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.

An optical modulator uses an optoelectronic phase comparator configured to provide, in the form of an electrical signal, a measure of a phase difference between two optical waves. The phase comparator includes an optical directional coupler having two coupled channels respectively defining two optical inputs for receiving the two optical waves to be compared. Two photodiodes are configured to respectively receive the optical output powers of the two channels of the directional coupler. An electrical circuit is configured to supply, as a measure of the optical phase shift, an electrical signal proportional to the difference between the electrical signals produced by the two photodiodes.

An integrated high speed electro-optical control loop for very high-speed linearization and temperature compensation of an electro-absorption modulator (EAM) for analog optical data center interconnect applications is disclosed. The control loop can function in a stable manner because the electronics and optical components are monolithically integrated on a single substrate in small form factor. Because of the small size enabled by monolithic integration, the temperatures of the optical blocks and electronics blocks are tightly coupled, and the control loop time delays and phase delays are small enough to be stable, even for very high frequency operation. This arrangement enables a low cost, low power analog transmitter implementation for data center optical interconnect applications using advanced modulation schemes, such as PAM-4 and DP-QPSK.

An electro-optic device may comprise a Mach-Zehnder modulator (MZM) and one or more components. The one or more components may apply a child DC bias with dither to arms of a first branch of the MZM and to arms of a second branch of the MZM, and determine a second harmonic of a first return signal. The one or more components may apply a child DC bias with phase-shifted dither to the arms of the first branch or to the arms of the second branch, and determine a second harmonic of a second return signal. The one or more components may determine, based on the second harmonics, whether the first branch and the second branch are operating at quadrature, and may selectively adjust parent DC biases, applied to the first branch and the second branch, based on whether the first branch and the second branch are operating at quadrature.

Disclosed is technology for controlling a bias using an integrated circuit (IC) instead of using a pilot tone. A bias control apparatus includes a photodetector configured to convert at least a portion of data included in an output from an optical modulator to an electrical signal; a power detector configured to convert a root mean square (RMS) value of an amplitude of the converted data to an analog voltage; a comparator configured to compare the output voltage and a pre-stored track hold value; and a bias controller configured to control a bias voltage to be within a preset range from an optimal voltage based on the comparison result.

An optical signal modulator comprising a modulator unit, a photodetector and an electrical signal combiner. The modular unit having an optical ingress port for optical radiation, a first and second optical output port each for modulated optical radiation, and an electrical ingress port for an electrical modulation signal. The optical radiation is modulated in response to the electrical modulation signal. The photodetector is connected to the second optical output port and configured to measure the modulated optical radiation that is emitted, and to provide a monitor signal. The electrical signal combiner having a first input port for an external electrical data signal, a second electrical input port for a correction signal based on the monitor signal, and an electrical output port that is connected to the electrical ingress port. The combiner generates the electrical modulation signal by combining the external electrical data signal and the correction signal.

A method and apparatus estimating direct current bias of an optical modulator and a receiver. The method includes: performing signal processing to obtain a phase noise compensated signal, extracting a receiving signal component based on the phase noise compensated signal, removing the receiving signal component from the phase noise compensated signal, and calculating a received signal power based on the signal with the receiving signal component being removed. The method includes calculating a direct current bias of the optical modulator based on the receiving signal component, the received signal power and a drive signal power of the optical modulator.

In order to provide an optical modulator capable of controlling a bias voltage to correspond to transmission characteristics of a modulation means even when a multi-level modulation scheme is applied, an optical modulator 10 is provided with: an amplitude information control means 20that generates amplitude information for controlling the amplitude of an information signal to correspond to transmission characteristics of a modulation means 50, adds a dither signal to the amplitude information, and outputs the amplitude information; a bias value control means 30 that generates and outputs a bias value for controlling the center of the amplitude of the information signal to correspond to the transmission characteristics of the modulation means 50; a data output means 40 that corrects the amplitude of information data on the basis of the amplitude information, and outputs the information data as the information signal; the modulation means 50 that corrects the center of the amplitude of the information signal on the basis of the bias value, modulates continuous wave light by using the information signal, and outputs a modulation signal; and an adjustment means 60 that extracts, from the modulation signal, the dither signal added to the amplitude information, and adjusts the amplitude information and the bias value such that the differential value of the intensity of the dither signal added to the amplitude information becomes zero.

Embodiments of this disclosure provide a bias control apparatus and method of a modulator of an optical transmitter and an optical transmitter. By obtaining respective output power signals of a first Mach-Zehnder modulator and a second Mach-Zehnder modulator constituting the modulator of the optical transmitter, information on a phase bias may be extracted according to the two output power signals and an overall output power signal of the modulator of the optical transmitter, so as to control the phase bias by using the information, thereby efficiently improving a sensitivity of the control of the bias, and being applicable to various types of modulation formats.

Disclosed are bias control methods for Mach-Zehnder modulators for the generation of optical QAM signals while ensuring correct I/Q polarity of the generated optical QAM signal. One exemplary method involves temporarily offsetting I and Q biases from ideal transmission null bias points while another illustrative method temporarily makes I and Q data streams identical.