Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
1997-11-18
2001-03-06
Lee, John D. (Department: 2874)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S144000, C359S341430, C372S006000
Reexamination Certificate
active
06198870
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical waveguide and a 1.5 &mgr;m-band optical amplifier in which the optical waveguide is used.
Hitherto, the light amplifying silica glass fiber containing an activation ion of Er has been used in the optical amplifier for amplifying 1.5 &mgr;m optical signals. Thus, this glass fiber has played an important role in making the optical communication high-speed. In such optical amplifier, the Er ions can be excited by a pump light having a wavelength of 1.48 &mgr;m or 0.98 &mgr;m. As a result, the light emission of 1.5 &mgr;m-band can be obtained through the stimulated emission transition of
4
I
13/2
→
4
I
15/2
, as shown in FIG.
1
. It is known that an optical amplifier using the excitation at 0.98 &mgr;m has a lower noise than that of another optical amplifier using the excitation at 1.48 &mgr;m. In recent years, the wavelength multiplex communication system has drawn much attention in the course of the increase of the communication capacity. Thus, it has been required to get a light amplifying medium which can achieve an effective light amplification in a wide band. In view of this, there have been recent studies on the widening of the band of Er-doped silica fibers and on Er-doped halide glasses and Er-doped chalcogenide glasses. It is known that an optical waveguide and an optical fiber used therefor, which are made of Er-doped halide glass, Er-doped chalcogenide glass or oxyhalide glass glasses are expected to become a light amplifying medium used for the 1.5 &mgr;m -band wavelength multiplex communication. However, if the Er ions contained in these glasses are excited at 0.98 &mgr;m in an optical amplifier, the excited state absorption (ESA) of the Er ions tends to occur, as shown in FIG.
1
. The reason of this is that the phonon energy of halide glass, chalcogenide glass or oxyhalide glass is lower than that of oxide glass. With this, the chance of the occurrence of the multiphonon relaxation of the Er ions by the transition of
4
I
11/12
→
4
I
13/2
becomes small, and thus the fluorescent life time becomes long in the
4
i
11/12
level. As a result, the ESA loss of the Er ions increases, and thus the amount of the pump energy directed to the stimulated emission at 1.5 &mgr;m-band is decreased. With this, the amplification efficiency is lowered. Thus, it has been impossible to prepare an optical amplifier having low noise and wide band by using halide glass, chalcogenide glass or oxyhalide glass. In order to prepare such optical amplifier, it becomes necessary to shorten the fluorescent life time of the Er ions in the
4
I
11/12
level, In view of this, Japanese Patent Unexamined Publication No. 8-222784 discloses a light amplifying fiber containing in its core both of a first dopant of Er and a second dopant which is at least one selected from Tb, Dy and Eu. However, this second dopant may absorb the pump light and/or the signal light and thus decrease the amplification efficiency, in case that the absorption wavelength is varied by the effect of the host material composition, or that the second dopant is added in large amount.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a 1.5 &mgr;m-band optical amplifier having an optical waveguide having an Er-doped core made of halide glass, chalcogenide glass or oxyhalide glass, which amplifier has an effective light amplification by the excitation at 0.98 &mgr;m-band.
It is another object of the present invention to provide such optical waveguide.
According to the present invention, there is provided an optical waveguide comprising a core made of one member selected from the group consisting of halide glasses, chalcogenide glasses and oxyhalide glasses, The one member is doped with both of erbium (Er) and cerium (Ce).
According to the present invention, there is further provided a 1.5 &mgr;m-band optical amplifier comprising:
(a) a pump light source for producing a pump light;
(b) an optical multiplexer for combining said pump light with a signal light, to produce a combined light;
(c) the above optical waveguide for amplifying said signal light by receiving said combined light; and
(d) an optical isolator for suppressing a noise caused by a reflected light.
According to the present invention, the core of the optical waveguide is doped with both of erbium and cerium. With this, the ESA of the Er ions is effectively suppressed even in a particular glass (halide glass, chalcogenide glass or oxyhalide glass) having a low phonon energy. Therefore, it becomes possible to provide a highly efficient optical amplifier having low noise and wide band. With This, it becomes possible to construct an optical communication network having high credibility, high capacity and high speed.
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Y.G. Choi et al., “Enhanced 41 11/2 to 41 13/2 transition rate in Er3+ / Ce3+ codoped tellurite glasses”, Electronics Letters, vol. 35, No. 20, pp. 1765-1767, Sep. 1999.
Yu et al., Special characteristics of Er(3 +)-activated and Ce(3 +)-sensitized yttrium aluminium garnet laser crystals. J. Alloys and Compounds 217 (1995), 148-150, Jan. 1995.
“Yb3+energy transfer and rate-equations formalism in the eye safe laser material Yb:Er:Ca2Al2SiO7” B. Simondi-Teisseire, B. Viana, D. Vivien, A.M. Lejus, Optical Materials 6(1996) 267-274—(Nov.).
“Spectroscopic Investigation of the ER3+ Fluroescence Transitions at 540 NM and 1.5 M in Fluoride Phosphate and Phosphate Glasses” Ebendorff-Heidepriem H et al, Glastenchnische Berichte, vol. 66, No. 9, Sep. 1, 1993, pp. 235-244, XP000397565.
Kubota Yoshinori
Nishimura Natsuya
Central Glass Company Limited
Evenson, McKeown, Edwards & Lenahan P.L.L.C.
Lee John D.
Stahl Michael J
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