An optical transmission apparatus includes a modulation unit that generates modulated light by modulating light while bias on which a low-frequency signal is superimposed is applied thereto; an optical amplification unit that generates amplified light by amplifying the modulated light while holding an intensity of the amplified light at a changeable target value; an optical detection unit that generates an electric signal by performing photoelectric conversion on a part of the amplified light; an amplification unit that amplifies the electric signal while suppressing variation in the amplified electric signal, the variation being due to a change of the target value; and a control unit that detects a low-frequency component from the amplified electric signal the variation of which is suppressed and controls the bias on a basis of the detected low-frequency component, the low-frequency component being generated by the low-frequency signal.

An optical data transmitter comprising two or more serially connected optical modulators, each driven using a respective DAC. The digital signals applied to the individual DACs are produced using different respective subsets of the set of bitstreams representing the digital waveform or data stream to be transmitted, with the bitstream subsets being selected, e.g., such that (i) each of the individual DACs is able to support the digital resolution and sampling rate needed for properly handling the subset of bitstreams applied thereto and (ii) differences between average driving powers applied to different optical modulators are relatively small. In different embodiments, the two or more serially connected optical modulators can be arranged for generating optical communication signals of different modulation formats, e.g., PSK, ASK, PAM, IM, and QAM. Some embodiments can advantageously be used for generating optical communication signals employing constellations of relatively large sizes, e.g., larger than 1000 symbols.

An optical transmission apparatus includes a modulation unit that generates modulated light by modulating light while bias on which a low-frequency signal is superimposed is applied thereto; an optical amplification unit that generates amplified light by amplifying the modulated light while holding an intensity of the amplified light at a changeable target value; an optical detection unit that generates an electric signal by performing photoelectric conversion on a part of the amplified light; an amplification unit that amplifies the electric signal while suppressing variation in the amplified electric signal, the variation being due to a change of the target value; and a control unit that detects a low-frequency component from the amplified electric signal the variation of which is suppressed and controls the bias on a basis of the detected low-frequency component, the low-frequency component being generated by the low-frequency signal.

A transmission device including a multi-division optical modulator having a plurality of modulation segments, the transmission device includes a driver circuit configured to output binary data for each bit based on an input electrical signal, and an optical modulator configured to have a multilevel modulation segment driven by a first drive signal including two or more bit signal from the driver circuit, and plural binary modulation segments driven by second drive signal including only one bit signal from the driver circuit, wherein the multilevel modulation segment incudes a first phase shifter disposed on each arm of the optical modulator, the binary modulation segment includes a plurality of second phase shifters arranged along each arm of the optical modulator, and lengths of the second phase shifters are all the same and are shorter than a length of the first phase shifter.

Thermal tuning and quadrature control of opto-electronic devices using active extinction ratio tracking is proved by phase shifting, via a first phase shifter, a first optical signal carried on a first arm of an interferometer relative to a second optical signal carried on a second arm of the interferometer; combining the first optical signal with the second optical signal as an output signal; detecting a peak value in the output signal; and adjusting a relative phase offset imparted by the first phase shifter on the first optical signal relative to the second optical signal, based on the peak value, to increase an amplitude of the peak value. In various embodiments, the peak value is increased over time to maximize an extinction ratio of the optoelectronic device and maintain the extinction ratio in a maximized state during operation.

An optical transmission apparatus (100) includes an optical transmitter (200) including an optical modulator (220) and an observation optical modulator (230) that attenuate optical power of input continuous wave light by an electro-absorption effect and output the continuous wave light. The optical modulator (220) performs pulse amplitude modulation on the continuous wave light and outputs the optical signal. The apparatus also includes: a bias voltage generation unit (350) that generates a direct-current bias voltage and outputs the direct-current bias voltage to the optical modulator (220) and the observation optical modulator (230); a modulation signal generation unit (360) that generates an electrical signal for pulse amplitude modulation and outputs the electrical signal to the optical modulator (220); and a bias voltage control unit (340) that instructs the bias voltage generation unit (350) to adjust the direct-current bias voltage on the basis of an absorption amount of optical power in the optical modulator (220) and an absorption amount of optical power in the observation optical modulator (230).

Active relative intensity noise mitigation in nested interferometers using trans-impedance amplifiers is provided by splitting an optical carrier signal into a first version and a second version, wherein the first version is orthogonal to the second version; re-combining predefined portions of the first version and the second version to determine a noise level; modulating at least one of the first version and the second version based on the noise level to reduce the noise level; after modulating the at least one of the first version and the second version based on the noise level, encoding data onto at least one of the first version and the second version; and recombining the first version and the second version to transmit the data.

An optical module includes an optical device that outputs an optical signal corresponding to a control voltage, a voltage controller that applies the control voltage on which a dither signal is superimposed to the optical device, a monitor unit that monitors the optical signal output from the optical device, and outputs a monitor signal, a multiplier that multiplies the monitor signal by a reference signal corresponding to the dither signal, a filter unit that extracts a direct-current component included in a multiplication result, and a controller that causes the voltage controller to change the control voltage in accordance with the direct-current component. The controller changes the frequency of the dither signal or the reference signal such that the frequency of the reference signal is twice as large as that of the dither signal, when the direct-current component satisfies a predetermined condition.

A semiconductor laser (1) emits laser light. An electro-absorption optical modulator (2) modulates the laser light. The electro-absorption optical modulator (2) includes a plurality of electro-absorption regions (2a, 2b, 2c) having different extinction characteristics, whereby the extinction ratio curve of the optical device can be controlled to have a shape with multiple steps that is suited to driving conditions.

Provided is an optical transmission module which can generate PAM4 optical modulation signals without converting a plurality of binary electric signals to a multi-level electric signal. An optical transmission module (200) comprising: a light source (60) for emitting continuous waveform (CW) light; optical modulators (51,52,53) arranged in series with a path of the CW light configured to modulate the CW light by switching relatively large absorption and relatively small absorption of the optical modulators in response to a modulation signal applied to the respective optical modulators; and an arithmetic logic circuit (100) configured to receive a plurality of binary electrical signals, and then to perform logic operation on the plurality of binary electrical signals for generating a new plurality of binary electrical signals, wherein each of the new plurality of binary electrical signals is applied to the respective optical modulators as the modulation signal.