Apparatus for multiplexing or demultiplexing polarized waves

Abstract

A dielectric waveguide for spatially separating two orthogonal polarization components of an electromagnetic wave, or for forming an electromagnetic wave having two orthogonal polarization components by spatially combining two linearly polarized electromagnetic waves. The dielectric waveguide includes a first branch for carrying a first linearly polarized wave and a second branch for carrying a second linearly polarized wave. The dielectric waveguide includes a dual-polarization port including a first region and a second region. The first region and the second region of the dual-polarization port are cross-sections of the first branch and the second branch, respectively, the first region and the second region partially overlapping.

Description

TECHNICAL FIELD

[0001] The present invention relates to multiplexing and demultiplexing of polarized signals for transmission in a dielectric waveguide cable. BACKGROUND

[0002] Communicating over a dielectric waveguide (DWG) cable, also known as a polymer microwave fiber (PMF), is one of the options in medium distance applications to fill the performance gap between copper links and optical high speed data links. The combination of millimeter wave transceiver chips (30-300 GHz frequency), small antennas and cheap plastic optical fibers offers a robust, cost-effective and low weight high speed communication link for various applications. Compared to copper, DWG has lower losses and enables higher bandwidths. Compared to optical fiber, DWG is a cheaper and more mechanically robust technology. See Maxime De Wit; Simon Ooms; Bart Philippe; Yang Zhang; Patrick Reynaert; “Polymer Microwave Fibers: A New Approach That Blends Wireline, Optical, and Wireless Communication”; IEEE Microwave Magazine; Vol. 21 / 1, 2020.

[0003] As with other communication technologies, polymer microwave fiber (PMF) communication can be established on multiple orthogonal transmission channels to increase data throughput or to support duplex communication. In a single PMF, orthogonal transmission channels can be realized by two polarizations of the optical mode (e.g. the fundamental mode) of the PMF. Two signals with mutually orthogonal polarizations are also referred to as spatially orthogonal signals. To realize such a polarization diversity, an ortho-mode transducer (OMT) is required. An OMT is a waveguide polarizer device with three physical ports. In the context of the present technology, the term “port” refers to a cross-section of a waveguide, or a cross-section of a branch of a waveguide. In the present invention, a cross-section of an optical element (e.g. a cross-section of a waveguide or a cross-section of a branch of a waveguide) is understood to be a section (i.e. a cut) perpendicular to the main propagation direction of a wave (or signal) propagating in the optical element, i.e. perpendicular to the optical axis of the optical element. A port is not necessarily located at the end of a waveguide. The function of an OMT is to simultaneously separate or combine two spatially orthogonal signals within the same frequency band. An OMT is also referred to as an ortho-mode junction, polarization diplexer or dual-mode transducer.

[0004] Existing OMTs for PMF communication are typically dual-polarized coupler (antenna) designs. Such designs achieve polarization-selective coupling through coupler geometry. For example, such designs are used for patch antennas. See, e.g.,

[0005] Meyer A., Schneider M., “Robust design of a broadband dual-polarized transition from PCB to circular dielectric waveguide for mm-wave applications,” International Journal of Microwave and Wireless Technologies 12, 559-566, 2020;

[0006] U. Dey and J. Hesselbarth, “Millimeter-wave Chip-to-Chip Interconnect Using Plastic Wire Operating in Single and Dual Mode,” 2018 IEEE / MTT-S International Microwave Symposium - IMS, 2018;

[0007] Yu B, Ye Y, Ding X, Liu Y, Xu Z, Liu X, and Gu QJ, “Ortho-mode sub-THz interconnect channel for planar chip-to-chip communications,” IEEE Transactions on Microwave Theory and Techniques, 66, 1864-1873, 2018.

[0008] Such geometry-based couplers have four main disadvantages. First, dual-polarized coupler designs typically have a complex, bulky shape. It is difficult to integrate into a printed circuit board or chip package. Second, exciting separate polarizations is challenging. To support dual polarization, the coupler design compromises the performance of the separate polarizations. Third, coupling efficiency relies on manufacturing repeatability of the coupler structure to achieve good isolation. Fourth, the coupler structure needs to be redesigned when the substrate, frequency band, or bandwidth changes.

[0009] Existing PMF OMT coupler designs implement quadrature transmission channels in various ways. In one example, a PMF OMT implements polarization selectivity using a stacked patch coupler topology. If a multimode DWG is used, the transition between the microstrip line and the circular dielectric waveguide can be implemented through a DWG port structure that acts as a high-order mode filter. This design has no polarization-dependent functionality. Polarization selectivity is achieved only through the geometry of the coupler design. In another example, a PMF OMT implements polarization selectivity using a combination of parasitic patch topology, dielectric spheres, and metal holes. Again, polarization selectivity is achieved only through the geometry of the coupler design. In yet another example, a PMF OMT implements polarization selectivity using a differential probe topology. Again, polarization selectivity is achieved only through the geometry of the coupler design.

[0010] In an alternative approach to the above coupler design-based methods, the configuration of the interface between the electromagnetic components and the antenna (e.g., in the form of a patch or probe) imparts quadrature transmission channels for the polarized waves, with the OMT aperture created using metal waveguides. This design specifically involves a polarization-selective coupling interface between two metal waveguides. The polarization-selective coupling interface is used to enable horizontal polarization signals to pass between a first linear propagation path and a second linear propagation path of the two waveguides, but to prevent vertical polarization signals from passing between the first linear propagation path and the second linear propagation path. The result is polarization selectivity on the interface of a vertical plane between two different metal waveguides.

[0011] All of the above OMT designs rely on coupling the coupler itself for dual-polarization design. That is, the cross shape of the multiplexed signals is formed by the physical cross of the antennas.

[0012] It is desirable to develop an OMT that can provide dual-polarized waves to a dielectric waveguide cable while avoiding additional coupling loss between the connector and the PMF, is mechanically robust, has high coupling efficiency, and is flexible such that modifications to the design are minimized when used over a range of substrates, frequency bands, and bandwidths. SUMMARY

[0013] According to an aspect, there is provided a dielectric waveguide for spatially separating two orthogonal polarization components of an electromagnetic wave from each other or for forming an electromagnetic wave having two orthogonal polarization components by spatially combining two linearly polarized electromagnetic waves, the dielectric waveguide comprising a first branch for carrying a first linearly polarized wave and a second branch for carrying a second linearly polarized wave, the dielectric waveguide having a dual-polarization port comprising a first region and a second region partially overlapping, the first region and the second region being a cross-section of the first branch and a cross-section of the second branch, respectively. The term "port" refers to a cross-section of a waveguide or a cross-section of a waveguide branch. Obviously, a port can be a cross-section at an end of a waveguide. A cross-section of a portion of a waveguide is understood to be perpendicular to a principal propagation direction of an electromagnetic wave in the respective portion of the waveguide. In other words, a cross-section is a cut in a transverse plane (rather than a longitudinal plane) of the respective portion. The waveguide provides a simple and effective way of multiplexing or demultiplexing electromagnetic waves.

[0014] The dual-polarization port can have C4 symmetry. The dual-polarization port can have D4 symmetry. Waveguide symmetry supports the property that electromagnetic waves are highly symmetric and can improve the transmission characteristics of the waveguide. D4 symmetry has the additional advantage that the dual-polarization port can have two orthogonal axes of reflection, and thus, under geometric reflection in either of these two axes, the waves can be symmetric (i.e., invariant).

[0015] The first branch and the second branch can each have an elongated (e.g., rectangular, oval, or elliptical) cross-section. The elongated cross-section helps to carry the first polarization component and repel the second polarization component that is orthogonal to the first polarization component.

[0016] The first branch and the second branch can gradually spatially separate from each other. This helps to minimize distortion and loss of the waves when the waves are demultiplexed.

[0017] At least one of the cross-section of the first branch and the cross-section of the second branch can gradually rotate in space. Thus, a polarization vector of the wave in the first branch and / or a polarization vector of the wave in the second branch gradually rotate in space as the wave propagates in the respective branch. In one embodiment, the polarization vector of the first branch and the polarization vector of the second branch rotate relative to each other as the two waves propagate in the two branches, thereby minimizing distortion and loss while achieving orthogonal polarization in the dual-polarization port and, for example, parallel polarization in the two branches at a location away from the dual-polarization port.

[0018] The first branch and the second branch can be mutually symmetric under reflection across a plane of the dual-polarization port. Thus, the two polarization components can propagate symmetrically and characteristics such as loss, dispersion, and polarization can be kept similar in the two branches.

[0019] The ports of the first branch and the ports of the second branch can be spatially separated. This facilitates complete separation of the two orthogonal polarization components of the electromagnetic wave. It also facilitates connecting the waveguide to two spatially separated devices, one for each component.

[0020] The ports of the first branch and the ports of the second branch can be congruent and have the same orientation. Thus, the two ports can be particularly suitable for receiving or transmitting two waves with the same polarization. In this case, "congruent" means the same size and shape.

[0021] The longest axis of the ports of the first branch and the longest axis of the ports of the second branch can be oriented parallel to each other.

[0022] The longest axis of the ports of the first branch and the longest axis of the ports of the second branch can be oriented orthogonal to each other.

[0023] The ports of the first branch and the ports of the second branch can partially overlap, not parallel to each other.

[0024] The ports of the first branch and the ports of the second branch can take various relative configurations. Each configuration can have its own characteristics in terms of loss and dispersion.

[0025] The dielectric waveguide can be made of a polymer material.

[0026] According to another aspect, there is provided a method of guiding an electromagnetic wave, comprising injecting a wave into a dielectric waveguide as described in one of the above aspects. The two orthogonal polarization components can propagate in opposite directions at the dual-polarization port. The two orthogonal polarization components can propagate in the same direction at the dual-polarization port. BRIEF DESCRIPTION OF DRAWINGS

[0027] The application is now described, by way of example, with reference to the accompanying drawings. In the drawings:

[0028] Figure 1 Exemplary configurations of dielectric waveguides for multiplexing or demultiplexing polarized electromagnetic waves are shown.

[0029] Figure 2 A spatial sequence of cross-sections of the exemplary waveguide described in Figure 1

[0030] Figure 3 A plurality of exemplary implementations of waveguides in a communication system are shown. DETAILED DESCRIPTION

[0031] ​The proposed dielectric waveguide embodies a new type of orthomode transducer (OMT) or connector. In one application, the waveguide receives a signal comprising two orthogonal polarization components and spatially separates the two components. In one embodiment, the waveguide rotates the two components until they become spatially separated signals with parallel polarizations. Obviously, the waveguide can be used as a dual-polarized interface between a circular PMF and two single-polarized waveguides. To prevent additional coupling loss between the connector and the PMF, the connector can be made of a dielectric material similar to the PMF.

[0032] The dielectric waveguide or OMT multiplexes the polarization using three physical ports, such that one port comprises the combined polarization and the other two ports comprise the individual plane polarizations. In the proposed device, the multiplexing is achieved by appropriately selecting the physical dimensions, shape, and arrangement of the waveguide. The dielectric waveguide does not need to include any internal cross-antenna or filter for selecting the plane components of the signal.

[0033] Figure 1 An exemplary configuration of a dielectric waveguide 100 for multiplexing or demultiplexing polarized electromagnetic waves is shown. The dielectric waveguide can be used to spatially separate two orthogonal polarization components of an electromagnetic wave from each other. Alternatively, the dielectric waveguide can be used to form an electromagnetic wave with two orthogonal polarization components by spatially combining two linearly polarized electromagnetic waves. The dielectric waveguide includes a first branch 102 for carrying a first linearly polarized wave and a second branch 104 for carrying a second linearly polarized wave. The dielectric waveguide includes a dual-polarized port 106 comprising a first region 108 and a second region 110. The first region 108 and the second region 110 of the dual-polarized port 106 are the cross-sections of the first branch 102 and the second branch 104, respectively. The first region 108 and the second region 110 partially overlap.

[0034] In the shown example, the first region 108 and the second region 110 orthogonally intersect each other, such that the longest axis of the first region and the longest axis of the second region are at right angles to each other. That is, the first region 108 and the second region 110 overlap to form a cross-shaped (e.g., “+” shaped) cross-section. In operation, respective components of a dual-polarized electromagnetic wave are confined within respective first and second regions of the waveguide. The physical dimensions of the waveguide constrain the polarized waves in the orthogonal arrangement. The relative positions and orientations of the two separate linearly polarized waves present in the first branch 102 and the second branch 104 can be changed in a gradual manner, such that they are combined while following the physical constraints of the waveguide, eventually combining to form a single dual-polarized wave.

[0035] In this application, the word "port" refers to a cross-section of a waveguide or a cross-section of a waveguide branch. The port does not necessarily lie at an end of the waveguide. That is, the particular cross-section referred to by the term "port" can lie anywhere along the waveguide.

[0036] The first branch 102 has a port 112 distal from the dual-polarized port 106. Similarly, the second branch 104 has a port 114 distal from the dual-polarized port 106. In this example, the ports 112 and 114 each lie at an end of the respective branch.

[0037] A dielectric waveguide is a waveguide that is composed entirely or primarily of a dielectric material. Electromagnetic waves, such as millimeter waves or microwaves, can propagate in a dielectric medium in which the electromagnetic waves are guided by the outer boundary of the dielectric, i.e., by the geometry of the dielectric. The wavelength range in which the guiding effect is achieved roughly corresponds to the dimensions of the waveguide. Generally, the higher the dielectric constant, the better the guiding effect, but the higher the loss. A dielectric waveguide can be made of a polymer material.

[0038] In one use example, the waveguide makes the antennas (not shown) at the ends of the first branch 102 and the second branch 104 one-dimensional antennas. The two one-dimensional antennas can even be the same single antenna that is coupled to the two branches including linearly polarized waves, respectively. In this way, the single antenna can be used to input the same linearly polarized waves through the first branch and the second branch simultaneously, and then the waves can be multiplexed together to provide a dual-polarized wave for transmission. The dual-polarized wave can then be de-multiplexed at a far end to retrieve the two linearly polarized components including the same linear wave.

[0039] Alternatively, the input antennas for the first branch 102 and the second branch 104 can be oriented orthogonally to each other so that the input linearly polarized waves are orthogonal to each other before entering the waveguide. Thus, the two linearly polarized signals can not need to be rotated relative to each other within the waveguide in order to combine the two waves to form a single dual-polarized wave having orthogonal components. That is, the two linearly polarized waves can already be spatially oriented relative to each other so that they are orthogonal, but still in separate branches, and then only need to be brought together so that they intersect each other without needing to be rotated relative to each other. Thus, the dielectric waveguide can be configured so that the port of the first branch and the port of the second branch are oriented orthogonally to each other (not shown).

[0040] Dielectric waveguides can be configured such that the first and second branches are symmetrical about each other in reflections in a plane passing through the dual-polarized ports. For example, the plane can pass through the center of the dual-polarized ports between the branches, or through the midway between the two branches, such that the physical shapes of the branches are symmetrical in that plane. Therefore, the two polarization components can propagate symmetrically, and properties such as loss, dispersion, and polarization can remain the same or as similar as possible in the two branches. Similarly, dielectric waveguides can be configured such that the ports of the first and second branches are oriented parallel to each other.

[0041] Figure 2 It shows Figure 1 The sequence of ports or cross-sections of the waveguide shown is illustrated. The sequence begins with (a) a port for receiving or transmitting dual-polarized waves and ends with (e) two separate ports for receiving or transmitting two separate linearly polarized waves. The ports or cross-sections are shown such that the propagation direction of the polarized waves is perpendicular to the plane of the page. That is, all polarized waves propagate into or out of the page in one direction.

[0042] exist Figure 2 In part (a), port 106 is a cross-section of the waveguide at the location where a dual-polarized wave is transmitted within the waveguide. The dual-polarized port 106 can have C4 symmetry. This means that the dual-polarized port remains unchanged when rotated 90 degrees about its center. That is, if the dual-polarized port is rotated by an integer value of 90 degrees about the longitudinal axis of the waveguide, where the longitudinal axis is an axis parallel to the direction of electromagnetic wave propagation at the dual-polarized port, the ports appear identical. However, a port with C4 symmetry does not necessarily have reflection symmetry along any axis in the port plane. In other words, the first region 108 and the second region 110 (i.e., the cross-sections of the first branch 102 and the second branch 104 at the dual-polarized port 106) can be congruent and arranged at a 90-degree angle relative to each other. Here, "congruent" means identical in size and shape. The dual-polarized port 106 with C4 symmetry supports highly symmetrical electromagnetic waves and enables good transmission characteristics of the waveguide.

[0043] The dual-polarization port 106 can have D4 symmetry. D4 symmetry follows the same order of symmetry as a square. For example, the dual-polarization port can be cross-shaped or clover-shaped. D4 symmetry has the advantages of the aforementioned C4 symmetry. Furthermore, the dual-polarization port has two orthogonal reflection axes, and is symmetrical under reflection from either of these axes.

[0044] Figure 2Portions (b) through (d) of FIG. 1 show the ports of the waveguide as a first branch 102 comprising a first region 108 and a second branch 104 comprising a second region 110, the two branches gradually spatially separating from each other. By separating the two waves, which are respectively confined within the first region 108 and the second region 110, in a gradual manner, distortion and loss can be minimized. The degree of gradual separation depends on the frequency and wavelength of the waves, the index of refraction of the dielectric that the waveguide is made of, and the sharpness of the bends in the waveguide boundaries.

[0045] In Figure 2 Portions (c) through (e) of FIG. 1 also show that the cross-section of the first branch 102 and the cross-section of the second branch 104 gradually rotate in space relative to each other. Thus, as the two waves propagate in the two branches, the polarization vector of the wave in the first branch 102 and the polarization vector of the wave in the second branch 104 gradually rotate relative to each other. In one embodiment, the two vectors rotate from a 90-degree relative angle at the dual-polarization port to a 0-degree or 180-degree relative angle between the port of the first branch and the port of the second branch.

[0046] In Figure 2 Portion (e) of FIG. 1 shows that the first port of the first branch 102 and the second port of the second branch 104 spatially separate from each other. This physical separation helps the two orthogonal polarization components of the electromagnetic wave to fully separate. It also helps to connect the waveguide to two spatially separated devices, one device for each component. For example, the two spatially separated devices can be two separate and distinct antennas. The two spatially separated devices can be two waveguides (in particular, two single-polarization waveguides), or two transceivers, or a receiver and a transmitter. In the present context, the word “spatially separated” means disjoint and non-overlapping.

[0047] Figure 3 FIG. 2 shows multiple exemplary implementations of waveguides in a communication system. As described above, waveguides can be used to multiplex waves or to demultiplex waves. Thus, it should be understood that waveguides can be implemented at one or more ends of a communication path in multiple ways depending on the signal requirements and their purpose. Waveguides can be used in the following different Tx / Rx configurations.

[0048] Figure 3 Portion (a) of FIG. 3 shows a waveguide implemented in a dual-polarization transmission system. The waveguide functions as a polarization combiner on the transmit (TX) side and as a polarization splitter on the receive (RX) side.

[0049] Figure 3 Portion (b) of FIG. 3 shows a waveguide implemented in a single-polarization transmission system. The waveguide functions as an orthogonal polarization signal splitter on the receiver side, for example, in a setup where the polarization of the received signal is unknown.

[0050] Figure 3 Part (c) of FIG. 11 shows a waveguide implemented at the transmitter side of the system. In the example shown, the signal from the transmitter Tx is split by a splitter into two spatially separated signals. The two spatially separated signals are injected into two spatially separated ports of two branches of the waveguide. The two signals propagate in the two branches towards the dual-polarized port. At the dual-polarized port, the polarizations of the two signals will be orthogonal to each other.

[0051] Figure 3 Part (d) of FIG. 11 shows a waveguide implemented in a typical duplexing use case. In this example, the two orthogonal components of the dual-polarized wave are used for the transmit and receive components of the communication.

[0052] Accordingly, the waveguide can be configured such that the port of the first branch and the port of the second branch are congruent and have the same orientation, according to the requirements of various implementations. Thus, the two ports can be particularly suitable for receiving or transmitting two waves having the same polarization, i.e., having parallel polarization vectors. For example, the two ports can each have an elongated shape, such as an elliptical or rectangular shape. In this case, “congruent” means the same size and shape.

[0053] The waveguide presented herein is configured for a method of guiding electromagnetic waves. The method of guiding electromagnetic waves comprises injecting a wave into a waveguide configured as described herein. The injected electromagnetic wave can be a dual-polarized wave having two orthogonal polarization components. The two orthogonal polarization components can be a transmit wave and a receive wave, respectively. The two orthogonal polarization components can be two transmit waves, or the two orthogonal polarization components can be two receive waves. The two orthogonal polarization components can be received at a dual-polarized port by a first branch and a second branch, respectively.

[0054] The injected electromagnetic wave can be a first linearly polarized wave or a second linearly polarized wave. The first linearly polarized wave and the second linearly polarized wave can be a transmit wave and a receive wave, respectively. The first linearly polarized wave and the second linearly polarized wave can be two transmit waves, or the two orthogonal polarization components can be two receive waves.

[0055] The waveguide described above provides the advantage that any coupler design can be supported by the waveguide as a multiplexer. There is no necessary compromise of the individual polarizations. Furthermore, the proposed geometry, which is simpler and more flexible than existing approaches, can be more easily integrated into a printed circuit board or a chip package. Any shape required to fit the space available on the circuit board can be implemented. There is also no compromise of the performance of the coupling to implement the necessary shape. Furthermore, the dual-polarized coupling efficiency is essentially dependent on the geometry of the waveguide as a multiplexer. This is due to the nature of the coupling mechanism between linearly polarized waves. Furthermore, there is no need to redesign the waveguide to accommodate different substrates, frequency bands, or bandwidths. The basic mechanism of the waveguide as a multiplexer or demultiplexer remains the same when these parameters change.

[0056] The waveguide described above can be implemented in a system that includes dielectric waveguide cables (also known as polymer microwave fibers) having various cross-sections. For example, the cable or fiber cross-section can be cruciform to conform to the dual-polarized ports of the waveguide. Alternatively or additionally, the cable can have an elliptical cross-section. Other cross-sectional shapes can be employed, such as square, rectangular, or circular. One axis of the cable cross-section can be dimensioned relative to the other orthogonal axis of the cable cross-section to minimize or stop relative rotation of the dual-polarized signals inside the waveguide cable.

[0057] Applicant hereby discloses all individually disclosed features and any combination of two or more such features described herein. Such features or combinations of features can be implemented, to the exclusion of other features described herein, according to the ordinary skill in the art having access to this disclosure without necessarily causing the scope of the claims to be limited to such individual features or combinations of such features. Applicant indicates that aspects of the application can consist of any of these disclosed features alone or in combination with other disclosed features. Various modifications can be made to the application as described herein in light of the above teachings.

Claims

1. A dielectric waveguide (100), characterized in that, For spatially separating two orthogonal polarization components of an electromagnetic wave from each other, or for forming an electromagnetic wave having two orthogonal polarization components by spatially combining two linearly polarized electromagnetic waves, the electromagnetic wave being a millimeter wave or a microwave; The dielectric waveguide comprises a first branch (102) for carrying a first linearly polarized wave and a second branch (104) for carrying a second linearly polarized wave; The dielectric waveguide has a dual-polarization port (106) comprising a first region (108) and a second region (110) partially overlapping, the first and second regions being a cross-section of the first branch and a cross-section of the second branch, respectively, the first and second branches being mutually symmetrical under reflection across a plane passing through the dual-polarization port.

2. The dielectric waveguide of claim 1, wherein, The dual-polarization port has a C4 symmetry.

3. The dielectric waveguide of claim 1, wherein, The dual-polarization port has a D4 symmetry.

4. The dielectric waveguide according to claim 1, wherein The first and second branches are gradually spatially separated from each other.

5. The dielectric waveguide according to claim 1, wherein The first and second branches each have an elongated cross-section.

6. The dielectric waveguide according to claim 1, wherein At least one of the cross-section of the first branch and the cross-section of the second branch is gradually spatially rotated.

7. The dielectric waveguide of claim 1, wherein, The port (112) of the first branch and the port (114) of the second branch are spatially separated.

8. The dielectric waveguide of claim 7, wherein, The port of the first branch and the port of the second branch are congruent and have the same orientation.

9. The dielectric waveguide of claim 7 or 8, wherein, The longest axis of the port of the first branch and the longest axis of the port of the second branch are oriented mutually parallel.

10. The dielectric waveguide of claim 7 or 8, wherein, The longest axis of the port of the first branch and the longest axis of the port of the second branch are oriented mutually orthogonal.

11. The dielectric waveguide of any one of claims 1-6, wherein, The port of the first branch and the port of the second branch partially overlap and are not mutually parallel.

12. The dielectric waveguide according to any of the preceding claims 1 to 8, characterized in that, The dielectric waveguide is made of a polymeric material.

13. A method of guiding electromagnetic waves, characterized by, It comprises injecting the wave into the dielectric waveguide (100) of claim 1.

14. The method of claim 13, wherein, The two orthogonal polarization components propagate in opposite directions at the dual-polarization port.

15. The method of claim 13, wherein, The two orthogonal polarization components propagate in the same direction at the dual-polarization port.

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