Four-wave Mixing Measurements Research Articles

Strong third-order nonlinearity in amorphous silicon carbide waveguides.

Silicon carbide (SiC) photonic integrated platform has attracted significant research interest for on-chip optical applications, owing to its exceptional optical properties such as a broad transparency window, high refractive index, and strong nonlinearity. Among the various types of SiC, amorphous SiC (a-SiC) has particularly emerged as an accessible choice for forming thin-film SiC-on-insulator (SiCOI) stacks, demonstrating promising capabilities for wafer-scale photonic applications. In this work, we prepare three a-SiCOI samples using the plasma-enhanced chemical vapor deposition, with different refractive indices. We fabricate optical waveguides, conduct four-wave mixing measurements, and characterize the nonlinear refractive index in these samples. Our findings reveal that an increase in the refractive index of a-SiC leads to a corresponding increase in the nonlinear refractive index, which is comparable to that of silicon. Hence, a-SiC offers an approach to develop a SiC platform with a wider bandgap than that of silicon, minimizing two-photon absorption while also providing a higher refractive index and stronger nonlinearity compared to crystalline SiC.

Measurements of the dispersion, the dispersion slope and nonlinear coefficients of photonic crystal fibers based on degenerate four-wave mixing (FWM)

Abstract A simple and accurate method based on degenerate four-wave mixing (FWM) to evaluate optical fiber dispersion and nonlinearity is presented. We investigated the continuous wave degenerate FWM characteristics of two photonic crystal fibers (PCFs) and a SMF28 fiber. Simply by measuring and analyzing the continuous wave degenerate FWM conversion efficiency as a function of the wavelength difference between pump and signal waves, fitting between experimental data and analytical FWM conversion efficiency expression is carried out to determine the dispersion, dispersion slope and nonlinear coefficient of the fiber. The fiber parameters simultaneously obtained from a single set of FWM measurement for Single Mode Fiber 28 (SMF28) are found to be agreement with the manufacturer specifications for this fiber, thus validating the PCF results and, more generally, the acceptable accuracy of the simple method proposed here.

Demonstration of Stimulated Brillouin Scattering in a Silicon Suspended Microring With Photonic-Phononic Waveguide

We design and fabricate the suspended silicon microring with racetrack and spiral structure to exploit the resonantly enhanced stimulated Brillouin scattering (SBS). The designed photonic-phononic waveguide can provide the independent control on the optical and acoustic modes by introducing the silicon ridge waveguide into the phononic crystal slab as a line defect. We demonstrate efficient forward SBS in the two kinds of microrings and extract the characteristic Brillouin parameters through the heterodyne four-wave mixing measurement. The stronger inhomogeneous broadening effect in the spiral microring due to the structural variations is also observed. In addition, our microrings show the single mode transmission spectrum and high quality factor, which is beneficial to the enhanced intramodal forward SBS. This design can readily extend to other silicon-based platforms and paves the way toward on-chip photonic-phononic signal processing and Brillouin amplifier technologies.

Ultra-compact titanium dioxide micro-ring resonators with sub-10-μm radius for on-chip photonics

Microring resonators (MRRs) with ultracompact footprints are preferred for enhancing the light-matter interactions to benefit various applications. Here, ultracompact titanium dioxide ( TiO 2 ) MRRs with sub-10-μm radii are experimentally demonstrated. Thanks to the large refractive index of TiO 2 , the quality factors up to ∼ 7.9 × 10 4 and ∼ 4.4 × 10 4 are achieved for TiO 2 MRRs with radii of 10 μm and 6 μm, respectively, which result in large nonlinear power enhancement factors ( > 113 ) and large Purcell factors ( > 56 ). The four-wave mixing (FWM) measurements indicate that, compared to the large MRR, the FWM conversion efficiency of the ultracompact TiO 2 MRRs can be greatly improved (e.g., − 25 dB versus − 31 dB ), a harbinger of significant superiorities. Demonstrations in this work provide more arguments for the TiO 2 waveguides as a promising platform for various on-chip photonic devices.

Four-wave mixing in a triple-core microstructure fiber.

We experimentally demonstrate four-wave mixing (FWM) in a triple-core microstructure fiber for a pump wavelength of 1064 nm. We study the transition between the case where FWM happens primarily in a single core and the case where FWM is distributed among multiple cores. The effective nonlinear coefficient is reduced by a factor of 3 (the number of cores) for distributed-core FWM compared with that for single-core FWM. This effect also leads to a three-fold reduction in the FWM bandwidth for distributed-core FWM. We report on the wavelength and polarization dependence of the core-to-core coupling length, and how those phenomena produce power-dependent coupling among the cores. These are the first reported experimental measurements of FWM in a 3-core microstructure fiber providing critical information for their use as nonlinear optical devices.

Enhanced Four‐Wave Mixing in Silicon Nitride Waveguides Integrated with 2D Layered Graphene Oxide Films

AbstractLayered 2D graphene oxide (GO) films are integrated with silicon nitride (SiN) waveguides to experimentally demonstrate an enhanced Kerr nonlinearity via four‐wave mixing (FWM). SiN waveguides with both uniformly coated and patterned GO films are fabricated based on a transfer‐free, layer‐by‐layer GO coating method along with standard photolithography and lift‐off processes, yielding precise control of the film thickness, placement, and coating length. Detailed FWM measurements are carried out for the fabricated devices with different numbers of GO layers and at different pump powers, achieving up to ≈7.3 dB improvement in the FWM conversion efficiency for an uniformly coated device with one layer of GO and ≈9.1 dB for a patterned device with five layers of GO. A detailed analysis of the influence of pattern length and position on the FWM performance is performed. The dependence of GO's third‐order nonlinearity on layer number and pump power is also extracted, revealing interesting physical insights about the layered 2D GO films. Finally, an enhancement is obtained in the effective nonlinear parameter of the hybrid waveguides by over a factor of 100 relative to bare SiN waveguide. These results demonstrate the high nonlinear optical performance of SiN waveguides integrated with layered 2D GO films.

Ultrafast nonlinear optical properties and excited-state dynamics of Soret-band excited D-π-D porphyrins

Herein, we report results from our studies on the ultrafast nonlinear optical (NLO) properties and excited-state dynamics in three different porphyrin molecules designed in D-π-D fashion (phenothiazine-porphyrin-phenothiazine) and with two different central metal ions [Zn(II) and Cu(II)]. We have performed extensive target analysis of the femtosecond transient absorption data obtained conveying the true exited state/species spectra of each process with respective lifetimes along with microscopic rate constants of each excited state. The obtained life time values were in the range of 250–500 fs, 20–142 ps, 1.5–6.2 ns and 0.1–1.23 μs and have been associated from relaxation with the Sn, Hot S1 (to S1), S1, and T1 states. Furthermore, the third-order nonlinear (NLO) coefficients [two-photon absorption (TPA) and nonlinear refractive index (n2)] of CPPHT and ZPPHT exhibited superior values compared to HPPHT recorded with ~50 fs, 1 kHz repetition rate pulses at a wavelength of 800 nm. The magnitude of the TPA coefficients of these molecules was compared with some of the recently reported porphyrin moieties and were found to be superior. The time-resolved degenerate four-wave mixing (DFWM) measurements confirmed a large magnitude and an ultrafast response of the χ(3) in these molecules suggesting potential photonic and all-optical switching applications.

Ultrafast photophysical and nonlinear optical properties of novel free base and axially substituted phosphorus (V) corroles

The progression in synthetic procedures over the last two decades gave admittance to a wide variety of corroles for suitable potential applications such as photovoltaics, photonics, and bio-imaging. In this communication, we present results from our investigations of ultrafast photophysical processes and third-order nonlinear optical properties of newly synthesized donor-acceptor based free-base [(C6F5)3] and phosphorus [P-(OH)2(C6F5)3] corroles. The global analysis of the femtosecond transient absorption data based on the compartmental model revealed the corresponding time constants of several photophysical processes such as (a) internal conversion (τIC) in the 260–280 fs range (b) vibrational relaxation (τVR) in the 2.5-5 ps range and (c) nonradiative relaxation times (τnr) in the 4.15–7.6 ns range and finally (d) triplet lifetimes in the range of 25–50 μs. The two-photon absorption (TPA) cross-section measurements were performed using the femtosecond, kHz pulse Z-Scan technique at 600 nm and 800 nm and the retrieved TPA cross-section values were in the range of ~102 GM. Degenerate four-wave mixing measurements illustrated a large third-order nonlinear optical susceptibility χ(3) with a magnitude of 6.9 × 10−14 esu and instantaneous (sub-picosecond) response, suggesting a pure electronic contribution to the nonlinearity of these corroles. The discoveries from this study may help further to extend the capability of corroles as NLO materials for photonic applications.

2D Layered Graphene Oxide Films Integrated with Micro-Ring Resonators for Enhanced Nonlinear Optics.

Layered 2D graphene oxide (GO) films are integrated with micro-ring resonators (MRRs) to experimentally demonstrate enhanced nonlinear optics. Both uniformly coated (1-5 layers) and patterned (10-50 layers) GO films are integrated on complementary-metal-oxide-semiconductor (CMOS)-compatible doped silica MRRs using a large-area, transfer-free, layer-by-layer GO coating method with precise control of the film thickness. The patterned devices further employ photolithography and lift-off processes to enable precise control of the film placement and coating length. Four-wave-mixing (FWM) measurements for different pump powers and resonant wavelengths show a significant improvement in efficiency of ≈7.6 dB for a uniformly coated device with 1 GO layer and ≈10.3 dB for a patterned device with 50 GO layers. The measurements agree well with theory, with the enhancement in FWM efficiency resulting from the high Kerr nonlinearity and low loss of the GO films combined with the strong light-matter interaction within the MRRs. The dependence of GO's third-order nonlinearity on layer number and pump power is also extracted from the FWM measurements, revealing interesting physical insights about the evolution of the GO films from 2D monolayers to quasi bulk-like behavior. These results confirm the high nonlinear optical performance of integrated photonic resonators incorporated with 2D layered GO films.

Invited Article: Enhanced four-wave mixing in waveguides integrated with graphene oxide

We demonstrate enhanced four-wave mixing (FWM) in doped silica waveguides integrated with graphene oxide (GO) layers. Owing to strong mode overlap between the integrated waveguides and GO films that have a high Kerr nonlinearity and low loss, the FWM efficiency of the hybrid integrated waveguides is significantly improved. We perform FWM measurements for different pump powers, wavelength detuning, GO coating lengths, and number of GO layers. Our experimental results show good agreement with theory, achieving up to ∼9.5-dB enhancement in the FWM conversion efficiency for a 1.5-cm-long waveguide integrated with 2 layers of GO. We show theoretically that for different waveguide geometries an enhancement in FWM efficiency of ∼20 dB can be obtained in the doped silica waveguides and more than 30 dB in silicon nanowires and slot waveguides. This demonstrates the effectiveness of introducing GO films into integrated photonic devices in order to enhance the performance of nonlinear optical processes.

Biexcitons in monolayer transition metal dichalcogenides tuned by magnetic fields

We present time-integrated four-wave mixing measurements on monolayer MoSe2 in magnetic fields up to 25 T. The experimental data together with time-dependent density function theory calculations provide interesting insights into the biexciton formation and dynamics. In the presence of magnetic fields the coherence at negative and positive time delays is dominated by intervalley biexcitons. We demonstrate that magnetic fields can serve as a control to enhance the biexciton formation and help search for more exotic states of matter, including the creation of multiple exciton complexes and excitonic condensates.

Investigation of Intermodal Four-Wave Mixing for Nonlinear Signal Processing in Few-Mode Fibers

We present a theoretical and experimental investigation of inter-modal four-wave mixing (FWM). After analyzing the phase-matching condition as the fundamental condition for efficient FWM, we show the impact of the individual mode’s propagation characteristics, such as differential mode delay and chromatic dispersion on the power of the generated idler. We verify the theoretical analysis with experimental measurements of intermodal FWM. We conclude that efficient broadband intermodal FWM can only be achieved for one specific FWM process and requires very close values of chromatic dispersion in all interacting fiber modes.

Spatially and temporally resolved IR-DFWM measurement of HCN released from gasification of biomass pellets

For the first time, to the best of the authors’ knowledge, nonintrusive quantitative measurement of hydrogen cyanide (HCN) released during the devolatilization phase of straw pellets gasification is demonstrated with high spatial and temporal resolution. Mid-infrared degenerate four-wave mixing (IR-DFWM) measurements of HCN were performed by probing the interference-free P(20) line in the v1 vibrational band at around 3 µm and the IR-DFWM signal was detected with an upconversion-based detector, providing discrimination of thermal noise and increased sensitivity. A novel single-pellet setup consisting of a multi-jet burner was used to provide hot flue gas environments with an even and well-defined temperature distribution, for single straw pellet gasification at atmospheric pressure. The environments had temperatures of 1380 K, 1540 K and 1630 K with a constant oxygen concentration of 0.5 vol%. In order to quantify the amount of HCN released during the devolatilization of straw pellets, calibration measurements were performed in well-defined HCN gas flows. Selected hot water lines were probed with IR-DFWM in the interrogated volume to obtain the instantaneous temperature, which were used to correct the temperature effect. HCN concentrations up to 1500 ppm were detected during the devolatilization stage, and the results indicate a strong temperature dependence of the HCN release.

Demonstration of optical nonlinearity in InGaAsP/InP passive waveguides

We report on the study of the third-order nonlinear optical interactions in InxGa1-xAsyP1-y/InP strip-loaded waveguides. The material composition and waveguide structures were optimized for enhanced nonlinear optical interactions. We performed self-phase modulation, four-wave mixing and nonlinear absorption measurements at the pump wavelength 1568 nm in our waveguides. The nonlinear phase shift of up to 2.5π has been observed in self-phase modulation experiments. The measured value of the two-photon absorption coefficient α2 was 19 cm/GW. The four-wave mixing conversion range, representing the wavelength difference between maximally separated signal and idler spectral components, was observed to be 45 nm. Our results indicate that InGaAsP has a high potential as a material platform for nonlinear photonic devices, provided that the operation wavelength range outside the two-photon absorption window is selected.

Ps four-wave mixing measurements of electric field in a ns pulse discharge in a hydrogen diffusion flame

Time-resolved electric field in ns pulse discharge plasmas generated in room air and in an atmospheric pressure hydrogen diffusion flame has been measured by ps four-wave mixing, for plane-to-plane electrode geometry. Electric field is put on the absolute scale using the Laplacian field measured before breakdown. The results show that peak electric field during breakdown in the flame, approximately 40 kV/cm, is significantly lower compared to that in room air, 75 kV/cm, due to higher temperature of combustion products. In both cases, peak electric field is higher compared to DC breakdown field. Both in air and in the flame, the electric field follows the applied voltage before breakdown and decreases rapidly after breakdown, due to charge separation and plasma self-shielding. The electric field in air is compared with the predictions of an analytic model of ns pulse breakdown, showing good agreement between the predicted and the measured breakdown field. The model also predicts earlier breakdown as well as breakdown voltage reduction as the temperature is increased, in qualitative agreement with the experimental data. The use of the present ps four-wave mixing diagnostics for measurements of electric fields below ∼20 kV/cm in atmospheric pressure flames is challenging, due to low signal-to-noise. The sensitivity of the present diagnostics is controlled by the high temperature and low N2 fraction in the combustion product mixture, as well as by the limited bandwidth of the Stokes beam generated by the stimulated Raman cell, which provides access only to several rotational levels of nitrogen molecules. The present diagnostics will have much better sensitivity in high-pressure flames, since the four-wave mixing signal scales as the squared number density of nitrogen.

Four-wave mixing and nonlinear parameter measurement in a gallium-nitride ridge waveguide

Gallium-nitride (GaN) is a promising material platform for integrated electro-optic devices due to its wide direct bandgap, pronounced nonlinearities and high optical damage threshold. Low-loss ridge waveguides in GaN layers were recently demonstrated. In this work, we provide the first report of four-wave mixing in a GaN waveguide at telecommunication wavelengths, and observe comparatively high nonlinear propagation parameters. The nonlinear coefficient of the waveguide is measured as 1.6 ± 0.45 [W × m]−1, and the corresponding third-order nonlinear parameter of GaN is estimated as 3.4 ± 1e-18 [m2/W]. The results suggest that GaN waveguides could be instrumental in nonlinear-optical signal processing applications.

Quantum-correlated photon pairs generated in a commercial 45 nm complementary metal-oxide semiconductor microelectronic chip

Correlated photon pairs are a fundamental building block of quantum photonic systems. While pair sources have previously been integrated on silicon chips built using customized photonics manufacturing processes, these often take advantage of only a small fraction of the established techniques for microelectronics fabrication and have yet to be integrated in a process that also supports electronics. Here we report the first demonstration of quantum-correlated photon pair generation in a device fabricated in an unmodified advanced (sub-100-nm) complementary metal-oxide semiconductor (CMOS) process, alongside millions of working transistors. The microring resonator photon pair source is formed in the transistor layer structure, with the resonator core formed by the silicon layer typically used for the transistor body. With ultralow CW on-chip pump powers ranging from 4.8 to 400 μW, we demonstrate pair generation rates between 165 Hz and 332 kHz using >80% efficient WSi superconducting nanowire single-photon detectors. Coincidences-to-accidentals ratios consistently exceeding 40 were measured, with a maximum of 55. In the process of characterizing this source, we also accurately predict pair generation rates from the results of classical stimulated four-wave mixing measurements. This proof-of-principle device demonstrates the potential of commercial CMOS microelectronics as an advanced quantum photonics platform with the capability of large volumes and pristine process control, where state-of-the-art high-speed digital circuits could interact with quantum photonic circuits.

Supercontinuum-based three-color three-pulse time-resolved coherent anti-Stokes Raman scattering.

We demonstrate the use of a photonic crystal fiber (PCF) as a compact three-color fs laser system operating at 76 MHz, limited only by the repetition rate of the pump laser. The system is suitable for background-free time-resolved four-wave mixing measurements, which arguably reach fundamental limits in signal detectivity. We give a detailed characterization of the near transform-limited multi-color pulses that are extracted from the PCF, and prove the system through time-resolved coherent anti-Stokes Raman scattering measurements in bipyridyl ethylene and styrene.

Real-time imaging of chromophore alignment in photorefractive polymer devices through multiphoton microscopy

Abstract

Four-wave mixing in GaAs/AlAs triple-coupled cavity with InAs quantum dots

We have investigated a GaAs/AlAs triple-coupled multilayer cavity structure for an ultrafast wavelength conversion device. We found that significant improvement in the wavelength conversion was realized by introducing good nonlinear materials in the cavity layer, and that the precise control of the cavity modes was important to obtain stronger frequency conversion signals. We grew a triple coupled multilayer cavity structure with self-assembled InAs quantum dots (QDs) by molecular beam epitaxy and investigated the frequency separations of the cavity modes in relation to the cavity layer thickness using on the basis of the reflection spectra. Clear four-wave mixing (FWM) signals were demonstrated by time-resolved FWM measurements were performed at room temperature using a femtosecond laser system.