Optical: systems and elements – Optical amplifier – Particular pumping type
Reexamination Certificate
2000-06-12
2002-08-13
Moskowitz, Nelson (Department: 3662)
Optical: systems and elements
Optical amplifier
Particular pumping type
C359S341430, C372S006000, C372S070000
Reexamination Certificate
active
06433928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical amplifier, an optical amplification apparatus using such an optical amplifier, and an optical amplification method used in such an optical amplifier and such an optical amplification apparatus. The present invention is suitable to be applied to various field in which light having high output is required, particularly, fields such as optical fiber communication, satellite-to-satellite communication and the like in which high output optical signal is required, a laser marker field, medical and biological fields to which non-linear optics are applied, and a semiconductor manufacturing field.
2. Related Background Art
In the past, an electronic repeater having 3R (reshaping, regenerating and retiming) functions has been used for amplifying an optical signal. However, when an optical signal subjected to wavelength-division-multiplexion for achieving large capacity is amplified by the electronic repeater having 3R function, since it is required that combined light be once divided and the divided lights be amplified and then are combined again, the system becomes very complicated and expensive. Further, when optical signal is transferred at a very high speed, in the electronic repeater having 3R functions, if the speed of the optical signal is changed (for example, changed from 10 MHz to 10 GHz), the electronic repeater having 3R functions itself must be changed.
Thus, as large capacity and high speed long distance communication has been developed, an optical fiber amplifier has been proposed as an amplifier for solving the problems regarding the electronic repeater having 3R functions. As shown in
FIG. 9A
, in the optical fiber amplifier, when optical signal having a single mode is inputted to a single mode fiber A and a single mode pumping light (laser beam) generated from a pumping source (semiconductor laser) B is combined with the optical signal by a wave combining unit C, the combined light is transferred to an optical amplifier fiber D, where amplifying medium included in the optical amplifier fiber D is pumped by the pumping light, with the result that the optical signal is subjected to optical amplification by stimulated emission.
In order to give higher output to the optical signal by the said optical fiber amplifier, a high output pumping source must be used to input high output pumping light to the amplifying medium. However, the pumping light outputted from the single pumping source has limitation, as shown in
FIG. 9B
, a plurality of pumping sources B are prepared, and pumping lights from the respective pumping sources B are combined together by wave combining units E to obtain high output, and the combined pumping light is combined with the optical signal by a wave combining unit C.
An optical signal amplifying method utilizing the optical fiber amplifier shown in
FIG. 9A
has the following disadvantage. That is to say, size of a waveguide is limited to propagate the optical signal in a single mode. Namely, it allows a propose multi mode where transit signal is scramble to multi mode. On the other hand, if the waveguide is narrow, light power density is increased as the optical signal is amplified, thereby increasing distortion of the optical signal due to non-linear effect. After all, in the optical fiber amplifier in which the amplifying medium is included in the waveguide, the optical signal cannot be amplified more than a certain limit output.
An optical signal amplifying method utilizing the optical fiber amplifier shown in
FIG. 9B
has the following disadvantage. That is to say, when the pumping lights from the plurality of pumping sources are combined steppingly to obtain the pumping light having high output, energy loss generated each wave combination is increasingly accumulated, with the result that many parts are required for achieving the high output. Thus, the cost is increased and high energy is required, and, in actual, it is difficult to obtain the pumping light having high output greater than 2 Watts.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a high output optical amplifier in which distortion property and energy loss can be reduced as less as possible, and an optical amplification apparatus using such an optical amplifier, and an optical amplification method used in such an optical amplifier and such an optical amplification apparatus.
The present invention aims to achieve the above object by utilizing a geometrical feature in which light emitted from a light source positioned on one of foci of an ellipse is always focused on the other focus thereof. A light collecting technique such a geometrical feature has already been used on a solid-state laser. More specifically, as shown in
FIG. 10
, an amplifying medium (ruby crystal) G is positioned on one of focal axes of an elliptical cylindrical mirror F and a flash lamp H (to which an electric power is supplied from a power supply J) is positioned on the other focal axis thereof so that light outputted from the flash lamp H is effectively incident on the amplifying medium G in such a manner that the incident light is resonated in the amplifying medium G to increase the output above a predetermined threshold value.
Now, the present invention will be described more concretely.
According to a first aspect of the present invention, there is provided an optical amplifier comprising a substrate having a surface disposed on or adjacent to a focal axis passing through one of foci of an elliptical cylinder or an elliptical cone mainly made of SiO
2
-glass or crystal and extending in an optical signal propagating direction, an amplifying medium disposed on or adjacent to the other focal axis of the substrate, and a pumping source unit disposed on or adjacent to the surface of the substrate.
According to a second aspect of the present invention, in the optical amplifier according to the first aspect, reflection coating for reflecting pumping light is applied to surfaces other than a pumping light input inlet and both end faces of the amplifying medium which are optical signal input and output end faces, among outer surfaces of the substrate, and films capable of reflecting the pumping light and permitting passage of the optical signal are coated on the both end faces of the amplifying medium.
According to a third aspect of the present invention, in the optical amplifier according to the first or second aspect, the pumping source unit includes a plurality of pumping sources, and pumping density of the amplifying medium can be adjusted and controlled by changing distances between the pumping sources or by using pumping sources having different outputs or by making outputs of the pumping sources externally-controllable or by using self-controllable pumping sources.
According to a fourth aspect of the present invention, in the optical amplifier according to any one of the first to third aspect, a plurality of pumping sources are used in the pumping source unit so that, if any pumping source cannot emit predetermined output, such a pumping source can be replaced by a new one.
According to a fifth aspect of the present invention, in the optical amplifier according to any one of the first to fourth aspect, when it is assumed that a length of the substrate is L, a longer radius of the substrate is a, a distance between a center O and a focus F of the substrate is OF, a wavelength of optical signal is &lgr;, a minimum spot size of the optical signal is w0, a maximum width of the amplifying medium
3
is 2r, and a relationship between the minimum spot size w0 of the optical signal and the maximum width 2r of the amplifying medium
3
is w0=r, the substrate and the amplifying medium is selected to satisfy the following relationship:
2&lgr;×(
L
/2)/&pgr;
w
0≦
a−OF.
In an optical amplification apparatus according to the present invention, a lens collimating the optical signal to be incident on the amplifying medium is arranged in front of the optical signal input
Namiki Shu
Nukui Katsuya
Tashiro Yoshio
Moskowitz Nelson
The Furukawa Electric Co. Ltd.
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