Systems and methods of transmitting direct detection optical signal are provided. A direct detection optical transmitter according to illustrative embodiments includes a Mach Zehnder Modulator (MZM) configured to modulate laser light based on an electrical drive signal to generate a modulated optical signal and a complementary-modulated optical signal. The optical transmitter includes an optical finite impulse response (FIR) filter configured to receive the complementary-modulated optical signal and generate a filtered optical signal. The optical transmitter includes a polarization rotator configured to receive the filtered optical signal and output a rotated optical signal. The optical transmitter includes an optical combiner configured to combine the modulated optical signal and the rotated optical signal. The optical transmitter includes an output port configured to output the combined optical signal.

Provided is an Active Optical Cable (AOC) device for short-range optical communication. The AOC device includes an electrical wire between a transmitter and a receiver for the feedback of a monitoring signal from the receiver. The receiver further includes a monitoring circuit to control the compensation of a high frequency component of an equalizing filter, acquire the result of receiving signal size determination and a high frequency component compensation from the equalizing filter, and perform the feedback of the acquired monitoring signal to the transmitter through the electrical wire. The transmitter further includes a transmitter control circuit to receive the feedback monitoring signal from the receiver through the electrical wire and control a high frequency component control code of the high frequency component control circuit and an optical signal output size control code of the optical device driving circuit based on the received monitoring signal.

A receiver applies a calibration method to compensate for skew between input channels. The receiver skew is estimated by observing the coefficients of an adaptive equalizer which adjusts the coefficients based on time-varying properties of the multi-channel input signal. The receiver skew is compensated by programming the phase of the sampling clocks for the different channels. Furthermore, during real-time operation of the receiver, channel diagnostics is performed to automatically estimate differential group delay and/or other channel characteristics based on the equalizer coefficients using a frequency averaging or polarization averaging approach. Framer information can furthermore be utilized to estimate differential group delay that is an integer multiple of the symbol rate. Additionally, a DSP reset may be performed when substantial signal degradation is detected based on the channel diagnostics information.

A method, system, and apparatus enabled to selectively choose a baud rate for communication of optical data using a modem enabled to operate with an optical signal modulated at plurality of finely tuned baud rates.

A circuit and method for mitigating multi-path interference in direct detection optical systems is provided. Samples of an optical signal having a pulse amplitude modulated (PAM) E-field are processed by generating a PAM level for each sample. For each sample, the sample is subtracted from the respective PAM level to generate a corresponding error sample. The error samples are lowpass filtered to produce estimates of multi-path interference (MPI). For each sample, one of the estimates of MPI is combined with the sample to produce an interference-mitigated sample.

Methods and systems for waveguide delay based equalization with optical splitting in optical communication may include an optoelectronic circuit comprising an input waveguide, a directional coupler, an optical delay, photodetectors, a current mirror, and a transimpedance amplifier. The optoelectronic circuit may receive an input optical signal via the input waveguide, split the input optical signal into first and second output signals using the directional coupler, delay the first output signal using the optical delay, convert the delayed first output signal to a first electrical signal using a first photodetector, convert the second output signal to a second electrical signal using a second photodetector, amplify the second electrical signal using the current mirror, and sum the first and second electrical signals at inputs of the transimpedance amplifier to generate an output voltage.

The disclosed systems, apparatuses and methods are directed to controlling optical channel signal and an optical network equipment in optical networks. The methods comprise adjusting an optical channel spectrum based on bit error rates (BER) measured for a dithered optical channel signal. The optical channel spectrum is dithered such that a signal reference frequency is alternated between a first second signal reference frequency and a second signal reference frequency. BER is measured and analysed separately for the dithered signal reference frequency being detuned to the first and to the second signal reference frequencies. Based on a BER difference between BER at the first signal reference frequency and BER at the second signal reference frequency, the optical channel spectrum is shifted with regards to frequency in order to improve optical network performance.

Systems and methods of transmitting direct detection optical signal are provided. A direct detection optical transmitter according to illustrative embodiments includes a Mach Zehnder Modulator (MZM) configured to modulate laser light based on an electrical drive signal to generate a modulated optical signal and a complementary-modulated optical signal. The optical transmitter includes an optical finite impulse response (FIR) filter configured to receive the complementary-modulated optical signal and generate a filtered optical signal. The optical transmitter includes a polarization rotator configured to receive the filtered optical signal and output a rotated optical signal. The optical transmitter includes an optical combiner configured to combine the modulated optical signal and the rotated optical signal. The optical transmitter includes an output port configured to output the combined optical signal.

A transmitter (1) is configured to transmit an optical signal, the transmitter comprising an optical dispersion compensator (10) configured to compensate for chromatic dispersion of the optical signal. The optical dispersion compensator comprises a plurality of delay elements (20; 40). The plurality of delay elements (20; 40) have a combined response providing a delay to the transmitted optical signal which varies with frequency.

A receiver applies a calibration method to compensate for skew between input channels. The receiver skew is estimated by observing the coefficients of an adaptive equalizer which adjusts the coefficients based on time-varying properties of the multi-channel input signal. The receiver skew is compensated by programming the phase of the sampling clocks for the different channels. Furthermore, during real-time operation of the receiver, channel diagnostics is performed to automatically estimate differential group delay and/or other channel characteristics based on the equalizer coefficients using a frequency averaging or polarization averaging approach. Framer information can furthermore be utilized to estimate differential group delay that is an integer multiple of the symbol rate. Additionally, a DSP reset may be performed when substantial signal degradation is detected based on the channel diagnostics information.