Driving an optical modulator is described. A control circuit generates first and second input voltages based on a target phase modulation between first and second optical waveguide arms of the optical modulator. An offset control circuit generates first and second offset signals. A linear modulator driver receives the first and second offset signals, generates a first output voltage for biasing the first optical waveguide arm using the first offset signal, and generates a second output voltage for biasing the second optical waveguide arm using the second offset signal. Feedback circuitry can feed the first and second output voltages to the offset control circuit, which can generate the first and second offset signals using the first and second output voltages. The output voltages bias the waveguide arms so the optical modulator operates close to the target phase modulation, even in the presence of manufacturing errors.

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.

An optical semiconductor chip of the present disclosure includes a high frequency line between an electrode pad receiving a modulation signal and a modulation electrode on the optical waveguide having a light absorption layer. The depletion layer capacitance generated in the light absorption layer is canceled by an inductor component of the high frequency line. When a portion directly below the high frequency line is embedded with a low-dielectric-constant material or is made hollow, the parasitic capacitance is further reduced. The high frequency line may have a zigzag shape as well as a linear shape. The electrode pad on the optical semiconductor chip can be connected to other substrates including RF lines for modulation signal input by bumps or wire bonding.

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 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.

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.

An optical modulator includes: an optical waveguide element including an optical waveguide formed on a substrate and a signal electrode for controlling a light wave propagating through the optical waveguide; a drive circuit for outputting two high-frequency signals; and two terminating resistors for respectively terminating outputs of the two high-frequency signals from the drive circuit. The output of one of the high-frequency signals of the drive circuit propagates through the signal electrode of the optical waveguide element and is terminated by a first terminating resistor which is one of the terminating resistors. The output of the other of the high-frequency signals of the drive circuit is terminated by a second terminating resistor which is the other of the terminating resistors. A resistance value of the second terminating resistor is greater than a resistance value of the first terminating resistor.

High bandwidth (e.g., > 100 GHz) modulators and methods of fabricating such are provided. An optical modulator comprises transmission lines configured to provide a respective radio frequency signal to a respective plurality of segmented capacitive loading electrodes; pluralities of segmented capacitive loading electrodes in electrical communication with a respective one of the transmission lines and in electrical communication with an interface layer of a semiconductor waveguide structure; and the semiconductor waveguide structure. The semiconductor waveguide structure is configured to modulate an optical signal propagating therethrough based at least in part on the respective radio frequency signal. The semiconductor waveguide structure comprises the interface layer, which (a) comprises a semiconductor material and (b) is configured such that an interface resistance of the modulator is ≤ 4 Ohms. The interface resistance is a serial resistance between the interface layer and respective electrodes of the pluralities of segmented capacitive loading electrodes.