Integrated pump combining module

Details Integrated pump combining module Integrated pump combining module

2001-10-05

2003-08-19

Mack, Ricky (Department: 2873)

Optical: systems and elements

Single channel simultaneously to or from plural channels

C359S494010, C359S490020, C359S490020

Reexamination Certificate

active

06608723

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The present invention relates to pump beam combination techniques, and more particularly to a device which provides polarization beam combining, wavelength division multiplexing, and isolation in the reverse path.
BACKGROUND OF THE INVENTION
In order to increase pump power input to optical amplifiers such as EDFA, PDFA, and Raman Amplifiers, beams from multiple input lasers are typically combined.
FIG. 1
shows an approach typical of the prior art for combining pump input laser beams. In this example, two pump laser beams
105
,
110
with wavelength &lgr;
1
and power P but orthogonal polarizations are fed into a first polarization beam combiner (PBC)
120
. (Beam
105
is horizontally polarized, i.e. polarized in the plane of the page, while beam
110
is vertically polarized, i.e. polarized perpendicular to the plane of the page.) Similarly, two laser beams
130
,
135
with wavelength &lgr;
2
and power P but orthogonal polarizations are fed into a second PBC
145
. Through the action of the PBCs
120
and
145
, the two beams
105
,
110
at &lgr;
1
are combined into a beam having power 2P, as are the beams
130
,
135
at &lgr;
2
. The combined beams
125
and
150
, respectively, then enter a Wavelength Division Multiplexer (WDM)
155
, which combines the two beams into a single beam
160
of power 4P (neglecting loss) with wavelengths &lgr;
1
and &lgr;
2
. In order to prevent undesirable feedback, for example system noise, along the reverse path to the pump lasers, isolators are used at the output (
165
) and optionally at the four inputs (
115
,
140
) to the PBCs. Typically, &lgr;
1
and &lgr;
2
will be in the range of about 1400 nm to about 1550 nm but may also be in the range of about 1000 nm to about 1600 nm. The input beams to the PBCs are typically carried through polarization maintaining (PM) optical fibers. The output of the PBCs and WDM are typically carried through single mode (SM) optical fibers.
According to the prior art, therefore, at least four discreet optical components are required to provide a combined pump laser output: two PBCs, one WDM, and at least one isolator.
SUMMARY OF THE INVENTION
The invention provides systems and methods for combining optical beams.
In one embodiment, the method comprises providing a first beam angle turner which includes first and second birefringent wedges and a first Faraday rotator disposed between the first and second wedges, providing a second beam angle turner which includes third and fourth birefringent wedges and a second Faraday rotator disposed between the third and fourth wedges, providing a wavelength division multiplexer (WDM) that is disposed between the first and second beam angle turners and that transmits light of a first wavelength and that reflects light of a second wavelength, receiving and combining into a first combined exit beam first and second optical beams of the first wavelength, receiving and combining into a second combined exit beam third and fourth optical beams of the second wavelength, and transmitting the first combined exit beam and reflecting the second combined exit beam. The first and second wedges and the first Faraday rotator are disposed in relation to each other and contoured such that the first and second optical beams incident on the first wedge at a first prescribed separation angle are combined into the first combined exit beam at the first wavelength that exits the second wedge opposite the first Faraday rotator. The third and fourth wedges and the second Faraday rotator are disposed in relation to each other and contoured such that the third and fourth optical beams incident on the third wedge at a second prescribed separation angle are combined into the second combined exit beam that exits the fourth wedge opposite the second Faraday rotator. The first beam angle turner, the second beam angle turner and the WDM are disposed in relation to each other such that that the first combined exit beam that exits the second wedge passes through the WDM and is incident upon the fourth wedge opposite the second Faraday rotator and such that the second combined exit beam that exits the fourth wedge is reflected by the WDM and is incident upon the fourth wedge opposite the second Faraday rotator. The third and fourth wedges, the second Faraday rotator and the WDM are further disposed in relation to each other and contoured such that the first combined exit beam passes through the second beam angle turner and exits the third wedge and follows an exit beam path intersecting the third wedge opposite the second Faraday rotator, the second combined exit beam passes back through the second beam angle turner and exits the third wedge opposite the second Faraday rotator and joins the exit beam path, light of the first wavelength reflected back along the exit beam path passes through the second beam angle turner and passes through the WDM, and light of the second wavelength that is reflected back along the exit beam path passes through the second beam angle turner, is reflected from the WDM and passes again back through the second beam angle turner and exits the third wedge without interfering with either the third or fourth incident beams. The first and second wedges, the first Faraday rotator and the WDM are further disposed in relation to each other and are contoured such that the reflected light of the first wavelength, that is reflected back along the exit beam path through the second beam angle turner and the WDM, passes through the first beam angle turner and exits the first wedge without interfering with either the first or second incident beams. The first combined exit beam comprising the first and second incident beams of the first wavelength and the second combined exit beam comprising the third and fourth incident beams of the second wavelength are combined into a third combined exit beam that follows the exit beam path and that includes the first and second wavelengths. Reflected light reflected back along the exit beam path is isolated from the first, second, third and fourth incident beams.
In another embodiment, the method comprises providing a first beam angle turner which includes first and second birefringent wedges, providing a second beam angle turner which includes third and fourth birefringent wedges and a Faraday rotator disposed between the third and fourth wedges, providing a wavelength division multiplexer (WDM) that is disposed between the first and second beam angle turners and that transmits light of a first wavelength and that reflects light of a second wavelength, receiving and combining into a first combined exit beam first and second optical beams of the first wavelength, receiving and combining into a second combined exit beam third and fourth optical beams of the second wavelength, and transmitting the first combined exit beam and reflecting the second combined exit beam. The first and second wedges are disposed in relation to each other and contoured such that the first and second optical beams incident on the first wedge at a first prescribed separation angle are combined into the first combined exit beam at the first wavelength that exits the second wedge opposite the first wedge rotator. The third and fourth wedges and the Faraday rotator are disposed in relation to each other and contoured such that the third and fourth optical beams incident on the third wedge at a second prescribed separation angle are combined into the second combined exit beam that exits the fourth wedge opposite the Faraday rotator. The first beam angle turner, the second beam angle turner and the WDM are disposed in relation to each other such that that the first combined exit beam that exits the second wedge passes through the WDM and is incident upon the fourth wedge opposite the Faraday rotator and such that the second combined exit beam that exits the fourth wedge is reflected by the WDM and is incident upon the fourth wedge opposite the Faraday rotator. The third and fourth wedges, the Faraday rotator and the WDM are further disposed in re

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