The present invention relates to telecommunication techniques and integrated circuit (IC) devices. More specifically, embodiments of the present invention provide an off-quadrature modulation system. Once an off-quadrature modulation position is determined, a ratio between DC power transfer amplitude and dither tone amplitude for a modulator is as a control loop target to stabilize off-quadrature modulation. DC power transfer amplitude is obtained by measuring and sampling the output of an optical modulator. Dither tone amplitude is obtained by measuring and sampling the modulator output and performing calculation using the optical modulator output values and corresponding dither tone values. There are other embodiments as well.

An optical transmitter includes optical modulation means for modulating a laser beam with a driving signal and outputting an optical signal; monitor means for detecting a part of the optical signal and outputting a monitor signal; bias voltage applying means for applying, to the optical modulation means, a bias voltage on which a dither signal is superimposed; average optical intensity detection means for detecting an average optical intensity of the optical signal from the monitor signal; top dither signal detection means for detecting, from the monitor signal, a top dither signal that is superimposed on a waveform with maximum optical intensity included in the optical signal; and bias voltage control means for controlling the bias voltage based on the average optical intensity and the top dither signal.

A Mach-Zehnder modulator for modulating optical signals, and comprising: a plurality of modulating waveguide sections; at least one bias electrode in electrical communication with at least one modulating waveguide section and configured to apply at least one electrical bias signal to one or more of the modulating waveguide sections; and an output optical combiner comprising a plurality of inputs and a plurality of outputs, wherein the plurality of inputs of the combiner are in optical communication with output sides of the plurality of modulating waveguide sections, and wherein a plurality of the outputs of the combiner are monitor outputs.

To provide a modulation control method and an optical transmission device that realize high reliability by more stably performing bias control of an optical modulator using an optical QAM scheme, an optical transmitter according to the present invention comprises a first waveguide and a second waveguide, wherein each of the first waveguide and the second waveguide are provided with an optical modulator that modulates a carrier light with a modulation driving signal that has multiple strength level values, a phase shift unit that provides a predetermined phase difference between a first optical signal outputted from the first waveguide and a second optical signal outputted from the second waveguide, a light detector that detects and photoelectrically converts a portion of a multiple value optical signal obtained by multiplexing the first optical signal and the second optical signal which have been provided with the phase difference and a control circuit that, on the basis of signal amplitude information obtained by a signal amplitude detector from wideband signal components from the light detector, corrects a first voltage provided to the first waveguide and corrects a second voltage provided to the second waveguide.

A control device that may be implemented in a single IC chip is provided that is capable of controlling EAM bias voltages and DFB bias currents and of monitoring the EAM photocurrents and received signal strength indicators (RSSIs) in a multi-channel optical transceiver module. The control device IC chip can be manufactured at relatively low cost with relatively high yield, and can be implemented in a relatively small area. To implement the control device in a single IC chip, multiple supply voltage domains are used in the IC chip, one of which is a negative supply voltage domain and one of which is a positive supply voltage domain. In order to provide these different supply voltage domains, a level shift circuit is employed in the IC chip that converts signals from the positive to the negative supply voltage domain, and vice versa, and changes the voltage levels, as needed.

The present disclosure discloses a method and an apparatus for automatically controlling a bias voltage of an optical modulator. The method includes: calculating a new Q bias voltage based on an acquired Q reference phase, a Q harmonic phase, a Q harmonic amplitude, a Q bias voltage and a Q error feedback coefficient, calculating a new I bias voltage based on an I reference phase, an I harmonic phase, an I harmonic amplitude, an I bias voltage and an I error feedback coefficient, and calculating a new P bias voltage based on a P reference phase, a P harmonic phase, a P harmonic amplitude, a P bias voltage and a P error feedback coefficient.

A method and an apparatus for digitally and automatically controlling a bias voltage of an electro-optic optical modulator are disclosed. The method includes: outputting a scanning bias voltage; acquiring a first optical signal; converting the first optical signal into a first electrical signal; outputting a first direct current signal; calculating an operating bias voltage at each operating point and a half-wave voltage; calculating an error feedback coefficient and a dither amplitude; outputting an operating bias voltage and a dither signal with the dither amplitude; acquiring a second optical signal; converting the second optical signal into a second electrical signal; outputting a harmonic component; calculating a harmonic amplitude and a shift phase; calculating a new bias voltage; and using the new bias voltage as the operating bias voltage.

An optical communications apparatus comprising a host (100) and an optical module (200) comprising a Mach-Zehnder modulator (202), MZM, wherein the optical module is removably connected to the host via a connection path, the optical communications apparatus comprising: a signal generator (101) at the host, configured to generate a plurality of calibration signals at a plurality of frequencies; a host interface (102) configured to transmit the calibration signals to the optical module via the connection path; a module interface (201) configured to receive the transmitted calibration signals; wherein the MZM is configured to use the calibration signals to modulate a laser light source (206) and biased to a point at which average output power is proportional to the output modulated signal; an optical detector configured to measure an average magnitude of an output of the MZM when each of the calibration signals is used to modulate the laser light source; one of a host calibration unit (103) and a module calibration unit (203), configured to determine a magnitude response of the connection path based on the measured average magnitudes and magnitudes of the respective calibration signals, and further configured to determine a pre-emphasis characteristic based on the magnitude response, the pre-emphasis characteristic for application to signals transmitted by the optical transmitter in use.

An optical transmitter includes: an optical modulator including an MZ interferometer, a drive signal input electrode, and a phase difference adjustment bias electrode; a drive amplifier; a phase difference adjustment bias voltage generator; a dithering unit that applies dithering of a predetermined frequency to an amplitude of a drive signal or to a half-wave voltage of the MZ interferometer; a controller unit that changes a phase difference adjustment bias voltage based on a modulation component of the frequency that is superimposed onto modulated light that is output from the optical modulator, to thereby bias the MZ interferometer to a null point; and a synchronous detection circuit that synchronously detects the modulation component of the frequency that is superimposed onto the modulated light. The controller unit changes the phase difference adjustment bias voltage such that a result of synchronous detection by the synchronous detection circuit becomes maximized or minimized. Whether the controller unit maximizes or minimizes the result of synchronous detection is determined by a difference between a phase of a referenced clock signal and a phase of the dithering, and does not depend on the amplitude of the drive signal.

An optical transmitter that transmits an optical signal includes a dither superimposing circuit configured to generate a dither signal, the dither signal being used to control an operation of the optical transmitter to output the optical signal, and a control circuit configured to control intermittent superimposition of the dither signal onto a target to be controlled.