Optical: systems and elements – Optical amplifier – Multiple pass
Reexamination Certificate
2000-10-25
2002-05-21
Tarcza, Thomas H. (Department: 3662)
Optical: systems and elements
Optical amplifier
Multiple pass
C359S346000, C372S099000, C372S093000
Reexamination Certificate
active
06392791
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to optical systems for performing a defined function using an optical beam that propagates along an optical path within the optical system, and more particularly, to an optical system and method for folding the optical path of the optical beam into a defined volume of the optical amplifier such that the optical amplifier has at least one of a minimized volume and a reduced operating temperature.
BACKGROUND OF THE INVENTION
In the past few years, there has been an increased use of laser technology in many technical fields, including not only communications, but also in the manufacturing industry and the medical field. For example, the communications industry has replaced much of its existing electrical wiring with optic cable for the transmission of data and voice. Further, the welding and cutting industry has developed laser technology for cutting and welding, while the medical field has used laser technology to perform surgical procedures and other diagnostic testing. Given its versatility, laser technology is currently being considered for a broad range of uses. For example, laser technology has been discussed as a viable technology for transmitting high quantities of power from one location to another for use as a power source. This technology would not only be useful for remote geographic locations that do not have an existing power grid, but also for space-based applications.
One important aspect of many laser-based technologies is the ability to amplify the optical beam of the laser to a desired power level. For this purpose, optical amplifiers have been developed which amplify an optical beam by impinging the beam on a laser-active material. A second optical beam, referred to as an optical pump beam, energizes the laser-active material and increases the power level of the laser-active material. This power is transferred to the optical beam being amplified as it passes through the laser-active material.
Although conventional optical amplifiers are typically suitable for many laser applications, there are some drawbacks associated with these conventional systems. Specifically, many high gain optical amplifiers are typically designed to have an elongated rod-like geometry. The gain path for an optical beam incident on the optical amplifier is composed of short gain regions followed by long regions having no gain. For applications requiring large laser gains, these conventional rod-shaped amplifiers may become extremely elongated and significantly increase the volume and mass of the laser application. For example, welding and cutting systems that require a relatively large amount of laser power may require an optical amplifier that far exceeds design and size limitations for the welder or cutter. More importantly, in spaced-based applications, where volume and mass are at a premium, the incorporation of a large-scale optical amplifier may not be possible.
In light of this, optical amplifiers have been developed which attempt to minimize the volume and mass of the optical amplifier. One such class of optical amplifiers is typically referred to as a multi-pass optical amplifier. A multi-pass optical amplifier typically controls the path of the optical beam to be amplified such that the optical beam is passed several times through a laser-active material. With each pass, the optical beam is amplified. By using the same laser-active material and directing the optical beam on the same laser-active material, the size of the optical amplifier may be reduced.
For example, U.S. Pat. Nos. 5,546,222 and 5,615,043 both to Plaessmann et al. provide one illustration of a multi-pass laser. Specifically, with reference to
FIG. 1
, the multi-pass laser
40
disclosed in these patents defines a laser-active material
42
located between two reflectors
44
and
46
. A pump beam source
48
is located in close proximity to the multi-pass laser and directs a pump beam
50
via lenses
52
and
54
at the laser-active material. The multi-pass laser further includes an outlet
56
from which the optical beam that is amplified escapes. Further, the multi-pass amplifier of this reference includes a transparent material
58
to direct the optical beam to the reflector
46
. In this multi-pass laser system, an optical beam
60
to be amplified enters the optical amplifier and is directed on the laser-active material, where it is amplified. The amplified beam is then reflected back and forth between the reflectors
44
and
46
through the laser-active material until the optical beam exits the optical amplifier. Although this optical amplifier does provide a method for amplifying an optical signal, it does have some limitations.
Specifically, the temperature of laser-active material must be properly regulated to ensure the desired amplification and optical beam quality. Allowing the laser-active material to overheat may not only affect the amplified optical beam, but may also subject the laser-active material to undue stress. For this reason, with reference to
FIG. 1A
, the conventional multi-pass optical amplifier connects the laser-active material
42
to a thermally conductive housing
61
. While this configuration aids in the reduction of heat in the laser-active material, it does have drawbacks.
For example, the heat sink configuration of the conventional multi-pass amplifier illustrated in
FIG. 1A
removes heat from a direction perpendicular to the path that the optical signal follows through the laser-active material. This, in turn, creates thermal induced gradients perpendicular to the path of the optical beam that may cause distortions in the refractive index of the laser-active material. In this conventional multi-pass optical amplifier, however, the heat sink cannot be placed such that it removes heat in a direction parallel to the path of the optical beam, as it would obstruct the optical beam.
FIG. 2
illustrates a second type of multi-pass optical amplifier disclosed in U.S. Pat. No. 5,553,088 to Brauch et al. This multi-pass optical amplifier
62
includes three active reflectors
64
a-c
each connected to a separate substrate
66
a-c
and having individual pump sources
68
a-c
directed at each active reflector. These active reflectors each include a laser-active layer
70
and a reflective layer
72
. To amplify an optical beam, the optical beam is directed at the first active reflector
64
a,
where it is amplified and reflected to the second active reflector
64
b.
This is continued for the second and third active reflectors. Advantageously, the substrates
66
a-c
to which the active reflectors are connected are heat sinks, which remove heat from the active reflectors in a direction essentially parallel to the path of the optical signal impinging on the active reflectors. As such, thermally induced gradients in the index of refraction are reduced.
Although the conventional multi-pass optical amplifier disclosed in the Brauch patent does alleviate some of the problems associated with heat removal, it also has some drawbacks. Specifically, as discussed, it is advantageous to minimize the volume and mass of the optical amplifier. However, the multi-pass optical amplifier illustrated in
FIG. 2
only impinges the optical beam once on each active reflector and uses a separate pump beam for each active reflector. The multi-pass optical amplifier of
FIG. 2
would require several active reflectors and associated pump beam devices to generate an optical beam with high gain, thereby requiring a multi-pass optical amplifier of an undesirable scale.
With reference to
FIG. 3
, the Brauch '088 patent further discloses a device for repeatedly supplying a pump beam to an active reflector. Specifically, this device
74
includes an active reflector
76
, a pump beam source
78
, and a plurality of reflectors
80
-
88
. Further, the device includes two coupling devices
90
and
92
for directing the optical beam
94
to be amplified to the active reflector
76
. The pump beam systematically reflects between the reflectors a
Cole Spencer Trent
Fork Richard Lynn
Alston & Bird LLP
Sommer Andrew R
Tarcza Thomas H.
University of Alabama in Huntsville
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