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We demonstrate a sub-GHz RF-photonic filter based on phase and amplitude control of a wideband all-fiber frequency parametric comb with 25-GHz tone spacing. The narrow bandwidth filter construction based on 221 comb tones was enabled by fourth-order dispersion compensation of the dispersive element. The filter integrity was further tested by retrieval of a set of digital modulated RF channels.

Signals arising in nearly all disciplines, including telecommunications, mechanics, biology, astronomy, and nature are generally modulated, carrying corresponding signatures in both the temporal and spectral domains. This fact was long recognized by cyclostationary and cumulant analysis, providing qualitatively better means to separate stochastic from deterministically modulated radiation. In contrast to simple spectral analysis, the cyclostationary technique provides a high level of spectral discrimination, allowing for considerable signal selectivity even in the presence of high levels of background noise and interference. When performed with sufficient resolution, cyclostationary analysis also provides the ability for signal analysis and classification. Unfortunately, these advantages come at a cost of large computational complexity posing fundamental detection challenges. In the case of modern ultrawideband signals, the requirements for persistent cyclostationary analysis are considerably beyond the processing complexity of conventional electronics. Recognizing this limit, we report a new photonically assisted cyclostationary analyzer that eliminates the need for high-bandwidth digitization and real-time Fourier processors. The new receiver relies on mutually coherent frequency combs used to generate a Fourier representation of the received signal in a computation-free manner. With the advent of practical, cavity-free optical frequency combs, the complexity for cyclostationary analysis can be greatly reduced, paving a path toward persistent wideband cyclostationary analysis in an ultrawideband operating regime.

We demonstrate the first sub-GHz flat-top RF-photonic filter based on a wide-band 25 GHz-pitched parametric comb. A narrow filter was constructed by fourth order dispersion compensation of the fiber for the first time. The filter performance was tested by digital modulated RF data retrieval.

Transient signals accompanied by a high noise level pose both basic and practical detection challenges. Disciplines that range from communication and astronomy to molecular physics face a very similar detection problem. When phenomena of interest are repetitive, different averaging techniques can be applied in order to elevate the signal above the detection threshold. In contrast, nonrepetitive signals, commonly occurring in communication and astronomy, cannot be processed using averaging techniques. With the advent of near-noiseless replication techniques, single-instance signal separation from noise has become possible. Here, we demonstrate that a single-instance signal can be mapped to 300 optical carrier frequencies and detected with low-bandwidth receivers to generate detection gains of 24 dB with respect to a single integrating receiver with the same bandwidth. The spectral-replicating receiver was used to detect a single-instance signal with power that was four times lower than the accompanying noise level.

A 100% reach extension is demonstrated in a coherent four-channel wavelength division multiplexed system by employing full-bandwidth frequency-referenced transmitter-side digital back propagation. Frequency referenced optical carriers are generated by injection locking distributed feedback lasers to a reference optical frequency comb and the performance of digital back propagation is evaluated with and without the frequency reference. In addition, we investigate the effect of an implementation with reduced computational complexity by limiting the number of steps-per-span used in the back propagation computation. Lastly, we measure the penalties generated by an inaccurate fiber dispersion parameter in the back propagation model.

We demonstrate fourth order dispersion compensation of fiber using a pulse shaper to synthesize a sub-800 MHz flat-top microwave photonic filter based on a wideband optical parametric comb.

The Generalized Nonlinear Schrodinger Equation (GNLSE) finds several applications, especially in describing pulse propagation in nonlinear fiber optics. A well-known and thoroughly studied phenomenon in nonlinear wave propagation is that of modulation instability (MI). MI is approached as a weak perturbation to a pump and the analysis is based on preserving those terms linear on the perturbation and disregarding higher-order terms. In this sense, the linear MI analysis is relevant to the understanding of the onset of many other nonlinear phenomena, but its application is limited to the evolution of the perturbation over short distances. In this work, we propose quasi-analytical approximations to the propagation of a perturbation consisting of additive white noise that go beyond the linear modulation instability analysis. Moreover, we show these approximations to be in excellent agreement with numerical simulations and experimental measurements.

Getting around the capacity crunch The growing appetite for an ever-faster Internet and enhanced long-haul communication requires the pumping of more light down optic fibers. However, light-induced nonlinearities limit how much light can be pumped into the fiber without compromising the signal. This limitation has led to the prospect of a “capacity crunch.” Temprana et al. eliminated the effects of nonlinearity by using digital back-propagation methods with mutually coherent laser pulses from a single frequency comb. Science , this issue p. 1445

A novel optical frequency synthesizer capable of generating a multitude of narrow linewidth oscillations, fully compatible with high-speed fiber-optic transmission requirements, is presented. The new device is based on an ultra-dense and wideband parametric comb capable of generating more than 1800 spectral lines with 6.25 GHz spacing within 100 nm (C + L band) of optical bandwidth and 3 dB spectral flatness. The parametric comb generation relies on the highly efficient nonlinear interaction of the ultra-short and high peak power pulse train in the precisely controlled dispersive medium. The generated comb source is used for coherent transmission of 1520 Nyquist ultra-dense wavelength division multiplexed channels in a flex-grid compatible optical access network architecture, offering up to 30 Gb/s per user over a 50 km of standard single mode fiber with estimated aggregate capacity of 32 Tb/s. The line spacing tunablity and one-to-multiple coherent cloning capability make the proposed multicarrier generator a strong contender fully capable of replacing thousands of discrete lasers in optical data communication systems.

We study the limitations and their origins in the nonlinear effects mitigation in fiber-optic communication systems. The carrier frequencies uncertainty and their stochastic variations are identified as the major impeding factor for successful inter-channel nonlinear impairments management. Furthermore, the results clearly point out to the significant benefits of employing fully frequency referenced carriers in transmission, with frequency combs representing an immediately available solution. Finally, frequency referenced transmitters and/or receivers are shown as critical for availing longer reach at high spectral efficiencies in transmission.

We report the first use of the CW-seeded parametric comb as a multiwavelength source for coherent channel transmitters. The new comb source relies on a multistage parametric mixer design seeded by a single kilohertz-linewidth master laser. The resultant frequency comb provides more than 120 tones in a 100-nm-wide continuous band, all possessing kilohertz-scale linewidth inherited from the master laser. The applicability of the new comb source as a coherent channel carrier was quantified by error-vector magnitude and bit-error rate metrics of individual spectral lines modulated by QPSK signaling. The performance of the new source exceeded that of the standard tunable coherent transmitter while providing a qualitatively lower frequency uncertainty and drift.

We present a high-speed flexible photonic-assisted Discrete Fourier Transform (DFT) processor based on a dual, phase-locked optical parametric combs. A 25-point DFT at 500 Million-DFT-point per second throughput is achieved relying on slow, 20 MS/s Analog to Digital Converter (ADC).

We demonstrate WDM transmission of seven 50 GHz-spaced 400 Gb/s (30 GBaud) DP-256-QAM channels over 52 km of SMF. Transmission relied on a frequency comb, generating kHz-linewidth, high OSNR carriers to demonstrate compatibility with metro and inter-data-center applications.

We demonstrate nine-fold wavelength multicasting of 4- and 16-QAM signals in a two-stage, dual-pump silicon mixer. Characterized multicast performance varied for up to 10 dB for the generated copies over 15 nm.

Four-mode phase-sensitive (4MPS) process has been employed in a parametric mixer based wavelength multicaster, enhancing the multicasting conversion efficiency and signal-to-noise ratio. In addition, the 4MPS parametric multicaster is an outstanding candidate for all-optical regeneration, owing to its inherent capabilities to clamp amplitude fluctuations by the saturated parametric effect and to squeeze phase distortions by the phase sensitive process. The investigation in this paper focuses on the 4MPS multicaster operated in the saturation gain regime, including theoretical simulations and experimental demonstrations on amplitude and phase noise regeneration over 20 multicasting signal copies.

The effects of dispersion parameter mismatch and limited steps-per-span are investigated in a system employing Transmitter-Side Digital Back Propagation with Frequency Referenced Carriers.

We demonstrate a two-fold reach extension of 16 GBaud 16-Quadrature Amplitude Modulation (QAM) wavelength division multiplexed (WDM) system based on erbium doped fiber amplifier (EDFA)-only amplified standard and single mode fiber -based link. The result is enabled by transmitter-side digital backpropagation and frequency referenced carriers drawn from a parametric comb.

We propose a transmitter based on injection locking a low-cost Fabry-Perot laser to a reference Optical Frequency Comb. We demonstrate transmission of 50 GBaud 16-QAM over 2125 km relying on Digital Back Propagation.

We demonstrate the first high-count signal replication accompanied with phase-and-amplitude-noise-squeezing in a four-mode phase-sensitive process. Errorless detection of the phase-modulated information on a 5.8-GHz-phase-noise broadened carrier has been accomplished over 20-copies in a parametric multicaster.

The stability enabled by frequency combs can allow correction of nonlinear crosstalk among WDM channels—and, potentially, boost single-mode fiber capacity well beyond the conventionally defined ceiling.

A scalable analog-to-digital converter based on polychromatic sampling and optical-domain frequency referencing is described. The new architecture relies on low-distortion replication of an optical signal to spectrally distinct copies and subsequent polychromatic parametric sampling. Frequency comb referencing of parametric replication and sampling was used to convert processor distortions into quasi-stationary impairments and enable a practical equalization implementation. The operation of the new digitizer was demonstrated at 30 GS/s, achieving 6.5 effective number of bits in the first Nyquist zone. In contrast to conventional analog-to-digital converters, the new preprocessor sampling bandwidth is not restricted to the first Nyquist zone, and can operate in the second and third Nyquist zones beyond 40 GHz.

A low phase noise frequency comb generated from a continuous-wave seed is experimentally demonstrated across continuous C- and L-bands. Parametrically generated carriers with optical signal-to-noise ratio in excess of 45 dB were used to generate 16-ary quadrature amplitude modulated signals. We characterize 20 GBaud channels' performance that was varied by only 1.7 dB across the combined C/L band.

We demonstrate wavelength conversion of QPSK signals in a single-pump FOPA with 20 dB conversion efficiency. Phase distortions in the idler arising from pump-phase modulation were compensated after coherent detection using a novel time-domain approach.