Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1997-07-09
2001-11-13
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
Reexamination Certificate
active
06317253
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical amplifier apparatus for amplifying a signal light having wavelengths of 1.06 &mgr;m band, and in particular, to a 1.06 &mgr;m band optical amplifier apparatus utilizing an induced emission in an optical fiber by an excited rare-earth element.
2. Description of the Related Art
Conventionally, direct amplification of a signal light of 1.06 &mgr;m band wavelengths has been implemented by using either a solid-state laser type optical amplifier (hereinafter, referred to as a first prior art example; See, for example, H. Plaessmann et al., “Multipass diode-pumped solid-state optical amplifier”, Optics Letters, Vol. 18, pp. 1420-1422, 1993) or a dielectric optical waveguide type optical amplifier using quartz (hereinafter, referred to as a second prior art example; See, for example, Mitsuhiro Wada et al., “Amplification characteristic of Nd-doped integrated type optical amplifier devices by LD excitation”, 1992 Spring Conference of The Institute of Electronics, Information and Communication Engineers, SB-9-1, pp. 423-424, 1992).
However, in order to obtain enough large gain with the constitution of these first and second prior art examples, it has been necessary to prolong the optical path length over which signal light and excitation light overlap each other within the crystal of an amplification medium. Since the density of the amplification medium is limited by the saturation density, it has been necessary to prolong the crystal of the amplification medium or to make the signal light reciprocate over the crystal of the amplification medium many times. As a result, the system would be increased in size as one problem. Moreover, as a further problem, it would be very hard for the second prior art example to obtain high gain more than 10 dB while the first prior art example would be more affected by shifts of the optical axis due to environmental variations. Furthermore, the gain in these prior art examples is dependent largely on polarized waves of the signal light, such that the gain would change with variations in polarized waves of the signal light as a further problem.
Further, for downsizing of the apparatus, an optical amplifier apparatus using an optical fiber doped with rear-earth elements (hereinafter, referred to as a third prior art example) has been disclosed in Japanese Patent Laid-Open Publication No. 1-94329. This apparatus of the third prior art example, however, could not able to amplify a signal light having wavelengths of 1.06 &mgr;m band.
SUMMARY OF THE INVENTION
An essential object of the present invention is therefore to provide an optical amplifier apparatus capable of amplifying a signal light having wavelengths of 1.06 &mgr;m band without causing the gain to change due to variations in polarized waves of the signal light.
Another object of the present invention is to provide an optical amplifier apparatus smaller in size and lighter in weight as compared with those of the prior art examples.
In order to achieve the above-mentioned objective, according to one aspect of the present invention, there is provided an optical amplifier apparatus comprising:
a first optical isolator for making an incident signal light having wavelengths within the 1.06 &mgr;m band pass therethrough in one direction from an input end thereof to an output end thereof, and outputting the signal light;
an optical fiber including a core mainly composed of silica glass and doped with a predetermined rare-earth element and the other elements, and a cladding of silica glass, the optical fiber transferring in a single mode the signal light outputted from the first optical isolator means;
an excitation light source generating excitation light having an excitation wavelength of 0.8 &mgr;m band;
an optical multiplexer for multiplexing the excitation light generated by the excitation light source with the signal light transferred by the optical fiber, by outputting the excitation light generated by the excitation light source to the optical fiber, and for transferring and outputting the signal light having wavelength of 1.06 &mgr;m band amplified by induced emission in the optical fiber due to the rare-earth element excited by the excitation light; and
a second optical isolator means for making the signal light output from the optical multiplexer pass therethrough in one direction from an input end thereof to an output end thereof, and outputting the signal light as an amplified signal light.
In the above-mentioned optical amplifier apparatus, the excitation wavelength is preferably set within a range from 0.800 &mgr;m to 0.815 &mgr;m.
In the above-mentioned optical amplifier apparatus, the rare-earth element is preferably Nd, and one of said other elements Al, and
wherein an addition density of Al is set within a range from 500 ppm to 15,000 ppm.
In the above-mentioned optical amplifier apparatus, another one of the other elements is preferably Ge, and
wherein an addition density of GeO
2
with which said core is doped is set within a range from 5 weight % to 35 weight %.
In the above-mentioned optical amplifier apparatus, a product of a doping amount of Nd into the optical fiber and a length of the optical fiber is preferably set within a range from 2 km-ppm to 15 km-ppm.
In the above-mentioned optical amplifier apparatus, a difference between refractive indexes of the core and the cladding of the optical fiber is preferably set within a range from 0.8% to 2%.
In the optical amplifier apparatus with the above-mentioned arrangement, the first isolator makes an incident signal light having wavelengths of 1.06 &mgr;m band pass therethrough in one direction from the input end thereof to the output end thereof. Subsequently, the silica glass optical fiber transfers in a single mode a signal light output from the first optical isolator. Then, the optical multiplexer outputs the excitation light to the optical fiber, thereby combining the excitation light with the incident signal light, and transfers and outputs the signal light having wavelengths of 1.06 &mgr;m band amplified by induced emission in the optical fiber caused by rear-earth elements excited by the excitation light. Further, the second optical isolator makes the signal light outputted from the optical multiplexer means pass therethrough in one direction from the input end thereof to the output end thereof, and then outputs an amplified output signal light.
According to the present invention, a signal light having wavelengths of 1.06 &mgr;m band can be amplified without causing the gain to change due to any polarization variation of the signal light. Further, the optical amplifier apparatus of the present invention is advantageously small in size and light in weight as compared with the prior art examples.
REFERENCES:
patent: 4674830 (1987-06-01), Shaw et al.
patent: 4723824 (1988-02-01), Shaw et al.
patent: 4859016 (1989-08-01), Shaw et al.
patent: 4938556 (1990-07-01), Digonnet et al.
patent: 5210808 (1993-05-01), Grasso et al.
patent: 5319652 (1994-06-01), Moeller
patent: 1-94329 (1989-04-01), None
patent: 1-94329 (1989-05-01), None
Miyazaki et al.,Electronic Letters,vol. 30(25) Dec. 8, 1994 pp. 2142-2143.
Digonnet et al. (IEEE Journal of Quantum Elect.) (1990) No. 6, pp. 1105-1110.
Marcerou et al. (Journal of Luminescence) (1990) No. 1, pp. 108-110.
Petrov et al. (Soviet Tech. Phys. Letters) 1991 No. 2, pp. 123-124.
Stone et al. (Applied Optics) 1974 vol. 13(6), pp. 1256-1258.
Mitsuo Yamaga et al., Theoretical Analysis of . . . , The Transactions of The IECE of Japan, vol. E 69, No. 9, pp. 956-967, 09/86.
Henry Plaessmann et al. Multipass Diode Pumped . . . , Optics Letters, Optical Soc. of America, vol. 18, No. 17, pp. 1420-1422, 09/93.
Mitsuhiro Wada et al., Amplification Characteristics . . . , The Institute of Electronics, Information and Communication Engineers, Japan, Spring Conference, SB-9-1, pp. 4-423-424, Mar. 1992.
Gozen Toshikazu
Karasawa Yoshio
Miyazaki Tetsuya
Yoshida Minoru
ATR Optical & Radio Comm. Research
Hellner Mark
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