JPH1155220A - Method for extending optical transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost per optical transmission device by setting a modulation system in a station-side device to be a modulation system for collectively converting amplitude modulation signals whose frequencies are multiplexed into frequency modulation signals, converting the electric signal converted into the frequency modulation signal by the modulation system into an optical signal, m-branching the optical signal and connecting the respective signals to the existing optical transmission lines of n-branches. SOLUTION: Frequency bands are divided and multiplexed in a multiplex AM signal (a) inputted to a first input terminal 1. An AM collective modulator 31 inputs the multiplex AM signal (a) and converts the signal into an FM collective modulation signal (b). An optical transmitter 32 converts the signal into the optical signal and transmits it to the existing optical transmission line 4 via an m-branching unit 33. An optical receiver 51 converts the optical signal transmitted through the optical transmission line 4 into the electric signal and an FM demodulator 52 demodulates the FM collective modulation signal (c). Thus, the original multiplex AM signal (d) is restored. The restored multiplex AM signal is outputted to an output terminal 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for transmitting a wideband signal by an optical signal. In particular, the present invention relates to a technology for adding an existing 1: n optical transmission device.

[0002] The present invention relates to cable television (CAT).
It is suitable for use in signal transmission in V). In particular, CA
It is suitable for simultaneous transmission of TV and video-on-demand (VOD) and other video signals or data communication and other communication signals on the same transmission path.

[0003]

2. Description of the Related Art In a video transmission system such as CATV,
In order to reduce the cost, it is urgently required that one transmitting device delays a signal toward many receiving devices. In addition to a normal video signal, it is required to send another video signal only to a destination for which transmission has been requested, such as VOD.

When transmitting a frequency-multiplexed amplitude modulated signal (hereinafter referred to as a "multiplexed AM signal"), conventionally,
A method of transmitting an intensity-modulated optical signal as it is using this frequency multiplexed signal as a modulation input (this is called a “direct transmission method”).
Has been used. FIG. 9 shows such a conventional example. In this conventional example, an input terminal 1 to which a multiplexed AM signal is input, an optical line terminal 3 for converting the multiplexed AM signal input to the input terminal 1 into an optical signal, and an optical signal from the optical line terminal 3 An optical transmission line 4 for branching and transmitting, a subscriber unit 5 for receiving each of the n-branched optical signals, and an output terminal 6 for outputting a multiplexed AM signal converted into an electric signal by the subscriber unit 5 And The optical line terminal 3 includes an electric / optical converter 35 that converts a multiplexed AM signal into an optical signal, and an optical signal amplifier 36 that amplifies the output of the electric / optical converter 35 and sends the amplified signal to the optical transmission line 4. Prepare. The subscriber device 5 includes an optical / electrical converter 55 for converting an optical signal from the optical transmission line 4 into an electric signal, and an electric signal amplifier 56 for amplifying the output of the optical / electrical converter 55.

There is also known a method in which a second signal is frequency-multiplexed with a multiplexed AM signal and transmitted in a similar manner. FIG. 10 shows such a conventional example. This conventional example has an input terminal 2 to which a second signal is input, in addition to the configuration shown in FIG.
And an output terminal 7 for outputting a second signal. The optical line terminal 3 has a frequency for multiplexing the second signal input to the input terminal 2 with the multiplexed AM signal input from the input terminal 1. The multiplexing device 37 is provided, and the subscriber-side device 5 is provided with a frequency separating device 57 that separates the output of the electric signal amplifier 56 into a multiplexed AM signal and a second signal.

In the direct transmission systems shown in FIGS. 9 and 10, since the light receiving sensitivity is low, the level difference between transmission and reception cannot be increased, and the transmission distance and the number of optical branches in the optical transmission system must be increased. There is a problem that can not be. In order to solve this problem, a method of collectively converting a multiplexed AM signal into a frequency-modulated signal and transmitting an intensity-modulated optical signal using the modulated signal as a modulation input (hereinafter, referred to as an "FM collective conversion method") Was developed. FIG. 11 shows such a conventional example.

In the conventional example shown in FIG. 11, an FM batch modulator 38 which collectively converts a multiplexed AM signal into a frequency modulation signal, and converts the output of the FM batch modulator 38 into an optical signal are transmitted to the optical line terminal 3. And an optical transmitter 39 for transmitting to the optical transmission line 4. The subscriber unit 5 includes an optical receiver 58 that receives an optical signal from the optical transmission line 4 and an FM demodulator 59 that performs an FM demodulation of the output of the optical receiver 58.

In this method, the level difference between transmission and reception can be increased because of the high light receiving sensitivity, and the transmission distance and the number of optical branches in the optical transmission system can be increased. In addition, although the signal to be transmitted optically has a wide band, it can be demodulated with a simple circuit by using a high-speed IC, and the channel can be selected from the demodulated signal by a general-purpose tuner for CATV. Can be.

[0009]

In the direct transmission system, the receiving sensitivity is low, so that the number of branches during transmission cannot be increased. It is important to increase the number of branches that can be performed in order to reduce the cost per subscriber, and the problem of branching is an important issue.

[0010] On the other hand, the FM batch conversion method can increase the number of branches during transmission. However, the number of branches is limited when using an already laid transmission line because of the direct transmission method. You cannot take advantage of the system.

In the case where a modulation signal other than amplitude modulation such as a frequency modulation signal is intensity-modulated as a modulation input and optically transmitted, the number of branches during transmission can be increased as compared with the case of an amplitude modulation signal. However, when transmitting simultaneously with the amplitude modulation signal, the number of branches allowed in the case of the amplitude modulation signal is limited. It is necessary to transmit a modulation signal other than amplitude modulation in order to realize VOD and the like, and it is required that the modulation signal can be transmitted simultaneously with the amplitude modulation signal without reducing the number of possible branches in optical transmission. .

SUMMARY OF THE INVENTION The present invention solves such a problem, and uses an existing transmission line to increase the number of branches per optical transmission device and reduce the cost per subscriber. The aim is to provide a method.

[0013]

SUMMARY OF THE INVENTION The present invention relates to a method of adding an optical transmission device for increasing the number of optical transmission devices in which an optical transmission path from one station device is branched into n branches. The modulation method is to convert the frequency-multiplexed amplitude-modulated signal into a frequency-modulated signal at a time. The electric signal converted to the frequency-modulated signal by this modulation method is converted into an optical signal, and the optical signal is branched into m signals. Each of them is connected to an existing n-branch optical transmission line.

A technique for collectively frequency-converting frequency-multiplexed amplitude-modulated signals is disclosed in a patent application (JP-A-8-274714) filed by the same applicant as the present application. The present invention makes use of this technology to improve the light receiving sensitivity, increase the number of optical branches in the transmission path, and use the existing transmission path.

The m-branch is preferably performed in the optical line terminal. m
As the optical signal to be branched, an electric signal converted into a frequency modulation signal by the modulation method and a second signal of a modulation method different in frequency from the electric signal and different from the modulation method are electrically combined. Then, an intensity-modulated optical signal can be used with the multiplexed output as a modulation input. Also,
An electric signal converted into a frequency modulated signal by the modulation method, and two electric signals each having a different frequency from the electric signal and a second signal of a modulation method different from the modulation method, each of which is intensity-modulated as a modulation input. Optical signals can be combined and used.

A technique for simultaneously transmitting a frequency-multiplexed amplitude-modulated signal and a second signal having a different modulation scheme from each other on the same transmission line has been disclosed in the patent application filed by the same assignee as the present application, and Japanese Patent Application No. 8-017849. No. (not disclosed at the time of filing the present application). The present application makes use of this technology, even when simultaneously transmitting a second signal that is a modulation method other than the amplitude modulation method on the same transmission line, the component of the number of optical branches when the amplitude modulation signal is transmitted as it is and This prevents the number of optical branches from being restricted by the existing transmission line.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 are block diagrams showing two embodiments of the present invention. Figure 1 shows a multiplexed AM
FIG. 2 shows the configuration of an optical transmission apparatus in the case of transmitting only a signal and transmitting a multiplexed AM signal and a second signal simultaneously.

In the embodiment shown in FIG. 1, an input terminal 1 to which a multiplexed AM signal is input, an optical line terminal 3 for converting the multiplexed AM signal input to the input terminal 1 into an optical signal, and an optical line terminal 3 An optical transmission line 4 for n-branching and transmitting an optical signal from
Subscriber-side device 5 for receiving each of n-branched optical signals
And the multiplex A converted into an electric signal by the subscriber unit 5
An output terminal 6 for outputting an M signal. The optical line terminal includes an FM batch converter 31 for batch-converting the multiplexed AM signal input from the input terminal 1 into an FM modulation signal, and an optical transmission for sending the obtained FM batch converted signal to the optical transmission line 4. Vessel 3
2 and an m-branch unit 33 that branches the output of the optical transmitter 32 into m. One branch output of the m-branch 33 is connected to the existing optical transmission line 4. The subscriber unit 5 includes an optical receiver 51 for receiving an optical signal from the optical transmission line 4 and an FM demodulator 52 for FM demodulating the reception output of the optical receiver 51.

In the embodiment shown in FIG. 2, a second input terminal 2 to which a second signal different from the multiplexed AM signal is input is provided. FM
A multiplexed optical transmitter 34 that multiplexes the output of the batch converter 31 and the second signal from the input terminal 2 to convert the multiplexed optical signal into an optical signal; Is provided. The subscriber unit 5 includes a multiplexed optical receiver 53 that receives the optical signal from the optical transmission line 4 and separates the signal subjected to the FM batch conversion from the second signal. FM demodulator 5 that performs FM demodulation of the signal that has been subjected to FM batch conversion
2 is provided. The other reception output of the multiplex optical receiver 53, that is, the second signal is output to the second output terminal 7.

In any of the embodiments, an m-branch 33 is provided inside the optical line terminal 3, and connects the optical transmitter 32 or the multiplexed optical transmitter 34 to the existing optical transmission line 4.

FIG. 3 shows signal waveforms at various parts of the optical transmission apparatus shown in FIG. 3A and 3B show signals on the transmitting side, FIG. 3A shows a multiplexed AM signal, and FIG. 3B shows an FM signal.
This shows the signals that have been converted collectively. (C) and (d) show signals on the receiving side, (c) shows a received FM batch converted signal, and (d) shows a demodulated multiplexed AM signal.

The operation of the optical transmission device shown in FIG. 1 will be described in more detail with reference to FIG. In the multiplexed AM signal (a) input to the first input terminal 1, a frequency band of f1 or f2 is divided and multiplexed. FM batch converter 31
Receives a multiplexed AM signal (a) and converts the signal into an FM batch conversion signal (b) using f3 or f4 as an occupied frequency band. The optical transmitter 32 converts this signal into an optical signal, and transmits the signal to the existing optical transmission line 4 via the m-branch 33. The optical receiver 51 converts the optical signal transmitted through the optical transmission line 4 into an electric signal, and demodulates the FM batch converted signal (c) by the FM demodulator 52 to obtain the original multiplexed AM signal (d). To restore. The restored multiplex AM signal is output to the output terminal 6.

FIG. 4 shows signal waveforms at various parts of the optical transmission apparatus shown in FIG. 4A to 4C show signals on the transmitting side, FIG. 4A shows a multiplexed AM signal, FIG. 4B shows a second signal, and FIG. 4C shows a signal that has been subjected to FM batch conversion. (D) shows a multiplex signal to be transmitted. further,
(E) to (g) are signals on the receiving side, (e) is a received batch FM modulation signal, and (f) is a demodulated multiplex A
The M signal, (g) shows a second signal separated from the received signal.

The operation of the optical transmission device shown in FIG. 2 will be described in more detail with reference to FIG. In the multiplexed AM signal (a) input to the first input terminal 1, a frequency band of f5 to f6 is divided and multiplexed. The second signal (b) input to the second input terminal 2 has f7 to f8 as the occupied frequency band. The FM batch converter 31 receives the multiplexed AM signal (a) as an input and converts this signal to f9 to f9.
10 is converted into an FM batch conversion signal (c) having an occupied frequency band. The multiplex optical transmitter 34 outputs the second signal and the FM signal.
The batch conversion signal (c) is converted into an electric signal or an optical signal and then multiplexed, and transmitted to the optical transmission line 4 as an optical multiplexed signal (d). The multiplexed optical receiver 53 converts the optical signal transmitted through the optical transmission line 4 into an electric signal and then separates it, or separates the optical signal at the optical signal stage and converts each into an electric signal, thereby converting the FM collective signal. (E) and the second signal (g)
And two electric signals are obtained. By demodulating the separated FM batch converted signal by the FM demodulator 52, the original multiplex A
The M signal (f) is restored. The restored multiplexed AM signal is output to a first output terminal 6 and the second signal is output to a second output terminal 7.

In the above embodiment, the frequency band of f7 to f8 and the frequency band of f to f10 cannot occupy the same band. However, each of the FM batch conversion signal and the second signal is converted into an optical signal. Any frequency band can be selected by multiplexing the signals and separating them at the optical signal stage and then converting them into electric signals.

FIGS. 5 and 6 show two structural examples of the multiplexed optical transmitter. In the configuration example shown in FIG.
41, and an optical transmitter 342. After the FM batch conversion signal and the second signal are multiplexed by the electric signal multiplexing unit 341, the electric signal is used as a modulation input, and the transmission semiconductor laser of the optical transmitter 342 is used. Is intensity-modulated. As the electric signal multiplexer 341, a power multiplexer is used. The configuration example illustrated in FIG. 6 includes two optical transmission units 343 and 344 and an optical multiplexing unit 345, and inputs the FM batch conversion signal and the second signal to separate optical transmission units 343 and 344 as modulation inputs. Then, the transmission semiconductor lasers having oscillation wavelengths different from λ ₁ and λ ₂ are intensity-modulated, and the obtained optical signals are multiplexed by the optical coupler of the optical multiplexing unit 345.

FIGS. 7 and 8 show examples of the configuration of a multiplexed optical receiver. The configuration example illustrated in FIG. 7 includes an optical / electrical conversion unit 531 and an electric signal distribution unit 532, and the optical / electrical conversion unit 531 converts a multiplexed signal light obtained by frequency-multiplexing the FM batch conversion signal and the second signal. The multiplexed electric signal is converted into an electric signal, and the multiplexed electric signal is frequency-separated by an electric signal distribution unit 532 to obtain an FM batch converted signal and a second signal. The configuration example illustrated in FIG. 8 includes a wavelength separation unit 533 and two optical / electrical conversion units 534 and 535, and a wavelength separation unit multiplexes the multiplexed signal light obtained by wavelength multiplexing the FM batch conversion signal and the second signal. After separation into different wavelengths of λ ₁ and λ ₂ , each optical signal is separated into a separate optical / electrical converter 53.
4 and 535 to obtain an FM batch conversion signal and a second signal.

[0028]

As described above, according to the present invention,
There is no restriction on the number of optical branches when the amplitude modulation signal is transmitted as it is, and no limitation on the number of optical branches due to the existing optical transmission line. Therefore, the maximum number of optical branches increased by using the FM batch conversion transmission method can be effectively used.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a view showing signal waveforms of respective units in the embodiment shown in FIG. 1;

FIG. 4 is a view showing signal waveforms of respective units in the embodiment shown in FIG. 2;

FIG. 5 is a block diagram illustrating a configuration example of an optical transmitter.

FIG. 6 is a block diagram showing another configuration example of the optical transmitter.

FIG. 7 is a block diagram illustrating a configuration example of an optical receiver.

FIG. 8 is a block diagram showing another configuration example of the optical receiver.

FIG. 9 is a block diagram showing a conventional example of transmitting an intensity-modulated optical signal as it is using a frequency multiplexed signal as a modulation input.

FIG. 10 is a block diagram showing a conventional example in which a second signal is frequency-multiplexed and transmitted to a multiplexed AM signal.

FIG. 11 is a block diagram showing a conventional example in which a multiplexed AM signal is collectively converted into a frequency modulation signal, and an intensity-modulated optical signal is transmitted using the modulation signal as a modulation input.

[Explanation of symbols]

 1, 2 input terminal 3 station side device 4 optical transmission line 5 subscriber side device 6, 7 output terminal 31, 38 FM batch converter 32, 39 optical transmitter 33 m branching device 34 multiplex optical transmitter 35 electric / optical conversion Device 36 optical signal amplifier 37 frequency multiplexing device 341 electric signal multiplexing unit 342, 343, 344 optical transmitting unit 345 optical multiplexing unit 51, 58 optical receiver 52, 59 FM demodulator 53 multiplexed optical receiver 55 optical / electrical converter 56 electric signal amplifier 57 frequency separation device 531 optical / electrical conversion unit 532 electric signal distribution unit 533 wavelength branching unit 534, 535 optical / electrical conversion unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/04 10/06 (72) Inventor Kiyomi Kumozaki Nippon Telegraph and Telephone Corporation 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Inside

Claims (4)

[Claims] 1. An optical transmission apparatus extension method for increasing the number of branches of an optical transmission apparatus in which an optical transmission path from one optical network unit is n-branched, wherein an amplitude obtained by frequency-multiplexing a modulation scheme in the optical network unit is provided. A modulation method for converting the modulation signal into a frequency modulation signal collectively is used. The electric signal converted into a frequency modulation signal by this modulation method is converted into an optical signal, and the optical signal is m-branched to each of the existing n-branches. A method for adding an optical transmission device, wherein the optical transmission device is connected to an optical transmission line. 2. The method for adding an optical transmission device according to claim 1, wherein m branching is performed in the optical line terminal. 3. An m-branched optical signal, an electric signal converted into a frequency modulation signal by the modulation method, and a second signal of a modulation method different in frequency from the electric signal and different from the modulation method. 3. The method for adding an optical transmission device according to claim 1, wherein the optical signal is electrically multiplexed, and the multiplexed output is used as a modulation input to use an intensity-modulated optical signal. 4. An m-branched optical signal, an electric signal converted into a frequency modulation signal by the modulation method, and a second signal of a modulation method different in frequency from the electric signal and different from the modulation method. 2 is used as a modulation input and two intensity-modulated optical signals are combined and used.
Or the method of adding an optical transmission device according to 2.