To clarify the characteristics of an optical modulator having output asymmetry due to a non-linear effect, an optical transmitter includes: a light source which outputs light of a predetermined wavelength; a modulator which modulates the light output from the light source using a modulation signal; a modulator drive unit which outputs a modulation signal to the modulator; a control unit which outputs a low-frequency signal to the modulator and a modulator driver, amplitude-modulates the modulation signal using the low-frequency signal, intensity-modulates the amplitude-modulated modulation signal using the low-frequency signal, and receives a monitor signal including a low-frequency signal component; and a detection unit which extracts a low-frequency component of an optical signal output from the modulator, and outputs the low-frequency component as a monitor 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 system for controlling an optical intensity and modulation of an optical data transmitter which includes current driver circuitry configured to provide a drive current to a laser diode wherein said current comprises a fixed component and a modulated component, said modulated component having a magnitude related to an input data stream. The monitor circuitry contains a photodiode and a first transimpedance amplifier coupled to said photodiode, said monitor circuitry configured to provide an output signal related to an optical intensity of said laser diode. The system further includes replica monitor circuitry containing a replica capacitor with a replica capacitance and a second transimpedance amplifier configured to be substantially identical in construction to said first transimpedance amplifier, said second transimpedance amplifier coupled to said replica capacitor. The system further includes replica capacitance control circuitry configured to control said replica capacitance of said replica capacitor to match a capacitance associated with said photodiode.

An optical transmitter includes a signal processor and transmission circuit. The signal processor modulates a first signal to generate a first modulated signal, determines a modulo amplitude that is larger than an amplitude of the first modulated signal, inserts a second modulated signal into the first modulated signal to generate a transmission signal, corrects a symbol of the transmission signal by using an amplitude of one or a plurality of previous symbols to generate a pre-equalized signal, and performs modulo calculation based on the modulo amplitude on the pre-equalized signal. The transmission circuit generates a modulated optical signal based on an output signal of the signal processor and transmits the modulated optical signal to a reception node. An amplitude of the second modulated signal is equal to the modulo amplitude.

A communication device includes a nested modulator composed of sub modulators and a phase shifter. The nested modulator is controlled by: modulating a double pulse by phase and intensity modulation according to transmission information, wherein the double pulse thus modulated is transmitted to another communication device; controlling bias voltages applied respectively to the sub modulators so that a first error rate on the intensity modulation is minimized; and controlling a bias voltage applied to the phase shifter so that a second error rate on the phase modulation is minimized.

One example includes an optical transmitter system. The system includes a waveguide to receive and propagate an optical signal. The system also includes a ring modulation system comprising a ring resonator that is optically coupled to the waveguide and is to resonate a given wavelength of the optical signal in response to an input data signal that is provided to a modulation amplifier to provide carrier injection to change a refractive index of the ring resonator to resonate the given wavelength of the optical signal to modulate the optical signal. The system further includes a tuning controller associated with the ring modulation system. The tuning controller can implement iterative feedback tuning of the ring modulation system based on a relative amplitude of an optical intensity of the given wavelength in the ring resonator and a variable reference amplitude to substantially stabilize the ring resonator with respect to the given wavelength.

An optical communication apparatus includes: a light-receiving device that receives an optical signal transmitted from another optical communication apparatus through an optical fiber and converts the optical signal into an electrical signal; a first measurement circuit that measures an average power and a modulation power of the optical signal based on the electrical signal; a light-emitting device that transmits the optical signal to the another optical communication apparatus by emitting light in accordance with a driving current; a driver that causes the light-emitting device to transmit the optical signal according to a transmission signal by controlling the driving current based on the transmission signal; and a processor that adjusts the driving current based on the average power and the modulation power.

In some embodiments, an apparatus includes an optical transmitter module that can be electrically coupled to an electrical serializer/deserializer and a controller. The optical transmitter module can include an electrical detector that can receive an in-band signal. The electrical detector can send to the controller a first power error signal and a second power error signal based on the in-band signal. The controller can send a correction control signal to the electrical serializer/deserializer based on the first power error signal and the second power error signal such that the electrical serializer/deserializer sends a pre-emphasized signal to the optical transmitter module based on the correction control signal. In such embodiments, the first power error signal, the second power signal and the correction control signal are out-of-band signals.

An optical transmitter includes, a processor that receives an input data signal from an outside and performs rotation processing for periodically or repeatedly rotating a polarization state or phase of the optical output signal upon the input data signal, an optical modulator that modulates light transmitted from a light source based on the input data signal, a digital-to-analog converter that converts an output of the processor into an analog electric signal, a driving circuit that amplifies an output of the digital-to-analog converter and drives the optical modulator, and a monitoring control circuit that monitors an optical output signal output from the optical modulator and adjusts at least one of an output of the digital-to-analog converter and a gain of the driving circuit based on a result of monitoring of the optical output signal.

An estimation apparatus for IQ imbalance of an optical transmitter, a compensation apparatus for IQ imbalance of an optical transmitter and electronic equipment; wherein, estimation and compensation of IQ imbalance of an optical transmitter are performed by directly using an estimation model based on a transform matrix of received signals and transmitted signals, therefore, a phase offset shift may be estimated accurately, and precision of estimation of drifts of various angles is ensured, furthermore, accurate recovery of the constellation diagram of received signals is achieved.