Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
2001-02-28
2004-04-20
Bevarnick, Rodney (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S123000
Reexamination Certificate
active
06724966
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical transmission line which is used when, for example, a wavelength division multiplexed optical transmission is carried out.
BACKGROUND ART
The amount of communication information has tended to increase dramatically due to the development of the information society. Along with the increase of information, the wavelength division multiplexed transmission (WDM transmission) is widely recognized in the communication field and now the era of the wavelength division multiplexed transmission has arrived. In a wavelength division multiplexed transmission, light with a plurality of wavelengths can be transmitted in a single optical fiber. Therefore, the wavelength division multiplexed transmission is an optical transmission system which is suitable for large capacity high speed communication and, at present, this transmission technology is being vigorously researched.
As is widely known in the art, a single mode optical fiber, having a zero-dispersion within the wavelength band in the vicinity of the wavelength of 1.3 &mgr;m, has been established on a global scale as the transmission network for optical communication. However, in the case that the previously established single mode optical fiber having a zero-dispersion in the vicinity of 1.3 &mgr;m is utilized and wavelength division multiplexed transmission is carried out by using the wavelength band in the vicinity of 1.3 &mgr;m, the 1.55 &mgr;m wavelength band, which is the gain band of a conventional optical amplifier, and the wavelength band do not agree with each other. Therefore, the problem arises that a conventional optical amplifier cannot be utilized for the wavelength division multiplexed transmission which uses the above described single mode optical fiber and, subsequently, long distance optical communication becomes difficult. Here, the above used term, “55 &mgr;m wavelength band”, means a wavelength band of which the center is approximately the wavelength 1550 nm, such as from 1530 nm to 1570 nm, and hereinafter the term, the 1.55 &mgr;m wavelength band, is used with this meaning.
Therefore, recently a system for carrying out an optical transmission by using a dispersion shift optical fiber, of which the zero-dispersion wavelength is shifted from the vicinity of 1.3 &mgr;m to the vicinity of 1.55 &mgr;m, and the above described optical amplifier has been proposed in order to solve the above described problem. When an optical signal is transmitted at a wavelength in the vicinity of 1.55 &mgr;m by using a dispersion shift optical fiber having a zero-dispersion in the wavelength in the vicinity of 1.55 &mgr;m, a signal light is amplified by the optical amplifier and a signal transmission becomes possible with little waveform distortion by dispersion.
However, while research of wavelength division multiplexed transmission technology has progressed, light signals have become of a higher power and, in the case that a dispersion shift optical fiber is used for the wavelength division multiplexed transmission, a non-linearity phenomenon due to the mutual action between each signal wave arises as a new problem. Therefore, a dispersion shift optical fiber which controls the above described wavelength dispersion and dispersion slope and which makes it possible to lower the non-linearity phenomenon is desirable as a dispersion shift optical fiber for the wavelength division multiplexed transmission.
Concerning the study for the solving of the non-linearity phenomenon, research for controlling a four light wave mixture has always been vigorous. The four light wave mixture greatly influences waveform distortion and, therefore, it is important to control this four light wave mixture. As an example of the study of four light wave mixture control, academic paper OFC '94 Technical Digest PD19, for example, reports a dispersion shift optical fiber of which the zero-dispersion wavelength is shifted from the signal light wavelength in order to control the four light wave mixture.
When an optical fiber for optical transmission has a zero-dispersion in the signal light wavelength band, a four light wave mixture can easily be produced. Therefore, the above described paper reports that control of the four light wave mixture is possible by allowing the dispersion shift optical fiber used for the optical transmission to have a microscopic dispersion at the wavelength of 1.55 &mgr;m, which is the signal light wavelength. Here, the above described microscopic dispersion is a dispersion of which the absolute value of, for example, the local dispersion (a dispersion per unit length) is approximately 2 to 3 ps
m/km.
Since the waveform distortions by the SPM (Self-phase Modulation) or the XPM (Cross-phase Modulation) occurring in the above described non-linearity phenomenon has become a serious problem, there has recently been much research into controlling those waveform distortions. As for a means to solve this problem, the academic report OFC '97 TuN
1
b, or the like, report research aimed at limiting the non-linearity refractive index (n
2
) to a small value. Moreover, research aimed at making this non-linearity refractive index a small value and research aimed at making the effective core section area of the dispersion shift optical fiber (A
eff
) a large value have drawn attention. The distortion &phgr;
NL
of the signal through the non-linearity phenomenon is, in general, represented by the following equation (1). Therefore, when the effective core section area of the optical fiber is large the waveform distortion of the signal through the non-linearity phenomenon can be made small.
&phgr;
NL
=(2
&pgr;×n
2
×L
eff
×P
)/(&lgr;×
A
eff
) (1)
Here, in the equation (1), &pgr; represents the circular constant, L
eff
represents the effective optical fiber length, P represents a signal light intensity and &lgr; represents a signal light wavelength, respectively.
The above described effective core section area is expressed by the following equation (2) by using a constant k and the mode field diameter (MFD) of the optical fiber. Therefore, the larger the mode field diameter is, the larger the effective core section area becomes and it is understood that low non-linearity can be achieved very effectively.
A
eff
=k
×(
MFD
)
2
(2)
In this way the expansion of the mode field diameter and the expansion of the effective core section area in an optical fiber used for the wavelength division multiplexed transmission are very important and they have drawn a lot of attention. The expansion of the mode field diameter and the expansion of the effective core section area in an optical fiber used in the wavelength division multiplexed transmission are reported in the academic paper OFC '96 WK15 and OFC '97 YuN2.
It is known that the non-linearity phenomenon can be caused more easily when the signal light intensity inputted to the optical fiber is larger. Therefore, it is proposed in the Japanese Unexamined Patent Publication No. Hei-9(1997)-211511 that an optical transmission line be formed by connecting an optical fiber with high non-linearity to the emission end of an optical fiber with low non-linearity so that the light emitted from the optical transmission line is controlled so as not to cause distortion resulting from the non-linearity phenomenon. Here, this proposal describes that the waveform distortion by the dispersion is also controlled by making the symbols of the dispersion value mutually different within the 1.5 &mgr;m wavelength band of the above described optical fiber forming the optical transmission line.
As proposed in the Japanese Unexamined Patent Publication No. Hei-9(1997)-211511, however, no concrete configuration or the like are shown with respect to the dispersion value of the optical fiber forming the optical transmission line and, instead, merely the configuration of the connection of the optical fiber with high non-linearity to the emission end of the optical fiber with low non-linearity is sho
Bevarnick Rodney
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Stahl Mike
The Furukawa Electric Co. Ltd.
LandOfFree
Optical transmission line does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical transmission line, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical transmission line will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3244636