Abstract: A system for reducing clipping may be used between a multichannel RF source and a laser to reduce or correct clipping that might occur in the laser as a result of negative spikes or peaks in a multichannel RF signal. The system generally includes a clipping correction circuit that receives the multichannel RF signal and responsive to the RF signal, prevents one or more of the negative peaks in the RF signal from causing clipping. The clipping correction circuit may either detect an envelope of the RF signal and/or may detect one or more peaks in the RF signal. One or more negative peaks may be prevented from causing clipping by adjusting a bias current provided by a bias control circuit and/or by modifying the RF signal with one or more clipping correction pulses coinciding with one or more negative peaks.

Abstract: A system for reducing clipping may be used between a multichannel RF source and a laser to reduce or correct clipping that might occur in the laser as a result of negative spikes or peaks in a multichannel RF signal. The system generally includes a clipping correction circuit that receives the multichannel RF signal and responsive to the RF signal, prevents one or more of the negative peaks in the RF signal from causing clipping. The clipping correction circuit may either detect an envelope of the RF signal and/or may detect one or more peaks in the RF signal. One or more negative peaks may be prevented from causing clipping by adjusting a bias current provided by a bias control circuit and/or by modifying the RF signal with one or more clipping correction pulses coinciding with one or more negative peaks.

Abstract: A method and system is disclosed for making time alignment for a data transmission system. A first reference clock signal is provided to a first multiplexer coupled to a data modulator through a data driver, and a second reference clock signal is provided to a second multiplexer coupled to a clock modulator through a clock driver. Phase adjustment of the reference clock signal are conducted before the first reference clock signal is provided to the first multiplexer, wherein the phase adjustment aligns a timing of data modulated by the data modulator with a periodically modulated light source generated by the clock modulator.

Abstract: A multiplexer of a transmission section generates a clock signal by multiplying a reference clock signal of a digital image signal by a predetermined number ‘K’. A parallel digital image signal is converted into a serial digital signal on the basis of the clock signal, and the serial digital signal is converted into an optical signal in an optical transmission section for transmitting. A demultiplexer extracts a reception clock signal from a serial digital reception signal which is converted into an electric signal in an optical reception section of a reception section, the serial digital reception signal is converted into a parallel signal and a signal corresponding to the parallel digital image signal on the basis of the reception clock signal, and a clock signal corresponding to the reference clock signal is recovered by multiplying the reception clock signal by ‘1/K’.

Abstract: A communication system includes an optical transmitter which is differentially driven and an optical receiver that outputs a differential signal. The optical transmitter creates the differential drive signal from an input signal and delivers the differential drive signal to a laser. The differential drive signal is generated with a transformer and RF chokes for floating the laser above ground. The signal detected by the receiver is input as a differential signal to a transformer which then passes the signal through amplifiers and a filter. The optical communication system provides an increased spurious-free dynamic range which is well suited for RF signals and other analog signals.

Abstract: Methods and apparatus are provided for reducing Raman crosstalk in a wavelength-division-multiplexing (WDM) optical fiber transmission system that transmits a multiplex of channels. Idle data is sent over one or more of the channels of the WDM system in order to maintain the optical link when user data is not being sent. The idle data has an idle data pattern, which can be controlled such that a power spectral density of a signal carried by at least one channel is shifted in order to reduce Raman crosstalk between the channels. For example, the power spectral density may be shifted away from lower frequencies of the channel, and toward the higher frequencies, by controlling the idle data pattern. Alternatively, the power spectral density may be shifted towards unused frequencies of the channel, by controlling the idle data pattern.

Abstract: An optical wavelength multiplexing frequency shift keying modulation system. The system includes an optical wavelength multiplexing signal acquisition unit for outputting an optical wavelength multiplexing signal. A n optical frequency shift keying modulation unit acquires an optical frequency shift keying signal, including an upper side band signal and a lower side band signal, by performing frequency modulation to the optical wavelength multiplexing signal output from the optical wavelength multiplexing signal acquisition unit. An optical frequency shift keying signal separation unit separates the optical frequency shift keying signal output from the optical frequency shift keying modulation unit into an upper side band signal and a lower side band signal.

Abstract: It is an object of the present invention to provide a control technique for reducing wavelength dependence of wavelength dispersion values and also for suppressing a change in wavelength transmission characteristic with a temperature variation or the like, in a VIPA-type wavelength dispersion compensator.

Abstract: A method of manufacturing an optical transmitter includes assembling a laser device on a module including a temperature sensor and a temperature controller. An optimum operating temperature of the laser to minimize optical distortion is determined at a temperature within a range between which distortions were determined at multiple temperatures. The temperature controller is selectively adjusted so as to operate the laser at the optimum temperature. The distortion may also be monitored during active laser operation. The temperature controller may be selectively adjusted, based on the monitoring of the distortion, so as to operate the laser at a new controlled temperature nearer that which produces the temperature-dependent distortion minimum.

Abstract: The disclosed device and method include varying phases of two data signals at a first predetermined frequency, performing multi-level phase modulation of a light based on the two data signals whose phases are varied at the first predetermined frequency, extracting a component having the first predetermined frequency from an optical signal subjected to the phase modulation, and controlling the phases of the two data signals based on the component extracted from the optical signal.

Abstract: An apparatus and a method for transmitting at least a digital optical signal with return-to-zero phase-shift keying, employing a single optical modulator with dual-drive design, the encoded optical signal having improved spectral efficiency and performances and being generated by transmitters with simplified scheme; an optical communication system comprising the transmitting apparatus, a transmission line and an apparatus to receive the optical signal.

Abstract: A method and apparatus for controlling bias and alignment in an optical signal transmitter for providing intensity modulation and DPSK modulation to an optical signal, e.g. in an RZ-DPSK modulation format. Output power in dither signals applied to the bias signals may be detected by a low speed photodetector. One or more of the bias signals may be adjusted in a low speed control loop in response to an error signal obtained by mixing the detected signal with the low frequency dither signals.

Abstract: An optical transmitter including a multi-lambda source to output injection light consisting of a plurality of injection wavelengths in channels, a circulator having a first port, a second port, and a third port, the circulator receiving the injection light at the first port, and outputting the received injection light to the second port, and further receiving signal light at the second port, and outputting the received signal light to the third port, an arrayed waveguide grating having a multiplexing port connected to the second port of the circulator, and a plurality of demultiplexing ports, spectrum-slicing injection light received from the circulator at the multiplexing port into a plurality of injection channels, and outputting the injection channels to the demultiplexing ports and further receiving and multiplexing a plurality of signal channels at the demultiplexing ports, into a signal light, and outputting the signal light to the multiplexing port, and a plurality of reflective semiconductor optical a

Abstract: An optical communication system includes an optical transmission apparatus and an optical receiving apparatus. The optical transmission apparatus includes an input port to receive an electric signal, a noise generator to generate noise, a transmission signal generator to generate a transmission signal by multiplexing the noise with the electric signal, and an electric/optical converter to convert the transmission signal into an optical signal and send out the optical signal to an optical transmission path. The optical receiving apparatus connected to the optical transmission apparatus via the optical transmission path and receiving the optical signal through the optical transmission path. The optical receiving apparatus includes an optical/electric converter to convert the optical signal received through the optical transmission path into a receive electric signal and a receiving filter to remove the noise from the receive electric signal.

Abstract: Optical dispersion imposed on a communications signal conveyed through an optical communications system is compensated by modulating the communications signal in the electrical domain. A compensation function is determined that substantially mitigates the chromatic dispersion. The communications signal is then modulated in the electrical domain using the compensation function. Electrical domain compensation can be implemented in either the transmitter or the receiver end of the communications system. In preferred embodiments, compensation is implemented in the transmitter, using a look-up-table and digital-to-analog converter to generate an electrical predistorted signal. The electrical predistorted signal is then used to modulate an optical source to generate a corresponding predistorted optical signal for transmission through the optical communications system.

Abstract: The present photonic RF generation and distribution system provides a system and method for distributing an RF output signal. The photonic RF distribution system includes two optical sources for generating optical signals. A first optical source (42) is operable to generate a first optical signal having an operating frequency. A second optical source (44) is operable to generate a second optical signal having an operating frequency. A modulator (46) is operable to impress an RF modulation signal on a tapped portion of the first optical signal such that a modulated signal is generated. A first coupler (52) combines the modulated signal with a tapped portion of the second optical signal, thereby forming a combined signal having a difference frequency component. A control photodetector (50) is responsive to the combined signal to generate a tone signal.

Abstract: An optical spike is generated at an arbitrarily selected location within an arbitrary optical link. The optical spike is generated by deriving a spike signal having a plurality of components, and launching the spike signal into the a transmitter end of the optical link. An initial phase relationship between the components is selected such that the involved signal components will be phase aligned at the selected location. In order to achieve this operation, the initial phase relationship between the components may be selected to offset dispersion induced phase changes between the transmitter end of the link and the selected location. One or more optical spikes can be generated at respective arbitrarily selected locations within the link, and may be used for performance monitoring, system control, or other purposes.

Abstract: The inventors propose herein a switch fabric architecture that allows broadcasting and fast channel access in the ns-range. In various embodiments of the present invention, 10 Gb/s receiver modules are based on a novel heterodyne receiver and detection technique, which is tolerant to moderate wavelength drifts of a local oscillator. A gain clipped electrical amplifier is used in the novel receiver as a rectifier for bandpass signal recovery.

Abstract: An optical transmitter and methods of generating an optical signal having SBS suppression are described. An optical transmitter having SBS suppression according to the present invention includes a signal generator that generates a SBS suppression signal. A laser generates a line width broadened optical signal having AM noise. A signal processor generates a modified SBS suppression signal from the SBS suppression signal. A modulator modulates the line width broadened optical signal having the AM noise with a payload modulation signal and with the modified SBS suppression signal to generate a payload modulated optical signal having SBS suppression and reduced AM noise.

Abstract: An optical transmit circuit that includes an electro-optic transducer driver and an electro-magnetic interference (“EMI”) reduction filter. The EMI reduction filter is coupled to an output terminal of the electro-optic transducer driver. This allows the EMI reduction filter to receive an electrical signal from the transducer driver. The EMI reduction filter then filters out a significant portion of the EMI of concern from the electrical signal.

Abstract: Optical impairments such as dispersion and fibre nonlinearity are compensated by generating a pre-distorted electrical signal at the transmitter. This signal is modulated onto a carrier signal, so that it is upconverted in frequency. This up converted signal is then used to modulate an optical source. Generally the optical signal will have two sidebands, one of which has the correctly pre-distorted information and the other which is unwanted. Information in the unwanted optical sideband is either filtered optically or electrically. In the preferred embodiments, the transmitter uses a tunable semiconductor laser with an integrated electroabsorption modulator to modulate the light. The preferred receiver is a coherent receiver with a tunable local oscillator laser. The receiver uses an electrical filter to remove the information in the unwanted sideband.

Abstract: An optical transmitter and an optical transmission method includes a plurality of light-emitting elements, a plurality of light-receiving elements for monitoring optical outputs from the light-emitting elements, a linear operation circuit for calculating optical output monitor signals by removing crosstalk parts from a plurality of photoelectric conversion currents outputted from the light-receiving elements, and a drive circuit for driving individually currents to apply to the light-emitting elements based on the optical output monitor signals.

Abstract: An optical RZ transmitter comprises an optical signal source and a pair of electro-optical modulators in tandem, one arranged to receive a NRZ electrical data signal and the other a clock signal at the data rate of the data signal. The phase difference between the data signal and the clock signal is controlled by adding a first dither signal to a bias signal applied to the modulator receiving the data signal, and a second dither signal, having a different frequency, to the phase difference. The amplitude of variations in the power of the optical output signal corresponding to cross-modulation of the first and second dither signals is detected and the phase difference is controlled in response to the detected amplitude.

Abstract: A method and system for mitigating effects of dispersion in an optical link. A pair of digital sample streams are synthesized representing a target optical E-field having a spectrum selected such that the convolution of the spectrum with itself yields a signal having beat terms that contain phase information of the target optical E-field. A complex optical modulator is driven in accordance with the computed orthogonal sample values.

Abstract: An optical transmission system including an optical transmitting device and an optical receiving device. The optical transmitting device includes a data signal splitting section for splitting data signal information into at least two parts and generating at least two electrical signals having different center frequencies and bands, a frequency multiplexing section for performing frequency multiplexing for the at least two electrical signals, and an electrical-to-optical conversion section for converting the frequency-multiplexed signal to an optical signal and sending it to an optical transmission path. The optical receiving device includes an optical-to-electrical conversion section for converting the optical signal to a frequency-multiplexed signal, a band demultiplexing section for demultiplexing the frequency-multiplexed signal to obtain at least two electrical signals, and a data signal recovering section for recovering the data signal based on the at least two demultiplexed electrical signals.

Abstract: The invention concerns a transmitter circuit comprising a light source (20) and arranged to operate said light source (20) to transmit optical communication signals in response to balanced electric input signals from a first (11) and a second (12) circuit point. The transmitter circuit comprises a first (21) and a second (22) circuit branch which extend from said first (11) and second (12) points, respectively. The light source (20) is connected between the circuit branches (21, 22). The components which are positioned on the circuit branches (21, 22) are selected such that the transmitter circuit is formed with a symmetry which is such that, under normal operation conditions, a balanced drive voltage is the case between the connection points (13, 15) of the light source (20) on the circuit branches (21, 22) and such that the modulation current which drives the light source (20) essentially only depends on the voltage difference between said connection points (13, 15).

Abstract: A method for transmitting digital data includes splitting a coherent optical carrier having a subcarrier into mutually coherent optical carriers, producing corresponding sequences of phase shifts in each of the mutually coherent optical carriers, and then, interfering the mutually coherent optical carriers. The interfering produces an output optical carrier whose subcarrier has modulated inphase and quadrature components with a corresponding sequence of pairs of values. The pairs of values of the modulated inphase and quadrature phase components produced by the interfering correspond to a sequence of coordinate pairs for the signal points the 4-PSK 2D, 16-QAM 2D, or 16-PSK 2D constellation.

Abstract: The multi-channel optical transmitter is composed of a tunable optical signal source, an optical multiplexer and an intensity reducer. The tunable optical signal source includes a tunable laser, and additionally includes an optical signal output through which it outputs an optical signal to one of the inputs of the optical multiplexer. The intensity reducer is for reducing the intensity of the optical signal output by the optical signal source during tuning of the tunable laser. The intensity reducer prevents the tunable optical signal source from injecting high levels of noise into the channels during tuning of the tunable optical signal source.

Abstract: An optical transmitter for an optical fiber transmission system is described. The optical transmitter includes an optical source that generates an optical signal having a wavelength at an output. An optical intensity modulator modulates the optical signal with an electrical modulation signal to generate a modulated optical signal at an output. At least one parameter of the optical intensity modulator is chosen to suppress at least one of phase and sideband information in the modulated optical signal. An optical fiber is coupled to the output of the optical intensity modulator. The suppression of the at least one of the phase and the sideband information in the modulated optical signal increases an effective modal bandwidth of the optical fiber.

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: In a system connecting a transmitter and a receiver using transmission paths and repeaters (in-line amplifiers), red chirping whose ? parameter is performed for an optical signal on a transmitting side. Each of the repeaters includes a dispersion-compensator for compensating the amount of dispersion on a preceding transmission path. The amount of dispersion compensation of the dispersion-compensator included in the transmitter is made constant. The dispersion-compensator included in the receiver is arranged in order to compensate the amount of dispersion on a preceding transmission path. A spread of a pulse width on a transmission path can be efficiently compensated by using the compensation capability of the dispersion-compensators and the red chirping on the transmitting side.

Abstract: An optical transmitter comprises an amplitude modulation unit performing amplitude modulation of only a one-side amplitude of a main signal with a low-frequency signal having a predetermined frequency. An optical modulator receives an input signal generated after the one-side amplitude modulation, and modulates an incoming light in response to the received signal in accordance with a predetermined modulation-characteristic curve to output an optical output signal. An operating point control unit applies a predetermined bias voltage to the optical modulator to control a level of the input signal substantially applied to the modulation-characteristic curve so that the one-side amplitude of the main signal is applied to a minimum portion of the modulation-characteristic curve of the optical modulator.

Abstract: A wavelength multiplex transmission system is provided to reduce crosstalk among wavelengths and reduce deterioration of signals. At a transmission apparatus, one input signal is differentially divided into two; each of the two is converted to an optical signal; and then they are wavelength-multiplexed and transmitted. When crosstalk is arisen in the wavelength multiplex transmission system, the crosstalk is superposed on the two optical signals. The crosstalk is equally superposed on each of the signals with inverted polarities. Accordingly, converting the optical signals to electrical signals and then differentially combining them at a receiving apparatus, their signal components are accumulated, while their crosstalk components are cancelled out. Thereby, in the wavelength multiplex transmission system, deterioration of optical signals due to crosstalk can be reduced.

Abstract: Processing a received optical signal in an optical communication network includes equalizing a received optical signal to provide an equalized signal, demodulating the equalized signal according to an m-ary modulation format to provide a demodulated signal, decoding the demodulated signal according to an inner code to provide an inner-decoded signal, and decoding the inner-decoded signal according to an outer code. Other aspects include other features such as equalizing an optical channel including storing channel characteristics for the optical channel associated with a client, loading the stored channel characteristics during a waiting period between bursts on the channel, and equalizing a received burst from the client using the loaded channel characteristics.

Abstract: A cosite interference rejection system allows cancellation of large interfering signals with an optical cancellation subsystem. The rejection system includes an interference subsystem coupled to a transmit system, where the interference subsystem weights a sampled transmit signal based on a feedback signal such that the weighted signal is out of phase with the sampled transmit signal. The optical cancellation subsystem is coupled to the interference subsystem and a receive antenna. The optical cancellation subsystem converts an optical signal into a desired receive signal based on an interfering coupled signal and the weighted signal. The weighted signal is therefore used to drive the optical cancellation subsystem. The rejection system further includes a feedback loop for providing the feedback signal to the interference subsystem based on the desired receive signal.

Abstract: An optical transmission system for optimizing the bias of a laser diode during an SCM analog optical transmission includes an optical transmitter for converting a baseband electric signal into an optical signal using a laser diode according to the set bias and outputting the optical signal through an optical line, an optical receiver for converting the optical signal transmitted from the optical transmitter into the baseband electric signal, a recovery unit for detecting an error generated according to the bias of the laser diode on the basis of the electric signal converted by the optical receiver, and a bias adjuster for optimally adjusting the bias of the laser diode on the basis of a value of the error detected by the reproducer.

Abstract: A fiber optic communication system is provided that includes a light source adapted to emit a system optical signal and an electrical signal source adapted to provide a data input electrical signal. Additionally, the fiber optic communication system includes a feed forward photonic modulation circuit adapted to receive the data input electrical signal and the system optical signal and output a final modulated optical signal substantially free from residual error.

Abstract: System and method for even order and odd order nonlinear distortion of a compensating signal that removes substantially all of the nonlinear distortion in one order or in two orders. Two or more diodes are arranged in at least one of an anti-series configuration and an anti-parallel configuration in which a circuit voltage is equal to a selected odd order and/or to a selected even order in current, plus higher order terms that are often negligible. The diodes may be replaced by other selected nonlinear devices.

Abstract: Laser line-width compensation is performed by detecting noise in an optical signal output by a laser of an optical communications system and controlling a complex modulator to cancel the detected noise. Line-width compensation can be performed for both amplitude and phase noise in the optical signal. Noise measurements are used to compute a complex scalar. The complex scalar is used by a compensation processor to modify an input signal that is to be transmitted by the optical communications system. The modified input signal controls the complex modulator, which modulates the output signal to cancel the noise.

Abstract: The present invention relates to a method for the modulation of the signal power in optical transmission systems comprising an optical amplification device. Also a method for the detection of bit errors in the processing of digitalized transmitted data is disclosed whereby the data are transmitted by an optical transmission system.

Abstract: Cost-reduction in an optical communication unit is achieved by using spectrum-sliced modulated broadband light for transmitting upstream signals, instead of using laser light. An optical communication system includes at least one pair of optical communication units that each has a bi-directional network interface in which physical bit rates of transmission signals and reception signals are identical, an optical transmitter, and an optical receiver, and that performs bi-directional transmissions via at least one optical fiber. One optical communication unit includes a physical bit rate down-converter that lowers the physical bit rate of transmission signals from the bi-directional network interface and outputs to the optical transmitter, and the other optical communication unit includes a physical bit rate up-converter that raises the physical bit rate of signals received by the optical receiver and outputs to the bi-directional network interface.

Abstract: A distortion monitor for a non-linear device is provided. The control circuit includes an input coupleable to receive a signal from the non-linear device and a first frequency monitor coupled to the input. The frequency monitor monitors the level of one of even and odd order distortion at a first frequency and creates a first signal indicative of the level of the distortion without the use of a pilot tone.

Abstract: Optical equalization across N (an integer, N>1) channels of a multi-channel link of a communications network, is accomplished by averaging effects of optical performance variations within each of the M (an integer, M>1) parallel data signals. At a transmitting end node of the link, each one of the M data signals are distributed across the N channels of the link. Thus a substantially equal portion of each data signal is conveyed through the link in each one of the N channels. At a receiving end node of the link, respective bit-streams received over the N channels to are processed recover the M data signals. As a result, bit error rates of the bit-streams received through each channel are averaged across the M data signals, all of which therefore have a substantially equal aggregate bit error rate.

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 transmitter and methods of generating an optical signal having SBS suppression are described. An optical transmitter having SBS suppression according to the present invention includes a signal generator that generates a SBS suppression signal. A laser generates a line width broadened optical signal having AM noise. A signal processor generates a modified SBS suppression signal from the SBS suppression signal. A modulator modulates the line width broadened optical signal having the AM noise with a payload modulation signal and with the modified SBS suppression signal to generate a payload modulated optical signal having SBS suppression and reduced AM noise.

Abstract: This invention discloses a method to easily extract a header from an optical packet. An optical data transmission method to transmit an optical packet composed of a header and data containing steps of generating a second clock which has a frequency equal to one integer of that of a first clock carrying the data and synchronizes with the first clock, and carrying the header information on the second clock.

Abstract: A system for matching a optical filter characteristic of a first filter tunable in wavelength with an optical first signal comprises a modulator for modulating at least a part of the first signal with a modulation signal before being applied to the first filter. An analyzing unit derives a control signal for tuning the first filter by analyzing the modulated first signal after passing the first filter in conjunction with the modulation signal.

Abstract: A transmitter for optical communication systems includes a source of optical radiation, a source of complex non-information signals, and a modulator unit in communication with the source of optical radiation. The modulator unit is also in communication with the source of complex non-information signals. The modulator has an input adapted to receive information-bearing signals.

Abstract: The transmission system is suitable for amplitude modulated controlled phase optical signals (S) having an optical phase in each low level pulse that precedes or follows a high level pulse. The system includes an optical link (L) and, to allow a high transmitting power, optical corrector means (FG) are provided for applying optical filtering to the signal R at the exit (B) of the link and/or at one point or a plurality of points of the link (L), to compensate widening of its spectrum that the controlled phase signal (S) may suffer because of phase self-modulation during its transmission. Application to long-haul optical transmission.

Abstract: In an optical transmission system, a multiplexer frequency-division-multiplexes a plurality of signals, and outputs the resultant signal to an FM modulator. The FM modulator converts the frequency-division-multiplexed signal into an FM modulated signal through frequency modulation using the frequency-division-multiplexed signal as an original signal. A frequency-divider converts the FM modulated signal into a frequency-divided FM modulated signal whose frequency is ½n (n is an integer of not less than 1) the frequency of the FM modulated signal. An optical modulator has a predetermined input-voltage vs. output-optical-power characteristic, and is biased at the minimum point (voltage) about the output optical power. The optical modulator modulates an unmodulated light fed from a light source with the applied frequency-divided FM modulated signal to produce an optical signal whose optical carrier component is suppressed, and sends the optical signal to an optical transmission line.