A semiconductor-based Mach-Zehnder modulator (MZM) is configured for push-pull bias dithering to control the MZM bias at a desired set point. When two such MZM modulators are connected in parallel to form an IQ modulator, bias settings for both MZMs and the IQ bias may be controlled from an output of the IQ modulator to minimize both the IQ offset and the quadrature error of the output signal constellation even for non-ideal MZMs with low extinction ratios.

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.

A controller includes an amplification ratio control unit, an amplification unit, a digital conversion unit, and a driving current control unit. The amplification ratio control unit is configured to generate an amplification ratio signal based on an ambient temperature of a laser diode. The amplification unit configured to amplify, based on the amplification ratio signal, a detection current from a photodiode configured to detect light output from the laser diode, and output the detection current as a voltage signal. The amplification ratio signal controls an amplification ratio of the amplification unit. The digital conversion unit is configured to convert the voltage signal into a digital signal. The driving current control unit is configured to control a driving current of a driver configured to drive the laser diode based on the digital signal.

A superposition circuitry superposes a dither signal on a reference DC bias voltage and outputs a resultant voltage as a bias voltage to an MZ modulator, during control of a driving voltage amplitude. During the control of the driving voltage amplitude to the MZ modulator, an amplitude setter determines, by varying the amplitude of an output voltage from an amplifier, a plurality of amplitudes of output curves from a synchronous detector, each of which is obtained by varying the reference DC bias voltage output from a bias controller, and the amplitude setter sets the amplification factor of the amplifier, based on an amplitude of the output voltage from the amplifier that corresponds to an amplitude satisfying a predetermined condition, out of the plurality of the amplitudes of the output curves from the synchronous detector.

A debugging method and device for an operating point voltage of a parallel MZI electro-optical modulator. The parallel MZI electro-optical modulator comprises a Parent MZI (2) formed by a parallel connection of a Child MZI (3) in an I path and a Child MZI (4) in a Q path. The debugging method comprises: fixing a bias voltage of one Child MZI of the Child MZI (3) in the I path and the Child MZI (4) in the Q path; gradually adjusting a bias voltage of the other Child MZI, testing a parent extinction ratio PER of the Parent MZI (2) when different bias voltages are applied, and finding a corresponding bias voltage as an operating point voltage of the other Child MZI when the PER of the Parent MZI (2) reaches a minimum value, and then finding a corresponding bias voltage as an operating point voltage of the one Child MZI when the PER of the Parent MZI (2) reaches a minimum value; setting the bias voltages of two Child MZIs as operating point voltages corresponding to the two Child MZIs respectively, adjusting a phase modulation voltage of the Parent MZI (2) until the parallel MZI electro-optical modulator reaches an optimum output effect, and determining the phase modulation voltage of the Parent MZI (2). The method and device are simple; and the debugging process thereof is fast and efficient.

An OMA controller circuit utilizes a first ADC with an input coupled for receiving a residual error signal indicating a difference between a monitoring signal and a target data signal. A second ADC has an input coupled for receiving the target data signal. A first digital filter has an input coupled to an output of the first ADC, and a second digital filter has an input coupled to an output of the second ADC. A digital multiplier has a first input coupled to an output of the first digital filter and a second input coupled to an output of the second digital filter. An integrator has an input coupled to an output of the digital multiplier and an output providing an average error signal with sign and magnitude. The digital multiplier uses a four quadrant multiplier to perform a cross-correlation on the residual error and the target data signal.

An optical transmission device includes a light source that is driven according to a multicarrier modulation signal in which data is allocated to a plurality of subcarriers to transmit an optical multicarrier modulation signal to another optical transmission device, and a control unit that controls a driving condition of the light source, based on the number of bits allocatable to each of the subcarriers of the multicarrier modulation signal, the number of bits being determined according to transmission characteristics of the optical multicarrier modulation signal in the other optical transmission device.

An electro-absorption modulator (EAM) comprising an integrated high speed electro-optical control loop for very high-speed linearization and temperature compensation for analog optical data center interconnect applications is disclosed. The control loop can function in a stable manner because the electronics and optical components are monolithically integrated on a single substrate in small form factor. Because of the small size enabled by monolithic integration, the temperatures of the optical blocks and electronics blocks are tightly coupled, and the control loop time delays and phase delays are small enough to be stable, even for very high frequency operation. This arrangement enables a low cost, low power analog transmitter implementation for data center optical interconnect applications using advanced modulation schemes, such as PAM-4 and DP-QPSK.

A linearized electro-optic modulator includes a substrate comprising a first Mach Zehnder interferometer comprising a first and second optical waveguide and a second Mach Zehnder interferometer comprising a first and a second optical waveguide. A signal electrode is positioned on the substrate to receive a modulation signal. First and second ground electrodes are positioned on the substrate and are electrically connected to ground potential. The signal electrode and the first and second ground electrodes are positioned so that an electric field generated by the signal electrode modulates both the first and second Mach Zehnder interferometers to generate a first and a second linearized modulated optical signal.

An electro-absorption modulator (EAM) comprising an integrated high speed electro-optical control loop for very high-speed linearization and temperature compensation for analog optical data center interconnect applications is disclosed. The control loop can function in a stable manner because the electronics and optical components are monolithically integrated on a single substrate in small form factor. Because of the small size enabled by monolithic integration, the temperatures of the optical blocks and electronics blocks are tightly coupled, and the control loop time delays and phase delays are small enough to be stable, even for very high frequency operation. This arrangement enables a low cost, low power analog transmitter implementation for data center optical interconnect applications using advanced modulation schemes, such as PAM-4 and DP-QPSK.