In some embodiments, an apparatus includes an optical transmitter module that can be electrically coupled to an electrical serializer/deserializer and a controller. The optical transmitter module can include an electrical detector that can receive an in-band signal. The electrical detector can send to the controller a first power error signal and a second power error signal based on the in-band signal. The controller can send a correction control signal to the electrical serializer/deserializer based on the first power error signal and the second power error signal such that the electrical serializer/deserializer sends a pre-emphasized signal to the optical transmitter module based on the correction control signal. In such embodiments, the first power error signal, the second power signal and the correction control signal are out-of-band signals.

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.

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.

The present disclosure provides a dither-free bias control of an optical modulator (OM) for the externally-modulated transmitter with the silicon-based Mach-Zehnder modulator (MZM), while the nonlinear distortions (NLDs) are generated by the plasma dispersion effect of the silicon-based MZM. The present disclosure proposes to intentionally offset the bias point of the MZM from its quadrature points, and therefore the Mach-Zehnder interference (MZI)-induced even-order NLDs can be generated to cancel the plasma dispersion-induced even-order NLDs. In addition, the MZM bias control is also proposed to arbitrarily adjust and lock in the bias point of an OM so a transmitter with the integrated MZM may reach the best even-order NLDs by offsetting from the quadrature points. Moreover, while the proposed scheme could arbitrarily adjust and lock in the bias of MZM, the receiver sensitivity may be optimized by using such a bias control scheme to adjust the extinction ratio of multi-level signals.

Embodiments of this disclosure provide a method and apparatus for monitoring a modulation depth of a dither signal and an optical transmitter. The apparatus includes a detector to detect an optical signal output by a Mach-Zehnder modulator to obtain an electrical signal, a dither signal at a determined frequency is superimposed on a direct current bias voltage of the Mach-Zehnder modulator; a frequency-doubling dither signal synchronization detection module to perform synchronization detection on the electrical signal and a frequency-doubling dither signal at a frequency twice the determined frequency, to obtain an amplitude of a signal component contained in the electrical signal at a frequency identical to the frequency of the frequency-doubling dither signal A signal processor is to calculate a modulation depth of the dither signal superimposed on the direct current bias voltage according to the amplitude of the signal component at the frequency identical to the frequency of the frequency-doubling dither signal.

An RF signal to be carried by an optical link is modulated onto two optical beams. The modulators are tuned differently so that the distortion products carried on one beam are relatively larger compared to the fundamental compared with other beam. One of the beams is optically upconverted by the appropriate Brillouin shift frequency and the two beams counter-propagated through an optical waveguide in order to create a Brillouin grating. The grating acts to separate the distortion products from the fundamental so as to provide at an output of the link a signal in which the distortion products are insignificant is not absent.

An RF signal to be carried by an optical link is modulated onto two optical beams. The modulators are tuned differently so that the distortion products carried on one beam are relatively larger compared to the fundamental compared with other beam. One of the beams is optically upconverted by the appropriate Brillouin shift frequency and the two beams counter-propagated through an optical waveguide in order to create a Brillouin grating. The grating acts to separate the distortion products from the fundamental so as to provide at an output of the link a signal in which the distortion products are insignificant is not absent.

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.

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.

An optical transport system configured to compensate nonlinear signal distortions using a backward-propagation algorithm in which some effects of polarization mode dispersion on the nonlinear signal distortions are accounted for by employing two or more different approximations of said effects within the bandwidth of the optical communication signal. In an example embodiment, the corresponding digital signal processor (DSP) is configured to switch between different approximations based on a comparison, with a fixed threshold value, of a difference between frequencies of various optical waves contributing to the nonlinear signal distortions, e.g., through four-wave-mixing processes. In different embodiments, the backward-propagation algorithm can be executed by the transmitter's DSP or the receiver's DSP.