Abstract: In a wavelength division multiplexing optical transmission system, in order to know an influence amount of a temperature dependency of a dispersion slope, a method of monitoring a dispersion variation amount in two or more of wavelength channels is provided. Further, a method of compensating a wavelength dependency of a temperature dependency of the dispersion by providing an appropriate dispersion individually to the channels or summarizingly for all of bandwidths based on the monitored dispersion variation amounts is provided. According to the present invention, in the WDM optical transmission system, a deterioration in a transmission characteristic by influence of a temperature variation of the dispersion slope can be reduced.

Abstract: For determination of the bandwidth of optical fibers, the invention proposes a method which comprises the injection of light at a first optical power level and at a first frequency into an optical fiber, as well as the measurement of a first signal level as a function of the optical power level of the light passing through the fiber at the first frequency, the injection of light at the second optical power level and at a second frequency into the optical fiber, the measurement of a second signal level as a function of the optical power level of the light passing through the fiber at the second frequency, and the determination of the bandwidth of the fiber as a function of the first and second optical power levels and/or of the measured first and second signal levels using a predetermined rule which describes the frequency-dependant attenuation response of the fiber.

Abstract: When transmitting in higher-order modes (HOMs), the chances of dielectric breakdown in the bulk glass can be reduced by judicious selection of the mode of transmission. Since energy distributions in the HOM profile change with the mode order, one can calculate the peak intensity for any given HOM. Correspondingly, one can calculate whether any portion of the transmitted pulse will exceed the breakdown threshold for the optical fiber through which the HOM signal is being transmitted. Should the calculated energy exceed the dielectric breakdown threshold, another HOM with a lower peak intensity can be selected for signal transmission. Disclosed are systems and methods for selecting an appropriate HOM to reduce the likelihood of dielectric breakdown.

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 while ensuring the desired signal quality.

Abstract: A method for calibrating the calculation of a laser power measurement with respect to specified operational and/or environmental parameters in an optoelectronic device, such as an optical transceiver module having a laser diode, is disclosed. In particular, the method includes sensing analog data that relates to light emission from the laser diode using a monitor photodiode disposed in the optical transceiver module. Additional sensors are then used to sense analog data that relates to the temperature and voltage of the monitor photodiode. The analog data is converted into digital data, then a formulaic relationship that relates the light emission data to the temperature and voltage data is used to calculate the laser power of the laser diode. Calibration by this method accounts for unintended effects caused by temperature and voltage fluctuations in the optical transceiver module.

Abstract: An all optical fiber bit stream reader system for examining the data contents of an optical fiber involving the conversion of a temporal timing signal into a spatially located signal is provided. The invention generally comprises generating and detecting a signal indicating the presence of data, in a manner which is minimally destructive to the data. One embodiment comprises providing a piece of optical fiber that exhibits a nonlinear response through a two photon absorption process and subsequent emission of a photon corresponding to the two photon absorption process. Such a fiber could comprise a conventional doped silica fiber into which an additional dopant has been introduced. Another embodiment involves modifying the index of refraction of the cladding of the optical fiber line. This causes a fraction of the electric field or light pulse guided through the fiber (if present) to be coupled out of the fiber. Thereafter, the pulse can be detected.

Abstract: One method embodiment for monitoring an optical pathway includes emitting an optical signal from an optical emitter, encoding the optical signal with a monitoring optical code division multiple access (OCDMA) code, directing the optical signal with the monitoring OCDMA code into the optical pathway, receiving reflected light associated with the monitoring OCDMA code from the optical pathway, and determining a status of the optical pathway based on the reflected light.

Abstract: The present invention relates to a method of and apparatus for evaluating the position of a time-varying disturbance on an optical waveguide. The steps include: transmitting sensing signals onto the optical waveguide, which sensing signals have imposed thereon a modulation which is dependent, at least in part, on their time of transmission; receiving returned sensing signals, which signals have been exposed to the disturbance; and, from the previously imposed modulation on the returned sensing signals, evaluating the position of the disturbance. Because the sensing signals have a modulation that is dependent at least in part on their transmission time, the round-trip time for the signals to travel to and from a disturbance can be inferred. From this round trip time, or a value related thereto, it is possible to directly or indirectly evaluate the position of the disturbance.

Abstract: In optical communication systems, an optical signal which is modulated with a data signal is transmitted from an optical transmitter, and is launched into a fiber-optic transmission link. The present invention provides a method and an apparatus for the measurement of the distribution of the reflectivity along an optical transmission line implemented by using the signal processing based on the cross-correlation function between the data signal with which the optical transmitter is modulated and the back-reflected signal returned to the optical transmitter to provide the in-service monitoring of the fiber-optic transmission link.

Abstract: According to halt of a Raman pumping light source, a transmitting light power of a first light which is subject to receive a Raman gain is controlled to increase. In this state, a first input/output light power for a first light of an optical transmission line is measured, the first input/output light power being used for determining a reference of loss characteristic of the optical transmission line. A second input/output light power for a second light of the optical transmission line is measured, the second light not being subject to receive the Raman gain, the second input/output light power being used for determining a fluctuation of the reference.

Abstract: A transmitter for an optical transmission system transmits an optical sub carrier multiplexed signal comprising number of sub-carriers, onto an optical transmission path, and provides spectral shaping by different magnitudes of the sub-carriers, or different modulation formats for different sub carriers. This spectral shaping can reduce performance degradation by Kerr effect optical non linearities. This can mean higher input powers may be launched. The magnitudes can provide a signal spectrum which is lower near a center of a band of sub carriers than near an edge of the band. Such spectral shaping can be provided in the receiver either to undo the pre emphasis in the transmitter, or to reduce non linearities from components at the receiving side.

Abstract: An optical communications system has a plurality of spans between a transmitter and a receiver. The receiver has optical to electrical conversion circuitry for converting the received optical signal to an electric signal, analogue to digital conversion circuitry and digital signal processing means for analysing the electrical digital signal. The digital signal processing means derives information concerning characteristics of individual spans from the electrical digital signal. This enables parameters such as per-span variations in provisioned power, local dispersion and span loss to be measured. In-service measurements of system characteristics can be used to enable optimisation of the network operation.

Abstract: A method of controlling optical signal traffic in an optical network between a transmitter and a plurality of receivers, where the transmitter is adapted to compensate optical impairments based on at least one optical parameter, includes steps of identifying each path between the transmitter and the plurality of receivers, determining a respective optical parameter for each path, selecting one of the receivers for receiving an optical signal from the transmitter, and enabling the transmitter to generate the optical signal using the respective optical parameter of the path between the transmitter and the selected receiver. By preconfiguring compensation parameters for the various paths in the network, an all-optical network can be implemented wherein optical signals can be switched, added or dropped without having to match dispersion maps or perform optical-electrical-optical regeneration.

Abstract: An apparatus and method for deriving fiber characteristics between two nodes in an optical communication network are disclosed. A roundtrip time for a signal to travel between two nodes is measured by sending the signal via the optical supervisory channel from a first node to a second node, which is configured for loopback operation. Fiber characteristics can be calculated based on the measured roundtrip time.

Abstract: A passive optical arrangement for indicating the presence of a change in ownership along a fiber optic cable span uses an attenuation unit at a splice location that will severely attenuate an optical signal propagating along the span at a predetermined “marker” wavelength. Particularly well-suited in combination with determining the physical location of a fault along a fiber optic cable, the arrangement allows a technician to use an OTDR at the marker wavelength to determine both the physical location of the fault as well as the physical location of a change in ownership (if any) between the technician and the fault location, since the presence of the attenuation unit will register as a large step-wise change in signal propagation.

Abstract: A relation between a light input power monitor value of an optical transmission signal before passing through a fiber and an input signal amplitude monitor value is recorded in advance in a storage device. Next, actual optical-transmission-waveform is inputted into an optical receiver module, and then comparisons between a light input power monitor value and an input signal amplitude monitor value, and respective monitor values in the case without having the waveform distortion as described above are performed in an operation device to calculate a waveform distortion value. According to the waveform distortion level calculated herein, an optimum threshold value and an optimum phase adjusting value, at which receiver sensitivity is maximized, are calculated in the operation device to control a threshold-value adjusting circuit and a phase-value adjusting circuit, thereby a threshold value and a phase value that are optimum for an input distortion level can be established.

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: Methods and apparatuses are provided for performing jitter measurements in a transceiver module. Accordingly, there is no need to use expensive test equipment that must be inserted into and removed from the network in order to obtain these measurements. In addition, because the measurements can be obtained at any time without any interruption in communications over the network, jitter performance can be monitored more closely and more frequently to facilitate better and earlier diagnosis of problems that can lead to failures in the network.

Abstract: There are provided a method and system for monitoring an optical transmission line. The system for monitoring the optical transmission line includes: an OTDR (optical time-domain reflectometer) transmitting a monitoring light to an optical transmission line, measuring a reflected light or backscattered light to monitor the optical transmission line; an optical amplification unit amplifying the monitoring light transmitted on the optical transmission line by using a gain clamped optical amplifier; and a filter unit removing a component having a wavelength outside a wavelength band of the monitoring light from a backward ASE (amplified spontaneous emission) generated by the optical amplification unit. Accordingly, it is possible to extend an optical transmission line monitoring distance of the OTDR. As a result, it is possible to prevent deterioration of the performance of the OTDR because of the backward ASE.

Abstract: An optical communication link has a plurality of light emitting elements and a plurality of light receiving elements associated with the respective light emitting elements, and a plurality of optical fibers each for conveying an optical signal emitted from one light emitting element to an associated light receiving element. The optical fibers have respective lengths that include at least two different lengths, and respective transmission losses per unit length that vary according the lengths of the optical fibers, so that variation of the transmission losses among the optical fibers due to difference in optical fiber length is prevented.

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: Intrusion detection of one section only of a multimode fiber uses a light signal launched into the fiber at a location spaced from the source through a single mode fiber to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the fiber. A small portion of the higher order signal modes at the a second location also spaced from the destination is sampled by a tap coupler and monitored for transient changes in the mode field power distribution which are characteristic of intrusion to activate an alarm. A fiber being used for data transmission can be monitored for intrusion by introducing a monitor wavelength different from that of the data signal. Central to this invention is the use of a bulk optic (commonly referred to as a pass/reflect) wavelength division multiplexer, one which maintains the modal distribution within the fiber.

Abstract: Intrusion detection for a multimode fiber optic cable uses a light signal launched into the fiber through the low ratio leg of a tap coupler to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the cable. A small portion of the higher order signal modes at the remote end is monitored for transient changes in the mode field power distribution which are characteristic of fiber intrusion to activate an alarm. The active signal of a multimode optical fiber is monitored for both signal degradation and transient power disturbance patterns that could indicate fiber damage or physical intrusion. A translator can be provided in an existing optical fiber system in which the data signals are translated in wavelength and/or launch conditions to optimize the monitoring signals in an otherwise non-optimized system.

Abstract: One embodiment of the invention relates to producing optical pulses for use on a transmission link. A light source is configured to produce an optical signal. A pulse generator is coupled to the light source. The pulse generator is configured to receive, for a first channel, the optical signal and a clock signal. The pulse generator is also configured to modify the optical signal based on the clock signal to produce an optical pulse having a predetermined pulse shape. The clock signal is associated with the predetermined pulse shape. The predetermined pulse shape being based on a transmission characteristic of the transmission link.

Abstract: An apparatus for measuring the characteristics of an optical fiber is provided. An optical pulse generator generates, from a coherent light, first and second optical pulses having a time interval which is equal to or shorter tan a life time of an acoustic wave in the optical fiber. A detector couples the coherent light with a Brillouin backscattered light which includes first and second Brillouin backscattered lights belonging to the first and second optical pulses respectively, thereby generating an optical signal. The detector further converts the optical signal into an electrical signal. A signal processor takes the sum of the electrical signal and a delay electrical signal which is delayed from the electrical signal by a delay time corresponding to the time interval, thereby generating an interference signal, and finds the characteristics of the optical fiber based on the interference signal.

Abstract: Intrusion detection of one section only of a multimode fiber uses a light signal launched into the fiber at a location spaced from the source through a single mode fiber to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the fiber. A small portion of the higher order signal modes at the a second location also spaced from the destination is sampled by a tap coupler and monitored for transient changes in the mode field power distribution which are characteristic of intrusion to activate an alarm. The active signal of a multimode optical fiber is monitored for both signal degradation and transient power disturbance patterns that could indicate fiber damage or physical intrusion. A translator can be provided in an existing optical fiber system in which the data signals are translated in wavelength and/or launch conditions to optimize the monitoring signals in an otherwise non-optimized system.

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: A single-to-multi mode converter and an optical code division multiple access system using the same. The mode converter includes first, second, and third optical waveguides. The first optical waveguide is formed of a single-mode optical fiber and outputs a single-mode optical signal. The second optical waveguide converts the single-mode optical signal output from the first optical waveguide to a multi-mode optical signal and allows the optical power of the single-mode optical signal to be coupled to each mode of the multi-mode optical signal. The third optical waveguide is formed of a multi-mode optical fiber and transmits the multi-mode optical signal output from the second optical waveguide.

Abstract: Optical connection verification schemes that do not cause electromagnetic interference. An all-optical connection verification scheme exploits optical coding based on a standard color scale such as RGB (red, green, blue). An RGB LED source is used to launch a three-color optical signal where the relative (or absolute) magnitudes of the color components identify the connection. On the receiver end, an RGB photodiode measures the relative (or absolute) magnitudes of the color components to verify the connection. Alternatively, one end of the connection may transmit white light with the other end reflecting back a similar three-color signal by use of a color-coded panel reflector.

Abstract: The centralized optical-fiber-based wireless picocellular system includes one or more service units at a central head-end station. The one or more service units are optically coupled to one or more transponders via respective one or more optical fiber RF communication links. The transponders are each adapted to provide within the associated picocell electromagnetic RF service signals from different service units, and receive electromagnetic RF service signals from any client device within the picocell. The service signal from the particular client device is sent over the optical fiber RF communication link back to one or more service units. The transponders are arranged along the length of one or more optical fiber cables, which can be distributed throughout a building infrastructure. This creates a picocellular coverage area that provides a number of different wireless services relative to the building infrastructure.

Abstract: A method and system enables measurement of polarization dependent loss (PDL) in an optical communications system including a plurality of cascaded optical components. An optical signal having a predetermined initial polarization state is launched into the optical communications system. A polarization state of the signal is detected at a selected detection point downstream of the launch point. The PDE is evaluated using the predetermined initial polarization state and the detected polarization state.

Abstract: A passive optical arrangement for indicating the presence of a change in ownership along a fiber optic cable span uses an attenuation unit at a splice location that will severely attenuate an optical signal propagating along the span at a predetermined “marker” wavelength. Particularly well-suited in combination with determining the physical location of a fault along a fiber optic cable, the arrangement allows a technician to use an OTDR at the marker wavelength to determine both the physical location of the fault as well as the physical location of a change in ownership (if any) between the technician and the fault location, since the presence of the attenuation unit will register as a large step-wise change in signal propagation.

Abstract: A multimode fiber system includes a transmitter for transmitting an optical signal and a receiver that receives the optical signal. At least one mode filter is coupled between the receiver and the transmitter and passes only a specific set of fiber modes from the transmitter to be received by the receiver. The at least one mode filter comprises a tapered core section that includes a double taper configuration joined at the narrowest regions and in which each end of the two tapers has dimensions compatible with the fiber at that end.

Abstract: The present invention provides a method and system for monitoring composite optical signals carried over plural fiber-optic lines within an optical network. Methods and systems in accordance with the present invention each utilize a single OPM to monitor each one of a set of sample proportions of composite signals split off from respective fiber-optic lines. In one embodiment, an optical performance monitoring system comprises a plurality of fiber-optic lines, each fiber-optic line carrying a respective composite optical signal, a plurality of optical taps, each optical tap being optically coupled to a respective one of the fiber-optic lines and splitting a portion of the composite optical signal thereof, a plurality of optical switches, each optical switch being optically coupled to a respective one of the optical taps and comprising either an Open configuration and a Closed configuration, an optical coupler, and an Optical Performance Monitor (OPM).

Abstract: A method and system for identification of a channel in an optical network is provided. The channel is identified by the use of unique combinations of two or more low frequencies, or tones, modulated onto the channel and optionally, a network parameter associated with the channel.

Abstract: An all optical fiber bit stream reader system for examining the data contents of an optical fiber involving the conversion of a temporal timing signal into a spatially located signal is provided. The invention generally comprises generating and detecting a signal indicating the presence of data, in a manner which is minimally destructive to the data. One embodiment comprises providing a piece of optical fiber that exhibits a nonlinear response through a two photon absorption process and subsequent emission of a photon corresponding to the two photon absorption process. Such a fiber could comprise a conventional doped silica fiber into which an additional dopant has been introduced. Another embodiment involves modifying the index of refraction of the cladding of the optical fiber line. This causes a fraction of the electric field or light pulse guided through the fiber (if present) to be coupled out of the fiber. Thereafter, the pulse can be detected.

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: The spectrum of a received WDM band or subband is analyzed to detect failure of, e.g., fiber or amplifiers along a line. In one implementation, measurements are taken within the optical spectrum at locations of expected data-carrying optical signals and at two locations just outside the wavelength range occupied by these signals. Magnitudes of adjacent measurements are compared to obtain differences. If none of the differences exceed a threshold, a fault may be determined.

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: 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: A method and system of intrusion detection system for a multimode fiber optic cable. A light signal is launched into the cable fiber to establish a narrow spectral width, under-filled non-uniform mode field power distribution in the cable. A small portion of the higher order signal modes arriving at the remote end of the cable is sampled and monitored for transient changes in the mode field power distribution. The power distribution changes with physical disturbance of the cable. When those changes are detected as being characteristic of fiber intrusion, the system activates an alarm. This method can sense and alarm any attempt to access the optical fibers in a fiber optic communication cable. In preferred embodiments, the active signal of a multimode optical fiber is monitored for both signal degradation and transient power disturbance patterns that could indicate fiber damage or physical intrusion.

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: A method for automatic initialization of an optical network is provided. A network management system (NMS) performs remote determination of span losses and sets the operating points of network components. The initialization method comprises remotely and automatically setting target gains of optical amplifiers and signal power levels at transmitters and receivers to required operating values. The methods for initialization of the optical network of the embodiments include gain excursion minimization (GEM) for individual channels passing through amplifiers and/or pre-emphasis of the optical link, where channel powers at the transmitters are biased to compensate for the effects of optical amplifiers gain ripple.

Abstract: A method includes taking backscattering light of a first wavelength in a first direction of a first transmission line and coupling the same so that the light may travel in a second direction of a second transmission line; taking a second wavelength in the first direction of the first transmission line and coupling the same so that the second wavelength may travel in the first direction of the second transmission line; taking backscattering light of the first wavelength in the second direction of the second transmission line and coupling the same so that the backscattering light may travel in the first direction of the first transmission line; taking the second wavelength in the second direction of the second transmission line and coupling the same so that the second wavelength may travel in the second direction of the first transmission line.

Abstract: A transmitting-end device generates a pilot signal with a pilot signal generation section, and transmits a pilot signal to a receiving-end device. At the receiving-end device, a transmission rate modification section detects the transmission band of an optical transmission line based on the amplitude of the pilot signal, and decides a data transmission rate acceptable to the receiving-end device by taking into account the transmission band of the optical transmission line. Based on a maximum data transmission data acceptable to the transmitting-end device and the data transmission rate thus decided, a control section in the receiving-end device arbitrates a data transmission rate between it and the transmitting-end device.

Abstract: An optical communication apparatus comprises an optical transmitter (1) which emits light signals corresponding to external electric signals (11) using light emitted from a short-wavelength light-emitting element (14) such as a yellow light-emitting diode of maximum wavelength in a range of 560–590 nm or a green light-emitting diode of maximum wavelength in a range of 490–550 nm; a plastic fiber (2) including a methacrylate polymer core free from benzene rings and having one end connected optically with the short-wavelength light-emitting element (14), the core containing less than 5 ppm free sulfur; and an optical receiver (3) having a photodetector element (31) connected optically with the other end of the plastic fiber (2) and adapted to producing an output electric signal (35) in accordance with the output from the photodetector element (31).

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: Signal reflection mitigation in fiber-optic networks. Signal reflections are mitigated using near-end echo cancellation, threshold adjustment and/or error correction code. Signal reflections in a receive signal that are caused by near-end connectors may be mitigated using an echo cancellation signal. Signal reflections caused by other discontinuities on a fiber-optic network may be mitigated by using error correction code. Also, an average value of a reflected signal maybe detected and used to set an adjusted threshold value to interpret logical values of an electronic or optical signal.

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.