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.

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.

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 transmitter includes an optical modulator configured to modulate an input light and output an optical signal, a bias controller configured to control a bias applied to the optical modulator, an attenuator configured to attenuate the optical signal output from the optical modulator and output the attenuated optical signal, a positive monitor configured to detect a forward optical signal included in the attenuated optical signal output from the attenuator, a negative monitor configured to detect a complementary optical signal included in the attenuated optical signal output from the attenuator, and a controller configured to control the bias controller based on a sum of a first dither of a positive signal output from the positive monitor and a second dither of a negative signal output from the negative monitor.

A bias control method of a nested optical modulator includes detecting a frequency component that has a frequency equal to a frequency of a dither signal and that is included in an output of the optical modulator, with changing a voltage value of a first bias, to measure a first error-detection value, obtaining a first error-detection curve representing a relationship between the first error-detection value and the voltage of the first bias, obtaining a first correction value based on the first error-detection curve, and obtaining the first error-detection value obtained when the first bias voltage value is equal to a voltage value obtained by adding the first correction value to the first bias voltage value at a zero-crossing point of the first error-detection curve, as a first error control value. The first bias is controlled so that the first error-detection value is the first error control value.

An adjusting method for stabilizing optical characteristic parameters applicable to transmitter optical subassemblies with silicon photonic chips is provided. The adjusting method might include: sensing an initial optical signal emitted by the transmitter optical subassembly with first control component, controlling phase setting parameter of the silicon photonic chip with the first control component to change the transmitter optical subassembly from emitting the initial optical signal to emitting a first modified optical signal, transmitting a power target value to second control component when the first modified optical signal conforms to the phase target value and sensing the first modified optical signal with the second control component, and controlling a bias current of the transmitter optical subassembly according to the first modified optical signal and the power target value to change the transmitter optical subassembly from emitting the first modified optical signal to emitting a second modified optical signal.

A method of controlling an optical modulator having a first child modulator, a second child modulator, and a parent modulator includes applying a first bias, on which a first dither signal with frequency f1 is superimposed, to the first child modulator, applying a second bias, on which a second dither signal with frequency f2 different from f1 is superimposed, to the second child modulator, applying a third bias, on which a third dither signal with frequency f3 different from both f1 and f2 is superimposed, to the parent modulator. A first error component having the f1 frequency, and a second error component having a beat frequency of f2 and f3 frequencies are detected from the output light from the optical modulator, and a first error signal is generated from the first error component and the second error component to adjust the first bias.

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.

An optical transmitter includes quadrature modulators and light receiving elements to which inverted output light of output light from the quadrature modulators is input, the quadrature modulators including parent Mach-Zehnder modulators in respective paths of a first pair of paths into which carrier light from a light source is split, the parent Mach-Zehnder modulators including child Mach-Zehnder modulators including first phase modulation units, and second phase modulation units. When blocking a transmission optical signal, the voltage amplitude of a transmission electrical signal to be applied to the quadrature modulator is adjusted such that it is smaller than a half-wave voltage, at most two dither signals are applied to the first phase modulation units, a component output by the light receiving element, the component having n times a frequency of the dither signals, is detected, and bias voltages to be applied to the first phase modulation units are controlled such that the component having n times the frequency is minimized.

Embodiments pertain to an optical transmitter, including a thermally unregulated light emitting device and a sloped or graded passband filter. The light emitting device is configured to receive a bias current and output an optical signal within a wavelength band. The sloped or graded passband filter is configured to attenuate an output power of the optical signal in the wavelength band. The light emitting device has a maximum bias current limit, a maximum operating temperature limit, and maximum and minimum output power limits, and the sloped or graded passband filter has an insertion loss in the wavelength band that decreases as the light emitting device temperature increases and/or the optical signal wavelength increases within the wavelength band. The attenuated optical signal is within the maximum and minimum output power limits when the bias current is at or below the maximum bias current limit and the light emitting device outputs the optical signal at or below the maximum operating temperature limit.