Abstract: A test has been developed that is known as the transmitter waveform dispersion penalty (TWDP) test. The TWDP test has been used to test and certify various optical data transmission devices. Similar tests are being developed to test optical receivers such as a difference waveform distortion penalty (dWDP). A test pattern used to generate the transmitted sequence by the device under test is a PRBS9. The PRBS9 test pattern begins with a run of nine ones and has a length of 511 bits. According to the teachings herein, a test pattern of less than 511 bits is generated to perform the TWDP and dWDP tests. The test pattern may include a sequence of bits specifically designed to provide reliable test penalty calculation without the costly and time consuming aspects of the conventional TWDP and dWDP tests using the PRBS9 pattern.

Abstract: The invention relates to a method for easily and rapidly preemphasizing an optical multiplex signal transmitted by an emitter to a receiver consisting wherein signal-to-noise ratios are equalized by means of simple measurement or new adjustment of signal power on the bandwidth of the optical multiplex signal, at least in the receiver, instead of measuring the noise output power or the signal-to-noise ratio. Said invention is based on a balance of the signal-to-noise ratios which are authorized by a transmitting system, in which the spectral influences of gain profiles, noise effects and dampings are taken into consideration. In particular, when DWDM transmission techniques are applied, in which adjacent channel spacings of the optical multiplex signal are very low, the inventive method makes it possible to use a small number of sensitive and high-resolution measuring instruments for pre-emphasis control.

Abstract: In an optical communication-use receiving circuit of the present invention, the pulse width of the received pulse which is a binary signal corresponding to the signal optical pulse is specified by using an integration circuit and a trigger generating circuit. If the pulse width of the received pulse is not shorter than a predetermined value, a signal having a fixed pulse width is outputted as an output signal from a one-shot pulse generating circuit, so that a pulse having a constant pulse width corresponding to the specified communication speed is outputted. Accordingly, if the pulse width deriving from the signal optical pulse is larger than a certain value, the communication is deemed as a low-speed communication, and a pulse having a constant pulse width corresponding to the communication speed is outputted. As a result, it is possible to realize a small-size receiving circuit and a small-size electronic device which require no external switching-over terminal.

Abstract: An arrangement has a WDT (Wavelength-Dependent Tap) coupled in an OCS (Optical Communication System) and an OPM (Optical Performance Monitoring) function coupled to the WDT. The WDT is adapted to receive from the OCS an input optical signal having noise and channels at respective channel wavelengths. The WDT couples to an output some of the input optical signal at the channel wavelengths and most of a noise power at wavelengths between the channel wavelengths, and couples a remaining portion of the input optical signal back into the optical communication system. The optical performance monitoring function determines a power characteristic of the input optical signal as a function of a power from the output. The power characteristic may be an OSNR (Optical Signal-to-Noise Ratio) determined as a function of a signal power and a noise power of the output optical signal.

Abstract: An optical access network system having a function of correcting upstream signal waveform distortions occurring in the PON section, wherein a central office side apparatus comprises a main controller to notify each subscriber connection apparatus of a transmission grant period, an equalizer of a tap gain adaptive control type to correct waveform distortions of signals received from the subscriber connection apparatuses, an equalizer controller, and a parameter table for storing, for each subscriber connection apparatus, the initial values of tap gains to be set for the equalizer. The main controller issues a switchover request for switching the equalization characteristic to the equalizer controller each time notifying a subscriber connection apparatus of a transmission grant period, and the equalizer controller retrieves the initial values of the tap gains for the subscriber connection apparatus from the parameter table in response to the switchover request, and sets these values to the equalizer.

Abstract: Span information (information about conditions of a path between a node of interest and another, adjacent node connected thereto) retained in respective nodes is cumulatively transmitted from a add-drop node, which is to become a starting-point node of a certain wavelength path, toward a add-drop node, which is to become an end-point node of the wavelength path. The end-point node autonomously determines a path satisfying predetermined transmission conditions as an optimal pathway of said wavelength path, on the basis of cumulative span information transmitted over the respective plural pathways from the starting-point node to the node of interest. As a result, a load imposed on line design to be performed by a client can be mitigated, and an optimization design for each path (wavelength) matching a mesh-type optical network can be performed.

Abstract: A method of assessing the feasibility of a composite optical path in an optical communications network in which the composite path is composed of two optical paths k1 and k2 is described. The method comprising the steps of: defining, for each individual optical path k and with type i interface, at least one parameter indicating its feasibility, calculating a quality Q factor Q?_i,k1+k2 of the signal for the composite path, estimated considering the deterioration which affects transmission over the paths k1 and k2 and comparing this quality Q?_i,k1+k2 with a value Qbare_i which is defined as the lowest value which can be taken on by a mapping function Q_i(.) for interface i and which gives the Q factor as a function of the OSNR received evaluated under the conditions that are considered to be the worst case that can be accepted whilst ensuring the desired signal quality and wherein the composite connection is considered feasible if Q?_i,k1+k2>=Qbare_i.

Abstract: Optical signal-to-noise ratio (OSNR) monitoring methods and apparatus are described. A tunable optical filter filters an optical channel containing an optical signal and noise. The total signal and noise power at the output of the filter is measured as the transmittance passband of the filter is varied and the maximum and minimum powers are determined. The ratio between the maximum and minimum powers is then used to determine the OSNR of the optical channel, which, for example, can be a wavelength channel in a wavelength division multiplexing (WDM) system. The ratio of the maximum signal power to the minimum signal power and the ratio of the maximum noise power to the minimum noise power are pre-determined based on the signal modulation format type and filter passband characteristics.

Abstract: A wavelength converter for binary optical signals includes an interferometer structure (110) for generating an output signal by modulating a received local signal (LS) according to the modulation of a fUrther received first input signal (IS 1). When such interferometer structures (110) are operated in a standard mode it is known in the art to control the power of the input signal such that the extinction ratio of the output signal is kept minimal. The invention also controls the power of the input signals to achieve the minimal extinction ratio when the wavelength converter and in particular the interferometer structure (110) is operated in a differential mode receiving two input signals.

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 network terminal, which includes an optical transmitter, monitors the status of the optical transmitter, such as the output or the power consumption of the optical transmitter, to determine when the optical transmitter is illegally transmitting. When an illegal transmission is detected, the optical network terminal removes power from the optical transmitter.

Abstract: A method and device for determining in-band noise of an optical signal. The optical signal is split to produce two optical signal components, of distinct polarisation, such that the respective noise component in each signal component is uncorrelated. The optical signal components are converted to the electrical domain to produce electrical signal components. The signal component powers are equalised either in the optical domain or the electrical domain. The equalised electrical signal components are then subtracted together to cancel the correlated portions of the signal components (e.g. the data signal), such that only uncorrelated signal components (e.g. noise) are output for measurement.

Abstract: A system and method for detecting digital symbols carried in a received optical signal. The system comprises a functional element operative to receive a stream of samples of an electrical signal derived from the received optical signal and to evaluate a non-linear function of each received sample, thereby to produce a stream of processed samples. The system also comprises a detector operative to render decisions about individual symbols present in the received optical signal on the basis of the stream of processed samples. In an embodiment, the non-linear function computes substantially the square root of each received sample.

Abstract: An optical receiver having compensation for signal level transients. The receiver includes an OE converter, a transient threshold compensator, a threshold combiner and a CDR system. The OE converter receives the incoming optical signal and provides a modulated electrical signal having a high speed response for tracking the modulation on the optical signal and an averaged electrical signal having a moderate speed response for tracking changes in the average level of the optical signal. The transient threshold compensator processes the averaged electrical signal for providing a transient feedforward adjustment. The threshold combiner combines the transient feedforward adjustment with a lower speed BER feedback threshold adjustment for providing a decision threshold signal. The CDR system uses the decision threshold signal for recovering a clock, providing the BER feedback threshold adjustment, and estimating the data carried by the modulation.

Abstract: An optical receiver circuit is constructed to be immune to interference from external interference signals. The optical receiver circuit includes a differential amplifier having an optical reception device connected to one input of the differential amplifier. The optical receiver circuit also includes an electrical element for simulating the electrical behavior of the reception device in the illumination-free state. The electrical element is connected to the other input of the differential amplifier.

Abstract: A cable modem termination system is disclosed with flexible mapping of upstreams to downstreams and flexible mapping of downstreams to optical nodes and optical nodes to upstream receivers and the ability to add singe upstreams or downstreams as needed for load balancing. Multiple downstreams can share the same upstream. Multiple receivers can be coupled to the same upstream. Monitoring of upstream performance for overperforming or underperforming modems can be carried out, and new upstreams with higher and/or lower throughtput can be created to service the overperformers and/or underperformers. Modems can be grouped into logical groups with different performance levels and serviced by different upstreams or different upstream logical channels on the same upstream physical channel. An upstream linecard with a digital crosspoint switch is disclosed with the switch operated during contention intervals to allow reception with or without aggregation of noise where multiple upstream share the same receiver.

Abstract: A transmission apparatus that receives an optical signal by selecting any one of a plurality of provided optical signal transmission paths through protection control is configured to include a plurality of optical signal outputting sections that output the optical signals transmitted through said optical signal transmission paths respectively as optical signals having wavelengths that are different from each other, a wavelength selective optical switch capable of selectively outputting light of a wavelength corresponding to any one of the optical signals coming from the optical signal outputting sections on the basis of the frequency of a controlling frequency signal, and an optical switch controlling section that supplies said controlling frequency signal to the wavelength selective optical switch so as to output the optical signal coming from the optical signal transmission path side that is selected by said protection control among the optical signals coming from the optical signal outputting sections.

Abstract: An apparatus and a method for monitoring optical signal-to-noise ratio are provided. It can be applied in dense wavelength-division multiplexed networks to monitor the transmission quality of each optical channel. The apparatus comprises an optical circulator, a tunable optical filter, a dithering signal, a dithered reflector, and two photodiodes. It can be integrated on a single chip. The invention utilizes the dithering and reflection functions of the dithered reflector, and passes the signal and the noise through the tunable optical filter once and twice, respectively. When the tunable optical filter is scanning and filtering the whole spectrum, the signal and noise powers are measured by the two photodiodes, respectively. The OSNR for each optical channel is then calculated according to the signal and noise powers. It can monitor channel location, wavelength drift, and OSNR by including a wavelength locker to act as an optical channel analyzer.

Abstract: A method and apparatus is disclosed for measurement and monitoring of in-band optical signal to noise ratio (OSNR). A two channel optical spectrum analyzer (OSA) is advantageously applied in acquiring wavelength division multiplex (WDM) signal data after it has been split according to polarization, then deriving the in-band OSNR from acquired data due to its narrow bandwidth, selective spectral shape, and capability to analyze two components of a polarized signal simultaneously. The in-band OSNR can be measured without interrupting optical transmission traffic in the network.

Abstract: The invention discloses a digital adjusting method for an optical receiver module, and the method implements real-time monitor of parameters, on-line adjustment and non-linear compensation. The digital optical receiver module includes elements as follow: a voltage output circuit of optical power detection 24, a DC/DC voltage boost circuit 22 and a bias voltage adjusting unit which is consisted of an optical-electronic conversion circuit 21; a digital adjusting unit 25, an analog-digital converter (A/D converter) 26 and a memory 27. The digital adjusting unit 25 makes on-line adjustment and implements temperature compensation and dark current compensation of the optical receiver module. The A/D converter 26 monitors the optical power, the working temperature and the bias voltage of the optical detector in real time. The memory 27 stores parameters of the optical receiver module for comparison with a detected optical power and measured temperature etc. and for on-line interrogation.

Abstract: A dispersion compensator is provided that includes an input port 102 for receiving a WDM optical signal and a dispersion compensating element 110 coupled to the input port for substantially compensating the WDM optical signal for dispersion that has accumulated along an external transmission path. The dispersion compensator also includes an output port 104 for directing the dispersion compensated WDM optical signal to an external element and a dynamic power controller 106, 108, 112, 114, 116 for maintaining a total power of the WDM signal below a prescribed level prior to receipt of the WDM optical signal by the dispersion compensating element.

Abstract: In an optical signal monitoring method in wavelength multiplexing and an optical network, an area corresponding to a characteristic pattern of an eye pattern of an optical signal to be monitored, which characterizes a deterioration, is extracted from a database storing a map which associates a quality deterioration factor and deterioration amount of the optical signal with the characteristic pattern of the area of the eye pattern of the optical signal. The extracted pattern is collated with the map stored in the database to monitor the quality deterioration factor and deterioration amount of the optical signal, an occurrence time of a deterioration, duration of a deterioration, a deterioration occurrence cycle, and a deterioration duration cycle. An optical signal monitoring apparatus is also disclosed.

Abstract: This invention concerns the field of telecommunication networks using optical fibres. The invention relates to a method of determining a connection path between two points in an optical network comprising several paths to connect said two points, each path comprising optical fibre spans and power amplifiers, said method comprising different steps depending on the degree of knowledge of network optical data. This data consists of the optical losses LI in optical fibre spans, the maximum allowable input power IP into said spans and the maximum output power PA from the amplifiers.

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: The present invention relates to a system for testing the connection paths of a switch fabric by using a spontaneously emitted signal as a test signal. The system includes at least one first module and at least one second module, wherein each one of the second modules is associated to one of the first modules through a connection path in the switch fabric. Each of the first modules is capable of obtaining a respective first measurement of a characteristic of the spontaneously emitted signal supplied to the switch fabric, and each of the second modules is capable of obtaining a respective second measurement of the characteristic of the spontaneously emitted signal. The system further includes a processing module in communication with each of the first and second modules for determining a feature of the optical component based on the first and second measurements.

Abstract: An optical performance monitor (OPM) adapted to (i) sample an autocorrelation function corresponding to an optical signal transmitted in an optical network and (ii) based on the sampling, characterize two or more impairments concurrently present in the optical signal. In one embodiment, the OPM has an optical autocorrelator (OAC) coupled to a signal processor (SP). The OAC receives the optical signal from the network, generates two or more samples of its autocorrelation function, and applies said samples to the SP. The SP processes the samples and generates two or more signal metrics. Based on the signal metrics and reference data corresponding to the impairments, the SP then obtains a measure of each of the impairments.

Abstract: An apparatus and method for simultaneous channel and optical signal-to-noise ratio (OSNR) monitoring is adapted to function in multi-channel wavelength-division-multiplexed (WDM) optical communication systems. A polarization controller is sequentially adjusted to perform the sequential polarization control with an optical signal. A polarization-selective electro-optic modulator acts as a polarizer and provides a signal dithering to improve the detection sensitivity. A beam splitter splits the dithered optical signal into two clusters. A photodetector receives the first cluster and measures the OSNR. An optical element receives the second cluster and monitors the channel wavelength of multiple channels. The apparatus can be packaged into a compact module and integrated on a chip. The channel monitoring covers a wide wavelength range and is tunable. The OSNR monitoring can be accurate over a wide dynamic range.

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: A method and system for handling information in a noisy environment in the form of at least one information carrying mode is disclosed. A plurality of encoded modes are generated by linear transformation of the information carrying mode, said encoded modes being provided on respective independent channels. The encoded modes are linearly combined to generate at least one decoded mode. A set of receiver channels is provided for receiving the decoded mode wherein one of said set of receiver channels is designated as a useful channel, and a useful signal is supplied as the decoded mode if it is received on the useful channel an discarded if it is received on the other receiver channels of the set, wherein the useful signal represents said information substantially uncorrupted by noise. The technique is applicable to quantum, classical or mesoscopic environments. The invention also provides a method and system for generating correlated states using a similar filtration technique.

Abstract: An apparatus for accelerating assessment of an optical transmission system using Bit Error Rate (BER) tests calculates Q-factors for at least two different extinction ratios from measured test BER values, and extrapolates to determine a Q-factor for an operational extinction ratio, whereby the operational BER value for the operational extinction ratio can be calculated.

Abstract: The present invention provides a fast testing system and method for optical transceiver, which integrates multiple testing machines in the testing environment for the optical transceiver, so that the user can employ the testing system for optical transceiver for rapid and simultaneous measurement of multiple products, and further improving the production efficiency. Moreover, with a combination of optical channel selector with a set of digital communication analyzer and spectrum analyzer, a plurality of products to be tested can be switched for parametric inspection, and by combining a tree coupler to synchronously transmit the measurement signals of the standard sample to the product to be tested in a multi-port transmission to further measure the bit error ratio. Thus, the product analysis report for the user is in real-time, so as to effectively improve the competitiveness of the industry.

Abstract: Disclosed is an apparatus for monitoring an optical signal-to-noise ratio in a WDM optical network. The apparatus includes an orthogonal polarization component module for receiving an optical signal and outputting it after removing a signal component thereof at a specific frequency band; and calculation means for measuring both average signal and noise component intensity of the optical signal outputted from the orthogonal polarization component module. By removing a signal component at a specific frequency bandwidth and passing only a noise component through, it is possible to easily measure the noise intensity within a signal bandwidth that cannot be measured in general. A frequency band is set within a signal bandwidth, and the signal intensity is minimized at the set frequency band, so that it is possible to measure the optical signal-to-noise ratio even for a signal whose amplified spontaneous emission noise spectrum is not flat, irrespective of the signal pattern length.

Abstract: In a receiver operable in response to a data signal, an eye aperture size is detected along a time axis by an eye aperture detection circuit and is controlled by a control circuit so that it becomes a maximum. The eye aperture detection circuit determines different decision time points of the same level arranged along a time axis and judges whether or not an error is caused to occur at each of the decision time points, so as to detect the eye aperture size and to produce detection results. The control circuit processes the detection results in accordance with a predetermined algorithm to successively vary the eye aperture size and to keep the data signal at an optimum amplitude.

Abstract: A device (D) is dedicated to controlling the power of optical signals in a transparent switching node of an optical communication network that switches bands of wavelengths. The device includes, firstly, a controller (12) for comparing input optical power measurements to a selected first threshold and generating instructions representative of the comparison result, secondly, a measuring device (10A) for delivering measurements representative of the input optical power of the optical signals at one output at least of the switch (4), and thirdly, a processor between the switch (4) and the multiplexer (6) of the node and which control the optical power of the signals coming from the switch (4) as a function of the instructions they receive, so that the optical power of the signals at the input of the multiplexer (6) is maintained substantially constant.

Abstract: Conventionally, an adjustment of an optical power level of an input Pin of an optical amplifier module is made with an optical variable attenuator. An optical coupler for measuring the optical power level of Pin and an optical variable attenuator are replaced by a variable optical coupler. The branch ratio of the variable optical coupler is varied, whereby the input optical power level Pin to an optical amplifier module is adjusted. As a result, an optical loss is reduced by an amount corresponding to the elimination of the optical attenuator, and also the OSNR of the optical amplifier module is improved.

Abstract: The present invention relates to a variable clamp equalization method and apparatus, the method includes measuring optical signal to noise ratio (OSNR) values for each wavelength, computing a raw power adjustment value for each wavelength, computing a raw power adjustment correction factor for each computed raw power adjustment value based on a computed OSNR range value in accordance with a pre-defined variable clamp value schedule, wherein a larger clamp is scheduled for use when the computed OSNR range value is larger, and a smaller clamp is scheduled for use when the computed OSNR range value is smaller. The method further includes determining a clamped power adjustment value for each wavelength, applying the corresponding determined clamped power adjustment value to each wavelength, and iterating the aforementioned until the computed OSNR range value is within pre-defined boundaries, whereby the signal is considered equalized.

Abstract: A high-sensitivity signal-to-noise ratio (SNR) determining apparatus measures the in-band SNR of an optical data signal by detecting and demodulating the optical signal and analyzing a narrow bandwidth of the resulting electrical data spectrum at half the data clock frequency, or more generally, a predetermined frequency equal to a multiple M of one-half the clock frequency, fclk/2, where M is an integer equal to or greater than one, may be used. When the optical signal is a WDM signal, a tunable filter isolates a single channel for detection. The detected electrical signal is subjected to both an in-phase and quadrature narrowband RF demodulation using a local oscillator at precisely half the clock frequency. Using this technique, the magnitude of the data portion of the optical signal becomes the in-phase component and the magnitude of the noise present in the optical signal becomes the quadrature component.

Abstract: Methods of determining the performance and the advanced failure of an optical communication channel. Performance of an optical communication channel may be determined by receiving light signals, generating a measure of an average received optical power in the received light signals and monitoring changes in the measure of the average received optical power. Advanced failure of an optical communication channel may be determined by transmitting a light signal at one end of the optical communication channel, propagating the light signal in an optical transmission medium, receiving the light signal at an opposite end of the optical communication channel, generating an electrical signal responsive to the receiving of the light signal. determining a measure of an average received optical power in the received light signal in response to the electrical signal, and monitoring changes in the measure of the average received optical power.

Abstract: A monitoring system includes first and second evaluation sections for obtaining an averaged Q-factor parameter and a waveform distortion parameter from an optical signal amplitude histogram collected from optical signals under measurement. The monitoring system further includes a third evaluation section for determining both averaged Q-factor parameter and waveform distortion parameter, and for making a decision as to whether the main factor of the optical signal quality degradation is waveform distortion or not by comparing the averaged Q-factor parameter and waveform distortion parameter with their initial values or initial characteristics which are obtained when no optical signal quality degradation is present.

Abstract: It is disclosed that a method and apparatus that automatically monitors each channel's optical signal-to-noise ration (OSNR) using optical filter and polarization extinction method in wavelength division multiplexing (WDM) scheme-based optical transmission systems. OSNR is simply measured using optical filter by comparing amplified spontaneous emission (ASE) over the signal band, of which bandwidth has changed, while leaving signal intensity intact, with that original signal and, OSNR measurement is allowable over a wider range of OSNR by minimizing the ratio of signal to ASE over the signal band using polarization extinction method.

Abstract: This invention provides a technique for realizing low-cost optical signal waveform monitoring with improved realtimeness to be applied to signal quality monitoring in an actual optical transmission system, and a technique for stably controlling an optical transmitter/receiver and various compensators by means of this waveform monitoring. Opening/closing of a optical gate is controlled by means of a clock signal synchronized with an optical signal input from a photocoupler and having a period equal to the bit interval of data or N (N: a positive integer) times longer than the bit interval to allow each pulse of the optical signal for one bit of data to pass through the optical gate for only part of the time width of the gate. A photoelectric conversion element to which the optical signal transmitted through the optical gate for only part of the time width obtains an average light intensity of the input optical signal. Information on this average light intensity is output to a monitoring output section.

Abstract: The present invention provides a method and an apparatus for monitoring optical signal to noise ratio (OSNR) in a wavelength division multiplexing optical transmission system. The present invention utilizes a polarization nulling method and a tunable optical bandpass filter in order to reliably monitor the OSNR by considering a finite polarization nulling ratio, polarization mode dispersion and non-linear birefringence of the optical system in real time measurement of the OSNR. Further, the tunable optical bandpass filter is controlled to filter all wavelength bands of wavelength division multiplexed signals. Since the invention may monitor a plurality of demultiplexed optical signals with a single apparatus, the overall cost of the OSNR monitoring equipment is significantly reduced.

Abstract: A system and method for improving the transmission quality of a WDM optical communications system begins by determining the bit-error rate for an optical channel before forward error correction is performed at a receiver. The pre-corrective bit-error rate is fed back through a feed back circuit that includes a parameter adjustment module which adjusts an optical signal parameter based on the bit-error rate. As examples, the signal parameter may be a channel power, dispersion, signal wavelength, the chirp or eye shape of an optical signal. The feedback circuit may also adjust various parameters within the WDM system, including amplifier gain, attenuation, and power for one or more channels in the system. By adjusting these parameters based on a pre-corrective bit-error rate, transmission quality is improved and costs are lowered through a reduction in hardware.

Abstract: In a method of analyzing an optical communications signal, a threshold is established under control of a processor, and a decision circuit compares the amplitude of the signal to the threshold. A counter samples the output of the decision circuit and counts, over many periods of the signal, those samples indicating that the amplitude of the signal is above the threshold. The threshold generating, comparing, and counting are repeated for several thresholds within a range corresponding to an expected amplitude range of the signal. The stored counts and thresholds represent an amplitude histogram N(VT) for the signal. The derivative dN/dVT of the function N(VT) represents the probability density function (PDF) for the signal amplitude and can be used to derive performance information such as bit error rate and optical signal-to-noise ratio (OSNR).

Abstract: A tunable dispersion compensator whose passband center wavelength changes when the amount of dispersion compensation is changed is suitably adjusted. The relationship between temperature for keeping the center wavelength constant and the amount of dispersion compensation is stored in advance. After controlling the amount of dispersion compensation to achieve best or optimum transmission quality, the amount of dispersion compensation is converted into temperature in accordance with the stored relationship and, based on that, the temperature is controlled to keep the center wavelength constant.

Abstract: The invention is aimed at providing a simple noise light elimination technique capable of eliminating noise light components contained in a signal light, together with wavelength components same as for the signal wavelength, with the condition of the light remaining as is, and an optical transmission system. To this end, an optical transmission system applied with a noise light elimination method according to the present invention comprises a high output type optical repeater and a noise light elimination unit for each required repeating span. This noise light elimination unit includes a dummy transmission path that, when a light of a power exceeding a threshold value is input, generates a return light due to stimulated Brillouin scattering (SBS). The signal light amplified in the optical repeater up to the power exceeding the threshold value is input to the dummy transmission path via an optical input/output section of the noise light elimination unit.

Abstract: A method and system for multi-level power management in an optical network is provided. They include three levels of power management. The first level of power management dynamically changes equipment settings in each module of equipment so that required module setpoint values in each module are achieved. The second level of power management determines module setpoint values for each module of equipment within each node in the optical link so that required node setpoint values are achieved. The third level of power management determines node setpoint values at each node in the optical link so that the optical link meets predetermined power specifications. If any of the three levels cannot achieve the required setpoint values, an error signal is generated by that level of power management and sent to the level of power management above it, thus initiating a higher level of power management.

Abstract: If a repeater supervisory control (SV), a pre-emphasis automatic adjustment (PE), a receiving side threshold value automatic adjustment (Vth), a transmitting side dispersion compensation value setting (VDC(T)), and a receiving side dispersion compensation value setting (VDC(R)) are executed for an optical main signal, these controls are executed in the above described priority order. Accordingly, if the controls are independently executed, or if two or more controls simultaneously occur, a control with a higher priority is executed. In this way, a transmission quality of an optical signal is prevented from being badly influenced as a result that the controls are simultaneously executed.

Abstract: A method for determining signal quality in optical transmission systems, wherein the effective signal-to-noise ratio is determined by measuring amplitude histograms of a signal and by calculating characteristic histogram moments and additional interference is ascertained by comparing the characteristic histogram moments with the optical signal-to-noise ratio.

Abstract: A scanning optical monitoring system and method are appropriate for high speed scanning of a WDM signal band. The system and method are able to identify dropped channels or, more generally, discrepancies between the determined or detected channel inventory and a perpetual inventory for the WDM signal, which perpetual inventory specifies the channels that should be present in the WDM signal assuming proper operation of the network. The system includes a tunable optical filter that scans a pass band across a signal band of a WDM signal to generate a filtered signal. A photodetector then generates an electrical signal in response to this filtered signal. A decision circuit compares the electrical signal to a threshold and a controller, which is responsive to the decision circuit, inventories the channels in the WDM signal.