Four-wave Mixing Bragg Scattering Research Articles

Non-resonant Bragg scattering four-wave mixing at near-visible wavelengths in low-confinement silicon nitride waveguides

Quantum state coherent frequency conversion processes—such as Bragg-scattering four-wave mixing (BSFWM)—hold promise as a flexible technique for networking heterogeneous and distant quantum systems. In this Letter, we demonstrate BSFWM within an extended (1.2-m) low-confinement silicon nitride waveguide and show that this system has the potential for near-unity frequency conversion in visible and near-visible wavelength ranges. Using sensitive classical heterodyne laser spectroscopy at low optical powers, we characterize the Kerr coefficient (∼1.55 W−1m−1) and linear propagation loss (∼0.0175 dB/cm) of this non-resonant waveguide system, revealing a record-high nonlinear figure of merit (NFM = γ/α ≈ 3.85 W−1) for BSFWM of near-visible light in non-resonant silicon nitride waveguides. We predict how, at high yet achievable on-chip optical powers, this NFM would yield a comparatively large frequency conversion efficiency, opening the door to near-unity flexible frequency conversion without cavity enhancement and resulting bandwidth constraints.

Nonreciprocal Frequency Domain Beam Splitter.

The canonical beam splitter-a fundamental building block of quantum optical systems-is a reciprocal element. It operates on forward- and backward-propagating modes in the same way, regardless of direction. The concept of nonreciprocal quantum photonic operations, by contrast, could be used to transform quantum states in a momentum- and direction-selective fashion. Here we demonstrate the basis for such a nonreciprocal transformation in the frequency domain through intermodal Bragg scattering four-wave mixing (BSFWM). Since the total number of idler and signal photons is conserved, the process can preserve coherence of quantum optical states, functioning as a nonreciprocal frequency beam splitter. We explore the origin of this nonreciprocity and find that the phase-matching requirements of intermodal BSFWM produce an enormous asymmetry (76×) in the conversion bandwidths for forward and backward configurations, yielding ∼25 dB of nonreciprocal contrast over several hundred GHz. We also outline how the demonstrated efficiencies (∼10^{-4}) may be scaled to near-unity values with readily accessible powers and pumping configurations for applications in integrated quantum photonics.

Mode switching using optically induced long-period gratings: a theoretical analysis.

We show that optically induced long-period grating (OLPG) is a particular case of inter-modal Bragg-scattering four-wave mixing (BS-FWM). To carry out such analysis, a vector model for the inter-modal BS-FWM was proposed and further tailored to investigate the energy transfer induced by OLPGs. Both processes, BS-FWM and OLPGs, have been proposed for in-line all-optical mode switching in transmission systems with space-division multiplexing (SDM). In this scope, we demonstrate that the bandwidth of OLPGs is larger than the BS-FWM. Furthermore, we show that OLPG-based mode switching can take place in two windows, if both pump beams are launched near the zero value of the differential mode-group delay, and the central wavelength and the bandwidth of such windows can be tuned by properly adjusting the wavelength and the optical power of the pump beams.

Bloch oscillations in photonic spectral lattices through phase-mismatched four-wave mixing.

Here we investigate the Bloch oscillations (BOs) in a photonic spectral lattice created with four-wave mixing Bragg scattering (FWM-BS). By injecting a signal and two pumps with different frequencies into a silicon nitride waveguide, a spectral lattice can be created for the generated idlers through successive FWM-BS. The phase-mismatch during FWM-BS acts as an effective force that induces BOs in the spectral lattice. Both the oscillation period and amplitude are determined by the magnitude of the effective force. With cascaded FWM-BS processes, the spectrum of idlers experiences a directional shift as the phase differences of pumps are modulated. Additionally, introducing long-range couplings in the spectral lattice will change the trajectory of BOs within each period. The pattern of BOs for a single frequency input can also be tailored. This Letter provides a new platform to realize BOs in the frequency dimension and paves a promising way for broadband frequency control with all-optical schemes.

Optical Single-Sideband Generation by Dual-Stage Four-Wave Mixing Bragg Scattering

In this letter, we propose a novel approach for optical single-sideband (SSB) generation by utilizing four-wave mixing Bragg scattering (FWM-BS). The scheme comprises three stages: the initial FWM-BS stage, the spectral phase control stage, and the final FWM-BS stage. Constructive or destructive interference can occur between the sidebands generated in the two FWM-BS stages, depending on the spectral phase mask applied between the stages. By applying an appropriate phase mask, one sideband can be eliminated by destructive interference, while the other sideband is magnified by constructive interference, thus realizing SSB generation. Both upconverted and downconverted SSB generations can be achieved. To verify the scheme, we experimentally demonstrate 50-GHz optical frequency upconversion and downconversion separately for multi-channel 16-Gbaud QPSK signals.

Polarization-insensitive phase conjugation using single pump Bragg-scattering four-wave mixing in semiconductor optical amplifiers.

We explain the generation of four wave mixing (FWM) components at the front and back facets of semiconductor optical amplifiers (SOAs) based on the Bragg-scattering from the propagating gratings in the SOAs. We propose a counter-propagating cross-polarized degenerate pumping scheme for the polarization-insensitive conjugate generation, simultaneously in both input and output ports of the SOA for the first time. The corresponding Bragg scattering processes along with the phase matching conditions are described and the detuning performance of the generated conjugate in either port are experimentally validated. Polarization-insensitive phase conjugate generation at both input and output ports of the SOA through Bragg scattering FWM is further demonstrated.

Parametric spectrotemporal analyzer based on four-wave mixing Bragg scattering.

A parametric spectro-temporal analyzer (PASTA) has been demonstrated as an ultrafast single-shot spectral analyzing technique. However, the relatively complex system configuration and the limited wavelength measurement range limit its practical application. In this work, a new system design utilizing a four-wave mixing Bragg scattering (FWM-BS) process is presented that significantly simplifies the implementation. More importantly, owing to the large parametric conversion bandwidth of the FWM-BS process, the maximum wavelength measurement range has been expanded to around 30nm. In addition, the detection sensitivity is also enhanced by 10dB. Our work thus represents a critical step in realizing the practical application of the PASTA technique.

Low control-power wavelength conversion on a silicon chip.

We demonstrate controlled wavelength conversion on a silicon chip based on four-wave mixing Bragg scattering (FWM-BS). A total conversion efficiency of 5% is achieved with strongly unbalanced pumps and a controlling peak power of 55 mW, while the efficiency is over 15% when using less asymmetric pumps. The numerical simulation agrees with the experimental results. Both time domain and spectral domain noise measurements show as low as 2 dB signal-to-noise ratio (SNR) penalty because of the strong pump noise, two-photon absorption, and free-carrier absorption in silicon. We discuss how the scheme can be used to implement an all-optically controlled high-speed switch.

High-efficiency frequency conversion in the single-photon regime

In this Letter we demonstrate frequency conversion in the single-photon regime through Bragg-scattering four-wave mixing with near-unit efficiency in a 750 m long commercially available dispersion-engineered highly nonlinear fiber, where all photons and pump laser frequencies are in the low-loss telecommunications band. We achieve 99.1%±4.9% downconversion and 98.0%±5.0% upconversion of photons by 12 nm using a weak coherent state with an average input of 0.27 photons per detection gate window.

Bragg-Scattering conversion at telecom wavelengths towards the photon counting regime

We experimentally study Bragg-scattering four-wave mixing in a highly nonlinear fiber at telecom wavelengths using photon counters. We explore the polarization dependence of this process with a continuous wave signal in the macroscopic and attenuated regime, with a wavelength shift of 23 nm. Our measurements of mean photon numbers per second under various pump polarization configurations agree well with the theoretical and numerical predictions based on classical models. We discuss the impact of noise under these different polarization configurations.

Bragg-Scattering Four-Wave Mixing in Nonlinear Fibers with Intracavity Frequency-Shifted Laser Pumps

We experimentally study four-wave mixing in highly nonlinear fibers using two independent and partially coherent laser pumps and a third coherent signal. We focus our attention on the Bragg-scattering frequency conversion. The two pumps were obtained by amplifying two Intracavity frequency-shifted feedback lasers working in a continuous wave regime.