FR2762733A1 - OPTICAL SIGNAL AMPLIFICATION CONTROL SYSTEM - Google Patents

Abstract

To amplify in bulk an optical signal multiplexed in wavelength in which several signals with different wavelengths to be transmitted on a fiber optic cable are multiplexed, the system comprises means for always detecting the number of different wavelengths and means for block amplification of the multiplexed signal. The system controls the amplification means to amplify the multiplexed signal in block to a desired level according to the number detected.

Description

OPTICAL SIGNAL AMPLIFICATION CONTROL SYSTEM

DESCRIPTION

  Technical Field The present invention relates to an optical signal amplification control system for amplifying a wavelength-multiplexed optical signal with different wavelengths to be transmitted over a fiber optic cable, and more particularly relates to a control system optical signal amplifier used to amplify a signal

  optical multiplexed in wavelength in block.

  STATE OF THE PRIOR ART It is well known that an optimal output power of the optical signal is necessary in a long distance transmission over a fiber optic cable since if the output power is

  too low or too high this poses problems.

  Therefore, in the long-distance transmission of an optical signal over a fiber optic cable, a wavelength-multiplexed signal is amplified as a block to obtain optimum output power using repeater amplifiers

  placed at multiple repeat points.

  The first of the conventional amplification control systems operates by storing a predetermined reference level in a repeater amplifier, by amplifying an optical signal to be input as far as the reference level, and then by

providing this signal as an output.

  The second system operates by transmitting wavelength multiplex number information from a transmitting end to a repeater amplifier and performing amplification in the repeater amplifier based on the wavelength multiplex number information wave. At the same time, in such a conventional optical signal amplification control system, the total output power of an optical signal wavelength-multiplexed is controlled so as to be constant even during the optical signal amplification in which multiple signals with different

  wavelengths are multiplexed in wavelength.

  However, in such a command, the output power for each signal (wavelength) must be modified according to the number of multiplexed wavelengths. Namely, the greater the number of multiplexed wavelengths, the more the light output power per wavelength is reduced. The optimal output power per wavelength should vary depending on the number of multiplexed wavelengths. Thus, it is desirable that an optimal output power value can be determined as a function of the information on the number of wavelength multiplexes when amplifying a wavelength multiplexed signal. Furthermore, it is desirable that an optimal output power value can be modified in real time as a function of a variation in the number of wavelengths multiplexed in an optical communication such as

  the number of multiplexed wavelengths can vary.

  However, the first system cannot be adapted to the variation in the number of multiplexed wavelengths. The second system involves the transmission of wavelength multiplex number information from a transmitting end to a repeater amplifier, thereby increasing the amount of information to be transmitted over the fiber cable.

  optical and making the system all the more complex.

  In addition, when a light wave network using only light is built in the future, the number of multiplexed wavelengths to be transmitted over a fiber optic cable will be dynamically changed. In such a case, the number of wavelengths in the second system is very

difficult to manage.

  In addition, erroneous wavelength number information may be transmitted due to the presence of noise, etc. If the second system is controlled by such erroneous information, it may result in an optical signal transmission error. SUMMARY OF THE INVENTION Consequently, the object of the present invention is to propose an optical signal amplification control system which can carry out optimal controls of the output power as a function of the number of wavelengths multiplexed without transmitting d number of multiplexings in

  wavelength from a transmitting end.

  Another object of the invention is to provide an optical signal amplification control system which can perform optimal control of the output power in real time even when the number of wavelengths in an optical signal multiplexed in length input waveform is

dynamically changed.

  According to the invention, an optical signal amplification control system, intended for block amplifying a wavelength multiplexed signal in which several optical signals with different wavelengths to be transmitted over a fiber optic cable are multiplexed, characterized in that it comprises: means for always detecting the number of different multiplexed wavelengths in the wavelength multiplexed signal; and amplification means for block amplifying the wavelength-multiplexed signal; and in that the optical signal amplification control system controls the amplification means for block amplifying the wavelength multiplexed signal to a desired level according to the detected number of lengths

different wave.

Brief description of the drawings

  The invention will be explained in more detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram showing an optical signal amplification control system in a preferred embodiment according to

the invention.

  Description of preferred embodiments

  An optical signal amplification control system according to the preferred embodiment will be

  explained with reference to Figure 1.

  With reference to FIG. 1, 1 is an optical coupler for monitoring the input, 2 is a wavelength division multiplex (WDM) optical coupler for multiplexing an input signal and an excitation laser light, and 3 is a fiber erbium doped (EDF) which is obtained by doping an optical fiber with the erbium ion and which amplifies an optical signal in the band of 1.55 mt when an excitation light at 1.48 gm

is applied in it.

  In addition, 4 is an optical coupler for monitoring the output, 5 is a phase grating or PHASAR (AWG) device intended for demultiplexing the wavelength-multiplexed light supplied as input into lights of different wavelengths, 6 is an excitation laser light source (hereinafter called "excitation DL"), 7 is an automatic output power control (APC) circuit, 8 is a photodetector (PD), and 9 is a photodetector in network (hereinafter called "network PD") In parallel, means for detecting the number of wavelengths, which are defined here, consist of the optical coupler for monitoring input 1, of PHASAR (AWG) 5 and of the network PD 9. In addition, amplification means, which are defined here, consist of the excitation DL 6, the optical coupler with wavelength multiplexing 2 and the erbium-doped fiber 3 In addition, the control of the amplification means as a function of the number of mult wavelengths Iplexed, which is defined here, is carried out by the optical coupler to monitor the output 4 and the APC circuit 7 to which the information of number of wavelengths is delivered by the means of

  detection of number of wavelengths.

  In operation, an optical signal in which several optical signals with different wavelengths are multiplexed (wavelength multiplexed signal) is input on the input side (INPUT), then part of the wavelength multiplexed signal is separated from its main signal by the optical coupler to monitor input 1 and applied to the PHASAR (AWG) 5. The PHASAR (AWG) 5 divides the wavelength-multiplexed signal applied to it into several signals with lengths different wavelengths, and these different divided signals with different wavelengths are received, as they are, by the

  network photodetector (network PD) 9.

  So the number of wavelengths in the wavelength multiplexed signal to be entered on the side

  input can be detected.

  At the same time, the optical coupler for monitoring input 1, the PHASAR (AWG) 5 and the network PD 9 can operate in real time. Therefore, even when the number of wavelengths in the input wavelength multiplexed signal arriving at the input side (INPUT) is likely to vary, the change may be

detected in real time.

  Thus, the information concerning the number of wavelengths (number of signals) to be detected by the network PD 9 is sent to the APC circuit 7 to automatically control the light output power. The APC circuit 7 chooses an optimal output power according to the number of wavelengths on the basis of this information, by controlling the excitation DL

  6 to provide the selected optimal output power.

  Furthermore, the main signal is multiplexed with the optical output of the excitation laser diode 6 by the optical coupler with wavelength multiplexing 2, entered into the fiber doped with erbium 3, amplified by the fiber doped with erbium 3, and output via the optical coupler to monitor output 4 on the output side (OUTPUT). This time, part of the output signal is divided by the optical coupler to monitor output 4, whose level of

  output is monitored by photodetector 8.

  The monitored information is then delivered to the

  APC 7 circuit, thus ensuring a counter control

reaction.

  Thus, the APC circuit 7 determines an optimal value of the entire amplification level of the wavelength-multiplexed signal as a function of the information on the number of multiplexing wavelengths obtained from the network photodetector 9, and provides feedback control of the drive current of the excitation DL 6 so that the level of the output signal can have this optimum value

  while monitoring the output signal level.

  Although, in this embodiment, the means for detecting the number of wavelengths consist of the optical coupler for monitoring the input 1, of the PHASAR (AWG) 5 and of the network photodetector 9, they are not limited to this composition. The means for detecting the number of wavelengths can be any means consisting of means for separating a part of the wavelength-multiplexed signal to be transmitted, means for dividing the separated part of the multiplexed signal in wavelength wave in lights of different wavelengths and means for detecting the divided lights of different wavelengths

  in order to count the number of wavelengths.

  Although, in the present embodiment, the amplification means consist of the excitation DL 6, the optical coupler with wavelength multiplexing 6 and the fiber doped with erbium 3, they do not not limit to this composition. The amplification means can be any means capable of amplifying the multiplexed signal as a whole.

  wavelength up to a desired level.

  Although the invention has been described with reference to a specific embodiment for a

  complete and clear description, the claims

  annexed should not be so limited but should be understood as covering all modifications and construction variants which may appear to those skilled in the art and which enter

  precisely in the basic education stated here.

Claims (6)

  1. Optical signal amplification control system for block amplifying a wavelength-multiplexed signal in which several optical signals with different wavelengths to be transmitted over a fiber optic cable are multiplexed, characterized in that it comprises: means for always detecting the number of said different multiplexed wavelengths in said wavelength multiplexed signal; and amplifying means for block amplifying said wavelength-multiplexed signal; and in that said optical signal amplification control system controls said amplification means for block amplifying said wavelength-multiplexed signal to a desired level based on said detected number of said different wavelengths.   2. An optical signal amplification control system according to claim 1, in which: said means for detecting the number of wavelengths comprises separation means for separating part of said wavelength-multiplexed signal to be transmitted, means for dividing said separate portion of said wavelength-multiplexed signal into lights with different wavelengths, and counting means for counting said number of said different multiplexed wavelengths in said wavelength-multiplexed signal into detecting said lights divided with different lengths wave.   The optical signal amplification control system according to claim 2, wherein: said separation means comprises a phase grating device (5), and said counting means comprises a grating photodetector (9). The optical signal amplification control system according to claim 1, wherein: said amplifying means comprises an excitation laser light source (6), an optical coupler with wavelength division multiplexing (2) for multiplexing excitation light from said excitation laser light source with said wavelength-multiplexed signal, and a fiber doped with erbium (3).   The optical signal amplification control system according to claim 1, further comprising: feedback control means of said amplification means to ensure that said wavelength-multiplexed signal is output with said desired level based on said detected number of said different wavelengths while   monitoring the output level after amplification.   The optical signal amplification control system according to claim 5, wherein: said feedback control means determines said desired level based on said detected number of said different wavelengths and controls said amplification means for amplify said multiplexed signal in block   wave until said desired level.