Raman-assisted phase sensitive amplifier using a fiber Bragg grating-based tunable phase shifter.

A low-loss Raman-assisted phase sensitive amplifier (PSA) with a ∼20 dB signal net gain is experimentally demonstrated. The amplitude and phase adjustment for PSA are achieved by using non-uniform Raman gain and a tunable fiber Bragg grating (FBG), respectively. The total component loss of the system is measured to be ∼8 dB. By tuning the FBG central wavelength, (1) an up to 5.6 dB signal gain improvement is obtained; and (2) a ∼4 dB receiver sensitivity enhancement is observed for 20 and 25 Gbaud quadrature phase shift keying signals and a 10 Gbaud 16-quadrature amplitude modulation signal.

Pilot-tone-based self-homodyne detection using optical nonlinear wave mixing.

An all-optical pilot-tone-based self-homodyne detection scheme using nonlinear wave mixing is experimentally demonstrated. Two scenarios are investigated using (1) multiple wavelength-division-multiplexed channels with sufficient power of the pilot tones and (2) a single channel with a low-power pilot tone. The eye diagram and bit error rate of the system are studied by tuning various parameters such as pump power, relative phase, and pilot-to-signal ratio.

Simultaneous all-optical phase noise mitigation and automatically locked homodyne reception of an incoming QPSK data signal.

Simultaneous phase noise mitigation and automatic phase/frequency-locked homodyne reception is demonstrated for a 20-32 Gbaud QPSK signal. A phase quantization function is realized to squeeze the phase noise of the signal by optical wave mixing of the signal, its third-order harmonic, and their corresponding delayed variant conjugates, converting the noisy input into a noise-mitigated signal. In a simultaneous nonlinear process, the noise-mitigated signal is automatically phase- and frequency-locked with a "local" pump laser, avoiding the need for feedback or phase/frequency tracking for homodyne detection. Open eye-diagrams are obtained for in-phase and quadrature-phase components of the signal and ∼2 dB OSNR gain is achieved at BER 10-3.

Experimental demonstration of phase-sensitive regeneration of a binary phase-shift keying channel without a phase-locked loop using Brillouin amplification.

All-optical phase regeneration of a binary phase-shift keying signal is demonstrated at 10-30 Gb/s without a phase-locked loop in a phase-sensitive amplification-based system using Brillouin amplification of the idler. The system achieves phase noise reduction of up to 56% and up to 11 dB OSNR gain at 10-5 bit error rate for the 10 Gb/s signal. The system's sensitivity to different parameters and stability is also evaluated.

Reconfigurable optical inter-channel interference mitigation for spectrally overlapped QPSK signals using nonlinear wave mixing in cascaded PPLN waveguides.

A reconfigurable all-optical inter-channel interference (ICI) mitigation method is proposed for an overlapped channel system that avoids the need for multi-channel detection and channel spacing estimation. The system exhibits a 0.5-dB implementation penalty compared to a single-channel baseline system. Experiments using a dual-carrier QPSK overlapped system with both 20G-baud and 25G-baud under different channel spacing conditions evaluate the performance of the method. Improved signal constellation and receiver sensitivity demonstrate the effectiveness of this approach. This results in over 4-dB OSNR of benefit when the system Q-factor reaches a forward error correction (FEC) threshold of 8.5 dB under less-than-baudrate channel spacing conditions.

Experimental demonstration of tunable homodyne detection of WDM and dual-polarization PSK channels by automatically locking the channels to a local pump laser using nonlinear mixing.

This Letter proposes a method for tunable automatically locked homodyne detection of wavelength-division multiplexing (WDM) dual-polarization (DP) phase-shift keyed (PSK) channels using nonlinear mixing. Two stages of periodically poled lithium niobate (PPLN) waveguides and an LCoS filter enable automatic phase locking of the channels to a local laser.

All optical signal level swapping and multilevel amplitude noise mitigation based on different regions of optical parametric amplification.

All optical signal level swapping and multilevel amplitude noise mitigation are experimentally demonstrated using the three gain regions of optical parametric amplification, i.e., linear, saturation, and inversion. The two-amplitude-shift-keying and eight-quadrature-amplitude-modulation optical communication systems with baud rates of both 10 and 20 Gbaud have been employed to demonstrate the proposed approaches. Less than 1% error-vector-magnitude degradation is observed after signal level swapping. For amplitude noise mitigation, a more than 20% decrease in amplitude error is confirmed.

Optical channel de-aggregation of quadrature-phase-shift-keying and eight-phase-shift-keying data using mapping onto constellation axes.

An eight-phase-shift-keying signal is experimentally de-aggregated onto two four-pulse amplitude modulation signals using nonlinear processes in optical elements. Quadrature-phase-shift-keying signals are similarly de-multiplexed into two binary phase shift keying signals by mapping the data points onto the constellation axes. De-multiplexing performance is evaluated as a function of the optical signal-to-noise ratio of the incoming signals. The effect of phase noise is also studied.

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.

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.

Experimental demonstration of robustness and accuracy of a DLI-based OSNR monitor under changes in the transmitter and link for different modulation formats and baud rates.

We experimentally studied the performance of a delay-line interferometer-based optical signal-to-noise ratio (OSNR) monitor that is pre-calibrated in optimal conditions for 25-Gbaud pol-muxed quadrature-amplitude-modulation (QAM) signals, when unpredicted changes outside the monitor occurred either in the transmitter or the link.

Reconfigurable 2D optical tapped-delay-line to perform correlation on images.

We demonstrate a reconfigurable 2D optical tapped-delay-line (OTDL) to correlate quadrature-phase-shift-keying (QPSK) 20 Gbaud data. By implementing two independent tapped-delay-lines which performs correlation over rows (inner sum), along with a coherent multiplexing of the correlated rows which performs correlation over columns (outer sum), a 2D correlator is achieved with average error vector magnitude (EVM) of ∼7.8%. Here we also search different 2×2 patterns in a 31×31 image and successfully recognize the target patterns in the image.

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 tunable optical generation of higher-order modulation formats using nonlinearities and coherent frequency comb.

We demonstrate a tunable, optical generation scheme of higher-order modulation formats including pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM). Using this method, 100.4 Gbit/s 16-QAM and 120 Gbit/s 64-QAM were generated from 50.2 and 40 Gbit/s QPSK signals at EVMs of 7.8% and 6.4%, and 60 Gbit/s 8-PAM were generated at an EVM of 8.1% using three 20-Gbit/s BPSK signals. We also demonstrated a successful transmission of 80 Gbit/s 16-QAM through 80 km SMF-28 after compensating with 20 km DCF. All signals were generated, transmitted, and detected with BER below the forward error correction threshold.

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 in-service wavelength division multiplexing optical-signal-to-noise ratio performance monitoring and operating guidelines for coherent data channels with different modulation formats and various baud rates.

We demonstrated a delay-line interferometer (DLI)-based, optical-signal-to-noise ratio (OSNR) monitoring scheme of 100 Gbit/s polarization multiplexed quadrature-phase-shift-keying (PM-QPSK) four-channel WDM at 50-GHz International Telecommunication Union (ITU) grid with <0.5 dB error for signals with up to 26 dB of actual OSNR. We also demonstrated data format transparency and baud rate tunability of the OSNR monitor by measuring the OSNR for a 200 Gbit/s PM-16-QAM (25-Gbaud) signal and a 200 Gbit/s PM-QPSK (50-Gbaud) signal. We also explored and studied different monitor parameters, including the shape of the filter spectrum, the bandwidth of the filter, DLI delay, and DLI phase-detuning to determine the design guidelines for a desired level of accuracy for the OSNR monitor in an optical network.

Simultaneous and independent processing of multiple input WDM data signals using a tunable optical tapped delay line.

We demonstrate a tunable optical tapped delay line that can simultaneously and independently operate on multiple wavelength-division multiplexed (WDM) data signals. The system utilizes the wavelength-dependent speed of light, together with nonlinear wavelength conversion stages. A phase-preserving scheme enables coherent addition of the weighted taps. We reconfigured the system to perform separate simultaneous correlation (data pattern recognition), equalization, and modulation format conversion on four and eight WDM binary/quadrate phase-shift keyed channels at 26 and 20 Gbaud, respectively. The aggregate throughput of 416 Gb/s is achieved.