Apparatus, circuits and methods for reducing mismatch in an electro-optic modulator are described herein. In some embodiments, a described optical includes: a splitter configured for splitting an input optical signal into a first optical signal and a second optical signal; a phase shifter coupled to the splitter; and a combiner coupled to the phase shifter. The phase shifter includes: a first waveguide arm configured for controlling a first phase of the first optical signal to generate a first phase-controlled optical signal, and a second waveguide arm configured for controlling a second phase of the second optical signal to generate a second phase-controlled optical signal. Each of the first and second waveguide arms includes: a plurality of straight segments and a plurality of curved segments. The combiner is configured for combining the first and second phase-controlled optical signals to generate an output optical signal.

A segmented optical modulator includes two optical modulator segments located along a main face of a photonic chip, and two RF transmission lines connected to drive a corresponding one of the two optical modulator segments. A signal electrode of one of the transmission lines includes a segment that is vertically capacitively coupled to a plurality of spaced ground-connected metallic elements disposed in sequence along a length of the segment above or below thereof so as to be capacitively coupled thereto.

An electro-optic device, such as an optical modulator, comprises: a driver for generating a plurality of identical time-synchronized copies of an input electrical signal, and a photonic integrated circuit, including an optical waveguide structure and a plurality of phase-modulating electro-optical modulator segments. Each one of the modulator segments configured to receive a respective one of the plurality of the copies of the input electrical signal. Instead of incorporating a required phase delay between the copies of the input electrical signal into the driver structure, a multi-layer interconnect substrate is provided that includes a plurality of insulating layers alternating with a plurality of conductive layers. The plurality of conductive layers are configured to include a plurality of delay lines, each one of the plurality of delay lines electrically coupled in between the driver and the photonic integrated circuit configured to transmit a respective one of the plurality of copies of the first input electrical signal.

An optical reception device includes: an optical demultiplexer that has an input port and output ports, and configured to demultiplex a wavelength-multiplexed signal light input from the input port into a signal light for each wavelength and output the signal light from each of the output ports; a multi-wavelength light output circuit configured to output a wavelength light for each wavelength included in the wavelength-multiplexed signal light to the input port of the optical demultiplexer; and a processor configured to control the optical demultiplexer and the multi-wavelength light output circuit, wherein the optical demultiplexer includes symmetric Mach-Zehnder interferometers that each have a pair of arms of different lengths, and adjustors respectively that adjust optical phases in the asymmetric Mach-Zehnder interferometers, the asymmetric Mach-Zehnder interferometers are connected to each other in a tree-like shape so as to connect the input port and the output ports.

An optical 90-degree hybrid includes two splitters, two combiners and four arm waveguides that connect output ports of the splitters and input ports of the combiners. Each of the splitters, the arm waveguides, and the combiners is a part of an optical waveguide. The optical waveguide is configured so that the phase error generated in the splitters due to wavelength change is suppressed by the phase error generated in the arm waveguides due to the wavelength change. The optical waveguide is further configured so that the phase error generated in the splitters due to deviation of a structure parameter from a certain value (e.g., design value) is suppressed by the phase error generated in the arm waveguides due to the deviation.

An optical transmitter includes: a mapper that generates an electric field information signal from transmission data; a phase rotation circuit that adds a phase rotation to the electric field information signal; a driver that generates a driving signal from the electric field information signal to which the phase rotation is added; a modulator that generates a modulated optical signal according to the driving signal; and a controller that controls a bias of the modulator according to a change in a carrier frequency of the modulated optical signal corresponding to the phase rotation that is added to the electric field information signal by the phase rotation circuit.

Optical modulators with semiconductor based optical waveguides interacting with an RF waveguide in a traveling wave structure. The semiconductor optical waveguide generally comprise a p-n junction along the waveguide. To reduce the phase walk-off between the optical signal and the RF signal, the traveling wave structure can comprise one or more compensation sections where the phase walk-off is reversed. The compensation sections can comprise a change in dopant concentrations, extra length for the optical waveguide and/or extra length for the RF waveguide. Corresponding methods are described.

An optical full-field transmitter for an optical communications network includes a primary laser source configured to provide a narrow spectral linewidth for a primary laser signal, and a first intensity modulator in communication with a first amplitude data source. The first intensity modulator is configured to output a first amplitude-modulated optical signal from the laser signal. The transmitter further includes a first phase modulator in communication with a first phase data source and the first amplitude-modulated optical signal. The first phase modulator is configured to output a first two-stage full-field optical signal. The primary laser source has a structure based on a III-V compound semiconductor.

A silicon optical modulator includes a silicon-on-insulator substrate and a first waveguide and a second waveguide arranged parallel to each other in the silicon-on-insulator substrate. The first waveguide includes a first PN junction. The second waveguide includes a second PN junction. At least one of the first PN junction and the second PN junction is disposed at an interface between a P type doped region and a N type doped region. The interface has an irregular shape that is not perpendicular to a plane in which the silicon-on-insulator substrate lies.

Methods and apparatus for controlling a bias voltage (20) supplied to an optical modulator that comprises a biasable component configurable to be biased by application of the bias voltage (20), the method comprising: providing a target for the modulator output power; applying, to the biasable component, a bias voltage (20) that biases the biasable component so that the output power is within a pre-defined range of the target; monitoring the output power and, if the output power of the modulator is determined to be outside the pre-defined range, varying the value of the bias voltage (20) to bring the output power back within the pre-defined range; and monitoring the optical input to the modulator and, if it has been disabled, maintaining the bias voltage (20) at its current level for a pre-determined length of time that is dependent upon how long the modulator has been operating at quadrature.