Abstract: A system is configured to receive a block of symbols, associated with a phase-modulated signal that includes data symbols that correspond to a payload associated with the signal, and control symbols; process the control symbols to identify an amount of phase noise associated with the control symbols; reset a phase, associated with each of the data symbols, based on the amount of phase noise and a reference phase; interleave the respective data samples, of each of the data symbols with other data samples, where the interleaved respective data samples cause errors, associated with the respective data samples, to be spread out among the other data samples and reduces an error rate relative to a prior data rate that existed before the interleaving; and perform forward error correction on the interleaved respective data samples.

Abstract: The present invention discloses a receiving apparatus, a sending apparatus, a system and a method for optical polarization division multiplexing.

Abstract: A DP-QPSK optical transmitter includes an outer MZM comprising a first parent MZM comprising a first child MZM and a second child MZM that modulates a QPSK signal with a first polarization. A second parent MZM includes a first child MZM and a second child MZM that modulates a QPSK signal with a second polarization. The outer Mach-Zehnder modulator multiplexes the first and second polarization embedded into a dual-polarization QPSK signal generation. A first optical detector detects the QPSK signal generated by the first parent MZM with the first polarization. A second optical detector optical detects the QPSK signal generated by the second parent Mach-Zehnder modulator with the second polarization. A bias control circuit generates bias signals on at least one output that stabilize the DP-QPSK signal in response to signals generated by the first and second optical detector using electrical time division multiplexing.

Abstract: A system receives traffic that includes four-bit symbols, the four-bit symbols being encoded using a four-bit phase modulation scheme; and processes the traffic to recover a four-bit symbol. The system also decodes the recovered four-bit symbol to obtain a three-bit symbol. The three-bit symbol is associated with a three-quadrature amplitude modulation (3QAM) scheme, and the decoding is performed without creating an error, within the traffic, when cycle slip occurs. The system outputs the traffic based on the three-bit symbol.

Abstract: Return To Zero (RZ) shaping is performed for a first I/Q modulator whose output corresponds to a first polarization component using a first two digital-to-analog convertors (DACs), each of which is sampled at approximately twice a modulation symbol rate or more and has an output with a first interleaving order that interleaves one of a first pair of intended drive signal patterns and zeros. RZ shaping is also performed for a second I/Q modulator whose output corresponds to a second polarization component using a second two DACs, each sampled at approximately twice the modulation symbol rate or more and having a second interleaving order that interleaves zeros and one of a second pair of intended drive signal patterns, the second interleaving order opposite the first interleaving order. The first polarization and the second polarization may be combined, thereby forming an Interleaved Return To Zero (IRZ) Polarization Division Multiplexed (PDM) signal.

Abstract: A system for suppressing even-order distortion in a photonic link includes a laser for providing laser light to a first input of a Mach-Zehnder modulator (MZM), where the MZM has a second input for receiving an RF input signal, a third input for applying a DC bias voltage to the MZM, and an optical signal output. A dc-voltage-biased photodiode has an input, coupled to the MZM optical signal output, and a modulated RF signal output. The MZM DC bias voltage is set at a value to generate an even-order distortion amplitude substantially equal to an even-order distortion amplitude from the photodiode and 180 degrees out of phase so as to substantially cancel the photodiode even-order distortion. The invention provides the cancellation of photodiode even-order distortion via predisortion linearization with a MZM biased slightly away from quadrature, employing a single fiber run and a single photodiode. The invention provides an improvement in carrier-to-intermodulation ratio (CIR) upwards of 40 dB.

Abstract: An optical modulator includes a light input/output unit receiving an incident optical signal which has not been modulated, splitting the incident optical signal into a first optical signal and a second optical signal, and transmitting the first and second optical signals to a first path and a second path, respectively, of an optical waveguide. A phase shifter is positioned in at least one of the first and second paths and modulates a phase of at least one of the first and second optical signals, which have been received through the first and second paths, respectively, in response to an electrical signal. A phase-modulated signal is output. A reflective grating coupler reflects signals respectively received through the first and second paths back along the first and second paths respectively.

Abstract: An optical transmitter comprises: first and second sets of optical in-phase and quadrature modulators; an integrable tunable laser assembly; a first polarization beam splitter that is configured to divide the continuous-waveform optical signal into a x-polarized tributary and a y-polarized tributary, each of the x-polarized tributary and the y-polarized tributary is modulated by one of the first and second sets of optical in-phase and quadrature modulators in accordance with the two respective input signals; a second polarization beam splitter that is configured to combine the modulated x-polarized tributary and the modulated y-polarized tributary into one optical signal; and an optical modulator that is configured to modulate the combined optical signal using a driving voltage, wherein the driving voltage has a bias point that is reduced by a predefined offset from a predefined reference voltage level.

Abstract: There is a need to prevent two receivers from converging on a state of receiving the same polarization state, fast start receivers, and ensure highly reliable operations. A polarization-multiplexed transmitter previously applies frequency shifts of frequencies +?f and ??f to X-polarization and Y-polarization digital information signals to be transmitted. Optical field modulators modulate and polarization-multiplex the signals. As a result, a frequency difference of 2?f is supplied to X-polarization and Y-polarization components. A polarization diversity coherent optical receiver 215 receives the signal. A frequency estimation portion in a digital signal processing circuit detects a frequency difference signal in both polarization components. This signal is used to a polarization splitting circuit in the digital signal processing circuit.

Abstract: Structures and methods of generating 8-QAM signals through the effect of a cascaded I/Q modulator and Mach-Zhender modulator. The 8-QAM signals are generated by applying one binary sequence to the dual-drive Mach-Zehnder modulator (MZM) and two binary sequences to the I/Q modulator. Operationally, the I/Q modulator generates QPSK constellation(s), while the dual drive MZM either maintains the QPSK constellation at an out ring, or attenuates its amplitude to the inner ring and rotates its phase by ?/4 phase depending on the binary data it was driven by.

Abstract: The embodiments of the present invention disclose an External Cavity Laser (ECL), relate to the field of Wave Division Multiplexing-Passive Optical Network (WDM-PON) technology, and effectively solve a problem of unstable output optical power of the ECL caused by polarization dependence. The ECL includes a gain medium, a filter, and a Faraday Rotator Mirror (FRM). The gain medium, the filter and the FRM constitute an oscillation cavity, and light emitted by the gain medium oscillates back and forth in the oscillation cavity.

Abstract: Embodiments of the present disclosure relate to a signal transmission method The signal receiving method includes: receiving a first transmit signal, where the first transmit signal includes a first polarized optical signal and a second polarized optical signal that are perpendicular to each other, where the first polarized optical signal is loaded with first data, the first transmit signal is an uplink signal, and the first data is uplink data, or, the first transmit signal is a downlink signal, and the first data is downlink data; splitting the first transmit signal into a first signal and a second signal according to power; separately rotating a first polarized optical signal and a second polarized optical signal of the second signal by 90 degrees; and performing coherent mixing on the rotated second signal and the first signal to obtain the first data.

Abstract: Provided is an optical module. The optical module includes: an optical bench having a first trench of a first depth and a second trench of a second depth that is less than the first depth; a lens in the first trench of the optical bench; at least one semiconductor chip in the second trench of the optical bench; and a flexible printed circuit board covering an upper surface of the optical bench except for the first and second trenches, wherein the optical bench is a metal optical bench or a silicon optical bench.

Abstract: Systems and methods are disclosed to perform four-dimensional optical multiband OFDM communication by organizing an N-dimensional (ND) signal constellation points as a signal matrix; performing 2D-inverse FFT and 2D-FFT to perform modulation and demodulation, respectively; and applying both orthogonal polarizations in the OFDM communication to deal with chromatic dispersion, PMD and PDL effects, and multidimensional signal constellation to improve optical signal-to-noise ratio (OSNR) sensitivity.

Abstract: An optical signal transmission system comprises a transmitter that phase-modulates two optical signals of a same frequency by asymmetrically chirping the two optical signals, combines the two optical signals that have been phase-modulated as polarization components according to polarization multiplexing, and transmits an optical signal that has been combined and obtained; and a receiver that receives said optical signal from said transmitter, compresses pulses of at least one of the polarization components of the optical signal, and splits the optical signal into two polarization components.

Abstract: Systems and methods are disclosed to provide optical communication by using subcarriers as individual bases functions, obtaining signal constellation points of an N-dimensional pulse amplitude modulation (ND-PAM) constellation diagram as an N-dimensional Cartesian product of a one-dimensional PAM; and transmitting the N-dimensional signal constellation point over all N orthogonal subcarriers serving as individual bases functions.

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: 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: A method of transmitting a data signal using an optical transmitter of an optical communications system. The optical transmitter is configured to modulate an optical carrier in successive signalling intervals to generate an optical signal. A modulation scheme is provided which comprises a multi-dimensional symbol constellation. The modulation scheme is designed such that an average degree of polarization of a modulated optical signal output from the optical transmitter has a first value when averaged across a first signalling interval, and has a second value when averaged across more than one and fewer than 100 signalling intervals. The second value is less than 10 percent of the first value. During run-time, an encoder of the optical transmitter encoding a data signal to be transmitted as symbols of the constellation, and a modulator of the optical transmitter modulating available dimensions of the optical carrier in accordance with the symbols.

Abstract: An optical modulator includes a splitter, phase modulators, amplitude modulators, intensity modulators, and a combiner. The splitter is configured to receive light, and split the light into portions of the light. Each of the phase modulators is configured to receive a corresponding one of the portions of the light, and modulate a phase of the portion of the light to provide a phase-modulated signal. Each of the amplitude modulators is configured to receive a corresponding one of the phase-modulated signals, and modulate an amplitude of the phase-modulated signal to provide an amplitude-modulated signal. Each of the intensity modulators is configured to receive a corresponding one of the amplitude-modulated signals, and modulate an intensity of the amplitude-modulated signals to provide an intensity-modulated signal. The combiner is configured to receive the intensity-modulated signals, combine the intensity-modulated signals into a combined signal, and output the combined signal.

Abstract: In an optical transmission system using an RZ code, in order to improve the quality of the modulated transmission signal, an RZ optical modulator includes an RZ carver that outputs a optical pulse train of the RZ code, a polarization adjustment device which improves and outputs a polarization extinction ratio of optical pulse train outputted from the RZ carver and an optical modulator which modulates and outputs the optical pulse train outputted from a polarization adjustment device.

Abstract: An optical communication system includes a polarization multiplexed orthogonal frequency-division multiplexing POLMUX-OFDM transmitter for generating a POLMUX-OFDM double sideband signal, an optical processing path for processing the double sideband signal from the transmitter; an analog-to-digital convert ADC-OFDM receiver coupled to the optical processing path for receiving the double sideband signal processed by the optical path; and a block-diagonal multiple-input multiple-output MIMO equalizer responsive to the receiver for enabling correct operation for a completely random incoming signal polarization state without adaptive polarization control at said receiver, which enables complexity.

Abstract: The present disclosure provides a polarization multiplexed transceiver, including: a transmitter; a receiver; circuitry within the transmitter configured to insert pilot tones as a reference state of polarization for a polarization multiplexed signal; and circuitry within the receiver configured to de-multiplex the polarization multiplexed signal using the pilot tones. The transmitted signal is constructed in such a manner as to facilitate the division of the receiver processing between the analog and digital domains such that the implementation may be simultaneously both highly spectrally efficient and power efficient.

Abstract: An optical modulation apparatus includes a first modulator, a second modulator, a multiplexer, a calculator and an adjustor. The first modulator configured to modulate light emitted by a light source using a first input signal and output a first modulated signal. The second modulator configured to modulate the light using a second input signal and output a second modulated signal. The multiplexer configured to multiplex the first and second modulated signals and output a multiplexed signal. The calculator configured to calculate a power difference between a higher-side frequency component having a frequency higher than a center frequency of the multiplexed signal and a lower-side frequency component having a frequency lower than the center frequency. The adjustor configured to adjust delays of the first and second input signals based on the power.

Abstract: An optoelectronic transmission system has a photoemitter semiconductor component and a photodetector semiconductor component. The photoemitter semiconductor component has a radiation source for converting a first electrical signal into a first electromagnetic radiation and a first polarization filter having a first polarization direction for filtering the first electromagnetic radiation. The photodetector semiconductor component has a second polarization filter having a second polarization direction for filtering a second electromagnetic radiation and a sensor element for converting a second electromagnetic radiation which has been polarized by the polarization filter into a second electrical signal. In this case, the first polarization direction of the first polarization filter is identical to the second polarization direction of the second polarization filter.

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: An apparatus comprises a coherent optical transmitter. The coherent optical transmitter comprises a first modulator for generating a first polarization, a second modulator for generating a second polarization, and a symbol interleaver configured to receive a first symbol stream intended to be transmitted on a first polarization and a second symbol stream intended to be transmitted on a second polarization, to direct one portion of symbols of the first symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the first symbol stream to the second modulator for modulation onto the second polarization, and to direct one portion of symbols of the second symbol stream to the first modulator for modulation onto the first polarization and another portion of the symbols of the second symbol stream to the second modulator for modulation onto the second polarization.

Abstract: A method of transmitting data using electromagnetic waves, comprising the steps of providing (101) a first electromagnetic signal (S1) having a first wavelength (?1) and a second electromagnetic signal (S2) having a second wavelength (?2) different from the first wavelength; dividing (102) each of the first (S1) and second (S2) electromagnetic signals into a first polarization component (S1x; S2x) having a first polarization direction and a second polarization component (S1y; S2y) having a second polarization direction orthogonal to the first polarization direction; modulating (103) the first polarization component (S1x) of the first electromagnetic signal (S1) to encode a first data stream (DS1); modulating (104) the second polarization component (S2y) of the second electromagnetic signal (S2) to encode a second data stream (DS2); and transmitting (105) a combined electromagnetic signal (Scomb) comprising the first and second polarization components of the first electromagnetic signal (S1) and the first and

Abstract: An optical transmitter includes: a first modulator that modulates a first optical signal with a first data signal; a second modulator that modulates a second optical signal with a second data signal; a multiplexer that multiplexes the first optical signal and the modulated second optical signal to output a multiplexed signal; a phase difference data generator that generates a phase difference signal corresponding to a phase difference between the modulated first optical signal and the modulated second optical signal from the multiplexed signal; and a controller that controls the phase difference between the modulated first optical signal and the modulated second optical signal based on the phase difference signal.

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: An optical transmitter for a WDM (Wavelength Division Multiplexing) passive optical network (PON) and a WDM PON comprising such an optical transmitter are disclosed. An optical transmitter comprises first mirror and second mirrors at first end and second ends of a cavity; an optical amplifier positioned within the cavity upstream from the first mirror and for amplifying light polarized in a first polarization plane; an optical waveguide for transmitting light from the optical amplifier to the second mirror and vice versa; a first non-reciprocal polarization rotator upstream of the optical amplifier and downstream of the optical waveguide; and a second non-reciprocal polarization rotator upstream of the optical waveguide and downstream of the first mirror; wherein the first and second non-reciprocal polarization rotators rotate the polarization of the light such that light which re-enters the optical amplifier after having been reflected by the second mirror is polarized in the first polarization plane.

Abstract: Techniques and configurations are provided to generate multiple coherent optical subcarriers. A laser source generates as output a light beam at a carrier frequency. A multicarrier generator is provided that is coupled to the laser source and comprises one or more dual carrier generators each configured to modulate the light beam at the same modulation frequency or different modulation frequencies so as to output a plurality of light beams each at a different subcarrier frequency that is offset from the carrier frequency. The multicarrier generator generates the plurality of light beams on individual outputs, e.g., fibers, without the need for an optical demultiplexing filter.

Abstract: A DP-QPSK optical transmitter includes an outer MZM comprising a first parent MZM comprising a first child MZM and a second child MZM that modulates a QPSK signal with a first polarization. A second parent MZM includes a first child MZM and a second child MZM that modulates a QPSK signal with a second polarization. The outer Mach-Zehnder modulator multiplexes the first and second polarization embedded into a dual-polarization QPSK signal generation. A first optical detector detects the QPSK signal generated by the first parent MZM with the first polarization. A second optical detector optical detects the QPSK signal generated by the second parent Mach-Zehnder modulator with the second polarization. A bias control circuit generates bias signals on at least one output that stabilize the DP-QPSK signal in response to signals generated by the first and second optical detector using electrical time division multiplexing.

Abstract: An optical transmitter includes: a modulator; an output light monitoring unit; and a control unit. The modulator includes a dividing unit dividing light inputted to the modulator into first and second branch lights; first and second modulation units performing phase modulation for the first and second branch lights, respectively; a rotator which rotates the polarization plane of one of the first and second modulated lights; and a polarization combining unit combining the first and second modulated lights. The output light monitoring unit monitors light intensity of the output of the polarization combining unit. The control unit controls at least one of the first and second modulation units, on the basis of a monitoring result by the output light monitoring unit. The control includes a light intensity control making the light intensity of the first and/or second modulated light smaller than a maximum value of a modulation curve light intensity.

Abstract: Methods and systems for a photonically enabled complementary metal-oxide semiconductor (CMOS) chip are disclosed. The CMOS chip may comprise a laser, a microlens, a turning mirror, and an optical bench, and may generate an optical signal utilizing the laser, focus the optical signal utilizing the microlens, and reflect the optical signal at an angle defined by the turning mirror. The reflected optical signal may be transmitted into the photonically enabled CMOS chip, which may comprise a non-reciprocal polarization rotator, comprising a latching faraday rotator. The CMOS chip may comprise a reciprocal polarization rotator, which may comprise a half-wave plate comprising birefringent materials operably coupled to the optical bench. The turning mirror may be integrated in the optical bench and may reflect the optical signal to transmit through a lid operably coupled to the optical bench.

Abstract: Systems, apparatus and method for modulating digital data onto an optical carrier to produce a modulated optical carrier in which symbol-modulated optical signals of orthogonal polarizations are temporally interleaved and adapted to be processed by electronic time-division demultiplexing to recover the digital data modulated onto the orthogonal polarizations of the optical signals.

Abstract: An apparatus and method for correcting for the polarization mode distortion of an optical signal is described. The optical data signal to be transmitted is processed by a switch configured to place the signal into a plurality of polarization states on a periodic basis. At the receiving end of the system, a portion to the signal is coupled to a polarimeter and the wavelength-dependent state of polarization (SOP) of the received signal determined for the plurality of polarization states imposed on the transmitted signal. The data for two of the transmitted polarization states is selected to be used as the basis for correcting the SOP so as to compensate for the wavelength dependence thereof. The corrections may be applied in an optical pulse shaper.

Abstract: A system receives a phase-modulated signal that carries client symbols and a sequence that includes first symbols on which a first tone is to be based and having a first power level, and second symbols on which a second tone is to be based and having a second power level; processes the sequence to generate the first tone and the second tone; determines a power difference based on the first power level and the second power level; retrieves condition information that identifies a threshold for determining whether a condition is associated with the signal; determines whether the power difference is greater than the threshold; and outputs an instruction, to adjust a parameter, used to transmit the signal, based on the determination that the condition is associated with the signal, where adjusting the parameter causes the power difference to decrease to a level that is less than the threshold.

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 invention provides a dual polarization transceiver (1) being switchable between two operation modes, wherein in a first operation mode an optical QAM—(Quadratur Amplitude Modulation) signal having a predetermined number (M) of constellation points is generated by said dual polarization transceiver (1) and wherein in a second operation mode an optical QPR—(Quadratur Partial Response) Signal having a predetermined number (L) of constellation points is generated by said dual polarization transceiver (1).

Abstract: It is an object of the present invention to provide an optical waveform shaping device of high resolution. The above-mentioned problem is solved by an optical waveform shaping device (10) comprising a branching filter (11) for dividing the light beam from a light source into light beams of each frequency, a condensing part (12) for condensing a plurality of light beams divided by the branching filter (11), a polarization separation means (13) for adjusting the polarizing planes of the light beams having passed through the condensing part (12), and a spatial light modulator (14) having a phase modulation part and an intensity modulation part where the light beams having passed through the polarizing plate (13) are incident.

Abstract: An optical modulation apparatus includes a first modulator, a second modulator, a multiplexer, a detector and an adjustor. The first modulator modulates light emitted by a light source using a first input signal and outputs a first modulated signal. The second modulator modulates the light using a second input signal and outputs a second modulated signal. The multiplexer multiplexes the first and second modulated signals and outputs a multiplexed signal. The detector is configured to detect a dip where power in a waveform of the multiplexed signal is equal to or smaller than a predetermined value. The adjustor is configured to adjust a delay of the first and second input signals based on power at the dip.

Abstract: A polarized-wave-multiplexing optical transmitter including: an optical combiner generating a polarized-wave-multiplexed optical signal by polarized-wave-multiplexing a first optical modulation signal and a second optical modulation signal; an optical power fluctuation portion fluctuating optical power of the first optical modulation signal and the second optical modulation signal periodically; a total-optical-power detection portion detecting fluctuation amount of total optical power of the polarized-wave-multiplexed optical signal; and an optical power controller reducing an optical power difference between the first optical modulation signal and the second optical modulation signal based on detection result of the total-optical-power detection portion.

Abstract: An apparatus comprising a laser transmitter having a first side and a second side, a filter coupled to the first side, a detector coupled to the second side, and a temperature controller coupled to the laser transmitter and the detector. Also disclosed is an apparatus comprising at least one processor configured to implement a method comprising receiving a photocurrent of a backward light from a laser, determining a wavelength shift offset between a wavelength of the output light and a filter transmission peak, and adjusting a temperature of the laser to substantially reduce the wavelength shift and align the wavelength of the output light with the filter transmission peak.

Abstract: In a polarization demultiplexing optical communication system (1000), an optical transmitter (100) provides a predetermined frequency deviation between carrier wave frequencies of optical signal to be transmitted, and provides a periodic fluctuation having a predetermined frequency to the light intensity of the optical signal to be transmitted. An optical receiver (300) extracts intensity information of a frequency component of the periodic fluctuation from the received optical signal, and calculates a wavelength dispersion value of the optical transmission line on the basis of the extracted intensity information. For this reason, it is possible to measure the wavelength dispersion value of the optical transmission line while operating the optical communication system.

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: An optical transmitter implemented with two QPSK (Quadrature Phase Shift Keying) modulators is disclosed. Each of the QPSK modulators provides a waveguide made of semiconductor material inducing the QCSE (Quantum Confined Stark Effect) by a bias supplied thereto. The optical performance of one of the QPSK modulators is determined by supplying a deep bias to the other of the QPSK modulator to eliminate the optical output therefrom.

Abstract: A transmitter in an optical communications system includes a digital signal processor for processing a data signal to generate a sample stream encoding successive symbols in accordance with a constrained phase modulation scheme having a constellation of at least two symbols and a modulation phase constrained to a phase range spanning less than 4?. A digital-to-analog converter converts the sample stream into a corresponding analog drive signal. A finite range phase modulator modulates a phase of a continuous wavelength channel light in accordance with the analog drive signal, to generate a modulated channel light for transmission through the optical communications system. A receiver in the optical communications system includes an optical stage for detecting phase and amplitude of the modulated channel light and for generating a corresponding sample stream, and a digital signal processor for processing the sample stream to estimate each successive symbol of the modulated channel light.