JP2001230758A - Optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system which can transmit plural different digital base band signals economically and with high quality through the use of a common optical transmission line with simple constitution. SOLUTION: The optical transmission system simultaneously transmits plural different digital base band signals by using a common optical transmission line 19. The system is provided with spread modulators 15 which applies spread spectrum modulation to the plural different digital base band signals with different spread codes respectively, a photoelectric converter 3 which converts a modulated electric signal into a light signal without secondary modulation and transmits it to the optical transmission line 19, a photoelectric converter 4 which converts the light signal received through the optical transmission line 19 into the electric signal and inverse spread demodulators 16 which inversely spectrumspreads the converted signals with codes corresponding to the different spread codes and demodulate them into the original digital base band signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system for transmitting a plurality of different digital baseband signals superimposed on an optical signal, and in particular, to various data and information (for example, various data) from terminals installed at a plurality of points. The present invention relates to an optical transmission system that simultaneously transmits digital baseband signals related to monitoring data, observation data, document information, video information, and the like using a common optical transmission path.

[0002]

2. Description of the Related Art Conventionally, as an optical transmission system for simultaneously transmitting a plurality of different digital baseband signals using a common optical transmission line, for example, the systems shown in FIGS. 4 to 8 are known.

FIG. 4 is a block diagram showing an optical transmission system of a first conventional example. As shown in FIG. 4, a conventional optical transmission system includes a plurality of signal sources 1 for generating and transmitting digital baseband signals, and a signal multiplexing system for multiplexing digital baseband signals transmitted from each signal source 1. Device 2
And an optical / optical converter 3 for converting a multiplexed electric signal into an optical signal and transmitting the optical signal to the optical transmission line 19, and a photodiode. An optical / electrical converter 4 for converting an optical signal transmitted via the path 19 into an electric signal, a signal separating device 5 for separating a multiplexed electric signal into respective digital baseband signals, And a receiver 6 for receiving the band signal.

[0004] The signal multiplexing device 2 multiplexes digital baseband signals from the respective signal sources 1 in a time-division multiplexing manner or sequentially sends out the packets in the form of packets. Also, the signal separation device 5
Is for distributing a time-division multiplexed signal or a packet signal to a corresponding receiver 6 according to a predetermined procedure.

FIG. 5 is a block diagram showing an optical transmission system of a second conventional example. As shown in FIG. 5, the optical transmission system of Conventional Example 2 includes a plurality of signal sources 1 for generating and transmitting digital baseband signals, and a plurality of signal sources 1 provided for each signal source 1 based on each digital baseband signal. An electrical / optical converter 3 for intensity-modulating and transmitting optical signals having different wavelengths, and an optical component such as a dielectric multilayer film.
Optical wavelength multiplexing device 7 for multiplexing optical signals from optical converter 3
An optical wavelength demultiplexer 8 which is composed of an optical component such as a dielectric multilayer film, and demultiplexes an optical signal transmitted from the optical wavelength multiplexing device 7 through the optical transmission line 19 for each different wavelength; The optical / electrical converter 4 converts the optical signal into a digital baseband signal, which is an electric signal, and a receiver 6 that receives the digital baseband signal from the optical / electrical converter 4.

The electric / optical converter 3 selects and sets a light source so that an optical signal having a different wavelength is assigned to each signal source 1.

FIG. 6 is a block diagram showing an optical transmission system of a third conventional example. The optical transmission system of the third conventional example is a system applied when the signal sources 1 are dispersedly arranged at different points, and as shown in FIG. By using the wavelength multiplexing device 7, a digital baseband signal at multiple points can be transmitted. Then, the digital baseband signal is received by the receiver 6 in the same procedure as in the optical transmission system of the second conventional example.

FIG. 7 is a block diagram showing an optical transmission system of a fourth conventional example. The optical transmission system of Conventional Example 4 is SC
This is an optical transmission system using the M (Sub-Carrier Multiplexing) method. As shown in FIG.
A plurality of signal sources for generating and transmitting digital baseband signals; and a plurality of digital modulators for superimposing and modulating the digital baseband signals transmitted from each signal source on high-frequency analog carriers having different frequencies. 9
And a frequency multiplexer 11 for multiplexing signals of different frequencies digitally modulated by the digital modulator 9.
And an optical-to-optical converter 3 for converting a multiplexed electrical signal into an optical signal, and a photodiode, and the like.
9 for converting an optical signal transmitted through
An electric converter 4, a frequency separation device 12 for separating a multiplexed signal into signals for each frequency, a digital demodulator 10 for demodulating the separated signal to an original digital baseband signal, and a demodulation by the digital demodulator 10. And a receiver 6 for receiving the obtained digital baseband signal.

The digital modulator 9 uses a digital modulation method such as ASK (Amplitude Shift Keying: a method of replacing a digital code with an amplitude change of a carrier),
FSK (Frequency Shift Keying: a method of replacing digital codes with carrier frequency changes), PSK (Phase
Shift Keying: a method of replacing a digital code with a phase change of a carrier).

FIG. 8 is a block diagram showing an optical transmission system of a fifth conventional example. The optical transmission system of the conventional example 5 is a system applied when the signal sources 1 are distributed and installed at different points, and uses a common electric / optical converter 3 for all the signal sources 1. Therefore, as shown in FIG. 8, an electrical / optical converter 3 and an optical multiplexer 13 composed of optical components such as an optical coupler are installed at each point. The optical signal multiplexed by the optical multiplexer 13 is transmitted through the optical transmission line 19 and received by the optical / electrical converter 4, and then transmitted to the original digital base by the same procedure as the optical transmission system of the conventional example 4. The band signal is extracted and received by the receiver 6.

[0011]

The above-described conventional optical transmission system has the following problems. In the optical transmission system of the first conventional example (see FIG. 4) using a time-division multiplexing method or a packet method, several methods have been established, such as synchronizing transmission and reception of a digital baseband signal, or distinguishing a destination by a header in a packet. However, it is necessary to adjust the transmission delay in the optical transmission line 19, etc.
As the signal transmission speed increases, the cost of the equipment increases.
Also, for signals requiring continuity such as audio and video signals, there is a need to increase the transmission rate, which places a burden on the design of transmission equipment and increases costs. There is.

An optical transmission system of the second conventional example (see FIG. 5) of the wavelength division multiplex system and an optical transmission system of the third conventional example (FIG. 6)
) Can be used while each signal source 1 occupies one wavelength continuously, and is therefore suitable for digital baseband signal transmission for transmitting audio and video. However, compared with other systems, the optical / electrical converters 4 for the number of wavelengths are required on the receiving side, and the optical wavelength multiplexing device 7, the optical wavelength demultiplexing device 8, and the wavelength There is a problem that the cost of equipment and the complexity of maintenance management increase because the electrical / optical converter 3 is required.

The optical transmission system of the fourth conventional example (see FIG. 7) of the subcarrier multiplexing system and the optical transmission system of the fifth conventional example (see FIG. 8) employ a method in which the frequency multiplexing method of the electric signal level is applied to the optical transmission. Since each signal source 1 can occupy one subcarrier frequency, it is suitable for transmitting digital baseband signals for transmitting audio and video. However, since the electric / optical converter 3 is intensity-modulated by the analog signal, the demand for the signal distortion characteristics and noise characteristics of the electric / optical converter 3 increases. Particularly, in the optical transmission system of the conventional example 5, since the optical signals from the plurality of electrical / optical converters 3 at different points are received by the common optical / electrical converter 4, the difference between the different optical signals can be reduced. Beat noise occurs in a frequency region corresponding to the wavelength difference, and strong noise occurs in a signal frequency region depending on the wavelength difference. In order to prevent the occurrence of such beat noise, it is necessary to select and control the optical wavelength of the electrical / optical converter 3.
For example, the center frequency of beat noise generated by light sources having different wavelengths around 1.55 μm is approximately 2.5 GHz when the wavelength difference is around 0.02 nm, and the noise spectrum spreads around the center frequency. Has a problem that the signal quality is significantly reduced due to the direct influence of the subcarriers. Therefore, usually, a process of selecting a semiconductor laser to be a light source and controlling the temperature of the semiconductor laser to adjust the wavelength is performed so that the wavelength interval of light is maintained at 0.2 nm or more. Therefore, there is a problem that maintenance management is complicated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a simple structure, economically, in transmitting a plurality of different digital baseband signals using a common optical transmission line. It is another object of the present invention to provide an optical transmission system capable of transmitting with good quality.

[0015]

SUMMARY OF THE INVENTION An optical transmission system according to the present invention is an optical transmission system for simultaneously transmitting a plurality of different digital baseband signals using a common optical transmission path. A modulating means for performing spread spectrum modulation with different spreading codes, and an electric / optical converting means for converting an electric signal modulated by the modulating means into an optical signal without secondary modulation and transmitting the optical signal to the optical transmission line. An optical / electrical conversion unit for receiving an optical signal from the electric / optical conversion unit via the optical transmission line and converting the optical signal into an electric signal; Demodulating means for despreading the spectrum with a code corresponding to the code and demodulating it to the original digital baseband signal.

At least one of the digital baseband signals is converted into an optical signal by electric / optical conversion means different from electric / optical conversion means for processing other digital baseband signals, and the converted optical signal is converted into an optical signal. Alternatively, after being combined with an optical signal converted from another digital baseband signal and transmitted to the optical transmission line, the signal may be simultaneously received by the same optical / electrical conversion unit.

[0017] At least one of the digital baseband signals may be converted to an optical signal at a different point from other digital baseband signals.

The light wavelength of the different electric / optical conversion means is:
Electricity for processing other digital baseband signals
It may be set to be different from the light wavelength of the light conversion means within a range of 0 nm or more and 0.2 nm or less.

[0019] The digital baseband signal may be a band-compressed signal.

The digital baseband signal demodulated by the demodulation means may have error correction means for performing error correction in order to reduce the influence of beat noise.

According to the optical transmission system of the present invention, a digital baseband signal generated by a plurality of signal sources is subjected to spread spectrum modulation with a spread code different for each digital baseband signal by a modulation means, and then subjected to electrical / electrical modulation.
The light is converted into an optical signal by an optical modulator and transmitted to an optical transmission line. The optical signal transmitted to the optical transmission line is converted into an electric signal by an optical / electrical conversion unit, and then subjected to spectrum despreading by a code corresponding to the different spreading code by a demodulation unit and demodulated to an original digital baseband signal. Is done.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an optical transmission system according to the first embodiment of the present invention.
As shown in FIG. 1, the optical transmission system according to the first embodiment includes a plurality of signal sources 1 for generating and transmitting different digital baseband signals and a digital baseband signal from the signal source 1, respectively. A plurality of spread modulators 15 for performing spread spectrum modulation with different spread codes;
A signal multiplexing device 17 for multiplexing the signals spread-spectrum modulated by the spread modulator 15 and an electric / electrical device for converting the signals multiplexed by the signal multiplexing device 17 into optical signals by direct intensity modulation.
An optical converter 3, an optical / electrical converter 4 for converting an optical signal transmitted from the electrical / optical converter 3 via the optical transmission line 19 into an electrical signal, and a signal converted by the optical / electrical converter 4 And a plurality of despread demodulators 16 for spectrum despreading the signal distributed by the signal distributor 18 with a code corresponding to the different spreading code to demodulate the signal into an original digital baseband signal. And a plurality of receivers 6 for receiving digital baseband signals demodulated by the respective despread demodulators 16.

When transmitting a large amount of data or a large amount of data, such as a video signal or an audio signal, in a short time, the signal source 1 generates a signal which is band-compressed according to a standard such as MPEG2. To send.

As a spread spectrum modulation method by the spread modulator 15, a pseudo noise PN (Pseu
do random noise) frequency hopping (F) that switches the frequency according to the PN sequence
H: Frequency Hopping) method, a method combining these methods, and the like are used.

The receiver 6 may have an error correction function for reducing the influence of beat noise on the received digital baseband signal in order to realize good transmission quality. In this error correction function, for example, it is preferable to correct an error pattern using a Reed-Solomon code that is resistant to random noise.

The digital baseband signals generated by the plurality of signal sources 1 are spread-spectrum-modulated by the spread modulator 15 using different spreading codes for the respective digital baseband signals, and then multiplexed by the signal multiplexing device 17 to be multiplexed. The light intensity is modulated by the optical converter 3 and transmitted to the optical transmission line 19. The optical signal transmitted to the optical transmission line 19 is converted into an electric signal by the optical / electrical converter 4 and then distributed by the signal distributor 18. Each despread demodulator 16 outputs a code corresponding to the different spreading code. The spectrum is despread, demodulated into the original digital baseband signal, and received by the receiver 6.

It should be noted that the signal distributor 18 can be easily realized by a branch circuit formed by simple electric wiring.

According to the first embodiment, since each signal source 1 can continuously occupy and use one spreading code, the continuity requirement for audio digital signals, video digital signals and the like can be obtained. Signal transmission can be easily realized.

Further, precise optical parts and precise setting and adjustment of wavelengths over a wide wavelength range are not required, and the electric signal which is spread spectrum modulated is converted into an optical signal without secondary modulation, and the optical signal is transmitted. Since it is transmitted to Road 19,
There is no need for a secondary modulator or a secondary demodulator. As a result, a system for simultaneously transmitting a plurality of different digital baseband signals with good quality using a common optical transmission line 19 is provided.
It can be provided simply and economically.

FIG. 2 is a block diagram showing an optical transmission system according to a second embodiment of the present invention. The second embodiment is a system which is applied when the signal sources 1 are dispersedly arranged at different points. As shown in FIG. 2, a plurality of electric / optical converters 3 are arranged at different points. And the optical multiplexer 13 is disposed, and the optical signals from the respective electrical / optical converters 3 are multiplexed by the optical multiplexer 13 and transmitted to the optical transmission line 19. Different from configuration.

In the second embodiment, the electric / optical converter 3
Can be set within a range of 0 to 0.2 nm. Even if it is set within this range, the quality of the transmitted video signal is good without being affected by the above-mentioned beat noise, and is at a level at which there is no problem in practical use. This is because the use of digital baseband signals improves noise immunity compared to analog signal systems,
This is because the use of the spread spectrum method effectively contributes to the improvement of noise resistance and the improvement of signal quality by error correction. Therefore, the configuration can be simplified as compared with the system using an analog carrier, and high-quality signal transmission can be economically realized.

By setting the mutual wavelength interval of the electric / optical converter 3 within the range of 0 to 0.2 nm, the selection of the light source and the wavelength become much easier. For example, when digital baseband signals are transmitted from eight different signal sources 1 and a distributed feedback semiconductor laser having a wavelength of 1.55 μm is used for the electrical / optical converter 3, the wavelength dependence of the set temperature is as follows. It is about 0.1 nm / K, and even when the mutual wavelength interval is set to a maximum of 0.2 nm, the set temperature range is +/− 7.
The temperature may be in the range of K. In such a temperature range, the modulation speed and the optical output of the semiconductor laser are not significantly affected, so that the wavelength can be easily adjusted by setting the temperature.

In both the first and second embodiments,
It has eight different signal sources 1 (in FIG. 2, each has one signal source 1 at eight points), and performs a multi-level spreading with a plurality of levels in the signal amplitude direction to secure a sufficient spreading factor. A transmission rate of 10 Mbps per channel can be realized.

Further, since the digital baseband signal is used and the spread spectrum system is adopted, even if the optical signal transmitted to the optical transmission line 19 is received by the same optical / electrical converter 4 at the same time, The occurrence of beat noise can be reduced, and the configuration of the system can be simplified.

FIG. 3 is a block diagram showing an optical transmission system according to a third embodiment of the present invention. In the second embodiment, a plurality of optical multiplexers 13 for multiplexing an optical signal converted by one electric / optical converter 3 with an optical signal converted by the other electric / optical converter 3 are provided. It is configured in a path type. On the other hand, in the third embodiment, as shown in FIG. 3, an optical multiplexer 20 such as an optical coupler that collectively multiplexes the optical signals converted by the plurality of electrical / optical converters 3 is used. It has a star configuration. This third
In this embodiment, the same effect as in the second embodiment can be obtained.

The present invention is not limited to the above embodiment, and various changes can be made within the technical scope described in the claims.

[0037]

According to the first aspect of the present invention, since the signal source of each digital baseband signal can continuously occupy and use one spread code, the audio digital signal and the video digital signal can be used. For example, signal transmission requiring continuity can be easily realized. It also eliminates the need for precise optical components and precise setting and adjustment of wavelengths over a wide wavelength range, and converts electrical signals that are spread-spectrum modulated into optical signals without secondary modulation and transmits them to the optical transmission line. Therefore, a secondary modulator and a secondary demodulator are not required. As a result, a system for simultaneously transmitting a plurality of different digital baseband signals with good quality using a common optical transmission line can be provided economically with a simple configuration.

According to the second aspect of the present invention, since the digital baseband signal is used and the spread spectrum method is adopted, the optical signal transmitted to the optical transmission line is transmitted to the same optical / electrical conversion means. Even if received at the same time, the generation of beat noise can be reduced, and the configuration of the system can be simplified.

According to the third aspect of the present invention, the present invention can be applied to a case where signal sources are distributed at different points.

According to the fourth aspect of the present invention, even if the mutual wavelength interval of the electric / optical conversion means is set within the range of 0 to 0.2 nm, the quality of the transmitted video signal is affected by the beat noise. Good without any problem and practically no problem at all. This is because the use of a digital baseband signal has improved noise immunity compared to the analog signal system, the noise immunity improved by using a spread spectrum system, and the signal quality improved by error correction. Because it is. Therefore, the configuration can be simplified as compared with the system using an analog carrier, and high-quality signal transmission can be economically realized.

According to the fifth aspect of the present invention, a large amount of data or a large amount of data can be transmitted in a short time.

According to the invention of claim 6, good transmission quality can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an optical transmission system according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating an optical transmission system according to a second embodiment of the present invention.

FIG. 3 is a block diagram illustrating an optical transmission system according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing an optical transmission system of a first conventional example.

FIG. 5 is a block diagram showing an optical transmission system of a second conventional example.

FIG. 6 is a block diagram showing an optical transmission system of a third conventional example.

FIG. 7 is a block diagram illustrating an optical transmission system of a fourth conventional example.

FIG. 8 is a block diagram illustrating an optical transmission system of a fifth conventional example.

[Explanation of symbols]

 1: signal source 2: signal multiplexing device 3: electric / optical converter 4: optical / electrical converter 5: signal separating device 6: receiver 7: optical wavelength multiplexing device 8: optical wavelength demultiplexing device 9: digital modulator 10: Digital demodulator 11: Frequency multiplexing device 12: Frequency demultiplexing device 13: Optical multiplexer 15: Spread modulator 16: Despread demodulator 17: Signal multiplexing device 18: Signal distributor 19: Optical transmission line 20: Optical multiplexing vessel

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyuki Omura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Kunio Otaka 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Seiya Shinoda 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. No. Takayamauchi F Term (Reference) 5J050 AA12 CC12 FF06 5K002 AA02 AA04 CA14 DA05 5K022 AA12 EE01 EE14 EE24 EE36

Claims (6)

[Claims] 1. An optical transmission system for simultaneously transmitting a plurality of different digital baseband signals using a common optical transmission line, wherein a modulation means for performing spread spectrum modulation of the plurality of different digital baseband signals with different spreading codes. Electrical / optical conversion means for converting an electrical signal modulated by the modulation means into an optical signal without secondary modulation and transmitting the optical signal to the optical transmission line; and converting the optical signal from the electrical / optical conversion means into an optical signal. An optical / electrical conversion means for receiving the signal via the optical transmission line and converting the signal into an electric signal; and subjecting the signal converted by the optical / electrical conversion means to spectrum despreading using a code corresponding to the different spread code. An optical transmission system, comprising: demodulation means for demodulating the digital baseband signal into a digital baseband signal. 2. At least one of the digital baseband signals is converted into an optical signal by an electric / optical conversion means different from an electric / optical conversion means for processing other digital baseband signals, and the converted light is converted into an optical signal. The signal is combined with an optical signal converted from another digital baseband signal, transmitted to the optical transmission line, and then simultaneously received by the same optical / electrical conversion means. 2. The optical transmission system according to 1. 3. The optical transmission system according to claim 2, wherein at least one of said digital baseband signals is converted into an optical signal at a point different from other digital baseband signals. 4. The light wavelength of said different electric / optical conversion means is:
Electricity for processing other digital baseband signals
The optical transmission system according to claim 2, wherein the optical transmission system is set to be different from an optical wavelength of the optical conversion unit within a range of 0 nm or more and 0.2 nm or less. 5. The digital baseband signal according to claim 1, wherein the digital baseband signal is a band-compressed signal.
The optical transmission system according to any one of the above items. 6. An apparatus according to claim 1, further comprising error correction means for performing error correction to reduce the influence of beat noise on the digital baseband signal demodulated by said demodulation means. Optical transmission system according to the two sections.