Optical waveguides – Having nonlinear property
Reexamination Certificate
1999-07-06
2002-02-12
Font, Frank G. (Department: 2877)
Optical waveguides
Having nonlinear property
C385S123000, C359S326000
Reexamination Certificate
active
06347174
ABSTRACT:
This application is a national phase of international application PCT/JP98/03010 filed Jul. 3, 1998 which designated the U.S.
TECHNICAL FIELD
The present invention relates to a nonlinear optical fiber for generating a nonlinear optical phenomenon with respect to input light, an optical fiber coil comprising the nonlinear optical fiber, and a wavelength converter comprising the nonlinear optical fiber or optical fiber coil as its component.
BACKGROUND ART
It has been known in general that, when light having a high intensity (high optical density) propagates through a medium, there occur various nonlinear optical phenomena due to the nonlinear polarization in the medium. For example, among these nonlinear optical phenomena, second-harmonic generation is a phenomenon caused by a second-order nonlinear effect, in which, when two photons having the same energy enter the medium, a new single photon having a doubled energy is generated. On the other hand, four-wave mixing is a phenomenon caused by a third-order nonlinear effect, in which, when three photons enter the medium, a new single photon is generated therefrom. These nonlinear optical phenomena occur with the highest efficiency when both energy conservation law and momentum conservation law hold true among the plurality of photons involved in the nonlinear optical phenomena.
Applications of wavelength conversion and the like using such nonlinear optical phenomena occurring in optical fibers have also been reported. For example, a first document of M. J. Homes, et al., IEEE Photon. Technol. Lett., Vol. 7 (1995) No. 9, pp. 1045-1047 reports a nonlinear optical fiber obtained when a dispersion-shifted optical fiber is doped with Ge (germanium) element. A second document of K. Inoue, et al., IEEE Photon. Technol. Lett., Vol. 4 (1992) No. 1, pp. 69-72 and a third document of K. Inoue, et al., Opt. Lett., Vol. 19 (1994) No. 16, pp. 1189-1191 report attempts at wavelength conversion using the four-wave mixing generated in a dispersion-shifted optical fiber.
In addition to the above-mentioned first to third documents, a fourth document of D. A. Pastel et al., OFC' 97 Technical Digest WL6b (1997) reports applications of nonlinear optical fibers and optical switches.
Further, in addition to the above-mentioned second and third documents, a fifth document of K. Inoue, IEEE Photon. Technol. Lett., Vol. 6 (1994) No. 12, pp. 1451-1453 reports a technique using the four-wave mixing in a dispersion-shifted optical fiber, which is a wavelength conversion technique in a wide wavelength band in which two excitation light beams having wavelengths different from each other are made incident on the optical fiber, and the wavelength of one of the excitation light beams is changed. Also, a sixth document of R. Ludwig, et al., Fiber and Integrated Optics, Vol. 15 (1996) pp. 211-223 reports an attempt at wavelength conversion using the four-wave mixing generated in a semiconductor amplifier.
DISCLOSURE OF THE INVENTION
Having studied the above-mentioned prior art, the inventors have found the following problems. Namely, in general, nonlinear optical phenomena occur weakly, with the third-order nonlinear optical phenomena being weaker than the second-order nonlinear optical phenomena, and therefore in any of the above-mentioned techniques it is necessary for the optical fiber to be elongated in order to attain nonlinear light (a new light component outputted as a result of a nonlinear optical phenomenon) having a sufficient intensity. In particular, for realizing a wavelength converter using the four-wave mixing generated in an optical fiber, the optical fiber for generating the nonlinear optical phenomenon is required to have a length of a few km or longer.
On the other hand, for realizing a wavelength converter or optical switch using a nonlinear optical phenomenon occurring in such an optical fiber, it is important technical problem to reduce the size of a coil constituting the optical fiber (hereinafter referred to as optical fiber coil). However, since the optical fiber is long as mentioned above, and its bending loss is large, it has been difficult for such an optical fiber coil to have a smaller size.
Meanwhile, the wavelength conversion technique disclosed in the above-mentioned sixth document is advantageous in that the apparatus itself can easily be made smaller since the four-wave mixing is generated in the semiconductor amplifier, and in that the band capable of wavelength conversion is wide, for example. Nevertheless, it has had a problem that noise is so high that the S/N ratio is low. By contrast, each of the wavelength conversion techniques disclosed in the second, third, and fifth documents is superior in terms of the S/N ratio since the four-wave mixing is generated in an optical fiber. Even in such a configuration, however, in order to attain converted light (a new light component generated by the wavelength conversion using the four-wave mixing) having a sufficient power, it is necessary for the optical fiber to have a length of a few km or longer, thus making it difficult for the optical fiber coil to reduce its size.
Also, due to the principle of the wavelength conversion using the four-wave mixing, the wavelength conversion efficiency is maximized when the excitation light wavelength is made to coincide with the zero-dispersion wavelength of the optical fiber, whereas the converted light drastically lowers its power as the difference between their wavelengths is greater. Hence, in the technique disclosed in the second document, the excitation light has a fixed wavelength, thereby the wavelength of the converted light is determined uniquely according to the signal light wavelength. Also, while the wavelength of the excitation light is made variable in the technique disclosed in the fifth document, the power of the converted light to be outputted would decrease as the wavelength shifts from the zero-dispersion wavelength. Namely, it has been very difficult to attain a wider band of wavelength conversion in the conventional wavelength converters using optical fibers.
In order to overcome the problems mentioned above, it is an object of the present invention to provide a nonlinear optical fiber which can generate a nonlinear optical phenomenon with high efficiency; an optical fiber coil, which can be made smaller, comprising the nonlinear optical fiber; and a wavelength converter with a compact configuration, which can output converted light having a desirable wavelength with high efficiency over a wide band, comprising the optical fiber coil or nonlinear optical fiber.
The nonlinear optical fiber according to the present invention is an optical fiber which generates a nonlinear phenomenon with respect to input light having a predetermined wavelength, e.g., one or more signal light components in the wavelength band of 1.55 &mgr;m (1500 nm to 1600 nm), comprises a core region and a cladding region provided at an outer periphery of the core region, and is mainly composed of SiO
2
. In order to realize a wavelength conversion technique for overcoming the above-mentioned problems, this nonlinear optical fiber has, as characteristics with respect to the input light, a mode field diameter (hereinafter referred to as MFD) of 5 &mgr;m or less, a polarization mode dispersion of 1 ps/km
½
or less, a zero-dispersion wavelength of not less than 1.5 &mgr;m but not greater than 1.6 &mgr;m, a cutoff wavelength of not less than 1.4 &mgr;m but not greater than 1.7 &mgr;m at a fiber length of 2 m, a transmission loss of 3 dB/km or less, and a nonlinear coefficient of at least 10/W/km.
Also, in the nonlinear optical fiber according to the present invention, at least the above-mentioned core region is doped with GeO
2
of not less than 15 mol % but not greater than 35 mol % on average, so as to realize a desirable refractive index profile. Thus, with respect to signal light in a desirable wavelength band (light in the 1.55-&mgr;m band having often been used recently), this nonlinear optical fiber not only generates a nonlinear phenomenon wi
Ishikawa Shinji
Kashiwada Tomonori
Nishimura Masayuki
Okuno Toshiaki
Onishi Masashi
Font Frank G.
McDermott & Will & Emery
Punnoose Roy M.
Sumitomo Electric Industries Ltd.
LandOfFree
Non-linear optical fiber, optical fiber coil, and wavelength... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-linear optical fiber, optical fiber coil, and wavelength..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-linear optical fiber, optical fiber coil, and wavelength... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2959225