Optical-level control method, optical-level control apparatus and wavelength-multiplexing optical network

An optical-level control method, comprising:

• demultiplexing a wavelength division multiplexed signal into optical signals corresponding to each wavelength of the wavelength division multiplexed signal, and supplying each optical signal to a respective variable optical attenuator of a plurality of optical attenuators, corresponding to the wavelength of the optical signal, the respective variable optical attenuator outputting an output optical signal having an optical level of a constant value;
• detecting a loss of light of an optical signal when an optical level of said optical signal directly input to a variable optical attenuator is lower than a predetermined threshold;
• setting an attenuation quantity of said variable optical attenuator for the wavelength for which said loss of light has been detected, at a fixed value determined in advance, when said loss of light is detected;
• and
• controlling said variable optical attenuator for the wavelength for which said loss of light has been detected, to return to said constant value when a predetermined trigger occurs.

An optical-level control method, comprising:

• demultiplexing a wavelength division multiplexed signal into optical signals corresponding to each wavelength of the wavelength division multiplexed signal, and supplying each optical signal to a respective variable optical attenuator corresponding to the wavelength of the optical signal, the respective variable optical attenuator outputting an output optical signal having an optical level of a constant value;
• detecting a loss of light of an optical signal for any wavelength, when an optical level of said optical signal directly input to a variable optical attenuator for a wavelength of said wavelengths is lower than a predetermined threshold;
• and
• maintaining said attenuation quantity applied by said variable optical attenuator for the wavelength at which said loss of light has been detected at an attenuation quantity before said loss of light is detected and controlled.

A method of adjusting optical level of an individual wavelength component of a wavelength division multiplexed optical signal, comprising:

• demultiplexing a wavelength division multiplexed signal into optical signals corresponding to each wavelength of the wavelength division multiplexed signal, and supplying each optical signal to a respective variable optical attenuator of a plurality of variable optical attenuators, corresponding to the wavelength of the optical signal, the respective variable optical attenuator maintaining a level of an output optical signal having a constant value;
• setting an attenuation of a variable optical attenuator at a reference value when a level of an optical signal directly input to the variable optical attenuator, is lower than a predetermined value;
• and
• returning to adjusting the attenuation of said variable optical attenuator for the wavelength component in a feedback loop for maintaining the level of the output optical signal to the constant value, after a predetermined time elapses or after a predetermined trigger occurs.

A method of adjusting attenuation of variable optical attenuators, comprising:

• demultiplexing an wavelength division multiplexed optical signal into individual wavelength components and inputting each individual wavelength component to a variable optical attenuator which maintains a constant power output;
• setting attenuation of a variable optical attenuator, at a reference value, when power of the individual wavelength component directly input to said variable optical attenuator, is lower than a predetermined value;
• and
• returning said variable optical attenuator to maintaining the constant power output for the individual wavelength component, after a predetermined time elapses or after a predetermined trigger event occurs.