Not applicable.
Not applicable.
The present disclosure relates to the field of optical communication systems including fiber optic communication systems. More specifically, the field of the invention relates to optical fiber communication systems comprising multiple-input-multiple-output (MIMO) architectures employing a combination of modulation techniques, including orbital angular momentum (OAM) of photons, spatial domain multiplexing (SDM) and wavelength division multiplexing (WDM).
Multiplexing is a method by which multiple channels of analog or digital data are combined on placed into a single shared media at the input end of the media. The media may be any communication media, such as, for example, an optical fiber. De-multiplexing is a method by which multiplexed signals are recovered from the shared media and separated into individual channels at the receiving end of the media. Optical multiplexing systems bring distinctive advantages over traditional non-optical systems. These advantages include significant bandwidth increase and higher data transmission rates. Multiplexing techniques in optical communications include, among others, time division multiplexing (TDM) wavelength division multiplexing (WDM), dense wavelength division multiplexing (DWDM), orbital angular momentum (OAM) multiplexing, spatial domain (or space division) multiplexing (SDM), time division multiplexing (TDM), and polarization division multiplexing (PDM).
TDM is a method for combining two or more separate streams of data, which may be digital data or analog data, for communication over a common channel, which may be for example a single optical fiber. In TDM, the incoming separate streams of data are divided into segments or packets which may be of equal or predetermined length. The packets may be encoded, encrypted, or otherwise manipulated for data integrity and security reasons. The packets containing data from the incoming separate streams of data are interleaved in time by the TDM multiplexer, resulting in a multiplexed data stream that contains packets of data from the incoming separate streams of data which are interleaved in time. After multiplexing, the multiplexed data signal is transmitted over a shared communication medium, such as an optical fiber, where it is received by a receiver. The multiplexed data signal is demultiplexed on the receive, or output end of the shared communication medium. The packets for each incoming separate streams of data are recovered from the multiplexed data signal and reassembled into their original format to recreate each original incoming separate streams of data.
WDM, illustrated in
In OAM multiplexing, two different orthogonal electromagnetic waves are multiplexed onto a single optical communication channel using two independent and different orbital angular momentums of the same azimuthal index. This momentum can be either clockwise (CW) or counter clockwise (CCW). Based on the azimuthal index, OAM can be detected using, among other techniques, a ridge-based segmented circular detector, such as the one shown in
SDM utilizes a MIMO configuration to increase the data capacity of optical fibers. The data carrying capacity of a standard optical fiber increases as helically propagating non-meridional SDM channels allow spatially separated channels to reuse optical frequencies within an optical fiber. SDM has been successfully tested up to several kilometers. It allows multiple channels of the same optical wavelength to propagate inside a single multimode carrier optical fiber (which may be, for example, 62.5/125 μm). Concentric donut shape rings, one ring for each independent channel, are generated at the output end of the system due to helical propagation of light while traversing the length of the fiber. A spatial domain de-multiplexer having photodetectors spatially arranged so that at least one photodetector, or a plurality of photodetectors, is individually illuminated by each of the independent concentric rings is used to separate the individual SDM output channels. Thus, each ring emitted from the receiving, or output, end of the optical fiber illuminates a specific photodetector, or plurality of photodetectors, for converting each ring into an independent channel of electrical data. As shown in
These SDM channels can also exhibit OAM thereby adding an extra degree of photon freedom. An SDM system can operate at different wavelengths without changing its radial distribution.
In accordance with the teachings disclosed herein, a hybrid optical fiber communications architecture is disclosed. By “hybrid”, it is meant that the invention comprises more than a single modulation modality. Thus, an embodiment of the invention comprises WDM and SDM signals or WDM, SDM and OAM signals in a single optical fiber. In the embodiment of the invention comprising SDM, OAM and WDM in a single optical fiber, two new degrees of photon freedom are added to optical communication channels for light energy propagating within the optical fiber, with the potential to increase the bandwidth of an optical fiber communication system by an order of magnitude or greater without increasing the number of optical fibers. In various embodiments the invention may comprise TDM multiplexing of baseband signals prior to input into the SDM multiplexer; or independent input baseband signals may be input directly into the SDM multiplexer.
A detailed description of the embodiments of a hybrid optical fiber communications architecture will now be presented with reference to
As used herein and in the appended figures, “Mux” means multiplexer.
As used herein and in the appended figures, “Demux” means demultiplexer.
As used herein, “optical fiber” and “fiber” means any optically transmissive waveguide, which includes but is not limited to multimode, single mode, step index, graded index optical fibers, and hollow core fibers.
Referring now to
Still referring to
Still referring to
Optical fiber 100 may be of any length, and is characterized in part by having a longitudinal axis. The optical signals 203a launched into optical fiber 100 may be launched at specific angles relative to the longitudinal axis so as to generate propagating SDM/OAM optical signals. Thus the optical signal carried by optical fiber 100 may comprise TDM, WDM and SDM/OAM signals, resulting in a fiber optic communication channel exhibiting a significant improvement in bandwidth over systems of the prior art.
Still referring to
In SDM, multiple optical channels of different optical wavelengths can be launched into a multimode optical fiber at different incident angles θ. These incident angles must be within the Numerical Aperture (NA) of the fiber. The optical channels will stay in the same spatial location within the fiber if they are launched at the same incident angle even though their wavelengths are different. The channels can have the same spatial location within the optical fiber but can have different orientation of angular momentum (clockwise and counter-clockwise). The channels are applicable in free space or any fiber (e.g. plastic, polymer, glass, single mode, multimode, hollow core, step index, photonic crystal, etc.).
Referring now to
Still referring to
Referring now to
The optical channels can also be launched into an optical transmission fiber at different complimentary angles θi and α where θi and α are measured between the longitudinal axis of the transmitting fiber (see item
The ability to simultaneously transmit two optical vortices of the same or similar OAM but opposite topological charge inside the fiber while preserving each's OAM provides the ability to transmit two channels at the same spatial location by using OAM in conjunction with intensity of light to detect signals instead of the conventional methods of employing intensity alone to detect the presence or absence of a signal.
Because the SDM channels carry OAM and the complementary input launch conditions can be used to launch two SDM channels at the same spatial location but with opposing OAMs, the five-channel SDM described above can be used to launch ten sets of WDM channels—five with clockwise OAM and another five with counter-clockwise OAM which is illustrated in
In addition, multiple channels of multiple wavelengths can be transmitted at the same time and occupy the same spatial location but they can be separated based on their optical wavelengths and unique OAM.
The embodiments of the invention described herein add two new degrees of photon freedom to optical communication channels and can therefore increase the bandwidth of an optical fiber communication system by an order of magnitude or greater.
An embodiment of the invention that comprises a WDM system as well as an SDM system is shown in
The NA of a fiber does not vary with wavelength. Therefore, according to the fiber geometry, light propagating inside optical fiber will exit the fiber at an angle equal to the incident angle provided that the medium at the input and output ends of the fiber is of the same optical index. In order to experimentally validate this, laser light of three different wavelengths (405 nm, 532 nm, and 635 nm) were launched at a single incident angle. At the output end of the fiber, the location of concentric donut shape rings was carefully measured and it was found that they take the same radial location irrespective of wavelength. Applying the inverse tangent law, transmitted angle is calculated based on the ring radius (r) and the distance of the fiber to screen (L). It was observed that transmitted angles are somewhat similar to the incident angles, which verifies that the outputs of the SDM channels are not affected by wavelength. Therefore, in SDM systems, the transmitted angle of the optical energy exiting the output end of the optical fiber is almost identical to the input angle, irrespective of the optical wavelength. The NA of the fiber remains unchanged and the SDM inputs will follow the same radial distribution. SDM channels are not affected by the wavelength. So, in SDM systems the NA is preserved, because the transmitted angle is almost identical to the input angle. Within the NA, the SDM inputs will follow the same radial distribution. The tables of
As described, three different laser sources operating at 405 nm, 532 nm, and 635 nm were used as experimental inputs for an SDM system. The output for all of these wavelengths appeared at the same spatial location. The actual location of the donut-shaped output depended on the input launch angle. Simulated results proved this observation to hold true for 1530 nm and 1565 nm optical wavelengths as well. Therefore, SDM supports broadband sources. It is also possible to launch light sources from multiple sets of narrowband sources using WDM multiplexers and then use an SDM beam combiner module to multiplex them spatially and then launch them over an SDM carrier fiber. These channels will propagate over the carrier fiber with minimal signal degradation and crosstalk and will appear at the output end of the SDM system, where a beam separator unit or the SDM de-multiplexer will route the individual wavelengths/WDM channels to the corresponding photo-detectors. In short, the system presented above allows each SDM donut shaped ring to carry the entire range of WDM channels. As a result, the WDM channel capacity will increase by a factor of ‘N’, where ‘N’ is the number of input channels in an SDM system. For example, for a five-channel SDM system (N=5), the fiber can carry five times the capacity offered by a single set of WDM channels which is illustrated in
As described above, SDM channels carry OAM and the complementary input launch conditions could be used to launch two SDM channels at the same location but with opposing OAMs. Therefore, it is possible to utilize the same five-channel SDM system presented earlier and launch ten sets of WDM channels; five with clockwise (CW) OAM and another five with counter-clockwise (CCW) OAM. The block diagram of such a system is presented in
As a result, the data capacity of such a system will increase by an order of magnitude. The table of
A detector to detect and demultiplex OAM signals is presented in
The table of
Column 1 of the table of
An embodiment of the invention that comprises a WDM system as well as both SDM and OAM systems is shown in
The optical field intensities exiting the output end of 1000 μm step index multimode fiber are depicted in
Analysis of the SDM outputs at complementary launch angles indicate that SDM channel location is independent of wavelength and the orientation of input launch angles determine the direction of OAM.
It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.
Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.
This non-provisional application for patent claims the benefit of priority to, and is a non-provisional application of, U.S. provisional patent application Ser. No. 62/113,060, filed in the United States Patent and Trademark Office (USPTO) on Feb. 6, 2015, which is incorporated herein in its entirety by reference. U.S. Pat. No. 8,396,371 to Murshid, et al. titled ORBITAL ANGULAR MOMENTUM IN SPATIALLY MULTIPLEXED OPTICAL FIBER COMMUNICATIONS, which issued Mar. 12, 2013 from the United States Patent and Trademark Office (USPTO), is herein incorporated by reference in its entirety. U.S. Pat. No. 7,639,909 to Murshid et al., METHOD AND APPARATUS FOR SPATIAL DOMAIN MULTIPLEXING IN OPTICAL FIBER COMMUNICATIONS, which issued Dec. 29, 2009 from the USPTO is herein incorporated by reference in its entirety. U.S. Pat. No. 7,174,067 to Murshid et al., METHOD AND APPARATUS FOR SPATIAL DOMAIN MULTIPLEXING IN OPTICAL FIBER COMMUNICATIONS, which issued Feb. 6, 2007 from the USPTO, is herein incorporated by reference in its entirety. All patents, patent applications, provisional applications, and publications referred to or cited herein are each incorporated by reference in their entirety, including all figures and tables, to the extent they are not inconsistent with the explicit teachings of this specification.
Number | Name | Date | Kind |
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7174067 | Murshid et al. | Feb 2007 | B2 |
7639909 | Murshid et al. | Dec 2009 | B2 |
8396371 | Murshid et al. | Mar 2013 | B2 |
9531427 | Henry | Dec 2016 | B2 |
20030174942 | Murshid | Sep 2003 | A1 |
20110150464 | Murshid et al. | Jun 2011 | A1 |
20150309249 | Murshid | Oct 2015 | A1 |
20150323405 | Halmetschlager | Nov 2015 | A1 |
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20160233959 A1 | Aug 2016 | US |
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62113060 | Feb 2015 | US |