Abstract: A method and system for detecting intrusions on a fiber optic network. The method and system monitors polarization variations of light being transmitted in the fiber optic network. It then determines intrusions in the fiber optic network based on the polarization variations. The polarization variations are then compared to a database of known activity which would cause polarization variations to determine unknown intrusions. An intrusion alert is initiated when the determined intrusion does not correspond to any known activity. The known activity is contained in an automated database for automatically comparing to the polarization variations. The intrusions may be cross-correlated on two partially adjacent fiber optic cables to determine the location of the intrusion.

Abstract: A method and apparatus for determining the dispersion characteristics of minimum phase filters using substantially only an amplitude response of a minimum phase filter under test includes fitting an amplitude spectrum of the minimum phase filter with a substantially straight line curve, and determining the dispersion characteristics of the minimum phase filter using the straight line curve and the relationships determined by the inventors. Various inventive equations determined by the inventors representative of the relationship between an amplitude response of a minimum phase filter and the dispersion characteristics of the minimum phase filter are used for determining the dispersion characteristics of the minimum phase filter.

Abstract: A radio relay system (1) comprises a wireless camera (11) and a signal receiving relay station (12). The wireless camera (11) wirelessly transmits signals to the signal receiving relay station (12) by using the OFDM modulation method. The wireless camera (11) and the signal receiving relay station (12) perform energy dispersion at the time of transmission-line-coding/decoding a transport stream. The PRBS seed (initial value) to be used for the energy dispersion can be externally modified and the user can arbitrarily select a value for the seed.

Abstract: An optical dispersion monitoring apparatus and an optical dispersion monitoring method are capable of monitoring dispersion accurately with a simple construction in an optical transmission system using the same. To this end, the optical dispersion monitoring apparatus includes a light receiving section converting an input optical signal into an electrical signal, a signal transition position detecting section detecting the voltage level of a waveform of the output signal from the light receiving section, at a crossing point of a rising edge and a falling edge, and a cumulative dispersion information extracting section comparing the voltage level at the crossing point with a reference signal to extracts cumulative dispersion information.

Abstract: If no alarm is input from an optical receiver, an FEC decoder, or a client signal monitor, a control circuit controls a variable dispersion equalizer such that a transmission error becomes smaller using information on the number of error corrections obtained from the FEC decoder and fixes a dispersion equalization value in the event that the error becomes equal to or lower than a specified value. If the alarm information is input, the control circuit switches control over the variable dispersion equalizer from an ordinary control to a search mode control for searching an optimal dispersion equalization value in a wide range to thereby search the optimal dispersion equalization value at a higher speed.

Abstract: Methods and systems for PMD compensation in an optical communication system are implemented by transmitting multiple optical signals through a common optical conduit to an optical compensator that adjustably rotates the polarization states of the multiple optical signals and transmits the rotated optical signals to an optical receiver. The receiver, upon sensing an excessive error condition, commands the optical compensator to change the polarization state of rotation, which changes the PMD profile of the received optical signals.

Abstract: An apparatus is provided for compensating for polarization mode dispersion which is caused during transmission of a light wave via an optical waveguide, to an optical communication network having such an apparatus, and a method for compensating for polarization mode dispersion which is caused during transmission of a light wave via an optical waveguide is also provided.

Abstract: A plurality of optical repeaters are provided on a transmission line between an optical transmitting station and an optical receiving station. A combined transmission line section is provided between optical repeaters. The combined transmission line section is composed of the first optical fiber, which is a positive-dispersion fiber, and the second optical fiber, which is a negative-dispersion fiber. Signal light is inputted to the first optical fiber in each combined transmission line section. Each optical repeater inputs pump light to the second optical fiber.

Abstract: The invention relates to the monitoring of polarization mode dispersion (PMD) using heterodyne detection for providing PMD compensation in optical networks, and an apparatus for monitoring PMD. In the present invention, a broadband PMD monitor is disclosed based on heterodyne detection with a tunable laser source which can be fed to a compensator such as an add/drop or other wavelength switch and polarization dependent attenuation means. A signal from a local oscillator is combined with an optical signal and the beat frequency amplitude and phase is analyzed for two orthogonal polarization states simultaneously to obtain a state of polarization. By averaging a plurality of polarization states within a channel, PMD can be estimated for compensation.

Abstract: The present invention provides a chromatic-dispersion measuring apparatus and method that can quickly measure chromatic dispersion in an optical fiber even when the optical fiber is short. Continuous light beams having the wavelengths ?1 and ?2 output from light sources are multiplexed by a multiplexer, are intensity-modulated by an intensity modulator, and are then output as optical signals. The output optical signals with the wavelengths ?1 and ?2 enter an optical fiber to be measured, and propagate therethrough. The optical signals emerging from the optical fiber are de-multiplexed by a de-multiplexer, and are received by corresponding photodetectors. Subsequently, the phase difference between the optical signals received by the photodetectors is detected by a phase detector. The chromatic dispersion of the optical fiber is calculated by an arithmetical circuitry on the basis of the detection result.

Abstract: An apparatus for measuring a set of frequency-resolved states of polarization (SOP) of an optical signal includes a local oscillator (LO), a polarization scrambler, a coupler for mixing the polarization-scrambled signal with the optical signal to produce a heterodyned signal with a radio frequency (RF) component, and an analyzer for passing a fixed polarization component and resolving the polarization and frequency from the RF component. The apparatus is used for measuring, monitoring or compensating the polarization mode dispersion (PMD) in a working channel of an optical telecommunication system. A method for measuring frequency-resolved SOP of an optical signal includes tuning and polarization-scrambling a local oscillator (LO), mixing the scrambled LO with the optical signal, and resolving the RF signal in frequency and polarization. The method is applied to measure and monitor PMD in a working optical channel, and to dynamically compensate for the PMD.

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: According to the system and method of the present invention, the frequency of an optical data signal is modulated on the transmitter side, and group transit time changes of the optical signal are detected on the receiver side. These group transit time changes are preferably determined via synchronous demodulation of a control signal of a voltage-controlled oscillator for timing recovery and are a measurement for any chromatic dispersion, which can be compensated via a chromatic dispersion compensator. The parasitic amplitude modulation generated with the frequency modulation can be used to obtain a reference signal for the synchronous demodulation.

Abstract: A method of simultaneously specifying the wavelength dispersion and nonlinear coefficient of an optical fiber. Pulsed probe light and pulsed pump light are first caused to enter an optical fiber to be measured. Then, the power oscillation of the back-scattered light of the probe light or idler light generated within the optical fiber is measured. Next, the instantaneous frequency of the measured power oscillation is obtained, and the dependency of the instantaneous frequency relative to the power oscillation of the pump light in a longitudinal direction of the optical fiber is obtained. Thereafter, a rate of change in the longitudinal direction between phase-mismatching conditions and nonlinear coefficient of the optical fiber is obtained from the dependency of the instantaneous frequency. And based on the rate of change, the longitudinal wavelength-dispersion distribution and longitudinal nonlinear-coefficient distribution of the optical fiber are simultaneously specified.

Abstract: Embodiments of the invention include system for monitoring the effectiveness of pulse shaping in a nonlinear optical fiber (40). The spectral content of the pulse, after passing through the nonlinear fiber (40), provides an indication of how effectively the pulse was regenerated. A portion of the pulse exiting the nonlinear fiber is tapped off and its pulse energy is measured in at least one selected spectral region. The selected spectral region is one in which the pulse tends to gain energy when effective regeneration is taking place. The information concerning the effectiveness of pulse shaping in a nonlinear optical fiber is fed back to dynamically change the residual dispersion at the regenerator input. The spectral measurement leads to a control signal (48) to indicate a level of performance of the system, or to improve the performance of the system by adjusting an operational parameter.

Abstract: A method of and apparatus for determining the spatial distribution of polarisation properties of an optical fiber (1). Pulses (7) of light are transmitted along the optical fiber (1) and the polarisation state of light backscattered from portions e and elements R of the optical fiber (1) detected. A spatial distribution of linear retardance ?, orientation of linear retardance axes q and circular retardance axes can be accurately determined. This has application in the analysis of Polarisation Mode Dispension (PMD) in telecommunications as well as, inter alia, strain, stress, temperature and electric current and voltage measurement using optical fibers.

Abstract: An optical receiver including a variable optical attenuator for controlling an optical loss value for each optical transmission line based on a predetermined optical loss value; a variable dispersion compensation module for controlling a wavelength dispersion value for each optical transmission line based on a predetermined dispersion value; an optical loss/dispersion controller for measuring the optical loss value and the wavelength dispersion value of every optical transmission line, outputting these values so that they are equal in all the optical transmission lines, and controlling the attenuator and the module based on the outputted predetermined values; a receive amplifier for receiving the optical signal whose light level is kept constant and amplifying the signal; and, a transmission line switch control module is provided for switching a working transmission line into a protection line if the optical signal level of the working line is lower than a threshold value.

Abstract: A transmission characteristic compensation system enables to reduce the generation of transmission deterioration by estimating an initially selected control direction, and also to compensate in advance with a setting value estimation so as to suppress the generation of transmission deterioration in advance. The transmission characteristic compensation control system includes a variable compensator having a control circuit; and an optimal setting value calculation portion for calculating an optimal setting value for the control circuit, wherein the optimal setting value calculation portion estimates future transmission deterioration on a predetermined time-by-time basis to set into the control circuit the optimal setting value for compensating the estimated transmission deterioration performed by the variable compensator.

Abstract: Device for detecting polarization mode dispersion of an optical data signal, which has at least one EXOR gate together with an averaging device for measuring at least one value of the autocorrelation function of a baseband signal distorted by polarization mode dispersion.

Abstract: A system and method for reducing timing and amplitude jitter in trnasmission of Retrun-to-Zero modulated pulses is described. In the reduction of amplitude jitter the modulated pulses must be phase coherent. The method comprises the steps of measuring a total dispersion of a transmission fiber link, computing an optimal amount of pre-chirp to be added at an input of said transmission fiber link, computing an optimal amount of pre-chirp to be added at an output of said transmission fiber link, adding said optimal amount of pre-chirp to said input of said tranmisssion fiber link and adding said optimal amount of pre-chirp to said output of said tranmisssion fiber link.

Abstract: An apparatus for monitoring polarization-mode dispersion and chromatic dispersion in optical networks in accordance with the present invention comprises; an optical distributor for distributing input optical signals, a first light receiver for photoelectrically converting the optical signals distributed by the distributor, a second light receiver for photoelectrically converting the optical signals to measure the average power of the optical signals distributed by the distributor, a filter for filtering output signals from the first light receiver, a power meter for measuring the frequency band of the optical signals filtered by the filter, an analog-to-digital (A/D) converter for converting the analog signals from the first and the second receivers into digital signals, a microprocessor for monitoring the polarization-mode dispersion and the chromatic dispersion of the optical signals by means of the digital signals from the A/D converter, and further a polarization scrambler in the optical signal sending-en

Abstract: A system for reducing the influence of polarization mode dispersion (PMD) in high speed fiber optical transmission channels. A signal is forward error correction (FEC) encoded according to an FEC code that defines a specified error tolerance per codeword. The invention then effectively randomizes the input polarization of the signal before transmission, in order to reduce the likelihood that PMD will distort one or more codewords beyond the allowed error tolerance. The invention will thereby increase the PMD-limited transmission distance in an optical transmission system.

Abstract: Techniques for monitoring frequency-dependent parameter and optical property such as optical dispersion in a modulated optical signal with sidebands based on optical vestigial sideband filtering. Monitoring implementations for both chromatic dispersion and polarization-mode dispersion are described as examples.

Abstract: Apparatus and method is described for using a silicon photon-counting avalanche photodiode (APD) to detect at least two-photon absorption (TPA) of an optical signal, the optical signal having a wavelength range extending from 1.2 ?m to an upper wavelength region that increases as the number of photons simultaneously absorbed by the APD increases beyond two. In one embodiment, the TPA count is used by a signal compensation apparatus to reduce dispersion of a received optical pulse communication signal subjected to group velocity dispersion, polarization mode dispersion, or other signal impairment phenomena which effect the TPA count. Another embodiment, the TPA count is used to determine the optical signal-to-noise ratio of a received optical pulse communication signal. Another embodiment uses the TPA count to determine the autocorrelation between a first and second optical pulse signals as a function of the relative delay between the first and second optical pulse signals.

Abstract: A method of simultaneously specifying the wavelength dispersion and nonlinear coefficient of an optical fiber. Pulsed probe light and pulsed pump light are first caused to enter an optical fiber to be measured. Then, the power oscillation of the back-scattered light of the probe light or idler light generated within the optical fiber is measured. Next, the instantaneous frequency of the measured power oscillation is obtained, and the dependency of the instantaneous frequency relative to the power oscillation of the pump light in a longitudinal direction of the optical fiber is obtained. Thereafter, a rate of change in the longitudinal direction between phase-mismatching conditions and nonlinear coefficient of the optical fiber is obtained from the dependency of the instantaneous frequency. And based on the rate of change, the longitudinal wavelength-dispersion distribution and longitudinal nonlinear-coefficient distribution of thee optical fiber are simultaneously specified.

Abstract: An exemplary embodiment of the invention is a dispersion compensation module for compensating dispersion in a communications network. The dispersion compensation module includes dispersion compensating fiber having a dispersion coefficient that varies with wavelength. A thermal regulator adjusts the temperature of the dispersion compensating fiber to adjust the dispersion characteristic of the dispersion compensating fiber. Alternate embodiments of the invention include a communications system using the dispersion compensation module and a method for compensating dispersion.

Abstract: Internet protocol based transmissions have historically been transmitted on a best efforts basis. There are proposals to provide differentiated services to allow different packets to be delivered with different service qualities depending on the bandwidth requirements of a particular flow. By performing bandwidth monitoring within the core network and performing packet dropping and/or queuing at the network ingress, the need for packet dropping and/or queuing within the core network is removed and furthermore the core network resources are not used by packets which will not be delivered to their destination but will instead be dropped within the core network.

Abstract: Disclosed herein are a method and system for compensating chromatic dispersion. The method includes the steps of generating WDM signal light by wavelength division multiplexing a plurality of optical signals having different wavelengths, transmitting the WDM signal light by an optical fiber transmission line, and receiving the WDM signal light transmitted by the optical fiber transmission line. The receiving step includes the steps of detecting chromatic dispersion related to at least one of the plural optical signals, and providing a variable dispersion compensator whose chromatic dispersion and dispersion slope are controlled so that the detected chromatic dispersion is reduced. According to this method, waveform degradation due to dispersion can be compensated with high accuracy in consideration of dispersion and dispersion slope.

Abstract: A suite of optical performance monitoring (OPM) methods, based on optical subcarrier multiplexing, are described by the invention. The strength of this approach lies in the simplicity of double sideband subcarrier signals and the fact that these signals travel the complete optical path with the baseband signal of interest. The subcarrier signals can be recovered using techniques described in the application and are immune to fiber dispersion induced fading.

Abstract: A device is provided for detecting polarization mode dispersion of an optical data signal, wherein the device includes at least two filters, each of which is respectively followed by a power detector. A better compensation can ensue due to the combination of a large monotony range and great steepness in the employment of a number of filters.

Abstract: In a method and system for evaluating distributed gain in an optical transmission system, a data signal and a residual pump laser signal propagating in opposite directions within a waveguide are monitored. Modulation of the residual pump laser signal is correlated with low frequency components of the data signal. This correlation is used to determine cross-talk between the data signal pump laser signals, as a function of location within the waveguide. The distributed gain is then evaluated from the cross-talk, using a known relationship, or proportionality, between gain and cross-talk.

Abstract: A system and-method for reducing timing and amplitude jitter in transmission of Retrun-to-Zero modulated pulses is described. In the reduction of amplitude jitter the modulated pulses must be phase coherent. The method comprises the steps of measuring a total dispersion of a transmission fiber link, computing an optimal amount of pre-chirp to be added at an input of said transmission fiber link, computing an optimal amount of pre-chirp to be added at an output of said transmission fiber link, adding said optimal amount of pre-chirp to said input of said transmission fiber link and adding said optimal amount of pre-chirp to said output of said transmission fiber link.

Abstract: A dispersion managed link for transmitting wavelength division multiplexed (WDM) optical signals and method for providing the link are disclosed. The link includes a plurality of spans serially connected by optical amplifiers. Each span includes an optically dispersive fiber connected to a dispersion compensating module (DCM). The fibers and DCMs are selected in accordance with a preferred dispersion map, which represents dispersion along the link, such that points of minimum and maximum dispersion have distributions that change in accordance with one another. The effects of self-phase modulation (SPM), inter-symbol interference (ISI), and cross-phase modulation on the signals are minimized. The preferred dispersion map may be one of ramp type, angular type or arcuate type, and in the case of the latter two, it may have a plurality peaks.

Abstract: A method and system for determining location and value of dispersion compensating modules (DCMs) in an optical network is provided. The method comprises evaluating possible DCM values and locations and successively adding selected combinations to the network until the dispersion limits of the network are met. This systematic method is applicable to a variety of network topologies. In one embodiment, the method for determining the location and value of the DCMs uses the amount of compensated effective dispersion over all lightpaths that pass through the DCM to select the combinations. In another embodiment, the method is repeated a number of times with different selections of DCM value and location combinations, and the method providing the least number of DCMs and the lowest DCM values is chosen.

Abstract: A method for determining optimal locations and values of dispersion compensating modules (DCMs) in an optical network is provided. The method comprises repeatedly evaluating possible combinations of DCM values and locations and adding to the combination having the lowest score until a solution of DCMs is formed that satisfies the dispersion limits of the network. This method provides an optimal solution with, for example, the lowest value of DCMs necessary to meet dispersion specifications. In one embodiment, the method for determining the optimal location and value of the DCMs uses a priority queue to store the different combinations of DCM values and locations. Modifications to the method include variations in the score function, for example to minimize the total cost of the DCMs. In another embodiment, a series of priority queues are used to improve the efficiency of the method by reducing the amount of processing required to sort the priority queues.

Abstract: An optical fiber selection system automatically recommends an appropriate optical fiber type for a communication network, based on input from a user. In one embodiment, the system includes a user computer system that is in communication with a vendor computer system. The vendor computer system executes code and performs a number of steps. Initially, the vendor computer system receives at least one technical parameter associated with the proposed communication network from the user, via the user computer system. Next, the vendor computer system automatically selects an optical fiber type for the communication network based on the least one technical parameter. Finally, the vendor computer system provides the selected optical fiber type to the user, via the user computer system.

Abstract: A method for determining interactions between a number of optical channels in a wavelength division multiplexed signal wherein, given that during broadband optical transmission, the quality of a “Dense Wavelength Division Multiplexed” signal is adversely affected by multiple channel interactions, the method is used to determine the governing effects, the Kerr effect and the non-linear scattering process by evaluating the spectral profile of the Q factor or of the bit error rate.

Abstract: While a discrimination level is scanned by a discrimination section, an average-value detecting section detects the average value of the discrimination output. This yields a distribution function of an input signal. Further, a differentiation section performs a differential process to acquire a probability density function. Average values or dispersion values of, for example, the mark level and space level of the input signal are computed from the distribution function and the probability density function. Accordingly, a Q value as a quality parameter can be obtained.

Abstract: An optical performance monitor particularly well-suited for use in dense wavelength-division multiplexed (DWDM) systems includes both a nonlinear optical detector and a conventional linear detector. The nonlinear optical detector, which may comprise a quadratic detector, is used to provide information, on a channel-by-channel basis, regarding chromatic dispersion, polarization mode dispersion and accumulated amplified spontaneous emission (ASE) noise in each signal wavelength.

Abstract: An optical channel dispersion compensating and monitoring apparatus when an optical signal transmits from an optical transmitter to an optical receiver through an optical fiber is disclosed. A WDM optical amplifier comprising the optical channel dispersion compensating and monitoring apparatus, for a long distance is also disclosed. A WDM optical channel dispersion compensating and monitoring apparatus comprises a dispersion compensating unit for compensating the optical signal distorted in the optical fiber at each channel when the optical signal transmits from an optical transmitter to an optical receiver through the optical fiber and an optical channel monitoring unit for converting an optical power as the portion of the compensated optical signal to electric signals and monitoring the converted electric signals.

Abstract: The invention pertains to optical fiber transmission systems, and is particularly relevant to transmission of large volumes of data over long distances at high rates. An improved apparatus and method for measuring dispersion in a fiber span is disclosed. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed. An improved apparatus and method for measuring dispersion in a fiber span. In particular, the invention teaches a highly accurate technique for measuring the fiber dispersion at a single wavelength. Transmitter and receiver structure and data processing algorithms are disclosed.

Abstract: An optical communication system which uses optical phase conjugation to compensate for chromatic dispersion and optical Kerr effect. The optical communication system includes a first fiber, a phase conjugator, and a second fiber. The first fiber transmits a light signal therethrough, and is a polarization maintaining fiber. The light signal is a linear polarized wave. The phase conjugator receives the light signal from the first fiber and produces a corresponding phase conjugate light signal. The second fiber receives the phase conjugate light signal from the phase conjugator and transmits the phase conjugate light signal therethrough. A wavelength division multiplexing optical communication system is also provided which uses optical phase conjugation to compensate for dispersion and optical Kerr effect.

Abstract: A method for the simultaneous graphical display of paths of optical wavelength channels in a telecommunications network together with one or more channel attributes is provided. The graphical display of the network also shows the direction of data flow transported by the channels. An audible or visual alarm for an error condition for a channel attribute on a link in the network can be produced if requires. The operator can also obtain detailed information on a channel by positioning the mouse over a channel.

Abstract: An optical device and method are presented for use in monitoring at least one optical channel of an input multi-channel light signal.

Abstract: The invention relates to a device for detecting the PMD of optoelectronic transmission lines. The inventive device is characterized in that it comprises a narrow-band, tuneable laser, whose illumination is superimposed with the illumination of the transmission line to be analysed and an optoelectronic heterodyne receiver which receives the superimposed signal.