Abstract: A transmission apparatus includes: a storage unit to store a table in which a wavelength terminated by each of transmission apparatuses is associated with each of the transmission apparatuses; a transmission unit to transmit a message including failure information to other transmission apparatus when a failure occurs; a switch controller to determine whether its own transmission apparatus is a last transmission apparatus that terminates the wavelength among transmission apparatuses that are present on a path up to a link where the failure, based on the table, when receiving the message from other transmission apparatus, and to perform a control of switching a transmission direction of a signal having the wavelength when the switch controller determines that its own transmission apparatus is the last transmission apparatus to terminate the wavelength; and a switch to switch a transmission direction of the signal for each wavelength under a control of the switch controller.

Abstract: Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

Abstract: Methods and systems for superchannel power pre-emphasis based on transmission criteria may determine a guardband used when transmitting multiple superchannels over an optical transport network. The guardband values may depend on various transmission criteria, such as a reach distance for the superchannels and a number of reconfigurable add-drop multiplexer nodes over a given optical path. An amount of power pre-emphasis for each superchannel may then be determined based on the actual guardband values used. Certain values used for superchannel power pre-emphasis based on transmission criteria may be pre-calculated and stored in advance.

Abstract: Input light includes a multicarrier signal and first CW light of a first optical frequency. A transmitter generates a modulated optical signal based on an inverted signal of a dropped signal. A light source generates second CW light of a second optical frequency. A delay element adjusts a phase difference between the modulated optical signal and the second CW light. The multicarrier signal, the first CW light, the modulated optical signal and the second CW light are input to nonlinear optical medium. A detector detects beat frequency component between the modulated optical signal and the second CW light. A controller controls the delay element so as to increase the beat frequency component. A difference between the first optical frequency and an optical frequency of the dropped optical signal is substantially the same as a difference between the second optical frequency and an optical frequency of the modulated optical signal.

Abstract: According to one embodiment of the present disclosure, a system for translating a boosting algorithm includes an interface communicatively coupled to a processor. The interface is operable to receive a trained boosting model. The processor is operable to identify a plurality of split-node variables associated with the trained boosting model. Each of the plurality of split-node variables comprises a variable name, a cutoff point, and a weight. The processor may aggregate the split-node variables by variable name and cutoff point and then combine the weights of each of the plurality of split-node variables having the same variable name and cutoff point. The processor may then create a linear model based on the combined variables.

Abstract: Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

Abstract: In one embodiment, a system for enhancing predictive modeling includes an interface operable to receive a first dataset. The system may also include a processor communicatively coupled to the interface that is operable to generate a holdout dataset based on the first dataset. The processor may also train each of a plurality of boosting models in parallel using the first dataset, wherein for each of a number of iterations, training comprises: building a one-level binary decision tree to train a split-node variable; calculating an impurity of the split-node variable; and calculating an optimal split node, wherein the optimal split node is the split-node variable with a lowest impurity between the plurality of boosting models. The system may then determine a final model based on one of the plurality of boosting models that provides the lowest error rate when applied to the holdout dataset.

Abstract: The present disclosure describes systems and methods for reconfiguring the links made by a plurality of optical circuit switches between the nodes of the first layer and the nodes of the second layer that reduces the throughput loss when the network transitions form a first logical topology to a second logical topology. More particularly, the first logical topology is realized by a specific physical topology, while the second logical topology may be realized by one or more physical topologies. The disclosure describes a method for selecting a second physical topology from the one or more physical topologies that will realize the second logical topology while reducing the number of links within each of the optical circuit switches that must be reconfigured (i.e, disconnected from their present ports and reconnected to new ports within the optical circuit switch) to transition from the first to second logical topology.

Abstract: A method for routing C-band and L-band optical signals, and a system, apparatus, and computer program that operate in accordance with the method. The method comprises selecting one or more C-band optical signals using one or more C-band components, resulting in one or more selected C-band optical signals. One or more L-band optical signals are selected using one or more L-band components, resulting in one or more selected L-band optical signals. The selected C-band and L-band optical signals are combined.

Abstract: An apparatus for an optical communications network comprising a demultiplexer, a plurality of add/drop optical switches for adding and dropping wavelength channels. The add/drop optical switches arranged in a matrix with a number of rows corresponding to a number of output ports of the demultiplexer and a number of columns corresponding to a number of transponders. Each drop optical switch has an express input port associated with an output port of the demultiplexer, a drop output port associated with an individual transponder, and an express output port. Each add optical switch has an express input port, an add input port associated with an individual transponder, and an express output port. The apparatus also comprises a multiplexer with a plurality of input ports associated with express output ports of the add/drop optical switches.

Abstract: An electro-optical switch (170) for receiving N data streams optically, each of said N data streams having an amplitude and a phase and each being located at an optical center frequency FO1+RFM, where FO1 is a first optical modulation frequency and RFM is a signal center frequency. The electro-optical switch is arranged to convert the N data streams to electrical data signals at the data stream's signal center frequency RFM, the electrical data signals having the amplitude and phase of the optical data stream. The electro-optical switch is further arranged to convert electrical data signals to optical output signals at optical center frequency FO2+RFOut with the amplitude and phase of the first electrical data signal maintained, and to transmit the optical output signals, with RFM and RFOut, being equal to or different from each other, and FO1 and FO2 also being equal to or different from each other.

Abstract: Methods and systems for optical communication in a submarine network are provided. An input signal is received from a terminal at a reconfigurable branching unit (BU), and the input signal is split into at least two parts, with one part being associated with one or more trunk terminals and another part being associated with one or more branch terminals. Each of one or more spectrum channels are selected and individually switched to one of a plurality of paths using at least one wavelength selective switch (WSS), with the at least one WSS being configured to transmit the one or more spectrum channels to their respective target output port and to combine signals switched to a specific port into a wavelength division multiplexing (WDM) signal. Individual spectrum channels are filtered out using at least one wavelength blocker (WB).

Abstract: A feed-forward equalizer can be used in the host optical receiver to perform at least some of the desired signal processing in the optical domain, e.g., prior to coherently detecting and digitizing the received optical signal(s). In some embodiments, the signal processing implemented in the feed-forward equalizer can at least partially compensate the adverse effects of chromatic dispersion, polarization-mode dispersion, and/or spatial-mode mixing/crosstalk imparted on the received optical signal(s) in the optical transport link. This reduces the signal-processing load of and the signal-processing requirements to the receiver's electrical DSP.

Abstract: This invention relates to provisioning wavelength-selective switches and reconfigurable optical add-drop multiplexers to minimize the bandwidth narrowing effect from the optical filters. Novel architectures and methods are disclosed that can significantly reduce bandwidth-narrowing on channels in a reconfigurable WDM network where a large number of optical filter elements are cascaded. Instead of blocking unused channels as in the prior art, unused channels are selectively provisioned depending on the state of their adjacent channels. Unused adjacent channels of an active channel are provisioned to follow the same path as the active channels. As each channels is deployed, the channel frequency is selected so as to minimize bandwidth narrowing.

Abstract: Methods and systems for post-transient gain control of optical amplifiers may include using a gain offset control module in an optical amplifier to generate a gain offset cancelling signal. The gain offset cancelling signal may be output to a gain control module in the optical amplifier to generate at least one of a pump signal and an attenuation control signal. In this manner, a gain offset may be cancelled for a plurality of wavelengths in an optical signal transmitted by an optical network.

Abstract: An optical-branching unit enables suppression of deterioration of the transmission characteristic of a survivor signal without executing complex control of constant-power output. Optical-amplification means amplifies and supplies a input optical signal, and when not receiving the optical signal, amplifies and supplies amplified spontaneous emission that the optical-amplification means generates. Detection means detects whether the optical signal is input to the optical-amplification means. When the optical signal is not input to the optical-amplification means, control means sets gain that determines the magnitude of amplification in the optical-amplification means to a predetermined value greater than gain at the time the optical signal is input to the optical-amplification means.

Abstract: An optical intensity control system for use with an optical switch providing individual signal paths between input and output ports. The system has optical splitters connectable to output multiplexers of the switch and has variable optical intensity controllers (VOICs) for insertion into the individual signal paths to individually control the intensity of optical signals present in the signal paths via intensity control signals. An equalizer is connected to the splitters and to the VOICs produces an estimate of the optical power of each individual switched optical signal and generates the intensity control signals. The equalizer is adapted to controllably isolate individual switched optical signals. In this way, individual and independent control of the power on each optical channel is provided.

Abstract: Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

Abstract: A multi-path provisioning scheme is provided to ensure full protection while reducing or minimizing resource overbuild. A signal to be provisioned is divided at a source node into a plurality of sub-signals that are independently routed from the source node to a destination node. Bandwidth for back-up traffic B is allocated in addition to bandwidth for primary traffic T. In some embodiments, the initial bandwidth B of the backup traffic equals the bandwidth of the primary traffic. The T+B traffic is initially distributed so that no link carries more than B traffic. The traffic distribution pattern is then iteratively revised to reduce the bandwidth requirements for the backup traffic while still meeting requirements for protection.

Abstract: A fiber optic sensing system. The fiber optic sensing system includes an optical source adapted to provide an optical signal at a plurality of wavelengths. The fiber optic sensing system also includes a plurality of wavelength taps for separating the optical signal into signal portions at each of the plurality of wavelengths. The fiber optic sensing system further includes a plurality of optical sensors, each of the optical sensors configured to receive one of the signal portions at a respective one of the plurality of wavelengths. The fiber optic sensing system still further includes a plurality of wavelength combiners for combining signal portions from the plurality of optical sensors into a recombined signal. Also included in the fiber optic sensing system is an optical receiver for receiving the recombined signal. The fiber optic sensing system also includes an optical fiber path between the optical source and the optical receiver.

Abstract: An optical channel monitor includes: a first optical device to include first, second and third optical ports, light input through the first optical port being led to the second optical port, light input through the second optical port being led at least to the third optical port; a second optical device to include fourth, fifth and sixth optical ports, light input through the fourth optical port being led to the fifth optical port, light input through the fifth optical port being led at least to the sixth optical port; an optical filter to include seventh and eighth optical ports optically connected to the second and fifth optical ports, respectively, a specified wavelength being transmitted between the seventh and eighth optical ports; a first photo detector to detect light output from the sixth optical port; and a second photo detector to detect light output from the third optical port.

Abstract: Various architectures of a multi-degree reconfigurable optical add-drop multiplexer with reduced contention are provided. These architectures allow the degree of contention reduction to be managed in a flexible and modular way. The degree of the node and the amount of add/drop at the node can also be managed in a flexible and modular way. This Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: An optical transport network based on multimode/multicore fibers includes a mode-multiplexer to multiplex independent data streams from one or more transmitters; a multimode erbium-doped fiber amplifier (MM EDFA) to compensate for MMF loss; a multimode optical add-drop multiplexer (MM OADM) to add and/or drop multimode channels in multimode networks; a multimode optical cross-connect; and a mode-demultiplexer to separate various mode streams to one or more receivers.

Abstract: A method and apparatus for visually indicating the connections between optical interfaces is provided. The optical interfaces may include multi-wavelength optical interfaces and uni-wavelength optical interfaces. The optical interfaces may reside within optical nodes contained within an optical network.

Abstract: A network element has at least one input, to which an optical signal can be fed, and at least one output, which is equipped to emit an optical signal; a first coupler having an input linked to the network element input and a first and a second output; an optical receiver having at least one input coupled to the second output of the first coupler and at least one output; an optical sender having at least one input of which is linked to the output of the optical receiver; a signal processing device being arranged in the signal path; a second coupler having a first input linked to the first output of the first coupler, a second input linked to the output of the optical sender, and an output which is linked to the first output of the network element.

Abstract: An intranodal reconfigurable optical add/drop multiplexer (ROADM) fiber management apparatus, and a system employing the apparatus. The apparatus comprises a plurality of ingress optical ports, a plurality of egress optical ports, and a plurality of optical interconnections interposed between ones of the plurality of ingress optical ports and ones of the plurality of egress optical ports. Each of the plurality of ingress optical ports corresponds to one of the plurality of egress optical ports. Each one of the plurality of ingress optical ports is optically coupled by way of the optical interconnections to at least one of the plurality of egress optical ports. Each one of the plurality of egress optical ports is optically coupled by way of the optical interconnections to at least one of the plurality of ingress optical ports.

Abstract: A method for shared mesh restoration includes configuring a switch to allow sharing of a plurality of backup line cards across a plurality of node degrees associated with a reconfigurable optical add/drop multiplexer (ROADM). The switch is communicatively coupled to the ROADM. The method further includes configuring a number of backup line cards coupled to the switch. The number of backup line cards is based on determining a number of active backup lightpaths for each of a plurality of network failures associated with each of the plurality of node degrees of the ROADM, identifying which node degree and failure has the largest number of active backup lightpaths for all of the plurality of node degrees of the ROADM and for each of the plurality of network failures, and determining the number of backup line cards to configure based on the identified largest number of active backup lightpaths.

Abstract: A device for inserting/extracting at least one optical subband into an optical channel consisting of a plurality of optical subbands. The device includes an extraction means that is capable of extracting a first optical subband belonging to the optical channel, a suppression means that is arranged so as to obtain a filtered optical channel from the optical channel wherein at least one second subband is suppressed, and a coupling means that is capable of inserting a replacement optical subband in place of the second subband in the filtered optical channel so as to obtain a modified optical channel. The device moreover relates to an optical insertion/extraction switcher, using one or more insertion/extraction devices, and to the corresponding insertion/extraction methods.

Abstract: Methods and apparatus to deploy fiber optic based access networks are disclosed. An example access network comprises a first fiber optic cable segment to couple an optical access head-end to a first pedestal and to transport user data, a second fiber optic cable segment to couple the first pedestal to a second pedestal and to transport a first portion of the user data to the second pedestal, a drop cable segment to couple the first pedestal to a customer premises and to transport a second portion of the user data to the customer premises, and a switch at the first pedestal to route the first portion of the user data between the first and second fiber optic cable segments and to route the second portion of the user data between the first fiber optic cable segment and the drop cable segment.

Abstract: A reconfigurable optical add drop multiplexer (ROADM) includes local interfaces at which optical signals of different wavelengths are locally input into the ROADM, and a network interface configured to connect the ROADM to a network from which multiplexed optical signals of different wavelengths are transmitted to the network. In a first configuration, the ROADM is configured to transmit from the network interface to the network multiplexed signals of different wavelengths having a first minimum frequency difference. In a second configuration, the ROADM is configured to transmit from the network interface to the network multiplexed signals of different wavelengths having a second minimum frequency difference. The second minimum frequency difference is greater than the first minimum frequency difference. This arrangement reduces the power of four wave mixing cross products produced when optical signals of three wavelengths are multiplexed and transmitted from the ROADM to NZDSF or DSF fiber types.

Abstract: An optical adding and dropping device includes a drop section including an input port and having a through port and a plurality of drop ports set as output ports, a first multiplexer adapted to multiplex light from the through port and light from a plurality of add ports, and a spectrum foot removing section provided on the input side of the first multiplexer and adapted to remove a foot of a spectrum of light to be inputted from the add ports to the first multiplexer. The optical adding and dropping device can be configured at a low cost while it has adding and dropping functions.

Abstract: In an Optical Add-Drop Multiplexer, a drop section comprises a Wavelength Selective Switch (WSS) having at least one drop-port, the WSS being operative to couple a respective set of w (where w>1) wavelength channels from a received Wavelength Division Multiplexed (WDM) signal to each drop port. A respective 1:s power splitter is associated with each drop port. Each power splitter supplies the respective set of channels received from its drop port to each one of a corresponding set of coherent receivers. Each coherent receiver operates to receive a selected one of the respective set of channels.

Abstract: Systems and methods for data transport, including submarine reconfigurable optical add/drop multiplexers, branching units configured to receive signals from trunk terminals (TTs), and dummy light filters configured to pass useful signals through the filters, and to reflect dummy light. Optical interleavers are configured to separate useful signals into two or more groups of optical channels, and the optical channels are set to a frequency of either a left or a right portion of a total channel bandwidth. De-interleavers merge signal groups together from trunk terminals, and lasers at each of the transponders at the source terminals are configured to adjust a destination of a channel by fine tuning a frequency or wavelength of the one or more signals.

Abstract: An optical network interconnect device interconnects a first WDM network for transmitting a WDM optical signal with first wavelength spacing and a second WDM network for transmitting a WDM optical signal with second wavelength spacing that is wider than the first wavelength spacing. The optical network interconnect device includes a filter to remove a wavelength component which is not used in the second WDM network from an WDM optical signal transferred from the first WDM network to the second WDM network.

Abstract: Embodiments herein include a resilient add-drop module for use in one of multiple access subnetwork nodes forming an access subnetwork ring. The module comprises a dual-arm passive optical filter and a cyclic arrayed waveguide grating (AWG). The dual-arm passive optical filter is configured to resiliently drop any wavelength channels within a fixed band uniquely allocated to the access subnetwork node from either arm of the access subnetwork ring and to resiliently add any wavelength channels within the fixed band to both arms of the access subnetwork ring. The cyclic AWG is correspondingly configured to demultiplex wavelength channels dropped by the dual-arm filter and to multiplex wavelength channels to be added by the dual-arm filter. Configured in this way, the module in at least some embodiments advantageously reduces the complexity and accompanying cost of nodes in an optical network, while also providing resilience against fiber and node failures.

Abstract: A method, performed by a computer device, may include determining that an available spectrum, associated with an optically switched light path, has been allocated for one or more superchannels and identifying a leftover spectrum, associated with the one or more superchannels allocated for the optically switched light path. The method may further include selecting a use for the leftover spectrum; selecting one or more devices to configure based on the selected use; configuring the selected one or more devices to use the leftover spectrum; and sending data via the leftover spectrum using the configured one or more devices.

Abstract: Switching architectures for WDM mesh and ring network nodes are presented. In mesh networks, the switching architectures have multiple levels—a network level having wavelength routers for add, drop and pass-through functions, an intermediate level having device units which handle add and drop signals, and a local level having port units for receiving signals dropped from the network and transmitting signals to be added to the network. The intermediate level device units are selected and arranged for performance and cost considerations. The multilevel architecture also permits the design of reconfigurable optical add/drop multiplexers for ring network nodes, the easy expansion of ring networks into mesh networks, and the accommodation of protection mechanisms in ring networks.

Abstract: A multi-port wavelength selective switch includes a one dimensional array of input and output ports. The multi-port wavelength selective switch further includes a wavelength dispersive element configured to receive input optical signals from the input ports, and to disperse wavelength components thereof. Additionally, the multi-port wavelength selective switch includes an array of beam steering devices. Each beam steering device is controllable to a position at which the beam steering device directs a wavelength component of an input optical signal received through a first input port to an output port and directs the same wavelength component of an input optical signal received through a second input port away from all of the output ports.

Abstract: Example embodiments of the present invention relate to An optical node comprising of at least two optical degrees; a plurality of directionless add/drop ports; and at least one wavelength equalizing array, wherein the at least one wavelength equalizing array is used to both select wavelengths for each degree, and to perform directionless steering for the add/drop ports.

Abstract: A sending apparatus includes: a wavelength path multiplexing part; a sending wavelength path selection part; and an optical transmitter having optical sending parts. The wavelength path multiplexing part includes: sending wavelength path demultiplexing ports; and sending wavelength multiplexing ports connected thereto. The sending wavelength path multiplexing ports are connected to optical transmission paths respectively. The sending wavelength path selection part includes a wavelength multiplexing parts which multiplexing a set combination of optical signals among the optical signals inputted to the sending input ports and outputs it to any of the sending output ports. In the wavelength path sending or receiving by the wavelength path multiplexing/demultiplexing optical transmission apparatus, a non-selectable combination between a wavelength and a route can be avoided.

Abstract: A system to provide carrier frequency control in an optical network includes a first network element monitoring performance information and a second network element coupled to the first network element by the optical network. The second network element receives performance information from the first network element using an administration channel bandwidth, and modifies a carrier frequency associated with the second network element based on the performance information such that the carrier frequency is aligned to a center of a signal channel bandwidth. A method of providing carrier frequency control includes transmitting performance information by the first network element to the second network element using an administration channel bandwidth, and modifying the carrier frequency by the second network element based on the performance information such that the carrier frequency is aligned to the center of the signal channel bandwidth.

Abstract: A method and a Reconfigurable Optical Add Drop Multiplexer (ROADM) where blocking of a first optical signal carried over a specific optical channel in the ROADM is performed by compensating the first optical signal by a second optical signal created for that purpose.

Abstract: A colorless, reconfigurable, optical add-drop multiplexer (a colorless ROADM) is disclosed. The ROADM may include a de-interleaver, a diffraction grating, and a lens. The de-interleaver may separate an input signal into a first output signal, comprising odd channels, and a second output signal, comprising even channels. The diffraction grating may receive the first and second output signals from the de-interleaver. The diffraction grating may separate each of the first and second output signals into individual channels. The lens may collimate the individual channels received from the diffraction grating.

Abstract: The invention relates to a directionless and colorless reconfigurable optical add/drop multiplexer (ROADM) for a number of clients comprising: an add/drop interface for optical signals of at least one optical network, wherein each received optical signal is split by at least one optical splitter into optical signals which are applied to a downstream cross connector distributing the split optical signals to wavelength selectors of different clients, wherein each wavelength selector performs a wavelength selection of at least one wavelength from the distributed optical signals, wherein an optical signal having a selected wavelength (?) is applied to a client transponder of a client.

Abstract: An optical add/drop multiplexer including one or more optical drop multiplexers connected in free space or fused by optical fiber pigtails, a wavelength blocker with an input port connected to an output port of the optical drop multiplexer through the fusion of the fiber pigtails, one or more optical add multiplexers connected in free space or fused by fiber pigtails, a digital signal processor, an analog-to-digital signal converter, a digital-to-analog converter, and a plurality of electronic control and feedback loops for tuning and scanning an optical wavelength.

Abstract: An optical switching device includes plural wavelength selective switches that respectively have a first port and a plurality of second ports; and an optical coupler that has a plurality of third ports on an input-side or an output-side, respectively optically coupled to the first ports of the wavelength selective switches.

Abstract: A method includes determining a line rate selection for a flexible optical wavelength-division-multiplexing WDM network, determining a traffic routing in said network, and determining simultaneously a channel routing, wavelength assignment and spectrum allocation in said network based on an auxiliary graph.

Abstract: In order to achieve a higher spectral efficiency of OFDM sub-bands, optical signals using orthogonal frequency division multiplexing are transmitted through an optical network in the form of a continuous waveband optical signal. An optical add/drop multiplexer (1) splits the continuous waveband optical signal into an express path and a drop path. A band pass filter (4) is provided in the drop path to extract a sub-band carrying at least one of said OFDM modulated optical signals (DROP). The band pass filter (4) has a filter bandwidth that covers the sub-band to be extracted. A band-stop filter (3) is provided in the express path to remove the sub-band to be extracted from the continuous waveband optical signal (IN). The band stop filter (3) has a filter bandwidth which is narrower than the band pass filter (4). An OFDM modulated optical add signal (ADD) can be added into the wavelength gap created through the band stop filter (3).

Abstract: Method and system for band blocking in an optical telecommunication network. According to an embodiment, the present invention provides a system for optical network. The system includes an input that is configured to receive an input signal through a first optical input. The system also includes a band splitting module that is coupled to the input. The band splitting module is configured to separate the input signal into a plurality of bands. The plurality of bands includes a first band and a second band. The first band includes a first plurality of wave channels. The first plurality of wave channels is characterized by a first channel spacing. The second band includes a second plurality of wave channels, which is characterized by a second channel spacing.

Abstract: A reconfigurable optical add/drop multiplexer and a reconfigurable optical add/drop multiplexing method are provided. The reconfigurable optical add/drop multiplexer comprises: an optical processing unit for receiving a first optical signal containing a plurality of optical channels, processing the first optical signal to generate a second optical signal which is a part of the first optical signal, and outputting the second optical signal; and a coherent detection unit for performing a coherent detection on the second optical signal so as to separate from the second optical signal an optical channel contained therein, and outputting the optical channel.