Abstract: A method and apparatus for controlling phase alignment in a modulator of a transmitter in an optical communications system utilizes an RF power signature to tune phase alignment. A portion of the optical signal is tapped and converted to an electrical signal. An electrical band-pass filter and RF detector examines a narrow slice of the RF spectrum and utilize the detected RF power to control phase alignment between the data modulator and pulse carver. Another portion of the optical signal is multiplied by the pulse carver clock, filtered and integrated in order to generate a second phase control signal for controlling the relative phase of a dual arm modulator being used as the pulse carver in one embodiment.

Abstract: A method of controlling phase alignment in a modulator of a transmitter in an optical communications system uses a narrowband optical filter to monitor changes in power spectral density of a modulated output at and around the optical carrier frequency. In one embodiment, a method controls alignment of a carrier-suppressed-return-to-zero (CSRZ) pulse train in accordance with changes in the power spectral density of the CSRZ modulated optical signal at and around the optical carrier frequency and generates phase adjustment control signals by executing a phase-control loop to maintain the power spectral density of the CSRZ modulated output at the optical carrier frequency at a desired level.

Abstract: A modulator arrangement adapted to use a differential quadrature phase shift key for use in an optical wavelength division multiplex (WDM) optical communications system, comprising a precoder (16), which is adapted to generate drive voltages for first and second phrase modulators (6, 8) in dependence upon first and second data streams. The respective drive voltages for the first and second modulators (6, 8) are fed back to the precoder inputs with a delay related to the line speed of the data system, wherein the length of the delay corresponds to n bits.

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: Described are an optical transmitter and a method for generating a single sideband optical signal. The method includes generating a data signal at a first power level and at a second power level with a predetermined ratio being defined between the power levels. The data signal at the first power level is applied to a phase module disposed in a laser cavity of a semiconductor laser to generate a frequency modulated laser signal having a double sideband. The intensity of the frequency modulated laser signal is modulated in response to the data signal at the second power level to yield the single sideband optical signal. Optical transmitters implementing the method have an increased manufacturing yield and reliability, a lower fabrication cost and a decreased size compared to other optical single sideband optical transmitters.

Abstract: A chromatic dispersion generating apparatus of the present invention comprises a VIPA plate capable of emitting an incident light to different directions according to wavelengths, a three-dimensional mirror reflecting the light of respective wavelengths emitted from the VIPA plate at a previously set position to return them to the VIPA plate, and a control section that controls a position of the three-dimensional mirror and the temperature of the VIPA plate.

Abstract: An optical modulator is overdriven to increase its nonlinearity and therefore improve its response as it pertains to differential phase shift keyed (DPSK) transmission and a method of operating the same. In one embodiment, the MZM includes an MZM drive circuit coupled to the electrodes and configured to deliver to the electrode a DPSK drive signal bearing digital data and having a voltage that exceeds a normal drive voltage of the MZM by at least about 20%.

Abstract: A data modulation apparatus is proposed that includes a data modulator (20) for modulating data onto an optical signal at a predetermined bit rate. The resulting encoded optical signal is phase modulated by a phase modulator (50) that is driven by at least one waveform of a frequency that is 1/n of the predetermined bit rate, where n is an integer greater than 2. The application of a phase modulation at a frequency of a third or less of the bit rate of a digital data signal increases the non-linear tolerance of a transmission system by reducing the effect of non-linear pulse-to-pulse interactions. Moreover, this increase in non-linear tolerance is significantly better than that obtained by a phase modulation at one half of the data bit rate, while the implementation of a phase modulator at this lower frequency reduces the complexity of the transmitter.

Abstract: An optical transmitter includes a continuous wave optical source for generating an optical signal having a carrier frequency component, a clock modulator for performing a clock modulation upon the optical signal using a clock signal to generate a clock-modulated signal, and a data modulator for performing a data modulation upon the clock-modulated signal using a data signal. The clock signal has a half frequency of that of the data signal. The clock modulator is constructed by a single-end type phase modulator and at least one tap type optical filter.

Abstract: A delay interferometer and a demodulator including the delay interferometer and a balanced photodetector are provided. A half mirror splits an optical signal into first and second split beams of light which travel on first and second optical paths, respectively. A first reflector being disposed on the first optical path reflects the first split beam of light toward the half mirror. The second reflector being disposed on the second optical path reflects the second split beam of light toward the half mirror. At least one phase compensator being disposed between the half mirror and at least one of the first and second reflectors includes a medium that exhibits thermooptic effect and has temperature dependency of refractive index. The half mirror couples the first and second split beams of light to generate at least first and second coupled beams of light.

Abstract: The present invention relates to an apparatus and method for performing optical Differential Phase Shift Keying (DPSK) modulation, which transmits a phase difference between adjacent bits as information. The electrically band-limited optical DPSK modulating apparatus includes a light source, a Non-Return-to-Zero (NRZ) signal generator, a pre-coder, an electrical low pass filter, and a phase modulator. The NRZ signal generator generates a NRZ signal. The pre-coder codes the NRZ signal generated by the NRZ signal generator into a differential signal. The low pass “filter electrically limits a bandwidth of the differential signal obtained through the pre-coder. The phase modulator modulates an optical signal input from the light source into a DPSK signal using the differential signal having the bandwidth electrically limited by the low pass filter.

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: An optical transmitter for generating an optical signal includes: a precoder for coding an electrical signal of binary data; a continuous-wave (CW) light source for generating a continuous wave light; an optical phase modulator for modulating the phase of an optical signal outputted from the CW light source according to an electrical signal outputted from the precoder; a birefrigent material for bi-refracting a signal outputted from the optical phase modulator and for outputting the bi-refracted signal; and a polarizer for permitting only optical signals of a specific polarization direction to transmit therethrough when optical signals outputted from the birefrigent material are applied.

Abstract: A method of modulating an optical carrier. A target carrier modulation is computed based on an input data signal. An effective length of an optical modulator is then controlled based on the target carrier modulation.

Abstract: Minimum shift keying (MSK) is used as the coding scheme in a high bit rate optical transmission system, and the signal format is either RZ (return-to-zero) or NRZ (non-return-to-zero). The system can combine multiple individual channels with different wavelengths in a WDM or dense wavelength division multiplexed (DWDM) arrangement. Dispersion management can be provided using several techniques, such as quasi-linear transmissions or conventional RZ transmissions. At the transmitter, an optical MSK transmitter is used to modulate the phase of a stream of high bit rate (e.g., 40 Gbit/s) optical signals. Many such data streams can be combined in a wavelength division multiplexer and transmitted to a remote receiver, where the signal is wavelength division demultiplexed. The encoded data in each wavelength channel is then recovered by an MSK receiver, which may consist of a delay demodulator and a balanced detector.

Abstract: A method and apparatus is provided for transmitting a WDM optical signal. The method begins by modulating a plurality of optical channels that are each located at a different wavelength from one another with (1) a respective one of a plurality of information-bearing electrical signals that all embody the same broadcast information and (2) a respective one of a plurality of RF signals having a common functional broadcast waveform, at least one of the RF signals being out of phase with respect to remaining ones of the plurality of RF signals. Each of the modulated optical channels are multiplexed to form a WDM optical signal. The WDM optical signal is forwarded onto an optical transmission path.

Abstract: An apparatus, system and method wherein a multi-level data modulation format, such as DQPSK, is combined with symbol rate synchronous amplitude, phase, and/or polarization modulation.

Abstract: An optical transmitter for generating a modulated optical signal for transmission over a fiber optic link to a remote receiver including a laser; a modulator for externally modulating the optical output signal with a RF signal to produce an optical signal including a modulated information-containing component; and a phase modulator coupled either to the output of the modulator or directly to the output of the laser for canceling the noise signals generated in the laser.

Abstract: An optical transmitter for generating a modulated optical signal for transmission over a fiber optic link to a remote receiver including a laser; a modulator for directly amplitude modulating the laser with an analog RF signal to produce an optical signal including an amplitude modulated information-containing component; and a phase modulator coupled to the output of the laser for canceling the noise signals generated in the laser.

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: Disclosed is a duobinary optical transmission apparatus using a semiconductor optical amplifier (SOA). The duobinary optical transmission apparatus includes a light source for generating a carrier wave; a duobinary precoder for encoding an input (non return to zero) electric signal; a semiconductor optical amplification unit to amplify the encoded signal from the duobinary precoder, wherein the amplification unit receives an optical amplification gain difference that varies with a bias current combined with the encoded signal; and an optical band pass filter for receiving a phase-modulated optical signal from the semiconductor optical amplification unit, filtering the received optical signal to a prescribed bandwidth, and thereby generates a duobinary optical signal.

Abstract: The present invention relates to a device for detecting or generating and modulating optical signals, and having an angular dispersive element arranged to change angles of the optical signals or carrier and/or reference rays brought to interference.

Abstract: A demultiplex unit demultiplexes the optical output of a Mach-Zehnder optical modulator and inputs the demultiplexed optical output to a wavelength detection unit. The wavelength detection unit detects the wavelength deviations in the ascending or descending part of the optical signal and inputs the wavelength deviations to a detection unit. The detection unit detects the sign and magnitude of chirping in the magnitude of wavelength deviation and inputs the sign and magnitude of chirping to a driving voltage control unit. The driving voltage control unit compares the detected sign and amount of chirping with the target sign and magnitude of chirping, and a driving voltage generation circuit provides the Mach-Zehnder optical modulator with a suitable driving voltage.

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: The present invention relates to a method for transmitting data. An optical pulse stream comprising a plurality of return-to-zero optical pulses is prepared by modulating a phase of light output by an optical source to thereby encode data from a data source. The light of the optical pulse stream has a wavelength. The optical pulse stream is transmitted along an optical fiber of an optical network. Optical pulse streams of the invention enhance transmission performance at least in part by reducing noise at the receiver caused by fiber non-linearities.

Abstract: A single side band modulation device includes a first Mach Zehnder interferometer and a second Mach Zehnder interferometer. The first Mach Zehnder interferometer includes at least two output arms, and the second Mach Zehnder interferometer includes at least two output arms. Terminals of the output arms are connected with one another.

Abstract: A display device or a receiver device for use with coherent light. A controller applies phase shift values to a multi-region phase array at a frequency sufficiently higher than the flicker fusion rate of the human eye or other intended receiver in order to remove the perception of speckling artifacts which would otherwise appear due to the coherency of the light.

Abstract: Disclosed is a duobinary optical transmission apparatus. The duobinary optical transmission apparatusenhances nonlinear and dispersion characteristics for an intermediate-long distance transmission at a high-speed transfer rate without the use an electric LPF. The duobinary optical transmission apparatus includes a light source for generating a carrier wave, a duobinary optical signal generator for receiving a Non Return to Zero (NRZ) signal and generating a modulated optical signal generated by modulating the carrier wave according to the NRZ signal, and a Return to Zero (RZ) signal generator for converting the NRZ signal into a RZ (Return to Zero) signal. Therefore, optical intensity and a phase are modulated using only a single interferometer-type optical modulator.

Abstract: A method and system for transmitting information in a wavelength division multiplex (WDM) or other suitable multichannel optical communication system includes receiving a multichannel signal having a symbol rate and comprising a plurality of non-intensity modulated optical information signals. The non-intensity modulated optical information signals have a minimum channel spacing comprising a multiple of the symbol rate within 0.4 to 0.6 of an integer. The non-intensity modulated optical information signals are separated from the multichannel signal and each converted into an intensity modulated optical information signal using an asymmetric interferometer. A data signal is recovered from the intensity modulated optical information signal.

Abstract: An optical modulator provides for precoding of a high data rate phase modulated optical signal. According to one embodiment, the modulator includes a first phase modulator and a second phase modulator. The first phase modulator modulates an optical carrier signal according to a first data signal to generate a modulated optical signal. The second phase modulator modulates the modulated optical signal according to a time delayed version of its optical output signal. According to another embodiment, the modulator electrically precodes multiple data streams and modulates the precoded data streams using a series of phase modulators to generate a precoded optical data signal.

Abstract: Optical transmitter/receivers for use in a DWDM systems are provided. Transmission of data signals in a quadrature-return-to-zero (QRZ) format achieves a data transmission rate equal to eight times a base data rate, i.e., 80 Gbps over a 100 GHz channel if the base data rate is 10 Gbps, with high non-linear performance by setting the polarization state of the data bands such that non-linear effects induced by PMD are reduced. Additionally, a transmitter achieves a transmission data rate equal to 16 times the base data rate by sharpening the QRZ pulses and interleaving pulse-sharpened QRZ data signals in the time domain, further doubling the data rate. Using counterpropagation in the transmitter, carrier signals and data signals traverse the same length of fiber, reducing fringing effects in the transmitter. Related techniques enhance reception and detection of data at high data rates. A local pulse-sharpened carrier is mixed with a QRZ data signal at a detector reducing amplification noise by a factor of two.

Abstract: A differential quadrature phase shift keyed system includes a fiber optic source and a first fiber optic differential phase shift keyed demodulator coupled to the fiber optic source having a first phase differential. A second fiber optic differential phase shift keyed demodulator is coupled to the fiber optic source disposed parallel with the first fiber optic differential phase shift key demodulator. The second demodulator has a second phase shift differential equal to the first phase differential plus about 90 degrees.

Abstract: A method and apparatus for encoding optical power and non-payload data in an optical signal is described. The method involves producing a dither modulating signal having an amplitude of indicative of the optical power in the optical signal and having a phase representing the non-payload data, and modulating the optical signal with the dither modulating signal. The apparatus involves a waveform generator for producing an amplitude adjusted waveform having an amplitude responsive to the optical power of the optical signal and a binary phase shift keying modulator for binary phase shift keying the amplitude adjusted waveform in response to the non-payload data to produce a dither modulating signal having an amplitude indicative of the optical power in the optical signal and having a phase representing the non-payload data.

Abstract: An optically modulated signal is generated for use in transporting data by generating a so-called sub-carrier modulated optical signal and, then, vector modulating the sub-carrier modulated optical signal to yield the desired modulated optical signal for transmission. The vector modulation includes a phase component and an amplitude component. In one specific embodiment of the invention, an apparatus for use in generating a modulated optical signal includes a generator to generate a sub-carrier modulated optical signal including an optical carrier and at least one sub-carrier and an analog vector modulator coupled to receive both the sub-carrier modulated optical signal from the generator and a data signal. The analog vector modulator generates an output optical signal by phase modulating and/or amplitude modulating the sub-carrier of the received optical signal in response to the data signal.

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 wavelength-division multiplexed optical transmission system to keep the correlation of data patterns among wavelength channels to the low level, preventing large XPM and XGM from occurring when the correlation is strong, and assuring a stable transmitting quality.

Abstract: A method and apparatus for variable duty cycle generation of optical RZ data signals uses a single, NRZ-driven phase modulator followed by a optical delay-line interferometer. If desired, a differential encoder precodes an NRZ data signal before being applied to the data input of a phase modulator arranged to modulate the light emerging from a continuously operating laser. The output of the modulator is then applied to an optical delay interferometer, such that the optical signal is split into first and second optical signals, each of which is applied to a respective one of the two interferometer arms. The interferometer is arranged such that the signal in one of the arms is controllably delayed with respect to the other (a) by a fine delay (on the other of the optical wavelength) to produce destructive interference in the absence of phase modulation by said phase modulator, and (b) by a coarse delay (on the order of a bit period), to produce RZ pulses having the desired duty cycle.

Abstract: A communication system comprises a phase encoder, a phase shifter, and a modulator. The phase encoder receives user data and phase encodes the user data to form an encoded signal representing the user data. The phase shifter shifts a phase of the encoded signal to generate a phase shifted signal. The modulator receives a first optical signal and modulates the first optical signal with the encoded signal and the phase shifted signal to form an optical single sideband signal representing the user data. The modulator then transmits the optical single sideband signal representing the user data.

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: A phase modulation circuit for outputting a modulated signal of an input signal which has been modulated to a desired phase. The circuit includes a light emitting element for emitting light according to an input signal and outputting a modulated signal, a bias current source for supplying in advance to a light emitting element a bias current smaller than the light emitting threshold current of the light emitting element, a bias current control unit for controlling the bias current according to a desired phase for supplying to the light emitting element a modulation current for causing the light emitting element to emit light according to the input signal, and a modulation current control unit for controlling the modulation current according to the phase shift resolution in the phase modulation circuit. The modulation current control unit controls modulation current further according to the phase range in the phase modulation circuit.

Abstract: The invention relates to optical communications using techniques for providing efficient high speed polarization bit interleaving. One common architecture for high-speed time-division-multiplexing employs two modulators having a same bit rate, wherein two separately modulated streams of data bits are combined into a high-speed single serial stream of data bits, instead of providing a single higher-cost higher-speed modulator. The present invention has found with the availability of fast data modulators, that polarization bit interleaving can be employed more efficiently for higher speed data transmission in optical network systems by providing an optical modulator including a single data modulator, rather than multiplexing different data streams from different modulators.

Abstract: The present invention suppresses to a minimum the degradation of the transmission quality caused by chromatic dispersion characteristic of an optical transmission medium, and the interplay between the chromatic dispersion and non-linear optical effects in dense WDM transport systems. A baseband input data signal is pre-coded in advance by a pre-coding unit, phase modulation is carried out using a pre-coded signal by the optical phase modulating unit, and the phase modulated optical signal is converted to an RZ intensity modulated signal by the optical filter unit that performs phase-shift-keying to amplitude-shift-keying conversion. For example, an optical phase modulating unit generates an encoded DPSK phase modulated signal using a differential phase shirt keying (DPSK) format, and a phase modulated signal is converted to an RZ intensity modulated signal by the optical filter unit disposed downstream of the optical phase modulating unit.

Abstract: There is provided a WDM optical transmission system and transmission method that have excellent spectral efficiency. The WDM optical transmission system is provided with: an optical transmitting section having an optical transmitter that generates N wave (wherein N is an integer of 2 or greater) optical signals with an optical frequency spacing ?f [Hz] and modulated by a modulation bit rate B [bit/s] (wherein B/?f?1 [bit/s/Hz]) using a modulation device, and having a coupler that couples the optical signals; an optical receiving section provided with an optical DFT circuit of a sampling frequency ?f [Hz] that is equal to the optical frequency spacing; and a bit phase adjustor that makes bit phases of respective wavelength division multiplexed signals synchronous at an input of the optical DFT circuit.

Abstract: Binary information is subjected to RZ encoding and multi-level encoding, and the encoded signal is optically modulated.

Abstract: A card for transmitting data over at least one optical fiber includes a transmitter having at least one light source and a phase modulator for phase modulating light from the source so as to create phase-modulated optical signals in the light as a function of an input electronic data stream; and a receiver having an interferometer for reading received optical signals.

Abstract: An apparatus and method generating an optical pulse of picosecond class (having a high duty ratio), which accurately and stably operates at an arbitrary repetition frequency, has a high OSNR, and is not restricted by an RF modulation frequency, are provided. New modulation spectrum components are generated by performing phase modulation for light output from a single wavelength laser light source with an optical phase modulator. The phases of the modulation spectrum components are aligned by a phase adjuster, so that a pulse wave in a time domain is generated.

Abstract: A transmitter comprising a programmable optical vector modulator and method for coherent optical signal communication. The transmitter includes a transmitter laser whose output is coupled by way of an optical fiber to an amplitude modulator. The output of the amplitude modulator is coupled by way of a length of optical fiber to a phase modulator. The phase modulator generates a modulated light output from the transmitter. Amplitude modulation is achieved by inputting data and a data clock signal to amplitude symbol mapping logic whose outputs are selectively weighted, summed, amplified and input to the amplitude modulator to amplitude modulate the output of the transmitter laser.

Abstract: An optical return-to-zero (RZ) signal generator and related methods are described in which a phase modulator causes a phase change in an optical signal responsive to a transition in a driving signal, and in which an interferometer receives the optical signal from the phase modulator and generates an optical pulse responsive to that phase change. Preferably, the interferometer introduces a fixed, unmodulated time delay between its two signal paths, the fixed time delay being selected such that destructive interference occurs at an output of the interferometer when the phase of the optical signal received from the phase modulator remains constant. However, when a rising or falling edge of the driving signal causes phases changes in the optical signal, the destructive interference at the output of the interferometer is disturbed, and an optical pulse is generated. The driving signal is a differentially encoded version of an input information signal.

Abstract: A detector outputs a detection signal indicating amplitude variation of an input frequency-multiplexed signal. An amplitude controller adjusts the amplitude of the frequency-multiplexed signal by referring to the detection signal. A modulator modulates the amplitude-adjusted frequency-multiplexed signal to produce a predetermined modulated signal. A second multiplexer multiplexes the modulated signal and the detection signal to produce a multiplexed signal. An optical transmitter converts the multiplexed signal into an optical signal, and then sends it out to an optical transmission path. An optical receiver converts the received optical signal into an electrical signal. A separator separates the modulated and detection signals from the electrical signal. A demodulator demodulates the modulated signal to output the frequency-multiplexed signal. An amplitude adjuster adjusts the amplitude of the frequency-multiplexed signal by referring to the detection signal to reproduce the original amplitude variation.

Abstract: A photonic integrated device having a substrate layer, epitaxial layers formed on said substrate layer and a guiding layer formed by one of the epitaxial layers. An optical waveguide is formed within the guiding layer. In the waveguide are a splitter (4) having at least two outputs, each output being transmitted to a Mach-Zehnder modulator (6, 8), the phase of the output of at least one modulator being shiftable, the signals being recombined to provide an optical phase shift key (PSK) output (14) wherein a trench is etched into the substrate layer between each pair of modulators to isolate the modulators from one another.