Abstract: A transmitter of optical signals uses a single light transmitter to modulate a multi-carrier signal. The multi-carrier signal is generated by performing digital signal processing in the digital domain to generate a plurality of components by performing Hilbert transform filtering. The components are modulated on to an optical transmitter as in-phase and quadrature components, thereby generating a multi-carrier waveform using a single optical transmitter.

Abstract: The disclosure relates to a method for optical frequency-locked multi-carrier generation based on one directly-modulated laser (DML) and one phase modulator (PM) in cascade driven by sinusoidal waveform (at the same or different frequency). When the DML and PM is driven by the same frequency RF signal at 12.5 GHz, adopting this method, 16 optical subcarriers with 12.5-GHz frequency spacing are generated with power difference less than 3 dB. When the DML and PM is driven by the different frequency with DML at 12.5 Ghz and PM at 25 GHz, over 24 optical subcarriers are generated with 12.5-GHz frequency spacing and amplitude fluctuation less than 3 dB. The number of the generated optical subcarriers can be further increased when the driving power for the DML is increased.

Abstract: A system and method for improving receiver sensitivity of an DD-OFDM system without using frequency guard band. The method having: interleaving input data to the DD-OFDM system to generate interleaved data; encoding the input data with a first recursive systematic convolutional code to generate a first recursive systematic convolutional encoded data; encoding the interleaved data with a second recursive systematic convolutional code to generate a second recursive systematic convolutional encoded data; puncturing the first recursive systematic convolutional encoded data and the second recursive systematic convolutional encoded data to generate a parity sequence; and combining the input data with the parity sequence to generate coded DD-OFDM data; wherein the parity sequence is generated by using different puncturing rates for different OFDM subcarriers, so as to obtain higher spectral efficiency.

Abstract: Blind polarization demultiplexing algorithms based on complex independent component analysis (ICA) by negentropy maximization for quadrature amplitude modulation (QAM) coherent optical systems are disclosed. The polarization demultiplexing is achieved by maximizing the signal's non-Gaussianity measured by the information theoretic quantity of negentropy. An adaptive gradient optimization algorithm and a Quasi-Newton algorithm with accelerated convergence are employed to maximize the negentropy. Certain approximate nonlinear functions can be substitutes for the negentropy which is strictly derived from the probability density function (PDF) of the received noisy QAM signal with phase noise, and this reduces the computational complexity.

Abstract: An optical transmitter determines the transfer function in the reference-based pre-equalization for applying to an optically modulated signal at the transmitter. The determined pre-equalization transfer function is made robust to linewidth inaccuracy of the optical source by performing phase correction during the calculation of the pre-equalization transfer function. The phase correction includes averaging a number of consecutive received phase samples. The determined pre-equalization transfer function is applied to modulated signals prior to the transmission over an optical medium.

Abstract: A method for generating a 400 Gb/s single channel optical signal from multiple modulated subchannels includes carving respective modulated subchannels into return-to-zero RZ modulated subchannels having non-overlapping peaks with intensity modulators having a duty cycle less than 50%, and combining the subchannels into a single channel signal aggregating the bit rate of each of the subchannels. The subchannels are combined with a flat top optical component for increased subsequent receiver sensitivity.

Abstract: The present invention relates to optical transmitters, transceivers, and transponders used for transmission of information or data in any form through a physical medium dependent (PMD) network. The speed of such networks depends, in part, on the density of information that can be transmitted through the physical medium. Optical transmitters or transceivers can be used to transmit multiple independent signals simultaneously through the same medium using different directions or axes of polarization, where the difference in the directions or axes of polarization can be used to distinguish the multiple signals at the receiver. In this invention, we use a master laser (l0) to synchronize two slave lasers (l1 and l2) by its x-polarization and y-polarization components of carrier, respectively, so that two slave lasers can be enforced to lock on exactly the same wavelength l0 with perpendicular polarization directions.

Abstract: Embodiments of the present invention pertain to optical wireless architecture, and in particular to novel optical architecture to provide wireless (mm)-wave signals and symmetrical wireline service with long-reach. Certain embodiments of the invention pertain to a novel method and apparatus to provide 12.5-Gb/s wireless signals at 60-GHz millimeter (mm)-wave and 100-Gb/s symmetrical wireline service with 80 km long-reach, for example. Moreover, novel enabling techniques are employed to overcome fiber dispersion, reduce costs, and provide super-broadband and long-reach service.

Abstract: An optical transmitter transmits a dual polarization optical Nyquist frequency domain multiplexed signal. The signal includes a first polarization component and a second polarization component. Each component comprises multiple subchannels, possibly having different subchannel bandwidths and different modulation schemes. An optical receiver receives the signal and recovers transmitted data.

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: Systems, devices and techniques for processing received QPSK modulated optical signals include sampling the received signal at twice the baud rate, thereby producing samples that are then processed as 9-QAM symbols using a decision directed least squares optimization method. Data bits are then recovered from the resulting symbol estimates. The received optical signal may also include dual polarized signals for increased bandwidth capacity.

Abstract: We describe and demonstrate a novel and simple scheme to generate flattened optical subcarriers using only phase modulators driven by single frequency fundamental sinusoidal sources. 160.8 Gb/s PM-QPSK experiment over a single subcarrier has been demonstrated.

Abstract: In Software defined elastic optical networks, modulation format and constellation size may be flexibly modified. As a result, digital signal processing (DSP) algorithm should be compatible with different modulation schemes or readily reconfigurable at the optical coherent receiver. Therefore we propose a novel cascaded adaptive blind equalizers based on decision-directed modified least mean square (DD-MLMS) algorithm for polarization separation and carrier phase recovery. The algorithm is square quadrature amplitude modulation (QAM) independent so that it could be applied in the elastic optical systems. The 28 Gbaud polarization multiplexing quadrature phase shift keying (PM-QPSK) and PM-16QAM back-to-back transmission is demonstrated. The results show that the performance is very close to the general algorithm but with a benefit of the reduced operation complexity.

Abstract: Techniques for optical communications using optical orthogonal frequency division multiplexing (OFDM) include operating a signal transmitter to modulate laser light to produce modulated light that carries, in optical domain, OFDM subcarriers for carrying communication information, without a frequency guard band between the OFDM subcarriers, and pilot subcarriers for channel estimation at a signal receiver, each pilot subcarrier being free of communication information, and controlling optical power of the pilot subcarriers to vary with optical frequencies of the pilot subcarriers so that optical power of a pilot subcarrier at a high optical frequency is different from optical power of another pilot subcarrier at a low optical frequency.

Abstract: Systems, devices and techniques for processing an optical signal transmitted from a source over a transmission medium having a length L and performing compensation of non-linear distortions include formulating the compensation as a digital back propagation algorithm by logically dividing the length L into N steps and compensating non-linear distortions for each step as a function of an attenuation adjusting constant parameter that can be selected from a range between 0.3 and 0.7.

Abstract: A method of generating a multi-subcarrier optical signal is disclosed. A local oscillator oscillates one or more data signals to generate one or more oscillating data signals. A series of modulators phase modulate a lightwave to generate a phase modulated lightwave, wherein the series of modulators are driven by the one or more oscillating data signals. The intensity modulator modulates the phase modulated lightwave, the intensity modulator being driven by one of the oscillating data signals, to generate the multi-subcarrier optical signal.

Abstract: An optical transmitter includes a dividing optical coupler, a first optical modulator driven by an I component of a first signal and a I component of a second signal for modulating a lightwave, a DC bias of the first optical, a second optical modulator driven by a Q component of the first signal and a Q component of the second signal for modulating a lightwave, a DC bias of the second optical modulator, a phase shifter, and a combining optical coupler for combining the modulated lightwave from the first optical coupler and the phase shifted Q components of the first and second signals for generating a quadrature amplitude modulated signal.

Abstract: A method and apparatus for generating sub-carriers is disclosed. Coherent optical sub-carriers with sub-carrier spacing are generated for carrying an orthogonal frequency division multiplexed (OFDM) signal. Multiple peaks are generated by cascading multiple phase modulators driven by different radio frequency sources.

Abstract: A heterodyne optical signal detector and method performed thereby, the signal detector including an optical signal spectrum shaper operable to modify the shape of the frequency spectrum of a received optical signal, a laser local oscillator (LO), and polarization beam splitters (PBSs) to divide the signal and the LO into orthogonal components, waveguides in which intermediate frequency (IF) signals are formed, balanced photodetectors (BPDs) arranged to receive the IF signals and operable to convert the IF signals into electric signals, and analog to digital converters (ADCs) that digitize the electric signals.

Abstract: A simplified coherent receiver based on heterodyne detection with only two balanced photo detectors (PD) and two analog-to-digital converters (ADC) is disclosed. The polarization diversity hybrid can be simplified relative to the conventional one. The detected intermediate frequency signals are first down converted to baseband with I/Q separation.