Abstract: The present invention provides a bidirectional optical signal traffic-directing and amplification module which is used in a method for simultaneous real-time status monitoring and troubleshooting of a high-capacity single-fiber hybrid passive optical network that is based on wavelength-division-multiplexing techniques.

Abstract: Normality of links on a spare path or the links and nodes is monitored. When the spare path cannot be used, at least any one of nodes at both ends in a segmented path section is changed to another node on a working path. The segmented path section is changed to set another spare path. When a fault monitoring section which can accumulatively detect abnormal information is changed to the changed partial working path section, alarm generation in the fault monitoring section is prevented to release the prevention after completion of the change.

Abstract: A method includes receiving a restoration indicator associated with a path that includes an optical cross-connect (OXC). The OXC is reconfigured from a standby configuration to a restoration configuration in response to the restoration indicator. An optical signal received in a first direction at a first wavelength is optically regenerated to produce an optical signal in the first direction at a second wavelength. An optical signal received in a second direction at the second wavelength is optically regenerated to produce an optical signal in the second direction at the first wavelength.

Abstract: An optical network transmission channel failover switching device is proposed, which is designed for use in conjunction with an optical network for providing a transmission channel failover switching function, which is characterized by the provision of a pair of two-to-two (2×2) optical switches and an optical transceiver module for providing a backup channel monitoring function that can be used to activate the failover switching action. This feature allows the utilization of the optical network system to have enhanced reliability, serviceability, and security.

Abstract: An apparatus, system and method are provided for a switchable fiber termination (SFT) incorporated into an optical network device that responds to a test signal received via an optical network carrying data. The test signal may be a part of a multiplexed signal carrying data and is separated from the data by a wavelength division multiplexer. The SFT may be used to determine the characteristics of an optical network, including the operational status of optical network devices.

Abstract: The optical switch, having a plurality of ports capable of switching optical signal routes in a network in the form of light, includes a detection means for detecting information in regard to the transmission condition of an optical signal passing through each port; and a control means for exchanging the transmission condition information between each switch and controlling the ports, so as to select one route from among a plurality of routes transmitting the optical signal based on the difference of transmission condition information between the relevant switches. The transmission condition information is the power of the optical signal. When the difference between each switch exists, or when at least one switch intervenes in the middle of the transmission route, by selecting a transmission route which minimizes accumulated differences among the switches, configuring a tree structure conventionally performed through manual operation can be set automatically in an optical network system.

Abstract: Each of a plurality of semiconductor optical amplifiers operates as an optical gate switch and selects an optical signal indicated by a gate control signal from an optical gate switch control unit. A plurality of photodetectors monitor the power of an optical signal input through a corresponding input port. A VOA control unit calculates an amount of attenuation corresponding to each input port based on the power of each optical signal. A variable optical attenuator attenuates the selected optical signal according to the calculated amount of attenuation in synchronization with the gate control signal.

Abstract: A system and method is provided for controlling switching between multiple primary and diverse optical paths in an optical switching system. The system has a primary upstream optical path, a diverse upstream optical path, one or more primary downstream optical paths, and one or more diverse downstream optical paths. The method comprises the steps of monitoring a signal level of the primary upstream optical path, determining if the signal level of the primary upstream optical path is above a set threshold, and automatically switching both upstream and downstream paths from the primary optical paths to the diverse optical paths if the signal level of the primary upstream optical path is below the predetermined threshold.

Abstract: An optical transmission apparatus comprises a preamplifier controlling unit for controlling a preamplifier so that amplified spontaneous emission including all wavelength bands of a wavelength-multiplexed signal beam is outputted toward a wavelength demultiplexing unit, with the wavelength-multiplexed signal beam not inputted, power monitors for monitoring optical powers of the amplified spontaneous emission fed from the preamplifier and wavelength-demultiplexed by the wavelength demultiplexing unit, and a determining unit for determining the continuity state of an optical propagation path of each wavelength component on the basis of a result of monitoring by the power monitors. The optical transmission apparatus allows the continuity test on optical propagation paths of channels including a channel not used at the time of a start of the operation to be made easier than the known techniques.

Abstract: A method is disclosed that integrates performance monitoring data and alarms reported by Layer 3 network elements with alarms and performance monitoring data reported by Layer 1 SONET/SDH network elements to isolate Layer 1 problems on DSX circuits embedded in SONET due to hard failures or errors.

Abstract: A light source supplies optical signal to an optical switch and a detector detects light receiving level. A control unit changes a deflection control amount for changing an angle of a tilt mirror, and outputs the deflection control amount to a driving unit. When an input and an output ports are same, optical offset of the tilt mirror is calculated based on optimal angle at which the light detector detects an optimal point of the light receiving level. Whenever the input and the output port are different, a structure parameter of the tilt mirror is calculated based on the optical offset and the optimal angle. The optical offset and the structure parameter are stored in a memory as a test result.

Abstract: A protection system protects paths of internetwork communication between WDM ring networks, and includes a plurality of optical wavelength multiplexing networks having a plurality of nodes and a network management system for monitoring conditions of the plurality of nodes. The nodes include a first node having add/drop functions of adding/dropping wavelength-multiplexed optical signals; a second node having a signal transfer function as well as the add/drop functions; and a third node having an internetwork connection function between the networks. Each first, second and third nodes further includes optical path cross-connect switches and a table for indicating conditions of the optical path cross-connect switches and a detected node fault condition. The network management system controls to set the optical path cross-connect switches in the first, second and third nodes so that the optimal optical path connection may be obtained according to the detected node fault condition indicated in the node tables.

Abstract: An optical path switching device includes compact and unpackaged components; the components are mounted onto a single platform; and the components are coupled by luminous flux. Connection between optical fibers is negated. In particular the optical path switching device includes an optical input, an optical output, an optical branching device and an optical signal detection device. At least two of the optical input, the optical output, the optical branching device and the optical signal detective device are mounted onto a single platform.

Abstract: A method is provided for detecting an optical reflection position in an optical switching unit by using a measuring system. Multiple switching commands are provided in order to direct a test light to an input port and an output port of the optical switching unit. Status information regarding the internal path of the test light is stored in a memory, along with flags corresponding to the magnitude of reflected light generated when the test light is reflected from an abnormal position along the internal path selected. The status information is stored in the form of a reflection alarm information table where the flags are stored in association with each of the internal paths. A rearmost connection among the optical interconnections in the optical switching unit is detected as an abnormal position based on the reflection alarm information table and the interconnection control table.

Abstract: A method includes receiving a restoration indicator associated with a path that includes an optical cross-connect (OXC). The OXC is reconfigured from a standby configuration to a restoration configuration in response to the restoration indicator. An optical signal received in a first direction at a first wavelength is optically regenerated to produce an optical signal in the first direction at a second wavelength. An optical signal received in a second direction at the second wavelength is optically regenerated to produce an optical signal in the second direction at the first wavelength.

Abstract: Optical transmission systems of the present invention include optical protection systems, apparatuses, and methods that provide increased reliability in the system. The optical system generally includes an optical switch having distinct, cooperating dedicated and shared protection sections. The shared protection sections in a plurality of nodes can be configured to provide a protection net, in which a plurality of traffic demands, or working channels, are commonly protected as protection group using one protection channels supported by the protection net.

Abstract: Method and apparatus for dynamic provisioning of reliable connections in the presence of multiple failures in optical networks are described. One embodiment is a method for allocation of protection paths after a failure in an optical network. The method comprises, responsive to a failure in an active lightpath, switching traffic on the active lightpath to a protection path; subsequent to the switching, identifying all active lightpaths in the network that no longer have an available protection path; and attempting to allocate a protection path to each of the identified active lightpaths.

Abstract: Where each of switches opposed to each other detects optical-signal shutoff or optical-signal deterioration on the reception side of its port, the switch brings a link of the port down and outputs an auto-negotiation configuration code, as an LAN signal. Upon receiving the LAN signal transmitted from the switch, a repeating-transmission apparatus transmits the transmitted signal to an auto-negotiation monitor. The auto-negotiation monitor performs code analysis for the transmitted LAN signal. Where the auto-negotiation monitor detects that the transmitted LAN signal is the auto-negotiation configuration code, it notifies a monitor apparatus that “The switch detects a failure and the link is down.”, as an alarm.

Abstract: An apparatus for shared optical performance monitoring (OPM) is provided. A wavelength sensitive device receives light at an input port and routes it wavelength selectively to a set of output ports. To perform optical performance monitoring on the output ports, a monitoring component of each output signal is extracted, and these monitoring components are then combined. A single OPM function is then performed on the combined signal. However, with knowledge of the wavelengths that were included in each output signal, a virtual OPM function can be realized for each output port. The per port functionality can include total power per port, power per wavelength per port, variable optical attentuation, dynamic gain equalization, the latter two examples requiring feedback.

Abstract: An optical access network employs a ring topology in which connections between the network units and between the network units and the optical line terminal are via a protection switch. The protection switch monitors connections from the optical network units to detect a loss of signal and, on detecting a loss of signal from an optical network unit, switches the respective optical network unit out of the ring, thus maintaining continuity of the ring topology.

Abstract: A modular cross connect system for optical telecommunication networks has the optical unit divided in at least two main bodies with one section for connection comprising the collimators and a main commutation section with MEMS devices. The first section is a fixed part while the second section is a readily removable section. The two sections face each other through a window and, in the first section, optics are provided for steering all or part of the optical signals from and to the main MEMS unit to a MEMS standby or protection plane to allow replacement of the main MEMS unit without interrupting service.

Abstract: Transparent network elements (10) pass data in a data communication plane (24) over optical links (42) and pass control information in a control communication plane (22) over a out-of-fiber/out-of-band (OF/OB) network (44), such as an IP-based network. Previously developed protection state machines (38), such as those used in traditional SONET/SDH systems can be used along with new protection state machines (38), such as shared ring protection state machines. Client State machines (40) and a signaling controller (30) interface between the protection state machines (38) and the OF/OB network (44) such that the protection state machines (38) are isolated from the technicalities of transmission in the separate network.

Abstract: An optical transmission system wherein a main signal light is amplified by Raman amplification, and noise light (ASS light) produced by the Raman amplification can be corrected with a simple configuration and with high accuracy.

Abstract: Two multiplexing/demultiplexing sections of working and protection sides are prepared for each of a plurality of optical transmission devices which constitute a system, and the optical transmission devices are synchronized with each other to execute switching between the working and protection sides so that one of the working and protection sides can be selected for the entire system. Each expansion device collects optical line trouble information for each of the working and protection sides, and transmits to a main device. The main device integrates the information with trouble information transmitted from expansion devices per expansion device. The main device converts the integrated trouble information into point information, totals for each of the working and protection sides, compares, and decides which of the working and protection sides is to be selected.

Abstract: A communication system includes nodes that exchange communications over optical fibers. In the event of a fault, the nodes implement ring protection for a first set of the communications and implement mesh protection for a second set of the communications. Ring protection may be used for two degree nodes and mesh protection may be used for higher degree nodes, or a customer may select between ring protection and mesh protection.

Abstract: An optical signal judging system for judging an optical signal outputted from an optical switch the selectively outputs any one of input optical signals, comprises: a converting unit converting at least two optical signals branching off from an optical signal source into optical signals having wavelength bands differing from each other, and thus outputting the optical signals to said optical switch, wherein said optical switch outputs any one of at least the two optical signals so converted as to have the wavelength bands differing from each other, which have been inputted from said converting unit.

Abstract: A bit-rate-transparent electrical space-division switching matrix is employed in an optical cross-connect and the input/output stage is constructed from simple, broadband optical receivers and transmitters. Since the switching matrix operates in unclocked manner, i.e. its switching function is not based on internal bit timing and frame timing, arbitrary signals can be switched though transparently at almost any bit rate, independently of the protocol-type being used. The inputs and outputs likewise operate fully independently of bit rate and protocol, since they only implement an O/E conversion or O/E conversion. By virtue of this structure, a simply constructed but extremely powerful optical cross-connect is created that can be employed equally for all types of optical signals within the stipulated wavelength-range.

Abstract: The present invention provides a method and system for monitoring composite optical signals carried over plural fiber-optic lines within an optical network. Methods and systems in accordance with the present invention each utilize a single OPM to monitor each one of a set of sample proportions of composite signals split off from respective fiber-optic lines. In one embodiment, an optical performance monitoring system comprises a plurality of fiber-optic lines, each fiber-optic line carrying a respective composite optical signal, a plurality of optical taps, each optical tap being optically coupled to a respective one of the fiber-optic lines and splitting a portion of the composite optical signal thereof, a plurality of optical switches, each optical switch being optically coupled to a respective one of the optical taps and comprising either an Open configuration and a Closed configuration, an optical coupler, and an Optical Performance Monitor (OPM).

Abstract: Incident signal beam pulses are transmitted by an on-state region, and an optical path for the signal beam pulses is spatially switched in an optical switch. Signal beam pulses transmitted by the on-state region of the optical switch are detected at a pixel corresponding to a transmitting region of a photo-detector equipped with a plurality of pixels. A timing computation unit acquires position information of a pixel at which a predetermined signal beam pulse has been detected, on the basis of a result of the detection conducted by the photo-detector, and computes timing of arrival of a predetermined signal beam pulse at the optical switch on the basis of the position information of the pixel and time when a region corresponding to the pixel is brought to an on-state.

Abstract: A network is protected against interruption of service while one or more faulty switches or optical fiber transmission lines are repaired or replaced, by an interconnecting configuration of small N×N optical input/output switches, where N is 2 or greater than 2. The switches are configured among protection and working transmission lines. The small number of fibers for each switch improves repair and installation connection reliability and permits configurations that flexibly meet differing requirements. Also the fault is monitored with a fault check signal.

Abstract: A protection system protects paths of internetwork communication between WDM ring networks, and includes a plurality of optical wavelength multiplexing networks having a plurality of nodes and a network management system for monitoring conditions of the plurality of nodes. The nodes include a first node having add/drop functions of adding/dropping wavelength-multiplexed optical signals; a second node having a signal transfer function as well as the add/drop functions; and a third node having an internetwork connection function between the networks. Each first, second and third nodes further includes optical path cross-connect switches and a table for indicating conditions of the optical path cross-connect switches and a detected node fault condition. The network management system controls to set the optical path cross-connect switches in the first, second and third nodes so that the optimal optical path connection may be obtained according to the detected node fault condition indicated in the node tables.

Abstract: A light source supplies optical signal to an optical switch and a detector detects light receiving level. A control unit changes a deflection control amount for changing an angle of a tilt mirror, and outputs the deflection control amount to a driving unit. When an input and an output ports are same, optical offset of the tilt mirror is calculated based on optimal angle at which the light detector detects an optimal point of the light receiving level. Whenever the input and the output port are different, a structure parameter of the tilt mirror is calculated based on the optical offset and the optimal angle. The optical offset and the structure parameter are stored in a memory as a test result.

Abstract: A protection arrangement for an optical switching system includes protection switching for switch planes in the optical core and for ports in the tributary cards. For a multiple layer switch core protection is also provided between layers. A first layer is for switching optical channels. The protection switches used may be 1×N, 2×N or 3×N MEMS optical switches. The 1×N MEMS provides for protection switching. The 2×N MEMS provides protection switching and testing capability. The 3×N MEMS provides for protection switching, testing and backup of the protection switching. Application of these protection switches is shown in lambda plane switch cores, multiple layer switch cores and combined switch cores.

Abstract: A wavelength-path-monitoring/correcting apparatus used in a transparent OXC is disclosed. The apparatus includes: a path-information-generating section for generating path-monitoring information; a plurality of optical couplers for coupling each output signal of the wavelength-division demultiplexers with the pertinent path-monitoring information; a plurality of optical switches for switching each optical signal inputted from the optical couplers; a plurality of wavelength-division multiplexers for multiplexing optical signals inputted through the optical switches; a path-information-detecting section for detecting the path-monitoring information from optical signals outputted from the wavelength-division multiplexers; and, a path-control section for comparing the path-monitoring information detected through the path-information-detecting section with predetermined optical-switching information and for correcting switched paths.

Abstract: Optical transmission systems of the present invention include optical protection systems, apparatuses, and methods that provide increased reliability in the system. The optical system generally includes an optical switch having distinct, cooperating dedicated and shared protection sections. The shared protection sections in a plurality of nodes can be configured to provide a protection net, in which a plurality of traffic demands, or working channels, are commonly protected as protection group using one protection channels supported by the protection net.

Abstract: A method of controlling deflection of an optical beam at a beam steering element. The method comprises receiving switching instructions indicative of a target one of a plurality of potential transmit or receive elements; determining a control signal associated with the target transmit or receive element; and applying the control signal to the beam steering element, thereby to cause deflection of the optical beam. Deflection of optical beams on the basis of the determined control signal allows greater pointing accuracy. Also, a port card, comprising a plurality of optical transmitter elements operative to produce respective optical beams from the input optical signals; and an array of beam steering elements operative to controllably orient the optical beams into respective transmit directions. The port card also comprises a controller for controlling the beam steering elements of the array using, for example, the above method.

Abstract: The present invention includes an optical transceiver having a fiber module with an optical data input and an electrical data output. The fiber module further includes a signal detect output that indicates the receipt of valid optical data. A physical layer device having a receive input is coupled to the electrical data output through a switch that is controlled by the signal detect output. The switch passes electrical data from the electrical data output of the fiber module to the receive input when the signal detect output indicates the receipt of valid optical data, and does not pass the electrical data when the signal detect output indicates invalid optical data. By using this configuration, the signal detects pins of the physical layer device are eliminated. In another embodiment, the switch is not utilized, and the electrical data output of the transceiver is ac-coupled to the differential receive input of the physical layer device.

Abstract: Disclosed are an apparatus and a method for shortening a processing time at each node in an optical network. A transmission optical cross-connect (OXC) determines a transmission rate corresponding to the transmission speed of the signal to be transmitted. An optical receiver and an optical transmitter are stabilized by means of the transmission rate. In addition, a transmission OXC transmits the transmission rate to an OXC aligned between the transmission OXC and the receiving OXC, thereby stabilizing the OXC. Each of the OXCs detects the transmission speed of the optical signal to be received so that a time required for converting the transmission speed is reduced.

Abstract: An all optical switching system which is optically switched, from the signal channel all the way to a router. Errors in the routers are detected, and indications of those errors are sent back to the optical switch. The optical switch uses a system which picks off a piece of the signal to use the control signal to control the switching.

Abstract: A method, system and device for simulating cable failures in a network are disclosed. In a first aspect, a plurality of optical cables which couple a plurality of devices within the network to each other are provided. The method and system includes providing at least one programmable device on one of the plurality of optical cables. The at least one programmable device allows for controlled simulated cable failures. In a second aspect, the network comprises: a plurality of devices and a plurality of optical cables for interconnecting the devices. The network also includes at least one programmable device coupled to one of the optical cables, the at least one programmable device allows for controlled simulated cable failures. In a third aspect, the programmable device is used in a network for simulating cable failures in the network. The network includes a plurality of devices and a plurality of optical cables for interconnecting the devices.

Abstract: An apparatus having n-number of working cross-connects for cross-connecting an n-bit input signals arriving from a plurality of input paths on a per-bit basis; n-number of first logic circuits for calculating the exclusive-ORs of each said n-bit and applying outputs to a standby cross-connect for providing outputs; n-number of second logic circuits for calculating the exclusive-ORs of said output signals from each of said working cross-connects and from the single standby cross-connect; and third logic circuits for selecting output signals of said working cross-connects and outputs of the second logic circuits. The apparatus detects the occurrence of an abnormality in working cross-connects by monitoring the outputs of the second logic circuits, identifies the faulty cross-connect by successively turning off one of the n-inputs to the first and second logic circuits, and select outputs from the second logic circuits instead of from the faulty cross-connect by using the third logic circuits.

Abstract: A bit-rate-transparent electrical space-division switching matrix is employed in an optical cross-connect and the input/output stage is constructed from simple, broadband optical receivers and transmitters. Since the switching matrix operates in unclocked manner, i.e. its switching function is not based on internal bit timing and frame timing, arbitrary signals can be switched though transparently at almost any bit rate, independently of the protocol-type being used. The inputs and outputs likewise operate fully independently of bit rate and protocol, since they only implement an O/E conversion or O/E conversion. By virtue of this structure, a simply constructed but extremely powerful optical cross-connect is created that can be employed equally for all types of optical signals within the stipulated wavelength-range.

Abstract: An apparatus and method for fault detection and isolation in an optical network is disclosed in which each node determines an appropriate response to a line fault or an equipment fault, obviating the need for a central computer to coordinate the actions of each node in response to a fault. Each network node includes a local controller and restoration elements for detecting and responding to faults. Each local controller correllates a first set of optical characteristics measured by optical detectors with the local node with a second set of optical characteristics for the channels reported to the local node from an upstream optical element, such as a neighboring upstream node, to determine if a line switch or equipment switch is required. In a preferred embodiment, each node is communicatively coupled to its neighboring node via an optical supervisory channel, with the neighboring nodes communicating status messages and data on channel characteristics via the optical supervisory channel.

Abstract: The invention concerns an interface device for a fiberoptic communication network. The interface device comprises an electric circuit arrangement 32, a first receiving section 34 for receiving a first transceiver module 24 and a second receiving section 36 for receiving a second transceiver module 26. The interface device also comprises a switching unit 54 for switching said electric circuit arrangement between at least a first and a second state. Furthermore, the interface device includes a controller 56 arranged to automatically control the switching unit 54 in response to at least one control signal such that said first or second states are selected depending on whether at least one control signal is received indicating either that no transceiver module 26 is attached to said second receiving section 36 or that no optical signal above a certain signal level is received by a transceiver module 26 attached to said second receiving section 36.

Abstract: A protection arrangement for an optical switching system includes protection switching for switch planes in the optical core and for ports in the tributary cards. For a multiple layer switch core protection is also provided between layers. A first layer is for switching optical channels. The protection switches used may be 1×N, 2×N or 3×N MEMS optical switches. The 1×N MEMS provides for protection switching. The 2×N MEMS provides protection switching and testing capability. The 3×N MEMS provides for protection switching, testing and backup of the protection switching. Application of these protection switches is shown in lambda plane switch cores, multiple layer switch cores and combined switch cores.

Abstract: A branch unit for a fiber optic system that includes a service path and a protection path, whereby the branch unit provides switching to account for problems due to fiber cuts and/or equipment failures that may occur in the fiber optic system. The service and protection paths meet at a branch point of the fiber optic network, or at a network protection equipment (NPE) that is located near a customer interface equipment. A plurality of switches are provided at the branch unit or NPE, along with a detector and a processor, to determine whether any signals are being received from the service path, and if not, to reconfigure the system to accept signals from the protection path.

Abstract: To verify the integrity of optical paths through and among optical switches, optical signals are provided with co-propagating supplemental signals. The supplemental signals preferably have at least one characteristic which allows distinguishing one supplemental signal from another. Associated with a port of a switch, means are provided for detecting a supplemental signal and determining if the supplemental signal indicates that a desired optical signal is passing through the port as expected and desired. Means for imparting or changing the distinguishing characteristic of a supplemental signal may also be employed to facilitate verifying the passage of optical signals.

Abstract: A system and method for facilitating full utilization of an ultra-wide optical communication band spanning the useable band of the optical transmission spectrum, and providing appropriate protection strategies on the same mesh/ring network for all channels within the ultra-wide optical communication band. A network node architecture includes a band splitter to receive all of the optical signals sent on various wavelengths within the wide optical communication band. The band splitter separates a first group of the optical signals from a second group of the optical signals based on their range of wavelength. The first group of optical signals are those within a first wavelength range of the optical communication band, and the second group is from the second wavelength range of the optical communication band. A cross-connect circuit receives the first and second groups of optical signals, and routes them to targeted output ports at the output section of the node.

Abstract: A method and an apparatus for switching channel connection between multiple optical channels synchronously and automatically. The apparatus employs an optical switch to interface among a plurality of optical channels, and an optical power meter to monitor data transmission over the plurality of optical channels by measuring the optical power level of optical signals over the channel. When signal transmission is detected over a specific optical channel, the optical switch is locked to the specific optical channel allowing data signals over the specific optical channel to be transmitted to a specific device or another optical channel through the optical switch. When no optical signal is detected over the channel, said optical switch will be switched to another optical channel, such that signal monitoring and switching channels among a plurality of optical channels is able to be performed synchronously and automatically.

Abstract: An exemplary method and optical network that provide optical network restoration using refreshed state tables are disclosed. The exemplary method for recovering from a failure in an optical network using refreshed switch state tables includes generating and storing connection information in switch state tables of associated optical switches that define optical link connections to be made in the event of a failure, monitoring whether a failure has occurred, and refreshing the switch state tables by continuing to generate and store connection information in the plurality of switch state tables that are associated with the plurality of optical switches of the optical network until the failure in the optical network is detected. Once the failure is detected, optical switching is automatically performed in the optical switches based on the lookup table connection information in the switch state tables that are associated with the optical switches.