Multi-channel all-optical signal processing based on parametric effects

Two different experiments that use parametric effects for the processing of multiple signals in a single fiber are reviewed. The first experiment uses optical phase conjugation to mitigate the effects of nonlinearity in transmission, whereas the second uses multiple phase-sensitive amplifiers to regenerate six different channels

Broadband quadrature-squeezed vacuum and nonclassical photon number correlations from a nanophotonic device

We report the first demonstrations of both quadrature squeezed vacuum and photon number difference squeezing generated in an integrated nanophotonic device. Squeezed light is generated via strongly driven spontaneous four-wave mixing below threshold in silicon nitride microring resonators. The generated light is characterized with both homodyne detection and direct measurements of photon statistics using photon number-resolving transition edge sensors. We measure $1.0(1)$~dB of broadband quadrature squeezing (${\sim}4$~dB inferred on-chip) and $1.5(3)$~dB of photon number difference squeezing (${\sim}7$~dB inferred on-chip). Nearly-single temporal mode operation is achieved, with raw unheralded second-order correlations $g^{(2)}$ as high as $1.87(1)$ measured (${\sim}1.9$~when corrected for noise). Multi-photon events of over 10 photons are directly detected with rates exceeding any previous quantum optical demonstration using integrated nanophotonics. These results will have an enabling impact on scaling continuous variable quantum technology.Comment: Significant improvements and updates to photon number squeezing results and discussions, including results on single temporal mode operatio

Harnessing optical micro-combs for microwave photonics

In the past decade, optical frequency combs generated by high-Q micro-resonators, or micro-combs, which feature compact device footprints, high energy efficiency, and high-repetition-rates in broad optical bandwidths, have led to a revolution in a wide range of fields including metrology, mode-locked lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum optics. Among these, an application that has attracted great interest is the use of micro-combs for RF photonics, where they offer enhanced functionalities as well as reduced size and power consumption over other approaches. This article reviews the recent advances in this emerging field. We provide an overview of the main achievements that have been obtained to date, and highlight the strong potential of micro-combs for RF photonics applications. We also discuss some of the open challenges and limitations that need to be met for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference

Frequency Multiplexing for Quasi-Deterministic Heralded Single-Photon Sources

Single-photon sources based on optical parametric processes have been used extensively for quantum information applications due to their flexibility, room-temperature operation and potential for photonic integration. However, the intrinsically probabilistic nature of these sources is a major limitation for realizing large-scale quantum networks. Active feedforward switching of photons from multiple probabilistic sources is a promising approach that can be used to build a deterministic source. However, previous implementations of this approach that utilize spatial and/or temporal multiplexing suffer from rapidly increasing switching losses when scaled to a large number of modes. Here, we break this limitation via frequency multiplexing in which the switching losses remain fixed irrespective of the number of modes. We use the third-order nonlinear process of Bragg scattering four-wave mixing as an efficient ultra-low noise frequency switch and demonstrate multiplexing of three frequency modes. We achieve a record generation rate of $4.6\times10^4$ multiplexed photons per second with an ultra-low $g^{2}(0)$ = 0.07, indicating high single-photon purity. Our scalable, all-fiber multiplexing system has a total loss of just 1.3 dB independent of the number of multiplexed modes, such that the 4.8 dB enhancement from multiplexing three frequency modes markedly overcomes switching loss. Our approach offers a highly promising path to creating a deterministic photon source that can be integrated on a chip-based platform.Comment: 28 pages, 9 figures. Comments welcom

Multistep Parametric Processes in Nonlinear Optics

We present a comprehensive overview of different types of parametric interactions in nonlinear optics which are associated with simultaneous phase-matching of several optical processes in quadratic nonlinear media, the so-called multistep parametric interactions. We discuss a number of possibilities of double and multiple phase-matching in engineered structures with the sign-varying second-order nonlinear susceptibility, including (i) uniform and non-uniform quasi-phase-matched (QPM) periodic optical superlattices, (ii) phase-reversed and periodically chirped QPM structures, and (iii) uniform QPM structures in non-collinear geometry, including recently fabricated two-dimensional nonlinear quadratic photonic crystals. We also summarize the most important experimental results on the multi-frequency generation due to multistep parametric processes, and overview the physics and basic properties of multi-color optical parametric solitons generated by these parametric interactions.Comment: To be published in Progress in Optic

Phase sensitive amplifiers for regeneration of phase encoded optical signal formats

We discuss the application of phase sensitive fiber optical parametric devices for the regenerative processing of high baud rate optical signals. We present recent advances in phase-sensitive amplification technology and its application to the regeneration of phase-encoded signals. By combining four wave mixing based parametric effects in highly nonlinear optical fibers and injection locking assisted synchronisation of multiple coherent lasers, we demonstrate how it possible to derive phase regeneration in signals with more than two levels of phase encoding

Coherent terabit communications with microresonator Kerr frequency combs

Optical frequency combs enable coherent data transmission on hundreds of wavelength channels and have the potential to revolutionize terabit communications. Generation of Kerr combs in nonlinear integrated microcavities represents a particularly promising option enabling line spacings of tens of GHz, compliant with wavelength-division multiplexing (WDM) grids. However, Kerr combs may exhibit strong phase noise and multiplet spectral lines, and this has made high-speed data transmission impossible up to now. Recent work has shown that systematic adjustment of pump conditions enables low phase-noise Kerr combs with singlet spectral lines. Here we demonstrate that Kerr combs are suited for coherent data transmission with advanced modulation formats that pose stringent requirements on the spectral purity of the optical source. In a first experiment, we encode a data stream of 392 Gbit/s on subsequent lines of a Kerr comb using quadrature phase shift keying (QPSK) and 16-state quadrature amplitude modulation (16QAM). A second experiment shows feedback-stabilization of a Kerr comb and transmission of a 1.44 Tbit/s data stream over a distance of up to 300 km. The results demonstrate that Kerr combs can meet the highly demanding requirements of multi-terabit/s coherent communications and thus offer a solution towards chip-scale terabit/s transceivers