An apparatus at least includes a processor to, after a first signal passes through a narrowband photodetector, perform frequency mix of the first signal with a first reference signal and a second reference signal respectively and perform noise reduction, to obtain a first detection signal and a second detection signal. The first signal is obtained after a measurement signal passes through a filtering module of an optical transmitting end, the measurement signal being transmitted in a path of multiple branches, signals not transmitted in other paths of the multiple branches, a frame structure of the measurement signal including at least one two-tone signal, two tones in the two-tone signal having a fixed tone interval. The processor is to calculate group delays at multiple frequency bins according to the first detection signal and the second detection signal; and determine a phase response of the filtering module of the optical transmitting end in the path according to the group delays at multiple frequency bins.

Active bias circuits for integrated devices are described. In one example, an active bias circuit includes a voltage control element to establish a control voltage, an active bias device to provide a power bias responsive to the control voltage, and a compensation circuit connected to the active bias device. The compensation circuit can be configured to set output impedance and compensate for parasitic capacitance of the active bias device. In another embodiment, the voltage control element can be omitted, and a control voltage can be relied upon to directly control the power bias output provided by the active bias device. The active bias circuit can be used to power a driver of an integrated optical transmitter, in one example, among other possible applications.

A processor comprises instructions to adjust a bias of an input signal in order to decrease a duty cycle of a pulse modulated optical signal. The bias can be increased, decreased, or maintained in response to one or more measured values of the signal. In many embodiments, a gain of the signal is adjusted with the bias in order to inhibit distortion. The bias can be adjusted slowly in order to inhibit audible noise, and the gain can be adjusted faster than the bias in order to inhibit clipping of the signal. In many embodiments, one or more of the bias or the gain is adjusted in response to a value of the signal traversing a threshold amount. The value may comprise a trough of the signal traversing the threshold.

An apparatus at least includes a processor to, after a first signal passes through a narrowband photodetector, perform frequency mix of the first signal with a first reference signal and a second reference signal respectively and perform noise reduction, to obtain a first detection signal and a second detection signal. The first signal is obtained after a measurement signal passes through a filtering module of an optical transmitting end, the measurement signal being transmitted in a path of multiple branches, signals not transmitted in other paths of the multiple branches, a frame structure of the measurement signal including at least one two-tone signal, two tones in the two-tone signal having a fixed tone interval. The processor is to calculate group delays at multiple frequency bins according to the first detection signal and the second detection signal; and determine a phase response of the filtering module of the optical transmitting end in the path according to the group delays at multiple frequency bins.

A processor comprises instructions to adjust a bias of an input signal in order to decrease a duty cycle of a pulse modulated optical signal. The bias can be increased, decreased, or maintained in response to one or more measured values of the signal. In many embodiments, a gain of the signal is adjusted with the bias in order to inhibit distortion. The bias can be adjusted slowly in order to inhibit audible noise, and the gain can be adjusted faster than the bias in order to inhibit clipping of the signal. In many embodiments, one or more of the bias or the gain is adjusted in response to a value of the signal traversing a threshold amount. The value may comprise a trough of the signal traversing the threshold.

An optoelectronic device for quadrature-amplitude modulation (QAM) and a method of modulating light according to the same. The device comprising: an input waveguide; two intermediate waveguides, each coupled to the input waveguide via an input coupler; and an output waveguide, coupled to each of the intermediate waveguides via an output coupler; wherein each intermediate waveguide includes a modulating component connected in series with a phase shifting component, and each modulating component is connected to a respective electronic driver, the electronic drivers together being operable to produce a QAM-N modulated output from light entering the device from the input waveguide.

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.

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 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).

A radio frequency (RF) photonic equalizer may include a first electro-optic (E/O) modulator configured to modulate an optical carrier based upon an RF input signal, a stimulated Brillouin scattering (SBS) medium coupled to the first E/O modulator, and a second E/O modulator configured to modulate the optical carrier based upon an equalizing function waveform. An optical circulator may be coupled to the SBS medium and the second E/O modulator, and a photodetector may be coupled to the optical circulator.