Abstract:
A coherent passive optical network extender apparatus includes an extender transceiver for communication with an associated optical headend. The extender transceiver includes at least one receiving portion, at least one transmitting portion, and an extension processor. The apparatus further includes a signal adaptation unit configured to convert a downstream electrical transmission lane into a plurality of individual wavelengths. Each of the converted individual wavelengths are for transmission to one of an optical node and an end user. The apparatus further includes a plurality of transceivers, disposed within the signal adaptation unit, and configured to process and transmit the converted individual wavelengths as a bundle for retransmission to the respective end users.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Patent Application Ser. No. 62/343,219, filed May 31, 2016, which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The field of the disclosure relates generally to fiber communication networks, and more particularly, to access networks capable of transmitting coherent optical signals. 
         [0003]    Fiber-to-the-premise (FTTP) based access networks have been widely deployed in many regions of the world. Increasing demand for high-speed data and video services is presently driving growth in access bandwidth requirements, up to gigabits per second (Gb/s) for residential offerings and multi-Gb/s for business. Conventional FTTP network architectures utilize a passive optical network (PON), for example, a Gigabit passive optical network (GPON) within ITU-T, or an Ethernet passive optical network (EPON) within IEEE. PON is point-to-multipoint, and can be an economical alternative to point-to-point Ethernet for moderate to large populations. GPON and EPON networks have been deployed in the last 10 years, and presently realize 2.5/1.25 Gb/s data rates for downstream and 1.25 Gb/s upstream, respectively. 10-Gb/s PON (XG-PON or IEEE 10G-EPON) is being quickly deployed for high-bandwidth applications. GPON and EPON have some technical differences in terms of signal encapsulation and dynamic bandwidth allocation, but both PON types are capable of carrying data over fiber through a passive optical network all the way from an optical hub to a customer premise. Additionally, both PON types use baseband digital signaling over the fiber to carry the information. 
         [0004]      FIG. 1  is a schematic illustration of a conventional PON system  100  for delivering PON to subscribers of a network operator. System  100  includes an optical headend (OHE)  102 , a splitter  104 , and a plurality of optical network units (ONU)  106  in communication with a plurality of customer premises  108 , respectively. Optical hub  102  is, for example, a central office, a communications hub, and includes an optical line terminal (OLT) for converting standard signals from a service provider (not shown) to the frequency and framing used by the PON system, and for coordinating multiplexing between conversion devices on the ONUs located on or near customers premises  108 . 
         [0005]    The OLT contains a central processing unit (CPU), passive optical network cards, a gateway router (GWR) and voice gateway (VGW) uplink cards . . . . ONUs  106  are downstream termination units for the respective customer premises  108 . System  100  may be configured, for example, for 1-to-32 or 1-to-64 split ratios, over a distance of 20 kilometers, and using a fixed set of wavelengths. In a typical configuration, a PON trunk fiber  110  carries optical signals from OHE  102  to splitter  104 . Splitter  104  then splits the optical signals from PON trunk fiber  110  into the different fixed wavelengths, which are then carried between splitter  104  and ONUs  106  by individual short fibers  112 . 
         [0006]    Conventional architectures like system  100 , however, presently experience several drawbacks. Most OHEs, for example, have fewer PON trunk fibers available to the splitter, or node, than are required for the increasing number of subscribers. Additionally, many modern cable operators utilize a Data Over Cable Service Interface Specification (DOCSIS) infrastructure that may potentially transmit as far as 100 miles, which is considerably farther than distances supported by conventional PON technologies, which are typically limited to 20 kilometers (km). Therefore, a conventional PON extension system has been utilized to extend the transmission range of PON networks up to these increasing ranges required by a cable operator. 
         [0007]      FIG. 2  is a schematic illustration of a conventional PON extension system  200  for deploying a PON over distances greater than 20 km. System  200  includes an OHE  202 , a PON extender  204 , and a plurality of ONUs  206 , which may be in communication with a plurality of respective customer premises (not shown). ONUs  206  transmit and receive optical carrier signals to/from PON extender  204  by short fibers/nodes  208 , and PON extender  204  connects with OHE  202  through trunk fiber  210 . Short fibers/nodes  208  recover PON signal streams from PON extender  204  and transmit the recovered signals to ONUs  206  using standard PON optics. Respective nodes of short fibers/nodes  208  may also function as splitters. ONUs  206  will include 32-64 ONUs per group, and will have a symmetric architecture (e.g., ONU  206 ( 1 ), 10/10G-EPON), or an asymmetric architecture (e.g., ONU  206 ( 1 )′, 10/1G-EPON). 
         [0008]    OHE  202  includes an OLT  212 , a plurality of hub transceivers  214 , and an optical multiplexer  216 . Hub transceivers  214  may be Wavelength-Division Multiplex Small Form Factor Pluggable transceiver (PXFP-WDM) modules. Hub transceivers  214  may also each be a combination of at least one receiver and at least one transmitter (not separately shown). Hub transceivers  214  are each configured to transmit a downstream optical signal λ D  to multiplexer  216 , and similarly receive an upstream optical signal λ u  from multiplexer  216  (where multiplexer  216  also functions as a demultiplexer). Multiplexer  216  combines the plurality of downstream optical signals λ D  for downstream transmission over trunk fiber  210 . Similarly, multiplexer  216  also splits the upstream transmission from trunk fiber  210  into the plurality of respective upstream optical signals λ U . 
         [0009]    PON extender  204  includes a demultiplexer  218 , a plurality of extender transceivers  220 , and a plurality of respective extender optics  222  for each extender transceiver  220 . Extender transceivers  220  each include at least one digital signal processor (DSP, not shown) and are, for example, a 10G multisource agreement (MSA) transceiver module. Extender optics  222  are, for example, 10G EPON optics. Transmission between the respective hub transceivers  214  and extender transceivers  220  over trunk fiber  210  represents a PON trunk link  224 . Transmission between the respective extender optics  222  and ONUs  206  over short fibers/nodes  208  represents a PON access link  226 . PON extenders are sometimes referred to as “PON concentrators” due to their ability to carry multiple PONs on a single fiber between the OLT and the PON extender. 
         [0010]    PON extension system  200  disposes OLT  212  within OHE  202 , and represents a centralized architecture for utilizing Wavelength-Division Multiplex (WDM) optics, as opposed to standard PON optics with fixed wavelengths, to deploy 10G-EPON where there is a limited number fibers for the number of subscribers, and for distances over 20 km. That is, WDM technology is used to multiplex a plurality of PON streams λ onto a single fiber (i.e., trunk fiber  210 ). Electrical and optical interface specifications for PON extension system  200  are standardized by the Society of Cable Telecommunications Engineers (SCTE). The centralized structure of PON extension system  200  generally simplifies maintenance, reduces operational costs, and improves reliability for cable operators. 
         [0011]    PON extension system  200 , however, has several limitations with respect to scalability for the increasing per-subscriber data rates, and with respect to newer technologies used by cable operators, as well as their related services and applications. Conventional PON extender architectures not configured, for example, sufficiently to employ upcoming technologies such as next-generation PON (NG-PON, NG-PON2) based on time and wavelength division multiplexing (TWDM), which deploys at 40-Gb/s or more, or 100G-EPON, which are multi-wavelength PON systems. The conventional PON extender is unable to meet wavelength resource requirements of these newer technologies. For a PON extender to increase data transmission from 10 Gb/s to 40 Gb/s, for example, the PON extender would have to manage at least four wavelengths each in the upstream and downstream directions for every ONU, or else upgrade the 10G MSA transceivers to 25-40 Gb/s per channel with direct detection. Conventional PON extenders are not configured to manage eight or more discrete modules in parallel for each ONU, and merely upgrading a 10G MSA transceiver may significantly impair the chromatic dispersion of the signals transmitted therethrough. 
       BRIEF SUMMARY 
       [0012]    In an embodiment, a coherent passive optical network extender apparatus includes an extender transceiver for communication with an associated optical headend. The extender transceiver includes at least one receiving portion, at least one transmitting portion, and an extension processor. The apparatus further includes a signal adaptation unit configured to convert a downstream electrical transmission lane into a plurality of individual wavelengths. Each of the converted individual wavelengths are for transmission to one of an optical node and an end user. The apparatus further includes a plurality of transceivers, disposed within the signal adaptation unit, and configured to process and transmit the converted individual wavelengths as a bundle for retransmission to the respective end users. 
         [0013]    An optical network communication system utilizes a passive optical network (PON). The system includes an optical headend. The optical headend includes an optical line terminal and a hub transceiver. The optical line terminal is configured to convert standard signals to a frequency and framing of the PON for transmission from the hub transceiver, and to coordinate multiplexing throughout the system. The system further includes a trunk fiber configured to carry transmitted signals from the hub transceiver, and a coherent PON extender configured to recover coherent optical signals transmitted over the trunk fiber. The coherent PON extender is further configured to retransmit the recovered coherent optical signals. The system still further includes an extension fiber configured to carry the retransmitted coherent optical signals to one of an optical network unit and/or a customer premises. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
           [0015]      FIG. 1  is a schematic illustration of a conventional PON system. 
           [0016]      FIG. 2  is a schematic illustration of a conventional PON extension system. 
           [0017]      FIG. 3  is a schematic illustration of an exemplary fiber communication system utilizing coherent PON transmission. 
           [0018]      FIG. 4  is a schematic illustration of an exemplary fiber communication system utilizing the coherent PON extender depicted in  FIG. 3 , implementing a power-split connection. 
           [0019]      FIG. 5  is a schematic illustration of an exemplary fiber communication system utilizing the coherent PON extender depicted in  FIG. 3 , implementing a wavelength-split connection. 
       
    
    
       [0020]    Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems including one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
       DETAILED DESCRIPTION 
       [0021]    In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
         [0022]    The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. 
         [0023]    “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
         [0024]    Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
         [0025]    According to the embodiments herein, a coherent PON extension system is capable of deploying optical transmissions, including NG-PON and 100 G-EPON, for fiber trunk links spanning over 100 miles. The coherent PON extension embodiments described herein are particularly advantageous in the deployment of coherent technologies in FTTP access networks. 
         [0026]    Coherent technologies have been recently implemented for optical metro and access networks, in both brown- and green-field deployments. Digital coherent systems utilize digital signal processing (DSP) techniques, and achieve high spectral efficiency (SE), higher data rate per channel, and superior receiver sensitivity that allows for extended power budget. Coherent detection is capable of high frequency selectivity through local oscillator (LO) tuning capability, which enables closely spaced, dense/ultra-dense WDM (DWDM) without requiring additional narrow band optical filters. Coherent detection systems recover a multi-dimensional signal, which, among other things, compensates for linear transmission impairments such as chromatic dispersion (CD) and polarization-mode dispersion (PMD). Coherent detection more efficiently utilize the spectral resources, and may take advantage of future network upgrades through the use of multi-level advanced modulation formats. This utilization of coherent optics has now migrated from long haul and metro networks, to data-center interconnect (DCI) and near-future access networks. 
         [0027]    Accordingly, the coherent PON extension systems and methods described herein advantageously implement coherent technologies to achieve high speed/data rate transmission over existing fiber trunk links for distances greater than 100 km, or 100 miles in some instances. The present embodiments feature a novel and advantageous PON extender architecture that utilizes coherent optics within the trunk link to significantly increase bandwidth capacity, while also simplifying the operational complexity of system hardware by minimizing the number of parallel electronic/optical WDM modules. 
         [0028]    Utilizing coherent detection technologies, the receiver sensitivity is significantly greater as compared with conventional direct detection technologies. The coherent PON extension system herein thus provides higher spectral efficiency the in a conventional PON extension system. Unlike the conventional PON extension system, the present coherent PON extension system is compatible with DWDM operation. According to the systems and methods described herein, cable operators utilizing the coherent PON extension system realize more efficient fiber utilization, while also achieving centralized OLT configuration that serves more customer premises utilizing the existing infrastructure the operator. In some embodiments, the coherent PON extension systems and methods described herein one or both of wavelength-split and power-split architectures for a multi-wavelength PON transmission scheme. 
         [0029]      FIG. 3  is a schematic illustration of an exemplary fiber communication system  300  utilizing coherent PON transmission. System  300  includes an OHE  302 , a coherent PON extender  304 , at least one node/splitter  306 , a plurality of downstream termination units  308  and a plurality of respective end users  310 . Units  308  may be, for example, an ONU or a cellular base station (including small cell base stations). End users  310  may be, for example, a customer device or customer premises (e.g., a home, apartment building, or residential radio frequency over glass (RFoG) subscriber) or a business user (including point to multipoint fiber networks with business EPON subscribers). OHE  302  is, for example, a central office or a communications hub. 
         [0030]    In an exemplary embodiment, system  300  implements a PON and a DWDM PON architecture. 
         [0031]    OHE  302  communicates with coherent PON extender  304  by way of trunk fiber  312 , and PON extender  304  communicates with node/splitter  306  over extension fiber  314 . In an exemplary embodiment, one or more of trunk fiber  312  and extension fiber  314  communicate both the upstream and downstream transmission over the same fiber. In some embodiments, one or more of trunk fiber  312  in extension fiber  314  communicate upstream transmission over one fiber, and downstream transmission over a different fiber. 
         [0032]    OHE  302  includes an OLT  316  and a hub transceiver  318 . Hub transceiver  318  includes a transceiver processor  320 , a hub transmitting portion  322 , and a hub receiving portion  324 . In an exemplary embodiment, transceiver processor  320  includes one or more processing components, including without limitation, an analog to digital converter (ADC), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a forward error correction (FEC) unit, a digital to analog converter (DAC), and one or more multiplexers/demultiplexers. 
         [0033]    In some embodiments, each of hub transmitting portion  322  and hub receiving portion  324  have their own dedicated transceiver processor and processing components. In the exemplary embodiment, hub transmitting portion  322  includes an optical circulators and modulator, and hub receiving portion  324  includes an integrated coherent transmitter. Exemplary architectures of hub transceiver and processing components are described in greater detail in co-pending U.S. patent application Ser. No. 15/283,632, filed Oct. 3, 2016, and co-pending U.S. patent application Ser. No. 15/590,464, filed May 9, 2017, the disclosures of both which are incorporated by reference herein. Additionally, system  300  is illustrated in  FIG. 3  with only one hub transceiver  318  for ease of explanation. A person of ordinary skill in the art though, will understand that OHE  302  may utilize a plurality of separate transceivers, which may be multiplexed according to the co-pending disclosures. 
         [0034]    Coherent PON extender  304  includes an extender transceiver  326  and a signal adaptation unit  328 . The architecture of extender transceiver  326  may be similar to that of hub transceiver  318 , and includes in extender processor  330 , an extender receiving portion  332 , and an extender transmitting portion  334 , as well as one or more of the additional components described above. Signal adaptation unit  328  includes a signal adapter processor  336 , a plurality of adapter transceivers  338 , and at least one multiplexer  340 . 
         [0035]    In operation of system  300 , optical signals λ 1D -λ 4D  in the downstream electrical lane and optical signals λ 1U -λ 4U  in the upstream optical lane are communicated between OLT  316  and transceiver processor  320  of hub transceiver  318 . The downstream optical lane is multiplexed at OHE  302  and transmitted over trunk fiber  312  to coherent PON extender  304 . Similarly, the upstream optical lane is received by OHE  302  and demultiplexed into the respective upstream optical signals. The upstream and downstream optical lanes are communicated between extended processor  330  and signal adapter processor  336 . Signal adapter processor  336  pairs the individual upstream and downstream optical signals with their respective counterparts, for further transmission to/reception of the optical signal pairs with respective ONU transmitters  342  and ONU receivers  344 . 
         [0036]    In some embodiments, system  300  represents a 36 decibel (36-dB) optical link budget, and each of the downstream and upstream electrical lanes are 10G electrical lanes. That is, trunk fiber  312  carries a 40G coherent optical transmission in each of the upstream and downstream directions, e.g., λ 40G-coherent-down  and λ 40G-coherent-up.  The 36-dB optical link budget may be applied, for example, to a 4×10G NG-PON2 network. System  300  thus represents a significant improvement over conventional system  200  ( FIG. 2 , above), which cannot, in a stable manner, configure each ONU  206  to transmit four separate wavelengths in parallel with a per wavelength channel line rate of 10 Gb/s. 
         [0037]    In other embodiments, system  300  represents a 30-dB optical link budget, and each of the downstream and upstream electrical lanes are 25G electrical lanes. That is, trunk fiber  312  carries a 100G coherent optical transmission in each of the upstream and downstream directions, e.g., λ 100G-coherent-down  and λ 100G-coherent-up.  The 30-dB optical link budget may be applied, for example, to a 4+25G EPON network (100G-EPON). System  300  thus represents a further improvement over conventional system  200  ( FIG. 2 , above), which would suffer from chromatic dispersion impairment if the conventional extender receivers  220  were upgraded to carry a channel line rate of 25 Gb/s. The matching processing components between OHE  302  and coherent PON extender  304  (e.g., such as the ASIC) removes the chromatic dispersion deficiencies experienced by the conventional PON extenders. 
         [0038]    In an exemplary embodiment, system  300  further utilizes TWDM. In some embodiments, each coherent trunk link of system  300  is based on dual-polarization quadrature phase-shift keying (DP-QPSK) or 16-ary quadrature amplitude modulation (16-QAM) formats for 40G and 100G coherent links, with one wavelength of a wavelength pair for downstream transmission, and the other wavelength of the pair for upstream transmission. Additionally, utilization of an ASIC in hub transceiver  318  and extender receiver  326  removes DSP chromatic dispersion, and only requires use of hard-decision FEC instead of soft-decision FEC from the FEC unit. According to the advantageous embodiments illustrated in  FIG. 3 , a cable operator will realize a substantial improvement on optical link power budget, and for even greater transmission distances, for example, over 100 km. The improved architecture of system  300  further eliminates the need for costly gearboxes (e.g., Serializer/De-serializer or SERDES) for electrical signal conversion. Instead, system  300  more seamlessly interfaces with the total data rate of an NG-PON network, for example, thereby substantially mitigating the deficiencies of conventional PON extenders, such as system transmission impairment and receiver sensitivity. 
         [0039]      FIG. 4  is a schematic illustration of an exemplary fiber communication system  400  utilizing coherent PON extender  304  depicted in  FIG. 3 , as well as additional complementary components of system  300 . System  400  is implemented, for example, for an NG-PON network or a 100G-EPON network, and utilizes a power-split connection for servicing various remote nodes of the network. In the exemplary embodiment, the trunk link of system  400  is a 100G/200G DWDM coherent 100 km link. 
         [0040]    System  400  includes an OHE  402 , a plurality of coherent PON extenders  404 , a plurality of remote nodes  406 , a plurality of end users  408 , a trunk fiber  410 , and a plurality of extension fibers  412 . In this example, end users  408  may each include one or more ONUs or base stations, for servicing one or more customer devices/premises business users. OHE  402  is otherwise is similar to OHE  302  ( FIG. 3 ), coherent PON extenders  404  are similar to coherent PON extender  304 , and remote nodes  406  are similar to node/splitter  306 . System  400  further includes a power splitter/combiner  414  disposed between OHE  402  and the plurality of coherent PON extenders  404 . OHE  402  communicates with coherent PON extenders  404 , through power splitter/combiner  414 , by way of trunk fiber  410 . Coherent PON extenders  404  communicate with remote nodes  406  over respective extension fibers  412 . Trunk fiber  410  may span, for example, a distance of 100 km, and extension fibers  412  may span a distance of 20 km. In some embodiments, each coherent PON extender  404  may represent 1, 2, 3, or more PON OLTs. For example, as depicted in  FIG. 4 , extender  404 ( 1 ) represents a single OLT, extender  404 ( 2 ) represents three OLTs, and extender  404 ( 3 ) represents to OLTs. 
         [0041]    In operation, system  400  utilizes power splitter/combiner  414 , located along trunk fiber  410  between OHE  402  and coherent PON extenders  404  in a point-to-multipoint configuration. The narrow filtering functional capability of coherent detection technology allows the system  400  to advantageously utilize the tunable ability of an LO (not shown) and a transmitted wavelength to power-split the coherent optical link among multiple coherent PON extenders. System  400  thus achieves optical demultiplexing within a coherent optical receiver (e.g., receiver/receiving portions  324 ,  332 ,  338 ,  344 ,  FIG. 3 ) having a wavelength tunable capability of LO sources for each coherent PON extender  304 . In some embodiments, multiple LO sources are utilized for each coherent PON extender  404  representing multiple PON OLTs (e.g., extenders  404 ( 2 ),  404 ( 3 )). According to the advantageous architecture depicted in  FIG. 4 , system  400  thus is capable of performing as two cascade PON systems, with the coherent optical link (headend-to-extender) as the first stage, and a standard PON (node-to-end user) as the second stage. 
         [0042]      FIG. 5  is a schematic illustration of an exemplary fiber communication system utilizing the coherent PON extender depicted in  FIG. 3 , implementing a wavelength-split connection. Similar  500  is similar to system  400 , in that it may be implemented with an NG-PON network or a 100G-EPON network, and may further include a 100G/200G DWDM coherent 100 km link. Additionally, a person of ordinary skill in the art will comprehend how the wavelength-split principles of system  500 , described below, may be implemented in combination with the power-split principles system  400 , described above. 
         [0043]    System  500  includes an OHE  502 , a plurality of coherent PON extenders  504 , a plurality of remote nodes  506 , a plurality of end users  508 , a trunk fiber  510 , and a plurality of extension fibers  512 , similar to system  400 , above. System  500  further includes a plurality of WDM filters  514  that serve as add/drop points  514  along trunk fiber  510 . In an exemplary embodiment, each of coherent PON extenders  504  may service the same, or different, type of PON network. For example, coherent PON extender  504 ( 1 ) may represent a 10×10G PON OLT for a 10G GPON or EPON network; coherent PON extender  504 ( 2 ) may represent a 100G PON OLT for an NG-PON2 or 100G-EPON network; coherent PON extender  504 ( 3 ) may represent a 3×100G PON OLTs for an NG-PON2 or 100G-EPON network. 
         [0044]    In operation, system  500  implements DWDM coherent optics and utilizes a cascade of WDM filters  514  (as opposed to power splitter/combiner  414 ,  FIG. 4 ) along the headend-to-extender trunk link to create multiple add/drop locations for the plurality of coherent PON extenders  504 . In an exemplary embodiment, downstream optical signals are multiplexed at OHE  502  into respective 100G or 200G coherent wavelength channels on the same fiber (e.g., trunk fiber  510 ) for transmission to the plurality of coherent PON extenders  504 . Single-channel or multiple-channels coherent PON extenders may then be connected to the main trunk link through the add/drop WDM filters  514 . Each connected coherent PON extender  504  may then recover the received optical signals and retransmit recovered signals to the respective remote node over respective extension fibers  512 , with the signals are then transmitted to the plurality of end users  508  with standard PON formats. 
         [0045]    In the exemplary embodiment, each coherent PON extender  504  may be implemented for a single PON, dual PONs, or multiple PONs. The architecture of system  500  is further advantageously compatible with conventional PON extender system  200  (for 10G PON), but offers greater flexibility than the conventional PON extension systems to reach more clusters of residential and business areas. System  500  achieves still further flexibility over the conventional PON extension systems by being able expand the amount of data transmitted by adjusting the baud rate, modulation format, and/or other parameters, before additional wavelengths must be added to carry the additional data. Wavelengths are considered a precious resource within the modern cable fiber infrastructure. 
         [0046]    According to the advantageous systems and methods described above, a coherent PON extension architecture utilizes coherent optics in either or both ends of the trunk link to deliver coherent signals over longer trunk fiber distances. The systems and methods described herein utilizing existing fiber infrastructures to increase the capacity of the infrastructures to utilize expanding and next generation PON technologies, but without requiring the addition of unnecessary wavelengths. According to the embodiments described herein, future high bandwidth demand can be met utilizing existing network infrastructures, while also simplifying the operational complexity of the PON hardware by minimizing the number of parallel electronic/optical WDM modules. The present systems and methods thus significantly extend the life of existing fiber infrastructures, while more efficiently using existing optical wavelengths. Through the techniques described herein, a fiber communication network may realize significantly increased scalability, to flexibly grow according to increasing demand from users of both cable operator and cellular services. 
         [0047]    Exemplary embodiments of fiber communication systems and methods are described above in detail. The systems and methods of this disclosure though, are not limited to only the specific embodiments described herein, but rather, the components and/or steps of their implementation may be utilized independently and separately from other components and/or steps described herein. Additionally, the exemplary embodiments can be implemented and utilized in connection with other access networks utilizing fiber and coaxial transmission at the end user stage. 
         [0048]    This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
         [0049]    Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, a particular feature shown in a drawing may be referenced and/or claimed in combination with features of the other drawings. 
         [0050]    Some embodiments involve the use of one or more electronic or computing devices. Such devices typically include a processor or controller, such as a general purpose central processing unit (CPU), a graphics processing unit (GPU), a microcontroller, a reduced instruction set computer (RISC) processor, an application specific integrated circuit (ASIC), a programmable logic circuit (PLC), a field programmable gate array (FPGA), a DSP device, and/or any other circuit or processor capable of executing the functions described herein. The processes described herein may be encoded as executable instructions embodied in a computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. The above examples are exemplary only, and thus are not intended to limit in any way the definition and/or meaning of the term “processor.” 
         [0051]    This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.