
z (within 1 octave). By setting the band within 1 octave, the second-order distortion component is not generated in the optical signals received by the photodetectors 81 and 82. Further, by setting the band to 0.9 to 1.8 GHz, it is possible to use a consumer device such as a ready-made satellite broadcasting tuner as the FM demodulator 101.

Further, with respect to the wavelength groups, the frequency arrays of adjacent wavelength groups which are not the same are shifted so as to be different from each other. For example, it is set as follows. In the 1.31 μm band, as shown in FIGS. 3A and 3B, the first wavelength group λ
₁₁ , the carrier of the second wavelength group λ ₁₂ is arranged at the array interval B.
Of the carrier wavelengths in the front and rear wavelength groups are not overlapped. Also, 1.55
Also in the μm band, as shown in FIGS. 3C and 3D, the carrier waves in the second wavelength group λ ₂₂ are shifted from the first wavelength group λ ₂₁ by ¼ of the arrangement interval B, and the wavelengths before and after are shifted. The carrier frequency arrays in the groups are made non-overlapping. However, the arrangement of the carrier waves may overlap in the wavelength groups belonging to different wavelength bands. For example, the arrangement of the wavelength group λ ₁₁ shown in FIG. 3A and the arrangement of the wavelength group λ ₂₁ shown in FIG. There is.

With respect to the wavelength group, the optical signals from a plurality of transmitting stations 11 to 1n belonging to the same wavelength group are adjusted so that the optical level when they are multiplexed becomes a desired level. When the light of the wavelength group consisting of is received by the light receiver 92, distortion or the like is prevented.

The receiving station 2 is a wavelength division type optical demultiplexer 12,
Optical demultiplexers 91 and 92, optical filter 94, light receivers 81 and 8
2, FM demodulators 101 to 10n, monitor TVs 111 to 1
It is composed of 1n. The light incident on the receiving station 2 is first transmitted to the 1.31 μm band and 1.
The optical signals of the 55 μm band are demultiplexed, the optical signals of the respective wavelength bands are separated into wavelength groups by the optical demultiplexers 91 and 92, and the light receivers 81 and 82 receive the signals for each wavelength group. Further, the electric signals received and converted by the light receivers 81 and 82 are FM
The demodulators 101 to 10n restore the original video signals and display them on the monitor TVs 111 to 11n.

[0030]

Second Embodiment of the Invention Second Embodiment of Optical Signal Transmission Method of the Present Invention
The embodiment will be described in detail with reference to FIGS.
The optical signal transmission method shown in FIG. 4 includes transmitting stations 11 to 1n, a receiving station 2 and a common optical transmission line 7. Each transmitting station 11
In 1n, the transmitted signal captured by the camera 3 is the modulator 41.
Are modulated to subcarrier signals of different frequencies by ~ 4n,
Further, it is converted into an optical signal by the electro-optical converter 5 having different oscillation wavelengths λ1 to λn. Each optical signal is sent to the common optical transmission line 7 via the optical multiplexers 61 to 6n such as an optical coupler,
It is sent to the receiving station 2. In this optical transmission system, the optical signals of the transmitting stations 11 to 1n are divided into two wavelength groups Gλ1 and Gλ2 as shown in FIG. For example, the optical wavelengths λ1 to λi of the transmitting stations 11 to 1i
Is the wavelength group Gλ1 and the optical wavelengths λi + of the transmitting stations 1i + 1 to 1n.
1 to λn are classified as the wavelength group Gλ2.

In the optical transmission system of FIG. 4, a wavelength division type optical demultiplexer 1 for separating the optical signals of n waves that have passed through the common optical transmission line 7 into the receiving station 2 for each wavelength group to which they belong.
Optical / electrical converters 81 and 82 for receiving the two and the split optical signals are installed. When the n-wave optical signal passes through the wavelength division type optical demultiplexer 12, as shown in FIG. 2, the n-wave optical signals are separated into wavelength groups Gλ1 and Gλ2 to which the optical signals of λ1 to λi belong, respectively. The signal is guided to the optical / electrical converter 81 and belongs to the wavelength group Gλ2 λi + 1 to
The optical signals of λn are guided to the optical / electrical converters 82, respectively.

Wavelength λ1 incident on the optical / electrical converter 81
The optical signals of ˜λi are reconverted into subcarrier signals of different frequencies, guided to the demodulators 101 to 10i via the demultiplexer 91, and only the subcarrier signals of a predetermined frequency are demodulated therein. The original transmitted signal is obtained on the monitors 111 to 11i. Wavelength λ incident on the optical / electrical converter 82
The optical signals of i + 1 to λm are sent to the demultiplexer 9 as in the above case.
It is guided to the demodulators 10i + 1 to 10n via 2 and demodulates only the subcarrier signal having a predetermined frequency, and the original transmitted signals are obtained by the monitors 11i + 1 to 11n.

As the wavelength division type optical demultiplexer 12, one having a wavelength longer than that of a certain wavelength such as an optical filter having the same wavelength band or an optical filter having a wavelength band of 1.3 μm / 1.55 μm and a filter having a shorter wavelength than the certain wavelength are used. An optical component that can be separated and taken out is used. Here, the wavelength groups Gλ1 and G
The wavelength array of λ2 is as shown in FIG. λ1
The adjacent i wavelengths of λi are wavelength groups Gλ1, λi + 1 to
The adjacent n-i wavelengths of λn belong to Gλ2.
In this optical transmission system, since the optical signal levels from the transmitting stations received by the receiving station 2 are non-uniform, the light receiving level difference between adjacent optical signals is Δp as shown in FIG. However, in this optical transmission system, since the optical / electrical converters 81 and 82 to be received are different for each wavelength group, the maximum light receiving level difference in each optical / electrical converters 81 and 82 is (i-1) Δp and (N-i-1) [Delta] p, and the maximum difference in the received light level is very small compared to the case where one optical / electrical converter receives an optical signal of n waves.

As in the case of the conventional example, FIG. 6 shows the relationship between the number n of transmitting stations in this system and the CNR of the optical signal having the lowest light receiving level. However, one wavelength group is assumed to have half the number of stations as all the transmitting stations. As is clear from FIG. 6, it is understood that about 36 simultaneous transmission stations can be obtained. It can also be seen from this figure that the effect of beat noise is mitigated in the case where the number of transmitting stations n is large because the number of optical signals received by one optical / electrical converter is reduced.

[0035]

Embodiment 3 of the Invention The third embodiment of the optical signal transmission method of the present invention
The embodiment will be described with reference to FIG. FIG. 7 shows an example of a wavelength arrangement in the case where the oscillation wavelength of the electro-optical converter included in each transmitting station is in the wavelength band around 1.3 μm. In an optical signal transmission method or the like for performing bidirectional communication, the used wavelength band is often different between the upstream system and the downstream system, and in some cases, only one wavelength band can be used for the upstream system.
Even in such a case, split the all-optical signal into multiple wavelength groups,
If the optical / electrical converters that receive them are different, the number of stations that can be simultaneously transmitted can be increased as in the case described above even if the light receiving level is uneven. In this case, the wavelength interval for each wavelength group is set according to the wavelength separation characteristic of the wavelength division type optical demultiplexer of the receiving station.

[0036]

Fourth Embodiment of the Fourth Embodiment of Optical Signal Transmission Method of the Present Invention
The embodiment will be described with reference to FIG. FIG. 8 is an example of a wavelength array when the wavelength bands are different for each wavelength group. In this case, the wavelength band of the wavelength group Gλ1 is 1.3 μm, and the wavelength group Gλ2 is
The wavelength band of is set to 1.5 μm. In this case, a wavelength division type optical demultiplexer that can be separated and taken out for each wavelength group by a 1.3 μm / 1.55 μm band optical filter or the like is used.

[0037]

Fifth Embodiment of the Invention Fifth Embodiment of Optical Signal Transmission Method of the Present Invention
The embodiment will be described with reference to FIG. In FIG. 9, the common optical transmission line 7 for the signal light is configured in a loop shape, and when trouble occurs such as disconnection of the transmission line, the optical transmission line 7 can be used to perform communication from the reverse direction of normal communication. It was done like this. In this optical communication system, normally each transmitting station 1
The signal lights from 1 to 1n are set so as to be input to the A port of the receiving station 2. However, for example, when a disconnection occurs at a point of the optical transmission line 7 marked with x, the transmission direction of the optical signal is It is adapted to be switched and input to the B port of the receiving station 2.

When the receiving level of each signal light at the receiving station 2 is set to be uniform during normal communication, if the transmission direction of the signal is switched when the transmission line is disconnected, the setting is destroyed and the receiving level is changed. Although the light reception levels of the respective signal lights are not uniform in the transmission method of the present invention, the difference in the light reception levels of the respective signal lights is the same as in the normal communication even if the signal transmission direction is switched. Yes, the quality of the transmitted signal is not compromised.

The above-described optical signal transmission method of the present invention is not limited to the bus type system form shown in FIG. 4, but is also an optical transmission form for collecting optical signals from multiple points such as a bus star type and a star type. It can be applied to the system, and can sufficiently exert the effect also in these optical transmission systems.

In the above description, the case where a large number of optical signals having different wavelengths are divided into two wavelength groups has been described, but the present invention is not limited to this, and two or more optical signals belonging to one wavelength group are combined into one. If it is a method of receiving with an optical / electrical converter,
It is also possible to set the wavelength group to 3 or more. However, in that case, a wavelength division type optical demultiplexer for separating an optical signal for each wavelength group and an optical / electrical converter of the same number as the number of wavelength groups are required.

[0041]

According to the optical signal transmission method of the first aspect of the present invention, the wavelength-multiplexed optical signals transmitted from a large number of transmitting stations are divided into two or more wavelength groups. For each wavelength group, and since the wavelengths belonging to one wavelength group are simultaneously received by one light receiver, the following effects are obtained. . Multiple stations and multiple channels are possible without widening the frequency band of the transmitted signal. . Since there are a plurality of optical receivers, the number of receivable optical signal waves is improved as compared with the case where one optical receiver receives all optical signals. Therefore, by reducing the number of transmitted signals of each transmitting station and increasing the number of lightwaves of the transmitting station, that is, by increasing the number of signal lightwaves, the number of channels of the entire optical signal transmission system is not decreased, and the light source of each transmitting station is generated. It is possible to suppress the generated distortion component and ensure good communication.

In the optical signal transmitting method according to the second aspect of the present invention, a large number of optical signals having different wavelengths transmitted from a large number of transmitting stations are divided into two or more wavelength groups, and those signals are transmitted on the transmitting side. The following effects are obtained because the light is sent from the transmitting side without being controlled so that the light receiving level at the receiving side is made uniform, and light is received by one optical / electrical converter for each wavelength group. . Since the maximum received light level difference between many optical signals in one wavelength group is smaller than that in the case where one optical / electrical converter receives all optical signals, the optical signal level of each transmitting station is controlled. Therefore, it is possible to secure a large number of stations capable of simultaneous transmission without making the light receiving level of each signal light in the light receiver uniform. Moreover, the optical transmission system can be simplified, and the flexibility of the system is improved. . By dividing a large number of optical signals into wavelength groups, the number of optical signals received by one optical / electrical converter is reduced, and the influence of beat noise is mitigated even if the number of transmitting stations is large. . Since the optical signal level of each transmitting station is not controlled to make the light receiving level of each signal light in the light receiver uniform, the light receiving level of many optical signals received by the optical / electrical converter is not uniform even during normal communication. is there. Therefore, even if the optical transmission path 7 is looped and the optical signal transmission direction is switched, the light reception level difference of each signal light is the same as that during normal communication, and the quality of the transmission signal is not impaired.

In the optical signal transmission method according to claim 3 of the present invention, since all of the two or more wavelength groups are in the same wavelength band,
It is not necessary to separate the optical signal for each wavelength band on the receiving station 4 side, and when the number of channels is small, the system configuration becomes simple and effective.

In the optical signal transmission method according to claim 4 of the present invention, since the two or more wavelength groups belong to different wavelength bands, it is necessary to separate the optical signal for each wavelength band at the receiving station side. Since the optical signal can be arranged in each wavelength band, it is possible to further increase the number of stations and the number of channels.

In the optical signal transmission method according to the fifth aspect of the present invention, the frequency arrays of the transmitted signals are shifted so that adjacent wavelength groups do not overlap with each other. Therefore, the optical signals of the respective wavelength groups are received by the photodetector 5. In doing so, the influence of optical signals of other wavelength groups can be reduced, and noise can be reduced.

In the optical signal transmission method according to the sixth aspect of the present invention, the frequency arrangement of the transmitted signals is set to be evenly spaced within the wavelength group, so that it is practical as is the case with existing CATV systems. A signal transmission system can be constructed.

In the optical signal transmission method according to the seventh aspect of the present invention, the frequency arrangement of the transmitted signals is set at equal intervals within the wavelength group, and adjacent wavelength groups are shifted so as not to overlap with each other, so that low noise is generated. You can build a practical system with.

In the optical signal transmitting method according to the eighth aspect of the present invention, the frequency arrangement of the transmitted signal is within one octave, so that the second-order distortion component generated in the photodetector is not generated within the signal band, and accordingly, The requirements for the performance characteristics of various devices connected to each transmission system, particularly the light source, the light receiver, and the FM demodulator are alleviated, and the cost of the device can be reduced.

In the optical signal transmission method according to claim 9 of the present invention, the wavelength band of two or more wavelength groups is 1.31 μm or 1.
Since the thickness is 55 μm, it is possible to easily realize the same optical signal communication as the conventional optical signal communication.

In the optical signal transmission method according to claim 10 of the present invention, the wavelength band of one of the two or more wavelength groups is 1.31 μm and the wavelength band of the other wavelength group is 1.55 μm. Therefore, the optical signal communication similar to the conventional optical signal communication can be easily realized.

In the optical signal transmission method according to the eleventh aspect of the present invention, since the optical transmission line 7 is looped so that the transmission direction of the optical signal can be switched and transmitted, it is also compatible with the redundant transmission system. It becomes possible, the flexibility of the optical transmission system is improved, and the effect when put to practical use is great.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an optical signal transmission method of the present invention.

FIG. 2 is an explanatory diagram showing an example of wavelength allocation in the optical signal transmission method of the present invention.

FIG. 3 is an explanatory diagram showing an example of carrier frequency allocation of a transmitted signal in the optical signal transmission method of the present invention.

FIG. 4 is a schematic diagram showing an example of an embodiment of an optical signal transmission method of the present invention.

FIG. 5 is a schematic diagram showing a relationship between an array of optical signal wavelengths and a light receiving level at a receiving station in the optical signal transmission method of the present invention.

FIG. 6 is a schematic diagram showing an example of the relationship between the number n of transmitting stations and CNR for an optical signal having the lowest received light level in the optical signal transmission method of the present invention.

FIG. 7 is a schematic diagram of a second example showing the relationship between the array of optical signal wavelengths and the received light level at the receiving station in the optical signal transmission method of the present invention.

FIG. 8 is a schematic diagram of a third example showing a relationship between an array of optical signal wavelengths and a light reception level at a receiving station in the optical signal transmission method of the present invention.

FIG. 9 is a schematic view showing another example of the embodiment of the optical signal transmission method of the present invention.

FIG. 10 is a schematic diagram showing an example of a conventional optical signal transmission method.

FIG. 11 is a schematic diagram showing another example of a conventional optical signal transmission method.

12 is a schematic diagram showing an example of a wavelength array of optical signals and a light receiving level in the optical signal transmission method of FIG.

FIG. 13 is a schematic diagram showing an example of the relationship between the number n of transmitting stations and CNR for an optical signal having the lowest light receiving level in the conventional optical signal transmission method.

[Explanation of symbols]

 11-1n transmitting station 2 receiving station 7 optical transmission line 12 wavelength division type optical demultiplexer 31-3n signal source 41-4n modulator 51-5n electrical / optical converter (light source) 61-6n optical multiplexer 81, 82 Optical / electrical converter 91, 92 Demultiplexer 94 Optical filter 101-10n Demodulator 111-11n Monitor 87 Signal source 88 FM modulator 89 Optical multiplexer Gλ1, Gλ2 Wavelength group λ1-λm Signal light wavelength

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Atsushi Kiyomura 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Tomoyuki Kato 2-6-1, Marunouchi, Chiyoda-ku, Tokyo No. Furukawa Electric Co., Ltd. (72) Inventor Masao Kubota 1-1-3 Uchiyuki-cho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc. Power Co., Ltd. (72) Inventor Yukihisa Shinoda 1-1-3 Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Ltd.

Claims (11)

[Claims] 1. A transmission signal is placed on a carrier wave of a specific frequency in each of a plurality of transmitting stations, an optical signal generated from a light source of each transmitting station is modulated by this signal, and these optical signals are transmitted by a common optical transmission. In the optical signal transmission method in which the wavelength-division-multiplexed optical signal is sent to the optical path and wavelength-division-multiplexed and frequency-division-multiplexed and transmitted to the receiving station side, the wavelength-division-multiplexed optical signal is divided into two or more wavelength groups. An optical signal transmission method characterized in that wavelengths belonging to one wavelength group are received simultaneously by one light receiver for each group. 2. A transmission signal is placed on a carrier of a specific frequency in each of a number of transmitting stations, an optical signal generated from a light source of each transmitting station is modulated by this signal, and these optical signals are transmitted by a common optical transmission. In an optical signal transmission method in which signals are sent out to the optical path, wavelength-multiplexed and frequency-multiplexed and transmitted to the receiving station side, control is performed so that the light receiving level of each optical signal at the receiving station is made uniform at each transmitting station. Signal light is sent out from each transmitting station without any delay, and the wavelength-multiplexed optical signals are divided into two or more wavelength groups, and these wavelength groups belong to each wavelength group and belong to one wavelength group. An optical signal transmission method characterized in that wavelengths are simultaneously received by one light receiver. 3. The optical signal transmission method according to claim 1 or 2, wherein two or more wavelength groups are all in the same wavelength band. 4. The optical signal transmission method according to claim 1 or 2, wherein two or more wavelength groups belong to different wavelength bands. 5. The optical signal transmission method according to any one of claims 1 to 4, wherein the frequency arrays of the transmitted signals are shifted so that adjacent wavelength groups do not overlap each other. . 6. The optical signal transmission method according to any one of claims 1 to 5, wherein the frequency array of the transmitted signals is set at equal intervals within the wavelength group. 7. The optical signal transmission method according to any one of claims 1 to 6, wherein the frequency arrays of the transmitted signals are arranged at equal intervals within the wavelength group, and adjacent wavelength groups are shifted so as not to overlap each other. An optical signal transmission method characterized by the above. 8. The optical signal transmission method according to any one of claims 1 to 7, wherein the frequency arrangement of the transmitted signals is within one octave. 9. The optical signal transmission method according to each of claims 1 to 8, wherein two or more wavelength groups are all in the same wavelength band, and the wavelength band is around 1.3 μm or around 1.5 μm. An optical signal transmission method characterized by the above. 10. The optical signal transmission method according to claim 1, wherein two or more wavelength groups belong to different wavelength bands, and one of the two or more wavelength groups has a wavelength band. Is around 1.3 μm, and the wavelength band of the other wavelength group is around 1.5 μm. 11. The optical signal transmission method according to any one of claims 1 to 10, wherein an optical transmission line connecting two or more transmitting stations and a receiving station is formed in a loop shape so that the optical transmission line is disconnected. In case of trouble, the optical signal transmission method is characterized in that the optical transmission line is used to perform optical transmission from the opposite direction to that in normal communication.