A Mach-Zehnder modulator (MZM) includes a first optical path with a first diode coupled to a first voltage signal node and configured to modify a phase of a first light signal transmitted through the first optical path. A further diode is positioned in the first optical path and configured to introduce a phase shift to the first light signal. A second optical path includes a second diode coupled to a second voltage signal node and configured to modify a phase of a second light signal transmitted through the second optical path. A first voltage signal carried on the first voltage signal node and a second voltage signal carried on the second voltage signal node each vary between a reverse biasing voltage level and a forward biasing voltage level. An optical coupler is coupled to the first and second optical paths.

An optical transmitter includes an optical modulator configured to modulate light from a light source; and a processor configured to generate a drive signal that is input into the optical modulator. The processor inserts a bias control signal amplitude-modulated at a low frequency, into an analog signal at fixed intervals, to generate the drive signal.

Systems and methods described herein include methods and systems for controlling bias voltage provided to an optical modulating device. The optical modulating device is biased at a bias point that is different from a null point of the device such that an offset to the received optical power due to limited extinction ratio is reduced.

A system for transmitting a sequence of at least two data bursts in a fibre optical communications system includes: selection circuitry configured to select one of a data input value, a logical high value or a logical low value such that the selection circuitry selects the data input value during a data transmission period during a defined burst period and selects one of the logical high value and the logical low value during an extension time period during the defined burst period and immediately following the data transmission period, such that for the sequence of at least two bursts, at least one burst has a logical low value extension period and at least one burst has a logical high value extension period; drive circuitry configured to apply a current to a laser diode, the current corresponding to the value selected by the selection circuitry during the defined burst period or a zero value otherwise, the current being such that the laser diode is configured to provide an optical output; an optical sensor module configured to provide a sensor module output corresponding to the optical output of the laser diode; wherein the sensor module output is configured to provide an electrical output proportional to the laser diode's optical output corresponding to the logical high value and the logical low value in the sequence of at least two bursts, and further configured to provide an output corresponding to an average value of the sensor module output during only the data transmission period during the sequence of bursts; and a controller configured to receive values regarding desired minimum and maximum optical output power levels of the laser diode and to receive the electrical output from the optical sensor module proportional to the optical output power level corresponding to the logical high and the logical low values, and to receive the output corresponding to the average value of the sensor module output during only the data transmission period during the sequence of bursts; wherein the controller is configured to use the received information to provide control values for the drive circuitry.

An optical modulator uses an optoelectronic phase comparator configured to provide, in the form of an electrical signal, a measure of a phase difference between two optical waves. The phase comparator includes an optical directional coupler having two coupled channels respectively defining two optical inputs for receiving the two optical waves to be compared. Two photodiodes are configured to respectively receive the optical output powers of the two channels of the directional coupler. An electrical circuit is configured to supply, as a measure of the optical phase shift, an electrical signal proportional to the difference between the electrical signals produced by the two photodiodes.

An optical module includes: an optical modulator, a superimposing unit, an offset adding unit, a detector, and a bias controller. The optical modulator includes a first modulator to generate a first optical signal, a second modulator to generate a second optical signal and a phase shifter to provide a specified phase difference between the first optical signal and the second optical signal so as to generate a modulated optical signal. The superimposing unit superimposes a low frequency signal on a DC bias of the first modulator. The offset adding unit adds an offset to a DC bias of the second modulator. The detector detects a low frequency component from output light of the optical modulator. The bias controller controls a DC bias that is applied to the phase shifter based on the low frequency component detected by the detector.

Systems and methods for In-phase and Quadrature modulation. The method includes i) processing In-phase digital signals and Quadrature digital signals and generating PT modulated In-phase analog signals and PT modulated Quadrature analog signals, ii) receiving an optical signal, iii) modulating the optical signal in accordance with the PT modulated In-phase analog signals and the PT modulated Quadrature analog signals and generate PT modulated In-phase optical signals and PT modulated Quadrature optical signals, iv) biasing the PT modulated In-phase optical signals and the PT modulated Quadrature optical signals to a null point, v) adjusting a phase bias point of the PT modulated Quadrature optical signals and generating phase adjusted PT modulated Quadrature optical signals, and vi) combining the PT modulated In-phase optical signals and phase adjusted PT modulated Quadrature optical signal and generate a combined PT modulated optical signal to be transmitted towards a receiver.

To improve the signal quality of the optical signal emitted by a reconfigurable transmitter after a reconfiguration event, an optical transmitter includes a modulator, a digital signal processor, and a controller. The modulator is for modulating light by a driving signal with a reconfigurable format. The digital signal processor is for processing digital data to be transmitted by using parameters in order to generate the driving signal. The controller is for controlling the digital signal processor changing the parameters so as to keep the driving signal stable before and after changing the reconfigurable format.

An electro-optic device may comprise a Mach-Zehnder modulator (MZM) and one or more components. The one or more components may apply a child DC bias with dither to arms of a first branch of the MZM and to arms of a second branch of the MZM, and determine a second harmonic of a first return signal. The one or more components may apply a child DC bias with phase-shifted dither to the arms of the first branch or to the arms of the second branch, and determine a second harmonic of a second return signal. The one or more components may determine, based on the second harmonics, whether the first branch and the second branch are operating at quadrature, and may selectively adjust parent DC biases, applied to the first branch and the second branch, based on whether the first branch and the second branch are operating at quadrature.

A system is configured to determine a first power level of a first signal output from a first modulator, and determine a second power level of a second signal output from a second modulator. The first signal may include a first optical signal associated with a particular polarization orientation, and the second signal may include a second optical signal associated with the particular polarization orientation. The system is configured to determine a relationship between the first power level and the second power level, and to set, based on the relationship between the first power level and the second power level, a reverse bias voltage associated with the first modulator, where the reverse bias voltage may be used to control the first power level of the first signal.