An optical modulator has a continuous wave laser input, an RF input, a bias and dither input and an output. A photodiode connected to an output tap produces a voltage that is amplified. Noise is removed from the amplified output. A spread-spectrum dither harmonic is generated and supplied to a multiplier with the amplified and filtered feedback and is used to create a DC bias. A spread-spectrum dither is created and added to the DC bias. Spread spectrum dither and bias both are applied to the bias input of optical modulator. The bias and spread spectrum dither controller is usable with other non-optical modulators and other electronic devices.

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.

Embodiments of the present disclosure are directed toward techniques and configurations for phase offset adjustment in an electro-optical modulator. In one embodiment, the apparatus may include an electro-optical modulator having first and second arms, to modulate light passing through the arms according to an electrical data signal provided to the electro-optical modulator, to output an optical data signal that combines first and second light portions outputted by the first and second arms respectively; and a control module to convert the first and second light portions into first and second power signals indicative of respective phases of the first and second light portions, determine a balance between the first and second power signals, and adjust a phase of one of the first or second light portions, to achieve a bias point to provide the balanced optical data signal. Other embodiments may be described and/or claimed.

A bias control circuit for an optical modulator including a pair of optical waveguides and a power monitor is disclosed. The bias control circuit includes a bias generator, a differential amplifier, and a controller. The bias generator provides a bias signal to one of the optical waveguides. The bias signal includes a dither signal having a predetermined frequency. The differential amplifier receives a monitor signal from the power monitor and a reference signal, and generates an amplified signal corresponding to a difference between the monitor signal and the reference signal. The controller detects frequency components contained in the amplified signal. The frequency components originates from the dither signal. The controller generates a control signal according to intensity of the frequency components. The bias signal is adjusted according to the control signal provided from the controller.

This invention provides an optical transmitter that internally compensates for PDL with a high degree of precision and can output high-quality transmission signals. The optical transmitter is provided with the following: a light-outputting means for generating an optical signal; a data-outputting means for outputting a data sequence generated on the basis of information to be transmitted; a driving means for applying, to an optical modulator, a bias voltage with a pilot signal superimposed thereon; the optical modulator, which, upon the application of the bias voltage, modulates the abovementioned optical signal on the basis of the aforementioned data sequence and outputs the modulated signal; and a controlling means for controlling the bias voltage in accordance with the strength of the pilot signal extracted from the modulated signal.

An optical network unit may include a light sensitive unit suitable for receiving NRZ and/or PAM signals effectively. The optical network unit may include a laser transmission unit for providing NRZ and/or PAM signals effectively.

It is necessary to improve the signal quality of the optical signal emitted by a reconfigurable transmitter after a reconfiguration event, therefore, an optical transmitter according to an exemplary aspect of the invention includes a modulation means for modulating light by a driving signal with a reconfigurable format; a digital signal processing means for processing digital data to be transmitted by using parameters in order to generate the driving signal; and a control means for controlling the digital signal processing means by means of changing the parameters so as to keep the driving signal stable before and after changing the reconfigurable format.

An optical transmitter includes: a mapper configured to generate an electric-field-information signal from transmission data; a training-signal-generation section configured to generate a training signal; a training-signal-insertion section configured to insert the training signal into the electric-field-information signal; a driver configured to generate a drive signal from the electric-field-information signal into which the training signal is inserted; a modulator configured to generate an optical-modulation signal based on the drive signal; an optical receiver configured to generate an intensity signal indicating intensity of the optical-modulation signal; a training-signal-extraction section configured to extract an intensity-training signal corresponding to the training signal, from the intensity signal; a coder configured to generate a coded-training signal by coding the intensity-training signal extracted by the training-signal-extraction section using the training signal generated by the training-signal-generation section; and a distortion detection section configured to detect waveform distortion of the optical-modulation signal, based on the coded-training signal.

An optical modulator for generating quadrature amplitude modulation (nQAM) and phase-shift keying (nPSK) signals with tunable modulation efficiency. The modulator includes a controlling circuit for adjusting the modulation efficiency or modulation depth of the modulator by controlling the direct current (DC) bias.

An optical transmitter for modulating light from a light source to generate an optical transmission signal with use of a data sequence as an electric signal, the optical transmitter including: a mapping section for mapping the data sequence to be converted into multi-level data based on modulation multi-level degree information indicating multi-level degree of the modulation; a D/A converter for converting the multi-level data output from the mapping section into an analog signal; an optical modulator to be driven based on the analog signal output from the D/A converter, for modulating the light from the light source; and a bias control section for setting control polarity of DC bias control of the optical modulator based on the modulation multi-level degree information.