Abstract: The present invention provides a wavelength-switched reconfigurable optical add-drop multiplexer (R-OADM) with wavelength broadcasting capability, such that asymmetric video signal distribution and the like can be performed without sacrificing with respect to component complexity and expense. The present invention utilizes an optical splitting and combining device with the wavelength-switched R-OADM to allow the R-OADM to support network-wide wavelength broadcasts without requiring external regeneration and extra optical transceiver equipment.

Abstract: Various architectures for implementing multi-band reconfigurable optical add-drop multiplexing with converged signal addition and removal are provided. Under the described architectures, channel isolation is improved, performance requirements for switching elements are lower, and it may be possible to reduce the number of line side switching elements by a factor of two. The use of additional spectrum per fiber with the described architectures results in fewer required ports per switching element. The degree of contention at signal addition and removal is also reduced. Moreover, the architectures support optical networks with higher capacities per fiber and therefore conserve fiber assets. The architectures are modular in nature, allowing a network to be deployed in a single-band setting and later upgraded to support multiple bands. 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: A method and apparatus for performing an automatic power adjustment wherein a signal power level of an optical signal transmitted by an optical transceiver via an s optical span to a far-end device is adjusted automatically in response to a determined span loss of the optical span to achieve a predetermined desired receive signal power level of the optical signal at the far-end device.

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: A reconfigurable optical switching device comprising a Tunable Filters Array (TFA) unit incorporating tunable optical filters, wherein the arrangement is such that one and the same TFA unit is utilized both for performing a drop function of the device in a colorless and reconfigurable manner, and a through function of the device in a reconfigurable manner.

Abstract: Methods and systems for optical signal grooming that include providing one or more input signals, each having one or more modulated subcarriers, to a grooming processor; and grooming the input signals at a subcarrier level with the grooming processor to produce one or more output signals by arranging the modulated subcarriers in the output signals according to a grooming operation such that the modulated subcarriers are not demodulated or decoded prior to grooming.

Abstract: A wavelength selective switch includes a substrate. On the substrate, the wavelength selective switch includes at least one input port, a dispersive element, a light converging element, a light deflecting member, an output port, and a driving mechanism which drives at least one of the dispersive element, the light condenser element, and the light deflecting member, and drive by the driving mechanism is a rotational drive around an axis perpendicular to the substrate, for the dispersive element, and is a translational drive in a direction of dispersion of wavelength with respect to the substrate, for the light condenser element or the light deflecting member.

Abstract: The present invention discloses a method and a system for shared protection in WDM loop network. The WDM loop network comprises at least one node, and each node is divided into a multiplexing segment layer, a channel layer and a sub-wavelength layer. The method for shared protection comprises the following steps: A, the multiplexing segment layer, the channel layer and the sub-wavelength layer of each node are detected respectively; B, the detection point generates fault information when at least one of the multiplexing segment layer, the channel layer and the sub-wavelength layer goes wrong; and a controller of each node, according to the fault information, determines the protection control state of the present node and notifies the respective executor; wherein the protection control state includes service adding, service passing through, and service dropping; C, the executor of each node controls the corresponding node to switch to the protection control state determined in step B.

Abstract: The present invention reduces the number of amplifiers and reduces the maximum output of an optical transmission device. A wavelength selection unit selects and outputs, as a drop signal, any given wavelength of optical signal from an input optical signal. An amplifier amplifies at each wavelength the drop signal output by the wavelength selection unit. In this case, the number of amplifiers is set smaller than the number of wavelengths of the input optical signal. Also, the wavelength selection unit selects a number of wavelengths of drop signals corresponding to the number of amplifiers, and outputs the drop signals to the amplifiers at each wavelength.

Abstract: The present invention reduces the number of amplifiers and reduces the maximum output of an optical transmission device. A wavelength selection unit selects and outputs, as a drop signal, any given wavelength of optical signal from an input optical signal. At each wavelength, an amplifier amplifies the drop signal output by the wavelength selection unit. In this case, the number of amplifiers is set lower than the number of wavelengths of the input optical signal. Also, the wavelength selection unit selects a number of wavelengths of drop signals corresponding to the number of amplifiers, and outputs the selected drop signals to the amplifiers at each wavelength.

Abstract: An optical demultiplexing structure and method for demultiplexing channels from a wavelength multiplexed optical signal comprising a first optical filter (115), a second optical filter (117), and at least one third optical filter (120), wherein the first filter has a band-pass characteristic for extracting a first set of channels from the optical signal, and the second filter has a cut-off wavelength corresponding to a wavelength within the pass-band of the first filter, and wherein the first filter is connected to the second filter, the second filter extracting a second set of channels from the channels that remain after extraction of first the set of channels by the first filter, and wherein the at least one third filter has a passband to extract a subset of channels from the second set of channels spaced apart from the first set of channels. The corresponding multiplexing structure and method are also described.

Abstract: An optical device for optically multiplexing or demultiplexing light of different predetermined wavelengths is provided, the optical device comprising at least one first waveguide (11) and at least one second waveguide (12) formed on a substrate (10), wherein the at least one first waveguide and the at least one second waveguide intersect at an intersection, comprising a diffraction grating structure (13) formed at the intersection. There exists a first wavelength or wavelength band travelling within the first waveguide (11) exciting the grating structure and being diffracted an angle corresponding to an outcoupling direction and there exists a second wavelength or wavelength band, different from the first wavelength or wavelength band, travelling within the second waveguide (12) exciting the grating structure and being diffracted at an angle corresponding to the same outcoupling direction.

Abstract: Systems and apparatus for data communications comprising a plurality of wavelength tunable submodules in an array is provided. Each submodule has a wavelength tunable laser, and each submodule comprises, as an individual unit, a self-contained wavelength locker having optical and/or optoelectronic functions. The system may be a transponder array comprising a plurality of WDM or DWDM modules. In some embodiments, the individual submodules may comprise photonic integrated wavelength tunable lasers with other optical, electrical and optoelectronic components. Each wavelength tunable submodule incorporated into the module or array can have the same or different optical wavelength and other parameters including but not limited to modulation format. By utilizing the wavelength tunable laser submodules to build a module or array, the need for individual modules dedicated to wavelength sub-bands in the array is eliminated. The same tunable module can be used to fill all the wavelengths on a transmission fiber.

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 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: In a multi-chip module (MCM), integrated circuits are coupled by optical waveguides. These integrated circuits receive optical signals from a set of light sources which have fixed carrier wavelengths. Moreover, a given integrated circuit includes: a transmitter that modulates at least one of the optical signals when transmitting information to at least another of the integrated circuits; and a receiver that receives at least one modulated optical signal having one of the carrier wavelengths when receiving information from at least the other of the integrated circuits. Furthermore, the MCM includes switchable drop filters optically coupled to the optical waveguides and associated integrated circuits, wherein the switchable drop filters pass adjustable bands of wavelengths to receivers in the integrated circuits. Additionally, control logic in the MCM provides a control signal to the switchable drop filters to specify the adjustable bands of wavelengths.

Abstract: A reconfigurable optical add drop multiplexer core device includes a light distributor, a light combiner, and first and second sets of add and drop ports. The light distributor is configured to receive an optical signal along a primary input of the reconfigurable optical add drop multiplexer core device and to distribute the received optical signal along a plurality of subtending outputs. The light combiner is configured to receive optical signals along a plurality of subtending inputs, to combine the received optical signals into a combined signal, and to output the combined signal. The add and drop ports in the first set function as add and drop ports, respectively, and the add and drop ports in the second set function as both add and drop ports, respectively, and as express ports connectable to another reconfigurable optical add drop multiplexer core device.

Abstract: An optical transmission apparatus includes an amplifier, a first output port to select a wavelength from the wavelength-division-multiplexed signal light amplified and output signal light with the selected wavelength to an operation line, a second output port to output multiplexed light obtained by multiplexing any one of first spontaneous emission light and second spontaneous emission light to a preliminary line, the first and the second spontaneous emission light being parts of spontaneous emission light generated by the amplifier, the first spontaneous emission light being in a wavelength range that is not selected, and the second spontaneous emission light being in a wavelength range other than a range of the wavelength-division-multiplexed signal light, and a judger to judge a continuity state of the operation line by using the signal light output to the operation line and a continuity state of the preliminary line.

Abstract: An optical add/drop multiplexer (OADM) and system incorporating the same for maintaining loading of WDM channels with loading signals or information signals when signals are added or dropped. The OADM may include reconfigurable band pass filters having a transmittance characteristic controllable using a command signal. Selective filtering of loading signals and/or information signals received from branch and trunk paths allows an output WDM signal including information signals on utilized channels and loading signals on all unutilized channels.

Abstract: A fiber optic coupler includes a housing that receives upstream optical signals from drop optical fibers that are optically coupled to optical network units in a power splitting passive optical network and provides an aggregate upstream optical signal to a trunk optical fiber that is optically coupled to an optical line terminal in the power splitting passive optical network, without having passed through a power splitter. At least one reflector and/or refractor in the housing is oriented to reflect and/or refract at least one upstream optical signal from at least one of the drop optical fibers, so as to produce the aggregate upstream optical signal for the trunk optical fiber. Various configurations of reflectors and/or refractors may be provided. Relative methods are also disclosed.

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: ROADM node systems and methods of operation are disclosed. ROADM node systems may include transponder aggregators including transponders to add signals for switching through the ROADM node. The transponder aggregators may be constrained from adding signals on adjacent channels for simultaneous use. Further, the transponder aggregators may include an optical coupler in lieu of an optical multiplexer. The ROADM system may include a set of wavelength selective switches associated with output ports that can provide an additional filtering function for the added signals prior to transmission on a WDM network.

Abstract: New designs of optical devices, particularly for dropping a selected wavelength or a group of wavelengths as well as demultiplexing a multiplexed signal into several signals, are disclosed. An optical device employs thin film filters with reflectors to reassemble as a fiber Bragg grating. Depending on implementation, a reflector may be a mirror or a coated substrate disposed in a unique way to reflect a light beam from a filter back to a common port of a device. The reflector may also be coated accordingly to bypass a certain portion of the light beam for other purposes. As a result, the optical devices so designed in accordance with the present invention are amenable to small footprint, enhanced impact performance, lower cost, and easier manufacturing process.

Abstract: A space division multiplexed (SDM) transmission system that includes at least two segments of transmission media in which a spatial assignment of the two segments is different is provided. For example, the SDM transmission may include a first segment of transmission media having a first spatial assignment and a second segment of transmission media having a second spatial assignment, wherein the first spatial assignment differs from the second spatial assignment. An example method obtains an optical signal on a first segment of transmission media having a first spatial assignment and forwards the optical signal on a second segment of transmission media with a different spatial assignment. The transmission media may be a multi-core fiber (MCF), a multi-mode fiber (MMF), a few-mode fiber (FMF), or a ribbon cable comprising nominally uncoupled single-mode fiber (SMF).

Abstract: An optical intensity control system for use with an optical switch providing individual signal paths between input and output ports. The system has a optical splitters connectable to output multiplexers of the switch and also has variable optical intensity controllers (VOICs) for insertion into the individual signal paths. The VOICs individually control the intensity of optical signals present in the signal paths in accordance with intensity control signals. An equalizer is connected to the splitters and to the VOICs, for producing an estimate of the optical power of each individual switched optical signal and generating the intensity control signals. The equalizer is adapted to controllably isolate individual switched optical signals.

Abstract: An optical add/drop multiplexer (OADM) having an Add path for adding optical channel signals input through a plurality of Add ports to an outbound dense wavelength division multiplexed (DWDM) signal, and a Drop path for switching selected channels from an inbound DWDM signal to one or more of a plurality of Drop ports. The OADM has a loopback connection between the Add path and the Drop path. The loopback connection couples a selected loopback channel wavelength from the Add path to the Drop path. The physical connection between a transceiver and the OADM can be verified by connecting the transmitter to an Add port of the OADM and the receiver to a Drop port of the OADM. The OADM is controlled to switch the selected loopback channel wavelength in the Drop path to at least one intended drop port to which the receiver should be connected, and the transmitter is controlled to transmit a predetermined test signal using the loopback channel wavelength.

Abstract: An apparatus includes a first optical switching complex, a second optical switching complex in optical communication with the first optical switching complex, and an optical add/drop module in optical communication with the first optical switching complex and the second optical switching complex. At least one of the optical switching complexes includes a wavelength selective switch that is configured to be arranged in a cascaded configuration that, when so configured, results in an increase in a number of available transmit and receive ports available per degree of the apparatus.

Abstract: The invention provides a burst transmission optical fiber wavelength routed ring network and method comprising a plurality of nodes on a network ring where each node can drop and add a wavelength. The network has a control means to control the wavelength to be transmitted on the network ring in a burst transmit mode from each node over a scheduling interval. The invention provides a random generator for generating a plurality of gap intervals over the scheduling interval, such that the gap intervals allow for wavelengths from different nodes to transmit wavelengths in said gaps to achieve a fair access to bandwidth and fair latency in the ring network.

Abstract: An optical add-drop network and wavelength allocation for the same wherein the system bandwidth is separated into a dedicated channel band and re-used channel bands, separated by guard bands, to allocate terminal connections to achieve a minimum number of re-used channel bands for the desired terminal connectivities.

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: The present disclosure describes a reconfigurable optical add-drop multiplexer including a wavelength selective switch configured to filter wavelengths of an optical signal; and an optical equalizer, coupled to the wavelength selective switch, configured to equalize the optical signal to mitigate optical filtering effects caused by the wavelength selective switch.

Abstract: The present disclosure provides optimized configurations for a directionless reconfigurable optical add/drop multiplexer application. The present invention includes an add module with improved optical signal-to-noise through placing amplifiers prior to a multi-cast optical switch. The present invention includes various drop module configurations utilizing distributed gain, channel selective filters, and bi-directional configurations to reduce power consumption and complexity. Additionally, the present invention includes an integrated broadcast and select architecture.

Abstract: A scalable reconfigurable (or tunable) optical add/drop multiplexer (SROADM) is disclosed. The SROADM includes a pair of acoustic optic tunable filters (AOTF) and a wavelength blocker (WB). A first input port receives an initial wavelength division multiplexer (WDM) optical signal including to-be-dropped optical signal(s). A second input port(s) receives optical signal(s) to be added, which has the same wavelength(s) as that optical signal(s) to be dropped. In one embodiment, the WB is connected to the AOTFs through free space coupling. In another embodiment, the coupling is achieved by optical fiber fusion splicing. The latter method has advantage of using commercially available products and easier assembly while a more compact size is achievable by the free space coupling. The device is scalable in terms of number of add/drop ports and capacity to process any number of wavelength channels.

Abstract: In an illustrative embodiment, a data interface circuit is provided. The data interface circuit comprises data sources, input blocks, a space switch, output blocks and a multi-core processor. The data interface circuit allows data provided in different voltage ranges and sampling frequencies to be transmitted to the appropriate core in the multi-core processor via the switch. Data conversion elements in the input blocks convert data from the data sources and having varying voltage ranges and sampling frequencies into data having a voltage range and sampling frequency suitable for the space switch. Analogously, data conversion elements in the output blocks convert data from the space switch into data having a voltage range and sampling frequency suitable for the corresponding core in the multi-core processor. In one embodiment, level shifters and FIFO buffers are used in the input blocks and output blocks.

Abstract: In today's reconfigurable optical add/drop multiplexer (ROADM) based optical node, ROADMs multiplex (and demultiplex) colored optical signals to form wavelength-division multiplexed (WDM) signals. Transponders connected to the ROADMs' add/drop ports convert noncolored optical signals to colored optical signals (and vice versa). Dedicating transponders to given ports degrades the node's ability to route around network failures. Example embodiments of the invention include an optical node and corresponding method for routing optical signals within an optical node that compensate for this inflexibility. The optical node may include two ROADMs to transmit respective WDM signals onto at least two internode network paths and a routing module that can direct channels of the same wavelength along different internode network paths.

Abstract: An attenuation amount corresponding to each wavelength at OADM node is optimized according to a calculation result in a network management system (NMS), so that an optical signal level diagram according to traffic volume variations is set, the level diagram allows each of optical signal quality indexes at terminal nodes for all wavelengths to be maintained at a required threshold value or more, and allows an optical signal quality index of a specific wavelength to be improved. Then, an FEC circuit in an optical receiver corresponding to the specific wavelength is turned OFF or the error correction ability is lowered, whereby power consumption of an overall optical network is efficiently reduced.

Abstract: A three-arm-Mach-Zehnder interferometer for splitting/combining first and second wavelength bands is provided, wherein the optical device includes first and second optical splitting/combining elements; a differential optical delay device comprising first, second and third optical paths; the first, second and third optical paths of the differential optical delay device are configured to introduce, at a wavelength ?z within the first optical band, a phase delay of 2?m.

Abstract: An apparatus for managing an optical signal includes a system optics card including an add filter, a drop filter, electrical backplane connector, and a mechanical front panel including express input and output ports providing channels to other system optics cards. The card transports information over a first optical transport link and receives information over a second optical transport link. The card identifies at least one network channel on the second optical transport link destined for a client device. The drop filter delivers the identified network channel to the optical converter card for delivery to the client device. The add filter receives client channels from the optical converter card generated by the client device. The card also transports the client channels of the client device over the first optical transport link. The electrical backplane connector is connectable to a chassis for housing the system optics cards and other system optics cards and/or other optics cards.

Abstract: Example embodiments may include a coaxial Free Space Optical (FSO) telescope providing a simplified and more precise structure. Example embodiment telescopes include a prism structure having at least two parallel surfaces associated with a filter and mirror. The filter may reflect or transmit optical signals based on their electromagnetic characteristics. Example embodiment systems include example embodiment coaxial FSO telescopes and transmitters and receivers for receiving and transmitting optical signals. A V-groove and/or lens array may be included in example embodiment FSO systems.

Abstract: An optical transport system having an optical add-drop multiplexer configured to reduce inter-channel crosstalk by driving Mach-Zehnder pulse carvers in its optical transmitters with electrical drive signals whose swing range is smaller than voltage 2V? of said Mach-Zehnder pulse carvers.

Abstract: An optical hub node apparatus can be configured to include N+1 or more route units (10) by connecting N or less route units (10) selected from among the N+1 or more route units (10) to a route unit (10) including N (N:integer of 2 or more) ports to which other route units (10) are detachably connected. As a result, as compared with a case where N+1 route units (10) are completely interconnected in a meshed manner, the number of the route units (10) can be increased. Thus, the number (degree) of optical transmission apparatuses connectable to the optical hub node apparatus can be increased.

Abstract: Described are an FSK modulator and a method for large-alphabet FSK modulation. The FSK modulator and the method are based on filtering of a multi-tone optical source such as a mode-locked laser which provides a comb distribution of tones. A frequency-selective component selects for transmission a subset of the tones. In various embodiments the frequency-selective component is a Mach-Zehnder interferometer filter or a microring resonator filter. A second frequency-selective component selects a subset of the tones from the comb distribution provided by the first frequency-selective component. Still more frequency-selective components can be used according to the number of tones supplied by the multi-tone optical source to the FSK modulator. The optical signal exiting the last frequency-selective component includes only a single tone which corresponds to the symbol to be transmitted.

Abstract: Fault tolerance may be achieved in a branched optical communication system such that a fault in one optical path may not affect optical signals coupled from a healthy optical path. In general, a flexible branching unit is configured, when adding and dropping channels, to select channels from a healthy path and not from the faulty path (e.g., a trunk path or a branch path) to prevent non-uniform channel loading on the trunk path after the branching unit. In this manner, a fault detected on the trunk path may not affect signals from the branch path and a fault detected on the branch path may not affect signals from the trunk path, thereby providing fault tolerance. A flexible branching unit may also be capable of adjusting the number and selection of channels that are added and dropped at the branching unit.

Abstract: Channel power management may be achieved in a branched optical communication system such that uniform loading is provided across branch channels on a branch drop path without passing information signals that are not intended for the branch terminal to the branch drop path. In general, a system and method consistent with the present disclosure reuses one or more loading signals (e.g., noise bands) from the branch add path to maintain uniform loading in the branch drop path of the same branch. The system and method thus prevents trunk channels from being dropped to a branch terminal when those trunk channels are not intended for the branch terminal.

Abstract: Signal wavelengths ?1, ?2, ?3 of signal light components multiplexed at signal multiplexing sections 31, 41, 51 of multiplexing stations 3, 4, 5 installed on the input end side of an EDFA 2 on an optical transmission line 1 are set such that the wavelength-dependent noise figure of EDFA 2 successively decreases from the signal wavelength ?1 multiplexed at the signal multiplexing section 31 closest to the input end of EDFA 2 to ?2 and ?3. On the other hand, the transmission length of individual signal light component before being fed into the EDFA 2 is the shortest in the signal light component at ?1 and successively increases at ?2 and ?3. Thus, the order of magnitude of input signal light power is the same as the order of highness of noise figure in EDFA 2, whereby fluctuations in S/N ratio in the resulting amplified light are reduced.

Abstract: An integrated wavelength selectable photodiode includes a device package having an input that receives an optical signal. A set-and-hold, thermally tunable thin-film filter is positioned in the device package and includes an input that is optically coupled to the input of the device package. The set-and-hold, thermally tunable thin-film filter passes light with a predetermined optical bandwidth to an output. An optical element collimates an incident optical beam onto the input of the set-and-hold, thermally tunable thin-film filter. A detector is positioned in the device package and includes an input that is optically coupled to the output of the set-and-hold, thermally tunable thin-film filter. The detector detects data received by the integrated wavelength selectable photodiode.

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 transmission system including: first, second, and third stations; a main transmission path that bi-directionally couples the first station with the second station; and an optical add/drop multiplexer (OADM) disposed on the main transmission path, the OADM branching light from the first and second station, combining light from the third station to the main transmission path; wherein the OADM includes an input determination unit and an optical path switching unit, the input determination unit detects the power of the lights, and determines whether each of the input lights is lost or not, and the optical path switching unit forms a loop-back route based on the determination.

Abstract: The inventions relate to a method for operating a controllable selective optical add/drop channel for fiber-optic communication system provided with 2N of wavelength-division multiplexing channels, whose optical frequencies are retunable at a constant frequency separations ?v between adjacent channels, with the aid of the inventive controllable optical add/drop multiplexers (70, 80, 90) that comprise multi-stage structures of optical filters ({75-i}, {85-i}, {95-i}), that are connected in different manner and provided with devices, for example electro-optical and thermo-optical phase shift devices, for controllable tuning the transmissions characteristics thereof. The optical filters are embodied in the form of single-stage (20), two-stage (40) and/or multi-stage (60) asymmetric Mach-Zehnder interferometers. The controllable optical add/drop multiplexer can be produced according to integrated optic technique in the form of monolithic solid-state device.

Abstract: The invention facilitates optical signals generated from customer premise equipment (CPE) at the edges of the metro domain networks. The CPEs are connected to extension terminals that transform the optical signal originating at the CPE into a suitable format for long haul transmission. The optical signal then propagates to a primary terminal where the signal is multiplexed with other optical signals from other extension terminals. The multiplexed signals are then transmitted over LH or ULH network to a second primary terminal where the signal is then demultiplexed from other optical signals and transmited to the proper extension terminal. At the extension terminal, the demultiplexed optical signal is transformed from its LH format back into a format suitable for interconnection to a CPE. Using this architecture, the signal under goes optical-to-electrical conversion only at the extension terminals or end points. These end points can be located in lessee's facility.