JPH0923193A - Optical signal transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently execute distortionless subcarrier multiplexed transmission by simple device constitution by independently multiplexing a data signal and a control signal with a subcarrier and transmitting the multiplexed subcarrier. SOLUTION: Steady light to be a light carrier signal from a light source 11 is branched by a photocoupler 12 and branched signals are respectively supplied to a main signal light modulator 13 and a control signal modulator 14 and output signal light components from the modulators 13, 14 are multiplexed by a polarized wave multiplexer 15 in a state that respective polarized waves mutually interset at right angles. Since a main signal and a control signal are respectively independently converted into optical signals and orthogonally multiplexed, signal light independently multiplexing respective optical signals with a sub-carrier without mutually exerting influence upon the optical signals can be obtained. In a relay node or a receiver, the signal light is converted into an electric signal and a main signal component and a control signal component are extracted through an electrid filter to obtain the main signal or the control signal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the transmission of optical signals. In particular, the present invention relates to an optical signal transmitter that superimposes and transmits different signals on different carrier frequency bands.

[0002]

2. Description of the Related Art In an optical transmission system, not only a data signal to be transmitted (hereinafter referred to as "main signal") but also a control signal for monitoring or controlling a transmission system is sent. For example, information about the destination of the main signal and a monitor signal for monitoring the operating state of each transmission device are transmitted as control signals. Since the amount of information transmitted as the control signal is sufficiently smaller than that of the main signal, its transmission speed may be sufficiently lower than that of the main signal.

A simple method of transmitting the control signal is to fold the control signal sequence into the main signal sequence by time division multiplexing. However, this method is not efficient because it is necessary to demodulate all the signals together with the main signal and take out the control signal sequence from the main signal when it is desired to read only the control signal at a node in the middle of the transmission system.

As a method of avoiding such complexity, there is a method of using subcarrier multiplexing. For example, if the transmission speed of the main signal is B [bit / s], the frequency spectrum of the transmission signal has a spread of about B [Hz]. On the other hand, a frequency out of the spectrum spread of the main signal is set as a carrier frequency, and the carrier frequency component is modulated by the control signal. On the receiving side, a filter is used to extract only the carrier frequency component of the control signal. Only the control signal can be obtained. In this case, since it is not necessary to demodulate the main signal component, it is possible to obtain the control signal with a simpler configuration than the method using time multiplexing. Hereinafter, a carrier frequency component different from the main signal is referred to as "subcarrier", and multiplexing a plurality of signals using subcarriers is referred to as "subcarrier multiplexing".

Next, a case where the control signal transmission method by subcarrier multiplexing is used for an optical transmission system will be described. In optical transmission, a Mach-Zehnder optical modulator is often used to convert an electric signal into an optical signal. As a direct method of performing carrier multiplexing using a Mach-Zehnder optical modulator, subcarrier multiplexing is performed at the electrical stage,
There is a method of driving the Mach-Zehnder optical modulator by the signal.

[0006]

However, this method has a problem in relation to the modulation characteristic of the Mach-Zehnder optical modulator. This will be described with reference to FIG. 5 showing the relationship between the modulation characteristic of the Mach-Zehnder optical modulator and the drive electric signal.

The modulation characteristic of the Mach-Zehnder optical modulator is shown in FIG.
As shown in (3), it is sinusoidal and is not linear with respect to the drive signal. Therefore, if the Mach-Zehnder optical modulator is driven by the subcarrier-multiplexed signal as it is, the output signal is distorted. For example, "1",
When transmitting a digital signal of "0", in order to obtain the maximum modulation efficiency, the applied voltage corresponding to "1" is the peak position of the sinusoidal curve, and the voltage corresponding to "0" is the valley position. It is common to set However, if the control signal is superimposed on this with subcarrier multiplexing, the superimposed component is folded back at the peaks or valleys of the sinusoidal curve of the modulation characteristic, and the output subcarrier frequency becomes a double wavelength. .

In order to avoid this, the amplitude of the main signal component is made small, and the maximum and minimum of the drive voltage in the subcarrier multiplexed state are set so as to correspond to the peaks and valleys of the modulated sine wave curve, respectively. do it. However, with such a setting, the amplitude of the main signal must be set according to the amplitude of the subcarrier signal. That is, the two cannot be set independently. Therefore, the system setting becomes complicated. Also, although there is no folding back at the peaks or valleys of the sinusoidal curve, the subcarrier component is modulated in a region with poor linearity, resulting in a distorted signal with high frequency components.

An object of the present invention is to solve the above problems and to provide an optical signal transmitter capable of efficiently transmitting a plurality of signals by subcarrier multiplexing.

[0010]

The present invention is characterized in that a main signal component and a control signal component are independently subcarrier-multiplexed.

That is, the optical signal transmitting apparatus of the present invention is an optical signal transmitting apparatus for modulating and transmitting one optical carrier signal by two signals having different carrier frequency bands,
A branching means for branching the optical carrier signal output from one light source into two, a modulating means for independently modulating the two optical carrier signals branched by the branching means by the two signals, and a modulating means And a multiplexing unit that multiplexes the obtained two optical signals. The multiplexing means may include a polarization multiplexer that multiplexes the two optical signals with their polarizations substantially orthogonal to each other. As two signals having different carrier frequency bands, one of them can be a data signal to be transmitted, and the other can be a control signal for managing and controlling the transmission system.

The relay node for relaying the optical signal thus transmitted or the optical signal receiving device for receiving the optical signal has means for directly converting a part or all of the transmitted signal light into an electric signal. And a means for extracting one or both of two signals having different carrier frequency bands from the electric signal.

[0013]

1 is a block diagram showing the configuration of an optical transmission device for performing signal transmission by subcarrier multiplexing.
This optical transmission device is provided with an optical signal transmission device 1 and modulates one optical carrier signal by a main signal and a control signal having different carrier frequency bands, that is, performs subcarrier multiplexing and transmits. This subcarrier-multiplexed signal light is transmitted via the transmission path 2 and the relay node 3, and is received by the optical signal receiving device 4. Each relay node 3 extracts a control signal from the transmitted signal light and manages and controls the transmission system based on the extracted control signal.

FIG. 2 is a block diagram showing the details of the optical signal transmitter 1 and shows an embodiment of the present invention. The optical signal transmitter 1 includes an optical coupler 12 that branches an optical carrier signal output from one light source 11 into two, and two optical carrier signals that are branched by the optical coupler 12 as a main signal and a control signal ( Optical modulators 13 and 14 that are independently modulated by subcarriers, and polarization multiplexers that combine the two optical signals obtained by the optical modulators 13 and 14 so that the polarizations thereof are substantially orthogonal to each other. And 15.

The light source 11 outputs stationary light as an optical carrier signal, and this stationary light is input to the optical modulators 13 and 14 branched by the optical coupler 12. Light modulator 13, 14
The output lights from are combined by the polarization combiner 15 with their polarizations orthogonal to each other. Here, the optical modulator 13 is driven by the main signal and the optical modulator 14 is driven by the control signal, and the main signal and the control signal are independently converted into the optical signal. Then, the modulated lights are added together by the polarization multiplexer 15.
Since the additions are performed so that the polarized waves are orthogonal to each other, they do not affect each other. That is, the main signal and the control signal are independently subcarrier-multiplexed at the optical signal stage. Therefore, with the configuration of FIG.
It is possible to obtain signal light in which the main signal component and the control signal component are independently subcarrier-multiplexed.

FIG. 3 is a block diagram showing a configuration example of the relay node 3. The relay node 3 includes an optical coupler 31, a light receiver 32, and an electric filter 33. The optical coupler 31 splits a part of the signal light sent to the optical receiver 3
2 directly converts the branched signal light into an electric signal. This electric signal includes a main signal component and a control signal component, and the control signal can be obtained by extracting the control signal component (carrier frequency component on which the control signal is carried) by the electric filter 33. it can.

FIG. 4 is a block diagram showing a configuration example of the optical signal receiving device 4. The optical signal receiving device 4 includes a light receiver 41.
And electrical filters 42, 43. The light receiver 41 converts the transmitted signal light into an electric signal, and the electric filter 42 extracts the main signal component and the electric filter 43 extracts the control signal component. As a result, both the main signal and the control signal can be obtained.

Here, the case where the relay node 3 extracts only the control signal and the optical signal receiving device 4 which is the final end of the transmission system extracts both the main signal and the control signal has been described. However, the main signal may be extracted, or the optical signal receiving device 4 may be configured to extract only the control signal.

The signal transmitted by subcarrier multiplexing is not limited to the main signal and the control signal, and the present invention can be similarly applied to the case of subcarrier multiplex transmission of two general signals. .

[0020]

As described above, the optical signal transmitter of the present invention independently transmits two signals by subcarrier multiplexing. This enables efficient subcarrier multiplex transmission with a simpler device configuration than the conventional one.

[Brief description of drawings]

FIG. 1 is a block configuration diagram showing an optical transmission device that performs signal transmission by subcarrier multiplexing.

FIG. 2 is a block configuration diagram showing details of an optical signal transmission device.

FIG. 3 is a block diagram showing a configuration example of a relay node.

FIG. 4 is a block diagram showing a configuration example of an optical signal receiving device.

FIG. 5 is a diagram showing a relationship between a modulation characteristic of a Mach-Zehnder optical modulator and a drive electric signal.

[Explanation of symbols]

 1 Optical signal transmitter 2 Transmission line 3 Relay node 4 Optical signal receiver 11 Light source 12 Optical coupler 13, 14 Optical modulator 15 Polarization multiplexer 31 Optical coupler 32, 41 Light receiver 33, 42, 43 Electric filter

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Claims (3)

[Claims] 1. An optical signal transmitter for modulating and transmitting one optical carrier signal by two signals having different carrier frequency bands, and a branching unit for branching an optical carrier signal output from one light source into two. A modulation means for independently modulating the two optical carrier signals branched by the branching means by the two signals, and a multiplexing means for multiplexing the two optical signals obtained by the modulation means. An optical signal transmitter characterized by: 2. The optical signal transmission device according to claim 1, wherein the multiplexing means includes a polarization multiplexer for multiplexing the two optical signals by causing polarizations to be substantially orthogonal to each other. 3. The optical signal according to claim 1, wherein one of the two signals having different carrier frequency bands is a data signal to be transmitted and the other is a control signal for managing and controlling a transmission system. Transmitter.