B. P.-P. Kuo

Overcoming Kerr-induced capacity limit in optical fiber transmission

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 Digital back-propagation is used to mitigate light-induced nonlinear effects in optic fiber. Nonlinear optical response of silica imposes a fundamental limit on the information transfer capacity in optical fibers. Communication beyond this limit requires higher signal power and suppression of nonlinear distortions to prevent irreversible information loss. The nonlinear interaction in silica is a deterministic phenomenon that can, in principle, be completely reversed. However, attempts to remove the effects of nonlinear propagation have led to only modest improvements, and the precise physical mechanism preventing nonlinear cancellation remains unknown. We demonstrate that optical carrier stability plays a critical role in canceling Kerr-induced distortions and that nonlinear wave interaction in silica can be substantially reverted if optical carriers possess a sufficient degree of mutual coherence. These measurements indicate that fiber information capacity can be notably increased over previous estimates.

Tunable Parametric All-Fiber Short-Wavelength IR Transmitter

In this paper, the performance of an all-fiber short-wave IR (SWIR) transmitter with wideband tunability and high peak power is reported. Transmitter construction relied on parametric process in highly nonlinear fiber to convert a seed laser at 1260 nm to 2155 nm SWIR channel with record 39 dB efficiency and translation over 900 nm spectral range. We demonstrated 61 W of peak converted power at 2 ¿m and 26 W at 2.15 ¿ m. Efficient conversion was made possible by engineered fourth-order dispersion of the highly nonlinear fiber and construction of a low-noise pump source in a 1550 nm band.

Nonlinearity Cancellation in Fiber Optic Links Based on Frequency Referenced Carriers

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.

Microsecond Parametric Optical Delays

In this paper, we present the first wavelength-preserving, tunable all-optical delay lines surpassing the microsecond range. Experimental demonstrations with 10-Gb/s data streams, tunable over 1.83 ¿s, as well as 40-Gb/s data tunable over 1.56 ¿s, characterized by a record delay-bandwidth product of 78 000, are presented and analyzed in detail.

Two-fold transmission reach enhancement enabled by transmitter-side digital backpropagation and optical frequency comb-derived information 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.

Subnoise detection of a fast random event

Detecting a transient needle in a haystack Discriminating signals within a noisy environment is an issue crucial to many disciplines, from observational astronomy to secure communication and imaging. If the signal is periodic, then averaging over many measurements can help enhance the signal-to-noise ratio. However, for signals that present as a single transient event, the detection capability has been limited. Ataie et al. developed a detector that can lift that limitation by combining signal cloning with frequency combs and signal-processing techniques (see the Perspective by Vasilyev). Their detector could detect signals buried within noise that would otherwise be undetectable. Science, this issue p. 1343; see also p. 1314 Single transient signals can be detected even when buried within a noisy environment. [Also see Perspective by Vasilyev] Observation of random, nonrepetitive phenomena is of critical importance in astronomy, spectroscopy, biology, and remote sensing. Heralded by weak signals, hidden in noise, they pose basic detection challenges. In contrast to repetitive waveforms, a single-instance signal cannot be separated from noise through averaging. Here, we show that a fast, randomly occurring event can be detected and extracted from a noisy background without conventional averaging. An isolated 80-picosecond pulse was received with confidence level exceeding 99%, even when accompanied by noise. Our detector relies on instantaneous spectral cloning and a single-step, coherent field processor. The ability to extract fast, subnoise events is expected to increase detection sensitivity in multiple disciplines. Additionally, the new spectral-cloning receiver can potentially intercept communication signals that are presently considered secure.

Ultrafast optical control by few photons in engineered fiber

Toward the control of light with light Optic fibers form the backbone of the communications sector and carry huge amounts of data around the globe. Nissim et al. show that small perturbations within the core of a fiber give rise to interactions between photons. The strength of the interaction could be controlled by carefully characterizing and splicing together different lengths of fiber. The interactions between the photons were enhanced so that a strong signal beam could be switched off with just a few photons. Science, this issue p. 417 Ultrafast photon-photon control is achieved in an engineered optic fiber. Fast control of a strong optical beam by a few photons is an outstanding challenge that limits the performance of quantum sensors and optical processing devices. We report that a fast and efficient optical gate can be realized in an optical fiber that has been engineered with molecular-scale accuracy. Highly efficient, distributed phase-matched photon-photon interaction was achieved in the fiber with locally controlled, nanometer-scale core variations. A three-photon input was used to manipulate a Watt-scale beam at a speed exceeding 500 gigahertz. In addition to very fast beam control, the results provide a path to developing a new class of sensitive receivers capable of operating at very high rates.

A fully frequency referenced parametric polychromatically sampled analog-to-digital conversion

We present a novel scalable photonically-sampled analog-to-digital-converter based on parametric multicasting, polychromatic sampling and frequency referenced lasers. A sampling rate of 30-GS/s is achieved with three subrate-channels with a 6.2-ENOB performance of a 19-GHz signal.

Octave-spanning coherent supercontinuum generation in silicon on insulator from 1.06 μm to beyond 2.4 μm

Efficient complementary metal-oxide semiconductor-based nonlinear optical devices in the near-infrared are in strong demand. Due to two-photon absorption in silicon, however, much nonlinear research is shifting towards unconventional photonics platforms. In this work, we demonstrate the generation of an octave-spanning coherent supercontinuum in a silicon waveguide covering the spectral region from the near- to shortwave-infrared. With input pulses of 18u2009pJ in energy, the generated signal spans the wavelength range from the edge of the silicon transmission window, approximately 1.06 to beyond 2.4u2009μm, with a −20u2009dB bandwidth covering 1.124–2.4u2009μm. An octave-spanning supercontinuum was also observed at the energy levels as low as 4u2009pJ (−35u2009dB bandwidth). We also measured the coherence over an octave, obtaining , in good agreement with the simulations. In addition, we demonstrate optimization of the third-order dispersion of the waveguide to strengthen the dispersive wave and discuss the advantage of having a soliton at the long wavelength edge of an octave-spanning signal for nonlinear applications. This research paves the way for applications, such as chip-scale precision spectroscopy, optical coherence tomography, optical frequency metrology, frequency synthesis and wide-band wavelength division multiplexing in the telecom window.

All optical wavelength multicaster and regenerator based on four-mode phase-sensitive parametric mixer

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.