Embodiments of the present disclosure relate to the field of optical communication systems. More particularly, the present disclosure relates to the use of Raman pumping to increase capacity and reach of repeaterless optical communication systems.
In optical communication systems, wavelength division multiplexing (WDM) or dense wavelength division multiplexing (DWDM) is used to transmit optical signals long distances where a plurality of optical channels, each at a particular wavelength, propagate over fiber optic cables. However, certain optical communication systems, in particular long-haul networks of lengths greater than about 500 kilometers, inevitably suffer from deleterious effects due to a variety of factors including scattering, absorption, and/or bending. To compensate for losses, optical amplifiers are typically placed at regular intervals, for example about every 50 kilometers, to repeat and boost the optical signal. However, such repeatered systems may be expensive to build and maintain in contrast to repeaterless systems that do not rely on multiple optical amplifiers to boost the optical signal.
Despite fairly complex transmit and receive terminals involving high-power boosters and Raman pumps, repeaterless systems may provide a lower overall system cost compared to repeatered systems as repeaterless systems avoid the need to power-feed, supervise and maintain costly in line erbium-doped fibre amplifiers (EDFAs). In certain repeaterless systems, Raman amplifiers are used to avoid such system complexity and costs. Generally, Raman amplification is accomplished by introducing the signal and pump energies along the same optical fiber. A Raman amplifier uses Stimulated Raman Scattering (SRS), which occurs in silica fibers when an intense pump beam propagates through it. SRS is an inelastic scattering process in which an incident pump photon loses its energy to create another photon of reduced energy at a lower frequency. The remaining energy is absorbed by the fiber medium in the form of molecular vibrations (i.e., optical phonons). That is, pump energy of a given wavelength amplifies a signal at a longer wavelength. The pump and signal may be co-propagating or counter propagating with respect to one another. Thus, optical WDM transmission up to a few hundred kilometers in a Digital Line Section (DLS) can be implemented using repeaterless systems making them an attractive candidate for island hopping, festoons as well as optical add-drop multiplexer (OADM) branches in transoceanic networks.
In long repeaterless systems, the WDM or DWDM channels need to be launched with higher powers from the transmitter to result in adequate optical signal-to-noise ratio (OSNR) and performance on the receive end. Various non-linear transmission effects may limit the maximum possible launch power and, as a result, the system reach and capacity. In certain geographic conditions, it may be desirable to provide increased capacity or reach while maintaining launch powers within a DLS of a repeaterless system. Thus, a need exists for an improved pumping arrangement to increase capacity and reach in an undersea repeaterless DLS.
Exemplary embodiments of the present disclosure are directed to a novel architecture for undersea repeaterless fiber optic communication systems to facilitate increased capacity or reach. In an exemplary embodiment, a communications system includes a first and second communications stations and a repeaterless communications link connecting the first and second stations. An intermediate station is coupled to the repeaterless communications link via a dedicated Raman pumping path where a Raman pump, associated with the intermediate station, is coupled to the dedicated Raman pumping path for increasing gain of a communications signals sent from the first and second communications stations.
In an exemplary method, a communication signal is propagated from a first station to a second station along a repeaterless communication link. Signal gain is provided to the communication signal via a Remote Optically Pumped Amplifier (ROPA) coupled to the communication link where the ROPA is excited by a Raman pump propagating from the receiver station. A Raman pumping signal is provided from an additional Raman pump coupled to the communication link via a dedicated Raman pumping path from an intermediate station located between the first and second stations. The Raman pumping signal is provided to the communication link at an undersea body. Signal gain is provided to the communication signal via a ROPA coupled to the communication link and excited by the additional Raman pump.
It will be appreciated that for simplicity and/or clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, if considered appropriate, reference numerals have been repeated among the figures to indicate corresponding and/or analogous elements.
In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components and/or circuits have not been described in detail. In addition, the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements throughout.
In the following description and/or claims, the terms coupled and/or connected, along with their derivatives, may be used. In particular embodiments, connected may be used to indicate that two or more elements are in direct physical and/or electrical contact with each other. Coupled may mean that two or more elements are in direct physical and/or electrical contact. However, coupled may also mean that two or more elements may not be in direct contact with each other, but yet may still cooperate and/or interact with each other. For example, “coupled” may mean that two or more elements do not contact each other but are indirectly joined together via another element or intermediate elements. Finally, the terms “on,” “overlying,” and “over” may be used in the following description and claims. “On,” “overlying,” and “over” may be used to indicate that two or more elements are in direct physical contact with each other. However, “over” may also mean that two or more elements are not in direct contact with each other. For example, “over” may mean that one element is above another element but not contact each other and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect. In the following description and/or claims, the terms “comprise” and “include,” along with their derivatives, may be used and are intended as synonyms for each other.
Presently disclosed embodiments provide an architecture for undersea repeaterless systems that utilizes dedicated pumping paths originating from an intermediate station to boost signal power in a DLS. Referring now to
The system 100 further includes a dedicated pumping path 140 originating from an intermediate station C, 150. The pumping path 140 may include a plurality of dedicated pump delivery fibers which supplies optical pump signals to communication link 130 via undersea body 160 positioned between the first and second stations 110, 120. Undersea body 160 includes one or more optical couplers configured to route the optical pump signals from intermediate station 150 via delivery path 140 to the DLS formed between stations 110 and 120. As will be described in greater detail, the illustrated system architecture facilitates increased capacity (or reach) on the repeaterless link between the first and second stations 110, 120. Communications signals are propagated only between the first and second stations identified by arrows “SPG” (shown in
As noted above, the intermediate station 150 has no telemetry equipment, and so no DLS communication exists between the first station 110 and the intermediate station 150, or between the second station 120 and the intermediate station 150. The intermediate station 150 or station C includes first and second Raman pumps 152A, 152B which are connected, via first and second communications lines 140A, 140B of the Raman pumping path 140, to respective communication lines 130A, 130B of the communication link 130. The first and second communications lines 140A, 140B are coupled to the first and second communication lines 130A, 130B via respective optical couplers 162A, 162B associated with the undersea body 160. The first and second Raman pumps 152A, 152B are coupled into the communication link 130 in a co-propagating direction (identified by arrows “B”).
The Raman pumps 152A, 152B launched from the intermediate station 150 propagate through the optical fibers of the communications lines 140A, 140B until they reach respective optical couplers 162A, 162B of the undersea body 160. Since the Raman pumps 152A, 152B are coupled to the communication link 130 in a co-propagating direction, the Raman pumps 152A, 152B cause signal gain in the transmission fibers of the communication link 130.
In one embodiment, the Raman pumps 152A, 152B excite additional ROPAs associated with the communication link 130. Thus, additional ROPAs (identified as ROPA 2, ROPA 3) are located close to the undersea body 160 in each of the communications lines 130A, 130B of the communication link 130. The proximity of the additional ROPAs (identified as ROPA 2, ROPA 3) to the undersea body 160 is governed by the length of link 140 and its concomitant loss. The smaller the optical loss at the link 140, then the further away from the undersea body 160 ROPA 2, ROPA 3 can be located. Generally, the proximity of the ROPAs to undersea body 160 depends on several factors such as, but not limited to, Erbium efficiency, length, coupler losses, pump attenuation in link 140, etc.
It will be appreciated that the disclosed architecture of
Each of the intermediate stations 350A, 350B includes additional Raman pumps coupled to the communication link 330 in a co-propagating direction. ROPAs 1 and 4 are excited by the Raman pumps located at the first and second stations 310, 320 in the manner described in relation to
The
Although the claimed subject matter has been described with a certain degree of particularity, it should be recognized that elements thereof may be altered by persons skilled in the art without departing from the spirit and/or scope of claimed subject matter. It is believed that the subject matter will be understood by the forgoing description, and it will be apparent that various changes may be made in the form, construction and/or arrangement of the components thereof without departing from the scope and/or spirit of the claimed subject matter or without sacrificing all of its material advantages, the form herein before described being merely an explanatory embodiment thereof, and/or further without providing substantial change thereto. It is the intention of the claims to encompass and/or include such changes.
The method described herein may be automated by, for example, tangibly embodying a program of instructions upon a computer readable storage media capable of being read by machine capable of executing the instructions. A general purpose computer is one example of such a machine. A non-limiting exemplary list of appropriate storage media well known in the art would include such devices as a readable or writeable CD, flash memory chips (e.g., thumb drives), various magnetic storage media, and the like.
The features of the method have been disclosed, and further variations will be apparent to persons skilled in the art. All such variations are considered to be within the scope of the appended claims. Reference should be made to the appended claims, rather than the foregoing specification, as indicating the true scope of the disclosed method. The functions and process steps herein may be performed automatically or wholly or partially in response to user command. An activity (including a step) performed automatically is performed in response to executable instruction or device operation without user direct initiation of the activity.
The systems and methods disclosed herein are not exclusive. Other systems and methods may be derived in accordance with the principles of the disclosure to accomplish the same objectives. Although the systems and methods have been described with reference to particular embodiments, it is to be understood that the embodiments and variations shown and described herein are for illustration purposes only. Modifications to the current design may be implemented by those skilled in the art, without departing from the scope of the invention. The processes and applications may, in alternative embodiments, be located on one or more (e.g., distributed) processing devices accessing a network linking the elements of the disclosed systems. Further, any of the functions and steps provided in