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: An apparatus and method of line coding to mitigate collision induced errors in Wavelength Division Multiplexing (WDM) optical communications systems is disclosed. The apparatus and method prevents Soliton-Soliton-Collision induced errors by reducing a variance in a number of possible collisions between solitons in multiple channels in a WDM fiber optic communication system using a sliding window criterion. The sliding window criterion defines a set of parametric values based on physical properties of the transmission network, a transmission frequency and a defined data block size. N-bit codes are iteratively selected and sequentially assigned to segments of a mapping table indexed by all possible unique combinations of “1”s and “0”s in a block of data. Input data blocks are mapped to corresponding code words having a reduced number of transitions for transmission on the fiber optic network. Received code words are converted back to a data stream corresponding to the input data stream.

Abstract: Herein, it is described a method for implementing a Performance Monitoring function according to data retrieved through FEC (Forward Error Correction), in a telecommunication network, which is based on the correlation of information relating to “corrected” and “uncorrected” blocks deriving from the implementation of the FEC function.

Abstract: The present invention enables interface conversion verification with a single chip and improves problem isolation. Exemplary embodiments of the present invention can provide this by modifying the input data pattern (e.g., creating a 40G, or pseudo OC-768, frame by multiplexing four OC-192 frames, two bytes at a time) to provide per port demultiplexing of data streams at the output of the interface converter.

Abstract: An apparatus for determining an error ratio of individual channels of a WDM optical signal comprises a wavelength-selective filter for separating the individual channels of the WDM signal and a measurement circuit for measuring an error ratio of one channel using a first decision threshold level. The measurement circuit is operable to cycle through all channels, taking an error ratio measurement for each channel in sequence with a predetermined decision threshold level. Control circuitry alters the decision threshold level for successive cycles of the measurement circuit. The apparatus measures error ratio values for each channel in turn, building up an error ratio vs. threshold pattern enabling the Q value to be obtained. Although the time taken to build up the error ratio pattern for an individual channel is not shortened, measurements are taken on each channel at much shorter intervals.

Abstract: A method for monitoring the transmission quality of an optical transmission system, such as, for example, an optical wavelength division-multiplex network. An amplitude histogram of an optical signal (transmission signal) transmitted over the transmission system may be plotted and classified, with the assistance of a neural network, according to bit error rates and/or causes of faults. The need for setting requirements for transmission mode, transmission format and/or transmission timing cycle of the transmission system may be eliminated. The amplitude histogram may be implemented for any signal, and causes of faults, which are not able to be determined by a conventional bit rate classification, may be allocated.

Abstract: To equalize the performance of multiple channels travelling along diverse subsets of a main optical path, a channel-specific figure of merit for each channel is determined and a site-specific figure of merit for each site which is a drop site for at least one channel is determined. The channel-specific figure of merit for a particular channel could be a figure of merit (such as OSNR, Q or BER) for that channel at the particular channel's drop site, while the site-specific figure of merit for a particular drop site may be the average figure of merit for all channels received at the particular drop site. Equalization is then achieved by adjusting the power of each channel as a function of the difference between the channel-specific figure of merit for that channel and the site-specific figure of merit for that channel's drop site.

Abstract: Link robustness, chromatic dispersion and polarization mode dispersion (PMD) immunity can be improved in fiber optical system by using a method for receiving an optical double sideband signal over an optical fiber system, comprising the steps of splitting the received optical double sideband signal into an upper sideband signal and a lower sideband signal, photodetecting the upper sideband and the lower sideband, equalizing the photodetected upper sideband signal and the lower sideband signal, and combining the equalized upper sideband signal with the equalized lower sideband signal. While PMD compensation is envisioned as a major application, one may also use the method and system for chromatic dispersion compesation or dispersion slope compensation in high bit rate systems, i.e. using dispersion compensation fiber (DCF) for coarse compensation and diversity receiver with electrical equalizer for fine tuning.

Abstract: A multi-purpose bit error rate tester (MPBERT) and a method of bit error rate (BER) testing of electrical and optical components and subsystems of electrical and optical communications systems is provided. The invention provides for bit error rate testing both in the optical and the electrical domain, and for bit error rate testing at higher than achievable rates in the electrical domain by multiplexing and demultiplexing in the optical domain. An MPBERT constructed according to the invention incorporates at least one optical multiplexer, and advantageously incorporates at least one optical demultiplexer, and in some embodiments uses high data rate optical RZ to NRZ conversion and high data rate optical NRZ to RZ conversion.

Abstract: This invention provides an optical transmission with a demultiplexer for demultiplexing an input optical signal into optical signals of different channels and a multiplexer for multiplexing the optical signals outputted from the demultiplexer.

Abstract: Disclosed is a bit-rate-independent optical receiver including: a bit rate sensing unit for optoelectrically converting an input optical signal, while outputting a bit rate sensing signal; a variation sensing unit for outputting a bit rate variation sensing signal; a temperature sensing unit for sensing an internal temperature and outputting a temperature sensing signal; a signal reproducing unit for reproducing data and clocks, and in response to a clock correction signal, reproducing the data and clocks based on the clock correction signal; and, a control unit for calculating the bit rate based on the voltage level of the bit rate sensing signal in response to receiving the variation sensing signal, and compensating the calculated bit rate for errors resulting from a variation in temperature, and outputting a clock correction signal indicative of the temperature-compensated bit rate to the signal reproducing unit.

Abstract: An on-chip parallel data generator, including a Built In Self Test (BIST) generator, is integrated into a laser driver array of a parallel optical communication transmitter so that all optical outputs switch simultaneously. The BIST generator requires only one clock input which clocks the BIST generator for all channels. The optical outputs respond to either the on-chip BIST generator or the electrical inputs if a valid signal is present on the inputs.

Abstract: An optical receiver threshold may be optimized in real time based on a forward error correction (FEC) error statistics. A relative number of corrected ones as compared to corrected zeros is tracked. The threshold is shifted in response to an imbalance between the two types of errors.

Abstract: Methods and network nodes are provided which are adapted to perform protection switching on the basis of raw signal quality information, such as raw BER information, in a manner which instigates the protection switching before an actual failure has occurred. In some embodiments, these methods leverage forward error correction and uncorrected BER to effect traffic redirection before faults are observed at layer 2 and above. This is as opposed to the method of switching layer 2 traffic in response to bitstream characteristics observed at that layer.

Abstract: An apparatus and method for detecting a signal in an optical data network is disclosed. A peak power level and an average power level are measured for an optical input to an optical detector. A threshold power level is associated with each average power level that is sufficient to distinguish a data signal form optical noise at the average power level. A signal is detected if the measured peak power level exceeds the threshold power level appropriate for the average power level. In one embodiment, a threshold value of a ratio of the peak power level to the average power level is calculated and a signal is detected if the ratio of the measured peak power level to the average power exceeds the threshold value.

Abstract: A self-healing bit rate transducer in an optical transmission system includes a demultiplexer for demultiplexing optical signals into different wavelength channels; bit rate receivers for converting the demultiplexed optical signals into the corresponding electrical signals, for generating a bit-rate error signal, and for generating a temperature reference signal; a detecting section for generating a signal indicative of the bit rate of the optical signals outputted from the demultiplexer; and a controller for comparing the detected bit rate with a predetermined data to generate a control signal that is used to adjust the bit rate of the respective bit rate receiver.

Abstract: In an optical fiber communication system, for signal monitoring a transparent optical network (all-optical networks), i.e. a system without digital intermediate regeneration, the bit error probability (BEP) is calculated by dismodulating and sampling the signal and generating an amplitude histogram. This histogram serves mainly for modeling the signal distortions. A family of amplitudes that represent the average of a noise-infested sub-signal is determined from the histogram for each status of the signal (logical “0” or “1”). The variance of the individual noise signal overlaid on every amplitude value is calculated from the parameters of the receiver as well as from the optical signal-to-noise ratio (OSNR). The bit error probability is calculated with adequate precision from these parameters.

Abstract: An optical transmission apparatus implemented as an OADM (Optical Add/Drop Multiplexer) includes quality monitors each for monitoring the quality of a signal arriving on a particular optical transmission path. A monitor/control unit converts quality signals output from the quality monitors to path-by-path bit error rates, or estimation values, and compares them to select a route. The monitor/control unit then generates a metric value “1” for the route selected and adds it to one of identical metric values, which are assigned to routes to the same destination, that corresponds to the route selected. The monitor/control unit can therefore select a route closer to actual transmission path conditions. A method of determining an optimal route for optical transfer is also disclosed.

Abstract: In order to monitor the signal quality in transparent optical transmission paths, the signal is sampled asynchronously, the distribution of the sample results in recorded and a signal quality parameter is formed, in that only those flanks which are located away from the maxima of the distribution are evaluated.

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 communication system capable of performing efficient Wavelength Division Multiplexing (WDM) transmission by flexibly handling connection services. A Bit Error Rate (BER) measurement unit measures BER of individual optical signals with different wavelengths. A BER transmission unit transmits BER information to the sending end. A wavelength assignment unit assigns each wavelength to at least one of high Quality-of-Service (QoS) communication and low QoS communication. A wavelength-assignment exchanging unit identifies low quality wavelengths with high BERs being used for the high QoS communication, and unless the low quality wavelengths being used for the high QoS communication outnumber the high quality wavelengths with low BERs being used for the low QQS communication, it exchanges the low quality wavelengths and an equal number of the high quality wavelengths. An optical signal transmission unit multiplexes the wavelengths to transmit the optical signals.

Abstract: An increase in the code error rate in a received signal is detected in a light receiver. An loss of signal detector circuit for a light receiver 20 comprises a main discrimination circuit 8a for comparing the intensity of an electric signal obtained by converting a light signal by photoelectric conversion using a photoelectric conversion element 1 with a predetermined discrimination threshold; a reference discrimination circuit (8b, 8c, . . . ) for comparing the intensity of the electric signal with regard to a reference threshold which differs from the discrimination threshold; and an operation circuit 9 for detecting loss of the signal based on the results of the comparisons performed by the main discrimination circuit 8a and the reference discrimination circuit (8b, 8c, . . . ).

Abstract: Performance monitoring and equalization of DWDM optical links equipped with optical add/drop multiplexers (OADMs) at one or more sites is effected by selecting a direction of transmission and the end sites from the point of view of equalization. Performance monitoring and equalization of DWDM optical links equipped with optical add/drop multiplexers (OADM) is presented in this application. This approach in involves conceptually converting a multiple ends system to a “two-end” system with analogous channels (AC) to simplify the network management and equalize the DWDM channel performance. All analogous channels are treated as originating at a source analogous end and terminating at a destination analogous end for the purpose of equalization. The input power for all ACs, is adjusted at the source AE to obtain equal channel performance at the destination AE.

Abstract: A system, method and apparatus for monitoring impairment related parameters such as Q factor within an all-optical system by using forward error correction (FEC) to derive a bit error rate (BER), which BER is used to determine the impairment related parameters.

Abstract: The invention provides an automatic bandwidth adjustment method and system in a passive optical network (PON) comprising an optical line terminal (OLT) connected to a plurality of optical network units (ONUs). A particular embodiment of the method according to the invention comprises the steps of transmitting data between at least one of the ONUs and the OLT, detecting if there is any undelivered data in the data being transmitted, queuing the undelivered data in an undelivered data block (UDB) in an upstream frame of the ONU, informing the OLT of the undelivered data using the undelivered data block (UDB), reading the UDB, adjusting bandwidth of the ONU according to the UDB, informing the ONU whether the PON is busy using an unused bandwidth block (UBW), and rejecting a new transmission request between the ONU and the OLT if the PON is busy or unavailable.

Abstract: An optical signal quality monitoring system and method are provided for monitoring signal quality of a plurality of optical signals in a network. The system includes a plurality of input taps for acquiring multiple optical signals from multiple optical fibers of an optical network. The system also includes an optical switch for receiving the tapped optical signals and selecting one of the tapped optical signals at a time as an output, and an optical channel selector for selecting one signal channel at a time of the selected optical signal. The system further includes an optical signal quality measurement device for analyzing the selected optical channel of the selected optical signal and determining a signal quality of the selected optical channel.

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: To optimize the resources of an optical transmission network using wavelength division multiplexing, assigning carrier frequencies to signals to be transmitted consists in associating N sets of optical frequencies of the comb with N respective ranges of consecutive error rate values, each of the sets comprising frequencies generating a mean error rate in the associated range, defining a measured signal transmission constraint level that is a function of the transmission constraint parameter(s) and may take N distinct values referred to as constraint values, associating the N constraint values in increasing order respectively with the N sets of frequencies in decreasing order of the error rate values of the associated N ranges, assigning any signal to be transmitted a constraint value obtained by applying the measurement, and assigning the signal to be transmitted a carrier frequency belonging to one of the sets of frequencies that is associated with a constraint value at least equal to the constraint value as

Abstract: A method for estimating the bit-error-ratio (BER) for a segment or whole of an optical communications network by measuring the actual distribution of bits (1s and 0s) in a transmitted data set as a function of threshold value, and directly estimating the BER at an optimal threshold value using a Q-fitting algorithm.

Abstract: A method for measuring the signal quality of an optical data signal is provided. To measure the signal quality, and in particular the signal-to-noise ratio of an optical data signal which has data-free time intervals, the signal strength of the transmitted optical data signal is measured during a data transmission. The signal strength of the noise signal is determined during the data-free time intervals. The signal-to-noise ratio is determined and used as a criterion for the signal quality of the optical data signal.

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: Disclosed herein is a method of optimizing an output signal of an optical receiver using FEC and an optical receiving system using the method. In the method of the present invention, optical signals transmitted through an optical cable are converted into digital data of bits “1” and “0” on the basis of a reference voltage, and errors generated during transmission of the optical signals are corrected using the FEC. The method includes extracting numbers of occurrence of errors for bits “1” and “0” recovered through the FEC. Thereafter, the extracted numbers of occurrence of errors for bits “1” and “0” are compared with each other. A reference voltage used to judge levels of the signals to be level “1” or “0” is controlled if the numbers of occurrence of errors for bits “1” and “0” are not equal to each other.

Abstract: An apparatus and method for uniformly sharing across a plurality of channel signals FEC coding gain which may be achieved through FEC encoding of a higher baud rate electrical data signal or through multiplexed or combined electrical data signals from multiple data sources prior to their subsequent demultiplexing and separate generation into optical channel signals which are multiplexed and launched onto an optical transmission medium. The optical signal generation is achieved through reverse multiplexing of the higher baud rate data signal or of the multiplexed, FEC encoded plural data signals.

Abstract: A method and a system for performing pre-emphasis of one or more optical channels respectively carrying one or more optical signals, by effecting bit rate of the one or more of the signals, thereby adjusting BER value thereof.

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: A method of and system for estimating the bit error rate of a channel in an optical communication system includes a method of and system for measuring the in-band cross-talk of the channel in a wavelength division multiplexed system. A single channel is selected from the plurality of channels in the optical communication system. The signal in this single channel is passed to a digital signal processor proportional to the time rate of change of a phase of an optical source generating the signal. The digital signal processor converts the filtered signal into the frequency domain, and a spectrum analyzer determines the features of the in-band cross-talk from the signal in the frequency domain. The features of the in-band cross-talk may be combined with other measured noise features, such as the power spectral density, to estimate BER.

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: An optical transmission system exploits the reduced signal-to-noise (SNR) requirements for low-bit rate channels to devise a new wavelength channel allocation scheme which increases the number of channels that a WDM system can support. Wavelengths of low-bit rate channels are assigned outside a flat-gain window (i.e., flat-passband region) of the system. The channel allocation scheme uses the high-bit rate channels located in the flat-passband region of wavelengths and the lower-bit rate channels located outside this passband region with progressively lower-bit rate channels located farther outside this passband region. Low-bit rate channels are also assigned to region(s) of the passband where the non-linear threshold power level of the system may be exceeded.

Abstract: The present invention addresses the need for optical transmission systems, apparatuses, and methods having increased flexibility and reliability. Optical systems of the present invention are configured to provide alarms, provision, and/or perform protection switching, if the number of corrected errors exceeds a threshold criteria. Various system parameters, in addition to protection thresholds, can be adjusted based on the relationship between the number of one errors, zero errors, and/or total errors being corrected in the system.

Abstract: A receiver in an optical network with a bit rate detection circuit for automatically detecting input signal data bit rates to automatically adjust the frequency of a voltage controlled oscillator in the receiver is disclosed. The receiver has a data rate detection and frequency adjustment circuit which automatically detects the data rate of an input signal and automatically adjusts the frequency of the VCO in the receiver in accordance with the data rate of the input signal. The data rate detection and frequency adjustment circuit detects the data rate of the input signal by converting the input signal into a DC voltage value that varies with respect to the data rate of the input signal.

Abstract: A method and apparatus for managing state-of-polarization (SOP) controllers along an optical communications link. When the polarization-mode dispersion (PMD) in the link exceeds a preset limit as determined by a PMD compensator, the SOP controller is directed to change rotation angle in an arbitrary fashion. This shift is only undertaken after other indicators are examined to determine that PMD is the main problem affecting the link, and not simply a consequence of a separate problem that the SOP controller rotation angle should not try to fix. By reducing unnecessary SOP adjustments which can disrupt data traffic, the reliability of the optical link is improved.

Abstract: A method and apparatus for optical performance monitoring that provides for multi-rate and multi-protocol monitoring includes, identifying a protocol associated with each of a plurality of communication signals using respective data rates extracted therefrom, determining, for each of the plurality of communication signals, a respective bit-error rate (BER), and generating an alarm indicative of BER excursions beyond a protocol appropriate BER threshold level

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: A system and method are disclosed for providing a transmission capacity on a data transmission path, wherein such data transmission capacity is provided with regard to a user on a transmission path by using at least one limiting unit.

Abstract: We demonstrate a novel type of data receiver, which has superior performance compared to a standard receiver when an input signal is distorted by timing jitter. A method and apparatus for improved timing jitter tolerance includes sampling an input signal more than once within a bit slot of the input signal and determining, using logic circuitry, from a combination of at least a subset of the samples, a resulting logic state for an output signal.

Abstract: An optical communication network system is disclosed, which includes an optical switching apparatus. The optical switching apparatus includes an optical switch for switching and setting routes of an optical signal without being converted, a control unit for instructing the optical switch to execute a route switching operation, and a performance monitor for detecting performance of the optical signal having a route set by the optical switch. The performance monitor issues an alarm when the performance detected is deteriorated from predetermined performance. The control unit includes an alarm masking unit for masking the alarm issued from the performance monitor at least for a predetermined masking period from a starting time of a switching operation by the optical switch, and thus preventing the alarm from being issued.