Abstract: The present disclosure provides methods and systems for detecting small span loss changes in fiber optic networks. The present invention utilizes existing equipment without additional hardware to provide span loss measurements in a highly accurate manner. In an exemplary embodiment, the present invention utilizes power measurements associated with an optical supervisory channel (OSC) at both ends of a fiber span. These measurements are periodically sampled taking into account propagation delay along the fiber span. Further, these measurements are integrated or time-averaged to account for temporary fluctuations. The present invention can be utilized for intrusion detection (i.e., unwanted fiber taps), fiber degradation, and fiber aging performance. The present invention satisfies the criteria for a feasible (i.e., makes use of current architecture), cost-effective (i.e., does not require additional hardware), and highly accurate solution (i.e., capable of detecting span loss changes of 0.01 dB or 0.03%).

Abstract: Systems and methods are described for an optiplex. A method includes: conveying a first narrowcast signal to a first optical combiner; conveying a second narrowcast signal to a second optical combiner; tapping into said first narrowcast signal; monitoring a first characteristic of said first narrowcast signal; tapping into said second narrowcast signal; monitoring a second characteristic of said second narrowcast signal; combining a broadcast signal with the first narrowcast signal using the first optical combiner; and combining said broadcast signal with the second narrowcast signal using the second optical combiner.

Abstract: A method for monitoring wavelength-division multiplexed (WDM) signal for detecting signal drift of objective signals, including generation of one or more objective signals and a guard signal. The guard signal has a wavelength that is within a range defined by a guard channel. The first and second objective signals and the guard signal are wavelength-division multiplexed to generate a wavelength-division multiplexed signal. The first objective signal, the second objective signal, and the guard signal are assigned to a first multiplexed objective channel, a second multiplexed objective channel, and a multiplexed guard channel, respectively. The wavelength-division multiplexed signal is received by a monitor and then the error rate of the multiplexed guard channel is determined.

Abstract: An optical network device of a passive optical network is introduced. The optical network device includes a light source, a control unit, and a variable optical attenuator. The light source can generate an optical signal. The control unit can generate a magnetic signal based on a control signal capable of providing information relating to a distance between the optical network device and an optical line termination. The variable optical attenuator can adjust a polarization angle of the optical signal based on the magnetic signal.

Abstract: A disclosed optical add/drop multiplexing device demultiplexes a first signal into multiple signals according to wavelengths, drops one or more of the demultiplexed signals to a transponder, adds one or more signals output from the transponder, multiplexes these signals into a second signal, and outputs it. The device includes an injecting unit for injecting one of measurement signals, each of whose wavelength corresponds to that of a different demultiplexed signal, into a core of a multicore cable within the device, the core being used to transmit the different demultiplexed signal having the corresponding wavelength; a preventing unit for preventing the one measurement signal from emanating; a measuring unit for measuring, for each wavelength, levels of the one measurement signal before and after the corresponding core; a calculating unit for calculating loss of the corresponding core, based on the measured levels; and an informing unit for reporting the calculated loss.

Abstract: An electroabsorption optical modulator used as a sampling element has two optical terminals and a power supply terminal, the two optical terminals are used to input and output light, and the power supply terminal imparts an electric field to an optical path connecting the two optical terminals. The electroabsorption optical modulator has a characteristic in which an absorption index is changed with respect to the light beam propagating through the optical path according to a level of the electric field. A monitoring (synchronization sampling) object optical signal is input into one of the two optical terminals of the electroabsorption optical modulator. A predetermined direct-current voltage exhibiting a high absorption index for the monitoring (synchronization sampling) object optical signal is imparted to the power supply terminal of the electroabsorption optical modulator.

Abstract: An optical communication system comprising a transmitter including a data register having a plurality of outputs, each output comprising a separate data channel, a plurality of signal processors, each signal processor corresponding to a data, a plurality of laser modules, each laser module coupled to an output of a corresponding signal processor, wherein each laser module modulates the modified signal from its corresponding data channel onto an optical carrier having a selected wavelength, and an optical multiplexer coupled to an output of all the laser modules.

Abstract: An economical optical network is constituted by effectively using network resources by using the minimum number of, or minimum capacity of 3R repeaters. 3R section information corresponding to topology information on the optical network to which an optical node device itself belongs is stored, and the 3R section information stored is referred so as to autonomously determine whether or not the optical node device itself is an optical node device for implementing the 3R relay when setting an optical path passing through the optical node device itself. Alternatively, when the optical node device itself is a source node, another optical node device for implementing the 3R relay among the other optical node devices through which the optical path from the optical node device itself to the destination node passes is identified, and this identified optical node device is requested to implement the 3R relay when setting an optical path in which the optical node device itself is a source node.

Abstract: A transponder having a dynamic remapping circuit remaps a value of decision threshold voltage Vdtc and a value of optical power RXP to a reference voltage Vref to minimize the bit error rate BER of a communication system. The dynamic remapping circuit implements a bilinear mapping of Vdtc and RXP to Vref with three bilinear remapping constants “a”, “b”, and “c” selected to align a remapped value of Vdtc_opt to a selected Vdtc normalization value, Vdtc_norm. A transponder in accord with an embodiment of the invention prevents BER from exceeding a threshold value of BER whether RXP or OSNR, or both, remain constant, change continuously, or change intermittently. Constants “a”, “b”, and “c” are related to parameters resulting from mathematically fitting a line to data comprising Vdtc_opt versus RXP. Another embodiment comprises a method for dynamically optimizing Vdtc and RXP to Vref in a transponder with a bilinear remapping circuit.

Abstract: According to an aspect of an embodiment, a signal detector device includes a first monitor unit, a second monitor unit, and a discrimination unit, wherein the discriminator unit discriminates whether an inputted light includes a signal light on the bases of the first monitor unit for monitoring an intensity of the inputted light and the second monitor unit for monitoring an alternating current component intensity of the inputted light.

Abstract: A WDM signal monitoring system includes a measuring unit that measures power levels in a plurality of predetermined wavelength bands about a wavelength division multiplex signal, a waveform determination unit that determines an approximate waveform of each channel from each bit rate and modulation system of a plurality of channels which forms a wavelength division multiplex signal, and an approximation unit that determines a power level and a wavelength of each channel by approximating the power level in a plurality of wavelength bands which the measuring unit measured with the approximate waveform of each channel which the waveform determination unit determined.

Abstract: An optical signal monitoring system includes a bit rate information collecting unit and a monitoring unit. The bit rate information collecting unit gets bit rate information indicating a bit rate of an optical signal passing through an optical communication path. The monitoring unit extracts a monitoring optical signal from the optical communication path. When the bit rate information is not able to get, the monitoring optical signal is judged to be a noise. This system can make a sharp distinction between a broad optical signal whose bit rate is over 40 Gbit/sec and the ASE noise. Further, this system can correct optical signals dependently to those bit rates.

Abstract: According to an aspect of an embodiment, an apparatus comprises: a correction level calculating unit that calculates a correction level, which is the input light level necessary to meet an optical signal-to-noise ratio at the maximum level of an optical noise signal; a loss-of-light detection threshold-value setting unit that compares the correction level with an initial threshold value to set a loss-of-light detection threshold value used in detection of any loss of light on the basis of the comparison result; and a loss-of-light detecting unit that compares the level of an input optical signal with the loss-of-light detection threshold value to determine that any loss of light is caused if the level of the input optical signal is lower than the loss-of-light detection threshold value.

Abstract: An algorithm is disclosed for performing alien-wavelength channel balancing on channels between optical network elements within an optic-fiber communications system. The algorithm determines initial values of various optimization parameters for each of the channels, such as the input launch power and operating conditions of optical amplifiers in the optical path, and calculates an initial total optimization offset for the channels based on the initial values of the optimization parameters for each of the channels. The algorithm then adjusts the optimization parameters to new values and calculates a new total optimization offset based on the new optimization parameter values. The algorithm repeats this process until the relative channel launch powers and optical amplifiers are optimized.

Abstract: The subject matter disclosed herein relates to determining a photosensor operating point.

Abstract: An optical transceiver stores an output A/D value which is A/D-converted from reference voltage in an EEPROM as correction data in preparing the optical transceiver. The optical transceiver, receiving a request for outputting a monitored value from an external device connected therewith, calculates a variation based on difference between the output A/D value which is A/D-converted from the reference voltage at the timing when the request for outputting the monitored value is received and the correction data stored in the EEPROM. Then, the optical transceiver uses the calculated variation to convert current of light-input power which is input thereinto into voltage, amplify the voltage, and A/D-convert the voltage to thereby correct the output A/D value. The optical transceiver outputs the corrected A/D value to the connected external device as the monitored value.

Abstract: A sampling optical pulse generation unit emits a sampling optical pulse. The sampling optical pulse has a period different from a predetermined offset time to integral multiplication of a clock period of a data signal, and the data signal modulates an optical signal of a monitoring target. An optical sampling unit performs sampling of the optical signal of the monitoring target using an electroabsorption optical modulator. The electroabsorption optical modulator has a characteristic in which an absorption index is changed with respect to light propagating through an optical path according to a level of an electric field. The optical signal of the monitoring target is input into one of two optical terminals of the electroabsorption optical modulator. The sampling optical pulse is input into another of the two optical terminals through a photocoupler.

Abstract: A method for laser safety protection in an optical communication system includes: a downstream station detecting whether an identification signal loaded by an upstream station on a main optical channel in a direction from the upstream station to the downstream station, exist on the main optical channel; if the identification signal is not detected, the downstream station executing a scheduled safety protection procedure. Methods for loading an identification signal on a main optical channel in an optical communication system and an optical amplifier of laser safety protection, which implement loading the identification signal by controlling the change of pump light of optical amplifier or the wave motion of signal light of main optical channel, are also provided. The solution makes it possible to reliably detect a fiber failure when RAMAN amplifiers or remotely-pumped amplifiers exist, thereby implementing laser safety protection.

Abstract: The invention relates to a data transmission unit for high bit-rate optical data signals, in particular, high bit-rate optical data signals with a backplane, which has a line structure connecting several plug-in positions for several receiver or transceiver cards to each other and/or to one or more additional data processing cards, with the cards, each held in one of the plug-in positions and each having at least one input port for a high bit-rate data signal. Each card also has at least one output port, to which the relevant one or more high bit-rate data signals can be fed, and each of these output ports is connected via a serial data line between the plug-in position holding the relevant receiver or transceiver card and an input port of a central selection unit with the relevant input port. The output ports connect serially to the central selection unit.

Abstract: Optical autodiscovery is provide between two optical modules to insure that when an optical signal is coupled between the two optical module, the optical signal from a first module does not interfere with operation of a second module. The autodiscovery is implemented by sending an optical identification signal from the first optical module via the coupling to the second optical module from which signal, the second optical module can verify and determined acceptance of the coupled first optical module. During this autodiscovery process, the optical identification signal from the first optical module may be attenuated or shifted in optical spectrum so as not to interfere with the operation of the second optical module. Autodiscovery may also be employed in cases where a first optical module is to receive an optical signal from a second module.

Abstract: A method and system for enabling lightpath monitoring in an optical network is disclosed. A single polarization modulator/scrambler introduces a pilot tone signal as an overlay on a plurality of optical signals on a source node and a performance monitoring unit detects the pilot tone signal to enable light path monitoring and identification through the optical network.

Abstract: A robust and redundant status link is established by a first multi-channel optoelectronic device with a second multi-channel optoelectronic device in a multi-channel communication link. Transmitter bias currents are effectively modulated with a status link modulation signal representative of status data and subsequently modulated with primary data modulation signals. The resulting signals are transformed into optical signals and transmitted over the link as main communication links combined with a status link. At the second device, the optical signals are received and converted to electrical signals. The receipt of the optical signals creates multiple receiver bias currents, which may be monitored to detect the status link modulation signal. The second device may adjust various operating parameters in response to the information conveyed by the status link.

Abstract: The present invention relates to a system for sensing of a disturbance on an optical link. Data traffic from an optical source with a short coherence length is transmitted along the link to a receiver station on one or more of a plurality of time-division-multiplexed channels. One of the channels is used to transmit encoded phase information relating to the phase characteristics of the optical source output. At the receiver station, the actual phase characteristics of the arriving light from the optical source is compared with the encoded phase information. Since a physical disturbance of the link is likely to alter the actual phase characteristics of the arriving light but not the encoded phase information, it is possible to determine if a physical disturbance has occurred. The system can conveniently be used to monitor an optical link carrying communications traffic.

Abstract: The present invention relates to controlling wavelength switching in a plurality of nodes that are provided to increase the distance of signal transmission in inverse MUX transmission in which a high-speed line is divided into a plurality of low-speed lines for transmission. A maximum skew occurring between adjacent nodes is measured, and switching of wavelength channels is performed in one or a plurality of nodes on the basis of the measured maximum skew to keep the skew of the entire inverse MUX transmission system at or below a prescribed value. The optical communication device is provided with an NNI functional block to which high-speed lines on the transmission channel side are connected, and a UNI functional block to which low-speed lines on the client side are connected.

Abstract: The specification describes optical performance monitors which are simplified by coupling single tunable optical filters to multiple channels being monitored. Optical measurements for more than one channel may be made simultaneously. The optical system architecture is preferably an optical performance monitor for a WDM system. In a system designed according to the invention n channels may be monitored using n photodetectors, n optical splitters, but only n/2 tunable optical filters. Additional system simplification may be obtained using optical switching elements coupled to the optical splitters.

Abstract: An object of the present invention is to continue to send and receive to/from a host when a failure has occurred in a storage device interface. A storage system includes a host and a storage device connected to the host via a communication line, wherein the storage device comprises a communication controller performing data communication with the host by using optical modules, and wherein the communication controller is provided with first optical modules performing data communication with the host; a second optical module performing data communication with the host, in place of a first optical module; and a controller switching, when a failure has occurred in any of the first optical modules, the first optical module in which the failure has occurred to the second optical module.

Abstract: An optical signal monitoring apparatus includes an optical interference unit, a sampling optical pulse generation unit, an optical sampling unit, a photoelectric converter, and a computation unit. The optical interference unit includes an optical brancher, a delay device, an optical phase adjuster, and an optical multiplexer. The optical brancher branches a monitoring object signal optical signal phase-modulated at a predetermined symbol rate into two optical paths. The delay device imparts delay corresponding to an integral multiple of one symbol to an optical signal branched in one optical path of the two optical paths. The optical phase adjuster brings an optical signal emitted delay device and an optical signal branched in another optical path of the two optical paths into a predetermined optical phase difference.

Abstract: A method and apparatus for distributed measurement of chromatic dispersion in an optical network is disclosed. The network comprises optical switching nodes interconnected by optical links. An optical link may comprise multiple spans, each span ending in a transport module which comprises signal-processing components. At least one optical switching node has a probing signal generator transmitting an optical probing signal along a selected path in the network. Probing-signal detectors placed at selected transport modules determine chromatic-dispersion values and send results to a processing unit which determines appropriate placement of compensators or appropriate adjustments of compensators placed along the path. A preferred probing signal has the form of wavelength modulated optical carrier which is further intensity modulated by a periodic, preferably sinusoidal, probing tone.

Abstract: Some optical communications networks include one ingress fiber, an n-way signal coupler, and n egress fibers, where each fiber may carry signals in one or both directions. A method and apparatus for testing and monitoring data communications immediately before and after the coupler is provided. Benefits include improved ability to identify and locate system faults, and improved ability to monitor data quality and content.

Abstract: Safety and power control arrangement and method for optical communication apparatus, where a first circuit pack emitting an optical signal (OS1) and at least a second and a third circuit pack (2, 3) are connected in series via optical fibers (4, 5). A power monitor (26) connected to an output (27) of the at least second circuit pack (2) reduces the signal power (PW2) output from the second circuit pack (2) to a pre-determined safe value if a loss-of signal monitor (34) of a next circuit pack (3) forwards a loss-of-signal control signal (LOC3). The advantage is that the maximum allowable value is achieved at the input of an interrupted fiber section and the non-interrupted circuits can still receive the optical signals with a reasonable power level.

Abstract: Various high loss loop back (HLLB) repeater architectures are disclosed that enable selectively monitoring (e.g., measuring, analyzing, etc) of Rayleigh signals from both inbound and outbound directions of an optical communication system. In one such embodiment, first and second optical test signal frequencies (or ranges) are used, in conjunction with selective filtering, for monitoring the outbound and inbound paths, respectively. The repeater architectures allow optical time domain reflectometry (OTDR) monitoring techniques to be employed, for example, in particularly long repeater spans, such as those in excess of 90 km in length.

Abstract: There is provided a shutdown controller that monitors the temperature of an optical multiplexer and maximizes the loss of an optical attenuator when a temperature monitor result is abnormal. An optical level change detection circuit section is disposed with respect to an optical level monitor of individual monitors in an optical add/drop multiplexer. An optical level monitor of a total main signal is disposed downstream of the optical multiplexer. The inconsistency of the wavelength number is detected by comparing the total of the optical level monitors of the individual channels with the optical level value of the optical level monitor, upon which shutdown control is performed in which the loss of the optical attenuator is maximized in only the channel whose optical level change is detected by the optical level change detection circuit section.

Abstract: A system and method is disclosed that allows real-time processing of child OPOI and rider service alarms from a parent OPOI which determines if one or more STS alarms are associated with a rider service, a child OPOI, or a parent OPOI. The system and method performs in real-time processing intervals required for alarm surveillance in a telecommunications network.

Abstract: An economical optical network is constituted by effectively using network resources by using the minimum number of, or minimum capacity of 3R repeaters. 3R section information corresponding to topology information on the optical network to which an optical node device itself belongs is stored, and the 3R section information stored is referred so as to autonomously determine whether or not the optical node device itself is an optical node device for implementing the 3R relay when setting an optical path passing through the optical node device itself. Alternatively, when the optical node device itself is a source node, another optical node device for implementing the 3R relay among the other optical node devices through which the optical path from the optical node device itself to the destination node passes is identified, and this identified optical node device is requested to implement the 3R relay when setting an optical path in which the optical node device itself is a source node.

Abstract: A method for processing overheads in an optical communication system and a signal processing device are disclosed. The method includes: in a receiving direction, conduct an O/E and S/P conversion for the received optical signal, extract overheads necessary for overheads processing; transmit the overheads in serial; conduct an S/P conversion of the overheads, add fixed reserved overheads, and revert the parallel overheads for overheads processing; in a transmitting direction, generate parallel overheads, extract overheads necessary for overheads processing; transmit the overheads in serial; conduct an S/P conversion of the overheads, revert the overheads, synthesize the overheads with the payload data before the P/S and E/O conversion, and generate and transmit the optical signal. In accordance with the disclosed method and device, a serial bus is employed to transmit overheads, which reduces the number of buses on the motherboard and lowers the complexity of system design.

Abstract: A method for preventing a temporary traffic interruption between two client ports and the consequent state transition of the receiving port in a communication network providing for the transmission of a data stream between two clients along at least one path when a fault condition is detected in the path. The method includes the steps of monitoring the data stream directed to the receiver and, upon detecting in the data stream an error sequence capable of starting the state transition, replacing the data stream with a filling data stream to prevent the receiver from detecting an error condition, and resuming the forwarding of the received data stream after a predetermined time interval. An apparatus able to mask to the receiver for the predetermined time interval, a storage area network and a computer program product are also disclosed.

Abstract: A method and a device for monitoring a cable system in the field of communications are provided. An optical signal emitted by an optical source to a transmission link of the cable system is divided into two paths of optical signals, in which one path of optical signals serve as local coherent light, and the other path of optical signals are transformed by multipath frequency shift to multiple paths of detection optical signals of different frequencies. A monitoring result is obtained by performing coherent detection, with the local coherent light, on the returned optical signals of the multiple paths of detection optical signals of different frequencies. The device includes an optical source, a multipath frequency shift module, and a coherency module.

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: Portable apparatus for measuring parameters of optical signals propagating concurrently in opposite directions in an optical transmission path between two elements, at least one of the elements being operative to transmit a first optical signal (S1) only if it continues to receive a second optical signal (S2) from the other (10) of said elements, comprises first and second connectors for connecting the apparatus into the optical transmission path in series therewith, and a device connected between the first and second connectors for propagating at least the second optical signal (S2) towards the one of the elements, and measuring the parameters of the concurrently propagating optical signals (S1, S2). The measurement results may be displayed by a suitable display unit. Where one element transmits signals at two different wavelengths, the apparatus may separate parts of the corresponding optical signal portion according to wavelength and process them separately.

Abstract: An optical signal detector is provided that detects an optical signal from an optical source using a plurality of optical sensors having different wavelength selectivities, thereby determining the peak wavelength of the optical signal and measuring the power of an optical signal corresponding to the peak wavelength. According to the optical signal detector, separate optical filters are not required and space and costs attributable to the installation of the optical filters can be saved, and thus there are effects in that the overall size and manufacturing costs of the device can be reduced.

Abstract: An optical control plane (OCP) distinct from an electronic control plane helps the setup of path routes in a DWDM network. The OCP determines the optical feasibility of any path route selected by the electronic control plane, such as operated under GMPLS protocol, and asks the electronic control plane for another path route if the optical feasibility is determined to be negative. The OCP can be set in a server or distributed across the nodes of the network.

Abstract: Embodiments of the present invention provide an optical port that can be configured to support either high speed or low speed optical signals. In particular, these embodiments comprise a switch that defines a data-rate dependent path between the front-end optics of a network node and internal processing electronic modules. As a result, either high speed or low speed pluggable adapters may be inserted within a port and supported by the processing electronic modules.

Abstract: A flexible open ring optical network includes a plurality of nodes connected by twin or other suitable optical rings. Each node is operable to passively add and passively drop traffic from the rings. The nodes may include a transport element for each ring. The transport elements include an optical splitter element and an optical combiner element. The optical splitter element is operable to passively combine an add signal including local add traffic and a first transport signal including ingress traffic from a coupled optical ring to generate a second transport signal including egress traffic for transmission on the coupled optical ring. The optical combiner element is coupled to the optical splitter element and is operable to passively split a third transport signal including the ingress traffic to generate a drop signal including local drop traffic and a fourth transport signal including the ingress traffic.

Abstract: Transmitting power and data to electronic components using a single optical fiber includes receiving a light power signal via the single fiber optic, converting the power light signal to electrical energy, at least a portion of which may be stored in an energy storage element, and, in response to a pause in the received light power signal, transmitting a light data signal via the single optical fiber, where power used in connection with data transmission is provided by electrical energy stored in the energy storage element. A photovoltaic element may be used to convert the light power signal into electrical energy. The photovoltaic element may be an array of photodiodes or a single photodiode. The energy storage element may be a capacitor. Transmitting a light data signal may be provided by a communication light source.

Abstract: A method and apparatus for controlling the power level of an optical signal includes detecting the loss of a supervisory signal counter-propagating in an optical fiber.

Abstract: A flexible open ring optical network includes a plurality of nodes connected by twin or other suitable optical rings. Each node is operable to passively add and passively drop traffic from the rings. The nodes may include a transport element for each ring. The transport elements include an optical splitter element and an optical combiner element. The optical splitter element is operable to passively combine an add signal including local add traffic and a first transport signal including ingress traffic from a coupled optical ring to generate a second transport signal including egress traffic for transmission on the coupled optical ring. The optical combiner element is coupled to the optical splitter element and is operable to passively split a third transport signal including the ingress traffic to generate a drop signal including local drop traffic and a fourth transport signal including the ingress traffic.

Abstract: One embodiment sets forth a technique for measuring chromatic dispersion using reference signals within the operational range of amplifiers used to refresh data signals. One red/blue laser pair in the transmission node is used for measuring dispersion and chromatic dispersion compensation is added at each line node in the system. Since reference and data signals propagate through each amplifier, the reference signals used to measure chromatic dispersion receive the same dispersion compensation (and will have the same residual dispersion) as the data signals. Therefore, any residual dispersion in the data signals will manifest itself in downstream dispersion measurements and, thus, can be corrected. The tunable dispersion compensator in each line node may be set to compensate for the measured dispersion, thereby compensating for both the chromatic dispersion of the link connecting the current node to the prior node and any uncorrected residual dispersion from prior nodes.

Abstract: An evaluation method of an optical receiver of an optical communication system, including a DPSK (Differential Phase Shift Keying) signal modulated by a specific data series, a delay interferometer for performing delay detection on the DPSK signal, an optical receiver for receiving each of two optical outputs of the delay interferometer and outputting a difference signal, and a spectrum analyzer for measuring a spectrum of an output electrical signal of the optical receiver, comprising monitoring a specific frequency component of the spectrum analyzer and detecting a delay difference and a deviation in optical reception level between the two outputs of the delay interferometer and the optical receiver.

Abstract: The present invention provides a method for determining the bandwidths of optical fibers, wherein the method provides the coupling of light with a first optical power and a first modulation frequency into an optical fiber, as well as measuring a first signal level as a function of the optical power of the light of the first modulation frequency, coupling light with the second optical power and a second modulation frequency into the optical fiber, measuring a second signal level as a function of the optical power of the light of the second modulation frequency, and determining the bandwidths of the optical fibers as a function of the first and second coupled optical [power and/or] the measured first and second signal levels while using a predetermined specification that describes the frequency-dependent attenuation response of the optical fiber, wherein the first and the second modulation frequencies have essentially the same value.

Abstract: Systems and methods for monitoring a data transmission link, especially an optical, bidirectional data transmission link, in which a digital transmit signal is transmitted on a first transmission path from a local end of the data transmission link toward a remote end of the data transmission link. A portion of the power of the transmit signal sent at the local end is transmitted, delayed by a non-zero delay time on a second transmission path as a control signal toward the remote end of the data transmission link. Both signals are received at the remote end and are tested for the presence of events of a predetermined type. A conclusion can be reached on the quality of the transmission link as a function of a time correlation and frequency of the appearance of events in the received transmit signal and in the received control signal.