Low-loss shared FTTH distribution network

A low-loss shared FTTH distribution network that enables optical communications within a subscriber area, including optical fibers routed from a point of distribution to the subscriber area, a tap device including an optical tap which interfaces a downstream optical fiber with a first optical fiber, and a straight-through optical fiber which is routed straight through the tap device. The tap device may include a splitter which splits the downstream optical fiber into multiple downstream optical fibers, and the tap device may include tap ports for the downstream optical fibers. Any number of straight-through optical fibers may be included which are routed straight through the tap device. A method including routing optical fibers within the subscriber area, tapping at least one optical fiber with a tap device to interface a downstream optical fiber, and routing at least one optical fiber straight through the tap device.

This application is related to the following co-pending U.S. Patent Application, which has a common assignee and at least one common inventor, and which is herein incorporated by reference in its entirety for all intents and purposes:

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to fiber optic networks, and more particularly to a low-loss shared FTTH distribution network that enables reliable and cost effective optical communications to the home in a low-loss manner.

2. Description of the Related Art

Fiber To The Home (FTTH) is an attractive option that has received a significant amount of attention in recent years. Significant technological advances have been made in fiber optic communications. FTTH promises to deliver “true” broadband access compared to existing access technologies including network connections based on phone lines (DSL) or coaxial cable. The hybrid-fiber-coax (HFC) architecture is a relatively recent development adopted by the cable industry in which optical signals are transported from a source of distribution (e.g., a headend) to multiple electro-optical conversion nodes via fiber optic cables. Each conversion node converts between optical signals and electrical signals using simple photo-detector technology, where the electrical signals are carried via coaxial cables routed from the conversion nodes to individual subscriber locations. Each subscriber location is typically a residential location (e.g., home, duplex, apartment building, etc.) or a business location or the like, where each subscriber location supports one or more individual subscribers. Current HFC designs call for fiber nodes serving about 500 homes on the average, although the nodes could be further segmented to smaller coaxial-serving areas.

A “last mile” solution to achieve FTTH would appear to be to replace the coax cables of an HFC architecture with fiber optic cables. The traditional Passive Optical Network (PON) approach to FTTH is to route a separate optical fiber to each subscriber location. Such a solution, however, results in about 1,000 fibers on the average between each local node and the neighborhoods served (2 per house for full duplex). The average number of fibers behind each person's home in such a configuration is about 200. This has proved to be an unwieldy architecture that is difficult to establish and prohibitively expensive to maintain. FTTH has not yet proved to be cost effective to deploy and/or operate using conventional approaches.

Experience from the coaxial cable configurations has demonstrated that cable problems can and do occur. Generally, damage to one or more cables reduces or otherwise eliminates service in corresponding downstream geographic areas. Coaxial cables are relatively inexpensive and easy to replace and/or repair. Fiber optic cables, on the other hand, are relatively expensive and difficult to repair. In proposed configurations, each cable has a multitude of optical fibers. During the installation process, the individual fibers must be identified and isolated to route each fiber to the appropriate location. Fiber optic cable repair has typically required very specialized equipment involving a sophisticated splicing operation that must be done in a relatively clean environment. The solution has been a truck or “splicing van” loaded with very expensive fiber optic splicing equipment. The general process is to clean, align and splice, which involves melting and firing the individual fibers. The splicing van must be deployed to the specific trouble spot in the network. Although access may be readily available at or near major thoroughfares, such as highways or rural access routes where van access is readily available, such access is more problematic behind homes in neighborhoods and many other hard to reach or remote locations.

It is desired to solve the last mile dilemma so that FTTH can become a viable and economic reality.

DETAILED DESCRIPTION

U.S. Pat. No. 6,678,442 entitled “Fiber Optic Connector For A Segmented FTTH Optical Network”, which is incorporated herein by reference in its entirety, addressed many of the problems of the traditional PON architecture. The segmented FTTH optical network disclosed utilized some of the same logical principles as in an HFC architecture while replacing the last mile coaxial cables with segmented fiber. As described therein, an optic fiber was routed from a node near multiple subscriber locations, and taps and splitters subdivided the optical signal to each subscriber location. The present disclosure significantly improves upon the segmented FTTH optical network disclosed and described therein. In one aspect, an optical communication architecture is described which employs an optic network to enable communications with each subscriber location. In another aspect, the architecture employs a combined analog and digital protocol. In yet another aspect, the architecture is flexible enough to enable a unique optical lambda to be assigned to each subscriber along a single fiber feeding multiple customer premises. In yet another aspect, connectorless tap/splitters are used to reduce signal loss and increase signal budget, which is particularly useful for maintenance of the fiber plant. Optical connectors may still be employed for repair of any one or more optical segments. In yet another aspect, fiber optics replace the coaxial cables used in conventional HFC networks while supporting substantially the same communication and protocols used for HFC networks. The fiber optic plant operates as a “dumb-pipe” that supports existing communications to minimize cost of fiber optic upgrade, and further supports most variations of optical communications to minimize cost of future upgrades.

FIG. 1is a simplified block diagram of an exemplary low-loss shared Fiber To The Home (FTTH) distribution network100implemented according to an embodiment of the present invention. One or more sources (not shown) are coupled via appropriate communication links to deliver source information to a headend103, which distributes the source information to one or more distribution hubs105via respective communication links104. Each distribution hub105further distributes source information to one or more FTTH nodes107via communication links106, where each FTTH node107in turn distributes the source information to one or more subscriber locations109via neighborhood links108routed to and throughout one or more zones110. In the embodiment shown, bidirectional communication is supported in which subscriber information from any one or more of the subscriber locations109is delivered to the corresponding distribution hub105via the corresponding links108and FTTH nodes107. Depending upon the nature of the subscriber information and the network architecture, the subscriber information may be delivered to the headend103or to an appropriate source by the corresponding distribution hub105. The signals that provide source information from an “upstream” source, such as the headend103and/or the hubs105and/or the FTTH nodes107, to the “downstream” subscriber locations109are referred to as “forward” signals and signals sourced from subscriber locations109towards the headend103are referred to as “reverse” signals.

It is noted that the headend103, the distribution hubs105, and the FTTH nodes107, may generically be referred to as points of distribution for source and subscriber information. Each point of distribution supports a successively smaller geographic area. The headend103, for example, may support a relatively large geographic area, such as an entire metropolitan area or the like. The larger geographic areas are further divided into smaller areas, each supported by a distribution hub105. The areas supported by each distribution hub105are further divided into successively smaller areas, such as neighborhoods within the metropolitan area, each supported by a corresponding FTTH node107. In the illustrated embodiment, each FTTH node107supports multiple zones110each including a range of subscriber locations. In one embodiment, each zone typically supports up to 60 subscriber locations and each FTTH node107supports up to 16 zones for a total of up to almost 1,000 subscriber locations (960 if each zone supports exactly 60 locations).

Many different types of sources are contemplated, such as computer or data networks, telephony networks, satellite communication systems, off-air antenna systems (e.g. microwave tower), etc. The computer networks may include any type of local, wide area or global computer networks, both public and private, such as including the Internet or the like. The telephony networks may include the public switched telephone network (PSTN) or other public or private telephony networks. The satellite communication systems and/or the antenna systems may be employed for reception and delivery of any type of information, such as television broadcast content or the like. The headend103may also include video on demand (VOD) equipment (not shown). Depending upon the network architecture, any one or more of the sources may be coupled directly to one or more of the distribution hubs, in the alternative, or in addition to being coupled to the headend103. The headend103includes appropriate equipment for data transmission, such as, for example, internal servers, firewalls, IP routers and switches, signal combiners, channel re-mappers, etc.

The particular configuration of the distribution network100upstream from the headend103to the FTTH nodes107may be designed according to any suitable optical communication configuration. Each of the communication links104and106may be any appropriate media, such as electrical or fiber optic cables or wireless or the like, or any combination of media, such as electrical and optical media and wireless or multiple optical media, etc. The communication links104may comprise optical links, such as, for example, SONET (Synchronous Optical Network) links or the like. The communication links106also comprise optical fibers or cables that are distributed between each FTTH node107and a corresponding distribution hub105. In one embodiment, the distribution network100is configured in a similar manner as an HFC distribution network, except that the links108are not coaxial cables and the FTTH nodes107do not convert between electrical and optical formats. Instead, the neighborhood links108comprise fiber optic cables that are distributed from each FTTH node107towards the respective subscriber locations109located in respective zones110. As described further below, each link108includes optical taps and splitters that subdivide the optical signal path to multiple subscribers. Optical amplifiers may be used to amplify the optical signals where and when necessary or desired.

The method used for upstream optical communications depends on the protocols and architecture employed. If each optical fiber supports bi-directional communications, then each link108includes a single optical fiber segment routed to each subscriber location. An optical ribbon cable incorporating 4 separate optical fibers is contemplated for implementing each of the links106. In the illustrated embodiments described below, each fiber of each link106is split into two signals at each FTTH node107forming two separate links108for each FTTH node107. Each link108may also be implemented with an optical ribbon cable including 4 separate optical fibers for a total of 8 downstream fibers per FTTH node107. It is noted, however, that the particular number of fibers provided to and distributed from each FTTH node107is arbitrary and depends upon the needs of the particular community and the optical communication methods employed. Many different types of electronic and optical communication protocols are possible and contemplated depending upon the particular communication and encoding methods chosen, such as Time Division Multiplexing (TDM) or Frequency Division Multiplexing (FDM) in the electrical domain. Either of these techniques can then be inserted into the optical domain using Wavelength Division Multiplexing (WDM), Coarse Wave Division Multiplexing (CWDM), or Dense WDM (DWDM), etc.

It is appreciated that the distribution network100including the FTTH configuration shown for solving the “last-mile” problem provides many advantages over networks that attempt to distribute a separate fiber from each FTTH node107to each subscriber location109of each supported zone, such as would be the case for the PON architecture. If the node supported500homes, it would require at least 500 separate optic fibers, each routed via a multi-fiber cable to each subscriber location. In contrast, the distribution network100distributes only a few optical fibers to each neighborhood, where each fiber is shared by multiple subscribers. Many communication protocols for enabling such shared optical communications are known and readily available, such as TDM, FDM, WDM, DWDM, etc. Since a reduced number of optical fibers are needed, the cost of routing optical cable from each FTTH node107to each subscriber location109is substantially reduced, resulting in a significantly more cost-effective network to establish. Furthermore, since the network includes substantially less fibers, it is significantly less costly to maintain.

The distribution network100employs a segmented configuration employing optical taps, splitters, amplifiers, etc., described below, that facilitate network configuration, and that further support the use of optical connectors for repair. Each FTTH node107generates enough optical power on each downstream optical fiber to allow a sufficient power loss budget for a certain number of optical connections and signal divisions. The power budget is chosen to provide a sufficient power level to each subscriber location109supported by that FTTH node107given the number of taps, splitters and connectors. Since only a limited number of subscriber locations109need be supported by each FTTH node107, the power budget is sufficient to maintain communications in the last mile and to re-establish communications in an expedient, efficient and cost-effective manner. If a cable of the link108is compromised (e.g., broken, damaged, destroyed, etc.), it is quickly and easily replaced or repaired using optical connectors. The connectors used for repair may be left in the network or later replaced with low-loss fused connections. The fiber optic plant is initially designed with a sufficient optical signal loss budget to accommodate a suitable or predetermined number of connector-based repairs, the exact location(s) of which need not be known at the time of installation. This is different from other architectural approaches which require that loss budget be established to accommodate connectors on each fiber at each tap and splitter in the plant. This new design approach provides significantly reduced signal loss in both the downstream and upstream directions, thus allowing for a reduction or possible elimination of additional optical amplifiers between the node and the subscriber locations.

FIG. 2is a simplified block diagram illustrating an exemplary node area200serviced by a corresponding FTTH node107with multiple zones for servicing up to approximately500subscriber locations. A fiber optic cable203is routed between a point of distribution201to the FTTH node107of the node area200. The point of distribution represents any hub105or the headend103or the like. In this configuration, the cable203includes four fibers F1, F2, F3and F4and the FTTH node107is a transportation amplifier that splits forward signals and combines reverse signals to service up to 16 zones, although only 8 zones are shown. For the node area200, each primary fiber F1-F4is split into two separate A and B fibers. In particular, the fiber F1is divided into separate fibers F1A and F1B, the fiber F2is divided into separate fibers F2A and F2B, and so on. The A fibers are grouped and routed via a cable labeled “A” and the B fibers are grouped and routed via a cable labeled “B”. Each zone is a logical group of subscriber locations109that share forward and return path bandwidth, and typically pass (or support) up to 60 subscriber locations109. As shown, the first cable A is routed from the FTTH node107to four zones Z1, Z3, Z5and Z7and the second cable B is routed from the FTTH node107to four zones Z2, Z4, Z6and Z8, not necessarily in numeric order. The fibers F1A-F4A of cable A support zones Z1, Z3, Z5and Z7, respectively, and the fibers F1B-F4B of cable B supports zones Z2, Z4, Z6and Z8, respectively. If each zone Z1-Z8represents up to 60 subscriber locations, then the node area200includes up to 480 subscriber locations. It is noted that each of the fibers F1A-F4A and F1B-F4B may further be divided by two to support an additional 8 zones for up to a total of 16 total zones or up to about 960 subscriber locations.

FIG. 3is a graph diagram illustrating an exemplary optical frequency plan employed by the distribution network100in which optical signal power in decibels referenced to 1 milliwatt (dBm) versus optical signal wavelength in nanometers (nm). It is by no means the only possible frequency plan, or information format, but is illustrated as an exemplary embodiment for purposes of illustration. In this case, the conventional C-Band of 1530-1565 nm is employed, which is divided into a forward “red” signal “R” within a wavelength range of about 1530-1544 nm and a reverse “blue” signal “B” within a wavelength range of about 1551-1565 nm. For subscriber location generated communications, a reverse “green” signal “G” centered at about 1310 nm is used. The blue signals are digital signals and the green signals are analog signals, as further described below. The forward red signal could be either analog or digital and the various components of the network are independent of the form of the forward path signal. In the initial configuration, the downstream signal is analog, thus allowing existing cable operators to deploy these network components in existing HFC cable plants without changing any headend or customer premises equipment. The signal colors referenced herein do not refer to actual color of the optical signal but are used instead as color codes to distinguish the particular information that is multiplexed onto a single fiber via different optical frequency bands.

FIG. 4is a schematic and block diagram of exemplary fiber optic paths from the FTTH node107to selected network interface units (NIU)409,413at corresponding subscriber locations109. The NIUs409and413are substantially identical with each other. Each NIU is an active, bidirectional interface between the fiber distributed to the subscriber location109and a coaxial cable distributed to one or more of the devices (e.g., customer premises equipment or CPE) within the corresponding subscriber location109. The FTTH node107is coupled to the4upstream fibers F1-F4from the point of distribution201and provides up to eight downstream fibers F1A-F4A and F1B-F2B as previously described. A selected downstream fiber, F2B, of the FTTH node107is shown routed to an upstream input/output (I/O) port401aof an optional middle distribution amplifier (MDA)401, shown with dashed lines, or otherwise to an upstream I/O port of a tap or splitter device, such as the upstream I/O port403aof tap/splitter403. The MDA401is a distribution amplifier that amplifies the red signal in the forward direction and that receives, digitizes where necessary, and combines two reverse signals, e.g., blue (digital) and green (analog), into a single reverse blue (digital) signal.

The MDA401is shown with dashed lines since it is optional and only used for substantially long runs of fibers in which the optical communications possibly need amplification, or if the number of reverse path signals require digitization to avoid time collisions with other reverse path signals further upstream. The function of forwarding the red signal and combining and digitizing reverse analog green signals is performed by the FTTH node107so that the MDA401is otherwise not necessary. In most configurations, an MDA401is not necessary for several reasons. There is very little optical signal loss over miles of optical fiber, whereas coaxial cables exhibit substantial electrical signal loss in as little as one-quarter mile. Thus, HFC cable plants required a significant number of amplifiers downstream of each node. In comparison, there is very little loss of signal in an optic fiber such that the signal need not be amplified for a significant distance, such as up to 20 miles. And the FTTH node107is usually located within several miles of the subscriber locations (e.g., within 20 miles), such that intermediate amplification is not necessary. In some configurations, an MDA401might be employed if there are a significant number of taps and/or splitters positioned after the FTTH node107to amplify the diminished signal strength for additional subscriber locations. Also, the MDA401might be used without an amplifier to manage the collision domain for reverse signals.

The MDA401includes a downstream I/O port401bcoupled to the downstream fiber which is routed to and interfaced with the upstream I/O port403aof the tap/splitter403. An optical tap is a passive signal distribution device which divides a portion of a bidirectional signal of a fiber into two signals on separate fibers, where the signal division may be symmetrical or asymmetrical. A first divided fiber path is provided to a downstream I/O port403band the second divided fiber path is provided to an internal splitter which further splits the tapped signal between 2-8 downstream signals. The downstream I/O port403bis interfaced with a downstream fiber which is shown routed to and interfaced with an upstream I/O port405aof an optional end of line amplifier (ELA)405, also shown using dashed lines, or otherwise to an upstream I/O port of a splitter device, such as the upstream I/O port407aof a splitter407. Each ELA is a distribution amplifier that manages the red signal in the forward direction and one or more green signals in the reverse direction. The ELA405is similar to the MDA401except that the ELA receives only green signals in the reverse direction and converts them to blue signals for transmission upstream in the reverse direction. In most configurations, the signal strength from the FTTH node107is sufficient for all subscriber locations so that ELAs are not necessary. Similar to the MDA401, the ELA405might be employed only if there are a significant number of taps and/or splitters positioned after the FTTH node107and it is desired to amplify the diminished signal strength for additional subscriber locations, or if the number of reverse path signals require digitization to avoid time collisions with other reverse path signals further upstream.

The ELA405is shown with a downstream I/O port405bwhich is coupled to a downstream fiber which is routed to and interfaced with the upstream I/O port407aof the splitter407. The splitter407internally splits the upstream path from the ELA405into multiple downstream paths coupled via a corresponding number of downstream I/O ports. A selected downstream I/O port407bof the splitter407is shown coupled to a downstream fiber which is routed to and interfaced with the external I/O port409aof the NIU409at a corresponding subscriber location.

Referring back to the tap/splitter403, the second divided fiber path is further internally split into a number of separate downstream signal paths provided via separate tapped I/O ports of the tap/splitter403. A selected tapped I/O port403cof the tap/splitter403is coupled to a downstream fiber which is routed to and interfaced with an upstream I/O port411aof an optional splitter411, which is substantially similar to the splitter407. A selected downstream I/O port411bof the splitter411is interfaced to the upstream I/O port413aof the NIU413at a different subscriber location. The splitter411is shown with dashed lines as it illustrates an optional configuration. In most typical situations, the tapped ports of the tap/splitter403would be coupled directly to NIUs of subscriber locations for a symmetrical configuration rather than being further split as illustrated.

In a typical symmetrical configuration, for example, the fiber optic stretch downstream of the tap/splitter403includes multiple tap/splitters in a series configuration, such as illustrated by the tap/splitters TS1, TS2, TS3and TS4of an initial configuration1100distributed along a fiber path of multiple fibers as shown inFIG. 11. The individual optical fibers numbered1-4inFIG. 11represent the individual optical fibers of an optical cable such as cable A or B shown inFIG. 2(e.g., optical fibers F1A-F4A or F1B-F4b). Each of the tapped ports of each tap/splitter in the series configuration supports an individual subscriber location. And the last downstream I/O port of the last tap/splitter in the series configuration is either terminated or linked to a last splitter, such as the splitter407, for supporting the last subscriber locations supported by the fiber cable from the FTTH node107.

The red signals from the FTTH node107are provided to the tap/splitter403, which forwards red signals to the optional splitter411and to the splitter407(via any intermediate tap/splitters). The splitter411forwards a split portion of the tapped and split red signal to the NIU413, and the splitter407forwards a split portion of the red signal to the NIU409. The NIU409receives forward red signals from the splitter407and provides communications from its subscriber location in the reverse direction via a corresponding analog green signal. The splitter407is a passive device which combines reverse green signals from multiple subscriber locations and forwards a combined green signal upstream. The NIU413receives forward red signals from the splitter411and provides communications from its subscriber location in the reverse direction via a corresponding analog green signal. The splitter411is a passive device which combines reverse green signals from multiple subscriber locations and forwards the combined green signal upstream to the tap/splitter403. The tap/splitter403is also a passive device which passes reverse green signals (e.g., from splitter411and NIU413) in the reverse direction to the FTTH node107or to the optional MDA401. As described further below, the FTTH node107transmits the red signals to the NIUs (e.g.,409,413) at the subscriber locations109in the forward direction, and converts green signals from the subscriber locations109in the reverse direction to a blue signal which is forwarded upstream. The FTTH node107also combines any blue reverse signals received from the optional MDA401or the optional ELA405with the green reverse signals into a combined blue signal, which is forwarded in the reverse direction upstream.

An ELA (e.g., ELA405), if used, converts reverse analog green signals from multiple downstream subscriber locations into a reverse digital blue signal, which is forwarded in the reverse direction upstream. The tap/splitter403is a passive device which simply forwards blue and green signals in the reverse direction. An MDA (e.g., MDA401), if used, is designed to combine green and any blue reverse signals into a combined blue signal, and to forward the combined blue signal upstream. In particular, the MDA401converts upstream analog green signals into a digital blue signal, combines digital blue signals into a combined reverse digital blue signal, and forwards the combined reverse digital blue signal upstream.

FIG. 5is a logical block diagram of an exemplary embodiment of the FTTH node107. The fibers F1-F4are each coupled via respective low-loss fiber couplings, denoted LFC, to respective one of four optical transceiver and processors501,502,503and504of the FTTH node107. Each fiber coupling LFC, as used throughout this disclosure and in the Figures, is shown with a dotted line and represents a continuous fiber (i.e., straight-through fiber without connector and only signal loss if via the fiber itself), or a fused fiber connection (i.e., two fibers with ends fused together with negligible signal loss). A fiber coupling denoted FC, represents either an LFC or an SC/APC fiber connector (with associated connector losses). A straight-through fiber is the optimal solution providing a continuous, uninterrupted fiber run. The initial network configuration includes as many straight-through fibers as possible and using as few fiber connectors as possible. A fused connection is the next best connection since it inserts only negligible loss as known to those skilled in the art. Fused connections are in an initial configuration only on the particular fiber which is tapped or split at splitters or tap/splitters. The remaining fibers that pass through tap/splitters are straight-through fibers in the initial configuration. A fiber connector provides the benefit of easy connection and disconnection but inserts signal loss. Fiber connectors are typically used for connecting subscriber locations to splitters (e.g., between the splitter411and the NIU413and between the splitter407and the NIU409), and as a temporary solution for making repairs.

One reason for this variation of connection points is that the connection may change over time. In an initial configuration of the distribution network100, most fibers are continuous with fused connections only when actually being tapped or split. In the event of damage to a fiber cable in which the cable or one or more fibers are sliced or cut, a fiber cable portion might be replaced with new cable and fiber connectors may be initially used to re-establish connection for each of the individual fibers. A “segment” or portion of a fiber cable, meaning the fiber cable positioned between adjacent devices (nodes, splitters, taps, amplifiers, NIUs, etc.), is easily replaced since it is relatively easy to identify a break in communications between adjacent devices. For example, if a fiber cable located between a splitter and a tap/splitter is damaged, then a new fiber cable may be connected between these two components using fiber connectors for each connection point and the remaining system remains unchanged. If the actual point of damage is identified, then the actual point of damage may be repaired without replacing the whole segment. If fiber connectors are used for the repair, then eventually those fiber connectors may replaced with fused connections. As described above, a fused connection is superior to a fiber connector in that a fused connection inserts only negligible loss. The architecture according the present invention, however, provides sufficient signal budget to allow relatively generous use of fiber connectors for certain connection points and for substantially all repairs. The fiber connectors insert some loss, but the budget allows the fiber connectors to remain for as long as necessary and even allow them to be permanent connections.

In this manner, it is appreciated that the fibers of the initial network configuration are “continuous” with a minimal number of fiber connections or fused fibers. In the event of damage, the point of damage is repaired with a connector or fused connection, or a cable segment with the damage is identified and replaced with a new cable segment using fiber connectors or fused connections, or a new segment of cable with connectors on each end is connected between the damaged ends of the original cable whereon connectors have been attached. Such replacement is relatively inexpensive and can be made very quickly and conveniently to bring the network up to operational status with minimal impact to the affected subscriber locations. A splicing van or the like is only necessary if convenient to make fused connections. And if connectors are used, then the connectorized fiber cable may remain operable in the network indefinitely. Eventually, the fiber connectors are optionally removed and the individual fibers fused together to remove the signal loss associated with the connectors. Such replacement may be performed at a subsequent and more convenient time.

Referring back toFIG. 5, each of the optical transceiver and processors501-504amplifies and splits the downstream red signal into two separate signals onto two separate downstream fibers via a corresponding fiber coupling LFC. As shown, the upstream fiber F1is split into the two separate downstream physical fibers F1A and F1B by the optical transceiver and processor501, the upstream fiber F2is split into the two separate downstream physical fibers F2A and F2B by the optical transceiver and processor502, the upstream fiber F3is split into the two separate downstream physical fibers F3A and F3B by the optical transceiver and processor503, and the upstream fiber F4is split into the two separate downstream physical fibers F4A and F4B by the optical transceiver and processor504. Each of the fibers F1A-F4A and F1B-F4B supports up to 2 zones each (e.g., F1A for zones1and9, F2A for zones2and10, F2A for zones3and11, F2B for zones2and12, F3A for zones5and13, F3B for zones6and14, F4A for zones7and15, and F4B for zones8and16). The node area200previously described was shown supporting one zone per fiber F1A-F4A and F1B-F4B, where an additional zone per fiber could be supported in the illustrated embodiment.

FIG. 6is a more detailed schematic and block diagram of the optical transceiver and processor501. The optical transceiver and processors502-504are configured in substantially identical manner and thus are not further shown or described. The fiber F1from the point of distribution201is coupled to a wavelength selective splitter601of the optical transceiver and processor501through a fiber coupling LFC. The red signal is provided to the input of an optical amplifier603, having its output coupled to an input of an optical splitter605. The splitter605is a 1×2 splitter which evenly splits the red signal power into two separate red signals RA and RB provided to respective inputs of first and second WDM filters607and609. The first WDM filter607passes the forward red signal RA to the downstream fiber run F1A for routing to and supporting zones1and9. The fiber F1A is coupled to the WDM filter607which provides respective reverse green and blue signals GA and BA to respective green and blue inputs of a processing circuit611within the optical transceiver and processor501. In a similar manner, the second WDM filter609passes the forward red signal RB to the downstream fiber run F1B for routing to and supporting zones2and10. The fiber F1B is coupled to the WDM filter609, which provides reverse green and blue signals GB and BB to respective green and blue inputs of the processing circuit611.

In one embodiment, the reverse green signals are modulated with 5-42 MHz radio frequency (RF) signals. The processing circuit611includes an Optical to Electrical to Optical (OEO) converter which re-times and re-shapes the signal for converting the green 1310 nm RF signal into a blue 1551-1565 nm digital output signal (approximately 1.2 gigabits). In this manner, the upstream analog green signals are converted to a blue digital signal which is combined with the reverse blue signals from the WDM filters607,609to generate a single combined blue signal B on optical signal path613at the output of the processing circuit611. The combined blue signal on path613is provided to the wavelength selective splitter601for providing the blue signals upstream to the point of distribution201. The subscriber locations in the zones1and9serviced by the FTTH node501receive the red signal sourced from the point of distribution201. The reverse signals generated by each and every subscriber location in zones1and9are provided to the point of distribution201via the FTTH node501.

FIG. 7is a more detailed schematic and block diagram of the optical transceiver and processor501. The fiber F1is coupled via a fiber coupling LFC to a C-Band WDM Red/Blue splitter701, which splits and provides the red forward signal to an optical amplifier703. A DC power supply704provides power to the amplifier703and other components (including photo diodes) of the optical transceiver and processor501as illustrated by a power bus702. The DC power supply704may be a central supply that is shared among the optical transceivers and processor501-504of a given FTTH node107. The DC power supply704provides power to a pump laser705used by the amplifier703to amplify the forward red signal. The pump laser705may also be shared among the optical transceivers and processor501-504of the FTTH node107. The amplified red signal is provided to an optical splitter706, which provides the first red signal portion RA to a C-Band WDM red/blue splitter707and which provides the second red signal portion RB to another C-Band WDM red/blue splitter708. The C-Band WDM red/blue splitter707provides the red signal RA to a course optical WDM splitter709, which provides the red signal RA onto the fiber F1A. Likewise, the C-Band WDM red/blue splitter708provides the red signal RB to another course optical WDM splitter710, which provides the red signal RA onto the fiber F1B.

The fiber F1A is coupled to the course optical WDM splitter709, which splits the red and blue signals from the reverse green signal GA and provides the reverse green signal GA to a photo diode713. The photo diode713converts GA from light to an electrical analog signal and provides it to one input of an analog to digital (A/D) conversion and digital framing circuit715. The course optical WDM splitter709provides the reverse blue signal BA to the C-Band WDM red/blue splitter707, which splits and provides the reverse blue (digital) signal BA to a photo diode711. The photo diode711converts BA from light to an electrical digital signal and provides it to another input of the A/D conversion and digital framing circuit715. The A/D conversion and digital framing circuit715digitizes the electrical analog signal, combines it with the digital return path signals from711and provides it to a first input of a digital interleave circuit717. In a similar manner, fiber F1B is coupled to the course optical WDM splitter710, which splits the red and blue signals from the reverse green signal GB and provides the reverse green signal GB to a photo diode714. The photo diode714converts GB from light to an electrical analog signal and provides it to a first input of another A/D conversion and digital framing circuit716. The course optical WDM splitter710provides the reverse blue signal BB to the C-Band WDM red/blue splitter708, which splits and provides the reverse blue signal BB to a photo diode712. The photo diode712converts BB from light to an electrical digital signal and provides it to a second input of the A/D conversion and digital framing circuit716.

The A/D conversion and digital framing circuit716digitizes the analog RF signal, combines it with the digital return path signals from712and provides it to a second input of the digital interleave circuit717. The digital interleave circuit717interleaves the digital signals from the A/D conversion and digital framing circuits715and716and provides a combined and interleaved signal to an input of a laser718. The laser718provides the combined reverse digital blue signal to an input of the red/blue splitter701, which provides the reverse signal onto the fiber F1for delivery to the point of distribution201.

FIG. 8is a schematic and block diagram of an exemplary embodiment of the MDA401. The MDA401is configured in a similar manner as the optical transceiver and processor501and includes similar components. As shown, the fiber F2B from the FTTH node107is provided through a fiber coupling LFC to a wavelength selective splitter801, which operates in a similar manner as the splitter601to deliver a red signal in the forward direction and a blue signal in the reverse direction. The forward red signal is shown provided to an optical amplifier (OA)803, which provides an amplified red signal to an input of a WDM filter804. The WDM filter804provides the forward red signal onto a downstream fiber805coupled via a fiber coupling LFC. In an alternative configuration, the optical amplifier803is eliminated and the forward red signal is provided directly to the WDM filter804from the wavelength selective splitter801. The MDA401, for example, may be inserted for managing the reverse signal collision domain rather than for amplifying the forward red signal. The downstream fiber805is routed to another component, such as the tap/splitter403as previously described. A digital blue reverse signal on the fiber805is passed by the WDM filter804and provided to one input of a directional coupler806within the MDA401. An analog green reverse signal on the fiber805is passed by the WDM filter804and provided to the input of a processing circuit807. The processing circuit807includes a subset of the circuitry of the processing circuit611, and operates to convert the reverse analog green signal into a digital blue signal, which is provided to another input of the directional coupler806. The digital blue signal provided by the processing circuit807is carried on a different wavelength within the blue frequency band that does not overlap the wavelength of the laser of processing circuit907in the downstream ELA405, which is described further below. Thus the directional coupler806can passively combine the two blue digital signals without the need for expensive digital framing and interleaving. The directional coupler806combines the blue signals and passes the combined blue signal to a reverse input of the wavelength selective splitter801, which provides the combined reverse blue signal onto the fiber F2B. In an alternative embodiment, the MDA401includes a more comprehensive processing circuit, such as one including similar functions as the processing circuit611, which combines the digital blue signals into a combined digital signal provided to the wavelength selective splitter801.

FIG. 9is a schematic and block diagram of an exemplary embodiment of the ELA405which is an optical amplifier that may be used to implement and any other ELA or zone amplifier in the distribution network100. The ELA405is configured in a similar manner as the MDA401and includes similar components in a somewhat simplified configuration. An upstream fiber902is provided via a fiber coupling LFC to a wavelength selective splitter901, which operates in a similar manner as the splitter601to deliver a red signal in the forward direction and a blue signal in the reverse direction. The forward red signal is provided to an optical amplifier903, which amplifies the red signal. The amplified red signal is provided to an input of a course WDM splitter904, which provides the forward red signal onto a downstream fiber905coupled via a fiber coupling LFC. In an alternative configuration, the optical amplifier903is eliminated and the forward red signal is provided directly to the WDM splitter904from the wavelength selective splitter901. The ELA405, for example, may be inserted for managing the reverse signal collision domain rather than for amplifying the forward red signal. An analog green reverse signal on the fiber905is passed by the WDM splitter904and provided to a processing circuit907, substantially similar to the processing circuit807, which converts the reverse analog green signal into a digital blue signal. One difference between processing circuit807and the processing circuit907is that processing circuit907includes a laser that operates on a slightly different wavelength within the blue frequency band that does not overlap the wavelength of the laser of processing circuit807in the MDA401. This enables the use of the less expensive directional coupler806within the MDA401as previously described. The reverse digital blue signal is provided to a reverse input of the wavelength selective splitter901, which passes the combined reverse blue signal onto the upstream fiber902. The specific details of the MDA401and the ELA405are both similar and simplified as compared to that shown inFIG. 7for the optical transceiver and processor501and thus is not further described.

FIG. 10is a logical optical layout diagram of an exemplary embodiment of the tap/splitter403, which includes one or more upstream ports1001, a corresponding number of downstream ports1003, and multiple tap ports1005. Optic fibers F1x,F2x,F3xand F4xrepresent the downstream fiber runs of the FTTH node107fibers F1, F2, F3and F4, respectively, which are provided to respective ones of the upstream ports1001. Three of the fibers F1x,F2x,and F3xpass through the upstream ports1001and the downstream ports1003in a continuous without being tapped or split by the tap/splitter403, whereas the signal of the fiber F4xis tapped and split. Thus, the fiber couplings LFC for the fibers F1x-F3xare straight-though fibers without a fused connection in the initial configuration. The LFC for the fiber F4xmay be a fused connection at both the upstream port1001and the downstream port1003. In this case, the fiber F4xis provided to an internal directional coupler or tap1007, which taps off a portion (e.g., 10-50%) of the optical signal of the F4xfiber and provides the tapped portion to an internal splitter1009. The splitter1009divides the tapped signal into multiple separate downstream signals provided onto separate fibers routed to subscriber locations or downstream devices, such as splitters, taps, etc. In this case, the splitter1009is a 1×4 splitter that evenly divides the tapped signal into four signals provided on corresponding fibers F4a,F4b,F4cand F4dat corresponding ones of the tap ports1005. The fiber couplings at the split downstream fibers F4a-F4dare shown as fiber couplings FC since the fibers may be fused or coupled via fiber optic connectors. Although fiber optic connectors insert signal loss, such connections are more convenient for service technicians servicing or repairing the tap/splitter403.

The amount of the F4xsignal tapped by tap1007depends on the location of the tap/splitter403in the architecture and the relative strength of the signal. A tap percentage of anywhere between 10-50% is typical for most applications. The remaining signal is passed to a corresponding output port1003carrying the remaining portion of the signal carried on the F4xfiber. Although a 1×4 splitter1009is shown, the signal splitter may be split by any practicable number, such as 1×2, 1×3, 1×6, 1×8, etc. The splitter1009divides the tapped signal by any desired percentage or proportion, where split signals are not necessarily equal to each other. For example, if 3 of the 4 split signals are to be provided to subscriber locations and the fourth is to be further tapped or split downstream, then the fourth signal may optionally have a greater percentage of signal strength than the first three to ensure sufficient signal strength for subscriber locations downstream of the port that is split.

FIG. 11is a diagram illustrating an implementation and use of the exemplary embodiment of the tap/splitter403shown inFIG. 10. Four tap/splitters TS1, TS2, TS3and TS4are shown in an initial configuration1100distributed along a fiber path of multiple fibers, such as along either of the fiber optic paths A or B shown inFIG. 2. In this case, there are four optical fibers numbered1-4. Each of the tap/splitters TS1-TS4are configured in a similar manner as the tap/splitter403including an internal tap and splitter1101and tap ports1103that subdivide the signal on a selected fiber into a number of downstream signals on corresponding fibers. In this case, the tap/splitter TS1subdivides the signal on fiber4into W different signals, the tap/splitter TS2subdivides the signal on fiber3into X different signals, the tap/splitter TS3subdivides the signal on fiber2into Y different signals, and the tap/splitter TS4subdivides the signal on fiber1into Z different signals, where W, X, Y and Z are integers. As with the tap/splitter403, the lower upstream/downstream ports are illustrated as being tapped and split, although this is only a representation as any selected fiber may be tapped and split in any given tap/splitter component. The individual fibers are illustrated crossing over each other (each labeled XOVR) to represent providing a different fiber to the lowest port of downstream tap/splitters, which is represented as the tap/splitter port.

In an initial configuration of the FTTH distribution network100, such as represented at1100, the optic fibers are continuous fibers with a minimum number of fiber connectors or fused fibers (or even no connectors or fused points). As illustrated, fiber1passes through the tap/splitters TS1-TS3as a continuous fiber, and is then subdivided into Z different signals by the tap/splitter TS4. Fiber1may be further routed to other taps and/or splitters or the like or to a subscriber location or may simply be appropriately terminated downstream of the tap/splitter TS4. Yet fiber1does not have any connectors entering or exiting any of the tap/splitters TS1-TS4, so that fiber1is either a continuous fiber entering and exiting each tap/splitter or is fused at the port of the tap/splitter TS4. In a similar manner, fiber2passes through the tap/splitters TS1and TS2as a continuous fiber and is subdivided into Y different signals by the tap/splitter TS3and then is routed to and through the remaining tap/splitter TS4without further taps or splits within TS4. Fused connections may be used on fiber2at the entry and exit ports of TS3. Fiber3passes through the tap/splitter TS1as a continuous fiber and is subdivided into X different signals by the tap/splitter TS2and then is routed to and through the remaining tap/splitters TS3and TS4. Fused connections may be used on fiber3at the entry and exit ports of TS2. Fiber4is subdivided into W different signals by the tap/splitter TS1and then is routed to and through the remaining tap/splitters TS2-TS4. Fused connections may be used on fiber4at the entry and exit ports of TS1. Each fiber may further be routed to downstream components or subscriber locations or properly terminated.

As understood by those skilled in the art, optic connectors insert signal loss in the fiber path, so that it is preferred to either run a continuous fiber or to fuse the fiber at tap/splitter locations. Such initial configuration1100minimizes signal loss and maximizes signal budget in the initial configuration. It is appreciated, however, that optic connectors could be inserted at each upstream, downstream and tap port of each tap/splitter TS1-TS4for each fiber. In spite of the relatively significant loss inserted by the sum of optic connectors in each fiber run, each fiber path traverses a limited number of zones (e.g., 4-8 zones) and amplifiers are used to boost the signal where and when necessary or desired. And as described above, the optical interfaces at the downstream tap ports may be fiber optic connectors for the convenience of service technicians. A significant benefit of minimizing the number of optic connectors in an initial configuration is to leave a significant remaining signal budget to allow connectors to be inserted at any time in the event of damage of the fiber cable. For example, in the event of damage of the fiber cable carrying the individual fibers1-4, as illustrated at1105, where the damage is shown as jagged double line1102representing damage to or split of one or more of the individual fibers1-4of the cable, repair may be made quickly and easily with optic connectors. As illustrated by a repaired configuration shown at1107, the repair may be made by inserting an optic connector1106at the location of each split in each of the fibers1-4within the fiber cable between the tap/splitters TS1and TS2. An alternative repair configuration is illustrated at1109, which is a more practical and convenient solution, in which the entire fiber cable segment between the tap/splitters TS1and TS2is replaced as shown at1109and an optic connector1106is inserted at each end of each of the individual fibers1-4at the respective ends of the inserted fiber cable segment.

In a conventional configuration such as implemented as a PON, specialized equipment, such as a splicing van with an internal clean environment and very expensive fiber optic splicing equipment, would be required to locate the damage, to access the damaged cable, and then to splice and fuse the individual fibers together to effectuate the repair. In the standard and conventional configuration, the fiber cable carries hundreds if not thousands of individual fibers, and each cable repair requires that each of the split fibers be individually located, spliced, and fused since the conventional architecture cannot afford the signal loss of optical connectors. The standard fiber optic architecture requires that very little signal loss be inserted into each fiber run, so that optic connectors are usually not used. Thus, the process can be expensive and consume a considerable amount of time. The subscriber locations that suffer loss of service may not be restored for a substantial period of time. And the repair process is very costly to the service provider, who typically passes such cost onto the subscribers/consumers.

In contrast, the repair process in either scenario1107or1109is conducted in a relatively quick and easy manner by a repair crew in the field. The repair crew does not need to have expensive fiber optic splicing equipment for repairing the individual fibers of the cable, and the truck need does not require the standard clean room environment and need not be a full-up splicing van. In accordance with an FTTH architecture implemented according to an embodiment of the present invention, each fiber cable includes a relatively small number of fibers, typically less than ten (e.g., 4), each of which is easily identified by its color coded sleeve, and each may be repaired with a simple optic connector rather than requiring the splicing and fusing process. The repair process illustrated at1107is sufficient if the specific location of the damage is known or easily identified. Often, however, the only information of the damage is that the subscriber locations serviced by the tapped ports of the tap/splitter TS1still have service whereas those serviced downstream from the tap/splitters TS2-TS4experience complete loss of service. By process of elimination, it is determined that the fiber cable between the tap/splitters TS1and TS2is damaged, so that this portion of the cable is replaced as illustrated at1109. And even if the repair is made with fused connections, the process is much easier as compared to PON architectures since the cable only includes a few fibers as compared to hundreds or thousands. Thus, even the fuse process is completed in much less time.

A sufficient amount of signal strength is available for all downstream subscriber locations even if one or more optic connectors have been inserted in each fiber run (at the point of damage or at either end of each individual fiber in a cable segment). Using optical connectors, the subscriber locations experience loss of service only for a relatively short period of time. The service provider may opt to leave the optical connectors in the network without further repair since the downstream subscriber locations receive adequate signal strength. Alternatively, the service provider may opt to splice and fuse the individual fibers1-4immediately or at a later and more convenient time. For example, if there has been a significant number of repairs for a given fiber run over time, it may be advantageous in some situations (to regain signal strength) or even necessary in others (to avoid potential loss of service at the end of the line) for the service provider to remove the optical connectors and splice the individual fibers together. In any event, it is appreciated that an FTTH architecture implemented according to an embodiment of the present invention is significantly more cost effective to establish, operate and maintain than conventional fiber optic configurations.

FIG. 12is a logical optical layout diagram of an exemplary embodiment of the splitter407, which includes an upstream port1201and multiple downstream ports1203. The upstream port1201is shown with a low-loss fiber coupling LFC representing either a continuous fiber or a fused connection, and the downstream ports are shown with a fiber connection LC which is either an LFC or an optical connector as previously described. It many configurations it is deemed more convenient to used connectors between the splitter and the NIU at the subscriber location. A selected optic fiber FNx (in which N is an integer from 1 to 4 representing a selected one of the downstream fiber runs of the FTTH node107fibers F1, F2, F3and F4, respectively), which is provided to the upstream ports1201. The fiber FNx is provided to an internal splitter1205. The splitter1205, which functions in a similar manner as the splitter1009, divides the signal into multiple separate downstream signals provided onto separate fibers routed to subscriber locations or downstream devices, such as splitters, taps, etc. In this case, the splitter1205is a 1×4 splitter that evenly divides the tapped signal into four signals provided on corresponding fibers FNa, FNb, FNc and FNd at corresponding ones of the downstream ports1203. Also, although a 1×4 splitter is shown, the splitter may be just as easily configured to split the signal by any practicable number, such as 1×2, 1×3, 1×6, 1×8, etc. The splitter1205divides the signal by any desired percentage or proportion, where split signals are not necessarily equal to each other in a similar manner as previously described for the splitter1009.

FIG. 13is a schematic and block diagram of an exemplary embodiment of the NIU409, and the NIU413is substantially identical. The subscriber link fiber optic segment, shown as a fiber SL, is provided to a course optical WDM splitter1303within the NIU409via an optic connector1301. The course optical WDM splitter1303enables the forward red signal to pass to a photo diode1305. The photo diode1305converts the optical red signal to a forward RF signal (e.g., 50-860 MHz), which is provided to the input of an RF amplifier1307. The output of the RF amplifier1307provides an amplified RF signal which is filtered by an RF diplex filter1309and then by a power diplex filter1311, which interfaces a coaxial cable1315via a coaxial cable connector1313. The coaxial cable1315is routed to various components at the corresponding subscriber location for delivering content carried by the red signal.

Signals generated at the subscriber location, such as subscriber commands or computer communications for the internet or the like, are converted and multiplexed onto a 5-40 MHz signal provided through the power diplex filter1311and the RF diplex filter1309and provided to an RF Pad1317. The RF Pad1317outputs the signal to an RF coupler1318, which provides the RF signal to an FP laser amplifier1319. The laser amplifier1319converts the RF signal to a corresponding green signal provided to an input of an optical switch1321. The optical switch1321, when activated, provides the green signal via a first output to an input of the course optical WDM splitter1303. The optical WDM splitter1303asserts the green signal onto the fiber SL via the connector1301for delivery to the FTTH node107or optional MDA401or ELA405in the reverse or upstream direction (and thus is one of the multiple reverse green signals). It is noted that upstream optical collisions between the multiple reverse green signals are eliminated through communication protocols already in place that ensure that the NIUs109of the fiber plant do not transmit simultaneously. Also, the source of the optical analog green signals (originating at the NIUs109) is not apparent or pertinent to upstream processing circuits (e.g.,611,807,907and circuits715,716,717of processor501). Rather, the processing circuits are agnostic to the contents of the optical signals and simply convert the optical analog signals to optical digital signals for interpretation by the headend103. The RF coupler1318has a second output which provides the RF signal, or a portion or variation thereof, to an RF detector1323. The RF detector1323generates an RF detection signal RFDET to a switch controller1325, which activates the optical switch1321when reverse RF signals are detected for enabling the green signal generated at the output of the laser amplifier1319to pass to the course optical WDM splitter1303. When not activated, the optical switch1321switches its output to an optical terminator1327for terminating the optic signal when not in use. A DC power supply1329provides power to various components of the NIU1311including an FP laser control circuit1331, which controls operation of the laser amplifier1319.

In operation, the switch controller1325turns on the optical switch1321to provide reverse green signals to the course optical WDM splitter1303only when a reverse RF signal is detected, or only at the appropriate time that reverse signals are allowed to be transmitted by the NIU409. Otherwise the reverse signal path is diverted to eliminate reverse green signals from subscriber locations that are not actually sending information. The illustrated embodiment shows a switched return laser (on/off) solution in which the optical path in the forward or upstream direction is turned on and off as needed. For this technique, the return signals are processed and buffered into a TDM format. The size of the available return bandwidth depends on the number of customers on the carrier. For a very simplified example, if 50 customers shared a forward bandwidth of 2.4 gigabits per second (Gbps), then a 2.4 Gbps laser is used to turn on and off slightly less than every 1/50 of a second. All of the transmitters are synchronized to the same 2.4 GHz frame rate with allowances for the known differences in network delays. The transmitter only sends the data sync framework in the 49 slots that belong to other users. In this manner the laser could turn on early enough to stabilize before sending a packet and have some trailing energy afterwards which insures that there are no glitches in the sync framing. There is also the opportunity to allow users additional bandwidth since statistically there would be a large percentage of idle packets. In one embodiment, heavy users are assigned more than one time slot if and when additional time slots are available.

There are many alternative options for the reverse communications from the subscriber locations to the headend. One significant technical challenge is managing or otherwise avoiding the combined energy back through the network from the optical sources from every active subscriber location. Depending on the number of combined sources, the network configuration potentially adds noise and distortions not found in a point to point single source optical link. In the on/off solution illustrated and other scenarios described below, the various signals collected from the subscriber location network are digitized. This involves an A/D conversion of the traditional 5-40 MHz analog band. There are opportunities to apply additional techniques such as DSP (Digital Signal Processing) to augment and enhance the return capabilities and capacity that may be implemented depending on their cost benefits. In the various scenarios described in which the incoming signals are processed and digitized, the resultant data stream is buffered and multiplexed (e.g., TDM) into a larger bit rate during the combining process. For the shared 2.4 Gbps among 50 subscriber location example, each subscriber location uniquely has about 48 megabits per second (Mbps) less overhead (e.g., framing, error correction, etc.). Typical return bandwidths in existing HFC networks including HSD, voice-over-IP (VoIP), and video-on-demand (VOD) typically do not exceed one Mbps with all services simultaneously active at the same time. It is also assumed in all cases that some number of customers share a given return wavelength.

In one alternative configuration, the return path of each subscriber location is attenuated rather than being turned completely off, and only as needed. This solution mirrors the on/off concept except that it allows that since there can be no data collisions, the only hurdle to overcome is the combined noise power generated by all of the transmit sources. If the inactive sources were attenuated significantly (e.g., 10-20 dBc) then the same objective is achieved.

Another alternative solution is a multiple wavelength method, which takes advantage of the fact that a typical EDFA has a 14-40 nanometer (nm) bandwidth. This method also does not require expensive filters to be implemented in the NIU. In this case, DWDM filters are placed at the headend or central office to sort the return colors. 10 colors spaced at 200 GHz are easily fit within the 14 nm bandwidth of the amplifier (although there may be linearity issues to be addressed in the EDFA amplifier (e.g.,703) to accommodate 10 colors). This solution may require a relatively clean, frequency stable, laser transmitter at the NIU, which may be costly. The cost of such a laser transmitter may be offset, however, by a simpler data process. It is possible to implement a straightforward A/D conversion of the bandwidth without further processing.

Another solution is an SCDMA (Synchronous Code Division Multiple Access) approach either with or without FDM. In this approach the return data information at the NIU is converted to an SCDMA output. The SCDMA carrier is wide enough to have enough processing gain to work within the very noisy environment of 100 combined laser transmitters, eliminating the need to “switch” inactive users. This is a robust signal protocol, which has been observed as recovering from 10 dBc below the analog noise floor with very good signal BER (Bit Error Rate) quality. Since the return signals do not have any bandwidth limitation, an FDM channelization between SCDMA groups can be overlaid to lower the number of users, which may reduce the electronics cost in the network.

Another solution is the use of consolation and conversion at the EDFA amplifiers. If it is assumed that the average Return amplifier has 50 or less active users, some tradeoffs are made to lower costs in the NIU by recovering the combined signals in the amplifier with an O/E conversion, processing the signal and retransmitting the combined signal on a separate wavelength (possibly 1490, 1310, or 1550 depending on the NIU's output). Then two conversions are made at the former node location, one for the local, un-amplified NIU and another for the amplified (2ndfrequency) group. The two groups are then combined for transmission back to the headend or central office.

The downstream function of the optical tap is that it acts on a fiber optic plant in a similar manner as traditional (RF) taps work on a coaxial plant. A portion of the amplified signal broadcast downstream from a node or zone amplifier is “tapped” and split evenly to each of the subscribers that are connected to the tap. Untapped optical signal is propagated downstream for use by other taps. This is different from other fiber to the home (FTTH) architectures in that other such end user splitting devices are at the end of the optical signal's transmission. In this architecture, the downstream signal my be further amplified via nodes or zone amplifiers several times with portions of the signal then tapped and distributed to subscribers along the transmission route.

The optical tap acts independent of the upstream collision domain which may employed. Depending upon the NIU in use, the tap supports the encoding of RF upstream transmission devices in the same way devices are polled in existing coaxial HFC plants today—given that the RF signal source has been converted to analog fiber transmissions by the NIU. Similarly, the tap works seamlessly if an NIU is polled by the node or zone amplifier for upstream signals that could occur in baseband digital format. Fundamentally, given a cable plant built with this architecture, no changes are needed to the fiber or taps in order for it to support 1) analog fiber upstream and downstream, 2) analog fiber downstream and baseband digital upstream, or 3) bidirectional baseband digital transmission. The NIU, the optical node and/or the zone amplifier and the customer premises equipment (e.g., the high speed data modem, set top box, etc.) may be configured to support any of these embodiments.

The NIUs in this architecture are as simple as an optical detector and RF converter (for receipt of downstream only broadcast signals), to bidirectional analog fiber transmissions with signals encoded using traditional HFC cable plant technologies, to analog fiber downstream with baseband digital upstream, to baseband digital bi-directionally, to baseband digital downstream with unique laser colors (frequencies) for each home upstream, to unique laser colors (frequencies) bi-directionally. The basic architecture and cable plant (fiber and taps) supports any of these configurations without modification.

A low-loss shared FTTH distribution network according to an embodiment of the present invention includes a cable with optical fibers which is routed from the point of distribution into multiple subscriber zones, each subscriber zone including at least one subscriber location, a tap device located within a first subscriber zone which includes an optical tap which taps a first one of the optical fibers with a downstream optical fiber providing at least a portion of an optical path provided to at least one first subscriber location within the first subscriber zone, and a straight-through optical fiber which is routed straight through the first subscriber zone and into a second subscriber zone.

The tap device may include ports (e.g., upstream and downstream ports) and the fibers may include fused connections and/or may be interfaced with fiber optic connectors. The tap device may further include a splitter which splits the downstream optical fiber into multiple downstream optical fibers. In this case of a splitter, the tap device may include tap ports for the downstream optical fibers. Each tap port may include a fused connection or a fiber optic connector. Also, any number of straight-through optical fibers may be included which are routed straight through first subscriber zone.

A low-loss shared optical plant according to an embodiment of the present invention includes a cable including optical fibers routed into multiple subscriber zones, each subscriber zone including at least one subscriber location, tap devices located within a first subscriber zone and including optical taps for interfacing downstream optical fibers with corresponding ones of the routed optical fibers, where each downstream optical fiber provides at least a portion of a corresponding one of multiple optical paths to first subscriber locations within the first subscriber zone, and at least one a straight-through optical fiber which is routed straight through the first subscriber zone and into a second subscriber zone. Multiple straight-through optical fibers may be included.

A method of distributing optical fibers of a shared FTTH network subscriber area according to an embodiment of the present invention includes routing a cable including multiple optical fibers into multiple subscriber zones, tapping at least one optical fiber with a tap device within a first subscriber zone to interface a downstream optical fiber which provides at least a portion of an optical path to a subscriber location within the first subscriber zone, and routing at least one optical fiber straight through the first subscriber zone and into a second subscriber zone. The method may include routing a cable which includes multiple optical fibers. The method may include routing at least two optical fibers straight through the first subscriber zone and into the second subscriber zone. The method may include tapping the optical fiber with multiple tap devices. The method may include routing at least one optical fiber straight through each of the corresponding number of tap devices and into the second subscriber zone. The method may include fusing at least one optical fibers and/or interfacing a downstream optical fiber with a fiber optic connector.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions and variations are possible and contemplated. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for providing out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims.