Optical transmission system for substantially equalizing the output signal level among frequency bands and substantially lowering the signal-to-noise ratio
AssigneeHitachi, Ltd.
InventorsTetsuya Uda, Hiroshi Masuda, Hirofumi Nakano, Eita Miyasaka, Satoshi Asamizu
Life of this patent
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Abstract
In the WDM systems, the OSNR and the signal loss among the optical signals are substantially minimized at the receiving terminal to combat the SRS effects. An equal amount of the signal loss is expected for every span in the transmission path so that the optical amplifier gain tilt is not affected among a number of wavelength frequencies in the optical signal. This is accomplished by controlling the amplification process according to a feedback from the monitoring units for monitoring the optical signal.
Claims33
A method of controlling optical signal during transmission between a first unit and a second unit, comprising the steps of:
- transmitting a wave division multiplexed optical signal having a predetermined set of ranges of wavelengths from the first unit to the second unit;
- amplifying the wave division multiplexed optical signal at the first unit to generate an amplified wave division multiplexed optical signal;
- monitoring a first average value of a total optical strength level of at least one of the ranges of the amplified wave division multiplexed optical signal at the first unit;
- monitoring a first probe optical strength level of at least one of the wavelengths of the amplified wave division multiplexed optical signal at the first unit;
- monitoring at a second unit a second average value of a total optical strength level of the at least one of the ranges of a received wave division multiplexed optical signal from the first unit;
- monitoring at the second unit a second probe optical strength level of the at least one of the wavelengths of the received wave division multiplexed optical signal from the first unit;
- transmitting the second average value of a total optical strength level and the second probe optical strength level from the second unit to the first unit;
- and
- adjusting said amplification at the first unit so that a sum of the first average value and the second average value of the total optical strength level is substantially matched with a sum of the first probe optical strength level and the second probe optical strength level in order to substantially reduce a gain tilt and an optical signal-to-noise ratio in the amplified wave division multiplexed optical signal.
A system for controlling optical signal during transmission between a first unit and a second unit via optical fiber, comprising:
- said first unit further comprising:
- an amplifier connected to said first optical fiber for amplifying a wave division multiplexed optical signal having a predetermined set of ranges of wavelengths according to a predetermined amplification characteristic to generate an amplified wave division multiplexed optical signal, said amplifier outputting the amplified wave division multiplexed optical signal to said second unit;
- a first monitor for monitoring a first average value of a total optical strength level of at least one of the ranges of the amplified wave division multiplexed optical signal;
- a second monitor for monitoring a first probe optical strength level of at least one of the wavelengths of the amplified wave division multiplexed optical signal;
- and
- an adjustment unit connected to said amplifier for adjusting the amplification characteristic of said amplifier;
- said second unit further comprising:
- a third monitor for monitoring a second average value of the total optical strength level of at least one of the ranges of the received wave division multiplexed optical signal from the first unit;
- and
- a fourth monitor for monitoring a second probe optical strength level of at least one of the wavelengths of the received wave division multiplexed optical signal from the first unit;
- wherein said second unit sends the second average value of the total optical strength level and the second probe optical strength level to said first unit, and said adjustment unit adjusts the amplification characteristic so that a sum of the first average value and the second average value of the total optical strength level substantially matches a sum of the first probe optical strength level and the second probe optical strength level in order to substantially reduce a gain tilt and an optical signal to noise ration in the amplified wave division multiplexed optical signal.
Dependencies are inferred from the claim text.