Abstract: In various embodiments, a monolithic integrated transmitter, comprising an on-chip laser source and a modulator structure capable of generating advanced modulation format signals based on amplitude and phase modulation are described.

Abstract: An optical transmitter for generating a modulated optical signal for transmission over dispersive fiber optic links in which a first information-containing radio frequency signal input is applied to a modulation circuit for directly modulating a semiconductor laser with the signal input. The output of the laser is applied to a phase modulator to which a second information-containing radio frequency signal is applied.

Abstract: A transmitter module includes a processor configured to receive input data, and determine input values corresponding to the input data; a digital-to-analog converter configured to receive the input values from the processor, and generate first and second voltage signals based on the input values; a laser configured to output light; a Mach-Zehnder modulator configured to receive the light from the laser and the first and second voltage signals from the digital-to-analog converter, and modulate the light based on the first and second voltage signals to generate a modulated optical signal that includes distortion; and a filter configured to receive the modulated optical signal from the modulator, process the modulated optical signal to reduce or eliminate the distortion and produce an output optical signal, and output the output optical signal.

Abstract: In the field of communications transmission, a method, a device, and a system for generating and receiving a phase polarization modulated signal are disclosed. The device for generating the phase polarization modulated signal includes: a Laser Diode (LD), a time division demultiplexer, a phase precoding module, a phase modulating module, a polarization precoding module and a polarization modulating module. The device for receiving the phase polarization modulated signal includes: an optical splitter, a polarizer, a phase demodulating and receiving unit, a Polarization Beam Splitter (PBS), a balanced receiver, a power divider, an exclusive OR, a delayer and a data interface processing unit. Therefore, problems in the prior art that a Differential Quadrature Phase Shift Keying (DQPSK) signal cannot bear and transmit information at a higher rate and that non-linear effect is strong during transmission are solved, and transmission performance of an optical signal is improved.

Abstract: A subcarrier system generates a phase comparison signal in a transmitter and transmits the phase comparison signal together with an optical subcarrier multiplex signal in the same transmission channel of an optical network. A receiver measures a phase distortion between a phase reference signal and the received phase comparison signal for each modulation section of the received subcarrier symbols, calculating at least one correction value and correcting time jitters or phase impairments of all parallel received or regained subcarrier symbols as a function of the phase distortion of the received phase comparison signal. Time jitter/phase jitter can be compensated without high hardware expenses.

Abstract: There is provided an optical transmitting device including a detector to detect a transmission rate of a transmission signal, a transmission method selector to determine a transmission method of the transmission signal, based on the transmission rate detected by the detector, a modulation signal generator circuit to generate a modulation signal from the transmission signal, based on the transmission method determined by the transmission method selector, and an optical modulator to generate a modulated optical signal from the modulation signal generated by the modulation signal generator circuit.

Abstract: The invention relates to a method in a transmitting node for transmitting a modulated optical carrier signal over an optical channel in an optical communications network to a receiving node. The method enables full use of the polarization domain within a Poincaré sphere when modulating the optical carrier signal.

Abstract: A communications device includes a transmitter device including first and second optical sources, a first optical coupler coupled to the first and second optical sources, and a first modulator coupled to the first optical coupler and to modulate a combined carrier signal including the first and second optical carrier signals with an RF input signal. The communications device includes a receiver device having a second modulator to further modulate the modulated combined carrier signal with an LO signal, a FM-PM discriminator coupled to the second modulator and to convert the modulated combined carrier signal to an intensity modulated combined carrier signal based upon the LO signal, a second optical coupler coupled to the FM-PM discriminator and to generate first and second intensity modulated carrier signals, and an optical-to-electrical converter coupled to the second optical coupler and to generate an IF signal.

Abstract: From an real valued OFDM signal (S0(t)) is a baseband signal (SB(t)) derived and converted into a complex single sideband modulation signal (n(t)). This is modulated onto an optical carrier (fOC) to generate a SSB transmission signal (SOT) having a small bandwidth an carrying the information in the envelope or in the power of the envelope. According to the modulation direct detection is possible. Only a small bandwidth is necessary for the transmission.

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: In one embodiment, a system includes at least one tone generator, a first transmitter, and a second transmitter. The at least one tone generator is operable to generate a plurality of modulation tones comprising at least a first modulation tone having a first tone frequency and a second modulation tone having a second tone frequency that is different from the first tone frequency. The first transmitter is operable to apply the first modulation tone to a first optical signal such that at least a portion of the first optical signal is divided into one or more sidebands. The second transmitter is operable to apply the second modulation tone to a second optical signal such that at least a portion of the second optical signal is divided into one or more sidebands.

Abstract: An optical signal control device includes an optical signal control unit and a drive circuit. The optical signal control unit includes m number of optical waveguides for propagating carrier light and (m×n) number of interaction regions, n number of interaction regions formed on each of the optical waveguides. The drive circuit includes (m×n) number of phase control units. The (m×n) number of phase control unit output a data signal for controlling the action of the (m×n) number of interaction regions to each of the (m×n) number of interaction regions. Each of the (m×n) number of phase control units outputs the data signal so that timing when the carrier light propagates to the interaction region to output the data signal and timing when the data signal arrives at the interaction region are synchronized. One of m and n is two or more.

Abstract: A spread spectrum waveform generator has a photonic oscillator and an optical heterodyne synthesizer. The photonic oscillator is a multi-tone optical comb generator for generating a series of RF comb lines on an optical carrier. The optical heterodyne synthesizer includes first and second phase-locked lasers, where the first laser feeds the multi-tone optical comb generator and the second laser is a single tone laser whose output light provides a frequency translation reference. At least one photodetector is provided for heterodyning the frequency translation reference with the optical output of the photonic oscillator to generate a spread spectrum waveform. A receiver pre-processor may be provided to operate on the spread spectrum waveform.

Abstract: A method and apparatus for providing a high peak power optical beam. The method includes interleaving pulse trains of different wavelengths and spatially and temporally overlapping the different wavelengths to produce an amplified output beam with very high peak power.

Abstract: The invention provides a system and method for secure communication that involve encoding and transmitting an optical orthogonal frequency division multiplexed (OFDM) signal. Each subcarrier of an optical carrier in OFDM transmission is modulated with data individually, and a variety of data format are used, such as QPSK, OOK, QAM, etc. The data format of each subcarrier may change in time according to a predetermined pattern. An optical receiver uncovers the data transmitted via an optical link. It is based on a coherent optical receiver and a digital signal processing (DSP) unit. A key to the data mapping and change is transmitted via the same optical link or by a separate channel. In one embodiment, the key is transmitted using quantum encryption technique. Besides subcarrier modulation encoding, the system may provide additional layers of security: optical carrier frequency hopping and polarization scrambling.

Abstract: A communications device includes a transmitter device having an optical source to generate an optical carrier signal, and a first modulator coupled to the optical source and to modulate the optical carrier signal with a radio frequency (RF) input signal, and an optical waveguide coupled to the transmitter device. The communications device includes a receiver device coupled to the optical waveguide and including a second modulator to further modulate the modulated optical carrier signal with a local oscillator (LO) signal, a frequency modulation-phase modulation (FM-PM) discriminator coupled to the second modulator and to convert the modulated optical carrier signal to an intensity modulated optical carrier signal based upon the LO signal, and an optical-to-electrical converter coupled to the FM-PM discriminator and to generate an intermediate frequency (IF) signal based upon the intensity modulated optical carrier signal.

Abstract: According to a first aspect, techniques are provided to optimize a Mach-Zehnder modulator drive waveform by distorting the outer modulation levels of the waveform, thereby equalizing eye openings of the received optical field, and in particular creating a wider and more defined central eye opening of the received optical field. According to a second aspect, techniques are provided to adjust in-phase (I) modulation levels based on the imperfect performance of a Mach-Zehnder modulator allocated to modulate quadrature-phase (Q) modulation levels, and conversely to adjust the Q modulation levels based on the imperfect performance of an MZ modulator allocated to modulate I modulation levels.

Abstract: The invention is directed to code labeling in an optical network. The network includes a transmitting station operable to transmit an optical signal. The network also includes an encoder coupled to the transmitting station operable to label the optical signal composed of a group of codes. A receiving station operable to receive the labeled group of optical codes is also provided. The receiving station is operable to read the optical signal if the label of the received group of codes corresponds to the group of codes assigned to the receiving station.

Abstract: A device is provided for use with a dither tone signal and an information signal. The device includes a laser diode, an electro-optic modulator, a first filter and a second filter. The laser diode can output a first light signal, whereas the electro-optic modulator can transmit a second light signal. The first filter can generate a first filtered signal based on the information signal. The second filter can generate a second filtered signal based on the dither tone signal. The first light signal is based on the dither tone signal, the information signal and the first filtered signal. The second light signal is based on the first light signal, the information signal, the dither tone signal and the second filtered signal. The filtered signals reduce or cancel the undesired leaked/interfering signals.

Abstract: The present disclosure provides a multi-carrier optical transmitter, receiver, transceiver, and associated methods utilizing offset quadrature amplitude modulation thereby achieving significant increases in spectral efficiency, with negligible sensitivity penalties. In an exemplary embodiment, an optical transmitter includes circuitry configured to generate a plurality of optical subcarriers, a plurality of data signals for each of the plurality of subcarriers, and a plurality of modulator circuits for each of the plurality of subcarriers, wherein each of the plurality of modulator circuits includes circuitry configured to offset an in-phase component from a quadrature component of one of the plurality data signals by one-half baud period.

Abstract: An eye mask is provided that is defined at least partially in terms of absolute, or non-relative, optical power level values. In essence, the eye mask of the invention is a hybrid of the traditional eye mask in that the eye mask of the invention includes power level values on the optical power axis that are based on the minimum OMA set forth in the applicable standard or data sheet specification rather than on measured power level values obtained from the part being tested. Using the hybrid eye mask of the invention obviates the need to perform at least some of the tests often used to measure transmitter attributes. In addition, using the hybrid eye mask of the invention reduces the possibility that a transmitter may fail the eye mask test even though the transmitter operates satisfactorily.

Abstract: An apparatus for use with an optical computation system may comprise a monolithic device with no free space optical components and may include a phase modulator and a polarization modulator. The phase modulator may be configured to receive a beam of light and two digital data streams and operable to modulate the phase of the beam of light to at least four phase states, the at least four phase states representing the two digital data streams. The polarization modulator may be configured to receive two additional digital data streams and the modulated beam of light from the phase modulator and operable to modulate the polarization of the beam of light to at least four polarization states, the at least four polarization states representing the two additional digital data streams.

Abstract: An optical signal transmitter includes: first outer modulator to generate first modulated optical signal, the first outer modulator including a pair of optical paths and a first phase shifter to give phase difference to the pair of optical paths; second outer modulator to generate second modulated optical signal, the second outer modulator including a pair of optical paths and a second phase shifter to give phase difference to the pair of optical paths; combiner to generate polarization multiplexed optical signal by combining the first and second modulated optical signals; phase controller to control the phase difference by the first phase shifter to A??? and control the phase difference by the second phase shifter to A+??; and power controller to control at least one of the first and second outer modulators based on AC component of the polarization multiplexed optical signal.

Abstract: After a startup of an optical transmitter, a control is started in such a way that a modulation amplitude of a driving signal of a phase modulator is set as 0, and that an operational point of a bias voltage is set as the lowest point of light transmission characteristics of the phase modulator. When the operational point of the bias voltage reaches the lowest point, the modulation amplitude of the driving signal is gradually increased from 0 to 2V?.

Abstract: In various embodiments, a monolithic integrated transmitter, comprising an on-chip laser source and a modulator structure capable of generating advanced modulation format signals based on amplitude and phase modulation are described.

Abstract: Provided is a multi-value optical transmitter in which a DC bias may be controlled to be stabilized so as to obtain stable optical transmission signal quality in multi-value modulation using a dual-electrode MZ modulator. The multi-value optical transmitter includes: D/A converters for performing D/A conversion on first and second modulation data which are set based on an input data series, so as to generate a first and a second multi-value signal, respectively; a dual-electrode MZ modulator including phase modulators for modulating light from a light source based on the first multi-value signal and the second multi-value signal, so as to combine optical signals from the phase modulators to output the optical multi-value signal; an optical output power monitor for detecting average power of the optical multi-value signal; and a DC bias control unit for controlling a DC bias for the dual-electrode MZ modulator, so as to maximize the average power.

Abstract: A method and apparatus for sending timing information using an optical signal. A first electrical signal comprising a pseudorandom binary sequence is generated. The first electrical signal comprising the pseudorandom binary sequence is modulated with a second electrical signal to form a modulated electrical signal. The second electrical signal includes timing data in a format used for global positioning systems. An optical carrier signal is modulated with the modulated electrical signal to form the optical signal using an optical transmitter.

Abstract: The present invention relates to an optical access system for dual service network, which mainly comprises an optical modulation device which is used to receive on-off keying (OOK) signal from cable network and radio frequency (RF) signal from wireless network, the optical modulation device then modulates the OOK signal and the RF signal to an optical signal and send out an output optical signal. Lastly, the output optical signal is being delivered to an optical receiving device through an optical fiber transmission channel, and the optical receiving device can access the OOK signal and RF signal from the output optical signal. In addition, the present invention does not require remote nodes (receiver side) to use any optical filter to discern on-off keying signal from cable network and RF signal from wireless network. The present invention can also apply to the field of wavelength-division multiplexing system.

Abstract: A method and system can propagate upstream cable modem signals and radio-frequency (RF) return video control signals over the same passive optical network (PON). The method and system can include various combinations of hardware and software to support this operation. Three exemplary embodiments of optical network terminals (ONT) of a DPON system improve performance of the system by ensuring that, in the event the upstream transmitters of two ONTs are turned on simultaneously, they will not interfere with each other. The system is designed such that in a situation of competing transmissions, the one which is received and processed by the head end out of two competing transmissions originating from a set top box and a cable modem, will be the one originating from the cable modem, which may use the DOCSIS cable modem protocol.

Abstract: Included are a first modulator, a second modulator, a first optical amplifier that amplifies an output of the first modulator at an amplification factor based on a first bias signal, a second optical amplifier that amplifies an output of the second modulator at an amplification factor based on a second bias signal, an optical phase adjuster that phase-rotates an output of the second optical amplifier, an optical multiplexer that multiplexes an output of the first optical amplifier with an output of the optical phase adjuster, and a second bias corrector that generates a first pulse signal and a second pulse signal, which are complementary to each other, and obtains a first bias value and a second bias value based on a change of strength of an output signal of the optical multiplexer. The first and second pulse signals are superimposed on the first and second bias signals, respectively.

Abstract: A polarization multiplexed optical transmitter includes first and second modulation units, combiner, phase controller, and signal controller. The first and second modulation units generate first and second modulated optical signals, respectively. The first and second modulation units include first and second phase shifter to give phase difference between optical paths of corresponding Mach-Zehnder interferometer, respectively. The combiner generates polarization multiplexed optical signal from the first and second modulated optical signals. The phase controller controls the phase difference by the first phase shifter to a target value and the phase difference by the second phase shifter to a value shifted by ? from the target value. The signal controller controls operation state of at least one of the first and second modulation units based on optical intensity waveform of the polarization multiplexed optical signal.

Abstract: The present method is for generating a 4-level optical signal and it includes providing a continuous wave CW optical source; modulating the CW optical source with a first intensity modulator driven by a binary electrical signal a n Gbits/s to generate an optical signal; employing a second intensity modulator as a pulse carving modulator that is driven by an RF signal at n GHz thereby generating a 4 level optical signal for subsequent detection by a receiver.

Abstract: An optical m-ary modulator includes an optical loop forming a polarization maintaining closed optical path. A loop input-output unit splits linearly polarized input signal light into a first component and a second component and feeds the first and second components into the optical loop in opposite directions. A pair of phase modulators modulate the first and second components according to respective control signals. The loop input-output unit recombines the modulated first and second components. The optical phase bias unit creates a phase difference between the first and second components so that they combine to form an m-ary modulated optical signal. Since the first and second components travel around the same optical path, when they recombine their phases are correctly aligned, making the modulator immune to environmental effects and permitting the use of high-speed optical modulation techniques.

Abstract: Disclosed are a device and a method for transmitting an optical data signal over an optical transmission channel, comprising a differential phase shift keying unit for differential phase shift keying of at least one serial data stream to generate a differential phase shift keying coded data stream; an amplitude shift keying unit for amplitude coding of at least two further serial data streams that can be selectively activated to generate an amplitude shift keying coded data stream; and a modulation unit for generating an optical data signal in accordance with a control signal that is, formed from the generated differential phase shift keying coded data stream and from the generated amplitude shift keying coded data stream.

Abstract: The present invention discloses a method and device for the bias control of an MZ modulator. The method comprises: during startup of an MZ modulator, inputting a linearly changing bias control voltage to the bias electrode of the MZ modulator and obtaining the output optical power of the MZ modulator so as to determine a bias control voltage corresponding to a preset operating point; then enabling a communication electrical signal to be input to the radio frequency electrode of the MZ modulator, carrying out an amplitude modulation on the communication electrical signal by a low-frequency sinusoidal pilot signal, and inputting the determined bias control voltage to the bias electrode simultaneously; and sampling the output optical signals of the MZ modulator, comparing the sampled optical signal with the pilot signal, and adjusting the bias control voltage input to the bias electrode according to the result of the comparison.

Abstract: A frequency up-conversion system includes an optical splitter, an optical modulator, an optical phase-shifter, and an optical coupler. In one embodiment of the present disclosure, the optical splitter is configured to split an optical wave into a first optical wave and a second optical wave, the optical modulator is configured to modulate the first optical wave to form a modulation wave, the optical phase-shifter is configured to shift the phase of the second optical wave by a predetermined phase to form a shifting wave, and the optical coupler is configured to couple the modulation wave and the shifting wave. In one embodiment of the present disclosure, the optical modulator and the optical phase-shifter are connected in a parallel manner.

Abstract: There is provided an optical modulation signal generating device in which an operation speed is not limited by a relaxation oscillation frequency of a laser, and high-speed modulation and long-distance transmission can be performed. The optical modulation signal generating device converts a signal from a signal source into an optical signal and outputs the optical signal to a transmission medium having frequency dispersion. The optical modulation signal generating device includes an optical source (102) for performing frequency modulation by the signal from the signal source to generate an optical signal having only a frequency modulation component, and a frequency filter (103) for converting the frequency modulation component of the optical signal into an intensity modulation component and a frequency modulation component.

Abstract: An optical spectrum analyzer and a method of spectrally analyzing an optical signal. The optical spectrum analyzer includes a wave shaper such as an optical modulator that shapes an optical signal, a dispersive element such as a dispersive fiber in which the shaped optical signal is dispersed, a detector that provides an output signal indicative of the dispersed shaped optical signal, and a signal processor that analyzes the output signal, for example by calculating a transform such as an inverse Fourier transform or a Fourier transform of the output signal, to provide a frequency spectrum of the optical signal.

Abstract: Polarization multiplexing with different differential phase shift keying (DPSK) schemes generally uses DPSK modulated signals modulated using different DPSK modulation schemes and combined with orthogonal polarizations relative to each other. The different DPSK modulation schemes may use different DPSK phase shifts to represent data, such as a regular DPSK modulation scheme and a ?/2 DPSK modulation scheme. By using different DPSK modulation schemes to represent data on the orthogonally polarized signals, the DPSK demodulators may effectively separate the orthogonally polarized signals using the property of the DPSK receivers. To optimize performance, the DPSK modulated signals may also be bit-interleaved when combined with orthogonal polarization.

Abstract: A device and a method for receiving a differential quadrature phase shift keying (DQPSK) signal and a method for obtaining a DQPSK signal are provided. The device includes: a splitter, configured to split the DQPSK signal to obtain two optical signals; two optical bandpass filters, connected to the splitter and configured to optically bandpass filter the two optical signals respectively, in which the two optical bandpass filters respectively have a positive frequency offset and a negative frequency offset from a central frequency of the DQPSK signal received by the splitter; and two photoelectric detectors, correspondingly connected to the two optical bandpass filters and configured to photoelectrically convert the filtered optical signals to obtain data signals.

Abstract: A modulator is disclosed that includes three arms between a splitter portion and a coupler portion. The modulator typically requires at most a ?/2 phase shift between constellation points. Accordingly, the modulator is more efficient and consumes less power.

Abstract: An optical transmission apparatus for suppressing deterioration of transmission quality due to XPM in a wavelength division multiplexing optical communication system in which an intensity modulation optical signal and a phase modulation optical signal exist in a mixed form. The apparatus has an intensity inversion signal light output section which outputs light having an intensity pattern obtained by inverting intensity changes of the intensity modulation optical signal near a wavelength of the intensity modulation optical signal in arrangement on wavelength axis of optical wavelengths that can be multiplexed as a wavelength division multiplexed signal as intensity inversion signal light, and a wavelength division multiplexed optical signal output unit which wavelength-division-multiplexes the intensity modulation optical signal, the phase modulation optical signal and light from the intensity inversion signal light output section and outputs a wavelength division multiplexed optical signal.

Abstract: A method of transmitting a plurality n data streams comprises modulating an optical carrier using differential M-ary phase shift key (DMPSK) signalling in which M=2n. Advantageously the method comprises using differential quaternary phase shift keying in which n=2. A particular advantage of the method of the present invention is that since the data is differentially encoded in the form of phase changes rather than absolute phase values this enables the modulated optical carrier to be demodulated using direct detection without requiring a phase-locked local optical oscillator. The invention is particularly applicable to WDM communication systems.

Abstract: A modulation method, especially an optical modulation method, using the principle of discrete IQ modulation. The modulation method includes generating a carrier signal (Sc) and splitting the carrier signal at a splitting position in an I branch signal and a Q branch signal; modulating the amplitude of the I branch signal according to a first modulation signal and modulating the amplitude of the Q branch signal according to a second modulation signal, each of the first and second modulation signals being arranged to adopt a given number of values according to a given number of constellation points of a given modulation scheme; phase shifting the signal in the Q branch versus the signal in the I branch; and combining the signals in the I branch and Q branch at a combining position. The combined modulated signal (Stx,mod) is arranged to be transmitted over a transmission path.

Abstract: A first modulation section performs low-speed digital modulation of first data. A second modulation section performs high-speed digital modulation of second data. A first light transmitting section alternately emits and quenches visible light in accordance with an output signal of the first modulation section to transmit a visible light signal which conveys the first data. A second light transmitting section changes an intensity of the infrared light in accordance with an output signal of the second modulation section to transmit an infrared light signal, which conveys the second data, in parallel with the visible light signal.

Abstract: An O/E conversion element converts an input NRZ optical signal into an electric signal. A clock recovery circuit recovers a clock signal from the electric signal obtained by the O/E conversion element. A phase modulator applies phase modulation to the NRZ optical signal, using the recovered clock signal. An intensity modulator applies intensity modulation to the NRZ optical signal, using the recovered clock signal. A dispersion medium compensates for a frequency chirp of an optical signal output from the intensity modulator.

Abstract: The present invention relates to an optical modulating device with frequency multiplying technique for electrical signals, which primary comprises a mixer, which generates a mixed data signal from a first electrical signal and a second electrical signal. The mixed data signal is then received by a first phase shift device to have its phase shifted and becomes a first shifted signal. The first electrical signal is further received by a second phase shift device to have its phase shifted and becomes a second shifted signal. The present invention further comprises an integrated electro-optic modulator (Mach-Zehnder modulator), which is used to receive an input optical signal, the mixed data signal, the first shifted signal, the second shifted signal and the first electrical signal mentioned above, the integrated electro-optic modulator will then modulates the input optical signal into a frequency multiplying output optical signal that carries the first electrical signal and the second electrical signal.

Abstract: A coherent optical transmitter circuit is disclosed in which controlled chirp is employed, enabling the suppression of nonlinear polarization scattering in dual polarization coherent systems, such as those which employ dual polarization-quadrature phase-shift keying (DP-QPSK). By separately chirping the modulated signals of each polarization tributary signal, the polarization state of the output DP-QPSK signal varies during a time period corresponding to a symbol bit period. Such controlled variations in the output DP-QPSK signal result in the mitigation of nonlinear effects associated with the network infrastructure over which the signal is transmitted, resulting in enhanced system performance. Enhanced system performance, for example, can be seen in greater reach and improved signal quality of the transmitted signal.

Abstract: A method and a device provide signal processing. The method contains the steps of separating a pilot signal from an analog signal, reducing or compensating a noise based on a local oscillator laser by demodulating the pilot signal, processing the demodulated pilot signal, and combining the processed demodulated pilot signal with the analog signal. Furthermore, a method for signal processing at a transmitter, according devices and a communication system are described.

Abstract: According to one embodiment of the invention, a 16-QAM optical modulator has a Mach-Zehnder modulator (MZM) coupled to a drive circuit that drives the MZM based on two electrical binary signals. The output of the MZM corresponds to an intermediary constellation consisting of four constellation points arranged on a straight line in the corresponding in-phase/quadrature-phase (I-Q) plane. Two of these constellation points correspond to a zero phase, and the remaining two constellation points correspond to a phase of ? radian. The 16-QAM optical modulator further has a phase shifter that modulates the output of the MZM based on two additional electrical binary signals. The resulting optical output signal corresponds to a star 16-QAM constellation, which is produced by incremental rotation of the intermediary constellation.