Mixing Wavelength Research Articles

Fully spectrum-sliced four-wave mixing wavelength conversion in a Semiconductor Optical Amplifier

Fully spectrum-sliced four-wave mixing wavelength conversion in a Semiconductor Optical Amplifier

Cascaded four-wave mixing all-optical wavelength converter based on highly nonlinear fiber deposited graphene oxide

The all-optical wavelength conversion using cascaded four-wave mixing (FWM) phenomena with graphene oxide (GO) and a highly nonlinear fiber (HNLF) device is demonstrated experimentally. GO has a strong third-order nonlinear effect and is an excellent nonlinear optical material for nonlinear optical wavelength conversion. The group velocity matching of pump and signal, HNLF, and GO amplification promote the cascaded nonlinear frequency mixing process. From the experimental and analytical results, the maximum spacing between signal and pump is 21 nm, and specifically, the order of cascaded FWM light increases from order 1 to order 2 with increasing GO, and the first-order FWM conversion efficiency increases to a maximum of −14.5 dB. To the best of our knowledge, this is the first time that cascaded FWM-based all-optical wavelength conversion in HNLF–GO with wide wavelength selectivity is investigated with combined pump and signal light. Our findings not only provide an effective method for achieving all-optical wavelength conversion in cascaded FWM but also offer the possibility of fabricating high-performance nonlinear optical devices.

Ultrahigh Efficiency Four-Wave Mixing Wavelength Conversion in Packaged Silica Microrod Resonator

Whispering-gallery-mode (WGM) resonator with high-quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) is a key platform for a wide range of fields including nonlinear optics, biosensing and quantum photonics. In this work, a packaged silica microrod resonator (PSMR) with ultrahigh- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\bf 9.0\times 10^{8}$</tex-math></inline-formula> is experimentally demonstrated. Ultrahigh four-wave mixing conversion efficiency of −8.6 dB at a pump power of 27 mW is achieved within this ultrahigh- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> PSMR. Furthermore, this PSMR shows high stability of resonant wavelength shift within 0.032 pm. This work suggests that the PSMR may be a promising platform for optical signal processing and quantum photonics.

A numerical study of the spectral radiative properties of packed bed with mixed bauxite and silica spheres

Bauxite and silica particles have gained increasing attention for applications in the field of concentrated solar power. In this work, a Monte Carlo ray-tracing simulation is performed to predict the radiative properties (absorptance, reflectance, and transmittance) of packed beds with mixed bauxite and silica spherical particles at wavelengths of 0.5, 2.6, 9.0, and 9.35 µm. These wavelengths are representative for the visible, near-infrared, and the mid-infrared regions that are important for solar and thermal radiation, respectively. A repeating unit-column approach is used to mathematically represent the particle bed. The effects of particle mixing ratio, volume fraction, and wavelength on the predicted radiative properties are examined. The obtained radiative properties are inputted to an inverse method to retrieve the effective absorption and scattering coefficients as well as the scattering albedo, which may be later used in a continuous-scale radiative heat transfer analysis. Furthermore, the independent scattering model is used to obtain the absorption coefficient and scattering albedo based on the absorption and scattering cross sections predicted by a Monte Carlo algorithm for a single particle. It is shown that the independent scattering model underpredicts the scattering coefficient for opaque particles but overpredicts the scattering coefficient for semitransparent particles for sufficiently high particle volume fractions. The radiative properties calculated from the independent scattering model are compared to the full Monte Carlo simulation of the particle bed to examine the influence of particle mixing on dependent scattering.

Efficient four-wave mixing wavelength conversion in a hybrid silicon slot and polymer microring resonator.

We present a silicon slot microring resonator for efficient frequency conversion via four-wave mixing (FWM). The slot consists of a narrow silicon waveguide pair with a gap of 80 nm, which is filled with a nonlinear optical polymer. The group velocity dispersion for the microring is controlled by engineering the geometry of the slot structure. Because of the large buildup factor of the slot microring, an FWM conversion efficiency of -27.4 dB is achieved with an optical pump power of less than 1.0 mW. From the measured power dependence of FWM generation, a nonlinear refractive index coefficient of 1.31 × 10-17 m2 W-1 is obtained at a wavelength of 1562 nm. This work presents a hybrid silicon slot and polymer microring as a potential nonlinear device for applications in integrated photonic devices.

Influence of wavelength photoperiods and N/P ratio on wastewater treatment with microalgae-bacteria.

This research investigates the effect of mixing wavelength light photoperiods (12 h blue, 8 h blue: 4 h green, 4 h blue: 8 h green, and 12 h green) and N/P ratios (1.3 to 8.3) on the growth microalgae-bacteria systems, organic matter, and nutrient removals. The highest microalgae-bacteria growth performance (μ = 0.2 d-1, 481.1 ± 15.3 mg DW L-1) was observed when a 8 h blue: 4 h green mixed wavelength and a low N/P ratio were used. For both N/P ratios, biomass productivity was favored when using the blue light dominated at longer time periods. Mechanisms for nitrogen removal by assimilation depend on the N/P ratio, achieving assimilation between 49 and 65% at a low N/P ratio. High nitrogen removal (>50%) showed a strong relation with alkalinity culture conditions (pH > 8.5). The mixing of wavelength photoperiods seems to be a promising strategy to achieve high biomass productivity and nutrient removal. However, for optimal conditions, N/P ratios in the wastewater should be considered.

Ultra-low-power four-wave mixing wavelength conversion in high-Q chalcogenide microring resonators.

A compact Ge11.5As24Se64.5 chalcogenide microring resonator is fabricated with an intrinsic quality factor of 3.0×105 in the telecom band. By taking advantage of the strong nonlinearity and cavity enhancement, highly efficient wavelength conversion via four-wave mixing is demonstrated using a microring resonator. Conversion efficiency of -33.7dB is obtained by using an ultra-low pump power of 63.8 µW. This work shows that Ge11.5As24Se64.5 chalcogenide microring devices are promising for quantum photonics.

Optimization of four-wave mixing wavelength conversion in a quantum-dot semiconductor optical amplifier based on the genetic algorithm

A novel approach based on the artificial neural network (ANN) and the genetic algorithm (GA) is presented for optimization of four-wave mixing (FWM) wavelength conversion in a quantum dot semiconductor optical amplifier (QD-SOA). First of all, we propose a simple, accurate, and fast model based on the feedforward ANN for the characteristics of FWM in a QD-SOA. To train the ANN, we collect the required data from a numerical model. In this model, the efficiency of FWM is obtained numerically taken into account the effect of pump/probe and the occupation probability of energy levels by using the slice technique. Then, the optimal design of QD-SOA as the FWM wavelength converter is performed using the GA.

Silicon/silicon-rich nitride hybrid-core waveguide for nonlinear optics.

A silicon/silicon-rich nitride hybrid-core waveguide has been proposed and experimentally demonstrated for nonlinear applications to fill the gap between the pure silicon waveguide and the pure silicon nitride waveguide with respect to the nonlinear properties. The hybrid-core waveguide presented here leverages the advantages of the silicon and the silicon-rich nitride waveguide platforms, showing a large nonlinearity γ of 72 ± 5 W-1 m-1 for energy-efficient four-wave mixing wavelength conversion. At the same time, the drawbacks of the material platforms are dramatically mitigated, exhibiting a reduced two-photon absorption coefficient βTPA of 0.023 cm/GW resulting in an increased nonlinear figure-of-merit as large as 21.6. A four-wave-mixing conversion efficiency as large as -5.3 dB has been achieved with the promise to be larger than 0 dB. These findings are strong arguments supporting the silicon/silicon-rich nitride hybrid-core waveguide to be used for energy-efficient nonlinear photonic applications.

Four-wave mixing in Ar-filled hollow core bandgap photonic crystal fiber.

To study the four-wave mixing (FWM) effect and wavelength conversion in a hollow core bandgap photonic crystal fiber filled with Ar, we conducted an experiment using a femtosecond laser with the pulse width of 120fs, a repetition rate of 76MHz, and tunable central wavelength from 760 to 980nm. It is observed that new spectra are generated in both sides of the pump at a special wavelength, which can exactly satisfy the phase matching conditions of FWM. Combining experimental results with theoretical analysis, we find that the experimental phenomenon is mainly caused by FWM, and some other nonlinear phase effects, such as self-phase modulation, stimulated Raman scattering, and the soliton effect, have also occurred in this nonlinear process.

Nonlinear Silicon Photonic Signal Processing Devices for Future Optical Networks

In this paper, we present a review on silicon-based nonlinear devices for all optical nonlinear processing of complex telecommunication signals. We discuss some recent developments achieved by our research group, through extensive collaborations with academic partners across Europe, on optical signal processing using silicon-germanium and amorphous silicon based waveguides as well as novel materials such as silicon rich silicon nitride and tantalum pentoxide. We review the performance of four wave mixing wavelength conversion applied on complex signals such as Differential Phase Shift Keying (DPSK), Quadrature Phase Shift Keying (QPSK), 16-Quadrature Amplitude Modulation (QAM) and 64-QAM that dramatically enhance the telecom signal spectral efficiency, paving the way to next generation terabit all-optical networks.

Temperature sensitivity of chromatic dispersion in nonlinear silica and heavy metal oxide glass photonic crystal fibers

In this paper we report on the examination of the temperature influence of the effective refractive index and on the dispersion characteristics in air-hole lattice photonic crystal fibers. We use an original method to measure the temperature influence on chromatic dispersion in an optical fiber, where both the thermal expansion of the fiber and its effective group refractive index are taken into account. We present the experimental and modeling results of dispersion characteristics for two types of non-linear fibers, a silica glass fiber and a soft glass fiber in the temperature range from 20°C to 420°C. We measured the zero dispersion wavelength shift of + 0.020 nm/°C for the fused silica fiber and + 0.045 nm/°C for the heavy metal oxide soft glass fiber. Experimental results are in agreement with numerical modeling. Finally, the influence of the temperature-induced change of the dispersion profile on nonlinear performance of the studied fiber structures is investigated numerically. Notable change of parametric gain maxima locations is observed even for small changes of the zero dispersion wavelength in relation to the pump laser wavelength in a four-wave mixing fiber-based wavelength conversion scenario.

Phase Conjugated and Transparent Wavelength Conversions of Nyquist 16-QAM Signals Employing a Single-Layer Graphene Coated Fiber Device.

We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. Using the fabricated graphene-assisted nonlinear optical device and employing Nyquist 16-ary quadrature amplitude modulation (16-QAM) signal, we experimentally demonstrate phase conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in graphene. We study the conversion efficiency as functions of the pump power and pump wavelength and evaluate the bit-error rate (BER) performance. We also compare the time-varying symbol sequence for graphene-assisted phase conjugated and transparent wavelength conversions of Nyquist 16-QAM signal.

Demonstration of format free wavelength conversion for optical networks

Wavelength converters play a crucial role in wavelength division multiplexing based optical networks. Presence of vast variety of signal formats makes independency of signal format an important requirement for a network. In this paper, format independency of a proposed method, which is based on an optical single side-band modulator (OSSB) and an array waveguide grating is experimentally confirmed. It is demonstrated that proposed method can up-and-down convert the wavelength of the QPSK modulated signal up to 75 GHz by three times conversion in the OSSB modulator, modulated at 25 GHz. Moreover, it is also confirmed that the spectral inversion does not occur in proposed method, by comparing with four wave mixing wavelength conversion method.

All-optical multi-channel wavelength conversion of Nyquist 16 QAM signal using a silicon waveguide.

We experimentally demonstrate on-chip all-optical multi-channel wavelength conversion of Nyquist 16 ary quadrature amplitude modulation (16 QAM) signal in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalties of wavelength conversion are ∼2 dB. The observed constellations of converted idlers indicate favorable performance of silicon-waveguide-based multi-channel wavelength conversion. We also experimentally study and compare the phase-conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in the silicon waveguide.

Low-power continuous-wave four-wave mixing wavelength conversion in AlGaAs-nanowaveguide microresonators.

We experimentally demonstrate enhanced wavelength conversion in a Q∼7500 deeply etched AlGaAs-nanowaveguide microresonator via degenerate continuous-wave four-wave mixing with a pump power of 24mW. The maximum conversion efficiency is -43 dB and accounts for 12dB enhancement compared to that of a straight nanowaveguide. The experimental results and theoretical predictions agree very well and show optimized conversion efficiency of -15 dB. This work represents a step toward realizing a fully integrated optical devices for generating new optical frequencies.

All-optical manipulation of non-degenerate FWM conversion bandwidth by gain-transparent SBS

We demonstrate all-optical manipulation of non-degenerate four-wave mixing (FWM) wavelength conversion bandwidth based on phase-matching control through gain-transparent stimulated Brillouin scattering (SBS). A 3-dB bandwidth of 26nm is achieved when the conversion efficiency is maximized, corresponding to 44% increase from the original value. The bandwidth can also be shrunk to a minimum of 15nm. The spectral dependence of conversion efficiency can potentially be synthesized randomly, leading to a large tunability in the bandwidth. The performance in bandwidth manipulation is also evaluated in the wavelength conversion of 10Gbit/s non-return-to-zero (NRZ) on-off-keying (OOK) signal.

All-incoherent wavelength conversion in highly nonlinear fiber using four-wave mixing

This work describes efficient and polarization insensitive, all-incoherent four-wave mixing wavelength conversion achieved within a short length of highly nonlinear fiber medium, created by using both spectrally sliced pump and probe channels from a single-amplified spontaneous emission source coupled to two narrowband Fiber Bragg grating (FBG) filters. This simple and cost-effective scheme is capable of generating a down-converted probe channel across a 17.2-nm wavelength span, while still maintaining a high conversion efficiency of around −22 dB and an optical-signal-to-noise ratio of ∼21 dB. The effects of pump power, FBG detuning, and polarization are also reported.

Mixing frequency induces [WO4]2− generating blue luminescence

In the process of investigating end-pumped continuous intra-cavity Raman laser, a strong blue luminescence at wavelength 473 nm (nanometer) in pure [XO4]2− (X = W, Y, …) has been observed. This luminescence is strange and inconsistent with the traditional single up-conversion luminescence theory, scintillation theory. Basing on the optics theory and scintillation crystal theory, we suggest a “mixing frequency inducing blue emission” mechanism to explain the phenomenon. The mixing wavelength 473.4 nm with the four wavelengths of 808, 890, 912, and 1.064 nm stimulates and induces the blue emission of the [WO4]2−. The mechanism is in good harmony with the experiment.

Extended tunable optical delay using gain-transparent stimulated Brillouin scattering control in four-wave-mixing wavelength conversion

We propose and experimentally demonstrate an extended range of tunable optical delay obtained from four-wave mixing wavelength conversion and dispersion. The conversion bandwidth and the maximum delay are enlarged through dynamic control of the optical phase by gain-transparent stimulated Brillouin scattering. The delay range is increased by 37%. Bit-error-rate measurements show a maximum power penalty of 2.0 dB with reference to back-to-back performance. The technique can be applied to different configurations of tunable delay lines constructed with a fiber parametric process and dispersion.