Abstract: A method of operating a WDM transmission system with at least one transmitter and at least one receiver connected by means of a dispersive transmission line.

Abstract: A method of laterally displacing at least a component of a light beam, the method comprising: a) directing the beam to enter a block of birefringent material at a first location, and at least the component of the beam to pass through the block on a first path to an exit location; and b) changing a polarization of the component of the beam after it has passed through the block, and directing it to pass back through the block from the previous exit location to a next exit location, following a next path oriented at changed angle due to its changed polarization state, at least one time; the component of the beam thereby being laterally displaced from the first location, when it exits the block a last time.

Abstract: The invention pertains to optical fiber transmission systems, and is particularly relevant to optical transport systems employing optical amplifiers. In particular the invention teaches an apparatus and method that allows cost effective co-directional operation of an optical amplifier to support full duplex traffic on a single fiber, and the design of an optical fiber transmission system based on this optical amplifier technology.

Abstract: An optical communication system (100; 2300) comprises at least a transmitter (110) apt to emit a differential phase shift keying (DPSK) optical signal having a bit-rate equal to R, at least a receiving system (1200) for receiving the differential phase shift keying optical signal; and an optical link (130) optically connecting the transmitter and the receiving system for transmitting the DPSK optical signal from the transmitter to the receiving system, wherein the receiving system comprises a coherent optical receiving device (1205) apt to coherently receive the propagated DPSK optical signal and to emit at least one electrical signal (I) related to the received DPSK optical signal, and wherein the receiving system further comprises at least one electrical filter (270) for filtering the at least one electrical signal and having ?3 dB double-side bandwidth greater than or equal to 0.44 R and lower than or equal to 0.68 R, and at least one squarer (280) for squaring the at least one filtered electrical signal.

Abstract: An optical signal, which is a low-speed signal superimposed on a high-speed phase modulated optical signal by intensity modulation, is used. In an optical receiver apparatus 40, a received signal is split, and one of the split signals is O/E converted and low frequency component alone is extracted via a filter 46. A clock is extracted from low-frequency component by CDR, and is compared with a preset frequency. Using the frequency difference obtained, dispersion compensation is performed with low accuracy. Next, the amount of phase control of the delay interferometer 21 is adjusted so that the amplitude of the electrical signal is maximized. An error rate is measured, and fine adjustment is performed to improve the error rate.

Abstract: A chromatic dispersion compensation control method for compensating the chromatic dispersion of an optical transmission path with a variable dispersion compensator inserted in the optical transmission path is disclosed.

Abstract: An economic way of determining the chromatic dispersion along a link of a DWDM network is provided. A transmitter modulates the output signals of two lasers operating at two different wavelengths and the modulated output signals are sent into the link. Detectors at each one of a plurality of detection sites along the link determine a phase difference in modulation between the output signals of the two lasers. The chromatic dispersion for each detection site can be calculated from the modulation frequency and determined phase differences at that site.

Abstract: An optical communications system comprises a transmitter, a receiver and an optical communications link between the transmitter and receiver. The transmitter comprises a current-driven directly modulated laser for providing a modulated optical signal and a current controller for controlling the current waveform applied to the laser. The current waveform applied to the laser is determined to compensate for the effects of the laser non-linearities and the fiber chromatic dispersion. This system applies pre-compensation to the directly modulated laser input current waveform to provide both pre-compensation for chromatic dispersion and compensation for the non-linearities of the directly modulated laser. These are two of the main limiting factors in providing a low cost high data rate and long reach optical communications system.

Abstract: This application describes devices and techniques for dynamically controlling polarization light at one or more locations along the optical transmission path to reduce optical noise and PMD in the optical signal. One device according to an implementation includes a polarization controller to receive an optical signal and operable to control polarization of the optical signal in response to a control signal, a fixed optical polarizer to receive output from the optical polarization controller and to produce an output optical signal, and a circuit to receive a fraction of the output optical signal from the fixed optical polarizer and operable to produce the control signal in response to an output power level of the output optical signal which controls the polarization controller to maximize the output power level.

Abstract: A dynamic dispersion compensation system and method are provided. The method dynamically compensates for dispersion in an optical signal by recovering a first clock and a second clock from a first polarization component and a second polarization component of the optical signal respectively, determining a delay time between the first clock and the second clock, determining the dispersion based on the delay time and dynamically compensating for the determined dispersion. The system comprises a polarization beam splitter, a clock recoverer, a dispersion determiner and a tunable dispersion compensation module and is operable to dynamically compensate for the dispersion in an optical signal.

Abstract: Methods and apparatus (100) for composing, generating and transmitting information-bearing optical signals are provided. An information-bearing electrical signal is composed (108) having desirable spectral properties, preferably configured to ensure that undesired interference between electrical spectral components generated in a square-law direct detection process (120) at a corresponding optical receiver (104) is substantially avoided. Predistortion (110) is advantageously applied to transmitted signals, in order to account for a nonlinear relationship arising in a modulation process (114) between electrical signal amplitude and corresponding optical field amplitude. Orthogonal frequency division multiplexing (OFDM) techniques may be applied to composed signals having the desired characteristics, and additionally may facilitate the application of frequency domain equalisation (128) in order to mitigate transmission impairments, including dispersion.

Abstract: Certain aspects of a method and system for optimum channel equalization between a host Serializer-Deserializer (SerDes) and an optical module may compensate and reduce dispersion loss along an electrical transmit path of a transmitter and an optical transmit path coupled to the transmitter via pre-emphasis. The data degradation as a result of the dispersion loss along the electrical transmit path of the transmitter and the optical transmit path coupled to the transmitter may be recovered by equalizing signals received via an electrical receive path of a receiver communicatively coupled to the transmitter.

Abstract: An optical packet network system of a ring type, capable of preventing degradation of an optical signal, can be implemented by providing a mechanism relatively simple in structure, capable of erasing light noise if the optical packet signal does not exists. In the optical packet network system made up by interconnecting respective nodes adjacent to each other, and connecting a sending source of an optical packet signal to a ring, a light noise removal function block is provided between the respective nodes adjacent to each other.

Abstract: An optical repeater device of the present invention comprises: a preamble compensating circuit 53, for taking out a normal data signal from burst signals propagating through a communication transmission path, and for adding a preamble signal before and/or after the data signal. Furthermore, the preamble compensating circuit 53 comprises: a detector circuit 53a, for inputting the burst signal, and for outputting only the normal data signal; a buffer circuit 53b, for storing the data signal output from the detector circuit 53a, and for outputting thereof; a preamble signal generation circuit 53d, for outputting at least one type of the preamble signal; and an data output select circuit 53e, for outputting the data signal at the time of the data signal input from the buffer circuit 53b, and for outputting the preamble signal from the preamble signal generation circuit 53d at any other time thereof.

Abstract: An automatic threshold voltage adjustment circuit, a method of automatically adjusting threshold voltage and an optical receiver for an optical communication system. In one embodiment, the circuit includes: (1) an amplitude detector configured to detect an amplitude of a received optical signal, (2) a variable resistor coupled to the amplitude detector and including a field-effect transistor configured to operate in a triad mode to provide a resistance that varies substantially linearly based on the amplitude and (3) an operational amplifier coupled to the variable resistor and configured to apply a variable gain based on the resistance to an input threshold voltage to yield an adapted threshold voltage.

Abstract: A distortion compensating apparatus which compensates for distortion in a waveform of a received light signal through a digital signal processing includes a plurality of fixed amount compensators which compensate for the distortion in the waveform at respective given compensating amounts. The combination of operating states of the plurality of fixed amount compensators is changed by on/off switching of each of the plurality of fixed amount compensators, and the plurality of fixed amount compensators are cascaded.

Abstract: The invention includes methods and apparatuses to adjust an optical signal transmitted through an optical amplifier, such as in a wavelength division multiplexed optical network. The methods and apparatus of the invention calculate polarization effects which cause degradation to the optical signal. A measurement of the polarization-related degradation of an optical signal is calculated by using at least one reference signal. In some embodiments of the invention, the reference signal is depolarized or has scrambled polarizations. The invention is typically used in long-haul optical networks.

Abstract: A method and device for reducing the distortion of optical pulses caused by the polarization mode dispersion in optical communication systems is provided. When an optical pulse having any polarization is transmitted through an optical communication system, which is optically anisotropic, at least in sections, the optical pulse may become distorted due to the different velocities of the various polarization components. This distortion of the optical pulses may reduces the maximum transmission rate of the system. A method is provided for functioning in response to the detected transmission quality of the communication system where a polarization-controlling device for setting the polarization of the optical pulse is driven in such a way that the transmission quality is maximized. An optical communication system, including an optical transmission medium, involves a device for determining the transmission quality of the communication system, a regulating device, and a polarization-controlling device.

Abstract: A chromatic dispersion monitoring apparatus according to the present invention comprises: a photodetector which photo-electrically converts an optical signal; a low-pass filter which limits a frequency bandwidth of the photo-electrically converted electrical signal to be within a range set according to a modulation format of the optical signal and a bit rate thereof; a DC elimination circuit which eliminates a direct current component of the bandwidth limited electrical signal; and a power detector which detects the power of the bandwidth limited electrical signal to detect the residual dispersion of the optical signal. As a result, it becomes possible to easily realize the chromatic dispersion monitoring apparatus of low cost, which is also capable to be arranged on an in-line.

Abstract: To compensate a waveform distortion by using a nature that a spectral shape is perfectly retained even if all the linear distortions occur on a time-axis. An optical pulse transmitted from an optical pulse transmitter (1) via an optical fiber transmission line (2) is transmitted. An optical Fourier transformer (3) receives an optical pulse, and optically Fourier-transforms an optical pulse on a time-axis onto a frequency-axis to reproduce the frequency spectrum of an optical pulse on a time-axis be effecting switching between frequency and time, thereby compensating a waveform distortion by a linear effect on the optical fiber transmission line (2). A photodetector (4) receives an optical pulse from the optical Fourier transformer (3) and transforms this into an electrical signal to thereby obtain a pulse waveform before a transmission over the optical fiber transmission line (2).

Abstract: Embodiments of an integrated circuit are described. This integrated circuit includes a clock-generator circuit configured to provide a clock signal and an optical clock path coupled to the clock-generator circuit. Note that the optical clock path is configured to distribute optical signals corresponding to the clock signal. Furthermore, note that a given optical signal has a phase which is different than phases of the other optical signals.

Abstract: An optical communication system combines strong electrical pre-filtering of data at the transmitter and digital feedback equalization (DFE) at the receiver to enhance spectral efficiency. The system can be applied to optical networking and digital communication systems, including binary modulated systems optical network systems.

Abstract: A propagation apparatus includes a plurality of dispersion compensation execution units which accept a signal of a single wavelength from a wavelength-multiplexed signal which is received and execute dispersion compensation on the signal by inputting the accepted signal to a tunable dispersion compensator with an adjusted dispersion value, and a dispersion value calculation unit which acquires each dispersion value adjusted by the plurality of the dispersion compensation execution units, approximates the dispersion value of the wavelength assigned to a newly built line by using the acquired dispersion values whose signal error rates are in a tolerable range, and sets the approximated dispersion value as an initial value in the tunable dispersion compensator of the newly built line.

Abstract: A dispersion compensation type optical signal receiving apparatus includes: an APD element for converting input signal light inputted from a transmission line into an electric signal; an amplifying device constituted with a preamplifier circuit and a limit amplifier circuit, which amplifies the electric signal converted by the APD element; an EDC IC for compensating the dispersion in the transmission line electrically; and a clock/data reproducing circuit for reproducing the clock and data signal contained in the input signal light, wherein there is provided a VOA for limiting the amplitude of the input signal light inputted to the APD element and an attenuation amount controlling circuit for controlling the attenuation amount of the VOA in accordance with the bias current of the APD element.

Abstract: For transmitting information on an optical fiber, a plurality of information carrier channels at different carrier frequencies and a plurality of filling channels are used. The filling channels are transmitted together with the information carrier channels along the fiber. The total optical power of the information carrier channels and the filling channels transmitted on the fiber is maintained constant by compensating every change of the optical power of the information carrier channels by an inverse change of the optical power of the filling channels. The change of the optical power of the filling channels is distributed to the individual filling channels such that a minimum displacement of the center of gravity of the common spectrum of information carrier channels and filling channels results.

Abstract: A semiconductor laser comprises an electrically isolated active section and at least one noise reducing section and operates on a ground state transition of a quantum dot array having inhomogeneous broadening greater than 10 nm. The laser preferably emits more than 10 optical modes such that a total relative intensity noise of each optical mode is less than 0.2% in the 0.001 GHz to 10 GHz range. The spectral power density is preferably higher than 2 mW/nm. An optical transmission system and a method of operating a quantum dot laser with low relative intensity noise of each optical mode are also disclosed.

Abstract: A method of reducing Raman tilt in a transmission apparatus capable of transmitting a plurality of signals, occupying contiguous channels in a transmission band, through a length of optical transmission cable which exhibits the Raman effect of transferring energy from the shorter wavelength signals at one end of the transmission band towards the longer wavelength signals at the other end of the transmission band, including the transmission of half the maximum number of signals at twice the normal channel frequency spacing at a higher-than-normal level and the transmission signals in selected ones, fewer than all, of the available channels at the normal channel spacing at a normal power level. As new channels are added at the lower frequency channel spacing, the powers of both neighboring channels are reduced to the normal power level.

Abstract: In order to enhance dispersion control, the apparatus includes a dispersion controller; a quality index generator generating a quality index representing a quality of an optical signal output from the dispersion controller; and a searching unit searching for an amount of dispersion control applying to the dispersion controller which amount optimizes the quality index, wherein the searching unit includes a splitting-half searching unit roughly searching, in a splitting half method, a range in which dispersion is controllable by the dispersion controller for an amount of dispersion control such that the quality index generated by the quality index generator becomes preferable, and a sweep searching unit thoroughly searching, by sweeping, a limited range based on the amount of dispersion searched by the splitting-half searching unit for an amount of dispersion control that optimizes the quality index generated by the quality index generator.

Abstract: An optical wavelength controlling method and a system thereof for an optical wavelength division multiplexing transmission system, wherein a plurality of wavelengths of channels are multiplexed and transmitted by an optical transmitting unit, and the multiplexed wavelengths are divided into the wavelengths of the channels by an optical receiving unit, are disclosed. The optical wavelength controlling method includes: a step of reducing optical power of the wavelength of a target channel, and transmitting the wavelengths; a step of evaluating channel crosstalk based on a code error rate of a channel adjacent to the target channel, and detecting a shift of the wavelength of the target channel; and a step of compensating for the shift of the wavelength of the target channel.

Abstract: An optical transmission apparatus includes an optical add drop multiplexer (OADM) that adds/drops an optical signal to/from a transmission path. The optical transmission apparatus further includes a pump light multiplexer and a dispersion compensation fiber that are located downstream of the OADM on the transmission path. The optical transmission apparatus is configured to house a pump light source connectable to the pump light multiplexer to Raman amplify an optical signal in the dispersion compensation fiber.

Abstract: An active cable that is configured to communicate over much of its length using one or more optical fibers, and that includes an integrated electrical connector at least one end. The active cable includes an integrated retiming mechanism. Thus, multiple links of cable may be used while reducing the chance that the jitter will exceed allowable limits. The cable may be an electrical to optical cable, and electrical to electrical cable, or one of many other potential configurations.

Abstract: A bias-control circuit that provides operating point control for a Mach-Zehnder modulator experiencing optical absorption at their interferometric arms. The bias control circuit generates compensation signals that are used to counter the thermally induced index shifts as a result of absorption. In addition, an operating point with desirable transmitter characteristics can also be arbitrarily chosen by over-compensating or under-compensating thermal effects.

Abstract: Methods and apparatus for optical-power control in an optical network employing wavelength-division multiplexed (WDM) optical-fiber links are devised to circumvent the effect of crosstalk caused by optical-power scattering. Each carrier signal is amplitude-modulated by an identifying tone, with the power of an identifying tone having a predetermined ratio to the power of its carrier signal. A fiber span within an optical-fiber link is tapped at a preferred monitoring point, and the power spectrum of the envelope of the tapped optical signal is measured. To estimate an individual carrier power, a temporary gain is applied and the power of a corresponding tone is measured. To control optical power of each wavelength carrier in several spans in the network, a network controller selects an order of processing the spans of interest, and selects the order of processing of each channel within each span.

Abstract: The invention relates in particular to an optical regeneration device for a signal carrying an item of information encoded by phase modulation of that signal, that signal being transmitted over an optical network and comprising a temporal succession of optical pulses. The device comprises an optical pulse nonlinear phase shift module, a linear pulse broadening module a linear pulse broadening module, and a module for the linear compensation of the broadening undergone by the pulses in the linear broadening module.

Abstract: A method for determining a value of chromatic dispersion compensation in an optical network including a plurality of nodes connected by at least one transmission line, the plurality of nodes including a plurality of dispersion compensators, the optical network including a plurality of wavelength paths between the optional nodes, the method includes determining a compensation value of the dispersion compensators in the optical network by the computer, the compensation value selecting that an error between the object value of the residual chromatic dispersion in accordance with of the first end node of the first path and the permissible value of the residual chromatic dispersion of the first end node of the first path is least, and the value of the residual chromatic dispersion of the first end is in the permissible value of the residual chromatic dispersion of the second end node of the second path.

Abstract: A regenerator (7.x, 7.1-7.3) for regenerating optical signals on optical transmission links (4), in particular for use in a Dense Wavelength Division Multiplex (DWDM) optical transmission system. The regenerator (7.x, 7.1-7.3) comprises optical amplification means (7.xa, 7.xd) for compensating optical power losses, and a deterministic adaptation unit (7.xb) comprising means being adapted to compensate deterministic transmission impairments of the optical transmission link (4), in particular optical dispersion compensating means being adapted to compensate for chromatic dispersion of said link (4). The proposed regenerator (7.x, 7.1-7.3) further comprises a non-deterministic adaptation unit (7.xc) comprising means for compensating time variant non-deterministic transmission impairments, in particular polarisation mode dispersion.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A method of suppressing effects of aliasing in a system for digitally processing a high speed signal having a symbol rate of 1/T. The high speed signal is sampled at a fractional multiple (N) of the symbol rate, wherein 1<N<2, to generate a corresponding sample stream, and filtered using a low-pass filter characteristic having a cut-off frequency corresponding to 1/2T. Phase distortions due to the filtering are compensated by digitally processing the sample stream.

Abstract: A system and method for dispersion compensation of an optical signal in a hybrid network includes generating optical traffic in a first set of one or more channels, wherein the traffic in the first set of channels is modulated using a first modulation technique. Optical traffic is generated in a second set of one or more channels, wherein the traffic in the second set of channels is modulated using a second modulation technique. An optical dispersion pre-compensation is applied to the second set of channels. The first set of channels and the second set of channels are combined to form an optical signal, and the optical signal is transmitted over an optical network.

Abstract: A wavelength dispersion compensation control method determining whether a clock component is contained in an optical signal received from an optical transmission path and, if a clock component if contained in the optical signal, extracting the clock component, and stopping control of a variable wavelength dispersion compensator when no clock component is extracted.

Abstract: Certain aspects of a method and system for optimum channel equalization between a host Serializer-Deserializer (SerDes) and an optical module may compensate and reduce dispersion loss along an electrical transmit path of a transmitter and an optical transmit path coupled to the transmitter via pre-emphasis. The data degradation as a result of the dispersion loss along the electrical transmit path of the transmitter and the optical transmit path coupled to the transmitter may be recovered by equalizing signals received via an electrical receive path of a receiver communicatively coupled to the transmitter.

Abstract: An arrangement is described for compensating intra-channel nonlinearities in an optical communications system which combines optical dispersion compensation with electronic pre-distortion (EPD). EPD with moderate lookup table size can effectively suppress intra-channel nonlinearities over optical transmission links incorporating optical dispersion compensation. The arrangement can be implemented for a variety of optical communications systems, including 10 Gb/s, 40 Gb/s and higher bit rate systems as well as single-channel and wavelength-division multiplexing (WDM) systems.

Abstract: A distortion compensator, an optical receiver and a transmission system including an operation selectively compensating for linear waveform distortion exerted on an optical signal via a plurality of distortion compensators and compensating for nonlinear waveform distortion exerted on the optical signal using nonlinear distortion compensators.

Abstract: The present invention includes a fast algorithm to compute the pre-equalized waveform for simultaneous compensation of the self-phase modulation and chromatic dispersion experienced by a high-speed optical signal, e.g., at 10 Gb/s, and shows that it is used for an automatic self-adapting pre-equalization when the knowledge on transmission link details is inaccurate or incomplete.

Abstract: A multimode optical fiber has an equivalent modal dispersion value (DMDinner&outer) of less than 0.11 ps/m for (??max×D)>0.07 ps/m as measured on a modified DMD graph. The modified DMD graph accounts for chromatic dispersion to ensure that the multimode optical fiber has a calculated effective bandwidth EBc greater than 6000 MHz-km when used with multimode transverse sources.

Abstract: A low-cost configuration of, and at the same time to control the variable dispersion compensator at a high speed in a variable dispersion compensator for compensating the wavelength dependent accumulated dispersion resulting from the wavelength dependency of the transmission fiber and fixed dispersion compensator in a long-distance high-speed WDM transmission system. In order to achieve the object mentioned above, the wavelength dependent representative characteristic of the transmission fibers 4-1 . . . n, and the wavelength dependent representative characteristic of the DCFs 13-1 . . . n are recorded and maintained in advance in the dispersion control circuit 5-1 . . .

Abstract: The invention relates to optical communication, in particular to compensation of non-linear distortions incurred in high bit-rate optical communication systems. A method and system for compensating self-phase modulation at an optical receiver of an optical transmission system using polarization division multiplexing and a modulation scheme with constant amplitude is proposed. The method comprises the step of performing a phase modulation on a received signal, wherein the received signal comprises two signal components associated with two orthogonal polarizations, each component comprising an in-phase sub-component and a quadrature-phase sub-component, thereby spanning a four-dimensional space. The phase modulation is determined by evaluating an error signal which depends on the distance in the four-dimensional space between the received signal after the phase modulation and a four-dimensional sphere defined by target constellation points of the optical transmission system.

Abstract: Provided are a frequency extracting apparatus and a signal extracting system employing the same. The signal extracting system can reduce the effect of an input signal pattern by extracting two frequency components and beating them to extract a desired clock signal, and improve a signal-to-noise ratio of an extracted clock signal. The frequency extracting apparatus includes: a circulator for changing an output direction of an input signal; a reflective filter for extracting a desired frequency component among frequency components of the input signal; a wavelength and amplitude controlling unit; and the frequency amplitude controller.

Abstract: An optical node apparatus according to the present invention amplifies a WDM signal light input to an input port, and thereafter, branches the amplified WDM signal light by an optical branching coupler to send the branched lights to first and second optical paths, and selects the light propagated through the first optical path by an optical switch to amplify the selected light by a post-amplifier, thereby outputting the amplified light from an output port, when the optical node apparatus is operated as an optical amplification repeating node. When the operational state is upgraded to an optical add/drop multiplexing node, an OADM section is connected between a set of connecting ports on the second optical path, and the adjustment of the OADM section is performed utilizing the WDM signal light branched by the optical branching coupler, and thereafter, the switching of the optical switch is performed to select the light on the second optical path side.

Abstract: An apparatus and method directed to testing and optimizing performance of an optical transmission system is disclosed, including at least one broadband dispersion compensation unit (DCU) or at least one depolarization device. The depolarization device may be used alone or in combination with the at least one broadband DCU. A method for optimizing performance of data channels in initial loading (IL) and full loading (FL) configurations of the optical transmission system is also disclosed.