Controller and control method are provided. In particular, a controller is disclosed as being configured to hold intensities of a monitor signal, which changes according to an output from a region in a device, before and after altering a state of a portion in the region and control the state of the portion based on a difference between the held intensities.

A drive unit outputs a modulation signal based on a data signal input from an optical communication apparatus through a pluggable electric connector. An optical modulator outputs an optical signal generated by modulating a light output from a light source based on the modulation signal. A control unit controls a modulation operation of the optical modulator. The control unit outputs a driver signal instructing to start a setting operation to the optical communication apparatus. The optical communication apparatus monitors the modulation operation of the optical modulator in response to the driver signal and performs an operation of correcting the data signal and/or an operation of outputting a control signal representing a control setting for the modulation operation to the control unit based on a monitoring result. The control unit controls the modulation operation of the optical modulator based on the control signal when receiving the control signal.

Controller and control method are provided. In particular, a controller is disclosed as being configured to hold intensities of a monitor signal, which changes according to an output from a region in a device, before and after altering a state of a portion in the region and control the state of the portion based on a difference between the held intensities.

An exemplary optical measurement system described herein includes a control circuit configured to output a global bias voltage and a module communicatively coupled to the control circuit. The module includes a light source configured to emit light directed at a target. The module further includes a plurality of detectors configured to detect arrival times for photons of the light after the light is scattered by the target. The module further includes a module control circuit configured to receive the global bias voltage and output a plurality of detector bias voltages based on the global bias voltage. The plurality of detector bias voltages include a respective detector bias voltage for each detector of the plurality of detectors.

An optical transmitter includes a bias supplying unit configured to supply a first bias voltage, a second bias voltage and a third bias voltage to an optical modulator. The bias supplying unit acquires a first voltage value at which an average value of an optical output signal becomes maximum by sweeping the first bias voltage, acquires a second voltage value at which an average value of the optical output signal becomes maximum by sweeping the second bias voltage, and acquires a third voltage value at which an average value of the optical output signal becomes maximum by sweeping the third bias voltage. The bias supplying unit determines a value of the first bias voltage based on the first voltage value, determines a value of the second bias voltage based on the second voltage value, and determines a value of the third bias voltage based on the third voltage value.

Example embodiments are described for a method and system for direct current (DC) bias control in downhole optical intensity modulators. After receiving an optical signal from a downhole intensity modulator, a harmonic distortion analysis is performed on the optical signal to determine whether a power spectrum of the optical signal deviates by a preselected amount from an expected power spectrum. The expected power spectrum occurs when a bias point is positioned at a quadrature point of a sinusoid associated with the optical signal. A DC bias voltage of the intensity modulator is subsequently adjusted in response to the harmonic distortion analysis.

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 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.

Methods and apparatus for coherent transmitter calibration are provided that employ direct detection (DD) using one single photodetector (PD). The provided method and apparatus do not require hardware for coherent reception, or additional ADCs for quality control. An additional optical tone is added to a QAM optical signal that is outside the band of the QAM optical signal. The result of this is that after direct detection, there is a correlation between the real and imaginary parts, and the imaginary part can be recovered with a Hilbert transform. The estimated QAM optical signal obtained by direct detection is used to perform a transmitter factory calibration method to calibrate for one or more transmitter impairments and/or to perform in-line self-calibration.

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.