Patent Application
20080050121
It is worthy to note that any reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
According to one aspect of the present invention, existing Wavelength Division Multiplexed (“WDM”) terrestrial and undersea technologies are merged into a feature-rich, yet low-cost platform that is purpose-built for the regional undersea market—a market that is significant, robust, and totally underserved by incumbent undersea suppliers.
Embodiments of the present invention are designed for undersea networks having maximum link distances of about 5,000 kilometers. Within this sector, the business model tracks extremely well to significant opportunities in the range of 350 to 4,000 kilometers. This range defines a market gap where current short-haul platforms hit a technological limit and long-haul solutions cannot be economically scaled downward.
In addition, an embodiment of an undersea network utilizes a small form factor optical amplifier that integrates with existing pressure housings and cable supplied by other companies to create a very low cost optical line amplifier, which is called a “repeater.”
Optical line interface (OLI) equipment allows transmission terminal equipment from most major terrestrial vendors to drive a market-specific amplified line having carefully managed transmission characteristics, including. for example chromatic dispersion compensation. The OLI provides all the functionality that is required for optical transmission through an undersea transmission line but which is absent from terrestrial transmission terminal equipment. A comprehensive set of system design and integration services wraps around the entire hardware suite to complete this market penetration strategy
By creating a terminal-independent and submarine cable-independent system platform, capital requirements for market entry are minimized while very attractive margins are realized. In addition, a multi-supplier platform provides the greatest leverage against each supplier's fundamental capabilities to ensure that regional network customers gain the most optimized and cost effective solution for the entire deployed network—from land-based terminal and interface equipment, to undersea amplified line, to network installation and maintenance.
Creating an end-to-end solution using commodity equipment from the more competitive terrestrial space drives additional customer benefits. These include: flexibility in network provisioning; network operational transparency; savings in operator training; and sparing costs. These advantages substantially drive down both customers' initial capital costs and operational expense, particularly when compared with less cost-optimized “vertically integrated” and heavily-customized solutions.
The regional undersea market is approximately positioned between short-haul “repeater-less” (also known as the “festoon” market) and the long-haul transoceanic repeatered markets. Typical regional network links (from landing point to landing point) run between 350 to 2,000 km in length and are used to implement intra-regional telecommunication networks and inter-connectivity solutions between regional and high-capacity transoceanic undersea networks. The regional market is characterized by moderate bandwidth capacity requirements compared with the long-haul market. Regional networks require significantly shorter link distances with a practical upper limit of around 5,000 km.
More than a mere “niche,” the regional undersea market represents a very significant opportunity in and by itself as carriers and network operators look to solve “connectivity” rather than capacity concerns.
By providing critically enabling technologies, a collection of outsourced commoditized products can be seamlessly integrated to create a new target market-responsive solution. This technology is divided into undersea and land-based equipment.
The technology developed for the undersea portion according to one aspect of the present invention is purposefully simple, modular, and robust to radically simplify system design, manufacturing and deployment. Development costs, product costs, and time to market are substantially reduced through this approach. The capabilities and feature set of the technology is further carefully selected to balance cost and performance in exact alignment with the requirements of the target market. For example, ultimate bandwidth capacity and fiber counts are both modest by long-haul standards. However, regional undersea customers typically have lower capacity requirements since they do not aggregate as much traffic as trans-oceanic service providers.
The land-based technology of the present invention is designed to perfectly complement the capability of the undersea technology. More specifically as the feature set of the undersea technology is purposefully streamlined to lower costs and increase reliability, the land-based technology requirements decrease as a result, thus opening up a broader range of terminal solutions to the customer. This provides the opportunity to offer a multi-vendor terminal solution through the use of the OLI of the present invention.
The repeater of the present invention employs a conventional rare-earth-doped fiber amplifier design, in which the amplifier bandwidth is carefully matched to the capacity requirements of the target market. Low parts count, the use of existing submarine-qualified components, and the judicious use of active controllers simplifies the amplifier design to increase reliability and manufacturability and sharply reduce cost and development time. When deployed in a line designed according to one aspect of the present invention, the amplifier avoids the necessity for bulk gain shape adjustments or dispersion compensation on a per amplifier basis. This results in an amplifier that radically simplifies system integration prior to deployment and increases system maintenance flexibility with a substantial reduction in both as-deployed and as-maintained system cost.
Each rare-earth doped optical amplifier contains a length of doped fiber that provides a gain medium, an energy source that pumps the doped fiber to provide gain, and a means of coupling the pump energy into the doped fiber without interfering with the signal being amplified. The rare-earth element with which the fiber is doped is typically erbium.
In optically amplified WDM communications systems, to achieve acceptable optical-signal-to-noise ratios (OSNR) for all WDM channels it is necessary to have a constant value of gain for all channel wavelengths. This is known as gain flatness and is defined as a low or zero value of the rate of change of gain with respect to wavelength at a fixed input level. Unequal gain distribution adversely affects the quality of the multiplexed optical signal, particularly in long-haul systems where insufficient gain leads to large optical-signal-to-noise ratio degradations and too much gain can cause nonlinearity induced penalties. Accordingly, rare-earth doped optical amplifiers often achieve gain flatness with the use of gain flattening filters.
The primary optical components of a rare-earth doped optical amplifier are shown in
Traditionally, the aforementioned optical components of the rare-earth doped optical amplifiers employed in submarine optical communications systems are designed and selected on a system-by-system basis to tailor such amplifier characteristics as output power, gain, bandwidth, and gain flatness. That is, doped fiber with different lengths and dopant levels, pump sources with different power levels and different wavelengths, filters with different transmission characteristics, and different insertion losses among the various components, are generally all parameters of the various optical components that must be determined.
In accordance with the present invention, a single design for the rare-earth doped optical amplifiers is employed for multiple submarine transmission systems. This can be readily accomplished because the present invention is predominantly focused on the regional submarine market in which number of wavelengths and system lengths are limited and excess system margin is sacrificed for ease of manufacture.
As used herein, a single optical amplifier design refers to a design in which the various optical components are chosen to be the same from amplifier to amplifier. Such optical components include the rare-earth doped fiber, the pump source or sources, the couplers or multiplexers, and the gain-flattening filter. For example, in some embodiments of the invention the gain-flattening filter may be selected to limit the bandwidth of the optical amplifier to about 28 nm, which minimizes the optical loss that will arise in this component.
A number of advantages accrue from the use of a single optical amplifier design. For example, system design is simplified because the system engineers only need to consider one amplifier design in the system models, inventory requirements for manufacturing are reduced, and system designs may be accomplished in less time. In addition, the cost of the individual optical components may be reduced because more identical components will need to be procured, thereby potentially reducing their per unit cost.
The aforementioned optical amplifier may be located in a small form factor repeater housing such as that disclosed in U.S. patent application Ser. No. 10/687,547, which U.S. patent application Ser. No. 10/687,547 is hereby incorporated by reference as if repeated herein in its entirety, including the drawings. In this embodiment of the invention the repeater housing comprises an existing submarine qualified pressure and tension housing produced by established suppliers in the submarine space. In one embodiment of the invention the existing submarine qualified pressure and tension housing is conventionally employed to house a submarine cable joint.
In some embodiments of the present invention, the optical amplifiers located in the small form factor repeaters are preferably configured to consume very low power to increase the inherent reliability of the pump lasers, reduce thermal loads, and lessen the power producing and carrying requirements on the DC power supply and undersea cable, respectively. Such a design not only increases overall amplifier reliability, but also substantially lowers costs in the cable because both the power conductor (typically formed from copper) and the dielectric sheathing (typically a medium or high-density polyethylene) can be made smaller in size. When configured as a full up repeater, the ultra-small-form-factor repeater of the present invention generates very small amounts of waste heat and thus can be stored in shipboard cable “tanks” or on deck without external cooling. Such features enhance ease of installation while lowering overall costs.
U.S. patent application Ser. No. 10/621,028 discloses one embodiment of an Optical Line Interface device that may be employed in an undersea telecommunications system in accordance with the present invention, which U.S. patent application Ser. No. 10/621,028 is hereby incorporated by reference as if repeated herein in its entirety, including the drawings. The land-based optical line interface (“OLI”) 12, 18 provides an open interface that enables a variety of unmodified terrestrial grade terminal products from multiple vendors to drive the undersea-amplified line. The OLI fits between the terminal equipment and the amplified line to provide optical signal conditioning and grooming at both the launch and receive end of the system. In addition, the OLI provides the required line monitoring, power feed, and optical service channel functionalities that are unique to the undersea telecommunications environment.
In its interface role, the OLI ensures that the terminal equipment—independent of terminal vendor, modulation format, launch power and other characteristics—successfully transmits and receives data over the undersea, amplified line. The OLI conditions the optical signal at both transmitter and receiver to compensate for line impairments, such as chromatic dispersion and cross-phase modulation, as well as to improve signal-to-noise ratio in the end-to-end system. Raman amplification may be provided in the OLI to increase system reliability and lower costs by increasing the distance from shore to the first repeater, thereby reducing incidents of external aggression close to shore while simultaneously eliminating or the reducing the need for repeater burial.
Similar to the fiber optic cable, the terminal equipment 11, 19 employed in this system 10 can be conventional land-line terminal equipment. This is another aspect of the present invention, in that most any type of pre-existing terminal equipment can be employed, enabling the system designer to purchase the most cost effective terminal equipment at the time. Moreover, this enables the system operator and builder to avoid maintaining supplies of terminal equipment, thereby reducing the inventory costs associated with this business. As such, this element of the system can be a commodity item. Examples of terminal equipment that are currently available and which may be used in connection with the present invention include, but are not limited to, the Nortel LH1600 and LH4000, Siemens MTS 2, Cisco 15808 and the Ciena CoreStream long-haul transport products. The terminal equipment may also be a network router in which Internet routing is accomplished as well the requisite optical functionality. Moreover, the terminal equipment that is employed may conform to a variety of different protocol standards, such SONET/SDH ATM and Gigabit Ethernet, for example.
In some embodiments of the invention the terminal equipment need not be conventional land-line terminal equipment. Rather, the terminal equipment may be pre-existing undersea terminal equipment available from third party vendors. Such equipment may be available from inventory and hence may prove to be the most cost effective terminal equipment at the time. Significantly, this pre-existing terminal equipment is customized for the third party vendor's own undersea transmission system and not for the regional undersea market addressed by the present invention.
The present inventions set forth herein make possible a wide variety of business methods and processes. Several of these are set forth below. Others should be apparent to those of skill in this art.
Although various embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the invention are covered by the above teachings and are within the purview of the appended claims without departing from the spirit and intended scope of the invention. For example, at least several of the business methods set forth herein are applicable to other markets than the undersea telecommunications market used in the above description. Furthermore, this example should not be interpreted to limit the modifications and variations of the invention covered by the claims but is merely illustrative of possible variations.
The present invention is related to co-pending and commonly assigned U.S. patent application Ser. No. 10/739,929, filed Dec. 18, 2003 and entitled “Method for Commoditizing Elements of Previously Specialized Communications Links,” which is incorporated by reference in its entirety herein.
