Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-02-24
2001-01-23
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S345000
Reexamination Certificate
active
06178039
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention recites a light source module and an optical amplifier which uses the light source module for optical communication and optical information processing.
DESCRIPTION OF THE RELATED ART
In a long distance optical fiber communication system, an optical relay is needed to amplify the light signal attenuated in an optical fiber being used as a transmission line. In an optical relay, there is an optical fiber amplifier which directly amplifies light using a rare-earth doped optical fiber as the amplification media. This optical fiber amplifier has a pumping light source module which causes the rare-earth doped optical fiber pump to produce the optical amplification. The pumping light from the pumping light source module and a signal light to be amplified are multiplexed at a WDM (Wavelength Division Multiplexer). The multiplexed pumping light and signal light are then transmitted to the rare-earth doped optical fiber. This system is called a forward pumping system.
There is also another system called the backward pumping system. In this system, the signal light to be amplified is input at one end of the rare-earth doped optical fiber with the pumping light source module connected at the other end of the rare-earth doped optical fiber via a WDM. The amplified signal light is output via this WDM. In order to produce stable amplification with a rare-earth doped optical fiber, the reflection factor of optical components connected to the input and output parts of the rare-earth doped optical fiber must be kept low when the signal light to be amplified and the light of the rare-earth doped optical fiber are the same wavelength. A large reflection factor leads to an oscillation inside the rare-earth doped optical fiber, and the amplifying operation may become unstable. Therefore, in the pumping light source module, it is advantageous to have a low reflection factor at the proximal end of the optical fiber.
In a conventional pumping light source module, the end of the optical fiber is polished on a slant to reduce reflection. The light to be amplified is reflected between the end of the optical fiber and the pumping light source element. An optical filter which enables the coupling of pumping light is inserted on a slant to the light axis.
At the pumping light source module, where the polished end of the optical fiber is on a slant, the reflection of the pumping light source element is unavoidable. The conventional method to avoid reflection of the end face of the pumping light source is to insert an optical isolator between the end of the optical fiber and the pumping light source element. The optical isolator reflects the light to be amplified. The disadvantage to the optical isolator is the loss of a few dB at the 980 nm band wavelength, which is a main pumping wavelength of the Er (erbium) doped optical fiber. The reduction in signal makes it difficult to transmit sufficient pumping light power to the optical fiber.
FIG. 1
is a block diagram showing the construction of a conventional optical fiber used for optical multiplex transmission. The Japanese Patent Laid-Open SHO 57-68940 discloses the structure of the optical fiber for optical multiplex transmission, as illustrated in FIG.
1
. As shown in
FIG. 1
, an optical fiber
17
, with both ends slanted at a 45° angle and polished as a light axis, transmits the plural wavelengths of light. Interference filter films
16
and
20
are positioned on the slanted end of the optical fiber, reflecting the light of wavelength &lgr;
1
, and allowing the transmission of &lgr;
2
. This structure enables one end of the optical fiber to transmit, and the other end to receive.
At the transmitting end, a luminous element
14
generating the light of the wavelength &lgr;
1
is positioned at a right angle to the light axis of the optical fiber
17
. A luminous element
15
generating the light of the wavelength &lgr;
2
is positioned parallel to the light axis of the optical fiber
17
. At the receiving end, a light receiving element
18
receives the light of the wavelength &lgr;
1
, which is reflected by the interference filter film
20
, positioned at a right angle to the light axis of the optical fiber
17
, and a light receiving element
19
is positioned parallel to the light axis of the optical fiber
17
to receive the light of the wavelength &lgr;
2
transmitted through the interference filter film.
The light of the wavelength &lgr;
1
generated by the luminance element
14
is totally reflected by the interference film
16
and is transmitted to the optical fiber
17
. The light of the wavelength &lgr;
2
generated by the luminance element
15
is transmitted through the interference filter film
16
and on to the optical fiber
17
. As a result, both lights are multiplexed with one another. As the light is transmitted through the optical fiber
17
, the light of the wavelength &lgr;
1
is totally reflected off to light receiving element
18
, and the light of the wavelength &lgr;
2
transmits through the interference filter film
20
to reach the light receiving element
19
. As a result, both lights are separated from one another.
In the technology of the Japanese Patent Laid-Open Application No. SHO 57-68940, only the structure of the optical fiber for the optical multiplex transmission is disclosed. The above-mentioned problem of optical amplification using a rare-earth doped optical fiber is not addressed.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a light source module and an optical amplifier which uses the light source module, for which internal oscillation within the optical fiber and the resultant destabilization of the amplifying operation is prevented by lowering the reflection factor for the light of the same wavelength band as the signal light.
Accordingly, in a first embodiment of the present invention, a light source module provides a light source element which outputs the light of the pumping wavelength of a rare-earth doped optical fiber. An optical fiber with the receiving end polished on a slant receives the outputted light from the light source element. An optical filter film provided at the receiving end of the optical fiber allows the outputted light from the light source element provided at the end of the optical fiber to penetrate, and causes the light of the amplification band wavelength of the rare-earth doped optical fiber to reflect.
In a second embodiment of the present invention, the rare-earth doped optical fiber of the first embodiment is an Er (erbium) doped optical fiber. The pumping wavelength is 1480 nm band and the amplification band wavelength is 1550 nm band.
In a third embodiment of the present invention, the rare-earth doped optical fiber of the first embodiment is an Er (erbium) doped optical fiber. The pumping wavelength is 980 nm band and the amplification band wavelength is 1550 band.
In a fourth embodiment of the present invention, the rare-earth doped optical fiber of the first embodiment is a PR (praseodymium) doped optical fiber. The pumping wavelength is 1016 nm band and the amplification band wavelength is 1300 nm band.
In a fifth embodiment of the present invention, an optical amplifier supplies the pumping light to a rare-earth doped optical fiber, and amplifies an inputted signal light. The amplifier provides a light source element which outputs the light of the pumping wavelength of said rare-earth doped optical fiber. The rare-earth doped optical fiber has a slanted end face for receiving the outputted light from the source element. An optical filter enables the transmission of the outputted light from the light source element and the reflection of the inputted signal light. An optical coupler transmits the pumping light from the other end face of optical fiber for pumping the rare-earth doped optical fiber.
In a sixth embodiment of the invention, the optical coupler of the fifth embodiment is situated at the input end of the rare-earth doped optical fiber, and is set up to multiplex the inputted
Hellner Mark
McGinn & Gibb PLLC
NEC Corporation
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