Optical waveguides – Polarization without modulation
Reexamination Certificate
2001-11-21
2004-11-02
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Polarization without modulation
C385S024000, C385S036000, C359S490020, C359S490020, C359S490020
Reexamination Certificate
active
06813397
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an optical multiplexing/de-multiplexing system, and in particular to a micro-optic polarization beam multiplexing/de-multiplexing system which integrates polarization beam combiner/splitter (PBC) and wavelength division multiplexer/de-multiplexer (WDM) into one optical module.
BACKGROUND OF THE INVENTION
Modern optical communication demands highly integrated and multi-functional optical components to achieve high performance in both long haul and metro optical networks. There is an increasing demand for an optical system with functions of both optical wavelength division multiplexing/de-multiplexing (WDM) and optical polarization division multiplexing/de-multiplexing (PDM). There are generally two approaches in the fiber optic passive component industry to meet this demand, the all fiber or fusion fiber approach and the micro-optic approach.
In all fiber or fusion fiber approach, a polarization beam combiner/splitter (PBC) can be fabricated by two polarization-maintaining (PM) fibers fused together. Thus, an all-fiber multiplexer/de-multiplexer can be fabricated as simple as a fiber coupler. U.S. Pat. No. 4,881,790 discloses an all-fiber system for coupling two pairs of polarized pumping sources with different wavelengths onto a single optical fiber for Raman pumping. In this system, two polarization selective couplers and one wavelength dependent type coupler are used to combine the two pairs of polarized pumping sources into two combined pumping sources with different wavelengths respectively and then multiplex the two combined pumping sources into one single pumping source.
In the micro-optic approach, an optical system with functions of both optical wavelength division multiplexing/de-multiplexing and optical polarization division multiplexing/de-multiplexing can be made as a combination of polarization beam combiners/splitters (PBC) and a wavelength division multiplexer/de-multiplexer (WDM). Optical polarization beam combiners/splitters (PBC) and wavelength division multiplexers/de-multiplexers (WDM) are known in the art. A micro-optic polarization beam combiner/splitter (PBC) can be as simple as a single piece of optical birefringent crystal, or thin film coating on a right angle prism (RAP), a Nicol prism, a Wollaston prism, a Rochon prism or a Sénarmont prism. Most of these prisms are made of biregringent material wedges serving as optical polarizers. These birefringent materials comprise Calcite, YVO
4
, Rutile, LiNbO
3
and their equivalents. A Micro-optic multiplexer/de-multiplexer is generally based on either of two mechanisms: angular dispersion or optic filtering. Two examples exhibiting angular dispersion are the prism and the blazed reflecting diffraction grating. Various wavelength-selective optical filters can also be used as an optical multiplexer/de-multiplexer.
U.S. Pat. No. 4,805,977 discloses an optical multiplexing system for combining and multiplexing two pairs of linear polarization beams into a single pumping source. In this system, a first polarization prism block combines the first pair of linear polarization beams having the same wavelength &lgr;
1
into a first combined beam and a second polarization prism block combines the second pair of linear polarization beams having the same wavelength &lgr;
2
into a second combined beam. An interference filter block is used to multiplex the first and second combined beams into a single pumping source. This prior art reference also discloses an optical multiplexing system for handling three pairs of linear polarization beams with different wavelengths by using three polarization prism blocks and two interference filter blocks. U.S. Pat. No. 6,052,394 discloses a high power pumping device which comprises a similar optical multiplexing system for multiplexing pumping radiations from four diodes by using two polarization beam combiners (PBC) and a wavelength division multiplexing combiner.
U.S. Pat. No. 5,740,288 discloses a variable polarization beam splitter, combiner and mixer. Each of the polarization beam combiner/splitter disclosed in this prior art reference can handle one pair of polarized beams. If two or more pairs of polarized beams with different wavelengths need to be combined, two or more polarization beam combiners are still needed.
In both existing approaches, it is a common drawback that an optical system with functions of both optical wavelength division multiplexing/de-multiplexing (WDM) and optical polarization division multiplexing/de-multiplexing (PDM) is made by simply cascading the function blocks of polarization beam combiner/splitter (PBC) and wavelength division multiplexer/de-multiplexer (WDM) in series. When the number of beams or the complexity of the optical system increases, the number of optical components and the size of the optical system increase accordingly while the total performance decreases.
In view of the above, it would be an advance in the art to provide a micro-optic multiplexing/de-multiplexing which is more compact, less components, high performance and cost-effective. It would be an especially welcome advance to provide a micro-optic multiplexing/de-multiplexing system that integrates one polarization beam combiner/splitter (PBC) and one wavelength division multiplexer/de-multiplexer (WDM), e.g. an optical filter, into one optical module that can handle two or more pairs of polarization-perpendicular beams of different wavelengths.
OBJECTS AND ADVANTAGES
It is a primary object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using only one polarization beam combiner and a filter.
It is a further primary object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using only one filter and one polarization beam splitter.
It is another object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using one polarizing prism as the polarization beam combiner and a filter. The polarizing prism can be selected from a group consisting of Wollaston prism, Rochon prism, Sénarmont prism and their equivalents.
It is another object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using only one filter and one polarizing prism as the polarization beam splitter. The polarizing prism can be selected from a group consisting of Wollaston prism, Rochon prism, Sénarmont prism and their equivalents.
It is a further object of the present invention to provide a micro-optic polarization beam multiplexing system for multiplexing two polarization-perpendicular pairs of beams of different wavelengths into an output beam by using one polarization beam combiner and a filter. The polarization beam combiner has two optical wedges and a Faraday rotator disposed between the two wedges.
It is another object of the present invention to provide a micro-optic polarization beam de-multiplexing system for de-multiplexing an input beam with two different wavelengths into two polarization-perpendicular pairs of beams of different wavelengths by using one filter and one polarization beam splitter. The polarization beam splitter has two optical wedges and a Faraday rotator disposed between the two wedges.
It is yet another object of the present invention to provide a micro-optic multiplexing system for pumping high gain Raman amplifiers and Erbium-doped fiber amplifiers (EDFA).
The micro-optic polarization beam multiplexing/de-multiplexing system of the present invention is not limited to
Lumen Intellectual Property Services Inc.
Rojas Omar
Sanghavi Hemang
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