Morteza Ziyadi

Phase noise mitigation of QPSK signal utilizing phase-locked multiplexing of signal harmonics and amplitude saturation.

We demonstrate an all-optical phase noise mitigation scheme based on the generation, delay, and coherent summation of higher order signal harmonics. The signal, its third-order harmonic, and their corresponding delayed variant conjugates create a staircase phase-transfer function that quantizes the phase of quadrature-phase-shift-keying (QPSK) signal to mitigate phase noise. The signal and the harmonics are automatically phase-locked multiplexed, avoiding the need for phase-based feedback loop and injection locking to maintain coherency. The residual phase noise converts to amplitude noise in the quantizer stage, which is suppressed by parametric amplification in the saturation regime. Phase noise reduction of ∼40% and OSNR-gain of ∼3  dB at BER 10(-3) are experimentally demonstrated for 20- and 30-Gbaud QPSK input signals.

Optical Nyquist channel generation using a comb-based tunable optical tapped-delay-line

We demonstrate optical Nyquist channel generation based on a comb-based optical tapped-delay-line. The frequency lines of an optical frequency comb are used as the taps of the optical tapped-delay-line to perform a finite-impulse response (FIR) filter function. A single optical nonlinear element is utilized to multiplex the taps and form the Nyquist signal. The tunablity of the approach over the baud rate and modulation format is shown. Optical signal-to-noise ratio penalty of 2.8 dB is measured for the 11-tap Nyquist filtering of 32-Gbaud QPSK signal.

Demonstration of reconfigurable optical generation of higher-order modulation formats up to 64 QAM using optical nonlinearity

We demonstrate a reconfigurable optical transmitter of higher-order modulation formats including pulse-amplitude-modulation (PAM) signals and quadrature-amplitude-modulation (QAM) signals. We generated six different modulation formats by multiplexing 10 Gbit/s on-off-keying (OOK) signals (10 Gbaud binary phase-shift keying, 4-PAM, 8-PAM quadrature phase-shift keying (QPSK), 16-QAM and 16-star-QAM with error-vector magnitudes (EVMs) of 8.1%, 7.5%, 7.8%, 8.2%, 7.2%, and 6.9%, respectively) and 80 Gbit/s 16-QAM with an EVM of 8.5%, as well as 120 Gbit/s 64-QAM with an EVM of 7.1%, using two or three 40 Gbit/s QPSK signals, respectively. We also successfully transmitted the generated 16-QAM signals through a 100 km transmission line with negligible power penalty.

Demonstration of all-optical phase noise suppression scheme using optical nonlinearity and conversion/dispersion delay.

We propose and demonstrate an all-optical phase noise reduction scheme that uses optical nonlinear mixing and tunable optical delays to suppress the low-speed phase noise induced by laser linewidth. By utilizing the phase conjugate copy of the original signal and two narrow-linewidth optical pumps, the phase noise induced by laser linewidth can be reduced by a factor of ∼5 for a laser with 500-MHz phase noise bandwidth. The error-vector-magnitude can be improved from ∼30% to ∼14% for the same laser linewidth for 40-Gbit/s quadrature phase shift keying signal.

Demonstration of optical multicasting using Kerr frequency comb lines

We experimentally demonstrate optical multicasting using Kerr frequency combs generated from a Si3N4 microresonator. We obtain Kerr combs in two states with different noise properties by varying the pump wavelength in the resonator and investigate the effect of Kerr combs on multicasting. Seven-fold multicasting of 20 Gbaud quadrature phase-shift-keyed signals and four-fold multicasting of 16-quadrature amplitude modulation signals have been achieved when low-phase-noise combs are input into a periodically poled lithium niobate waveguide. In addition, we find that the wavelength conversion efficiency in the PPLN waveguide for chaotic combs with high noise is similar to that for low-noise combs, while the signal quality of the multicast copy is significantly degraded.

Tunable radio frequency photonics filter using a comb-based optical tapped delay line with an optical nonlinear multiplexer

A radio frequency (RF) photonic filter is experimentally demonstrated using an optical tapped delay line (TDL) based on an optical frequency comb and a periodically poled lithium niobate (PPLN) waveguide as multiplexer. The approach is used to implement RF filters with variable bandwidth, shape, and center-frequency.

Tunable optical correlator using an optical frequency comb and a nonlinear multiplexer

We experimentally demonstrate a tunable optical correlator to search for multiple patterns among QPSK symbols. We utilize an optical frequency comb to generate the coherent signals and multiplex them coherently in a single PPLN waveguide. Multiple patterns with different lengths are successfully searched within QPSK symbols in a 40-Gb/s signal.

All-optical phase noise suppression using optical nonlinear mixing combined with tunable optical delays

We propose and demonstrate an all-optical scheme of phase noise reduction using optical nonlinearity and dispersion/conversion delay. This scheme is capable of reducing the standard deviation of phase noise with low frequency component (e.g., laser phase noise) by a factor of ~ 4 without degrading the data signal. The EVM can be reduced from 31% to 11% for ~500 MHz phase noise bandwidth on 20-Gbaud QPSK input.

Flexible, reconfigurable capacity output of a high-performance 64-QAM optical transmitter

We experimentally demonstrate a reconfigurable optical flexible transmitter to generate arbitrary optical QAM. Optical 16-QAM and 64-QAM is generated at EVM 8.5% and 7.2% respectively. We demonstrated successful transmission through 80-km SMF-28 after compensating with 20-km DCF with negligible penalty.

Effect of a breather soliton in Kerr frequency combs on optical communication systems.

In this study, we numerically investigate the effect of Kerr-comb-generated breather soliton pulses on optical communication systems. The breather soliton pulse amplitude and spectrum envelope oscillate periodically in time. Simulations show that the spectrum of each comb line in the breather soliton state has multiple sub-teeth due to the periodic oscillation of the comb spectrum. In the simulation, the comb output is modulated with different formats. We find that the sub-teeth distort quadrature phase-shift-keyed signals but have less of an effect on on-off-keyed signals.