Abstract: An optical communications system includes an optical transmitter that generates a modulated optical signal at an output. The modulated optical signal propagates through an optical link where the dispersion of the optical link is imprinted onto an optical spectrum of the modulated optical signal. A demodulator receives the modulated optical signal and filters at least a portion of the optical spectrum with the imprinted dispersion of the optical link, thereby mitigating effects of dispersion in the modulated optical signal and generating a demodulated optical signal at an output. An optical detector generates an electrical data signal from the demodulated 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) signaling 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 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: An optical homodyne communication system and method in which a side carrier is transmitted along with data bands in an optical data signal, and upon reception, the side carrier is boosted, shifted to the center of the data bands, and its polarization state is matched to the polarization state of the respective data bands to compensate for polarization mode dispersion during transmission. By shifting a boosted side carrier to the center of the data bands, and by simultaneously compensating for the effects of polarization mode dispersion, the provided system and method simulate the advantages of homodyne reception using a local oscillator. The deleterious effects of chromatic dispersion on the data signals within the data bands are also compensated for by applying a corrective function to the data signals which precisely counteracts the effects of chromatic dispersion.

Abstract: A communication system and a timing control method are proposed that optimize timing in a sender and thereby enable information to be stably transmitted at the right timing. Under instructions from a timing controller in a receiver, the timing of driving a phase modulator in a sender is shifted by one step after another, and the then amount of clock shift and result of interference are monitored at the receiver and stored in a memory. The optimum timing is determined based on the stored data. Thus, a clock for driving the phase modulator in the sender can be set at the right timing. This is equivalent to compensating for group velocity dispersion due to wavelength dispersion that occurs when an optical signal channel and a clock signal channel are transmitted by wavelength division multiplexing transmission.

Abstract: Data is encrypted onto an electromagnetic beam by providing an electromagnetic beam having a signal component having a modal state, wherein the signal component is susceptible to accumulation of a geometric phase, and a reference component, transmitted along a path over at least part of which the signal component accumulates a geometric phase by transformation of its modal state from a first to a second modal state, from the second to at least one further modal state, and then back to the first modal state; and modulating with the data the geometric phase so accumulated, by modulating the modal state transformations. Data is decrypted from a received electromagnetic beam by corresponding processing of the received electromagnetic beam and by comparing an overall phase of the signal component with an overall phase of the reference component so as to retrieve the modulation.

Abstract: The present invention relates to an optical receiver, and particularly, to an optical receiver by which a DQPSK-modulated optical signal is demodulated to a multilevel phase-modulated signal.

Abstract: The present invention provides an optical power level discriminating device and method for discriminating optical power levels. The optical discriminating device includes a splitter for receiving an optical signal having first and second signal states, and splitting the received optical signal into a first and a second branch optical signal. A first optical fiber for transporting the first branch optical signal is provided that is made of a material having a high non-linear refractive index providing a different non-linear phase shift to the first and second signal states of the first branch optical signal. A second optical fiber is provided for transporting the second branch optical signal with little or no non-linear effect. The discriminating device also includes a combiner for combining the first branch optical signal and second branch optical signal to produce an output optical signal.

Abstract: An apparatus detecting an optical carrier phase difference between adjacent optical pulses structuring an OTDM-DPSK signal, by generally-used optical and electrical elements, is provided. An OTDM-DPSK signal generating section has an optical splitter, a first phase modulator, a second phase modulator, an optical coupler, and a monitor signal branching device, and generates and outputs an OTDM-DPSK signal and a monitor signal. An optical carrier phase difference detecting section has an optical carrier interferometer, and an interference signal detecting section including a optical-to-electrical converter and a peak detection circuit. The monitor signal is inputted to the optical carrier interferometer, and an interference monitor signal is outputted. The interference monitor signal is inputted to the optical-to-electrical converter, and an electrical interference monitor signal is outputted.

Abstract: The present invention provides a light receiving apparatus using the DQPSK demodulation method. The light receiving apparatus comprises: one Mach-Zehnder interferometer for branching a received light signal into light signals at two arms to allow the branched two light signals to interfere with each other; one balanced photoelectric converter for converting the two interfered light signals, by using the Mach-Zehnder interferometer, into an electric signal corresponding to a difference between light intensities of the two light signals; and a phase adjuster for dynamically shifting the phase of a light signal passed through one of the two arms at the Mach-Zehnder interferometer.

Abstract: A demodulator includes a splitter, a first dielectric substance, and a combiner. The splitter splits a differential phase shift keying optical signal into a first light beam and a second light beam and outputs the first light beam to a first optical path and the second light beam to a second optical path. The first dielectric substance is disposed in the first optical path and has a refractive index higher than the average refractive index of the second optical path. The combiner combines the first light beam and the second light beam and causes the beams to interfere with each other. The difference in length between the first and second optical paths and the refractive index of the first dielectric substance are set such that the first light beam is delayed by one bit with respect to the second light beam.

Abstract: The present invention provides an optical phase modulation evaluating device that can measure and evaluate the precise degree of modulation in phase of an optical phase modulation signal in comparison with the conventionally-known optical phase modulation evaluating device. The optical phase modulation evaluating module includes: a bit delay device located on optical paths of the third and fifth light beams, and adapted to change the length of the optical paths to delay the third and fifth light beams by one bit per second; and an optical phase difference setting means for delaying either or both the ninth and tenth light beams by a designated phase angle which is not equal to zero, the optical phase difference setting means having a light transmissive plate located on an optical path for the ninth light beam, and a light transmissive plate located on an optical path for the tenth light beam.

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.

Abstract: Disclosed are a forward discrete/inverse-discrete Fourier transform device and method for optical orthogonal frequency division multiplexing (OFDM) communication and a transmitting and receiving apparatus. The forward inverse-discrete Fourier transform device includes N 1:N splitters for splitting subcarrier signals received from N inputs corresponding to the number of optical frequencies of subcarriers, a phase shift delay array module for shifting phases of the split signals from the 1:N splitters, N N:1 power couplers for coupling signals output from the phase shift delay array module, a time delay array module for performing time delay on optical OFDM symbols from the N:1 power couplers, and an N:1 power coupler for coupling signals output from the time delay array module.

Abstract: A waveform converting unit gives a change to a clock signal as a periodic voltage fluctuation that drives a pulse carver unit carrying out shaping into an RZ waveform. The pulse carver unit receives a bias voltage applied thereto from a bias voltage applying unit, is driven by the clock signal that is given a change by the waveform converting unit and that is amplified by an amplifying unit, and outputs an RZ pulse whose duty has been changed.

Abstract: Systems and methods are disclosed to process an optical signal with a pre-processing module to populate a non-linearity compensation look-up table based on a set of predetermined rules in a non-real-time off-line mode; and a transmitter applying said predetermined rules in real-time to multiple channel input data to generate a real-time symbol pattern, searching the look-up table with the real-time symbol pattern to determine a non-linearity compensation output, and modulating the optical signal with the compensation output.

Abstract: An optical code division multiplexing signal generator provided with an optical pulse light source, a first encoder to an Nth encoder, a first optical modulator to an Nth optical modulator, and a first optical circulator to an Nth optical circulator. The first optical circulator inputs an input optical pulse train to a first encoder, and inputs a first encoded optical pulse train output by Bragg reflection from the first encoder to the first optical modulator. The kth optical circulator inputs an input (k?1)th optical pulse train which has passed through the (k?1)th encoder to a kth encoder, and inputs a kth encoded optical pulse train output by Bragg reflection from the kth encoder to the kth optical modulator. Herein k takes all integers from 2 to N, and N is a positive integer of 2 or more.

Abstract: Modulator driver for driving an electro-optical modulator in a high-speed optical communications system. In accordance with aspects of the present invention, a modulator driver is presented comprising an input differential limiting amplifier which is coupled to a distributed differential current-switch configuration, where one set of outputs of the distributed differential current-switch configuration are grounded and the other set of outputs are connected to an artificial transmission line structure generating forward traveling and reverse traveling signals, with the reverse traveling signal termination bias inductively coupled to a separately adjustable positive bias voltage, whereby the circuit architecture reduces the number of components and transitions in the high-speed signal path and is compatible with compact, monolithic fabrication requiring a minimal amount of external components for operation. Other methods and apparatus are presented.

Abstract: A signal Data1 and Data2 are output from a DQPSK signal source. The output signal is input to the modulator drivers 1 and 2 of the differential output. A drive signal is applied from the drivers 1 and 2 to a modulator, and modulated light is output. An optical coupler 20 branches modulator output, and a power monitor 21 detects the power of the branched light. A detection result is transmitted to an amplitude control unit 22. The amplitude control unit 22 adjusts the amplitude of the drivers 1 and 2 such that the detection result of the power monitor 21 can be the maximum.

Abstract: The present invention provides apparatus for self-phase modulation noise calculation, apparatus for self-phase modulation noise elimination and optical coherent receiver. The apparatus for calculation comprises: a signal receiver to receive an input signal; a calculator connected to the signal receiver to calculate a self-phase modulation noise at the current instant by using the signal powers of an input signal waveform at the current instant and at several sampling instants adjacent to the current instant. The embodiments of the present invention calculates the self-phase modulation noise at a certain instant by using the signal powers at a plurality of digital sampling periods before and after this instant, and when the apparatus is used to calculate the self-phase modulation noise of each of the sub-spans in an optical fiber transmission link, in case that the calculation precision is ensured, the granularity of the sub-spans may be reduced, thereby lowering the complexity of the calculation.

Abstract: Optical communication apparatus, methods, systems are provided based on balanced-detection phase-shaped binary transmission (BD-PSBT).

Abstract: Apparatus and methods are provided for receiving differential phase-shift keyed (DPSK) optical signals subjected to tight optical filtering, such as may be experienced by 40 Gb/s and 100 Gb/s channels in a dense wavelength division multiplexing (DWDM) communications system with 50 GHz channel spacing. An optical DPSK receiver is described which employs an optical delay interferometer (ODI) demodulator having a free spectral range (FSR) that is larger than the symbol rate (SR) of the DPSK signal to be demodulated. The receiver includes means for introducing an additional power imbalance between the outputs of the ODI demodulator, and the additional power imbalance may be related to the ratio of FSR to SR. The additional power imbalance increases the signal tolerance to tight optical filtering, thereby achieving high spectral efficiency in applications such as DWDM.

Abstract: Signals can be superimposed on optical phase even when low-coherency light is used, and a bit rate and a signal coding format similar to those used in ordinary optical communications can be used. A transmitter includes an asymmetric interferometer or an antisqueezed light generator to convert a train of single pulses into a train of dual pulses. A receiver also includes an asymmetric interferometer that provides the same delay time as that between the dual pulses. The receiver allows pulses originating in the same light source to interfere, so that signals can be superimposed on the phase even when a low-coherency light source is used. The delay time (optical path length difference) provided in the asymmetric interferometer is set to be longer than half the period of the pulses outputted from the optical pulse source.

Abstract: An optical transmitting apparatus includes a modulating unit that branches an input light and performs independent phase modulation to branched optical signals of arms, a phase adjusting unit that changes a phase difference between the optical signals of respective arms according to a control signal, a combining unit that combines modulated lights having the phase difference, an acquiring unit that acquires a positive-phase signal and a negative-phase signal from the combining unit, a subtracting unit that obtains a difference between the positive-phase signal and the negative-phase signal acquired by the acquiring unit, a detecting unit detecting a power of a differential signal from subtraction by the subtracting unit, and a control unit that changes the control signal according to signal component intensity detected by the detecting unit.

Abstract: Provided are an auto-compensating quantum cryptography transceiver and method of transmitting a quantum cryptography key at a high speed. A quantum cryptography transmitter includes a wavelength converter, an optical attenuator, an optical phase modulator, and a Faraday mirror. A quantum cryptography receiver includes a polarization beam splitter, an optical coupler, an optical filter, and a photon detector. Thus, a limit of a transmission rate caused by Rayleigh scattering of an optical fiber can be overcome.

Abstract: Rhomb beam splitters are used to implement various optical demodulators, in particular PSK and DPSK demodulators. The parallel beam-splitting and reflective surfaces of the rhomb structure produce reflection and transmission beams that exit the beam splitter parallel to one another and with a relative phase shift determined by the distance between the surfaces. These features afford the advantages of low cost, compactness, easily tunable, and temperature-insensitive optical structures for constructing a variety of optical demodulators.

Abstract: An optical homodyne communication system and method in which a side carrier is transmitted along with data bands in an optical data signal, and upon reception, the side carrier is boosted, shifted to the center of the data bands, and its polarization state is matched to the polarization state of the respective data bands to compensate for polarization mode dispersion during transmission. By shifting a boosted side carrier to the center of the data bands, and by simultaneously compensating for the effects of polarization mode dispersion, the provided system and method simulate the advantages of homodyne reception using a local oscillator. The deleterious effects of chromatic dispersion on the data signals within the data bands are also compensated for by applying a corrective function to the data signals which precisely counteracts the effects of chromatic dispersion.

Abstract: A variety of adaptable electronic duobinary generating filters to be used in communication systems are provided, each filter generating an adaptable electronic duobinay signal which is optimized for system impairments. According to one exemplary implementation, an adaptable electronic duobinary generating filter comprises an adaptable delay-and-add circuit, having an adaptable electronic delay element having a delay ?T: 1/T being the bit rate of the binary data input into the adaptable delay-and-add circuit, and ? being an adaptation parameter which can be optimized depending on the system impairments. In one optional implementation, the adaptable electronic delay element can be programmably adaptable to optimize against deterministic system impairments. In another optional implementation, the adaptable electronic delay element can be dynamically adaptable to optimize against dynamically varying system impairments.

Abstract: A reduction in size and cost of an optical modulator is achieved with a simple configuration, while improving the modulation characteristics. An optical modulator modulates light branched by an optical coupler and then couples the light via the optical coupler. The optical coupler is formed in a substrate having electro-optic effects. An optical waveguide is formed in the substrate and, includes a turnback section and ends into which the light branched by the optical coupler is input. A signal electrode is provided in the substrate along the optical waveguide. A modulation signal to modulate the light passing through the optical waveguide is input to the signal electrode.

Abstract: A method is provided for co-site interference mitigation in an RF communication system. Spectral nulls created in an optical domain may be used to mitigate interfering signals in an RF signal. The method includes: receiving an RF input signal via an antenna; generating two optical signals that are each modulated using the RF signal; creating a phase delay in one of the two optical signals that corresponds with a spectral null at a frequency of an interfering signal; converting the two optical signals into two corresponding electrical signals and combining the two electrical signals to create spectral nulls via interference between the two signals and form a mitigated output signal. In this way, the spectral null offsets the amplitude of the interfering signal, thereby reducing the signal strength of the interfering signal.

Abstract: In a quaternary phase modulator including two phase modulators disposed in parallel and a phase adjuster that adjusts a phase difference when the outputs of the two phase modulators are combined, there are provided a second light source that introduces light propagated in a backward direction, a first controller that controls the bias of the two phase modulators so that the intensity of the backward light is a minimum on the input side of the quaternary phase modulator, and a second controller that controls the bias of the phase adjuster so that a result monitored by a photodiode having a bandwidth not exceeding the bit rate on the output side of the quaternary phase modulator is a minimum, the first controller being implemented after the second controller is implemented.

Abstract: A data transmission system comprising a transmitter and a receiver. The transmitter comprises a phase encoder for partitioning consecutive bit data to be input in data in units of X bits; and converting a 2x value indicated by the data of X bits in unique association with an (N/2?1)Y value of a Y symbol, and for confining use of signal points, from among the signal points of N-ary phase, only to a signal point P1 (at a phase angle 0) and N/2?2 signal points P(2n+2) (where 1?n<N/2?2). The receiver comprises a phase decoder for notifying an error detection when a signal point other than a signal point that are permitted to be used is received, and performing an error correction by changing the signal point to a signal point which has a smaller hamming distance.

Abstract: An apparatus, system and method wherein a polarization multiplexed differential phase shift keying format (POLMUX-DPSK) is provided with offset and bit-interleaved frequency channels and demodulated using a DPSK demodulator.

Abstract: Consistent with the present disclosure, optical signals are modulated in accordance with a higher order QAM modulation format, such as 8-QAM, to carry customer data, for example. The optical signals are converted to corresponding electrical signals, which are then subject to further processing. In particular, phase data associated with the higher order QAM constellation is processed, such that the outer points of the constellation are rotated to have the same phase as the inner points. As a result, both the inner and outer points resemble a constellation, and both may be more readily processed using feedforward or feedback carrier recovery. After such carrier recovery, the phase data is further processed so that the outer points are rotated back and the customer data can be extracted from the phase data.

Abstract: An optical gate switch circuit includes: an asymmetric Mach-Zehnder interferometer having an optical path that outputs control light and probe light to a second optical directional coupler via a first optical directional coupler and an optical phase modulation element, and another optical path that connects a third optical directional coupler to which the probe light is input, to the second optical directional coupler via a variable optical attenuator and an optical phase shifter; and a bandpass filter connected to the second optical directional coupler.

Abstract: A modulation method for optical communication comprises the step of generating an optical signal modulated between a plurality of different states of polarization and between different phase states. The plurality of states of polarization comprises first states of polarization. The first states of polarization define a single great circle on the Poincaré sphere. The method is characterized in that the plurality of states of polarization further comprise one or more second states of polarization located outside the great circle. Such additional second states of polarization increase the symbol alphabet.

Abstract: Entanglement-based QKD systems and methods with active phase tracking and stabilization are disclosed wherein pairs of coherent photons at a first wavelength are generated. Second harmonic generation and spontaneous parametric downconversion are used to generate from the pairs of coherent photons entangled pairs of photons having the first wavelength. Relative phase delays of the entangled photons are tracked using reference optical signals. Classical detectors detect the reference signals while single-photon detectors and a control unit generate a phase-correction signal that maintains the relative phases of phase-delay loops via adjustable phase-delay elements.

Abstract: An optical modulation device including waveform shapers that waveform-shape input data signals in synchronism with a rising or falling timing based on comparison with a reference level of an input clock signal, a multi-level phase modulator that generates a multi-level-phase-modulated optical signal based on the data signals waveform-shaped by the plurality of waveform shapers, and outputs the generated optical signal, and a level ratio controller that varies a relative level ratio of the reference level to an amplitude level of the clock signal input to the waveform shapers, based on the optical signal output from the multi-level phase modulator.

Abstract: A demodulator and method are provided. The demodulator for demodulating an optical signal, includes a splitter that splits a differential phase modulation signal into a first split light component and a second split light component, couples the first split light component to a first optical path and the second split light component to a second optical path, a first medium disposed on the first optical path, a second medium disposed on the second optical path and having a refractive index different from that of the first medium, and a combiner that combines the first split light component that has passed through the first medium and the second split light component that has passed through the second medium, wherein one of the first split light component and the second split light component is delayed in relation to the other.

Abstract: The invention provides an apparatus and method for time delaying different polarization components of a signal relative to one another, comprising a polarization signal splitter which splits first and second polarization components of an input signal into a first component signal and a second component signal such that said first component signal propagates along a first path and the second component signal propagates along a second path, wherein said first component signal reaches a location relative to when said second component reaches said location at times differing by a delayed time, and use of the apparatus in a communication system. The apparatus may be used for quantum cryptography, to convert a sender's polarization-qubit signal into a signal appropriate for channels and receivers based on phase-encoded schemes.

Abstract: A method includes generating at least two lightwave carriers from a lightwave source, the carriers having a wavelength spacing, creating an up-subchannel and a down-subchannel orthogonal to one another and spaced apart based on the fixed wavelength spacing from modulations of the lightwave carriers according to respective up-converted OFDM signals that are carrier suppressed, and combining one lightwave from the up-subchannel and one lightwave from the down-subchannel into an optical channel for transmission over an optical fiber.

Abstract: The present invention discloses a modulation device for generating an optical signal with quadruple frequency and the modulation method thereof. The modulation device in the present invention utilizes a commercial integrated modulator, a RF signal generator and a phase shifter to generate an optical signal with quadruple frequency. When the RF signal generator generates a first modulation signal, and the phase shifter shifts the first modulation signal by 90 degrees to generate a second modulation signal, the integrated modulator is biased to transmit the optical signal in maximum value and to modulate the first and second modulation signal so as to generate a output optical signal with quadruple frequency.

Abstract: Consistent with the present disclosure a transmitter is provided that transmits data in either a “quasi-DP-BPSK” (“QDP”) mode or in a DP-QPSK mode. In the QDP mode, data bits are transmitted as changes in phase between first and second phase states along a first axis or as changes in phase between third and fourth phase states along a second axis in the IQ plane. Although the transmitter outputs an optical signal that changes in phase between each of the four states, a sequence bit identifies which axis carries the data bit. The sequence bit is one of a series of sequence bits that may be generated by a pseudo-random number generator. The series of sequence bits can be relatively long, e.g., 32 bits, to permit sufficiently random changes in the axis that carries the data.

Abstract: Embodiments of the present invention provide a method and apparatus for producing a phase coded non-return-to-zero (PC-NRZ) optical signal. The method includes providing an input optical signal; providing first and second drive signals, the first drive signal having a first data pattern of first and second signal levels, the second drive signal having a second data pattern, the second data pattern having third and fourth signal levels that toggle at least when the first drive signal changes from the first signal level to the second signal level; and modulating amplitude of the input optical signal with the first drive signal and modulating phase of the input optical signal with the second drive signal to produce the PC-NRZ optical signal. A PC-NRZ optical transmitter and an optical transmission system applying the PC-NRZ optical transmitter are also provided.

Abstract: The method and system are disclosed for automatic feedback control of integrated optical quadrature modulator for generation of optical quaternary phase-shift-keyed signal in coherent optical communications. The method comprises the steps of detecting at least a part of an output optical signal from the QPSK modulator, extracting of a particular portion of the output signal in frequency domain, and processing the signal in frequency domain to optimize the transmission of an optical link. The system and method of optical communications in fiber or free space are disclosed that implement the quadrature data modulator with automatic feedback control.

Abstract: An optical amplification method and apparatus implemented using RZ-DPSK modulation or variants thereof and a deeply saturated semiconductor optical amplifier.

Abstract: An optical transmitter for converting an input data series into an optical multi-level signal and for outputting the same, includes an LUT in which data for executing optical multi-level modulation is stored and from which first modulation data and second modulation data are output based on the input data series. A DAC converts the first modulation data by D/A conversion to generate a first multi-level signal. A DAC converts the second modulation data by D/A conversion to generate a second multi-level signal. A dual-electrode MZ modulator includes a first phase modulator for modulating light from a light source in accordance with the first multi-level signal and a second phase modulator for modulating light from the light source in accordance with the second multi-level signal, and combines an optical signal from the first phase modulator and an optical signal from the second phase modulator to output the optical multi-level signal.

Abstract: A transmitter (3) for generating a DQPSK-modulated optical signal, including: a splitter (7) for dividing an optical carrier signal into a first and second branch (8a, 8b), a first and second Mach-Zehnder interferometer (9, 10) in the first and second branch (8a, 8b), respectively, a phase shifter (11) in one of the branches (8b) generating a nominal phase shift of .pi./2, and a combiner (7?) for combining the optical output signals of the two branches (8a, 8b). The transmitter (3) has a feedback circuit (12) generating at least a first and second bias signal (15.1 to 15.3) for adjusting a bias of at least the first and second Mach-Zehnder interferometers (9, 10), the feedback circuit (12) includes a detector for generating at least a first and second feedback signal from a sample signal extracted from the optical signal after the combiner (7?), and for each bias signal: a local oscillator generating an auxiliary signal modulating the bias signal (15.1 to 15.

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: Consistent with the present disclosure, a compact transmitter is provided that can generate optical signals having different modulation formats depending on optical link requirements. Preferably, the transmitter includes a photonic integrated circuit having multiple lasers and modulators. A control circuit adjusts the drive signals supplied to the modulators such that optical signals having a desired modulation format may be output from the modulators. Thus, for example, the transmitter may be used to output optical signals having a modulation format suitable for long haul or submarine links, as well as for links having a shorter distance.