Optical: systems and elements – Optical amplifier – Optical fiber
Reexamination Certificate
1999-06-09
2001-04-03
Hellner, Mark (Department: 3662)
Optical: systems and elements
Optical amplifier
Optical fiber
C359S344000, C359S337000
Reexamination Certificate
active
06212002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an optical amplifier. More particularly, the present invention relates to an optical amplifier of Michelson interferometer.
2. Description of Related Art
Typically, an optical fiber amplifier uses an erbium doped fiber (EDF) or other active fiber as a gain media. A semiconductor laser light source is also used to excite electrons from a lower energy level to a higher energy level as a pumping function. As an initial optical signal passes through the optical amplifier, it triggers the excited electrons to drop to its lower energy level through radiate photons, resulting in a stimulated emission. The optical signal therefore is amplified.
However, as the optical signal is amplified, a spontaneous emission, resulting in noise, does also simultaneously occur. The noise is also amplified by the optical amplifier to form an amplified spontaneous emission (ASE) noise and propagates along with the optical signal. The ASE noise not only reduces the light pumping efficiency, but also reduce a signal-to-noise ratio (SNR). As a result, the performance of the optical amplifier is degraded, and the communication quality is then deteriorated. It becomes a key point necessarily to be considered during designing the optical amplifier to suppress the ASE noise and increase an optical gain.
A U.S. Pat. No. 5,233,463 by Pirelli S.P.A. company (Italy) disclosed an optical amplifier using a two-level structure. Between the preamplifier and the post-amplifier, an optical isolator is added so as to isolate the ASE noise from the post-amplifier propagating in an opposite direction to the preamplifier. The preamplifier therefore can have greater optical gain, resulting in a better performance of the whole optical amplifier. However, the ASE noise originated from the preamplifier itself, which also includes optical fiber, is also amplified in the post amplifier. The performance in this manner is not at the best mode.
A U.S. Pat. No. 5,280,383 by AT&T Bell Lab. Disclosed another optical amplifier, which adds a filter after the isolator so as to filter away the ASE noise with a wavelength other than the desired wavelength used in communication. The filters only allows the light having the desired wavelength to pass and enter the post amplifier. Even though this manner can reduce the ASE noise, it also causes a large amount of insertion loss (IL). The transmission quality of the optical signal is greatly affected. Moreover, it is difficult to fabricate a filter with multiple windows. The solution with filter is not suitable for use in a communication system with multiple wavelengths.
A U.S. Pat. No. 5,283,686 by General Instrument Corp. disclosed an optical circulator and a fiber grating to reduce an accumulating rate of the ASE noise. The amplified optical signals and the ASE noise can simultaneously propagate to the fiber grating through the optical circulator. The fiber grating has a central wavelength, which is equal to the desired wavelength. The incident amplified optical signals are reflected by the fiber grating and are exported by the optical circulator at the other end, while the ASE noise will travel through the fiber grating. Therefore, the ASE is filtered out. The transmission quality of the optical signals remains without affection. However, the optical circulator is very expensive. It causes a great increase of fabrication cost. Moreover, the IL effect is still large. This is also not a good solution to improve the communication quality.
As previously mentioned, during the optical amplification process, the optical signals and the noise are amplified at the same time. The ASE noise can also propagate along with the amplified optical signals, resulting in a severe issue of the optical communication. The ASE noise not only reduce the efficiency, but also may cause communication error.
SUMMARY OF THE INVENTION
It is at least an objective to provide an optical amplifier using Michelson interferometer so as to perform band-pass filtering on an intended wavelength so that the ASE noise with wavelengths other than the intended wavelength is automatically filtered away. The optical pumping efficiency and optical gain are effectively improved, and the SNR is also greatly increased. Moreover, when the amplifier is used for a system with multiple wavelengths, the Michelson interferometer can also performs band-pass filtering on multiple wavelengths so as to effectively improved the optical gain and suppress the ASE noise. The SNR is therefore increased for each intended wavelength.
The invention provides an optical amplifying system having a structure with two amplification levels to amplify received optical signals. The optical amplifying system includes a Michelson interferometer, a preamplifier, and a post amplifier. In the preamplifier and the post-amplifier, respectively have a light pumping source, a wavelength multiplexer, and an optical gain media. The Michelson interferometer includes an optical coupler and an optical grating set composed of a pair of optical gratings. The optical gratings are located different optical passes, and its central wavelength is equal to the intended wavelength. The optical grating can be formed on a piezoelectric substrate or an electrothermal substrate so that the central wavelength can be changed by applying stress or heat. The intended wavelength reflected by the Michelson interferometer can therefore be adjusted. The preamplifier and the post-amplifier are coupled together through the optical coupler of the Michelson interferometer. Furthermore, an isolator can also be coupled between the preamplifier and the Michelson interferometer so as to avoid the backward-propagation noise.
As the preamplifier receives the optical signals, the preamplifier amplifies the optical signals and exports the pre-amplified optical signals to the optical coupler through a optical pass, such as an optical fiber. The optical coupler divides the optical signals into a first optical signal and a second optical signal, both of which respectively propagate to the pair of the optical gratings. The pair of the optical gratings filters the noise away and reflects the first optical signal and the second signal back to the optical coupler, which further performs a construction interference between the reflected optical signals. The first optical signal and the second optical signal are then combined into a third optical signal without ASE noise. The third optical signal continuously propagates to the post amplifier for amplification.
As embodied and broadly described herein, the invention provides the optical amplifying system with the Michelson interferometer so that the optical gain is improved, the ASE noise is effectively suppressed. The SNR is effectively improved. Moreover, the fabrication cost remains low. Furthermore, the optical amplifying system of the invention can also be efficiently used in a system with multiple wavelengths.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 5233463 (1993-08-01), Grasso et al.
patent: 5280383 (1994-01-01), Federici
patent: 5283686 (1994-02-01), Huber
patent: 5566018 (1996-10-01), Lee et al.
patent: 6011845 (2000-01-01), Hong
patent: 2246234 (1992-01-01), None
Lin Wen-Chin
Lin Ying-Tso
Sheu Lih-Gen
Hellner Mark
Huang Jiawei
Industrial Technology Research Institute
J C Patents
LandOfFree
Optical amplifier 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 amplifier, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical amplifier will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472116