Patent Application
20230361878
This disclosure relates generally to optical wavelength multiplexing, and more particularly to wavelength division multiplexing devices that improve network availability.
As use of the Internet continues to grow, optical communication systems are being required to carry ever larger amounts of data. In the access portion of the network, the density and frequency of transactions are also increasing the value of the data traffic over time. In particular, the emergence of fifth generation (5G) cellular networks has increased the demand for high-bandwidth data transmission to service the numerous cell sites and other nodes of the radio access network (RAN). The demand for front, mid, and back-hauling services by 5G RANs are driving demand for both higher data capacity and guaranteed availability levels. The reliance on networks for conducting business by way of video conferences and large file transfers from remote locations is also increasing demand for fiber to the x (FTTX) services that have guaranteed availability levels. Carriers cannot provide network availability levels sufficient to support the service level agreements (SLAs) being demanded based on currently deployed architectures, equipment, and processes. End users and vendors also lack cost effective solutions that could deliver the availability demanded by these large data capacity applications.
Field service test equipment, traditionally used to assure build quality before release into the network, cannot assure service quality in real time. End users are thus evaluating embedded network monitoring and preventative maintenance solutions in order to compete in a service level-based market. Accordingly, network carriers are being forced to upgrade their networks to enable compliance with SLAs that guarantee higher availability in the optical distribution portion of their networks, to support 5G key performance indicators, and to meet their client's availability goals.
In most cases, existing optical distribution networks can only provide three nines (99.9%) availability. However, the required availability in radio access networks and other critical infrastructure is typically four or five nines (99.99% or 99.999%) availability. To meet three nines availability, a network can only be unavailable for a total of nine hours a year. Four nines availability guarantees reduce the allowable downtime to 52 minutes a year. An SLA promising five nines availability is violated if the network is down for more than a total of five minutes in the span of a year.
The trend is for convergence of access networks so that network infrastructure is shared between RAN and FTTX services. A fiber break or other interruption along a fiber optic feeder or distribution cable can thus potentially affect multiple services. In order to restore these services quickly enough to avoid violating SLAs, the network must reroute affected traffic via an alternative path. This is currently accomplished by electrically switching and routing traffic signals in every node of the electrical portion of the network to switch traffic signals via alternative nodes.
However, providing an alternative path through electrical switching in each node is not practicable for optical networks in which multiple services coexist. This is largely because there is often only one optical path between the head-end and the network access point to which a network node that lost service is connected. To provide required service availability at these network nodes, the optical distribution network must include at least one independent direct optical link between the nodes in a network that provides an alternative to the primary path. This alternative path is commonly called a protection path. If data transmitted over the primary path does not arrive at the network node, the head-end switches transmission to the protection path.
For total protection, complete redundancy is required. Thus, the protection path must include not only the optical fiber, but also the transmitters and receivers at each end of the optical fiber. Such an arrangement is costly, particularly for WDM systems since multiple transmitters are required for each path. In cases where the degree of protection assured by full redundancy is not needed, transmitters can be switched between the primary and protection optical fibers. However, in order to switch the transmitters, information about a failure in the primary path must be obtained and relayed to the switch controller, which adds considerably to the complexity of the protection system. Thus, there is a need in fiber optic networks for improved devices and methods for increasing the availability of the network.
In an aspect of the disclosure, a network access point is provided. The network access point includes a first common port configured to receive a primary optical beam including a plurality of primary optical signals, a second common port configured to receive a secondary optical beam including a plurality of secondary optical signals, a wavelength division multiplexing device including a plurality of channel ports each configured to transmit a respective optical signal of a selected one of the plurality of primary optical signals or the plurality of secondary optical signals, and an optical coupling device configured to operatively couple at least one of the primary optical beam and the secondary optical beam to the wavelength division multiplexing device.
In an embodiment of the disclosed network access point, the optical coupling device may include a beam splitter configured to split each of the primary optical beam and the secondary optical beam into a first portion thereof and a second portion thereof, and the first portion of each of the primary optical beam and the secondary optical beam may be provided to the wavelength division multiplexing device.
In another embodiment of the disclosed network access point, the network access point may further comprise a tap port, and the second portion of each of the primary optical beam and the secondary optical beam may be provided to the tap port.
In another embodiment of the disclosed network access point, the beam splitter may be further configured to split an uplink optical beam into a first portion thereof and a second portion thereof, provide the first portion of the uplink optical beam to the first common port, and provide the second portion of the uplink optical beam to the second common port.
In another embodiment of the disclosed network access point, the optical coupling device may include an optical switch having a first switch state and a second switch state. While in the first switch state, the optical switch may operatively couple the first common port to the wavelength division multiplexing device and optically isolate the second common port from the wavelength division multiplexing device. While in the second switch state, the optical switch may operatively couple the second common port to the wavelength division multiplexing device and optically isolate the first common port from the wavelength division multiplexing device.
In another embodiment of the disclosed network access point, the network access point may further include an actuator and a sensing device. The actuator may be configured to switch the optical switch from the first switch state to the second switch state in response to receiving a trigger signal. The sensing device may be configured to generate the trigger signal in response to detecting one or both of a loss of signal at the first common port and a presence of signal on the second common port.
In another embodiment of the disclosed network access point, the sensing device may be further configured to detect a presence of signal at the first common port, and the actuator may be further configured to cause the optical coupling device to operatively couple the wavelength division multiplexing device to the first common port in response to the sensing device detecting the presence of signal at the first common port.
In another embodiment of the disclosed network access point, the actuator may include a first actuator state that causes the optical switch to be in the first switch state, a second actuator state that causes the optical switch to be in the second switch state, and a latching device configured to maintain the actuator in the first actuator state until the trigger signal is received from the sensing device.
In another embodiment of the disclosed network access point, the latching device may be further configured to release the actuator in response to receiving the trigger signal while the actuator is in the first actuator state, and in response to the actuator entering the second actuator state, maintain the actuator in the second actuator state until the actuator is reset.
In another embodiment of the disclosed network access point, the network access point may further include a first auxiliary port, and the optical switch may be further configured to operatively couple the first auxiliary port to the second common port while in the first switch state.
In another embodiment of the disclosed network access point, the network access point may include a second auxiliary port, and the optical switch may be further configured to operatively couple the second auxiliary port to the first common port while in the second switch state.
In another aspect of the disclosure, a method of increasing availability in an optical network is disclosed. The method includes transmitting the primary optical beam including the plurality of primary optical signals over the primary distribution cable to the first common port of the network access point, splitting the primary optical beam into the first portion thereof and the second portion thereof at the network access point, and providing the first portion of the primary optical beam to the wavelength division multiplexing device of the network access point. In response to detecting a problem in the primary distribution cable, the method stops transmitting the primary optical beam over the primary distribution cable and begins transmitting the secondary optical beam including the plurality of secondary optical signals over the secondary distribution cable to the second common port of the network access point. The method further includes splitting the secondary optical beam into the first portion thereof and the second portion thereof at the network access point, and providing the first portion of the secondary optical beam to the wavelength division multiplexing device of the network access point.
In an embodiment of the disclosed method, the method may further include providing the second portion of the primary optical beam or the second portion of the secondary optical beam to the tap port of the network access point.
In another embodiment of the disclosed method, the method may further include splitting the uplink optical beam into the first portion thereof and the second portion thereof at the network access point, providing the first portion of the uplink optical beam to the first common port, and providing the second portion of the uplink optical beam to the second common port.
In another aspect of the disclosure, another method of increasing service availability in an optical network is disclosed. The method includes transmitting the primary optical beam including the plurality of primary optical signals over the primary distribution cable to the first common port of the network access point, transmitting the secondary optical beam including the plurality of secondary optical signals over the secondary distribution cable to the second common port of the network access point, and operatively coupling the primary optical beam from the first common port of the network access point to the wavelength division multiplexing device of the network access point. In response to detecting the problem in the primary distribution cable, the method operatively couples the secondary optical beam from the second common port of the network access point to the wavelength division multiplexing device of the network access point.
In an embodiment of the disclosed method, the secondary optical beam may be transmitted over the secondary distribution cable in response to detecting the problem with the primary distribution cable.
In another embodiment of the disclosed method, the problem in the primary distribution cable may be detected based at least in part on the loss of signal at the first common port of the network access point.
In another embodiment of the disclosed method, the problem in the primary distribution cable may be detected based at least in part on a presence of signal at the second common port of the network access point.
In another embodiment of the disclosed method, the method may further include, in response to detecting a presence of signal at the first common port of the network access point while the second common port is operatively coupled to the wavelength division multiplexing device, optically coupling the first common port to the wavelength division multiplexing device and optically isolating the second common port from the wavelength division multiplexing device.
In another embodiment of the disclosed method, the method may further include, while the primary optical beam is operatively coupled from the first common port to the wavelength division multiplexing device, operatively coupling the second common port to the first auxiliary port, and in response to detecting the problem in the primary distribution cable, operatively coupling the first common port to the second auxiliary port of the network access point.
The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s), and together with the description serve to explain principles and operation of the various embodiments. Features and attributes associated with any of the embodiments shown or described may be applied to other embodiments shown, described, or appreciated based on this disclosure.
Various embodiments will be further clarified by examples in the description below. In general, the description relates to providing end-to-end protection in an optical network using wavelength division multiplexing (WDM). Protection schemes may include a network access point having one common port that is coupled to the optical network by a primary distribution cable and another common port that is coupled to the optical network by a secondary distribution cable. The network access point includes both WDM and optical coupling features that operatively couple one or more optical signals between the primary distribution cable and one or more drop cables when the network is operating in a normal state, and that operatively couple one or more optical signals between the secondary distribution cable and the one or more drop cables when the network is operating in a protection state. In this way, the network access device may minimize any interruption in optical communication between tail-end nodes connected to the drop cables and one or more head-end nodes that provide optical signals to, and receive optical signals from, one or both of the primary and secondary distribution cables.
The network access point 14 includes a WDM device 24 and optical coupling device 26 (e.g., an optical switch or beam splitter) that operatively couples the WDM device 24 to the primary and secondary distribution cables 20, 22. For protection schemes in which an optical beam may be transmitted simultaneously on each of the primary and secondary distribution cables 20, 22, the optical coupling device 26 may include an optical switch. The optical switch may be provided by any suitable device that selectively optically couples one of the primary and secondary distribution cables 20, 22 to the WDM device 24 while isolating the WDM device 24 from the other of the primary and secondary distribution cables 20, 22. When optical beams are being transmitted simultaneously through both the primary and secondary distribution cables, the secondary optical beam may be redundant to (i.e., a duplicate of) the primary optical beam. In other cases, the secondary optical beam may carry low-priority data traffic while the network is operating in the normal state. In this case, the low-priority data may be dropped and replaced with the data traffic previously carried by the primary optical beam in response to the network entering the protection state.
The WDM device 24 may be configured to split the optical beam received from the optical coupling device 26 into individual optical signals that are operatively coupled into respective drop cables 28. Each drop cable 28 may operatively couple the optical signal received from the WDM device 24 to a respective tail-end node 30, and operatively couple an optical signal received from the respective tail-end node 30 to the WDM device 24. The WDM device 24 may combine the individual optical signals received from each drop cable 28 into one optical beam and provide this optical beam to the optical coupling device 26. The optical coupling device 26 may, in turn, couple the combined optical beam received from the WDM device 24 into one or more of the distribution cables 20, 22 for transmission to the head-end node 12.
Each tail-end node 30 may include a network interface device (NID), optical network terminal (ONT), or other device that receives the optical signal and converts it to an electrical signal (e.g., TCP/IP over Ethernet) suitable for use by one or more devices at the end point (e.g., switches, routers, computers, cellular transceivers, etc.). Each tail-end node 30 may also generate an optical signal that carries data received by the tail-end node 30 from the end point devices for transmission over the drop cable 28 to the network access point 14.
For purposes of clarity, the above descriptions of
Architectures containing redundant optical paths such as depicted in
In the depicted embodiment, the transmitted portion of the optical beam 70 emitted by the primary common port 62 propagates toward the filters 68, and the reflected portion of the optical beam 70 emitted by the primary common port 62 propagates toward the tap port 64. Conversely, the transmitted portion of the downlink optical beam 70 emitted by the secondary common port 63 propagates toward the tap port 64, and the reflected portion of the optical beam 70 emitted by the secondary common port 63 propagates toward the filters 68.
The beam splitter 60 may include a pair of cemented prisms, a half-silvered mirror, a polarizing beam splitter, or any other suitable optical device. The beam splitter 60 may be configured to split the optical beam so that each of the transmitted and reflected portions includes about 50% of the incident beam, i.e., the beam splitter 60 may be a symmetric beam-splitter. However, it should be understood that embodiments of the network access point 14 are not limited to any specific beam splitting ratio, and non-symmetric beam-splitters may also be used.
The filters 68 may be arranged to sequentially receive the optical beam 70 and selectively pass an optical signal 72 embedded in the optical beam 70. Each optical port 62-66 may be configured to receive an optical fiber 74-78 and include a collimator 80 configured to optically couple a respective optical signal 72 to and from (i.e., between) the optical fiber 74-78 and its respective filter 68. Each filter 68 may be configured to transmit optical signals 72 having a wavelength λn within the range of wavelengths covered by the passband of the filter 68 and reflect other optical signals 72 having wavelengths λn outside the range of wavelengths covered by the passband of the filter 68.
Each filter 68 may separate out or add one or more optical signals 72 to the optical beam 70 depending on the wavelength of the optical signal 72 and direction in which the optical signal 72 is travelling. The filters 68 may thereby provide a WDM device that bi-directionally separates optical signals 72 received from the optical fiber 74, 75 at one of the primary or secondary common ports 62, 63, and combines optical signals 72 received from channel ports 65 for transmission into the optical fiber 74, 75 connected to the primary and secondary common ports 62, 63.
Although
The network access point 14 depicted by
A potential use for the secondary common port 63 may include splitting power equally in a “bridge and select” architecture that provides a redundant protection path in the network. This type of architecture may be enabled by transmitting a portion of the optical beam received at the primary common port 62 from the secondary common port 63 with a loss of 3 dB to provide a path back to a head-end node 12 that contains either a secondary transceiver 18 (
The reflector 92 may include a mirror, a prism, or any other suitable optical device that reflects or otherwise alters the path of the optical beam 70. The positioning device 94 may include an electro-optical or electro-mechanical device that selectively positions the reflector 92 in or out of the path of the optical beam 70. Technologies which may be used for the positioning device 94 may include, but are not limited to, Micro-Electro-Mechanical Systems (MEMS) and macroscopic electromagnetic relays. These technologies may also allow for latching devices that only require energy during the switching event, e.g., moving the reflector 92 from the primary position to the secondary position, or from the secondary position to the primary position. Insertion of the reflector 92 into the path of the optical beam 70 may be from the side, top, or bottom, and the switching process may be triggered by detecting one or both of a loss of signal or a presence of signal at a tap port or other suitable location. Loss of signal may be defined as a condition under which the amount of optical energy at a port is below a predetermined loss of signal threshold. Presence of signal may be defined as a condition under which the optical energy at a port is above a presence of signal threshold. These conditions may also be determined based on the amount of bit errors in a received signal, or any other metric indicative of the presence or absence of a usable optical signal.
The optical switch 100 may include a reflector 112 and a positioning device 114. The positioning device 114 may include a latching device 115 and an actuator 117 (e.g., a spring), and be configured to selectively position the reflector 112 in either a primary position or a secondary position. The latching device 115 may initially maintain the reflector 112 in the primary position, e.g., by locking the reflector 112 in the primary position. In response to receiving a trigger signal, the latching device 115 may release the reflector 112, thereby allowing the actuator 117 to move the reflector 112 from the primary position to the secondary position. When the reflector 112 reaches the secondary position, the latching device 115 may lock the reflector 112 in place, e.g., by latching the reflector 112 in the secondary position. The reflector 112 may remain in this position until the positioning device 114 is reset to the primary position, e.g., manually by a field operative, through remote actuation of a solenoid, or by any other suitable means.
Although
The optical coupling device 120 may be operated as a beam splitter 46 (
The optical coupling device 120 may also be operated as an optical switch 52 (
The primary branch port 126 of optical coupling device 120 may be operatively coupled to the primary distribution cable 20, the secondary branch port 128 may be operatively coupled to the secondary distribution cable 22, and the common port 122 may be operatively coupled to the WDM device 24. Incorporating a variable ratio coupler operable as a 1×2 or 2×2 switch into the network access point 14 may enable a switching operation using the optical ports of the variable ratio coupler as a path selection switch. Thus, the optical coupling device 120 may be operated as an optical switch (e.g., for the protection schemes 10, 40 depicted by
The sensing device 150 may include a primary monitoring device 158, a secondary monitoring device 160, and a sensor circuit 162. Each of the monitoring devices 158, 160 may include a photodetector or other suitable light-sensitive device that is operatively coupled to a respective branch port 146, 148 by a respective tap line 164, 166. Each tap line 164, 166 may couple a portion (e.g., 1%) of an optical beam received by its respective branch port 146, 148 to its corresponding monitoring device 158, 160. The sensor circuit 162 may be configured to receive signals from the monitoring devices 158, 160 and determine whether to operatively couple the common port 142 to the primary branch port 146 or the secondary branch port 148 based on the received signals.
The actuator 152 may include a transducer 168 (e.g., a coupler, solenoid, electric motor, etc.) and an energy storage device 170, and may be configured to adjust the physical relationship between the primary and secondary waveguides 154, 156 in a coupling region 172 between one of two states, similar to the optical coupling device 120 (
The actuator 152 may comprise an electro-mechanical mechanism that is pre-loaded to ensure rapid and reliable switching. For embodiments in which the actuator 152 is preloaded, the preloading may put the actuator 152 in a state such that the optical coupling device 140 operatively couples the primary branch port 146 to the common port 142. This may be considered a normal state during which the primary path is active. Network access points 14 may be shipped and installed in the normal state so that the drop cables 28 are initially operatively coupled to the primary path between the network access point 14 and head-end node 12.
In response to a protection event (e.g., an event that breaks the primary path or otherwise causes a persistent loss of signal which could result in a loss of data), the optical coupling device 140 may be triggered to connect the protection path to the WDM device 24. The optical coupling device 140 may be triggered automatically based on the output of the sensing device 150 integrated in the optical coupling device 140, or by an external signal received from a signaling system. The optical coupling device 140 may be triggered by a low energy transducer 168 powered by an energy storage device 170 including a long-life battery (e.g., 20 year battery), a wound spring, or any other device that can release sufficient energy to displace a keeper (e.g., a ball or shim). Displacing the keeper may allow the transducer 168 to relax into a switched state that causes the optical coupling device 140 to operatively couple the common port 142 to the protection path. In any case, the energy storage device 170 may only need to store sufficient energy to enable monitoring of received optical beams on the primary and secondary distribution cables 20, 22 periodically (e.g., once a second, a minute, or an hour) and sufficient to activate the transducer 168, which should occur infrequently.
Once the optical coupling device 140 is triggered, the network access point 14 may remain in the protection state until a truck rolls to restore the primary path, e.g., through repair as a result of intervention by a field operative. Once the repair has been made, the transducer 168 may be reset and the energy storage device 170 restored manually by the field operative, e.g., by inductively recharging the battery or supercapacitor, resetting the mechanical spring, etc. In an alternative embodiment, the network access point 14 may be configured to enable the optical coupling device 140 to be reset to the normal state remotely via a signaling system so that it is ready for another protection event without the need for a visit by the field operative.
A simple optical detection system may be incorporated into the network access point 14 in order to automatically switch the WDM device 24 from the primary path to the secondary path in the event of a failure in the primary path. A simple, reliable optical power detector with a response time in the millisecond range may be incorporated into the optical path using a very low ratio tap coupler, e.g., −20 dB coupling between the monitored optical waveguide and the tap port. A photodetector receiving light from the tap port may be operatively coupled to a control circuit designed to operate with extremely low power consumption. This may allow operation of the control circuit over a long period of time, e.g., 10 to 20 years. In an alternative embodiment of the network access point 14, a photodetector and controller may only be operatively coupled to the primary path such that a loss of signal on the primary distribution cable 20 triggers the network access point 14 to switch to the secondary distribution cable 22 without regard to the presence or absence of an optical beam on the secondary distribution cable 22.
The sensor circuit 162 may be configured to sample the output of the primary monitoring device 158 intermittently or continuously. In response to the optical signal detected by the primary monitoring device 158 falling below a predetermined threshold PT1, the sensing circuit 162 may sample the output of the secondary monitoring device 160. If the optical signal detected by the secondary monitoring device 160 is above a predetermined threshold PT2, the sensing circuit 162 may trigger the actuator 152 to switch the optical coupling device 140 from the normal state to the protection state. Thus, the above described embodiment of the sensing circuit 162 may only trigger the optical switch to implement the protection state if both the primary optical beam 180 is below a predetermined loss of signal threshold and the secondary optical beam 182 is above a predetermined presence of signal threshold.
The transducer 168 may be configured so that after the actuator 152 is triggered to implement the protection state, the actuator 152 remains locked in place, e.g., by a latching device. The transducer 168 may be configured to remain in this locked state until intervention by a field operative resets the actuator 152, e.g., by recharging the battery and/or resetting the trigger mechanism. This type of latching behavior may be referred to as non-revertive operation. Optical coupling devices 140 including this feature may be referred to as non-revertive optical switches. When operated as a non-revertive optical switch, the optical coupling device 140 cannot autonomously switch back to the normal state, but rather requires intervention. Use of non-revertive optical switches may be advantageous in certain situations because they do not require system-level intervention to operate. Advantageously, this feature may enable deployment of network access points 14 without the effort and complexity of providing systems-level intervention.
In cases where electrical power is available either locally or remotely, the signaling, detection, controlling, triggering, and resetting functions may be powered using external electrical power. Electrical power may be provided, for example, by a local utility power source or through a hybrid cable containing both an optical fiber and electrical conductors that carry power from a remote source.
In another embodiment, the network access point 14 may include a plurality of optical coupling devices 26 to enable full duplex operation. Full duplex operation may also be achieved using layered WDM demultiplexing technology. Having a plurality of optical coupling devices 26 may also enable optical switch functions (e.g., 1:N or N:1) that can be used to provide a WDM-based channel selector. As a WDM selector switch, this may provide automation of the specific WDM channel that is connected to the end user/end point. Cascading optical switches based on variable ratio optical couplers may enable the system to be scaled in a tree-and-branch architecture that extends a 1:2 optical switching function to 1:4, 1:8, etc.
In another embodiment, power-consuming elements of the network access point 14 may be provided with power using a remote optical power scheme. To this end, the head-end node 12 may include an optical source such as a high-power laser or transceiver. The optical source may transmit light at a wavelength corresponding to the telemetry band (1620 to 1650 nm), or some other suitable wavelength that does not interfere with optical signals carrying data. This out-of-band light may be received at the network access point 14 and converted to electrical energy to provide remote power. The out-of-band light may be routed into the optical distribution network and demultiplexed at the switch, where an energy harvesting system can convert the out-of-band light into electrical power. This electrical power may be used, for example, to charge a battery or ultracapacitor. The stored electrical energy may then be used to power selected components if and when a protection event occurs that requires switching to a protection path.
In another embodiment, a temporary latching effect may be achieved for a time sufficient to repair the optical network using a battery as the energy storage device. In this embodiment, the primary and secondary optical paths may be monitored. In response to detecting a protection event, a control device in the network access point may activate a low-energy optical switch, such as a MEMS optical switch. Because the low-energy optical switch requires little power, the battery may be capable of maintaining the network access point in the protection state for a sufficient amount of time to repair the primary path, e.g., several days. Once the repair has been made, the controller may cause the optical switch to revert to normal operation in response to receiving confirmation that the primary path has been restored. After restoration of the primary path, the battery can be recharged.
While the present disclosure has been illustrated by the description of specific embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features discussed herein may be used alone or in any combination within and between the various embodiments. Additional advantages and modifications will readily appear to those skilled in the art. The present disclosure in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the present disclosure.
This application claims the benefit of priority of U.S. Provisional Application No. 63/338,475, filed on May 5, 2022, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 63338475 | May 2022 | US |
