Abstract: The disclosure has application for use in establishing a communication link between a first location and a second location, the first location having an electrical driver circuit that receives input data to be communicated, and the second location having an electrical receiver circuit for producing output data representative of the input data. The method includes the following steps: providing a tilted charge light emitting device at the first location and coupled with the driver circuit such that the light produced by the tilted charge light-emitting device is a function of the input data; providing an optical fiber between the first and second locations; coupling light from the tilted charge light emitting device into the optical fiber; and providing, at the second location, a photodetector coupled with the optical fiber and with the receiver circuit; whereby electrical signals representative of the input data are output from the receiver circuit.

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: A driving apparatus supplies a drive signal to an optical modulator corresponding to a phase modulation format, and also, divides a part of an output light from the optical modulator; extracts some optical component of the divided light, which is distant from a carrier frequency by integral multiple of a modulation frequency, to detect a power of the optical component; and feedback controls a duty ratio of the drive signal or a cross-point level thereof so that the detected power approaches a minimum value. Thus, it is possible to stably perform phase modulation with high precision.

Abstract: Transmission-side communication apparatus 100 using a DQPSK (differential quadrature phase-shift keying) scheme is provided with: optical carrier generation section 102 which generates an optical carrier the frequency of which switches among a plurality of different frequencies within one symbol period; and modulation section 103 with which DQPSK-modulates the optical carrier generated by the optical carrier generation means in accordance with a modulation signal at an interval of the symbol period. There are provided: single delay interference section 121 which receives an optical signal obtained by DQPSK-modulating an optical carrier the frequency of which switches among a plurality of different frequencies within one symbol period and outputs an output light obtained by causing the optical signal 104 and a delay optical signal thereof to interfere with each other; and photoelectric conversion section 124 which converts the output light outputted by the delay interference means to an electric signal.

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: 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: An optical DQPSK modulator comprises a pair of phase modulators. Each of the pair of the phase modulators is provided with first and second driving signals. The first and second driving signals are amplified by first and second amplifiers, respectively. An RZ intensity modulator generates an optical RZ-DQPSK signal from an optical DQPSK signal output from the optical DQPSK modulator. A photodetector generates a monitor signal from the optical RZ-DQPSK signal. A gain adjuster unit adjusts the gains of the first and second amplifiers so as to minimize the power of the monitor signal.

Abstract: In general, optical communication systems and methods may implement a vestigial phase shift keying (PSK) modulation format to enable relatively high transmission rates with closer channel spacing and improved signal detection in a WDM optical communication system. A PSK modulated signal may be correlated with a phase shift, for example, using a delay line interferometer (DLI), to generate a vestigial PSK signal, which may be pre-filtered, combined, and transmitted in the WDM system. The correlation with a phase shift compresses and shifts the signal spectrum such that intersymbol interference (ISI) length may be reduced with minimal increase in the bit error rate (BER) when the vestigial PSK signal is detected.

Abstract: A phase shift keyed demodulator includes first and second beam splitters, a first optical path, a second optical path, and a wavelength tuner. The first beam splitter splits an input signal into first and second output signals. The second beam splitter splits each first and second output signal into a transmitted signal and a reflected signal. The first optical path includes an optical path of each transmitted signal from a beam splitting surface to a reflector and back to the beam splitting surface. The second optical path includes an optical path of each reflected signal from the beam splitting surface to a mirror surface and back to the beam splitting surface. A path difference introduces a delay between the transmitted signal and the reflected signal. The wavelength tuner tunes the demodulator to a predetermined central wavelength and introduces a phase shift between first and second transmitted signals.

Abstract: An optical receiver includes a first interferometer having a plurality of arms. The optical receiver further includes first tunable optical filters connected in series with the arms of the first interferometer, where each first tunable optical filter is tuned to filter a region of overlap in the optical frequency spectrum between adjacent optical channels.

Abstract: An optical modulator includes an optical modulation substrate, an electrical length adjusting substrate, a package containing the substrates, and a plurality of input ports for inputting high frequency electrical signals. The optical modulation substrate includes a substrate body made of an electro-optic material, a ground electrode and a plurality of signal electrodes provided on the substrate body, optical waveguides propagating lights interacting with the signal electrodes, respectively, and electrode input ports inputting the high frequency electrical signals into the signal electrodes, respectively. The signal electrode includes an interacting part, an input end part provided between the electrode input port and interacting part, and a terminal part. The electrical length adjusting substrate includes conductive lines connected to the input ports for inputting the high frequency electrical signals, respectively.

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 photonic millimeter-wave generator capable of combining wired and wireless communication facilities to further elongate the transmission distance comprises a laser generator for generating a first optical signal; an optical frequency comb generator coupled with the laser generator; and a pulse shaper coupled with the optical frequency comb generator. The optical frequency comb generator receives the first optical signal generated by the laser generator and outputs a second optical signal. The second optical signal contains multiple frequency components and is sent to the pulse shaper. The pulse shaper adjusts the amplitude and phase of the second optical signal and then outputs the signal as a third optical signal.

Abstract: An optical clock comprises a laser oscillator and modulating means arranged to cooperate with the laser oscillator to produce a series a series of phase-modulated optical pulses. The optical clock further comprises an optical fiber arranged to provide compression of the optical pulses, and may also comprise a step-recovery diode arranged to pulse-pick pulses output from the fiber to produce a series of optical clock pulses, depending on the mode of operation of the modulating means. Phase-modulation is carried out a frequency which provides sufficient linewidth broadening to inhibit stimulated Brillouin scattering within the optical fiber. An optical clock of the invention provides a robust and reliable alternative to clocks based on modelocked lasers, and may be assembled from inexpensive, commonly-available components. The repetition rate of a clock of the invention may easily be adjusted by electronic means. Unlike many modelocked lasers, a clock of the invention does not require precise optical alignment.

Abstract: The present invention is a method and an apparatus for optical modulation, for example for use in optical communications links. In one embodiment, an apparatus for optical modulation includes a first silicon layer having one or more trenches formed therein, a dielectric layer lining the first silicon layer, and a second silicon layer disposed on the dielectric layer and filling the trenches.

Abstract: A method of processing data is provided that includes receiving a plurality of binary electronic signals and generating an optical signal by a number of lasers that is equal to or greater than the number of binary electronic signals. The optical signal is generated at one of a plurality of intensity levels, and each intensity level represents a particular combination of bit values for the plurality of binary electronic signals. The optical signal is converted into an electronic signal having the plurality of intensity levels. An apparatus for processing data is provided that includes a plurality of lasers configured to emit light at a plurality of frequencies, and a plurality of modulators configured to receive a plurality of binary electronic signals and to modulate the light emitted by the lasers. An apparatus for transmitting data is provided that includes a photo receiver and an electronic signal generator.

Abstract: A system comprises an optical processor comprising a sideband generator, an optical filter, and a phase-shift-keying (PSK) modulator, wherein: the sideband generator generates optical frequency sidebands about a carrier frequency of an optical signal; the optical filter discriminates between the optical frequency sidebands and the optical carrier frequency such that optical sidebands of interest can be used to generate an optical millimeter-wave signal; the PSK modulator comprises an optical splitter, an optical phase delay unit, two or more optical gates, and an optical combiner; the optical splitter divides the optical millimeter-wave signal into two or more intermediate signals; the optical phase delay unit delays one or more of the intermediate signals to create distinct phase relationship between them; the optical gates modulate each intermediate signal individually, based on a control input; and the optical combiner combines the gated intermediate signals into a single, PSK-modulated optical millimeter-

Abstract: A transmitter modulator that is operable to modulate signals according to multiple modulation formats includes a first modulator, a second modulator, and a polarization beam combiner. The first modulator encodes a first signal according to a first modulation format. The second modulator encodes a second signal according to a second modulation format, the first signal orthogonally polarized with respect to the second signal. The polarization beam combiner combines the first signal and the second signal for transmission.

Abstract: An optical apparatus includes a quadrature phase shift keying modulator for generating a non-return-to-zero quadrature phase shift keyed NRZ-QPSK signal from a received lightwave, the modulator being driven by a radio frequency RF signal, an intensity modulator for carving the NRZ-QPSK signal to return-to-zero RZ pulses with a different duty cycle than that of the NRZ-QPSK, the intensity modulator being driven by a radio frequency RF clock signal to change the NRZ-QPSK to an RZ-QPSK signal, and an optical filter with a narrow band for filtering the signal from the intensity modulator to increase optical power that is useable by an optical digital coherent detection system.

Abstract: A non-feedback pre-encoder for optical DQPSK modulation includes four differential encoders, two power splitters, two delay lines, one exclusive OR gate and a cross switch. Each of two data streams input to the pre-encoder is divided into two identical streams by one of the power splitter, called an upper stream and a lower stream, respectively. Every upper stream is differentially encoded by one of the differential encoders, and outputs of the differential encoders are fed into the XOR gate. An output of the XOR gate drives the cross switch as a control signal. Two lower input data stream are delayed in the delay lines, and fed into the cross switch. The outputs of the cross switch are differentially encoded, separately, where outputs of the pre-encoder are provided. The invention eliminates the speed limitation due to the electrical propagation by constructing an all-forward control signal.

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: An optical transmitter subassembly of one embodiment includes a temperature controller, first to third bases, a laser diode, and an optical system. The temperature controller includes first and second plates, and temperature controlling elements put between the first and second plates. The first base has first and second regions, and is supported by the first plate. The second base is mounted on the first region. The third base is mounted on the second region. The laser diode is a tunable laser diode integrated with a Mach-Zehnder type optical modulator, and is mounted on the second base. The optical system is capable of fixing a wavelength of the laser diode and is mounted on the third base. Only a portion of the first base is mounted on the first plate. The portion of the first base includes the first region.

Abstract: A receiver includes wavelength demultiplexer for demultiplexing a received WDM light into light signals at respective central frequencies thereof, delay interferometer for converting a light signal output from wavelength demultiplexer into an intensity signal, and light detector for converting an output signal from delay interferometer into an electric signal. The interval between interferential frequencies of delay interferometer is 2/(2n+1) times the interval between the central frequencies of the WDM light. Logic inverting circuit outputs the output signal from the light detector while non-inverting or inverting the logic level thereof depending on the received central frequency.

Abstract: An optical transmission system includes an optical transmitter that includes first and second light sources, first and second phase modulators respectively modulating light from the first and the second light sources, and a polarized beam combiner combining the light output from the first and the second phase modulators to output an optical signal; and an optical receiver that includes a local oscillator, a polarization beam splitter splitting, according to polarization, the optical signal transmitted from the optical transmitter, and first and second digital coherent receivers corresponding to the first and the second phase modulators, and including a frontend that mixes light from the local oscillator and the polarization-split optical signal to output an electrical signal of real and imaginary parts, an analog-digital converting unit converting the electrical signal to a digital signal, and a digital signal processing unit estimating phase of the digital signal and extracting a signal.

Abstract: An acoustoelectric transducer comprising a laser source A and a light receiver H, wherein a soundfield S is provided by which the propagation velocity of the laser beam may be modulated according to the sound pressure while it traverses the soundfield S.

Abstract: An LD driver to generate an asymmetrical driving current with a relatively faster falling edge and an optical transmitter having the LD driver are disclosed. The LD driver includes a primary driver and the sub-driver connected in parallel to the primary driver. The primary driver converts the input signal or the delayed signal delayed from the input signal into the primary current. The sub-driver generates a symmetrical current tracing the input or the delayed signal, and an asymmetrical current formed by the OR operation between the input and delayed signals. The driving current is formed by adding the primary current, the symmetrical current and the asymmetrical current.

Abstract: A delay device that provides a delay amount to at least one of the in-phase signal and the quadrature signal, and a delay control section that controls the delay amount provided by the delay device based on a quality of the signals when the in-phase signal and the quadrature signal, to the at least one of which the delay amount is provided, at the delay device are converted into digital signals by the analog-digital converter, and the digital signal processing is carried out at the processor are provided. Thereby, the signal quality of recovered data at a receiving end of a multi-level phase modulation communication system is improved.

Abstract: An optical device comprising an optical device comprising a Mach-Zehnder interferometer having a first 2×2 optical coupler, a second 2×2 optical coupler, a first optical arm, and a second optical arm. The first and second arms connecting corresponding pairs of optical ports of the first and second 2×2 optical couplers. The second optical arm has a longer optical path than the first arm. The device also comprises one or more optical resonators optically coupled to the first optical arm and an optical splitter. The optical splitter is coupled to deliver a portion of an input optical signal to one port of the first 2×2 optical coupler and to deliver a remaining portion of the input optical signal to one port of the second optical coupler.

Abstract: An optical method for generating an optical quadrature duobinary QDB signal includes receiving a quadrature phase-shift-keying QPSK signal, and adding a delay to the received quadrature phase-shift-keying QPSK signal to generate an optical quadrature duobinary signal.

Abstract: Apparatuses and methods for modulating an optical signal are disclosed. One embodiment is a method comprising: phase modulating a slave laser which is injection locked to a master laser to produce an arcsine phase modulated optical signal, and combining the arcsine phase modulated optical signal with an output optical signal from the master laser.

Abstract: The differential group delay is measured in an optical fiber connection for an optical signal undergoing a phase modulation BPSK or DPSK by a digital signal at a given rate. A polarization controller at an emerging end of the connection scans polarization states of the modulated optical signal. An emulator iteratively introduces an additional delay in the modulated optical signal emerging from the connection and combines the delayed modulated optical signal and the non delayed modulated optical signal which are both polarized along two orthogonal axes into a resulting optical signal. A polarization controller and a fixed polarizer select a polarization state in the resulting optical signal along one of bisecting lines of the orthogonal axes into a linearly polarized signal. An eye diagram or a spectrum of the polarized signal is acquired by a digital oscilloscope or an optical spectrum analyzer to determine the differential group delay.

Abstract: Technologies are described herein for a phase deviation multiplication apparatus that implements an in-place multiplication approach for multiplying the phase deviation of an input signal while maintaining the frequency of the carrier signal within a frequency band of operation. According to an embodiment, a multi-stage phase deviation multiplication apparatus includes a plurality of sequentially arranged phase deviation multipliers, including at least a first phase deviation multiplier and a last phase deviation multiplier. The phase deviation multipliers have respective predetermined phase deviation multiplication factors. The first phase deviation multiplier receives an input signal and the last phase deviation multiplier generates a last phase deviated signal. The last phase deviated signal has a phase deviation multiplication factor that is the product of the respective predetermined phase deviation multiplication factors of the plurality of phase deviation multipliers.

Abstract: A demodulator includes: a splitter that branches a differential phase shift keying optical signal into a first branched optical signal passing through a first optical path and a second branched optical signal passing through a second optical path; a multiplexer that multiplexes the first branched optical signal having passed through the first optical path and the second branched optical signal having passed through the second optical path and makes interference between the first branched optical signal and the second branched optical signal; and a double refraction medium that reduces difference between phase differences between each polarized wave between the first branched optical signal and the second branched optical signal multiplexed by the multiplexer.

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: An optical transmitter includes: a data generating unit configured to generate a plurality of modulating signals; a driver configured to amplify the plurality of modulating signals generated by the data generating unit; a phase shifter configured to control a phase of at least one signal among the plurality of modulating signals to be input to the driver; a plurality of optical modulators connected in series to each other, and configured to modulate an optical signal on a basis of each of the modulating signals amplified by the driver; an optical coupler configured to branch the optical signal modulated by the optical modulator arranged at a last stage in the series; a photodiode configured to detect the optical signal branched by the optical coupler and convert the optical signal into an electric signal; and a phase control unit configured to control an amount of phase control of the phase shifter to maximize an intensity of the electric signal converted by the photodiode.

Abstract: It is provided an optical field transmitter comprising a light source, a DA converter and an optical field modulator. The optical field transmitter modulates an information signal into an optical field signal. The information signal includes one of multilevel signals arranged irregularly on a complex plane and multilevel signals arranged by combining mutually different numbers of phase values in at least two amplitude values. The optical field transmitter further comprises a phase pre-accumulation circuit for outputting phase pre-accumulation complex information obtained by previously accumulating a phase component of the information signal at predetermined time intervals. The DA converter converts the information signal including the output phase pre-accumulation complex information into an analog signal, and inputs the converted analog signal to the optical field modulator.

Abstract: In general, optical communication systems and methods may implement a vestigial phase shift keying (PSK) modulation format to enable relatively high transmission rates with closer channel spacing and improved signal detection in a WDM optical communication system. A PSK modulated signal may be correlated with a phase shift, for example, using a delay line interferometer (DLI), to generate a vestigial PSK signal, which may be pre-filtered, combined, and transmitted in the WDM system. The correlation with a phase shift compresses and shifts the signal spectrum such that intersymbol interference (ISI) length may be reduced with minimal increase in the bit error rate (BER) when the vestigial PSK signal is detected.

Abstract: The present invention discloses an apparatus and a method for controlling a driving amplitude of a DQPSK transmitter. The method includes: a DQPSK modulator modulating an optical signal emitted from a CW and without adding with modulated signal; a modulator feedback control unit is connected with a first bias point, a second bias point and a third bias point and controls the first bias point, the second bias point and the third bias point according to a part of the optical signal modulated by the DQPSK modulator; controlling the driving amplitude of a driver I according to temperature change of the driver I; controlling the driving amplitude of a driver Q according to temperature change of the driver Q. The present invention can be used to simplify complexity of the control circuit of the DQPSK transmitter, and therefore no extra optical signal-to-noise ratio cost would be created.

Abstract: A method and an apparatus for generating a differential quadrature phase shift keying (DQPSK) code optical signal are provided. The method may includes splitting an optical signal to obtain two polarized optical signals, modulating and phase-shifting one of the two polarized optical signals to obtain a phase-shifted and polarized optical signal, and modulating the other of the two polarized optical signals to obtain another polarized and modulated optical signal. The phase-shifted and polarized optical signal may be combined with the other polarized and modulated optical signal to obtain a polarization multiplexed optical signal. The method may further include, polarizing the polarization multiplexed optical signal to obtain the DQPSK code optical signal. The apparatus may include a polarization beam splitter (PBS), modulators, a phase-shift controller, a polarization beam combiner (PBC), and a polarizer.

Abstract: A high capacity optical transmitter implemented on a photonic integrated circuit chip comprises a single light source which supplies a continuous wave having a particular wavelength to a plurality of modulators to form modulated optical information signals. A phase shifter is coupled to at least one of the modulators and is used to shift the phase of the corresponding modulated optical information signal associated with a particular modulator. A polarization beam combiner receives each of the modulated optical information signals from the modulators and the modulated optical information signal from the phase shifter and combines each of these signals to form a polarization multiplexed differential quadrature phase-shift keying signal. The light source, the plurality of modulators, the phase shifter and the polarization beam combiner are all integrated on the chip.

Abstract: The present invention provides a system, apparatus and method to improve the signal-to-noise ratio performance in receivers configured to receive differential data signals. According to various embodiments of the invention, a received differential signal is processed to consider both forward-looking and backward-looking error components to improve SNR performance, and ultimately the reach of the optical line system. Additional processing is provided to further enhance noise tolerance related to chromatic dispersion.

Abstract: Methods, systems, and devices are described for formatting of data streams to be transmitted over fiber optic channels, and for processing received optical signals. A data transmission device may include a digital coding and modulation module that encodes a digital data stream, inserts unique words into the digital data stream, and modulates the encoded data stream and unique words onto optical channels for transmission over an optical fiber. A demodulation and decoding device may include a unique word identification module that identifies the unique words inserted in each optical channel stream, determines one or more characteristics of the plurality of optical channels based on the unique words, and provides the one or more characteristics to one or more other modules in the demodulator and decoding device.

Abstract: Provided is a channel assignment method in a wavelength-division-multiplexed transmission system. The channel assignment method includes obtaining information about signal modulation schemes from a plurality of optical transmitters, and assigning channels to the respective optical transmitters in consideration of the obtained information about the signal modulation schemes. Accordingly, in transmission of channels of different modulation formats, cross phase modulation is minimized, thereby reducing inter-channel interference.

Abstract: A demodulator comprises an input splitter, optical device sets, and couplers. The input splitter splits an input signal comprising symbols to yield a number of signals. A first optical device set directs a signal of along a first path. A second optical device set directs another signal along a second path to yield a delayed signal. At least a portion of the second path is in free space. A path length difference between the first path and the second path introduces a delay between the first signal and the second signal. A coupler receives a portion of the signal and a portion of the delayed signal to generate interference, where the interference indicates a phase shift between a phase corresponding to a symbol and a successive phase corresponding to a successive symbol.

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: 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: An optical signal generator includes a splitter, a first modulator, a second modulator, a signal-switching unit and a multiplexer. The splitter splits an optical pulse train into a first pulse train and a second pulse train. The first modulator receives the first pulse train and first data signal, and generates a first modulation signal by performing on-off-keying or phase modulation on the first pulse train based on the strength of the first data signal. The second modulator receives the second pulse train and second data signal, and generates a second modulation signal by performing the on-off-keying or phase modulation on the second pulse train based on the strength of the second data signal. The signal-switching unit delays pulses of the second modulation signal or adjusts a phase of a carrier included in the second modulation signal according to a switching signal. The multiplexer generates an optical modulation signal by multiplexing the first modulation signal and the second modulation signal.

Abstract: A first node receives a first phase modulated optical signal at a first wavelength from a master node. The first node also transmits a first amplitude modulated optical signal to the master node at the first wavelength using a portion of the first phase modulated optical signal as a light source.