Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1997-12-09
2001-03-20
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S199200, C359S199200
Reexamination Certificate
active
06204959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a signal light monitor and an optical amplifier using the same, which are used in an optical communication system.
2. Description of the Related Art
In an optical communication, as one means for increasing transmission capacity, a wavelength multiplexed light transmission system for transmitting a plurality of optical signals of different wavelengths by one optical fiber has been used. With an increase in demand for long-distance transmission, the use of a system having an optical amplifier interpolated in an optical fiber transmission line has become general.
Among optical amplifiers, an optical fiber amplifier using an optical fiber doped with rare earth element in its core as a gain medium and a semiconductor amplifier using stimulated emission phenomena inside a semiconductor are known. As a commercially available optical amplifier at present, an optical fiber amplifier is typically used.
In an optical communication system, in order to facilitate system maintenance, there has been an increase in demand for a function for monitoring a power of an optical light propagated on an optical fiber transmission line, its wavelength, its signal-to-noise ratio, fluctuation in a signal light wavelength, and so on, in a connection point between a terminal station device or an optical amplifier and the optical fiber transmission line. In the light amplifier, a level for sending out a light to the optical fiber transmission line is maintained constant and a transmission characteristic is made stable. Accordingly, its signal light output must be maintained constant. Also, a function for monitoring a signal light must be provided for controlling the operation of the optical amplifier.
Conventionally, as such an optical signal monitor, an optical signal power monitor installed inside an optical fiber amplifier has typically been used. In this conventional monitor, an optical branching device is disposed in the light output section of the optical amplifier. A part of a light output is branched by the optical branching device and received by an optical receiver. A pumping light output power of a pumping light source is controlled so that the level of this received light becomes constant. In this way, a light output of the optical fiber amplifier is maintained constant. However, if a signal light monitor for system maintenance employs the above-described system which is constructed in the manner that the optical branching device is disposed in the optical fiber transmission line and a branched light is received by the optical receiver, it is full light power including noise light that can be monitored. Consequently, even if this conventional system is used for the signal light monitor for system maintenance, a signal to noise ratio of a signal light, signal light power of each signal light wavelength of a wavelength multiplexed optical signal or fluctuation in a signal light wavelength cannot be monitored.
Furthermore, if the foregoing system were used as a monitor for controlling the optical amplifier, the following problem is involved in the conventional system. Generally, the optical amplifier outputs not only an amplified signal light and but also an amplified spontaneous emission (ASE) from a gain medium.
Consequently, it is impossible to monitor only signal light power in reality. A ratio of ASE light power in the entire output light power is changed according to an input light level of the optical amplifier. Thus, even if an output light level monitored by the optical receiver is controlled to be constant, signal light output power cannot be maintained constant.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide signal light monitor for realizing a function for monitoring power of each signal light for each signal light wavelength of a wavelength multiplexed signal light and a function for monitoring a signal light wavelength of a wavelength multiplexed signal light.
It is a second object of the present invention to provide an optical amplifier having a function for accurately controlling a signal light output to be constant irrespective of a spontaneously emitted light. In this case, the optical amplifier enables monitoring of a noise figure for each signal light wavelength of an amplified wavelength multiplexed signal light.
The first objective of the present invention is achieved by a signal light monitor, which comprises a first optical branching device disposed in an optical fiber transmission line for branching a part of an inputted signal light and outputting a first branched light, a first wavelength tunable filter for transmitting a first particular wavelength component of the first branched light and outputting a transmitted light and a first sweeper for sweeping a transmission center wavelength of the first wavelength tunable filter within the first particular wavelength range.
The signal light monitor of the present invention further comprises a first optical receiver for receiving a transmitted light outputted from the wavelength tunable filter and converting this light into an electric signal and a first sampling device for sampling a first electric signal and outputting first sampling data. The first sampling data is taken out from a first storage device for continuously storing the first sampling data on order of the time. Thus, the wave form of the first electric signal is stored in the first storage device as series of sampled data.
The signal light monitor yet further comprises first arithmetic processing section for identifying the existence of a signal light by detecting a steep change of the data stored in the first storage device, and for detecting a signal light power from a peak level of the steep change. The first arithmetic processing section also measures a signal light wavelength from a time when a peak of the steep change appears in the waveform stored in the first storage device. Furthermore, the first arithmetic processing section detects a noise light level from a bottom level of the steep change in the waveform, and calculates signal-to-noise ratio from the noise level and the above-described signal level.
The first wavelength tunable filter provided in the signal light monitor includes any one of an interference filter using a dielectric multilayer film, a Fabry-Perot etalon, a waveguide and a fiber grating.
The second objective of the present invention is achieved by a light amplifier, which comprises an optical amplifying section for amplifying an inputted signal light and outputting the amplified signal light and a first optical branching device for a signal light monitor having the above-described characteristics, the branching coupler being disposed in the output side of the light amplifying section.
The optical amplifier also comprises a signal light level control section for controlling the output of an optical amplifying section so as to maintain a signal light level constant. The light amplifier comprises a light amplification stopping function for stopping the operation of the light amplifying section if no signal light exists, based on the result of identifying the existence of a signal light by an arithmetic processor.
The optical amplifier is a light amplifying section for amplifying an inputted signal light and outputting the amplified signal light, and a signal light monitor having the above-described characteristics is disposed in the input side of the light amplifying section.
The optical amplifier comprises signal light monitors having the above-described characteristics in both input and output sides, and the above-described arithmetic processing section for perform the calculation based on the both the first and second storage device. The optical amplifier comprises a light amplification gain control function for calculating a gain of the light amplifying section based on a ratio between a signal light level of a signal light inputted to the light amplifying section and a signal light level of the output side and co
Fujita Masayuki
Saeki Miwa
Hellner Mark
NEC Corporation
Whitham, Curtis & Whitham
LandOfFree
Signal light monitor and optical amplifier using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Signal light monitor and optical amplifier using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Signal light monitor and optical amplifier using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2449859