An optical transmitter has an optical modulator with a Mach-Zehnder interferometer, a pilot signal generator configured to generate a pilot signal to be superimposed on a drive signal for driving the optical modulator or on a substrate bias voltage applied to the optical modulator, and a controller configured to detect a ratio between a pilot component and a direct current component contained in a light output from the optical modulator and control at least one of an amplitude of the drive signal and a level of the substrate bias voltage such that the ratio becomes a constant value.

Examples described herein relate to a receiver training method. To configure a static gain for at least one static gain amplifier and a target amplitude for a dynamic gain amplifier, a dynamic gain adjustment is disabled and the dynamic gain amplifier is configured to apply a predetermined fixed gain to the static gain amplified signal to generate a test signal. Furthermore, an effective static gain magnitude for at least one static gain amplifier and an effective amplitude for the test signal are determined based on a link performance metric. The static gain is set to the effective static gain magnitude, and a target amplitude for the dynamic gain amplifier is set to the effective amplitude. Then, the dynamic gain adjustment may be enabled to maintain an amplitude of a dynamic gain amplified signal at an output of the dynamic gain amplifier at the target amplitude by varying the dynamic gain.

Aspects of the subject disclosure may include, for example, obtaining two inputs x.sub.I and x.sub.Q based on a digital input signal, and causing a modulator to create two substantially orthogonal output dimensions I and Q based on the two inputs x.sub.I and x.sub.Q, by performing controlled introduction of a correlation between the two inputs x.sub.I and x.sub.Q for the modulator, and detecting a resulting output power of the modulator to facilitate operation of the modulator. Other embodiments are disclosed.

The present disclosure is directed to light-distribution systems on photonic integrated circuits (PIC) that split and amplify a light signal received from at least one remotely located laser into a plurality of amplified light signals, where amplification is provided by an integrated semiconductor optical amplifier (SOA). By locating the laser remotely with respect to the SOA-based PIC, the laser and PIC can be subjected to different ambient environmental conditions. Additionally, a lower-power laser can be used since the optical loss associated with splitting is compensated for by the amplification. As a result, lower current densities and optical powers can be used in both the source laser and the SOA. In some embodiments, the sequence of power splitting and amplification is repeated multiple times, thereby enabling system to scale gracefully.

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.

Provided is a method of controlling a temperature of an optical modulator including a first operation including repeatedly inputting a first input signal and a second input signal to the optical modulator, inputting a heater control value to the optical modulator, and obtaining an optimal heater control value at which a difference between a first output signal output corresponding to the first input signal and a second output signal output corresponding to the second input signal is maximized, a second operation including controlling the heater using the optimal heater control value, and inputting a third input signal to the optical modulator to set a third output signal corresponding to the third input signal as a reference value, and a third operation including feedback-controlling the heater control value so that a fourth output signal corresponding to a fourth input signal input to the optical modulator corresponds to the reference value.