To provide signal generating apparatus that is capable of controlling the DC bias of the optical modulator applicable to various kinds of modulation format, a signal processing apparatus includes a digital processing unit for deserializing an input digital data into parallel data lanes, for comparing the value of the digital data of symbol rate F to at least one predetermined threshold value, for selecting an offset value based on the result of the comparison; and for adding the selected offset value to the digital data, a converting unit for converting the digital data added the offset value to analog signals in each lane; an optical modulating unit for modulating a lightwave according to the analog signals with predetermined modulation format at the symbol rate F, where the modulated signal contains a frequency component at F/N.

The present invention is directed to communication systems and techniques thereof. More specifically, embodiments of the present invention provide a calibration system for optical transmitter. The calibration system provides a predetermined set of operating parameters to the optical transmitter and measures the second harmonic value of the transmitter output. A calibrated set of parameters is determined by selecting operating parameters associated with the minimum second harmonic value. There are other embodiments as well.

Systems and methods for detecting and correcting bias errors in optical coherent transponders are disclosed. An “outer” modulator in a transponder may, when properly biased, produce a phase offset of π/2 radians between in-phase and quadrature components of the optical signals transmitted in optical modulation formats by the transponder. The method may include providing input to a transponder to produce a periodic (and generally sinusoidal) output signal, measuring (using an optical power meter) the optical power of positive and negative harmonics of the signal while varying the amount of skew introduced by a de-skewing filter in the transponder, and determining that a curve representing the measurements performed on the positive harmonics and a curve representing the measurements performed on the negative harmonics are not orthogonal. The method may include adjusting the bias voltage of the modulator to make the two curves orthogonal, thus eliminating the bias error.

An optical communication device includes an optical modulator of a Mach-Zehnder type, a low frequency superimposing circuit configured to superimpose a low frequency signal on a substrate bias voltage applied to the optical modulator, a monitor configured to monitor a modulated light output from the optical modulator, and a substrate bias controller configured to control the substrate bias voltage based upon a low frequency component contained in a monitor signal output from the monitor.

An optical communication apparatus includes an optical modulator having a Mach-Zehnder interferometer with a pair of waveguides and configured to modulate a phase of light emitted from a light source, a first controller configured to control a first substrate bias voltage or an amplitude of a first drive signal applied to a first waveguide of the waveguide pair of the optical modulator based upon an output of the optical modulator or a wavelength of the light source; and a second controller configured to control a second substrate bias voltage or an amplitude of a second drive signal applied to a second waveguide of the waveguide pair of the optical modulator independently from the first controller, based upon the output of the optical modulator or the wavelength of the light source.

A control processor performs, in a startup sequence of an IQ optical modulator using a nested MZI, a first-stage process of controlling, so that a signal quality of an optical QAM signal output from a monitor port of the IQ optical modulator approaches a target quality, a voltage applied by a Bias_I voltage generator to I-component MZ optical modulator, a voltage applied by a Bias_Q voltage generator to a Q-component MZ optical modulator, and a voltage applied by a Bias_Ph voltage generator to a Bias_Ph phase adjusting means for controlling an optical path length of a parent MZI. After a completion of the first-stage process, the control processor changes a voltage output from the Bias_Ph voltage generator by a predetermined amount.

A control processor performs, in a startup sequence of an IQ optical modulator using a nested MZI, a first-stage process of controlling, so that a signal quality of an optical QAM signal output from a monitor port of the IQ optical modulator approaches a target quality, a voltage applied by a Bias_I voltage generator to I-component MZ optical modulator, a voltage applied by a Bias_Q voltage generator to a Q-component MZ optical modulator, and a voltage applied by a Bias_Ph voltage generator to a Bias_Ph phase adjusting means for controlling an optical path length of a parent MZI. After a completion of the first-stage process, the control processor changes a voltage output from the Bias_Ph voltage generator by a predetermined amount.

A drive unit outputs a modulation signal based on a data signal input from an optical communication apparatus through a pluggable electric connector. An optical modulator outputs an optical signal generated by modulating a light output from a light source based on the modulation signal. A control unit controls a modulation operation of the optical modulator. The control unit outputs a driver signal instructing to start a setting operation to the optical communication apparatus. The optical communication apparatus monitors the modulation operation of the optical modulator in response to the driver signal and performs an operation of correcting the data signal and/or an operation of outputting a control signal representing a control setting for the modulation operation to the control unit based on a monitoring result. The control unit controls the modulation operation of the optical modulator based on the control signal when receiving the control signal.

Embodiments herein relate to techniques for baseline wander (BLW) compensation. The technique may include identifying a data stream that is to be modulated by a ring modulator of an optical transmitter, wherein the data stream has a frequency operable to cause thermal-based BLW of an optical output of the optical transmitter. The technique may further include adjusting a time-varying direct current (DC) voltage bias of the ring modulator based on the frequency of the data stream. Other embodiments may be described and/or claimed.

A combinatorial optimization problem processing device is for associating a combinatorial optimization problem having N elements with an Ising model to process the combinatorial optimization problem. The combinatorial optimization problem processing device includes: a 1×2 Mach-Zehnder optical modulator that receives a polarized clock pulse train; an optical interference circuit that receives polarized clock pulse trains that were modulated by the Mach-Zehnder optical modulator; an optical coupler that couples output of the optical interference circuit with an initialization optical pulse train that creates a neutral state with respect to interactions between the elements; and a modulation signal generator that performs waveform shaping on an electrical signal obtained by photoelectrically converting an output signal of the optical coupler, generates a modulation signal for the Mach-Zehnder optical modulator, and externally outputs a monitor signal that represents a solution to the optimization problem. The optical interference circuit repeatedly allows a predetermined interaction in the Ising model to occur from the neutral state at a period corresponding to the N pulses of the polarized clock pulse train.